[Note that this file is a concatenation of more than one RFC.] Network Working Group D. Harrington Request for Comments: 3411 Enterasys Networks STD: 62 R. Presuhn Obsoletes: 2571 BMC Software, Inc. Category: Standards Track B. Wijnen Lucent Technologies December 2002 An Architecture for Describing Simple Network Management Protocol (SNMP) Management Frameworks Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document describes an architecture for describing Simple Network Management Protocol (SNMP) Management Frameworks. The architecture is designed to be modular to allow the evolution of the SNMP protocol standards over time. The major portions of the architecture are an SNMP engine containing a Message Processing Subsystem, a Security Subsystem and an Access Control Subsystem, and possibly multiple SNMP applications which provide specific functional processing of management data. This document obsoletes RFC 2571. Table of Contents 1. Introduction ................................................ 4 1.1. Overview .................................................. 4 1.2. SNMP ...................................................... 5 1.3. Goals of this Architecture ................................ 6 1.4. Security Requirements of this Architecture ................ 6 1.5. Design Decisions .......................................... 8 2. Documentation Overview ...................................... 10 2.1. Document Roadmap .......................................... 11 2.2. Applicability Statement ................................... 11 Harrington, et al. Standards Track [Page 1] RFC 3411 Architecture for SNMP Management Frameworks December 2002 2.3. Coexistence and Transition ................................ 11 2.4. Transport Mappings ........................................ 12 2.5. Message Processing ........................................ 12 2.6. Security .................................................. 12 2.7. Access Control ............................................ 13 2.8. Protocol Operations ....................................... 13 2.9. Applications .............................................. 14 2.10. Structure of Management Information ...................... 15 2.11. Textual Conventions ...................................... 15 2.12. Conformance Statements ................................... 15 2.13. Management Information Base Modules ...................... 15 2.13.1. SNMP Instrumentation MIBs .............................. 15 2.14. SNMP Framework Documents ................................. 15 3. Elements of the Architecture ................................ 16 3.1. The Naming of Entities .................................... 17 3.1.1. SNMP engine ............................................. 18 3.1.1.1. snmpEngineID .......................................... 18 3.1.1.2. Dispatcher ............................................ 18 3.1.1.3. Message Processing Subsystem .......................... 19 3.1.1.3.1. Message Processing Model ............................ 19 3.1.1.4. Security Subsystem .................................... 20 3.1.1.4.1. Security Model ...................................... 20 3.1.1.4.2. Security Protocol ................................... 20 3.1.2. Access Control Subsystem ................................ 21 3.1.2.1. Access Control Model .................................. 21 3.1.3. Applications ............................................ 21 3.1.3.1. SNMP Manager .......................................... 22 3.1.3.2. SNMP Agent ............................................ 23 3.2. The Naming of Identities .................................. 25 3.2.1. Principal ............................................... 25 3.2.2. securityName ............................................ 25 3.2.3. Model-dependent security ID ............................. 26 3.3. The Naming of Management Information ...................... 26 3.3.1. An SNMP Context ......................................... 28 3.3.2. contextEngineID ......................................... 28 3.3.3. contextName ............................................. 29 3.3.4. scopedPDU ............................................... 29 3.4. Other Constructs .......................................... 29 3.4.1. maxSizeResponseScopedPDU ................................ 29 3.4.2. Local Configuration Datastore ........................... 29 3.4.3. securityLevel ........................................... 29 4. Abstract Service Interfaces ................................. 30 4.1. Dispatcher Primitives ..................................... 30 4.1.1. Generate Outgoing Request or Notification ............... 31 4.1.2. Process Incoming Request or Notification PDU ............ 31 4.1.3. Generate Outgoing Response .............................. 32 4.1.4. Process Incoming Response PDU ........................... 32 4.1.5. Registering Responsibility for Handling SNMP PDUs ....... 32 Harrington, et al. Standards Track [Page 2] RFC 3411 Architecture for SNMP Management Frameworks December 2002 4.2. Message Processing Subsystem Primitives ................... 33 4.2.1. Prepare Outgoing SNMP Request or Notification Message ... 33 4.2.2. Prepare an Outgoing SNMP Response Message ............... 34 4.2.3. Prepare Data Elements from an Incoming SNMP Message ..... 35 4.3. Access Control Subsystem Primitives ....................... 35 4.4. Security Subsystem Primitives ............................. 36 4.4.1. Generate a Request or Notification Message .............. 36 4.4.2. Process Incoming Message ................................ 36 4.4.3. Generate a Response Message ............................. 37 4.5. Common Primitives ......................................... 37 4.5.1. Release State Reference Information ..................... 37 4.6. Scenario Diagrams ......................................... 38 4.6.1. Command Generator or Notification Originator ............ 38 4.6.2. Scenario Diagram for a Command Responder Application .... 39 5. Managed Object Definitions for SNMP Management Frameworks ... 40 6. IANA Considerations ......................................... 51 6.1. Security Models ........................................... 51 6.2. Message Processing Models ................................. 51 6.3. SnmpEngineID Formats ...................................... 52 7. Intellectual Property ....................................... 52 8. Acknowledgements ............................................ 52 9. Security Considerations ..................................... 54 10. References ................................................. 54 10.1. Normative References ..................................... 54 10.2. Informative References ................................... 56 A. Guidelines for Model Designers .............................. 57 A.1. Security Model Design Requirements ........................ 57 A.1.1. Threats ................................................. 57 A.1.2. Security Processing ..................................... 58 A.1.3. Validate the security-stamp in a received message ....... 59 A.1.4. Security MIBs ........................................... 59 A.1.5. Cached Security Data .................................... 59 A.2. Message Processing Model Design Requirements .............. 60 A.2.1. Receiving an SNMP Message from the Network .............. 60 A.2.2. Sending an SNMP Message to the Network .................. 60 A.3. Application Design Requirements ........................... 61 A.3.1. Applications that Initiate Messages ..................... 61 A.3.2. Applications that Receive Responses ..................... 62 A.3.3. Applications that Receive Asynchronous Messages ......... 62 A.3.4. Applications that Send Responses ........................ 62 A.4. Access Control Model Design Requirements .................. 63 Editors' Addresses ............................................. 63 Full Copyright Statement ....................................... 64 Harrington, et al. Standards Track [Page 3] RFC 3411 Architecture for SNMP Management Frameworks December 2002 1. Introduction 1.1. Overview This document defines a vocabulary for describing SNMP Management Frameworks, and an architecture for describing the major portions of SNMP Management Frameworks. This document does not provide a general introduction to SNMP. Other documents and books can provide a much better introduction to SNMP. Nor does this document provide a history of SNMP. That also can be found in books and other documents. Section 1 describes the purpose, goals, and design decisions of this architecture. Section 2 describes various types of documents which define (elements of) SNMP Frameworks, and how they fit into this architecture. It also provides a minimal road map to the documents which have previously defined SNMP frameworks. Section 3 details the vocabulary of this architecture and its pieces. This section is important for understanding the remaining sections, and for understanding documents which are written to fit within this architecture. Section 4 describes the primitives used for the abstract service interfaces between the various subsystems, models and applications within this architecture. Section 5 defines a collection of managed objects used to instrument SNMP entities within this architecture. Sections 6, 7, 8, 9, 10 and 11 are administrative in nature. Appendix A contains guidelines for designers of Models which are expected to fit within this architecture. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Harrington, et al. Standards Track [Page 4] RFC 3411 Architecture for SNMP Management Frameworks December 2002 1.2. SNMP An SNMP management system contains: - several (potentially many) nodes, each with an SNMP entity containing command responder and notification originator applications, which have access to management instrumentation (traditionally called agents); - at least one SNMP entity containing command generator and/or notification receiver applications (traditionally called a manager) and, - a management protocol, used to convey management information between the SNMP entities. SNMP entities executing command generator and notification receiver applications monitor and control managed elements. Managed elements are devices such as hosts, routers, terminal servers, etc., which are monitored and controlled via access to their management information. It is the purpose of this document to define an architecture which can evolve to realize effective management in a variety of configurations and environments. The architecture has been designed to meet the needs of implementations of: - minimal SNMP entities with command responder and/or notification originator applications (traditionally called SNMP agents), - SNMP entities with proxy forwarder applications (traditionally called SNMP proxy agents), - command line driven SNMP entities with command generator and/or notification receiver applications (traditionally called SNMP command line managers), - SNMP entities with command generator and/or notification receiver, plus command responder and/or notification originator applications (traditionally called SNMP mid-level managers or dual-role entities), - SNMP entities with command generator and/or notification receiver and possibly other types of applications for managing a potentially very large number of managed nodes (traditionally called (network) management stations). Harrington, et al. Standards Track [Page 5] RFC 3411 Architecture for SNMP Management Frameworks December 2002 1.3. Goals of this Architecture This architecture was driven by the following goals: - Use existing materials as much as possible. It is heavily based on previous work, informally known as SNMPv2u and SNMPv2*, based in turn on SNMPv2p. - Address the need for secure SET support, which is considered the most important deficiency in SNMPv1 and SNMPv2c. - Make it possible to move portions of the architecture forward in the standards track, even if consensus has not been reached on all pieces. - Define an architecture that allows for longevity of the SNMP Frameworks that have been and will be defined. - Keep SNMP as simple as possible. - Make it relatively inexpensive to deploy a minimal conforming implementation. - Make it possible to upgrade portions of SNMP as new approaches become available, without disrupting an entire SNMP framework. - Make it possible to support features required in large networks, but make the expense of supporting a feature directly related to the support of the feature. 1.4. Security Requirements of this Architecture Several of the classical threats to network protocols are applicable to the management problem and therefore would be applicable to any Security Model used in an SNMP Management Framework. Other threats are not applicable to the management problem. This section discusses principal threats, secondary threats, and threats which are of lesser importance. The principal threats against which any Security Model used within this architecture SHOULD provide protection are: Modification of Information The modification threat is the danger that some unauthorized entity may alter in-transit SNMP messages generated on behalf of an authorized principal in such a way as to effect unauthorized management operations, including falsifying the value of an object. Harrington, et al. Standards Track [Page 6] RFC 3411 Architecture for SNMP Management Frameworks December 2002 Masquerade The masquerade threat is the danger that management operations not authorized for some principal may be attempted by assuming the identity of another principal that has the appropriate authorizations. Secondary threats against which any Security Model used within this architecture SHOULD provide protection are: Message Stream Modification The SNMP protocol is typically based upon a connectionless transport service which may operate over any subnetwork service. The re-ordering, delay or replay of messages can and does occur through the natural operation of many such subnetwork services. The message stream modification threat is the danger that messages may be maliciously re-ordered, delayed or replayed to an extent which is greater than can occur through the natural operation of a subnetwork service, in order to effect unauthorized management operations. Disclosure The disclosure threat is the danger of eavesdropping on the exchanges between SNMP engines. Protecting against this threat may be required as a matter of local policy. There are at least two threats against which a Security Model within this architecture need not protect, since they are deemed to be of lesser importance in this context: Denial of Service A Security Model need not attempt to address the broad range of attacks by which service on behalf of authorized users is denied. Indeed, such denial-of-service attacks are in many cases indistinguishable from the type of network failures with which any viable management protocol must cope as a matter of course. Traffic Analysis A Security Model need not attempt to address traffic analysis attacks. Many traffic patterns are predictable - entities may be managed on a regular basis by a relatively small number of management stations - and therefore there is no significant advantage afforded by protecting against traffic analysis. Harrington, et al. Standards Track [Page 7] RFC 3411 Architecture for SNMP Management Frameworks December 2002 1.5. Design Decisions Various design decisions were made in support of the goals of the architecture and the security requirements: - Architecture An architecture should be defined which identifies the conceptual boundaries between the documents. Subsystems should be defined which describe the abstract services provided by specific portions of an SNMP framework. Abstract service interfaces, as described by service primitives, define the abstract boundaries between documents, and the abstract services that are provided by the conceptual subsystems of an SNMP framework. - Self-contained Documents Elements of procedure plus the MIB objects which are needed for processing for a specific portion of an SNMP framework should be defined in the same document, and as much as possible, should not be referenced in other documents. This allows pieces to be designed and documented as independent and self- contained parts, which is consistent with the general SNMP MIB module approach. As portions of SNMP change over time, the documents describing other portions of SNMP are not directly impacted. This modularity allows, for example, Security Models, authentication and privacy mechanisms, and message formats to be upgraded and supplemented as the need arises. The self-contained documents can move along the standards track on different time-lines. This modularity of specification is not meant to be interpreted as imposing any specific requirements on implementation. - Threats The Security Models in the Security Subsystem SHOULD protect against the principal and secondary threats: modification of information, masquerade, message stream modification and disclosure. They do not need to protect against denial of service and traffic analysis. - Remote Configuration The Security and Access Control Subsystems add a whole new set of SNMP configuration parameters. The Security Subsystem also requires frequent changes of secrets at the various SNMP entities. To make this deployable in a large operational environment, these SNMP parameters must be remotely configurable. Harrington, et al. Standards Track [Page 8] RFC 3411 Architecture for SNMP Management Frameworks December 2002 - Controlled Complexity It is recognized that producers of simple managed devices want to keep the resources used by SNMP to a minimum. At the same time, there is a need for more complex configurations which can spend more resources for SNMP and thus provide more functionality. The design tries to keep the competing requirements of these two environments in balance and allows the more complex environments to logically extend the simple environment. Harrington, et al. Standards Track [Page 9] RFC 3411 Architecture for SNMP Management Frameworks December 2002 2. Documentation Overview The following figure shows the set of documents that fit within the SNMP Architecture. +------------------------- Document Set ----------------------------+ | | | +----------+ +-----------------+ +----------------+ | | | Document | | Applicability | | Coexistence | | | | Roadmap | | Statement | | & Transition | | | +----------+ +-----------------+ +----------------+ | | | | +---------------------------------------------------------------+ | | | Message Handling | | | | +----------------+ +-----------------+ +-----------------+ | | | | | Transport | | Message | | Security | | | | | | Mappings | | Processing and | | | | | | | | | | Dispatcher | | | | | | | +----------------+ +-----------------+ +-----------------+ | | | +---------------------------------------------------------------+ | | | | +---------------------------------------------------------------+ | | | PDU Handling | | | | +----------------+ +-----------------+ +-----------------+ | | | | | Protocol | | Applications | | Access | | | | | | Operations | | | | Control | | | | | +----------------+ +-----------------+ +-----------------+ | | | +---------------------------------------------------------------+ | | | | +---------------------------------------------------------------+ | | | Information Model | | | | +--------------+ +--------------+ +---------------+ | | | | | Structure of | | Textual | | Conformance | | | | | | Management | | Conventions | | Statements | | | | | | Information | | | | | | | | | +--------------+ +--------------+ +---------------+ | | | +---------------------------------------------------------------+ | | | | +---------------------------------------------------------------+ | | | MIB Modules written in various formats, e.g.: | | | | +----------------+ +----------------+ | | | | | SMIv1 (STD 18) | | SMIv2 (STD 58) | | | | | | format | | format | | | | | +----------------+ +----------------+ | | | +---------------------------------------------------------------+ | | | +-------------------------------------------------------------------+ Harrington, et al. Standards Track [Page 10] RFC 3411 Architecture for SNMP Management Frameworks December 2002 Each of these documents may be replaced or supplemented. This Architecture document specifically describes how new documents fit into the set of documents in the area of Message and PDU handling. 2.1. Document Roadmap One or more documents may be written to describe how sets of documents taken together form specific Frameworks. The configuration of document sets might change over time, so the "road map" should be maintained in a document separate from the standards documents themselves. An example of such a roadmap is "Introduction and Applicability Statements for the Internet-Standard Management Framework" [RFC3410]. 2.2. Applicability Statement SNMP is used in networks that vary widely in size and complexity, by organizations that vary widely in their requirements of management. Some models will be designed to address specific problems of management, such as message security. One or more documents may be written to describe the environments to which certain versions of SNMP or models within SNMP would be appropriately applied, and those to which a given model might be inappropriately applied. 2.3. Coexistence and Transition The purpose of an evolutionary architecture is to permit new models to replace or supplement existing models. The interactions between models could result in incompatibilities, security "holes", and other undesirable effects. The purpose of Coexistence documents is to detail recognized anomalies and to describe required and recommended behaviors for resolving the interactions between models within the architecture. Coexistence documents may be prepared separately from model definition documents, to describe and resolve interaction anomalies between a model definition and one or more other model definitions. Additionally, recommendations for transitions between models may also be described, either in a coexistence document or in a separate document. Harrington, et al. Standards Track [Page 11] RFC 3411 Architecture for SNMP Management Frameworks December 2002 One such coexistence document is [RFC2576], "Coexistence between Version 1, Version 2, and Version 3 of the Internet-Standard Network Management Framework". 2.4. Transport Mappings SNMP messages are sent over various transports. It is the purpose of Transport Mapping documents to define how the mapping between SNMP and the transport is done. 2.5. Message Processing A Message Processing Model document defines a message format, which is typically identified by a version field in an SNMP message header. The document may also define a MIB module for use in message processing and for instrumentation of version-specific interactions. An SNMP engine includes one or more Message Processing Models, and thus may support sending and receiving multiple versions of SNMP messages. 2.6. Security Some environments require secure protocol interactions. Security is normally applied at two different stages: - in the transmission/receipt of messages, and - in the processing of the contents of messages. For purposes of this document, "security" refers to message-level security; "access control" refers to the security applied to protocol operations. Authentication, encryption, and timeliness checking are common functions of message level security. A security document describes a Security Model, the threats against which the model protects, the goals of the Security Model, the protocols which it uses to meet those goals, and it may define a MIB module to describe the data used during processing, and to allow the remote configuration of message-level security parameters, such as keys. An SNMP engine may support multiple Security Models concurrently. Harrington, et al. Standards Track [Page 12] RFC 3411 Architecture for SNMP Management Frameworks December 2002 2.7. Access Control During processing, it may be required to control access to managed objects for operations. An Access Control Model defines mechanisms to determine whether access to a managed object should be allowed. An Access Control Model may define a MIB module used during processing and to allow the remote configuration of access control policies. 2.8. Protocol Operations SNMP messages encapsulate an SNMP Protocol Data Unit (PDU). SNMP PDUs define the operations performed by the receiving SNMP engine. It is the purpose of a Protocol Operations document to define the operations of the protocol with respect to the processing of the PDUs. Every PDU belongs to one or more of the PDU classes defined below: 1) Read Class: The Read Class contains protocol operations that retrieve management information. For example, [RFC3416] defines the following protocol operations for the Read Class: GetRequest- PDU, GetNextRequest-PDU, and GetBulkRequest-PDU. 2) Write Class: The Write Class contains protocol operations which attempt to modify management information. For example, [RFC3416] defines the following protocol operation for the Write Class: SetRequest-PDU. 3) Response Class: The Response Class contains protocol operations which are sent in response to a previous request. For example, [RFC3416] defines the following for the Response Class: Response-PDU, Report-PDU. 4) Notification Class: The Notification Class contains protocol operations which send a notification to a notification receiver application. For example, [RFC3416] defines the following operations for the Notification Class: Trapv2-PDU, InformRequest-PDU. Harrington, et al. Standards Track [Page 13] RFC 3411 Architecture for SNMP Management Frameworks December 2002 5) Internal Class: The Internal Class contains protocol operations which are exchanged internally between SNMP engines. For example, [RFC3416] defines the following operation for the Internal Class: Report-PDU. The preceding five classifications are based on the functional properties of a PDU. It is also useful to classify PDUs based on whether a response is expected: 6) Confirmed Class: The Confirmed Class contains all protocol operations which cause the receiving SNMP engine to send back a response. For example, [RFC3416] defines the following operations for the Confirmed Class: GetRequest-PDU, GetNextRequest-PDU, GetBulkRequest-PDU, SetRequest-PDU, and InformRequest-PDU. 7) Unconfirmed Class: The Unconfirmed Class contains all protocol operations which are not acknowledged. For example, [RFC3416] defines the following operations for the Unconfirmed Class: Report-PDU, Trapv2-PDU, and GetResponse-PDU. An application document defines which Protocol Operations are supported by the application. 2.9. Applications An SNMP entity normally includes a number of applications. Applications use the services of an SNMP engine to accomplish specific tasks. They coordinate the processing of management information operations, and may use SNMP messages to communicate with other SNMP entities. An applications document describes the purpose of an application, the services required of the associated SNMP engine, and the protocol operations and informational model that the application uses to perform management operations. An application document defines which set of documents are used to specifically define the structure of management information, textual conventions, conformance requirements, and operations supported by the application. Harrington, et al. Standards Track [Page 14] RFC 3411 Architecture for SNMP Management Frameworks December 2002 2.10. Structure of Management Information Management information is viewed as a collection of managed objects, residing in a virtual information store, termed the Management Information Base (MIB). Collections of related objects are defined in MIB modules. It is the purpose of a Structure of Management Information document to establish the notation for defining objects, modules, and other elements of managed information. 2.11. Textual Conventions When designing a MIB module, it is often useful to define new types similar to those defined in the SMI, but with more precise semantics, or which have special semantics associated with them. These newly defined types are termed textual conventions, and may be defined in separate documents, or within a MIB module. 2.12. Conformance Statements It may be useful to define the acceptable lower-bounds of implementation, along with the actual level of implementation achieved. It is the purpose of the Conformance Statements document to define the notation used for these purposes. 2.13. Management Information Base Modules MIB documents describe collections of managed objects which instrument some aspect of a managed node. 2.13.1. SNMP Instrumentation MIBs An SNMP MIB document may define a collection of managed objects which instrument the SNMP protocol itself. In addition, MIB modules may be defined within the documents which describe portions of the SNMP architecture, such as the documents for Message processing Models, Security Models, etc. for the purpose of instrumenting those Models, and for the purpose of allowing their remote configuration. 2.14. SNMP Framework Documents This architecture is designed to allow an orderly evolution of portions of SNMP Frameworks. Throughout the rest of this document, the term "subsystem" refers to an abstract and incomplete specification of a portion of a Framework, that is further refined by a model specification. Harrington, et al. Standards Track [Page 15] RFC 3411 Architecture for SNMP Management Frameworks December 2002 A "model" describes a specific design of a subsystem, defining additional constraints and rules for conformance to the model. A model is sufficiently detailed to make it possible to implement the specification. An "implementation" is an instantiation of a subsystem, conforming to one or more specific models. SNMP version 1 (SNMPv1), is the original Internet-Standard Network Management Framework, as described in RFCs 1155, 1157, and 1212. SNMP version 2 (SNMPv2), is the SNMPv2 Framework as derived from the SNMPv1 Framework. It is described in STD 58, RFCs 2578, 2579, 2580, and STD 62, RFCs 3416, 3417, and 3418. SNMPv2 has no message definition. The Community-based SNMP version 2 (SNMPv2c), is an experimental SNMP Framework which supplements the SNMPv2 Framework, as described in [RFC1901]. It adds the SNMPv2c message format, which is similar to the SNMPv1 message format. SNMP version 3 (SNMPv3), is an extensible SNMP Framework which supplements the SNMPv2 Framework, by supporting the following: - a new SNMP message format, - Security for Messages, - Access Control, and - Remote configuration of SNMP parameters. Other SNMP Frameworks, i.e., other configurations of implemented subsystems, are expected to also be consistent with this architecture. 3. Elements of the Architecture This section describes the various elements of the architecture and how they are named. There are three kinds of naming: 1) the naming of entities, 2) the naming of identities, and 3) the naming of management information. Harrington, et al. Standards Track [Page 16] RFC 3411 Architecture for SNMP Management Frameworks December 2002 This architecture also defines some names for other constructs that are used in the documentation. 3.1. The Naming of Entities An SNMP entity is an implementation of this architecture. Each such SNMP entity consists of an SNMP engine and one or more associated applications. The following figure shows details about an SNMP entity and the components within it. +-------------------------------------------------------------------+ | SNMP entity | | | | +-------------------------------------------------------------+ | | | SNMP engine (identified by snmpEngineID) | | | | | | | | +------------+ +------------+ +-----------+ +-----------+ | | | | | | | | | | | | | | | | | Dispatcher | | Message | | Security | | Access | | | | | | | | Processing | | Subsystem | | Control | | | | | | | | Subsystem | | | | Subsystem | | | | | | | | | | | | | | | | | +------------+ +------------+ +-----------+ +-----------+ | | | | | | | +-------------------------------------------------------------+ | | | | +-------------------------------------------------------------+ | | | Application(s) | | | | | | | | +-------------+ +--------------+ +--------------+ | | | | | Command | | Notification | | Proxy | | | | | | Generator | | Receiver | | Forwarder | | | | | +-------------+ +--------------+ +--------------+ | | | | | | | | +-------------+ +--------------+ +--------------+ | | | | | Command | | Notification | | Other | | | | | | Responder | | Originator | | | | | | | +-------------+ +--------------+ +--------------+ | | | | | | | +-------------------------------------------------------------+ | | | +-------------------------------------------------------------------+ Harrington, et al. Standards Track [Page 17] RFC 3411 Architecture for SNMP Management Frameworks December 2002 3.1.1. SNMP engine An SNMP engine provides services for sending and receiving messages, authenticating and encrypting messages, and controlling access to managed objects. There is a one-to-one association between an SNMP engine and the SNMP entity which contains it. The engine contains: 1) a Dispatcher, 2) a Message Processing Subsystem, 3) a Security Subsystem, and 4) an Access Control Subsystem. 3.1.1.1. snmpEngineID Within an administrative domain, an snmpEngineID is the unique and unambiguous identifier of an SNMP engine. Since there is a one-to- one association between SNMP engines and SNMP entities, it also uniquely and unambiguously identifies the SNMP entity within that administrative domain. Note that it is possible for SNMP entities in different administrative domains to have the same value for snmpEngineID. Federation of administrative domains may necessitate assignment of new values. 3.1.1.2. Dispatcher There is only one Dispatcher in an SNMP engine. It allows for concurrent support of multiple versions of SNMP messages in the SNMP engine. It does so by: - sending and receiving SNMP messages to/from the network, - determining the version of an SNMP message and interacting with the corresponding Message Processing Model, - providing an abstract interface to SNMP applications for delivery of a PDU to an application. - providing an abstract interface for SNMP applications that allows them to send a PDU to a remote SNMP entity. Harrington, et al. Standards Track [Page 18] RFC 3411 Architecture for SNMP Management Frameworks December 2002 3.1.1.3. Message Processing Subsystem The Message Processing Subsystem is responsible for preparing messages for sending, and extracting data from received messages. The Message Processing Subsystem potentially contains multiple Message Processing Models as shown in the next figure. * One or more Message Processing Models may be present. +------------------------------------------------------------------+ | | | Message Processing Subsystem | | | | +------------+ +------------+ +------------+ +------------+ | | | * | | * | | * | | * | | | | SNMPv3 | | SNMPv1 | | SNMPv2c | | Other | | | | Message | | Message | | Message | | Message | | | | Processing | | Processing | | Processing | | Processing | | | | Model | | Model | | Model | | Model | | | | | | | | | | | | | +------------+ +------------+ +------------+ +------------+ | | | +------------------------------------------------------------------+ 3.1.1.3.1. Message Processing Model Each Message Processing Model defines the format of a particular version of an SNMP message and coordinates the preparation and extraction of each such version-specific message format. Harrington, et al. Standards Track [Page 19] RFC 3411 Architecture for SNMP Management Frameworks December 2002 3.1.1.4. Security Subsystem The Security Subsystem provides security services such as the authentication and privacy of messages and potentially contains multiple Security Models as shown in the following figure * One or more Security Models may be present. +------------------------------------------------------------------+ | | | Security Subsystem | | | | +----------------+ +-----------------+ +-------------------+ | | | * | | * | | * | | | | User-Based | | Other | | Other | | | | Security | | Security | | Security | | | | Model | | Model | | Model | | | | | | | | | | | +----------------+ +-----------------+ +-------------------+ | | | +------------------------------------------------------------------+ 3.1.1.4.1. Security Model A Security Model specifies the threats against which it protects, the goals of its services, and the security protocols used to provide security services such as authentication and privacy. 3.1.1.4.2. Security Protocol A Security Protocol specifies the mechanisms, procedures, and MIB objects used to provide a security service such as authentication or privacy. Harrington, et al. Standards Track [Page 20] RFC 3411 Architecture for SNMP Management Frameworks December 2002 3.1.2. Access Control Subsystem The Access Control Subsystem provides authorization services by means of one or more (*) Access Control Models. +------------------------------------------------------------------+ | | | Access Control Subsystem | | | | +---------------+ +-----------------+ +------------------+ | | | * | | * | | * | | | | View-Based | | Other | | Other | | | | Access | | Access | | Access | | | | Control | | Control | | Control | | | | Model | | Model | | Model | | | | | | | | | | | +---------------+ +-----------------+ +------------------+ | | | +------------------------------------------------------------------+ 3.1.2.1. Access Control Model An Access Control Model defines a particular access decision function in order to support decisions regarding access rights. 3.1.3. Applications There are several types of applications, including: - command generators, which monitor and manipulate management data, - command responders, which provide access to management data, - notification originators, which initiate asynchronous messages, - notification receivers, which process asynchronous messages, and - proxy forwarders, which forward messages between entities. These applications make use of the services provided by the SNMP engine. Harrington, et al. Standards Track [Page 21] RFC 3411 Architecture for SNMP Management Frameworks December 2002 3.1.3.1. SNMP Manager An SNMP entity containing one or more command generator and/or notification receiver applications (along with their associated SNMP engine) has traditionally been called an SNMP manager. (traditional SNMP manager) +-------------------------------------------------------------------+ | +--------------+ +--------------+ +--------------+ SNMP entity | | | NOTIFICATION | | NOTIFICATION | | COMMAND | | | | ORIGINATOR | | RECEIVER | | GENERATOR | | | | applications | | applications | | applications | | | +--------------+ +--------------+ +--------------+ | | ^ ^ ^ | | | | | | | v v v | | +-------+--------+-----------------+ | | ^ | | | +---------------------+ +----------------+ | | | | Message Processing | | Security | | | Dispatcher v | Subsystem | | Subsystem | | | +-------------------+ | +------------+ | | | | | | PDU Dispatcher | | +->| v1MP * |<--->| +------------+ | | | | | | | +------------+ | | | Other | | | | | | | | +------------+ | | | Security | | | | | | | +->| v2cMP * |<--->| | Model | | | | | Message | | | +------------+ | | +------------+ | | | | Dispatcher <--------->+ | | | | | | | | | +------------+ | | +------------+ | | | | | | +->| v3MP * |<--->| | User-based | | | | | Transport | | | +------------+ | | | Security | | | | | Mapping | | | +------------+ | | | Model | | | | | (e.g., RFC 3417) | | +->| otherMP * |<--->| +------------+ | | | +-------------------+ | +------------+ | | | | | ^ +---------------------+ +----------------+ | | | | | v | +-------------------------------------------------------------------+ +-----+ +-----+ +-------+ | UDP | | IPX | . . . | other | +-----+ +-----+ +-------+ ^ ^ ^ | | | * One or more models may be present. v v v +------------------------------+ | Network | +------------------------------+ Harrington, et al. Standards Track [Page 22] RFC 3411 Architecture for SNMP Management Frameworks December 2002 3.1.3.2. SNMP Agent An SNMP entity containing one or more command responder and/or notification originator applications (along with their associated SNMP engine) has traditionally been called an SNMP agent. Harrington, et al. Standards Track [Page 23] RFC 3411 Architecture for SNMP Management Frameworks December 2002 * One or more models may be present. +------------------------------+ | Network | +------------------------------+ ^ ^ ^ | | | v v v +-----+ +-----+ +-------+ | UDP | | IPX | . . . | other | +-----+ +-----+ +-------+ (traditional SNMP agent) +-------------------------------------------------------------------+ | ^ | | | +---------------------+ +----------------+ | | | | Message Processing | | Security | | | Dispatcher v | Subsystem | | Subsystem | | | +-------------------+ | +------------+ | | | | | | Transport | | +->| v1MP * |<--->| +------------+ | | | | Mapping | | | +------------+ | | | Other | | | | | (e.g., RFC 3417) | | | +------------+ | | | Security | | | | | | | +->| v2cMP * |<--->| | Model | | | | | Message | | | +------------+ | | +------------+ | | | | Dispatcher <--------->| +------------+ | | +------------+ | | | | | | +->| v3MP * |<--->| | User-based | | | | | | | | +------------+ | | | Security | | | | | PDU Dispatcher | | | +------------+ | | | Model | | | | +-------------------+ | +->| otherMP * |<--->| +------------+ | | | ^ | +------------+ | | | | | | +---------------------+ +----------------+ | | v | | +-------+-------------------------+---------------+ | | ^ ^ ^ | | | | | | | v v v | | +-------------+ +---------+ +--------------+ +-------------+ | | | COMMAND | | ACCESS | | NOTIFICATION | | PROXY | | | | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | | | | application | | | | applications | | application | | | +-------------+ +---------+ +--------------+ +-------------+ | | ^ ^ | | | | | | v v | | +----------------------------------------------+ | | | MIB instrumentation | SNMP entity | +-------------------------------------------------------------------+ Harrington, et al. Standards Track [Page 24] RFC 3411 Architecture for SNMP Management Frameworks December 2002 3.2. The Naming of Identities principal ^ | | +----------------------------|-------------+ | SNMP engine v | | +--------------+ | | | | | | +-----------------| securityName |---+ | | | Security Model | | | | | | +--------------+ | | | | ^ | | | | | | | | | v | | | | +------------------------------+ | | | | | | | | | | | Model | | | | | | Dependent | | | | | | Security ID | | | | | | | | | | | +------------------------------+ | | | | ^ | | | | | | | | +-------------------------|----------+ | | | | | | | +----------------------------|-------------+ | v network 3.2.1. Principal A principal is the "who" on whose behalf services are provided or processing takes place. A principal can be, among other things, an individual acting in a particular role; a set of individuals, with each acting in a particular role; an application or a set of applications; and combinations thereof. 3.2.2. securityName A securityName is a human readable string representing a principal. It has a model-independent format, and can be used outside a particular Security Model. Harrington, et al. Standards Track [Page 25] RFC 3411 Architecture for SNMP Management Frameworks December 2002 3.2.3. Model-dependent security ID A model-dependent security ID is the model-specific representation of a securityName within a particular Security Model. Model-dependent security IDs may or may not be human readable, and have a model-dependent syntax. Examples include community names, and user names. The transformation of model-dependent security IDs into securityNames and vice versa is the responsibility of the relevant Security Model. 3.3. The Naming of Management Information Management information resides at an SNMP entity where a Command Responder Application has local access to potentially multiple contexts. This application uses a contextEngineID equal to the snmpEngineID of its associated SNMP engine. Harrington, et al. Standards Track [Page 26] RFC 3411 Architecture for SNMP Management Frameworks December 2002 +-----------------------------------------------------------------+ | SNMP entity (identified by snmpEngineID, for example: | | '800002b804616263'H (enterpise 696, string "abc") | | | | +------------------------------------------------------------+ | | | SNMP engine (identified by snmpEngineID) | | | | | | | | +-------------+ +------------+ +-----------+ +-----------+ | | | | | | | | | | | | | | | | | Dispatcher | | Message | | Security | | Access | | | | | | | | Processing | | Subsystem | | Control | | | | | | | | Subsystem | | | | Subsystem | | | | | | | | | | | | | | | | | +-------------+ +------------+ +-----------+ +-----------+ | | | | | | | +------------------------------------------------------------+ | | | | +------------------------------------------------------------+ | | | Command Responder Application | | | | (contextEngineID, example: '800002b804616263'H) | | | | | | | | example contextNames: | | | | | | | | "bridge1" "bridge2" "" (default) | | | | --------- --------- ------------ | | | | | | | | | | +------|------------------|-------------------|--------------+ | | | | | | | +------|------------------|-------------------|--------------+ | | | MIB | instrumentation | | | | | | +---v------------+ +---v------------+ +----v-----------+ | | | | | context | | context | | context | | | | | | | | | | | | | | | | +------------+ | | +------------+ | | +------------+ | | | | | | | bridge MIB | | | | bridge MIB | | | | some MIB | | | | | | | +------------+ | | +------------+ | | +------------+ | | | | | | | | | | | | | | | | | | | | +------------+ | | | | | | | | | | | other MIB | | | | | | | | | | | +------------+ | | | | | | | | | | | | | +-----------------------------------------------------------------+ Harrington, et al. Standards Track [Page 27] RFC 3411 Architecture for SNMP Management Frameworks December 2002 3.3.1. An SNMP Context An SNMP context, or just "context" for short, is a collection of management information accessible by an SNMP entity. An item of management information may exist in more than one context. An SNMP entity potentially has access to many contexts. Typically, there are many instances of each managed object type within a management domain. For simplicity, the method for identifying instances specified by the MIB module does not allow each instance to be distinguished amongst the set of all instances within a management domain; rather, it allows each instance to be identified only within some scope or "context", where there are multiple such contexts within the management domain. Often, a context is a physical device, or perhaps, a logical device, although a context can also encompass multiple devices, or a subset of a single device, or even a subset of multiple devices, but a context is always defined as a subset of a single SNMP entity. Thus, in order to identify an individual item of management information within the management domain, its contextName and contextEngineID must be identified in addition to its object type and its instance. For example, the managed object type ifDescr [RFC2863], is defined as the description of a network interface. To identify the description of device-X's first network interface, four pieces of information are needed: the snmpEngineID of the SNMP entity which provides access to the management information at device-X, the contextName (device-X), the managed object type (ifDescr), and the instance ("1"). Each context has (at least) one unique identification within the management domain. The same item of management information can exist in multiple contexts. An item of management information may have multiple unique identifications. This occurs when an item of management information exists in multiple contexts, and this also occurs when a context has multiple unique identifications. The combination of a contextEngineID and a contextName unambiguously identifies a context within an administrative domain; note that there may be multiple unique combinations of contextEngineID and contextName that unambiguously identify the same context. 3.3.2. contextEngineID Within an administrative domain, a contextEngineID uniquely identifies an SNMP entity that may realize an instance of a context with a particular contextName. Harrington, et al. Standards Track [Page 28] RFC 3411 Architecture for SNMP Management Frameworks December 2002 3.3.3. contextName A contextName is used to name a context. Each contextName MUST be unique within an SNMP entity. 3.3.4. scopedPDU A scopedPDU is a block of data containing a contextEngineID, a contextName, and a PDU. The PDU is an SNMP Protocol Data Unit containing information named in the context which is unambiguously identified within an administrative domain by the combination of the contextEngineID and the contextName. See, for example, RFC 3416 for more information about SNMP PDUs. 3.4. Other Constructs 3.4.1. maxSizeResponseScopedPDU The maxSizeResponseScopedPDU is the maximum size of a scopedPDU that a PDU's sender would be willing to accept. Note that the size of a scopedPDU does not include the size of the SNMP message header. 3.4.2. Local Configuration Datastore The subsystems, models, and applications within an SNMP entity may need to retain their own sets of configuration information. Portions of the configuration information may be accessible as managed objects. The collection of these sets of information is referred to as an entity's Local Configuration Datastore (LCD). 3.4.3. securityLevel This architecture recognizes three levels of security: - without authentication and without privacy (noAuthNoPriv) - with authentication but without privacy (authNoPriv) - with authentication and with privacy (authPriv) Harrington, et al. Standards Track [Page 29] RFC 3411 Architecture for SNMP Management Frameworks December 2002 These three values are ordered such that noAuthNoPriv is less than authNoPriv and authNoPriv is less than authPriv. Every message has an associated securityLevel. All Subsystems (Message Processing, Security, Access Control) and applications are REQUIRED to either supply a value of securityLevel or to abide by the supplied value of securityLevel while processing the message and its contents. 4. Abstract Service Interfaces Abstract service interfaces have been defined to describe the conceptual interfaces between the various subsystems within an SNMP entity. The abstract service interfaces are intended to help clarify the externally observable behavior of SNMP entities, and are not intended to constrain the structure or organization of implementations in any way. Most specifically, they should not be interpreted as APIs or as requirements statements for APIs. These abstract service interfaces are defined by a set of primitives that define the services provided and the abstract data elements that are to be passed when the services are invoked. This section lists the primitives that have been defined for the various subsystems. 4.1. Dispatcher Primitives The Dispatcher typically provides services to the SNMP applications via its PDU Dispatcher. This section describes the primitives provided by the PDU Dispatcher. Harrington, et al. Standards Track [Page 30] RFC 3411 Architecture for SNMP Management Frameworks December 2002 4.1.1. Generate Outgoing Request or Notification The PDU Dispatcher provides the following primitive for an application to send an SNMP Request or Notification to another SNMP entity: statusInformation = -- sendPduHandle if success -- errorIndication if failure sendPdu( IN transportDomain -- transport domain to be used IN transportAddress -- transport address to be used IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model to use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN contextEngineID -- data from/at this entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN expectResponse -- TRUE or FALSE ) 4.1.2. Process Incoming Request or Notification PDU The PDU Dispatcher provides the following primitive to pass an incoming SNMP PDU to an application: processPdu( -- process Request/Notification PDU IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size of the Response PDU IN stateReference -- reference to state information ) -- needed when sending a response Harrington, et al. Standards Track [Page 31] RFC 3411 Architecture for SNMP Management Frameworks December 2002 4.1.3. Generate Outgoing Response The PDU Dispatcher provides the following primitive for an application to return an SNMP Response PDU to the PDU Dispatcher: result = -- SUCCESS or FAILURE returnResponsePdu( IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- same as on incoming request IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size sender can accept IN stateReference -- reference to state information -- as presented with the request IN statusInformation -- success or errorIndication ) -- error counter OID/value if error 4.1.4. Process Incoming Response PDU The PDU Dispatcher provides the following primitive to pass an incoming SNMP Response PDU to an application: processResponsePdu( -- process Response PDU IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN statusInformation -- success or errorIndication IN sendPduHandle -- handle from sendPdu ) 4.1.5. Registering Responsibility for Handling SNMP PDUs Applications can register/unregister responsibility for a specific contextEngineID, for specific pduTypes, with the PDU Dispatcher according to the following primitives. The list of particular pduTypes that an application can register for is determined by the Message Processing Model(s) supported by the SNMP entity that contains the PDU Dispatcher. Harrington, et al. Standards Track [Page 32] RFC 3411 Architecture for SNMP Management Frameworks December 2002 statusInformation = -- success or errorIndication registerContextEngineID( IN contextEngineID -- take responsibility for this one IN pduType -- the pduType(s) to be registered ) unregisterContextEngineID( IN contextEngineID -- give up responsibility for this one IN pduType -- the pduType(s) to be unregistered ) Note that realizations of the registerContextEngineID and unregisterContextEngineID abstract service interfaces may provide implementation-specific ways for applications to register/deregister responsibility for all possible values of the contextEngineID or pduType parameters. 4.2. Message Processing Subsystem Primitives The Dispatcher interacts with a Message Processing Model to process a specific version of an SNMP Message. This section describes the primitives provided by the Message Processing Subsystem. 4.2.1. Prepare Outgoing SNMP Request or Notification Message The Message Processing Subsystem provides this service primitive for preparing an outgoing SNMP Request or Notification Message: statusInformation = -- success or errorIndication prepareOutgoingMessage( IN transportDomain -- transport domain to be used IN transportAddress -- transport address to be used IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model to use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN contextEngineID -- data from/at this entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN expectResponse -- TRUE or FALSE IN sendPduHandle -- the handle for matching -- incoming responses OUT destTransportDomain -- destination transport domain OUT destTransportAddress -- destination transport address OUT outgoingMessage -- the message to send OUT outgoingMessageLength -- its length ) Harrington, et al. Standards Track [Page 33] RFC 3411 Architecture for SNMP Management Frameworks December 2002 4.2.2. Prepare an Outgoing SNMP Response Message The Message Processing Subsystem provides this service primitive for preparing an outgoing SNMP Response Message: result = -- SUCCESS or FAILURE prepareResponseMessage( IN messageProcessingModel -- typically, SNMP version IN securityModel -- same as on incoming request IN securityName -- same as on incoming request IN securityLevel -- same as on incoming request IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size able to accept IN stateReference -- reference to state information -- as presented with the request IN statusInformation -- success or errorIndication -- error counter OID/value if error OUT destTransportDomain -- destination transport domain OUT destTransportAddress -- destination transport address OUT outgoingMessage -- the message to send OUT outgoingMessageLength -- its length ) Harrington, et al. Standards Track [Page 34] RFC 3411 Architecture for SNMP Management Frameworks December 2002 4.2.3. Prepare Data Elements from an Incoming SNMP Message The Message Processing Subsystem provides this service primitive for preparing the abstract data elements from an incoming SNMP message: result = -- SUCCESS or errorIndication prepareDataElements( IN transportDomain -- origin transport domain IN transportAddress -- origin transport address IN wholeMsg -- as received from the network IN wholeMsgLength -- as received from the network OUT messageProcessingModel -- typically, SNMP version OUT securityModel -- Security Model to use OUT securityName -- on behalf of this principal OUT securityLevel -- Level of Security requested OUT contextEngineID -- data from/at this entity OUT contextName -- data from/in this context OUT pduVersion -- the version of the PDU OUT PDU -- SNMP Protocol Data Unit OUT pduType -- SNMP PDU type OUT sendPduHandle -- handle for matched request OUT maxSizeResponseScopedPDU -- maximum size sender can accept OUT statusInformation -- success or errorIndication -- error counter OID/value if error OUT stateReference -- reference to state information -- to be used for possible Response ) 4.3. Access Control Subsystem Primitives Applications are the typical clients of the service(s) of the Access Control Subsystem. The following primitive is provided by the Access Control Subsystem to check if access is allowed: statusInformation = -- success or errorIndication isAccessAllowed( IN securityModel -- Security Model in use IN securityName -- principal who wants to access IN securityLevel -- Level of Security IN viewType -- read, write, or notify view IN contextName -- context containing variableName IN variableName -- OID for the managed object ) Harrington, et al. Standards Track [Page 35] RFC 3411 Architecture for SNMP Management Frameworks December 2002 4.4. Security Subsystem Primitives The Message Processing Subsystem is the typical client of the services of the Security Subsystem. 4.4.1. Generate a Request or Notification Message The Security Subsystem provides the following primitive to generate a Request or Notification message: statusInformation = generateRequestMsg( IN messageProcessingModel -- typically, SNMP version IN globalData -- message header, admin data IN maxMessageSize -- of the sending SNMP entity IN securityModel -- for the outgoing message IN securityEngineID -- authoritative SNMP entity IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN scopedPDU -- message (plaintext) payload OUT securityParameters -- filled in by Security Module OUT wholeMsg -- complete generated message OUT wholeMsgLength -- length of the generated message ) 4.4.2. Process Incoming Message The Security Subsystem provides the following primitive to process an incoming message: statusInformation = -- errorIndication or success -- error counter OID/value if error processIncomingMsg( IN messageProcessingModel -- typically, SNMP version IN maxMessageSize -- of the sending SNMP entity IN securityParameters -- for the received message IN securityModel -- for the received message IN securityLevel -- Level of Security IN wholeMsg -- as received on the wire IN wholeMsgLength -- length as received on the wire OUT securityEngineID -- authoritative SNMP entity OUT securityName -- identification of the principal OUT scopedPDU, -- message (plaintext) payload OUT maxSizeResponseScopedPDU -- maximum size sender can handle OUT securityStateReference -- reference to security state ) -- information, needed for response Harrington, et al. Standards Track [Page 36] RFC 3411 Architecture for SNMP Management Frameworks December 2002 4.4.3. Generate a Response Message The Security Subsystem provides the following primitive to generate a Response message: statusInformation = generateResponseMsg( IN messageProcessingModel -- typically, SNMP version IN globalData -- message header, admin data IN maxMessageSize -- of the sending SNMP entity IN securityModel -- for the outgoing message IN securityEngineID -- authoritative SNMP entity IN securityName -- on behalf of this principal IN securityLevel -- for the outgoing message IN scopedPDU -- message (plaintext) payload IN securityStateReference -- reference to security state -- information from original request OUT securityParameters -- filled in by Security Module OUT wholeMsg -- complete generated message OUT wholeMsgLength -- length of the generated message ) 4.5. Common Primitives These primitive(s) are provided by multiple Subsystems. 4.5.1. Release State Reference Information All Subsystems which pass stateReference information also provide a primitive to release the memory that holds the referenced state information: stateRelease( IN stateReference -- handle of reference to be released ) Harrington, et al. Standards Track [Page 37] RFC 3411 Architecture for SNMP Management Frameworks December 2002 4.6. Scenario Diagrams 4.6.1. Command Generator or Notification Originator This diagram shows how a Command Generator or Notification Originator application requests that a PDU be sent, and how the response is returned (asynchronously) to that application. Command Dispatcher Message Security Generator | Processing Model | | Model | | sendPdu | | | |------------------->| | | | | prepareOutgoingMessage | | : |----------------------->| | : | | generateRequestMsg | : | |-------------------->| : | | | : | |<--------------------| : | | | : |<-----------------------| | : | | | : |------------------+ | | : | Send SNMP | | | : | Request Message | | | : | to Network | | | : | v | | : : : : : : : : : : : : : : : : | | | | : | Receive SNMP | | | : | Response Message | | | : | from Network | | | : |<-----------------+ | | : | | | : | prepareDataElements | | : |----------------------->| | : | | processIncomingMsg | : | |-------------------->| : | | | : | |<--------------------| : | | | : |<-----------------------| | | processResponsePdu | | | |<-------------------| | | | | | | Harrington, et al. Standards Track [Page 38] RFC 3411 Architecture for SNMP Management Frameworks December 2002 4.6.2. Scenario Diagram for a Command Responder Application This diagram shows how a Command Responder or Notification Receiver application registers for handling a pduType, how a PDU is dispatched to the application after an SNMP message is received, and how the Response is (asynchronously) send back to the network. Command Dispatcher Message Security Responder | Processing Model | | Model | | | | | | registerContextEngineID | | | |------------------------>| | | |<------------------------| | | | | | Receive SNMP | | | : | Message | | | : | from Network | | | : |<-------------+ | | : | | | : |prepareDataElements | | : |------------------->| | : | | processIncomingMsg | : | |------------------->| : | | | : | |<-------------------| : | | | : |<-------------------| | | processPdu | | | |<------------------------| | | | | | | : : : : : : : : | returnResponsePdu | | | |------------------------>| | | : | prepareResponseMsg | | : |------------------->| | : | |generateResponseMsg | : | |------------------->| : | | | : | |<-------------------| : | | | : |<-------------------| | : | | | : |--------------+ | | : | Send SNMP | | | : | Message | | | : | to Network | | | : | v | | Harrington, et al. Standards Track [Page 39] RFC 3411 Architecture for SNMP Management Frameworks December 2002 5. Managed Object Definitions for SNMP Management Frameworks SNMP-FRAMEWORK-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, OBJECT-IDENTITY, snmpModules FROM SNMPv2-SMI TEXTUAL-CONVENTION FROM SNMPv2-TC MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF; snmpFrameworkMIB MODULE-IDENTITY LAST-UPDATED "200210140000Z" ORGANIZATION "SNMPv3 Working Group" CONTACT-INFO "WG-EMail: snmpv3@lists.tislabs.com Subscribe: snmpv3-request@lists.tislabs.com Co-Chair: Russ Mundy Network Associates Laboratories postal: 15204 Omega Drive, Suite 300 Rockville, MD 20850-4601 USA EMail: mundy@tislabs.com phone: +1 301-947-7107 Co-Chair & Co-editor: David Harrington Enterasys Networks postal: 35 Industrial Way P. O. Box 5005 Rochester, New Hampshire 03866-5005 USA EMail: dbh@enterasys.com phone: +1 603-337-2614 Co-editor: Randy Presuhn BMC Software, Inc. postal: 2141 North First Street San Jose, California 95131 USA EMail: randy_presuhn@bmc.com phone: +1 408-546-1006 Co-editor: Bert Wijnen Lucent Technologies postal: Schagen 33 3461 GL Linschoten Netherlands Harrington, et al. Standards Track [Page 40] RFC 3411 Architecture for SNMP Management Frameworks December 2002 EMail: bwijnen@lucent.com phone: +31 348-680-485 " DESCRIPTION "The SNMP Management Architecture MIB Copyright (C) The Internet Society (2002). This version of this MIB module is part of RFC 3411; see the RFC itself for full legal notices. " REVISION "200210140000Z" -- 14 October 2002 DESCRIPTION "Changes in this revision: - Updated various administrative information. - Corrected some typos. - Corrected typo in description of SnmpEngineID that led to range overlap for 127. - Changed '255a' to '255t' in definition of SnmpAdminString to align with current SMI. - Reworded 'reserved' for value zero in DESCRIPTION of SnmpSecurityModel. - The algorithm for allocating security models should give 256 per enterprise block, rather than 255. - The example engine ID of 'abcd' is not legal. Replaced with '800002b804616263'H based on example enterprise 696, string 'abc'. - Added clarification that engineID should persist across re-initializations. This revision published as RFC 3411. " REVISION "199901190000Z" -- 19 January 1999 DESCRIPTION "Updated editors' addresses, fixed typos. Published as RFC 2571. " REVISION "199711200000Z" -- 20 November 1997 DESCRIPTION "The initial version, published in RFC 2271. " ::= { snmpModules 10 } -- Textual Conventions used in the SNMP Management Architecture *** SnmpEngineID ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "An SNMP engine's administratively-unique identifier. Objects of this type are for identification, not for addressing, even though it is possible that an address may have been used in the generation of a specific value. Harrington, et al. Standards Track [Page 41] RFC 3411 Architecture for SNMP Management Frameworks December 2002 The value for this object may not be all zeros or all 'ff'H or the empty (zero length) string. The initial value for this object may be configured via an operator console entry or via an algorithmic function. In the latter case, the following example algorithm is recommended. In cases where there are multiple engines on the same system, the use of this algorithm is NOT appropriate, as it would result in all of those engines ending up with the same ID value. 1) The very first bit is used to indicate how the rest of the data is composed. 0 - as defined by enterprise using former methods that existed before SNMPv3. See item 2 below. 1 - as defined by this architecture, see item 3 below. Note that this allows existing uses of the engineID (also known as AgentID [RFC1910]) to co-exist with any new uses. 2) The snmpEngineID has a length of 12 octets. The first four octets are set to the binary equivalent of the agent's SNMP management private enterprise number as assigned by the Internet Assigned Numbers Authority (IANA). For example, if Acme Networks has been assigned { enterprises 696 }, the first four octets would be assigned '000002b8'H. The remaining eight octets are determined via one or more enterprise-specific methods. Such methods must be designed so as to maximize the possibility that the value of this object will be unique in the agent's administrative domain. For example, it may be the IP address of the SNMP entity, or the MAC address of one of the interfaces, with each address suitably padded with random octets. If multiple methods are defined, then it is recommended that the first octet indicate the method being used and the remaining octets be a function of the method. Harrington, et al. Standards Track [Page 42] RFC 3411 Architecture for SNMP Management Frameworks December 2002 3) The length of the octet string varies. The first four octets are set to the binary equivalent of the agent's SNMP management private enterprise number as assigned by the Internet Assigned Numbers Authority (IANA). For example, if Acme Networks has been assigned { enterprises 696 }, the first four octets would be assigned '000002b8'H. The very first bit is set to 1. For example, the above value for Acme Networks now changes to be '800002b8'H. The fifth octet indicates how the rest (6th and following octets) are formatted. The values for the fifth octet are: 0 - reserved, unused. 1 - IPv4 address (4 octets) lowest non-special IP address 2 - IPv6 address (16 octets) lowest non-special IP address 3 - MAC address (6 octets) lowest IEEE MAC address, canonical order 4 - Text, administratively assigned Maximum remaining length 27 5 - Octets, administratively assigned Maximum remaining length 27 6-127 - reserved, unused 128-255 - as defined by the enterprise Maximum remaining length 27 " SYNTAX OCTET STRING (SIZE(5..32)) Harrington, et al. Standards Track [Page 43] RFC 3411 Architecture for SNMP Management Frameworks December 2002 SnmpSecurityModel ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "An identifier that uniquely identifies a Security Model of the Security Subsystem within this SNMP Management Architecture. The values for securityModel are allocated as follows: - The zero value does not identify any particular security model. - Values between 1 and 255, inclusive, are reserved for standards-track Security Models and are managed by the Internet Assigned Numbers Authority (IANA). - Values greater than 255 are allocated to enterprise-specific Security Models. An enterprise-specific securityModel value is defined to be: enterpriseID * 256 + security model within enterprise For example, the fourth Security Model defined by the enterprise whose enterpriseID is 1 would be 259. This scheme for allocation of securityModel values allows for a maximum of 255 standards- based Security Models, and for a maximum of 256 Security Models per enterprise. It is believed that the assignment of new securityModel values will be rare in practice because the larger the number of simultaneously utilized Security Models, the larger the chance that interoperability will suffer. Consequently, it is believed that such a range will be sufficient. In the unlikely event that the standards committee finds this number to be insufficient over time, an enterprise number can be allocated to obtain an additional 256 possible values. Note that the most significant bit must be zero; hence, there are 23 bits allocated for various organizations to design and define non-standard Harrington, et al. Standards Track [Page 44] RFC 3411 Architecture for SNMP Management Frameworks December 2002 securityModels. This limits the ability to define new proprietary implementations of Security Models to the first 8,388,608 enterprises. It is worthwhile to note that, in its encoded form, the securityModel value will normally require only a single byte since, in practice, the leftmost bits will be zero for most messages and sign extension is suppressed by the encoding rules. As of this writing, there are several values of securityModel defined for use with SNMP or reserved for use with supporting MIB objects. They are as follows: 0 reserved for 'any' 1 reserved for SNMPv1 2 reserved for SNMPv2c 3 User-Based Security Model (USM) " SYNTAX INTEGER(0 .. 2147483647) SnmpMessageProcessingModel ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "An identifier that uniquely identifies a Message Processing Model of the Message Processing Subsystem within this SNMP Management Architecture. The values for messageProcessingModel are allocated as follows: - Values between 0 and 255, inclusive, are reserved for standards-track Message Processing Models and are managed by the Internet Assigned Numbers Authority (IANA). - Values greater than 255 are allocated to enterprise-specific Message Processing Models. An enterprise messageProcessingModel value is defined to be: enterpriseID * 256 + messageProcessingModel within enterprise For example, the fourth Message Processing Model defined by the enterprise whose enterpriseID Harrington, et al. Standards Track [Page 45] RFC 3411 Architecture for SNMP Management Frameworks December 2002 is 1 would be 259. This scheme for allocating messageProcessingModel values allows for a maximum of 255 standards- based Message Processing Models, and for a maximum of 256 Message Processing Models per enterprise. It is believed that the assignment of new messageProcessingModel values will be rare in practice because the larger the number of simultaneously utilized Message Processing Models, the larger the chance that interoperability will suffer. It is believed that such a range will be sufficient. In the unlikely event that the standards committee finds this number to be insufficient over time, an enterprise number can be allocated to obtain an additional 256 possible values. Note that the most significant bit must be zero; hence, there are 23 bits allocated for various organizations to design and define non-standard messageProcessingModels. This limits the ability to define new proprietary implementations of Message Processing Models to the first 8,388,608 enterprises. It is worthwhile to note that, in its encoded form, the messageProcessingModel value will normally require only a single byte since, in practice, the leftmost bits will be zero for most messages and sign extension is suppressed by the encoding rules. As of this writing, there are several values of messageProcessingModel defined for use with SNMP. They are as follows: 0 reserved for SNMPv1 1 reserved for SNMPv2c 2 reserved for SNMPv2u and SNMPv2* 3 reserved for SNMPv3 " SYNTAX INTEGER(0 .. 2147483647) Harrington, et al. Standards Track [Page 46] RFC 3411 Architecture for SNMP Management Frameworks December 2002 SnmpSecurityLevel ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "A Level of Security at which SNMP messages can be sent or with which operations are being processed; in particular, one of: noAuthNoPriv - without authentication and without privacy, authNoPriv - with authentication but without privacy, authPriv - with authentication and with privacy. These three values are ordered such that noAuthNoPriv is less than authNoPriv and authNoPriv is less than authPriv. " SYNTAX INTEGER { noAuthNoPriv(1), authNoPriv(2), authPriv(3) } SnmpAdminString ::= TEXTUAL-CONVENTION DISPLAY-HINT "255t" STATUS current DESCRIPTION "An octet string containing administrative information, preferably in human-readable form. To facilitate internationalization, this information is represented using the ISO/IEC IS 10646-1 character set, encoded as an octet string using the UTF-8 transformation format described in [RFC2279]. Since additional code points are added by amendments to the 10646 standard from time to time, implementations must be prepared to encounter any code point from 0x00000000 to 0x7fffffff. Byte sequences that do not correspond to the valid UTF-8 encoding of a code point or are outside this range are prohibited. The use of control codes should be avoided. When it is necessary to represent a newline, the control code sequence CR LF should be used. Harrington, et al. Standards Track [Page 47] RFC 3411 Architecture for SNMP Management Frameworks December 2002 The use of leading or trailing white space should be avoided. For code points not directly supported by user interface hardware or software, an alternative means of entry and display, such as hexadecimal, may be provided. For information encoded in 7-bit US-ASCII, the UTF-8 encoding is identical to the US-ASCII encoding. UTF-8 may require multiple bytes to represent a single character / code point; thus the length of this object in octets may be different from the number of characters encoded. Similarly, size constraints refer to the number of encoded octets, not the number of characters represented by an encoding. Note that when this TC is used for an object that is used or envisioned to be used as an index, then a SIZE restriction MUST be specified so that the number of sub-identifiers for any object instance does not exceed the limit of 128, as defined by [RFC3416]. Note that the size of an SnmpAdminString object is measured in octets, not characters. " SYNTAX OCTET STRING (SIZE (0..255)) -- Administrative assignments *************************************** snmpFrameworkAdmin OBJECT IDENTIFIER ::= { snmpFrameworkMIB 1 } snmpFrameworkMIBObjects OBJECT IDENTIFIER ::= { snmpFrameworkMIB 2 } snmpFrameworkMIBConformance OBJECT IDENTIFIER ::= { snmpFrameworkMIB 3 } -- the snmpEngine Group ******************************************** snmpEngine OBJECT IDENTIFIER ::= { snmpFrameworkMIBObjects 1 } Harrington, et al. Standards Track [Page 48] RFC 3411 Architecture for SNMP Management Frameworks December 2002 snmpEngineID OBJECT-TYPE SYNTAX SnmpEngineID MAX-ACCESS read-only STATUS current DESCRIPTION "An SNMP engine's administratively-unique identifier. This information SHOULD be stored in non-volatile storage so that it remains constant across re-initializations of the SNMP engine. " ::= { snmpEngine 1 } snmpEngineBoots OBJECT-TYPE SYNTAX INTEGER (1..2147483647) MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times that the SNMP engine has (re-)initialized itself since snmpEngineID was last configured. " ::= { snmpEngine 2 } snmpEngineTime OBJECT-TYPE SYNTAX INTEGER (0..2147483647) UNITS "seconds" MAX-ACCESS read-only STATUS current DESCRIPTION "The number of seconds since the value of the snmpEngineBoots object last changed. When incrementing this object's value would cause it to exceed its maximum, snmpEngineBoots is incremented as if a re-initialization had occurred, and this object's value consequently reverts to zero. " ::= { snmpEngine 3 } snmpEngineMaxMessageSize OBJECT-TYPE SYNTAX INTEGER (484..2147483647) MAX-ACCESS read-only STATUS current DESCRIPTION "The maximum length in octets of an SNMP message which this SNMP engine can send or receive and process, determined as the minimum of the maximum message size values supported among all of the transports available to and supported by the engine. " ::= { snmpEngine 4 } Harrington, et al. Standards Track [Page 49] RFC 3411 Architecture for SNMP Management Frameworks December 2002 -- Registration Points for Authentication and Privacy Protocols ** snmpAuthProtocols OBJECT-IDENTITY STATUS current DESCRIPTION "Registration point for standards-track authentication protocols used in SNMP Management Frameworks. " ::= { snmpFrameworkAdmin 1 } snmpPrivProtocols OBJECT-IDENTITY STATUS current DESCRIPTION "Registration point for standards-track privacy protocols used in SNMP Management Frameworks. " ::= { snmpFrameworkAdmin 2 } -- Conformance information ****************************************** snmpFrameworkMIBCompliances OBJECT IDENTIFIER ::= {snmpFrameworkMIBConformance 1} snmpFrameworkMIBGroups OBJECT IDENTIFIER ::= {snmpFrameworkMIBConformance 2} -- compliance statements snmpFrameworkMIBCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for SNMP engines which implement the SNMP Management Framework MIB. " MODULE -- this module MANDATORY-GROUPS { snmpEngineGroup } ::= { snmpFrameworkMIBCompliances 1 } -- units of conformance snmpEngineGroup OBJECT-GROUP OBJECTS { snmpEngineID, snmpEngineBoots, snmpEngineTime, snmpEngineMaxMessageSize } STATUS current DESCRIPTION "A collection of objects for identifying and determining the configuration and current timeliness Harrington, et al. Standards Track [Page 50] RFC 3411 Architecture for SNMP Management Frameworks December 2002 values of an SNMP engine. " ::= { snmpFrameworkMIBGroups 1 } END 6. IANA Considerations This document defines three number spaces administered by IANA, one for security models, another for message processing models, and a third for SnmpEngineID formats. 6.1. Security Models The SnmpSecurityModel TEXTUAL-CONVENTION values managed by IANA are in the range from 0 to 255 inclusive, and are reserved for standards-track Security Models. If this range should in the future prove insufficient, an enterprise number can be allocated to obtain an additional 256 possible values. As of this writing, there are several values of securityModel defined for use with SNMP or reserved for use with supporting MIB objects. They are as follows: 0 reserved for 'any' 1 reserved for SNMPv1 2 reserved for SNMPv2c 3 User-Based Security Model (USM) 6.2. Message Processing Models The SnmpMessageProcessingModel TEXTUAL-CONVENTION values managed by IANA are in the range 0 to 255, inclusive. Each value uniquely identifies a standards-track Message Processing Model of the Message Processing Subsystem within the SNMP Management Architecture. Should this range prove insufficient in the future, an enterprise number may be obtained for the standards committee to get an additional 256 possible values. As of this writing, there are several values of messageProcessingModel defined for use with SNMP. They are as follows: 0 reserved for SNMPv1 1 reserved for SNMPv2c 2 reserved for SNMPv2u and SNMPv2* 3 reserved for SNMPv3 Harrington, et al. Standards Track [Page 51] RFC 3411 Architecture for SNMP Management Frameworks December 2002 6.3. SnmpEngineID Formats The SnmpEngineID TEXTUAL-CONVENTION's fifth octet contains a format identifier. The values managed by IANA are in the range 6 to 127, inclusive. Each value uniquely identifies a standards-track SnmpEngineID format. 7. Intellectual Property The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in RFC 2028. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 8. Acknowledgements This document is the result of the efforts of the SNMPv3 Working Group. Some special thanks are in order to the following SNMPv3 WG members: Harald Tveit Alvestrand (Maxware) Dave Battle (SNMP Research, Inc.) Alan Beard (Disney Worldwide Services) Paul Berrevoets (SWI Systemware/Halcyon Inc.) Martin Bjorklund (Ericsson) Uri Blumenthal (IBM T.J. Watson Research Center) Jeff Case (SNMP Research, Inc.) John Curran (BBN) Mike Daniele (Compaq Computer Corporation) T. Max Devlin (Eltrax Systems) John Flick (Hewlett Packard) Rob Frye (MCI) Wes Hardaker (U.C.Davis, Information Technology - D.C.A.S.) Harrington, et al. Standards Track [Page 52] RFC 3411 Architecture for SNMP Management Frameworks December 2002 David Harrington (Cabletron Systems Inc.) Lauren Heintz (BMC Software, Inc.) N.C. Hien (IBM T.J. Watson Research Center) Michael Kirkham (InterWorking Labs, Inc.) Dave Levi (SNMP Research, Inc.) Louis A Mamakos (UUNET Technologies Inc.) Joe Marzot (Nortel Networks) Paul Meyer (Secure Computing Corporation) Keith McCloghrie (Cisco Systems) Bob Moore (IBM) Russ Mundy (TIS Labs at Network Associates) Bob Natale (ACE*COMM Corporation) Mike O'Dell (UUNET Technologies Inc.) Dave Perkins (DeskTalk) Peter Polkinghorne (Brunel University) Randy Presuhn (BMC Software, Inc.) David Reeder (TIS Labs at Network Associates) David Reid (SNMP Research, Inc.) Aleksey Romanov (Quality Quorum) Shawn Routhier (Epilogue) Juergen Schoenwaelder (TU Braunschweig) Bob Stewart (Cisco Systems) Mike Thatcher (Independent Consultant) Bert Wijnen (IBM T.J. Watson Research Center) The document is based on recommendations of the IETF Security and Administrative Framework Evolution for SNMP Advisory Team. Members of that Advisory Team were: David Harrington (Cabletron Systems Inc.) Jeff Johnson (Cisco Systems) David Levi (SNMP Research Inc.) John Linn (Openvision) Russ Mundy (Trusted Information Systems) chair Shawn Routhier (Epilogue) Glenn Waters (Nortel) Bert Wijnen (IBM T. J. Watson Research Center) As recommended by the Advisory Team and the SNMPv3 Working Group Charter, the design incorporates as much as practical from previous RFCs and drafts. As a result, special thanks are due to the authors of previous designs known as SNMPv2u and SNMPv2*: Jeff Case (SNMP Research, Inc.) David Harrington (Cabletron Systems Inc.) David Levi (SNMP Research, Inc.) Keith McCloghrie (Cisco Systems) Brian O'Keefe (Hewlett Packard) Harrington, et al. Standards Track [Page 53] RFC 3411 Architecture for SNMP Management Frameworks December 2002 Marshall T. Rose (Dover Beach Consulting) Jon Saperia (BGS Systems Inc.) Steve Waldbusser (International Network Services) Glenn W. Waters (Bell-Northern Research Ltd.) 9. Security Considerations This document describes how an implementation can include a Security Model to protect management messages and an Access Control Model to control access to management information. The level of security provided is determined by the specific Security Model implementation(s) and the specific Access Control Model implementation(s) used. Applications have access to data which is not secured. Applications SHOULD take reasonable steps to protect the data from disclosure. It is the responsibility of the purchaser of an implementation to ensure that: 1) an implementation complies with the rules defined by this architecture, 2) the Security and Access Control Models utilized satisfy the security and access control needs of the organization, 3) the implementations of the Models and Applications comply with the model and application specifications, 4) and the implementation protects configuration secrets from inadvertent disclosure. This document also contains a MIB definition module. None of the objects defined is writable, and the information they represent is not deemed to be particularly sensitive. However, if they are deemed sensitive in a particular environment, access to them should be restricted through the use of appropriately configured Security and Access Control models. 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Harrington, et al. Standards Track [Page 54] RFC 3411 Architecture for SNMP Management Frameworks December 2002 [RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [RFC2578] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M. and S. Waldbusser, "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999. [RFC2579] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M. and S. Waldbusser, "Textual Conventions for SMIv2", STD 58, RFC 2579, April 1999. [RFC2580] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M. and S. Waldbusser, "Conformance Statements for SMIv2", STD 58, RFC 2580, April 1999. [RFC3412] Case, J., Harrington, D., Presuhn, R. and B. Wijnen, "Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3412, December 2002. [RFC3413] Levi, D., Meyer, P. and B. Stewart, "Simple Network Management Protocol (SNMP) Applications", STD 62, RFC 3413, December 2002. [RFC3414] Blumenthal, U. and B. Wijnen, "User-Based Security Model (USM) for Version 3 of the Simple Network Management Protocol (SNMPv3)", STD 62, RFC 3414, December 2002. [RFC3415] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3415, December 2002. [RFC3416] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Protocol Operations for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3416, December 2002. [RFC3417] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Transport Mappings for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3417, December 2002. [RFC3418] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Management Information Base (MIB) for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3418, December 2002. Harrington, et al. Standards Track [Page 55] RFC 3411 Architecture for SNMP Management Frameworks December 2002 10.2. Informative References [RFC1155] Rose, M. and K. McCloghrie, "Structure and Identification of Management Information for TCP/IP-based internets", STD 16, RFC 1155, May 1990. [RFC1157] Case, J., Fedor, M., Schoffstall, M. and J. Davin, "The Simple Network Management Protocol", STD 15, RFC 1157, May 1990. [RFC1212] Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16, RFC 1212, March 1991. [RFC1901] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Introduction to Community-based SNMPv2", RFC 1901, January 1996. [RFC1909] McCloghrie, K., Editor, "An Administrative Infrastructure for SNMPv2", RFC 1909, February 1996. [RFC1910] Waters, G., Editor, "User-based Security Model for SNMPv2", RFC 1910, February 1996. [RFC2028] Hovey, R. and S. Bradner, "The Organizations Involved in the IETF Standards Process", BCP 11, RFC 2028, October 1996. [RFC2576] Frye, R., Levi, D., Routhier, S. and B. Wijnen, "Coexistence between Version 1, Version 2, and Version 3 of the Internet-Standard Network Management Framework", RFC 2576, March 2000. [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", RFC 2863, June 2000. [RFC3410] Case, J., Mundy, R., Partain, D. and B. Stewart, "Introduction and Applicability Statements for Internet- Standard Management Framework", RFC 3410, December 2002. Harrington, et al. Standards Track [Page 56] RFC 3411 Architecture for SNMP Management Frameworks December 2002 Appendix A A. Guidelines for Model Designers This appendix describes guidelines for designers of models which are expected to fit into the architecture defined in this document. SNMPv1 and SNMPv2c are two SNMP frameworks which use communities to provide trivial authentication and access control. SNMPv1 and SNMPv2c Frameworks can coexist with Frameworks designed according to this architecture, and modified versions of SNMPv1 and SNMPv2c Frameworks could be designed to meet the requirements of this architecture, but this document does not provide guidelines for that coexistence. Within any subsystem model, there should be no reference to any specific model of another subsystem, or to data defined by a specific model of another subsystem. Transfer of data between the subsystems is deliberately described as a fixed set of abstract data elements and primitive functions which can be overloaded to satisfy the needs of multiple model definitions. Documents which define models to be used within this architecture SHOULD use the standard primitives between subsystems, possibly defining specific mechanisms for converting the abstract data elements into model-usable formats. This constraint exists to allow subsystem and model documents to be written recognizing common borders of the subsystem and model. Vendors are not constrained to recognize these borders in their implementations. The architecture defines certain standard services to be provided between subsystems, and the architecture defines abstract service interfaces to request these services. Each model definition for a subsystem SHOULD support the standard service interfaces, but whether, or how, or how well, it performs the service is dependent on the model definition. A.1. Security Model Design Requirements A.1.1. Threats A document describing a Security Model MUST describe how the model protects against the threats described under "Security Requirements of this Architecture", section 1.4. Harrington, et al. Standards Track [Page 57] RFC 3411 Architecture for SNMP Management Frameworks December 2002 A.1.2. Security Processing Received messages MUST be validated by a Model of the Security Subsystem. Validation includes authentication and privacy processing if needed, but it is explicitly allowed to send messages which do not require authentication or privacy. A received message contains a specified securityLevel to be used during processing. All messages requiring privacy MUST also require authentication. A Security Model specifies rules by which authentication and privacy are to be done. A model may define mechanisms to provide additional security features, but the model definition is constrained to using (possibly a subset of) the abstract data elements defined in this document for transferring data between subsystems. Each Security Model may allow multiple security protocols to be used concurrently within an implementation of the model. Each Security Model defines how to determine which protocol to use, given the securityLevel and the security parameters relevant to the message. Each Security Model, with its associated protocol(s) defines how the sending/receiving entities are identified, and how secrets are configured. Authentication and Privacy protocols supported by Security Models are uniquely identified using Object Identifiers. IETF standard protocols for authentication or privacy should have an identifier defined within the snmpAuthProtocols or the snmpPrivProtocols subtrees. Enterprise specific protocol identifiers should be defined within the enterprise subtree. For privacy, the Security Model defines what portion of the message is encrypted. The persistent data used for security should be SNMP-manageable, but the Security Model defines whether an instantiation of the MIB is a conformance requirement. Security Models are replaceable within the Security Subsystem. Multiple Security Model implementations may exist concurrently within an SNMP engine. The number of Security Models defined by the SNMP community should remain small to promote interoperability. Harrington, et al. Standards Track [Page 58] RFC 3411 Architecture for SNMP Management Frameworks December 2002 A.1.3. Validate the security-stamp in a received message A Message Processing Model requests that a Security Model: - verifies that the message has not been altered, - authenticates the identification of the principal for whom the message was generated. - decrypts the message if it was encrypted. Additional requirements may be defined by the model, and additional services may be provided by the model, but the model is constrained to use the following primitives for transferring data between subsystems. Implementations are not so constrained. A Message Processing Model uses the processIncomingMsg primitive as described in section 4.4.2. A.1.4. Security MIBs Each Security Model defines the MIB module(s) required for security processing, including any MIB module(s) required for the security protocol(s) supported. The MIB module(s) SHOULD be defined concurrently with the procedures which use the MIB module(s). The MIB module(s) are subject to normal access control rules. The mapping between the model-dependent security ID and the securityName MUST be able to be determined using SNMP, if the model- dependent MIB is instantiated and if access control policy allows access. A.1.5. Cached Security Data For each message received, the Security Model caches the state information such that a Response message can be generated using the same security information, even if the Local Configuration Datastore is altered between the time of the incoming request and the outgoing response. A Message Processing Model has the responsibility for explicitly releasing the cached data if such data is no longer needed. To enable this, an abstract securityStateReference data element is passed from the Security Model to the Message Processing Model. The cached security data may be implicitly released via the generation of a response, or explicitly released by using the stateRelease primitive, as described in section 4.5.1. Harrington, et al. Standards Track [Page 59] RFC 3411 Architecture for SNMP Management Frameworks December 2002 A.2. Message Processing Model Design Requirements An SNMP engine contains a Message Processing Subsystem which may contain multiple Message Processing Models. The Message Processing Model MUST always (conceptually) pass the complete PDU, i.e., it never forwards less than the complete list of varBinds. A.2.1. Receiving an SNMP Message from the Network Upon receipt of a message from the network, the Dispatcher in the SNMP engine determines the version of the SNMP message and interacts with the corresponding Message Processing Model to determine the abstract data elements. A Message Processing Model specifies the SNMP Message format it supports and describes how to determine the values of the abstract data elements (like msgID, msgMaxSize, msgFlags, msgSecurityParameters, securityModel, securityLevel etc). A Message Processing Model interacts with a Security Model to provide security processing for the message using the processIncomingMsg primitive, as described in section 4.4.2. A.2.2. Sending an SNMP Message to the Network The Dispatcher in the SNMP engine interacts with a Message Processing Model to prepare an outgoing message. For that it uses the following primitives: - for requests and notifications: prepareOutgoingMessage, as described in section 4.2.1. - for response messages: prepareResponseMessage, as described in section 4.2.2. A Message Processing Model, when preparing an Outgoing SNMP Message, interacts with a Security Model to secure the message. For that it uses the following primitives: - for requests and notifications: generateRequestMsg, as described in section 4.4.1. - for response messages: generateResponseMsg as described in section 4.4.3. Harrington, et al. Standards Track [Page 60] RFC 3411 Architecture for SNMP Management Frameworks December 2002 Once the SNMP message is prepared by a Message Processing Model, the Dispatcher sends the message to the desired address using the appropriate transport. A.3. Application Design Requirements Within an application, there may be an explicit binding to a specific SNMP message version, i.e., a specific Message Processing Model, and to a specific Access Control Model, but there should be no reference to any data defined by a specific Message Processing Model or Access Control Model. Within an application, there should be no reference to any specific Security Model, or any data defined by a specific Security Model. An application determines whether explicit or implicit access control should be applied to the operation, and, if access control is needed, which Access Control Model should be used. An application has the responsibility to define any MIB module(s) used to provide application-specific services. Applications interact with the SNMP engine to initiate messages, receive responses, receive asynchronous messages, and send responses. A.3.1. Applications that Initiate Messages Applications may request that the SNMP engine send messages containing SNMP commands or notifications using the sendPdu primitive as described in section 4.1.1. If it is desired that a message be sent to multiple targets, it is the responsibility of the application to provide the iteration. The SNMP engine assumes necessary access control has been applied to the PDU, and provides no access control services. The SNMP engine looks at the "expectResponse" parameter, and if a response is expected, then the appropriate information is cached such that a later response can be associated to this message, and can then be returned to the application. A sendPduHandle is returned to the application so it can later correspond the response with this message as well. Harrington, et al. Standards Track [Page 61] RFC 3411 Architecture for SNMP Management Frameworks December 2002 A.3.2. Applications that Receive Responses The SNMP engine matches the incoming response messages to outstanding messages sent by this SNMP engine, and forwards the response to the associated application using the processResponsePdu primitive, as described in section 4.1.4. A.3.3. Applications that Receive Asynchronous Messages When an SNMP engine receives a message that is not the response to a request from this SNMP engine, it must determine to which application the message should be given. An Application that wishes to receive asynchronous messages registers itself with the engine using the primitive registerContextEngineID as described in section 4.1.5. An Application that wishes to stop receiving asynchronous messages should unregister itself with the SNMP engine using the primitive unregisterContextEngineID as described in section 4.1.5. Only one registration per combination of PDU type and contextEngineID is permitted at the same time. Duplicate registrations are ignored. An errorIndication will be returned to the application that attempts to duplicate a registration. All asynchronously received messages containing a registered combination of PDU type and contextEngineID are sent to the application which registered to support that combination. The engine forwards the PDU to the registered application, using the processPdu primitive, as described in section 4.1.2. A.3.4. Applications that Send Responses Request operations require responses. An application sends a response via the returnResponsePdu primitive, as described in section 4.1.3. The contextEngineID, contextName, securityModel, securityName, securityLevel, and stateReference parameters are from the initial processPdu primitive. The PDU and statusInformation are the results of processing. Harrington, et al. Standards Track [Page 62] RFC 3411 Architecture for SNMP Management Frameworks December 2002 A.4. Access Control Model Design Requirements An Access Control Model determines whether the specified securityName is allowed to perform the requested operation on a specified managed object. The Access Control Model specifies the rules by which access control is determined. The persistent data used for access control should be manageable using SNMP, but the Access Control Model defines whether an instantiation of the MIB is a conformance requirement. The Access Control Model must provide the primitive isAccessAllowed. Editors' Addresses Bert Wijnen Lucent Technologies Schagen 33 3461 GL Linschoten Netherlands Phone: +31 348-680-485 EMail: bwijnen@lucent.com David Harrington Enterasys Networks Post Office Box 5005 35 Industrial Way Rochester, New Hampshire 03866-5005 USA Phone: +1 603-337-2614 EMail: dbh@enterasys.com Randy Presuhn BMC Software, Inc. 2141 North First Street San Jose, California 95131 USA Phone: +1 408-546-1006 Fax: +1 408-965-0359 EMail: randy_presuhn@bmc.com Harrington, et al. Standards Track [Page 63] RFC 3411 Architecture for SNMP Management Frameworks December 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Harrington, et al. Standards Track [Page 64] ========================================================================= Network Working Group J. Case Request for Comments: 3412 SNMP Research, Inc. STD: 62 D. Harrington Obsoletes: 2572 Enterasys Networks Category: Standards Track R. Presuhn BMC Software, Inc. B. Wijnen Lucent Technologies December 2002 Message Processing and Dispatching for the Simple Network Management Protocol (SNMP) Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document describes the Message Processing and Dispatching for Simple Network Management Protocol (SNMP) messages within the SNMP architecture. It defines the procedures for dispatching potentially multiple versions of SNMP messages to the proper SNMP Message Processing Models, and for dispatching PDUs to SNMP applications. This document also describes one Message Processing Model - the SNMPv3 Message Processing Model. This document obsoletes RFC 2572. Case, et al. Standards Track [Page 1] RFC 3412 Message Processing and Dispatching for SNMP December 2002 Table of Contents 1. Introduction ................................................ 3 2. Overview .................................................... 4 2.1. The Dispatcher ............................................ 5 2.2. Message Processing Subsystem .............................. 5 3. Elements of Message Processing and Dispatching .............. 6 3.1. messageProcessingModel .................................... 6 3.2. pduVersion ................................................ 6 3.3. pduType ................................................... 7 3.4. sendPduHandle ............................................. 7 4. Dispatcher Elements of Procedure ............................ 7 4.1. Sending an SNMP Message to the Network .................... 7 4.1.1. Sending a Request or Notification ....................... 8 4.1.2. Sending a Response to the Network ....................... 9 4.2. Receiving an SNMP Message from the Network ................ 11 4.2.1. Message Dispatching of received SNMP Messages ........... 11 4.2.2. PDU Dispatching for Incoming Messages ................... 12 4.2.2.1. Incoming Requests and Notifications ................... 13 4.2.2.2. Incoming Responses .................................... 14 4.3. Application Registration for Handling PDU types ........... 15 4.4. Application Unregistration for Handling PDU Types ......... 16 5. Definitions ................................................. 16 5.1. Definitions for SNMP Message Processing and Dispatching ... 16 6. The SNMPv3 Message Format ................................... 19 6.1. msgVersion ................................................ 20 6.2. msgID ..................................................... 20 6.3. msgMaxSize ................................................ 21 6.4. msgFlags .................................................. 21 6.5. msgSecurityModel .......................................... 24 6.6. msgSecurityParameters ..................................... 24 6.7. scopedPduData ............................................. 24 6.8. scopedPDU ................................................. 24 6.8.1. contextEngineID ......................................... 24 6.8.2. contextName ............................................. 25 6.8.3. data .................................................... 25 7. Elements of Procedure for v3MP .............................. 25 7.1. Prepare an Outgoing SNMP Message .......................... 26 7.2. Prepare Data Elements from an Incoming SNMP Message ....... 32 8. Intellectual Property ....................................... 37 9. Acknowledgements ............................................ 38 10. Security Considerations .................................... 39 11. References ................................................. 40 11.1. Normative References ..................................... 40 11.2. Informative References ................................... 41 12. Editors' Addresses ......................................... 42 13. Full Copyright Statement ................................... 43 Case, et al. Standards Track [Page 2] RFC 3412 Message Processing and Dispatching for SNMP December 2002 1. Introduction The Architecture for describing Internet Management Frameworks [RFC3411] describes that an SNMP engine is composed of: 1) a Dispatcher 2) a Message Processing Subsystem, 3) a Security Subsystem, and 4) an Access Control Subsystem. Applications make use of the services of these subsystems. It is important to understand the SNMP architecture and its terminology to understand where the Message Processing Subsystem and Dispatcher described in this document fit into the architecture and interact with other subsystems within the architecture. The reader is expected to have read and understood the description of the SNMP architecture, defined in [RFC3411]. The Dispatcher in the SNMP engine sends and receives SNMP messages. It also dispatches SNMP PDUs to SNMP applications. When an SNMP message needs to be prepared or when data needs to be extracted from an SNMP message, the Dispatcher delegates these tasks to a message version-specific Message Processing Model within the Message Processing Subsystem. A Message Processing Model is responsible for processing an SNMP version-specific message and for coordinating the interaction with the Security Subsystem to ensure proper security is applied to the SNMP message being handled. Interactions between the Dispatcher, the Message Processing Subsystem, and applications are modeled using abstract data elements and abstract service interface primitives defined by the SNMP architecture. Similarly, interactions between the Message Processing Subsystem and the Security Subsystem are modeled using abstract data elements and abstract service interface primitives as defined by the SNMP architecture. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119. Case, et al. Standards Track [Page 3] RFC 3412 Message Processing and Dispatching for SNMP December 2002 2. Overview The following illustration depicts the Message Processing in relation to SNMP applications, the Security Subsystem and Transport Mappings. +-------------------------------------------------------------------+ | SNMP Entity | | | | +---------------------------------------------------------------+ | | | Applications | | | | +-----------+ +--------------+ | | | | | Command | | Notification | | | | | | Generator | | Originator | +-----------+ +--------------+| | | | +-----------+ +--------------+ | Proxy | | Other || | | | +-----------+ +--------------+ | Forwarder | |Application(s)|| | | | | Command | | Notification | +-----------+ +--------------+| | | | | Responder | | Receiver | | | | | +-----------+ +--------------+ | | | +---------------------------------------------------------------+ | | ^ ^ ^ ^ | | | | | | | | v v v v | | +--------+-------+---------------+-----------+ | | ^ | | | +---------------------+ +-----------------+ | | | | Message Processing | | Security | | | Dispatcher v | Subsystem | | Subsystem | | | +------------------+ | +------------+ | | | | | | PDU Dispatcher | | +->| v1MP * |<--->| +-------------+ | | | | | | | +------------+ | | | Other | | | | | | | | +------------+ | | | Security | | | | | | | +->| v2cMP * |<--->| | Model | | | | | Message | | | +------------+ | | +-------------+ | | | | Dispatcher <-------->+ | | | | | | | | | +------------+ | | +-------------+ | | | | | | +->| v3MP * |<--->| | User-based | | | | | Transport | | | +------------+ | | | Security | | | | | Mapping | | | +------------+ | | | Model | | | | | (e.g., RFC 3417) | | +->| otherMP * |<--->| +-------------+ | | | +------------------+ | +------------+ | | | | | ^ +---------------------+ +-----------------+ | | | | +----------|--------------------------------------------------------+ v +------------------+ | Network | * One or more models may be present. +------------------+ Case, et al. Standards Track [Page 4] RFC 3412 Message Processing and Dispatching for SNMP December 2002 2.1. The Dispatcher The Dispatcher is a key piece of an SNMP engine. There is only one in an SNMP engine, and its job is to dispatch tasks to the multiple version-specific Message Processing Models, and to dispatch PDUs to various applications. For outgoing messages, an application provides a PDU to be sent, plus the data needed to prepare and send the message, and the application specifies which version-specific Message Processing Model will be used to prepare the message with the desired security processing. Once the message is prepared, the Dispatcher sends the message. For incoming messages, the Dispatcher determines the SNMP version of the incoming message and passes the message to the version-specific Message Processing Model to extract the components of the message and to coordinate the processing of security services for the message. After version-specific processing, the PDU Dispatcher determines which application, if any, should receive the PDU for processing and forwards it accordingly. The Dispatcher, while sending and receiving SNMP messages, collects statistics about SNMP messages and the behavior of the SNMP engine in managed objects to make them accessible to remote SNMP entities. This document defines these managed objects, the MIB module which contains them, and how these managed objects might be used to provide useful management. 2.2. Message Processing Subsystem The SNMP Message Processing Subsystem is the part of an SNMP engine which interacts with the Dispatcher to handle the version-specific SNMP messages. It contains one or more Message Processing Models. This document describes one Message Processing Model, the SNMPv3 Message Processing Model, in Section 6. The SNMPv3 Message Processing Model is defined in a separate section to show that multiple (independent) Message Processing Models can exist at the same time and that such Models can be described in different documents. The SNMPv3 Message Processing Model can be replaced or supplemented with other Message Processing Models in the future. Two Message Processing Models which are expected to be developed in the future are the SNMPv1 message format [RFC1157] and the SNMPv2c message format [RFC1901]. Others may be developed as needed. Case, et al. Standards Track [Page 5] RFC 3412 Message Processing and Dispatching for SNMP December 2002 3. Elements of Message Processing and Dispatching See [RFC3411] for the definitions of: contextEngineID contextName scopedPDU maxSizeResponseScopedPDU securityModel securityName securityLevel messageProcessingModel For incoming messages, a version-specific message processing module provides these values to the Dispatcher. For outgoing messages, an application provides these values to the Dispatcher. For some version-specific processing, the values may be extracted from received messages; for other versions, the values may be determined by algorithm, or by an implementation-defined mechanism. The mechanism by which the value is determined is irrelevant to the Dispatcher. The following additional or expanded definitions are for use within the Dispatcher. 3.1. messageProcessingModel The value of messageProcessingModel identifies a Message Processing Model. A Message Processing Model describes the version-specific procedures for extracting data from messages, generating messages, calling upon a securityModel to apply its security services to messages, for converting data from a version-specific message format into a generic format usable by the Dispatcher, and for converting data from Dispatcher format into a version-specific message format. 3.2. pduVersion The value of pduVersion represents a specific version of protocol operation and its associated PDU formats, such as SNMPv1 or SNMPv2 [RFC3416]. The values of pduVersion are specific to the version of the PDU contained in a message, and the PDUs processed by applications. The Dispatcher does not use the value of pduVersion directly. Case, et al. Standards Track [Page 6] RFC 3412 Message Processing and Dispatching for SNMP December 2002 An application specifies the pduVersion when it requests the PDU Dispatcher to send a PDU to another SNMP engine. The Dispatcher passes the pduVersion to a Message Processing Model, so it knows how to handle the PDU properly. For incoming messages, the pduVersion is provided to the Dispatcher by a version-specific Message Processing module. The PDU Dispatcher passes the pduVersion to the application so it knows how to handle the PDU properly. For example, a command responder application needs to know whether to use [RFC3416] elements of procedure and syntax instead of those specified for SNMPv1. 3.3. pduType A value of the pduType represents a specific type of protocol operation. The values of the pduType are specific to the version of the PDU contained in a message. Applications register to support particular pduTypes for particular contextEngineIDs. For incoming messages, pduType is provided to the Dispatcher by a version-specific Message Processing module. It is subsequently used to dispatch the PDU to the application which registered for the pduType for the contextEngineID of the associated scopedPDU. 3.4. sendPduHandle This handle is generated for coordinating the processing of requests and responses between the SNMP engine and an application. The handle must be unique across all version-specific Message Processing Models, and is of local significance only. 4. Dispatcher Elements of Procedure This section describes the procedures followed by the Dispatcher when generating and processing SNMP messages. 4.1. Sending an SNMP Message to the Network This section describes the procedure followed by an SNMP engine whenever it sends an SNMP message. Case, et al. Standards Track [Page 7] RFC 3412 Message Processing and Dispatching for SNMP December 2002 4.1.1. Sending a Request or Notification The following procedures are followed by the Dispatcher when an application wants to send an SNMP PDU to another (remote) application, i.e., to initiate a communication by originating a message, such as one containing a request or a notification. 1) The application requests this using the abstract service primitive: statusInformation = -- sendPduHandle if success -- errorIndication if failure sendPdu( IN transportDomain -- transport domain to be used IN transportAddress -- destination network address IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model to use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN contextEngineID -- data from/at this entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN expectResponse -- TRUE or FALSE ) 2) If the messageProcessingModel value does not represent a Message Processing Model known to the Dispatcher, then an errorIndication (implementation-dependent) is returned to the calling application. No further processing is performed. 3) The Dispatcher generates a sendPduHandle to coordinate subsequent processing. Case, et al. Standards Track [Page 8] RFC 3412 Message Processing and Dispatching for SNMP December 2002 4) The Message Dispatcher sends the request to the version-specific Message Processing module identified by messageProcessingModel using the abstract service primitive: statusInformation = -- success or error indication prepareOutgoingMessage( IN transportDomain -- as specified by application IN transportAddress -- as specified by application IN messageProcessingModel -- as specified by application IN securityModel -- as specified by application IN securityName -- as specified by application IN securityLevel -- as specified by application IN contextEngineID -- as specified by application IN contextName -- as specified by application IN pduVersion -- as specified by application IN PDU -- as specified by application IN expectResponse -- as specified by application IN sendPduHandle -- as determined in step 3. OUT destTransportDomain -- destination transport domain OUT destTransportAddress -- destination transport address OUT outgoingMessage -- the message to send OUT outgoingMessageLength -- the message length ) 5) If the statusInformation indicates an error, the errorIndication is returned to the calling application. No further processing is performed. 6) If the statusInformation indicates success, the sendPduHandle is returned to the application, and the outgoingMessage is sent. The transport used to send the outgoingMessage is returned via destTransportDomain, and the address to which it was sent is returned via destTransportAddress. Outgoing Message Processing is complete. 4.1.2. Sending a Response to the Network The following procedure is followed when an application wants to return a response back to the originator of an SNMP Request. Case, et al. Standards Track [Page 9] RFC 3412 Message Processing and Dispatching for SNMP December 2002 1) An application can request this using the abstract service primitive: result = returnResponsePdu( IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- same as on incoming request IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size of Response PDU IN stateReference -- reference to state information -- as presented with the request IN statusInformation -- success or errorIndication ) -- (error counter OID and value -- when errorIndication) 2) The Message Dispatcher sends the request to the appropriate Message Processing Model indicated by the received value of messageProcessingModel using the abstract service primitive: result = -- SUCCESS or errorIndication prepareResponseMessage( IN messageProcessingModel -- specified by application IN securityModel -- specified by application IN securityName -- specified by application IN securityLevel -- specified by application IN contextEngineID -- specified by application IN contextName -- specified by application IN pduVersion -- specified by application IN PDU -- specified by application IN maxSizeResponseScopedPDU -- specified by application IN stateReference -- specified by application IN statusInformation -- specified by application OUT destTransportDomain -- destination transport domain OUT destTransportAddress -- destination transport address OUT outgoingMessage -- the message to send OUT outgoingMessageLength -- the message length ) 3) If the result is an errorIndication, the errorIndication is returned to the calling application. No further processing is performed. Case, et al. Standards Track [Page 10] RFC 3412 Message Processing and Dispatching for SNMP December 2002 4) If the result is success, the outgoingMessage is sent. The transport used to send the outgoingMessage is returned via destTransportDomain, and the address to which it was sent is returned via destTransportAddress. Message Processing is complete. 4.2. Receiving an SNMP Message from the Network This section describes the procedure followed by an SNMP engine whenever it receives an SNMP message. Please note, that for the sake of clarity and to prevent the text from being even longer and more complicated, some details were omitted from the steps below. In particular, the elements of procedure do not always explicitly indicate when state information needs to be released. The general rule is that if state information is available when a message is to be "discarded without further processing", then the state information must also be released at that same time. 4.2.1. Message Dispatching of received SNMP Messages 1) The snmpInPkts counter [RFC3418] is incremented. 2) The version of the SNMP message is determined in an implementation-dependent manner. If the packet cannot be sufficiently parsed to determine the version of the SNMP message, then the snmpInASNParseErrs [RFC3418] counter is incremented, and the message is discarded without further processing. If the version is not supported, then the snmpInBadVersions [RFC3418] counter is incremented, and the message is discarded without further processing. 3) The origin transportDomain and origin transportAddress are determined. Case, et al. Standards Track [Page 11] RFC 3412 Message Processing and Dispatching for SNMP December 2002 4) The message is passed to the version-specific Message Processing Model which returns the abstract data elements required by the Dispatcher. This is performed using the abstract service primitive: result = -- SUCCESS or errorIndication prepareDataElements( IN transportDomain -- origin as determined in step 3. IN transportAddress -- origin as determined in step 3. IN wholeMsg -- as received from the network IN wholeMsgLength -- as received from the network OUT messageProcessingModel -- typically, SNMP version OUT securityModel -- Security Model specified OUT securityName -- on behalf of this principal OUT securityLevel -- Level of Security specified OUT contextEngineID -- data from/at this entity OUT contextName -- data from/in this context OUT pduVersion -- the version of the PDU OUT PDU -- SNMP Protocol Data Unit OUT pduType -- SNMP PDU type OUT sendPduHandle -- handle for a matched request OUT maxSizeResponseScopedPDU -- maximum size of Response PDU OUT statusInformation -- success or errorIndication -- (error counter OID and value -- when errorIndication) OUT stateReference -- reference to state information -- to be used for a possible ) -- Response 5) If the result is a FAILURE errorIndication, the message is discarded without further processing. 6) At this point, the abstract data elements have been prepared and processing continues as described in Section 4.2.2, PDU Dispatching for Incoming Messages. 4.2.2. PDU Dispatching for Incoming Messages The elements of procedure for the dispatching of PDUs depends on the value of sendPduHandle. If the value of sendPduHandle is , then this is a request or notification and the procedures specified in Section 4.2.2.1 apply. If the value of snmpPduHandle is not , then this is a response and the procedures specified in Section 4.2.2.2 apply. Case, et al. Standards Track [Page 12] RFC 3412 Message Processing and Dispatching for SNMP December 2002 4.2.2.1. Incoming Requests and Notifications The following procedures are followed for the dispatching of PDUs when the value of sendPduHandle is , indicating this is a request or notification. 1) The combination of contextEngineID and pduType is used to determine which application has registered for this request or notification. 2) If no application has registered for the combination, then: a) The snmpUnknownPDUHandlers counter is incremented. b) A Response message is generated using the abstract service primitive: result = -- SUCCESS or FAILURE prepareResponseMessage( IN messageProcessingModel -- as provided by MP module IN securityModel -- as provided by MP module IN securityName -- as provided by MP module IN securityLevel -- as provided by MP module IN contextEngineID -- as provided by MP module IN contextName -- as provided by MP module IN pduVersion -- as provided by MP module IN PDU -- as provided by MP module IN maxSizeResponseScopedPDU -- as provided by MP module IN stateReference -- as provided by MP module IN statusInformation -- errorIndication plus -- snmpUnknownPDUHandlers OID -- value pair. OUT destTransportDomain -- destination transportDomain OUT destTransportAddress -- destination transportAddress OUT outgoingMessage -- the message to send OUT outgoingMessageLength -- its length ) c) If the result is SUCCESS, then the prepared message is sent to the originator of the request as identified by the transportDomain and transportAddress. The transport used to send the outgoingMessage is returned via destTransportDomain, and the address to which it was sent is returned via destTransportAddress. d) The incoming message is discarded without further processing. Message Processing for this message is complete. Case, et al. Standards Track [Page 13] RFC 3412 Message Processing and Dispatching for SNMP December 2002 3) The PDU is dispatched to the application, using the abstract service primitive: processPdu( -- process Request/Notification IN messageProcessingModel -- as provided by MP module IN securityModel -- as provided by MP module IN securityName -- as provided by MP module IN securityLevel -- as provided by MP module IN contextEngineID -- as provided by MP module IN contextName -- as provided by MP module IN pduVersion -- as provided by MP module IN PDU -- as provided by MP module IN maxSizeResponseScopedPDU -- as provided by MP module IN stateReference -- as provided by MP module -- needed when sending response ) Message processing for this message is complete. 4.2.2.2. Incoming Responses The following procedures are followed for the dispatching of PDUs when the value of sendPduHandle is not , indicating this is a response. 1) The value of sendPduHandle is used to determine, in an implementation-defined manner, which application is waiting for a response associated with this sendPduHandle. 2) If no waiting application is found, the message is discarded without further processing, and the stateReference is released. The snmpUnknownPDUHandlers counter is incremented. Message Processing is complete for this message. 3) Any cached information, including stateReference, about the message is discarded. Case, et al. Standards Track [Page 14] RFC 3412 Message Processing and Dispatching for SNMP December 2002 4) The response is dispatched to the application using the abstract service primitive: processResponsePdu( -- process Response PDU IN messageProcessingModel -- provided by the MP module IN securityModel -- provided by the MP module IN securityName -- provided by the MP module IN securityLevel -- provided by the MP module IN contextEngineID -- provided by the MP module IN contextName -- provided by the MP module IN pduVersion -- provided by the MP module IN PDU -- provided by the MP module IN statusInformation -- provided by the MP module IN sendPduHandle -- provided by the MP module ) Message Processing is complete for this message. 4.3. Application Registration for Handling PDU types Applications that want to process certain PDUs must register with the PDU Dispatcher. Applications specify the combination of contextEngineID and pduType(s) for which they want to take responsibility. 1) An application registers according to the abstract interface primitive: statusInformation = -- success or errorIndication registerContextEngineID( IN contextEngineID -- take responsibility for this one IN pduType -- the pduType(s) to be registered ) Note: Implementations may provide a means of requesting registration for simultaneous multiple contextEngineID values, e.g., all contextEngineID values, and may also provide a means for requesting simultaneous registration for multiple values of the pduType. 2) The parameters may be checked for validity; if they are not, then an errorIndication (invalidParameter) is returned to the application. 3) Each combination of contextEngineID and pduType can be registered only once. If another application has already registered for the specified combination, then an errorIndication (alreadyRegistered) is returned to the application. Case, et al. Standards Track [Page 15] RFC 3412 Message Processing and Dispatching for SNMP December 2002 4) Otherwise, the registration is saved so that SNMP PDUs can be dispatched to this application. 4.4. Application Unregistration for Handling PDU Types Applications that no longer want to process certain PDUs must unregister with the PDU Dispatcher. 1) An application unregisters using the abstract service primitive: unregisterContextEngineID( IN contextEngineID -- give up responsibility for this IN pduType -- the pduType(s) to be unregistered ) Note: Implementations may provide a means for requesting the unregistration for simultaneous multiple contextEngineID values, e.g., all contextEngineID values, and may also provide a means for requesting simultaneous unregistration for multiple values of pduType. 2) If the contextEngineID and pduType combination has been registered, then the registration is deleted. If no such registration exists, then the request is ignored. 5. Definitions 5.1. Definitions for SNMP Message Processing and Dispatching SNMP-MPD-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF MODULE-IDENTITY, OBJECT-TYPE, snmpModules, Counter32 FROM SNMPv2-SMI; snmpMPDMIB MODULE-IDENTITY LAST-UPDATED "200210140000Z" ORGANIZATION "SNMPv3 Working Group" CONTACT-INFO "WG-EMail: snmpv3@lists.tislabs.com Subscribe: snmpv3-request@lists.tislabs.com Co-Chair: Russ Mundy Network Associates Laboratories postal: 15204 Omega Drive, Suite 300 Rockville, MD 20850-4601 USA Case, et al. Standards Track [Page 16] RFC 3412 Message Processing and Dispatching for SNMP December 2002 EMail: mundy@tislabs.com phone: +1 301-947-7107 Co-Chair & Co-editor: David Harrington Enterasys Networks postal: 35 Industrial Way P. O. Box 5005 Rochester NH 03866-5005 USA EMail: dbh@enterasys.com phone: +1 603-337-2614 Co-editor: Jeffrey Case SNMP Research, Inc. postal: 3001 Kimberlin Heights Road Knoxville, TN 37920-9716 USA EMail: case@snmp.com phone: +1 423-573-1434 Co-editor: Randy Presuhn BMC Software, Inc. postal: 2141 North First Street San Jose, CA 95131 USA EMail: randy_presuhn@bmc.com phone: +1 408-546-1006 Co-editor: Bert Wijnen Lucent Technologies postal: Schagen 33 3461 GL Linschoten Netherlands EMail: bwijnen@lucent.com phone: +31 348-680-485 " DESCRIPTION "The MIB for Message Processing and Dispatching Copyright (C) The Internet Society (2002). This version of this MIB module is part of RFC 3412; see the RFC itself for full legal notices. " REVISION "200210140000Z" -- 14 October 2002 DESCRIPTION "Updated addresses, published as RFC 3412." REVISION "199905041636Z" -- 4 May 1999 DESCRIPTION "Updated addresses, published as RFC 2572." Case, et al. Standards Track [Page 17] RFC 3412 Message Processing and Dispatching for SNMP December 2002 REVISION "199709300000Z" -- 30 September 1997 DESCRIPTION "Original version, published as RFC 2272." ::= { snmpModules 11 } -- Administrative assignments *************************************** snmpMPDAdmin OBJECT IDENTIFIER ::= { snmpMPDMIB 1 } snmpMPDMIBObjects OBJECT IDENTIFIER ::= { snmpMPDMIB 2 } snmpMPDMIBConformance OBJECT IDENTIFIER ::= { snmpMPDMIB 3 } -- Statistics for SNMP Messages ************************************* snmpMPDStats OBJECT IDENTIFIER ::= { snmpMPDMIBObjects 1 } snmpUnknownSecurityModels OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because they referenced a securityModel that was not known to or supported by the SNMP engine. " ::= { snmpMPDStats 1 } snmpInvalidMsgs OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because there were invalid or inconsistent components in the SNMP message. " ::= { snmpMPDStats 2 } snmpUnknownPDUHandlers OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because the PDU contained in the packet could not be passed to an application responsible for handling the pduType, e.g. no SNMP application had registered for the proper combination of the contextEngineID and the pduType. " ::= { snmpMPDStats 3 } Case, et al. Standards Track [Page 18] RFC 3412 Message Processing and Dispatching for SNMP December 2002 -- Conformance information ****************************************** snmpMPDMIBCompliances OBJECT IDENTIFIER ::= {snmpMPDMIBConformance 1} snmpMPDMIBGroups OBJECT IDENTIFIER ::= {snmpMPDMIBConformance 2} -- Compliance statements snmpMPDCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for SNMP entities which implement the SNMP-MPD-MIB. " MODULE -- this module MANDATORY-GROUPS { snmpMPDGroup } ::= { snmpMPDMIBCompliances 1 } snmpMPDGroup OBJECT-GROUP OBJECTS { snmpUnknownSecurityModels, snmpInvalidMsgs, snmpUnknownPDUHandlers } STATUS current DESCRIPTION "A collection of objects providing for remote monitoring of the SNMP Message Processing and Dispatching process. " ::= { snmpMPDMIBGroups 1 } END 6. The SNMPv3 Message Format This section defines the SNMPv3 message format and the corresponding SNMP version 3 Message Processing Model (v3MP). SNMPv3MessageSyntax DEFINITIONS IMPLICIT TAGS ::= BEGIN SNMPv3Message ::= SEQUENCE { -- identify the layout of the SNMPv3Message -- this element is in same position as in SNMPv1 -- and SNMPv2c, allowing recognition -- the value 3 is used for snmpv3 msgVersion INTEGER ( 0 .. 2147483647 ), -- administrative parameters msgGlobalData HeaderData, -- security model-specific parameters -- format defined by Security Model Case, et al. Standards Track [Page 19] RFC 3412 Message Processing and Dispatching for SNMP December 2002 msgSecurityParameters OCTET STRING, msgData ScopedPduData } HeaderData ::= SEQUENCE { msgID INTEGER (0..2147483647), msgMaxSize INTEGER (484..2147483647), msgFlags OCTET STRING (SIZE(1)), -- .... ...1 authFlag -- .... ..1. privFlag -- .... .1.. reportableFlag -- Please observe: -- .... ..00 is OK, means noAuthNoPriv -- .... ..01 is OK, means authNoPriv -- .... ..10 reserved, MUST NOT be used. -- .... ..11 is OK, means authPriv msgSecurityModel INTEGER (1..2147483647) } ScopedPduData ::= CHOICE { plaintext ScopedPDU, encryptedPDU OCTET STRING -- encrypted scopedPDU value } ScopedPDU ::= SEQUENCE { contextEngineID OCTET STRING, contextName OCTET STRING, data ANY -- e.g., PDUs as defined in [RFC3416] } END 6.1. msgVersion The msgVersion field is set to snmpv3(3) and identifies the message as an SNMP version 3 Message. 6.2. msgID The msgID is used between two SNMP entities to coordinate request messages and responses, and by the v3MP to coordinate the processing of the message by different subsystem models within the architecture. Values for msgID SHOULD be generated in a manner that avoids re-use of any outstanding values. Doing so provides protection against some replay attacks. One possible implementation strategy would be to use the low-order bits of snmpEngineBoots [RFC3411] as the high-order Case, et al. Standards Track [Page 20] RFC 3412 Message Processing and Dispatching for SNMP December 2002 portion of the msgID value and a monotonically increasing integer for the low-order portion of msgID. Note that the request-id in a PDU may be used by SNMP applications to identify the PDU; the msgID is used by the engine to identify the message which carries a PDU. The engine needs to identify the message even if decryption of the PDU (and request-id) fails. No assumption should be made that the value of the msgID and the value of the request-id are equivalent. The value of the msgID field for a response takes the value of the msgID field from the message to which it is a response. By use of the msgID value, an engine can distinguish the (potentially multiple) outstanding requests, and thereby correlate incoming responses with outstanding requests. In cases where an unreliable datagram service is used, the msgID also provides a simple means of identifying messages duplicated by the network. If a request is retransmitted, a new msgID value SHOULD be used for each retransmission. 6.3. msgMaxSize The msgMaxSize field of the message conveys the maximum message size supported by the sender of the message, i.e., the maximum message size that the sender can accept when another SNMP engine sends an SNMP message (be it a response or any other message) to the sender of this message on the transport in use for this message. When an SNMP message is being generated, the msgMaxSize is provided by the SNMP engine which generates the message. At the receiving SNMP engine, the msgMaxSize is used to determine the maximum message size the sender can accommodate. 6.4. msgFlags The msgFlags field of the message contains several bit fields which control processing of the message. The reportableFlag is a secondary aid in determining whether a Report PDU MUST be sent. It is only used in cases where the PDU portion of a message cannot be decoded, due to, for example, an incorrect encryption key. If the PDU can be decoded, the PDU type forms the basis for decisions on sending Report PDUs. When the reportableFlag is used, if its value is one, a Report PDU MUST be returned to the sender under those conditions which can cause the generation of Report PDUs. Similarly, when the reportableFlag is used and its value is zero, then a Report PDU MUST NOT be sent. The reportableFlag MUST always be zero when the message contains a PDU Case, et al. Standards Track [Page 21] RFC 3412 Message Processing and Dispatching for SNMP December 2002 from the Unconfirmed Class, such as a Report PDU, a response-type PDU (such as a Response PDU), or an unacknowledged notification-type PDU (such as an SNMPv2-trap PDU). The reportableFlag MUST always be one for a PDU from the Confirmed Class, including request-type PDUs (such as a Get PDU) and acknowledged notification-type PDUs (such as an Inform PDU). If the reportableFlag is set to one for a message containing a PDU from the Unconfirmed Class, such as a Report PDU, a response-type PDU (such as a Response PDU), or an unacknowledged notification-type PDU (such as an SNMPv2-trap PDU), then the receiver of that message MUST process it as though the reportableFlag had been set to zero. If the reportableFlag is set to zero for a message containing a request-type PDU (such as a Get PDU) or an acknowledged notification-type PDU (such as an Inform PDU), then the receiver of that message MUST process it as though the reportableFlag had been set to one. Report PDUs are generated directly by the SNMPv3 Message Processing Model, and support engine-to-engine communications, but may be passed to applications for processing. An SNMP engine that receives a reportPDU may use it to determine what kind of problem was detected by the remote SNMP engine. It can do so based on the error counter included as the first (and only) varBind of the reportPDU. Based on the detected error, the SNMP engine may try to send a corrected SNMP message. If that is not possible, it may pass an indication of the error to the application on whose behalf the failed SNMP request was issued. The authFlag and privFlag portions of the msgFlags field are set by the sender to indicate the securityLevel that was applied to the message before it was sent on the wire. The receiver of the message MUST apply the same securityLevel when the message is received and the contents are being processed. There are three securityLevels, namely noAuthNoPriv, which is less than authNoPriv, which is in turn less than authPriv. See the SNMP architecture document [RFC3411] for details about the securityLevel. a) authFlag If the authFlag is set to one, then the securityModel used by the SNMP engine which sent the message MUST identify the securityName on whose behalf the SNMP message was generated and MUST provide, in a securityModel-specific manner, sufficient data for the receiver of the message to be able to authenticate that Case, et al. Standards Track [Page 22] RFC 3412 Message Processing and Dispatching for SNMP December 2002 identification. In general, this authentication will allow the receiver to determine with reasonable certainty that the message was: - sent on behalf of the principal associated with the securityName, - was not redirected, - was not modified in transit, and - was not replayed. If the authFlag is zero, then the securityModel used by the SNMP engine which sent the message MUST identify the securityName on whose behalf the SNMP message was generated but it does not need to provide sufficient data for the receiver of the message to authenticate the identification, as there is no need to authenticate the message in this case. b) privFlag If the privFlag is set, then the securityModel used by the SNMP engine which sent the message MUST also protect the scopedPDU in an SNMP message from disclosure, i.e., it MUST encrypt/decrypt the scopedPDU. If the privFlag is zero, then the securityModel in use does not need to protect the data from disclosure. It is an explicit requirement of the SNMP architecture that if privacy is selected, then authentication is also required. That means that if the privFlag is set, then the authFlag MUST also be set to one. The combination of the authFlag and the privFlag comprises a Level of Security as follows: authFlag zero, privFlag zero -> securityLevel is noAuthNoPriv authFlag zero, privFlag one -> invalid combination, see below authFlag one, privFlag zero -> securityLevel is authNoPriv authFlag one, privFlag one -> securityLevel is authPriv The elements of procedure (see below) describe the action to be taken when the invalid combination of authFlag equal to zero and privFlag equal to one is encountered. The remaining bits in msgFlags are reserved, and MUST be set to zero when sending a message and SHOULD be ignored when receiving a message. Case, et al. Standards Track [Page 23] RFC 3412 Message Processing and Dispatching for SNMP December 2002 6.5. msgSecurityModel The v3MP supports the concurrent existence of multiple Security Models to provide security services for SNMPv3 messages. The msgSecurityModel field in an SNMPv3 Message identifies which Security Model was used by the sender to generate the message and therefore which securityModel MUST be used by the receiver to perform security processing for the message. The mapping to the appropriate securityModel implementation within an SNMP engine is accomplished in an implementation-dependent manner. 6.6. msgSecurityParameters The msgSecurityParameters field of the SNMPv3 Message is used for communication between the Security Model modules in the sending and receiving SNMP engines. The data in the msgSecurityParameters field is used exclusively by the Security Model, and the contents and format of the data is defined by the Security Model. This OCTET STRING is not interpreted by the v3MP, but is passed to the local implementation of the Security Model indicated by the msgSecurityModel field in the message. 6.7. scopedPduData The scopedPduData field represents either the plain text scopedPDU if the privFlag in the msgFlags is zero, or it represents an encryptedPDU (encoded as an OCTET STRING) which MUST be decrypted by the securityModel in use to produce a plaintext scopedPDU. 6.8. scopedPDU The scopedPDU contains information to identify an administratively unique context and a PDU. The object identifiers in the PDU refer to managed objects which are (expected to be) accessible within the specified context. 6.8.1. contextEngineID The contextEngineID in the SNMPv3 message uniquely identifies, within an administrative domain, an SNMP entity that may realize an instance of a context with a particular contextName. For incoming messages, the contextEngineID is used in conjunction with the pduType to determine to which application the scopedPDU will be sent for processing. For outgoing messages, the v3MP sets the contextEngineID to the value provided by the application in the request for a message to be sent. Case, et al. Standards Track [Page 24] RFC 3412 Message Processing and Dispatching for SNMP December 2002 6.8.2. contextName The contextName field in an SNMPv3 message, in conjunction with the contextEngineID field, identifies the particular context associated with the management information contained in the PDU portion of the message. The contextName is unique within the SNMP entity specified by the contextEngineID, which may realize the managed objects referenced within the PDU. An application which originates a message provides the value for the contextName field and this value may be used during processing by an application at the receiving SNMP Engine. 6.8.3. data The data field of the SNMPv3 Message contains the PDU. Among other things, the PDU contains the PDU type that is used by the v3MP to determine the type of the incoming SNMP message. The v3MP specifies that the PDU MUST be one of those specified in [RFC3416]. 7. Elements of Procedure for v3MP This section describes the procedures followed by an SNMP engine when generating and processing SNMP messages according to the SNMPv3 Message Processing Model. Please note, that for the sake of clarity and to prevent the text from being even longer and more complicated, some details were omitted from the steps below. a) Some steps specify that when some error conditions are encountered when processing a received message, a message containing a Report PDU is generated and the received message is discarded without further processing. However, a Report-PDU MUST NOT be generated unless the PDU causing generation of the Report PDU can be determined to be a member of the Confirmed Class, or the reportableFlag is set to one and the PDU class cannot be determined. b) The elements of procedure do not always explicitly indicate when state information needs to be released. The general rule is that if state information is available when a message is to be "discarded without further processing", then the state information should also be released at that same time. Case, et al. Standards Track [Page 25] RFC 3412 Message Processing and Dispatching for SNMP December 2002 7.1. Prepare an Outgoing SNMP Message This section describes the procedure followed to prepare an SNMPv3 message from the data elements passed by the Message Dispatcher. 1) The Message Dispatcher may request that an SNMPv3 message containing a Read Class, Write Class, or Notification Class PDU be prepared for sending. a) It makes such a request according to the abstract service primitive: statusInformation = -- success or errorIndication prepareOutgoingMessage( IN transportDomain -- requested transport domain IN transportAddress -- requested destination address IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model to use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN contextEngineID -- data from/at this entity IN contextName -- data from/in this context IN pduVersion -- version of the PDU * IN PDU -- SNMP Protocol Data Unit IN expectResponse -- TRUE or FALSE * IN sendPduHandle -- the handle for matching -- incoming responses OUT destTransportDomain -- destination transport domain OUT destTransportAddress -- destination transport address OUT outgoingMessage -- the message to send OUT outgoingMessageLength -- the length of the message ) * The SNMPv3 Message Processing Model does not use the values of expectResponse or pduVersion. b) A unique msgID is generated. The number used for msgID should not have been used recently, and MUST NOT be the same as was used for any outstanding request. 2) The Message Dispatcher may request that an SNMPv3 message containing a Response Class or Internal Class PDU be prepared for sending. Case, et al. Standards Track [Page 26] RFC 3412 Message Processing and Dispatching for SNMP December 2002 a) It makes such a request according to the abstract service primitive: result = -- SUCCESS or FAILURE prepareResponseMessage( IN messageProcessingModel -- typically, SNMP version IN securityModel -- same as on incoming request IN securityName -- same as on incoming request IN securityLevel -- same as on incoming request IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size sender can -- accept IN stateReference -- reference to state -- information presented with -- the request IN statusInformation -- success or errorIndication -- error counter OID and value -- when errorIndication OUT destTransportDomain -- destination transport domain OUT destTransportAddress -- destination transport address OUT outgoingMessage -- the message to send OUT outgoingMessageLength -- the length of the message ) b) The cached information for the original request is retrieved via the stateReference, including: - msgID, - contextEngineID, - contextName, - securityModel, - securityName, - securityLevel, - securityStateReference, - reportableFlag, - transportDomain, and - transportAddress. The SNMPv3 Message Processing Model does not allow cached data to be overridden, except by error indications as detailed in (3) below. Case, et al. Standards Track [Page 27] RFC 3412 Message Processing and Dispatching for SNMP December 2002 3) If statusInformation contains values for an OID/value combination (potentially also containing a securityLevel value, contextEngineID value, or contextName value), then: a) If a PDU is provided, it is the PDU from the original request. If possible, extract the request-id and pduType. b) If the pduType is determined to not be a member of the Confirmed Class, or if the reportableFlag is zero and the pduType cannot be determined, then the original message is discarded, and no further processing is done. A result of FAILURE is returned. SNMPv3 Message Processing is complete. c) A Report PDU is prepared: 1) the varBindList is set to contain the OID and value from the statusInformation. 2) error-status is set to 0. 3) error-index is set to 0. 4) request-id is set to the value extracted in step b). Otherwise, request-id is set to 0. d) The errorIndication in statusInformation may be accompanied by a securityLevel value, a contextEngineID value, or a contextName value. 1) If statusInformation contains a value for securityLevel, then securityLevel is set to that value, otherwise it is set to noAuthNoPriv. 2) If statusInformation contains a value for contextEngineID, then contextEngineID is set to that value, otherwise it is set to the value of this entity's snmpEngineID. 3) If statusInformation contains a value for contextName, then contextName is set to that value, otherwise it is set to the default context of "" (zero-length string). e) PDU is set to refer to the new Report-PDU. The old PDU is discarded. f) Processing continues with step 6) below. Case, et al. Standards Track [Page 28] RFC 3412 Message Processing and Dispatching for SNMP December 2002 4) If the contextEngineID is not yet determined, then the contextEngineID is determined, in an implementation-dependent manner, possibly using the transportDomain and transportAddress. 5) If the contextName is not yet determined, the contextName is set to the default context. 6) A scopedPDU is prepared from the contextEngineID, contextName, and PDU. 7) msgGlobalData is constructed as follows: a) The msgVersion field is set to snmpv3(3). b) msgID is set as determined in step 1 or 2 above. c) msgMaxSize is set to an implementation-dependent value. d) msgFlags are set as follows: - If securityLevel specifies noAuthNoPriv, then authFlag and privFlag are both set to zero. - If securityLevel specifies authNoPriv, then authFlag is set to one and privFlag is set to zero. - If securityLevel specifies authPriv, then authFlag is set to one and privFlag is set to one. - If the PDU is from the Unconfirmed Class, then the reportableFlag is set to zero. - If the PDU is from the Confirmed Class then the reportableFlag is set to one. - All other msgFlags bits are set to zero. e) msgSecurityModel is set to the value of securityModel. Case, et al. Standards Track [Page 29] RFC 3412 Message Processing and Dispatching for SNMP December 2002 8) If the PDU is from the Response Class or the Internal Class, then: a) The specified Security Model is called to generate the message according to the primitive: statusInformation = generateResponseMsg( IN messageProcessingModel -- SNMPv3 Message Processing -- Model IN globalData -- msgGlobalData from step 7 IN maxMessageSize -- from msgMaxSize (step 7c) IN securityModel -- as determined in step 7e IN securityEngineID -- the value of snmpEngineID IN securityName -- on behalf of this principal IN securityLevel -- for the outgoing message IN scopedPDU -- as prepared in step 6) IN securityStateReference -- as determined in step 2 OUT securityParameters -- filled in by Security Module OUT wholeMsg -- complete generated message OUT wholeMsgLength -- length of generated message ) If, upon return from the Security Model, the statusInformation includes an errorIndication, then any cached information about the outstanding request message is discarded, and an errorIndication is returned, so it can be returned to the calling application. SNMPv3 Message Processing is complete. b) A SUCCESS result is returned. SNMPv3 Message Processing is complete. 9) If the PDU is from the Confirmed Class or the Notification Class, then: a) If the PDU is from the Unconfirmed Class, then securityEngineID is set to the value of this entity's snmpEngineID. Otherwise, the snmpEngineID of the target entity is determined, in an implementation-dependent manner, possibly using transportDomain and transportAddress. The value of the securityEngineID is set to the value of the target entity's snmpEngineID. Case, et al. Standards Track [Page 30] RFC 3412 Message Processing and Dispatching for SNMP December 2002 b) The specified Security Model is called to generate the message according to the primitive: statusInformation = generateRequestMsg( IN messageProcessingModel -- SNMPv3 Message Processing Model IN globalData -- msgGlobalData, from step 7 IN maxMessageSize -- from msgMaxSize in step 7 c) IN securityModel -- as provided by caller IN securityEngineID -- authoritative SNMP entity -- from step 9 a) IN securityName -- as provided by caller IN securityLevel -- as provided by caller IN scopedPDU -- as prepared in step 6 OUT securityParameters -- filled in by Security Module OUT wholeMsg -- complete generated message OUT wholeMsgLength -- length of the generated message ) If, upon return from the Security Model, the statusInformation includes an errorIndication, then the message is discarded, and the errorIndication is returned, so it can be returned to the calling application, and no further processing is done. SNMPv3 Message Processing is complete. c) If the PDU is from the Confirmed Class, information about the outgoing message is cached, and an implementation-specific stateReference is created. Information to be cached includes the values of: - sendPduHandle - msgID - snmpEngineID - securityModel - securityName - securityLevel - contextEngineID - contextName d) A SUCCESS result is returned. SNMPv3 Message Processing is complete. Case, et al. Standards Track [Page 31] RFC 3412 Message Processing and Dispatching for SNMP December 2002 7.2. Prepare Data Elements from an Incoming SNMP Message This section describes the procedure followed to extract data from an SNMPv3 message, and to prepare the data elements required for further processing of the message by the Message Dispatcher. 1) The message is passed in from the Message Dispatcher according to the abstract service primitive: result = -- SUCCESS or errorIndication prepareDataElements( IN transportDomain -- origin transport domain IN transportAddress -- origin transport address IN wholeMsg -- as received from the network IN wholeMsgLength -- as received from the network OUT messageProcessingModel -- typically, SNMP version OUT securityModel -- Security Model to use OUT securityName -- on behalf of this principal OUT securityLevel -- Level of Security requested OUT contextEngineID -- data from/at this entity OUT contextName -- data from/in this context OUT pduVersion -- version of the PDU OUT PDU -- SNMP Protocol Data Unit OUT pduType -- SNMP PDU type OUT sendPduHandle -- handle for matched request OUT maxSizeResponseScopedPDU -- maximum size sender can accept OUT statusInformation -- success or errorIndication -- error counter OID and value -- when errorIndication OUT stateReference -- reference to state information -- to be used for a possible ) -- Response 2) If the received message is not the serialization (according to the conventions of [RFC3417]) of an SNMPv3Message value, then the snmpInASNParseErrs counter [RFC3418] is incremented, the message is discarded without further processing, and a FAILURE result is returned. SNMPv3 Message Processing is complete. 3) The values for msgVersion, msgID, msgMaxSize, msgFlags, msgSecurityModel, msgSecurityParameters, and msgData are extracted from the message. 4) If the value of the msgSecurityModel component does not match a supported securityModel, then the snmpUnknownSecurityModels counter is incremented, the message is discarded without further processing, and a FAILURE result is returned. SNMPv3 Message Processing is complete. Case, et al. Standards Track [Page 32] RFC 3412 Message Processing and Dispatching for SNMP December 2002 5) The securityLevel is determined from the authFlag and the privFlag bits of the msgFlags component as follows: a) If the authFlag is not set and the privFlag is not set, then securityLevel is set to noAuthNoPriv. b) If the authFlag is set and the privFlag is not set, then securityLevel is set to authNoPriv. c) If the authFlag is set and the privFlag is set, then securityLevel is set to authPriv. d) If the authFlag is not set and privFlag is set, then the snmpInvalidMsgs counter is incremented, the message is discarded without further processing, and a FAILURE result is returned. SNMPv3 Message Processing is complete. e) Any other bits in the msgFlags are ignored. 6) The security module implementing the Security Model as specified by the securityModel component is called for authentication and privacy services. This is done according to the abstract service primitive: statusInformation = -- errorIndication or success -- error counter OID and -- value if error processIncomingMsg( IN messageProcessingModel -- SNMPv3 Message Processing Model IN maxMessageSize -- of the sending SNMP entity IN securityParameters -- for the received message IN securityModel -- for the received message IN securityLevel -- Level of Security IN wholeMsg -- as received on the wire IN wholeMsgLength -- length as received on the wire OUT securityEngineID -- authoritative SNMP entity OUT securityName -- identification of the principal OUT scopedPDU, -- message (plaintext) payload OUT maxSizeResponseScopedPDU -- maximum size sender can accept OUT securityStateReference -- reference to security state ) -- information, needed for -- response If an errorIndication is returned by the security module, then: a) If statusInformation contains values for an OID/value pair, then generation of a Report PDU is attempted (see step 3 in section 7.1). Case, et al. Standards Track [Page 33] RFC 3412 Message Processing and Dispatching for SNMP December 2002 1) If the scopedPDU has been returned from processIncomingMsg, then determine contextEngineID, contextName, and PDU. 2) Information about the message is cached and a stateReference is created (implementation-specific). Information to be cached includes the values of: msgVersion, msgID, securityLevel, msgFlags, msgMaxSize, securityModel, maxSizeResponseScopedPDU, securityStateReference 3) Request that a Report-PDU be prepared and sent, according to the abstract service primitive: result = -- SUCCESS or FAILURE returnResponsePdu( IN messageProcessingModel -- SNMPv3(3) IN securityModel -- same as on incoming request IN securityName -- from processIncomingMsg IN securityLevel -- same as on incoming request IN contextEngineID -- from step 6 a) 1) IN contextName -- from step 6 a) 1) IN pduVersion -- SNMPv2-PDU IN PDU -- from step 6 a) 1) IN maxSizeResponseScopedPDU -- from processIncomingMsg IN stateReference -- from step 6 a) 2) IN statusInformation -- from processIncomingMsg ) b) The incoming message is discarded without further processing, and a FAILURE result is returned. SNMPv3 Message Processing is complete. 7) The scopedPDU is parsed to extract the contextEngineID, the contextName and the PDU. If any parse error occurs, then the snmpInASNParseErrs counter [RFC3418] is incremented, the security state information is discarded, the message is discarded without further processing, and a FAILURE result is returned. SNMPv3 Message Processing is complete. Treating an unknown PDU type is treated as a parse error is an implementation option. Case, et al. Standards Track [Page 34] RFC 3412 Message Processing and Dispatching for SNMP December 2002 8) The pduVersion is determined in an implementation-dependent manner. For SNMPv3, the pduVersion would be an SNMPv2-PDU. 9) The pduType is determined, in an implementation-dependent manner. For [RFC3416], the pduTypes include: - GetRequest-PDU, - GetNextRequest-PDU, - GetBulkRequest-PDU, - SetRequest-PDU, - InformRequest-PDU, - SNMPv2-Trap-PDU, - Response-PDU, - Report-PDU. 10) If the pduType is from the Response Class or the Internal Class, then: a) The value of the msgID component is used to find the cached information for a corresponding outstanding Request message. If no such outstanding Request message is found, then the security state information is discarded, the message is discarded without further processing, and a FAILURE result is returned. SNMPv3 Message Processing is complete. b) sendPduHandle is retrieved from the cached information. Otherwise, sendPduHandle is set to , an implementation defined value. 11) If the pduType is from the Internal Class, then: a) statusInformation is created using the contents of the Report-PDU, in an implementation-dependent manner. This statusInformation will be forwarded to the application associated with the sendPduHandle. b) The cached data for the outstanding message, referred to by stateReference, is retrieved. If the securityModel or securityLevel values differ from the cached ones, it is important to recognize that Internal Class PDUs delivered at the security level of noAuthNoPriv open a window of opportunity for spoofing or replay attacks. If the receiver of such messages is aware of these risks, the use of such unauthenticated messages is acceptable and may provide a useful function for discovering engine IDs or for detecting misconfiguration at remote nodes. Case, et al. Standards Track [Page 35] RFC 3412 Message Processing and Dispatching for SNMP December 2002 When the securityModel or securityLevel values differ from the cached ones, an implementation may retain the cached information about the outstanding Request message, in anticipation of the possibility that the Internal Class PDU received might be illegitimate. Otherwise, any cached information about the outstanding Request message is discarded. c) The security state information for this incoming message is discarded. d) stateReference is set to . e) A SUCCESS result is returned. SNMPv3 Message Processing is complete. 12) If the pduType is from the Response Class, then: a) The cached data for the outstanding request, referred to by stateReference, is retrieved, including: - snmpEngineID - securityModel - securityName - securityLevel - contextEngineID - contextName b) If the values extracted from the incoming message differ from the cached data, then any cached information about the outstanding Request message is discarded, the incoming message is discarded without further processing, and a FAILURE result is returned. SNMPv3 Message Processing is complete. When the securityModel or securityLevel values differ from the cached ones, an implementation may retain the cached information about the outstanding Request message, in anticipation of the possibility that the Response Class PDU received might be illegitimate. c) Otherwise, any cached information about the outstanding Request message is discarded, and the stateReference is set to . d) A SUCCESS result is returned. SNMPv3 Message Processing is complete. 13) If the pduType is from the Confirmed Class, then: Case, et al. Standards Track [Page 36] RFC 3412 Message Processing and Dispatching for SNMP December 2002 a) If the value of securityEngineID is not equal to the value of snmpEngineID, then the security state information is discarded, any cached information about this message is discarded, the incoming message is discarded without further processing, and a FAILURE result is returned. SNMPv3 Message Processing is complete. b) Information about the message is cached and a stateReference is created (implementation-specific). Information to be cached includes the values of: msgVersion, msgID, securityLevel, msgFlags, msgMaxSize, securityModel, maxSizeResponseScopedPDU, securityStateReference c) A SUCCESS result is returned. SNMPv3 Message Processing is complete. 14) If the pduType is from the Unconfirmed Class, then a SUCCESS result is returned. SNMPv3 Message Processing is complete. 8. Intellectual Property The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Case, et al. Standards Track [Page 37] RFC 3412 Message Processing and Dispatching for SNMP December 2002 9. Acknowledgements This document is the result of the efforts of the SNMPv3 Working Group. Some special thanks are in order to the following SNMPv3 WG members: Harald Tveit Alvestrand (Maxware) Dave Battle (SNMP Research, Inc.) Alan Beard (Disney Worldwide Services) Paul Berrevoets (SWI Systemware/Halcyon Inc.) Martin Bjorklund (Ericsson) Uri Blumenthal (IBM T. J. Watson Research Center) Jeff Case (SNMP Research, Inc.) John Curran (BBN) Mike Daniele (Compaq Computer Corporation) T. Max Devlin (Eltrax Systems) John Flick (Hewlett Packard) Rob Frye (MCI) Wes Hardaker (U.C.Davis, Information Technology - D.C.A.S.) David Harrington (Cabletron Systems Inc.) Lauren Heintz (BMC Software, Inc.) N.C. Hien (IBM T. J. Watson Research Center) Michael Kirkham (InterWorking Labs, Inc.) Dave Levi (SNMP Research, Inc.) Louis A Mamakos (UUNET Technologies Inc.) Joe Marzot (Nortel Networks) Paul Meyer (Secure Computing Corporation) Keith McCloghrie (Cisco Systems) Bob Moore (IBM) Russ Mundy (TIS Labs at Network Associates) Bob Natale (ACE*COMM Corporation) Mike O'Dell (UUNET Technologies Inc.) Dave Perkins (DeskTalk) Peter Polkinghorne (Brunel University) Randy Presuhn (BMC Software, Inc.) David Reeder (TIS Labs at Network Associates) David Reid (SNMP Research, Inc.) Aleksey Romanov (Quality Quorum) Shawn Routhier (Epilogue) Juergen Schoenwaelder (TU Braunschweig) Bob Stewart (Cisco Systems) Mike Thatcher (Independent Consultant) Bert Wijnen (IBM T. J. Watson Research Center) Case, et al. Standards Track [Page 38] RFC 3412 Message Processing and Dispatching for SNMP December 2002 The document is based on recommendations of the IETF Security and Administrative Framework Evolution for SNMP Advisory Team. Members of that Advisory Team were: David Harrington (Cabletron Systems Inc.) Jeff Johnson (Cisco Systems) David Levi (SNMP Research Inc.) John Linn (Openvision) Russ Mundy (Trusted Information Systems) chair Shawn Routhier (Epilogue) Glenn Waters (Nortel) Bert Wijnen (IBM T. J. Watson Research Center) As recommended by the Advisory Team and the SNMPv3 Working Group Charter, the design incorporates as much as practical from previous RFCs and drafts. As a result, special thanks are due to the authors of previous designs known as SNMPv2u and SNMPv2*: Jeff Case (SNMP Research, Inc.) David Harrington (Cabletron Systems Inc.) David Levi (SNMP Research, Inc.) Keith McCloghrie (Cisco Systems) Brian O'Keefe (Hewlett Packard) Marshall T. Rose (Dover Beach Consulting) Jon Saperia (BGS Systems Inc.) Steve Waldbusser (International Network Services) Glenn W. Waters (Bell-Northern Research Ltd.) 10. Security Considerations The Dispatcher coordinates the processing of messages to provide a level of security for management messages and to direct the SNMP PDUs to the proper SNMP application(s). A Message Processing Model, and in particular the v3MP defined in this document, interacts as part of the Message Processing with Security Models in the Security Subsystem via the abstract service interface primitives defined in [RFC3411] and elaborated above. The level of security actually provided is primarily determined by the specific Security Model implementation(s) and the specific SNMP application implementation(s) incorporated into this framework. Applications have access to data which is not secured. Applications should take reasonable steps to protect the data from disclosure, and when they send data across the network, they should obey the securityLevel and call upon the services of an Access Control Model as they apply access control. Case, et al. Standards Track [Page 39] RFC 3412 Message Processing and Dispatching for SNMP December 2002 The values for the msgID element used in communication between SNMP entities MUST be chosen to avoid replay attacks. The values do not need to be unpredictable; it is sufficient that they not repeat. When exchanges are carried out over an insecure network, there is an open opportunity for a third party to spoof or replay messages when any message of an exchange is given at the security level of noAuthNoPriv. For most exchanges, all messages exist at the same security level. In the case where the final message is an Internal Class PDU, this message may be delivered at a level of noAuthNoPriv or authNoPriv, independent of the security level of the preceding messages. Internal Class PDUs delivered at the level of authNoPriv are not considered to pose a security hazard. Internal Class PDUs delivered at the security level of noAuthNoPriv open a window of opportunity for spoofing or replay attacks. If the receiver of such messages is aware of these risks, the use of such unauthenticated messages is acceptable and may provide a useful function for discovering engine IDs or for detecting misconfiguration at remote nodes. This document also contains a MIB definition module. None of the objects defined is writable, and the information they represent is not deemed to be particularly sensitive. However, if they are deemed sensitive in a particular environment, access to them should be restricted through the use of appropriately configured Security and Access Control models. 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2578] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M. and S. Waldbusser, "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999. [RFC2580] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M. and S. Waldbusser, "Conformance Statements for SMIv2", STD 58, RFC 2580, April 1999. [RFC3411] Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for Describing Simple Network Management Protocol (SNMP) Management Frameworks", STD 62, RFC 3411, December 2002. Case, et al. Standards Track [Page 40] RFC 3412 Message Processing and Dispatching for SNMP December 2002 [RFC3413] Levi, D., Meyer, P. and B. Stewart, "Simple Network Management Protocol (SNMP) Applications", STD 62, RFC 3413, December 2002. [RFC3414] Blumenthal, U. and B. Wijnen, "The User-Based Security Model (USM) for Version 3 of the Simple Network Management Protocol (SNMPv3)", STD 62, RFC 3414, December 2002. [RFC3415] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3415, December 2002. [RFC3416] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Version 2 of the Protocol Operations for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3416, December 2002. [RFC3417] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Transport Mappings for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3417, December 2002. [RFC3418] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Management Information Base (MIB) for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3418, December 2002. 11.2. Informative References [RFC1901] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Introduction to Community-based SNMPv2", RFC 1901, January 1996. [RFC2028] Hovey, R. and S. Bradner, "The Organizations Involved in the IETF Standards Process", BCP 11, RFC 2028, October 1996. [RFC2576] Frye, R., Levi, D., Routhier, S. and B. Wijnen, "Coexistence between Version 1, Version 2, and Version 3 of the Internet-Standard Network Management Framework", RFC 2576, March 2000. [RFC3410] Case, J., Mundy, R., Partain, D. and B. Stewart, "Introduction and Applicability Statements for Internet- Standard Management Framework", RFC 3410, December 2002. Case, et al. Standards Track [Page 41] RFC 3412 Message Processing and Dispatching for SNMP December 2002 12. Editors' Addresses Jeffrey Case SNMP Research, Inc. 3001 Kimberlin Heights Road Knoxville, TN 37920-9716 USA Phone: +1 423-573-1434 EMail: case@snmp.com David Harrington Enterasys Networks 35 Industrial Way Post Office Box 5005 Rochester, NH 03866-5005 USA Phone: +1 603-337-2614 EMail: dbh@enterasys.com Randy Presuhn BMC Software, Inc. 2141 North First Street San Jose, CA 95131 USA Phone: +1 408-546-1006 EMail: randy_presuhn@bmc.com Bert Wijnen Lucent Technologies Schagen 33 3461 GL Linschoten Netherlands Phone: +31 348-680-485 EMail: bwijnen@lucent.com Case, et al. Standards Track [Page 42] RFC 3412 Message Processing and Dispatching for SNMP December 2002 13. Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Case, et al. Standards Track [Page 43] ======================================================================== Network Working Group D. Levi Request for Comments: 3413 Nortel Networks STD: 62 P. Meyer Obsoletes: 2573 Secure Computing Corporation Category: Standards Track B. Stewart Retired December 2002 Simple Network Management Protocol (SNMP) Applications Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Abstract This document describes five types of Simple Network Management Protocol (SNMP) applications which make use of an SNMP engine as described in STD 62, RFC 3411. The types of application described are Command Generators, Command Responders, Notification Originators, Notification Receivers, and Proxy Forwarders. This document also defines Management Information Base (MIB) modules for specifying targets of management operations, for notification filtering, and for proxy forwarding. This document obsoletes RFC 2573. Table of Contents 1 Overview ............................................... 2 1.1 Command Generator Applications ......................... 3 1.2 Command Responder Applications ......................... 3 1.3 Notification Originator Applications ................... 3 1.4 Notification Receiver Applications ..................... 3 1.5 Proxy Forwarder Applications ........................... 4 2 Management Targets ..................................... 5 3 Elements Of Procedure .................................. 6 3.1 Command Generator Applications ......................... 6 3.2 Command Responder Applications ......................... 9 3.3 Notification Originator Applications ................... 14 3.4 Notification Receiver Applications ..................... 17 3.5 Proxy Forwarder Applications ........................... 19 3.5.1 Request Forwarding ..................................... 21 Levi, et. al. Standards Track [Page 1] RFC 3413 SNMP Applications December 2002 3.5.1.1 Processing an Incoming Request ......................... 21 3.5.1.2 Processing an Incoming Response ........................ 24 3.5.1.3 Processing an Incoming Internal-Class PDU .............. 25 3.5.2 Notification Forwarding ................................ 26 4 The Structure of the MIB Modules ....................... 29 4.1 The Management Target MIB Module ....................... 29 4.1.1 Tag Lists .....................,........................ 29 4.1.2 Definitions ..................,......................... 30 4.2 The Notification MIB Module ............................ 44 4.2.1 Definitions ............................................ 44 4.3 The Proxy MIB Module ................................... 56 4.3.1 Definitions ............................................ 57 5 Identification of Management Targets in Notification Originators ............................... 63 6 Notification Filtering ................................. 64 7 Management Target Translation in Proxy Forwarder Applications ........................... 65 7.1 Management Target Translation for Request Forwarding ..................................... 65 7.2 Management Target Translation for Notification Forwarding ................................ 66 8 Intellectual Property .................................. 67 9 Acknowledgments ........................................ 67 10 Security Considerations ................................ 69 11 References ............................................. 69 A. Trap Configuration Example ............................. 71 Editors' Addresses ..................................... 73 Full Copyright Statement ............................... 74 1. Overview This document describes five types of SNMP applications: - Applications which initiate SNMP Read-Class, and/or Write-Class requests, called 'command generators.' - Applications which respond to SNMP Read-Class, and/or Write-Class requests, called 'command responders.' - Applications which generate SNMP Notification-Class PDUs, called 'notification originators.' - Applications which receive SNMP Notification-Class PDUs, called 'notification receivers.' - Applications which forward SNMP messages, called 'proxy forwarders.' Levi, et. al. Standards Track [Page 2] RFC 3413 SNMP Applications December 2002 Note that there are no restrictions on which types of applications may be associated with a particular SNMP engine. For example, a single SNMP engine may, in fact, be associated with both command generator and command responder applications. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 1.1. Command Generator Applications A command generator application initiates SNMP Read-Class and/or Write-Class requests, and processes responses to requests which it generated. 1.2. Command Responder Applications A command responder application receives SNMP Read-Class and/or Write-Class requests destined for the local system as indicated by the fact that the contextEngineID in the received request is equal to that of the local engine through which the request was received. The command responder application will perform the appropriate protocol operation, using access control, and will generate a response message to be sent to the request's originator. 1.3. Notification Originator Applications A notification originator application conceptually monitors a system for particular events or conditions, and generates Notification-Class messages based on these events or conditions. A notification originator must have a mechanism for determining where to send messages, and what SNMP version and security parameters to use when sending messages. A mechanism and MIB module for this purpose is provided in this document. Note that Notification-Class PDUs generated by a notification originator may be either Confirmed-Class or Unconfirmed-Class PDU types. 1.4. Notification Receiver Applications A notification receiver application listens for notification messages, and generates response messages when a message containing a Confirmed-Class PDU is received. Levi, et. al. Standards Track [Page 3] RFC 3413 SNMP Applications December 2002 1.5. Proxy Forwarder Applications A proxy forwarder application forwards SNMP messages. Note that implementation of a proxy forwarder application is optional. The sections describing proxy (3.5, 4.3, and 7) may be skipped for implementations that do not include a proxy forwarder application. The term "proxy" has historically been used very loosely, with multiple different meanings. These different meanings include (among others): (1) the forwarding of SNMP requests to other SNMP entities without regard for what managed object types are being accessed; for example, in order to forward an SNMP request from one transport domain to another, or to translate SNMP requests of one version into SNMP requests of another version; (2) the translation of SNMP requests into operations of some non-SNMP management protocol; and (3) support for aggregated managed objects where the value of one managed object instance depends upon the values of multiple other (remote) items of management information. Each of these scenarios can be advantageous; for example, support for aggregation of management information can significantly reduce the bandwidth requirements of large-scale management activities. However, using a single term to cover multiple different scenarios causes confusion. To avoid such confusion, this document uses the term "proxy" with a much more tightly defined meaning. The term "proxy" is used in this document to refer to a proxy forwarder application which forwards either SNMP messages without regard for what managed objects are contained within those messages. This definition is most closely related to the first definition above. Note, however, that in the SNMP architecture [RFC3411], a proxy forwarder is actually an application, and need not be associated with what is traditionally thought of as an SNMP agent. Specifically, the distinction between a traditional SNMP agent and a proxy forwarder application is simple: Levi, et. al. Standards Track [Page 4] RFC 3413 SNMP Applications December 2002 - a proxy forwarder application forwards SNMP messages to other SNMP engines according to the context, and irrespective of the specific managed object types being accessed, and forwards the response to such previously forwarded messages back to the SNMP engine from which the original message was received; - in contrast, the command responder application that is part of what is traditionally thought of as an SNMP agent, and which processes SNMP requests according to the (names of the) individual managed object types and instances being accessed, is NOT a proxy forwarder application from the perspective of this document. Thus, when a proxy forwarder application forwards a request or notification for a particular contextEngineID / contextName pair, not only is the information on how to forward the request specifically associated with that context, but the proxy forwarder application has no need of a detailed definition of a MIB view (since the proxy forwarder application forwards the request irrespective of the managed object types). In contrast, a command responder application must have the detailed definition of the MIB view, and even if it needs to issue requests to other entities, via SNMP or otherwise, that need is dependent on the individual managed object instances being accessed (i.e., not only on the context). Note that it is a design goal of a proxy forwarder application to act as an intermediary between the endpoints of a transaction. In particular, when forwarding Confirmed Notification-Class messages, the associated response is forwarded when it is received from the target to which the Notification-Class message was forwarded, rather than generating a response immediately when the Notification-Class message is received. 2. Management Targets Some types of applications (notification generators and proxy forwarders in particular) require a mechanism for determining where and how to send generated messages. This document provides a mechanism and MIB module for this purpose. The set of information that describes where and how to send a message is called a 'Management Target', and consists of two kinds of information: - Destination information, consisting of a transport domain and a transport address. This is also termed a transport endpoint. - SNMP parameters, consisting of message processing model, security model, security level, and security name information. Levi, et. al. Standards Track [Page 5] RFC 3413 SNMP Applications December 2002 The SNMP-TARGET-MIB module described later in this document contains one table for each of these types of information. There can be a many-to-many relationship in the MIB between these two types of information. That is, there may be multiple transport endpoints associated with a particular set of SNMP parameters, or a particular transport endpoint may be associated with several sets of SNMP parameters. 3. Elements Of Procedure The following sections describe the procedures followed by each type of application when generating messages for transmission or when processing received messages. Applications communicate with the Dispatcher using the abstract service interfaces defined in [RFC3411]. 3.1. Command Generator Applications A command generator initiates an SNMP request by calling the Dispatcher using the following abstract service interface: statusInformation = -- sendPduHandle if success -- errorIndication if failure sendPdu( IN transportDomain -- transport domain to be used IN transportAddress -- destination network address IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model to use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN contextEngineID -- data from/at this entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN expectResponse -- TRUE or FALSE ) Where: - The transportDomain is that of the destination of the message. - The transportAddress is that of the destination of the message. - The messageProcessingModel indicates which Message Processing Model the application wishes to use. - The securityModel is the security model that the application wishes to use. Levi, et. al. Standards Track [Page 6] RFC 3413 SNMP Applications December 2002 - The securityName is the security model independent name for the principal on whose behalf the application wishes the message to be generated. - The securityLevel is the security level that the application wishes to use. - The contextEngineID specifies the location of the management information it is requesting. Note that unless the request is being sent to a proxy, this value will usually be equal to the snmpEngineID value of the engine to which the request is being sent. - The contextName specifies the local context name for the management information it is requesting. - The pduVersion indicates the version of the PDU to be sent. - The PDU is a value constructed by the command generator containing the management operation that the command generator wishes to perform. - The expectResponse argument indicates that a response is expected. The result of the sendPdu interface indicates whether the PDU was successfully sent. If it was successfully sent, the returned value will be a sendPduHandle. The command generator should store the sendPduHandle so that it can correlate a response to the original request. The Dispatcher is responsible for delivering the response to a particular request to the correct command generator application. The abstract service interface used is: processResponsePdu( -- process Response PDU IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN statusInformation -- success or errorIndication IN sendPduHandle -- handle from sendPdu ) Levi, et. al. Standards Track [Page 7] RFC 3413 SNMP Applications December 2002 Where: - The messageProcessingModel is the value from the received response. - The securityModel is the value from the received response. - The securityName is the value from the received response. - The securityLevel is the value from the received response. - The contextEngineID is the value from the received response. - The contextName is the value from the received response. - The pduVersion indicates the version of the PDU in the received response. - The PDU is the value from the received response. - The statusInformation indicates success or failure in receiving the response. - The sendPduHandle is the value returned by the sendPdu call which generated the original request to which this is a response. The procedure when a command generator receives a message is as follows: (1) If the received values of messageProcessingModel, securityModel, securityName, contextEngineID, contextName, and pduVersion are not all equal to the values used in the original request, the response is discarded. (2) The operation type, request-id, error-status, error-index, and variable-bindings are extracted from the PDU and saved. If the request-id is not equal to the value used in the original request, the response is discarded. (3) At this point, it is up to the application to take an appropriate action. The specific action is implementation dependent. If the statusInformation indicates that the request failed, an appropriate action might be to attempt to transmit the request again, or to notify the person operating the application that a failure occurred. Levi, et. al. Standards Track [Page 8] RFC 3413 SNMP Applications December 2002 3.2. Command Responder Applications Before a command responder application can process messages, it must first associate itself with an SNMP engine. The abstract service interface used for this purpose is: statusInformation = -- success or errorIndication registerContextEngineID( IN contextEngineID -- take responsibility for this one IN pduType -- the pduType(s) to be registered ) Where: - The statusInformation indicates success or failure of the registration attempt. - The contextEngineID is equal to the snmpEngineID of the SNMP engine with which the command responder is registering. - The pduType indicates a Read-Class and/or Write-Class PDU. Note that if another command responder application is already registered with an SNMP engine, any further attempts to register with the same contextEngineID and pduType will be denied. This implies that separate command responder applications could register separately for the various pdu types. However, in practice this is undesirable, and only a single command responder application should be registered with an SNMP engine at any given time. A command responder application can disassociate with an SNMP engine using the following abstract service interface: unregisterContextEngineID( IN contextEngineID -- give up responsibility for this one IN pduType -- the pduType(s) to be unregistered ) Where: - The contextEngineID is equal to the snmpEngineID of the SNMP engine with which the command responder is cancelling the registration. - The pduType indicates a Read-Class and/or Write-Class PDU. Levi, et. al. Standards Track [Page 9] RFC 3413 SNMP Applications December 2002 Once the command responder has registered with the SNMP engine, it waits to receive SNMP messages. The abstract service interface used for receiving messages is: processPdu( -- process Request/Notification PDU IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size of the Response PDU IN stateReference -- reference to state information ) -- needed when sending a response Where: - The messageProcessingModel indicates which Message Processing Model received and processed the message. - The securityModel is the value from the received message. - The securityName is the value from the received message. - The securityLevel is the value from the received message. - The contextEngineID is the value from the received message. - The contextName is the value from the received message. - The pduVersion indicates the version of the PDU in the received message. - The PDU is the value from the received message. - The maxSizeResponseScopedPDU is the maximum allowable size of a ScopedPDU containing a Response PDU (based on the maximum message size that the originator of the message can accept). - The stateReference is a value which references cached information about each received request message. This value must be returned to the Dispatcher in order to generate a response. Levi, et. al. Standards Track [Page 10] RFC 3413 SNMP Applications December 2002 The procedure when a message is received is as follows: (1) The operation type is determined from the ASN.1 tag value associated with the PDU parameter. The operation type should always be one of the types previously registered by the application. (2) The request-id is extracted from the PDU and saved. (3) Any PDU type specific parameters are extracted from the PDU and saved (for example, if the PDU type is an SNMPv2 GetBulk PDU, the non-repeaters and max-repetitions values are extracted). (4) The variable-bindings are extracted from the PDU and saved. (5) The management operation represented by the PDU type is performed with respect to the relevant MIB view within the context named by the contextName (for an SNMPv2 PDU type, the operation is performed according to the procedures set forth in [RFC1905]). The relevant MIB view is determined by the securityLevel, securityModel, contextName, securityName, and the class of the PDU type. To determine whether a particular object instance is within the relevant MIB view, the following abstract service interface is called: statusInformation = -- success or errorIndication isAccessAllowed( IN securityModel -- Security Model in use IN securityName -- principal who wants to access IN securityLevel -- Level of Security IN viewType -- read, write, or notify view IN contextName -- context containing variableName IN variableName -- OID for the managed object ) Where: - The securityModel is the value from the received message. - The securityName is the value from the received message. - The securityLevel is the value from the received message. - The viewType indicates whether the PDU type is a Read-Class or Write-Class operation. - The contextName is the value from the received message. Levi, et. al. Standards Track [Page 11] RFC 3413 SNMP Applications December 2002 - The variableName is the object instance of the variable for which access rights are to be checked. Normally, the result of the management operation will be a new PDU value, and processing will continue in step (6) below. However, at any time during the processing of the management operation: - If the isAccessAllowed ASI returns a noSuchView, noAccessEntry, or noGroupName error, processing of the management operation is halted, a PDU value is constructed using the values from the originally received PDU, but replacing the error-status with an authorizationError code, and error-index value of 0, and control is passed to step (6) below. - If the isAccessAllowed ASI returns an otherError, processing of the management operation is halted, a different PDU value is constructed using the values from the originally received PDU, but replacing the error-status with a genError code and the error-index with the index of the failed variable binding, and control is passed to step (6) below. - If the isAccessAllowed ASI returns a noSuchContext error, processing of the management operation is halted, no result PDU is generated, the snmpUnknownContexts counter is incremented, and control is passed to step (6) below for generation of a report message. - If the context named by the contextName parameter is unavailable, processing of the management operation is halted, no result PDU is generated, the snmpUnavailableContexts counter is incremented, and control is passed to step (6) below for generation of a report message. (6) The Dispatcher is called to generate a response or report message. The abstract service interface is: Levi, et. al. Standards Track [Page 12] RFC 3413 SNMP Applications December 2002 returnResponsePdu( IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- same as on incoming request IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size of the Response PDU IN stateReference -- reference to state information -- as presented with the request IN statusInformation -- success or errorIndication ) -- error counter OID/value if error Where: - The messageProcessingModel is the value from the processPdu call. - The securityModel is the value from the processPdu call. - The securityName is the value from the processPdu call. - The securityLevel is the value from the processPdu call. - The contextEngineID is the value from the processPdu call. - The contextName is the value from the processPdu call. - The pduVersion indicates the version of the PDU to be returned. If no result PDU was generated, the pduVersion is an undefined value. - The PDU is the result generated in step (5) above. If no result PDU was generated, the PDU is an undefined value. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value from the processPdu call. - The statusInformation either contains an indication that no error occurred and that a response should be generated, or contains an indication that an error occurred along with the OID and counter value of the appropriate error counter object. Levi, et. al. Standards Track [Page 13] RFC 3413 SNMP Applications December 2002 Note that a command responder application should always call the returnResponsePdu abstract service interface, even in the event of an error such as a resource allocation error. In the event of such an error, the PDU value passed to returnResponsePdu should contain appropriate values for errorStatus and errorIndex. Note that the text above describes situations where the snmpUnknownContexts counter is incremented, and where the snmpUnavailableContexts counter is incremented. The difference between these is that the snmpUnknownContexts counter is incremented when a request is received for a context which is unknown to the SNMP entity. The snmpUnavailableContexts counter is incremented when a request is received for a context which is known to the SNMP entity, but is currently unavailable. Determining when a context is unavailable is implementation specific, and some implementations may never encounter this situation, and so may never increment the snmpUnavailableContexts counter. 3.3. Notification Originator Applications A notification originator application generates SNMP messages containing Notification-Class PDUs (for example, SNMPv2-Trap PDUs or Inform PDUs). There is no requirement as to what specific types of Notification-Class PDUs a particular implementation must be capable of generating. Notification originator applications require a mechanism for identifying the management targets to which notifications should be sent. The particular mechanism used is implementation dependent. However, if an implementation makes the configuration of management targets SNMP manageable, it MUST use the SNMP-TARGET-MIB module described in this document. When a notification originator wishes to generate a notification, it must first determine in which context the information to be conveyed in the notification exists, i.e., it must determine the contextEngineID and contextName. It must then determine the set of management targets to which the notification should be sent. The application must also determine, for each management target, what specific PDU type the notification message should contain, and if it is to contain a Confirmed-Class PDU, the number of retries and retransmission algorithm. Levi, et. al. Standards Track [Page 14] RFC 3413 SNMP Applications December 2002 The mechanism by which a notification originator determines this information is implementation dependent. Once the application has determined this information, the following procedure is performed for each management target: (1) Any appropriate filtering mechanisms are applied to determine whether the notification should be sent to the management target. If such filtering mechanisms determine that the notification should not be sent, processing continues with the next management target. Otherwise, (2) The appropriate set of variable-bindings is retrieved from local MIB instrumentation within the relevant MIB view. The relevant MIB view is determined by the securityLevel, securityModel, contextName, and securityName of the management target. To determine whether a particular object instance is within the relevant MIB view, the isAccessAllowed abstract service interface is used, in the same manner as described in the preceding section, except that the viewType indicates a Notification-Class operation. If the statusInformation returned by isAccessAllowed does not indicate accessAllowed, the notification is not sent to the management target. (3) The NOTIFICATION-TYPE OBJECT IDENTIFIER of the notification (this is the value of the element of the variable bindings whose name is snmpTrapOID.0, i.e., the second variable binding) is checked using the isAccessAllowed abstract service interface, using the same parameters used in the preceding step. If the statusInformation returned by isAccessAllowed does not indicate accessAllowed, the notification is not sent to the management target. (4) A PDU is constructed using a locally unique request-id value, a PDU type as determined by the implementation, an error-status and error-index value of 0, and the variable-bindings supplied previously in step (2). (5) If the notification contains an Unconfirmed-Class PDU, the Dispatcher is called using the following abstract service interface: Levi, et. al. Standards Track [Page 15] RFC 3413 SNMP Applications December 2002 statusInformation = -- sendPduHandle if success -- errorIndication if failure sendPdu( IN transportDomain -- transport domain to be used IN transportAddress -- destination network address IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model to use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN contextEngineID -- data from/at this entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN expectResponse -- TRUE or FALSE ) Where: - The transportDomain is that of the management target. - The transportAddress is that of the management target. - The messageProcessingModel is that of the management target. - The securityModel is that of the management target. - The securityName is that of the management target. - The securityLevel is that of the management target. - The contextEngineID is the value originally determined for the notification. - The contextName is the value originally determined for the notification. - The pduVersion is the version of the PDU to be sent. - The PDU is the value constructed in step (4) above. - The expectResponse argument indicates that no response is expected. Otherwise, Levi, et. al. Standards Track [Page 16] RFC 3413 SNMP Applications December 2002 (6) If the notification contains a Confirmed-Class PDU, then: a) The Dispatcher is called using the sendPdu abstract service interface as described in step (5) above, except that the expectResponse argument indicates that a response is expected. b) The application caches information about the management target. c) If a response is received within an appropriate time interval from the transport endpoint of the management target, the notification is considered acknowledged and the cached information is deleted. Otherwise, d) If a response is not received within an appropriate time period, or if a report indication is received, information about the management target is retrieved from the cache, and steps a) through d) are repeated. The number of times these steps are repeated is equal to the previously determined retry count. If this retry count is exceeded, the acknowledgement of the notification is considered to have failed, and processing of the notification for this management target is halted. Note that some report indications might be considered a failure. Such report indications should be interpreted to mean that the acknowledgement of the notification has failed, and that steps a) through d) need not be repeated. Responses to Confirmed-Class PDU notifications will be received via the processResponsePdu abstract service interface. To summarize, the steps that a notification originator follows when determining where to send a notification are: - Determine the targets to which the notification should be sent. - Apply any required filtering to the list of targets. - Determine which targets are authorized to receive the notification. 3.4. Notification Receiver Applications Notification receiver applications receive SNMP Notification messages from the Dispatcher. Before any messages can be received, the notification receiver must register with the Dispatcher using the registerContextEngineID abstract service interface. The parameters used are: Levi, et. al. Standards Track [Page 17] RFC 3413 SNMP Applications December 2002 - The contextEngineID is an undefined 'wildcard' value. Notifications are delivered to a registered notification receiver regardless of the contextEngineID contained in the notification message. - The pduType indicates the type of notifications that the application wishes to receive (for example, SNMPv2-Trap PDUs or Inform PDUs). Once the notification receiver has registered with the Dispatcher, messages are received using the processPdu abstract service interface. Parameters are: - The messageProcessingModel indicates which Message Processing Model received and processed the message. - The securityModel is the value from the received message. - The securityName is the value from the received message. - The securityLevel is the value from the received message. - The contextEngineID is the value from the received message. - The contextName is the value from the received message. - The pduVersion indicates the version of the PDU in the received message. - The PDU is the value from the received message. - The maxSizeResponseScopedPDU is the maximum allowable size of a ScopedPDU containing a Response PDU (based on the maximum message size that the originator of the message can accept). - If the message contains an Unconfirmed-Class PDU, the stateReference is undefined and unused. Otherwise, the stateReference is a value which references cached information about the notification. This value must be returned to the Dispatcher in order to generate a response. When an Unconfirmed-Class PDU is delivered to a notification receiver application, it first extracts the SNMP operation type, request-id, error-status, error-index, and variable-bindings from the PDU. After this, processing depends on the particular implementation. Levi, et. al. Standards Track [Page 18] RFC 3413 SNMP Applications December 2002 When a Confirmed-Class PDU is received, the notification receiver application follows the following procedure: (1) The PDU type, request-id, error-status, error-index, and variable-bindings are extracted from the PDU. (2) A Response-Class PDU is constructed using the extracted request-id and variable-bindings, and with error-status and error-index both set to 0. (3) The Dispatcher is called to generate a response message using the returnResponsePdu abstract service interface. Parameters are: - The messageProcessingModel is the value from the processPdu call. - The securityModel is the value from the processPdu call. - The securityName is the value from the processPdu call. - The securityLevel is the value from the processPdu call. - The contextEngineID is the value from the processPdu call. - The contextName is the value from the processPdu call. - The pduVersion indicates the version of the PDU to be returned. - The PDU is the result generated in step (2) above. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value from the processPdu call. - The statusInformation indicates that no error occurred and that a response should be generated. (4) After this, processing depends on the particular implementation. 3.5. Proxy Forwarder Applications A proxy forwarder application deals with forwarding SNMP messages. There are four basic types of messages which a proxy forwarder application may need to forward. These are grouped according to the class of PDU type contained in a message. The four basic types of messages are: Levi, et. al. Standards Track [Page 19] RFC 3413 SNMP Applications December 2002 - Those containing Read-Class or Write-Class PDU types (for example, Get, GetNext, GetBulk, and Set PDU types). These deal with requesting or modifying information located within a particular context. - Those containing Notification-Class PDU types (for example, SNMPv2-Trap and Inform PDU types). These deal with notifications concerning information located within a particular context. - Those containing a Response-Class PDU type. Forwarding of Response-Class PDUs always occurs as a result of receiving a response to a previously forwarded message. - Those containing Internal-Class PDU types (for example, a Report PDU). Forwarding of Internal-Class PDU types always occurs as a result of receiving an Internal-Class PDU in response to a previously forwarded message. For the first type, the proxy forwarder's role is to deliver a request for management information to an SNMP engine which is "closer" or "downstream in the path" to the SNMP engine which has access to that information, and to deliver the response containing the information back to the SNMP engine from which the request was received. The context information in a request is used to determine which SNMP engine has access to the requested information, and this is used to determine where and how to forward the request. For the second type, the proxy forwarder's role is to determine which SNMP engines should receive notifications about management information from a particular location. The context information in a notification message determines the location to which the information contained in the notification applies. This is used to determine which SNMP engines should receive notification about this information. For the third type, the proxy forwarder's role is to determine which previously forwarded request or notification (if any) the response matches, and to forward the response back to the initiator of the request or notification. For the fourth type, the proxy forwarder's role is to determine which previously forwarded request or notification (if any) the Internal- Class PDU matches, and to forward the Internal-Class PDU back to the initiator of the request or notification. Levi, et. al. Standards Track [Page 20] RFC 3413 SNMP Applications December 2002 When forwarding messages, a proxy forwarder application must perform a translation of incoming management target information into outgoing management target information. How this translation is performed is implementation specific. In many cases, this will be driven by a preconfigured translation table. If a proxy forwarder application makes the contents of this table SNMP manageable, it MUST use the SNMP-PROXY-MIB module defined in this document. 3.5.1. Request Forwarding There are two phases for request forwarding. First, the incoming request needs to be passed through the proxy application. Then, the resulting response needs to be passed back. These phases are described in the following two sections. 3.5.1.1. Processing an Incoming Request A proxy forwarder application that wishes to forward request messages must first register with the Dispatcher using the registerContextEngineID abstract service interface. The proxy forwarder must register each contextEngineID for which it wishes to forward messages, as well as for each pduType. Note that as the configuration of a proxy forwarder is changed, the particular contextEngineID values for which it is forwarding may change. The proxy forwarder should call the registerContextEngineID and unregisterContextEngineID abstract service interfaces as needed to reflect its current configuration. A proxy forwarder application should never attempt to register a value of contextEngineID which is equal to the snmpEngineID of the SNMP engine to which the proxy forwarder is associated. Once the proxy forwarder has registered for the appropriate contextEngineID values, it can start processing messages. The following procedure is used: (1) A message is received using the processPdu abstract service interface. The incoming management target information received from the processPdu interface is translated into outgoing management target information. Note that this translation may vary for different values of contextEngineID and/or contextName. The translation should result in a single management target. (2) If appropriate outgoing management target information cannot be found, the proxy forwarder increments the snmpProxyDrops counter [RFC1907], and then calls the Dispatcher using the returnResponsePdu abstract service interface. Parameters are: Levi, et. al. Standards Track [Page 21] RFC 3413 SNMP Applications December 2002 - The messageProcessingModel is the value from the processPdu call. - The securityModel is the value from the processPdu call. - The securityName is the value from the processPdu call. - The securityLevel is the value from the processPdu call. - The contextEngineID is the value from the processPdu call. - The contextName is the value from the processPdu call. - The pduVersion is the value from the processPdu call. - The PDU is an undefined value. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value from the processPdu call. - The statusInformation indicates that an error occurred and includes the OID and value of the snmpProxyDrops object. Processing of the message stops at this point. Otherwise, (3) A new PDU is constructed. A unique value of request-id should be used in the new PDU (this value will enable a subsequent response message to be correlated with this request). The remainder of the new PDU is identical to the received PDU, unless the incoming SNMP version and the outgoing SNMP version support different PDU versions, in which case the proxy forwarder may need to perform a translation on the PDU. (A method for performing such a translation is described in [RFC2576].) (4) The proxy forwarder calls the Dispatcher to generate the forwarded message, using the sendPdu abstract service interface. The parameters are: - The transportDomain is that of the outgoing management target. - The transportAddress is that of the outgoing management target. - The messageProcessingModel is that of the outgoing management target. - The securityModel is that of the outgoing management target. Levi, et. al. Standards Track [Page 22] RFC 3413 SNMP Applications December 2002 - The securityName is that of the outgoing management target. - The securityLevel is that of the outgoing management target. - The contextEngineID is the value from the processPdu call. - The contextName is the value from the processPdu call. - The pduVersion is the version of the PDU to be sent. - The PDU is the value constructed in step (3) above. - The expectResponse argument indicates that a response is expected. If the sendPdu call is unsuccessful, the proxy forwarder performs the steps described in (2) above. Otherwise: (5) The proxy forwarder caches the following information in order to match an incoming response to the forwarded request: - The sendPduHandle returned from the call to sendPdu, - The request-id from the received PDU. - The contextEngineID, - The contextName, - The stateReference, - The incoming management target information, - The outgoing management information, - Any other information needed to match an incoming response to the forwarded request. If this information cannot be cached (possibly due to a lack of resources), the proxy forwarder performs the steps described in (2) above. Otherwise: (6) Processing of the request stops until a response to the forwarded request is received, or until an appropriate time interval has expired. If this time interval expires before a response has been received, the cached information about this request is removed. Levi, et. al. Standards Track [Page 23] RFC 3413 SNMP Applications December 2002 3.5.1.2. Processing an Incoming Response A proxy forwarder follows the following procedure when an incoming response is received: (1) The incoming response is received using the processResponsePdu interface. The proxy forwarder uses the received parameters to locate an entry in its cache of pending forwarded requests. This is done by matching the received parameters with the cached values of sendPduHandle, contextEngineID, contextName, outgoing management target information, and the request-id contained in the received PDU (the proxy forwarder must extract the request-id for this purpose). If an appropriate cache entry cannot be found, processing of the response is halted. Otherwise: (2) The cache information is extracted, and removed from the cache. (3) A new Response-Class PDU is constructed, using the request-id value from the original forwarded request (as extracted from the cache). All other values are identical to those in the received Response-Class PDU, unless the incoming SNMP version and the outgoing SNMP version support different PDU versions, in which case the proxy forwarder may need to perform a translation on the PDU. (A method for performing such a translation is described in [RFC2576].) (4) The proxy forwarder calls the Dispatcher using the returnResponsePdu abstract service interface. Parameters are: - The messageProcessingModel indicates the Message Processing Model by which the original incoming message was processed. - The securityModel is that of the original incoming management target extracted from the cache. - The securityName is that of the original incoming management target extracted from the cache. - The securityLevel is that of the original incoming management target extracted from the cache. - The contextEngineID is the value extracted from the cache. - The contextName is the value extracted from the cache. - The pduVersion indicates the version of the PDU to be returned. - The PDU is the (possibly translated) Response PDU. Levi, et. al. Standards Track [Page 24] RFC 3413 SNMP Applications December 2002 - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value extracted from the cache. - The statusInformation indicates that no error occurred and that a Response PDU message should be generated. 3.5.1.3. Processing an Incoming Internal-Class PDU A proxy forwarder follows the following procedure when an incoming Internal-Class PDU is received: (1) The incoming Internal-Class PDU is received using the processResponsePdu interface. The proxy forwarder uses the received parameters to locate an entry in its cache of pending forwarded requests. This is done by matching the received parameters with the cached values of sendPduHandle. If an appropriate cache entry cannot be found, processing of the Internal-Class PDU is halted. Otherwise: (2) The cache information is extracted, and removed from the cache. (3) If the original incoming management target information indicates an SNMP version which does not support Report PDUs, processing of the Internal-Class PDU is halted. (4) The proxy forwarder calls the Dispatcher using the returnResponsePdu abstract service interface. Parameters are: - The messageProcessingModel indicates the Message Processing Model by which the original incoming message was processed. - The securityModel is that of the original incoming management target extracted from the cache. - The securityName is that of the original incoming management target extracted from the cache. - The securityLevel is that of the original incoming management target extracted from the cache. - The contextEngineID is the value extracted from the cache. - The contextName is the value extracted from the cache. - The pduVersion indicates the version of the PDU to be returned. Levi, et. al. Standards Track [Page 25] RFC 3413 SNMP Applications December 2002 - The PDU is unused. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value extracted from the cache. - The statusInformation contains values specific to the Internal-Class PDU type (for example, for a Report PDU, the statusInformation contains the contextEngineID, contextName, counter OID, and counter value received in the incoming Report PDU). 3.5.2. Notification Forwarding A proxy forwarder receives notifications in the same manner as a notification receiver application, using the processPdu abstract service interface. The following procedure is used when a notification is received: (1) The incoming management target information received from the processPdu interface is translated into outgoing management target information. Note that this translation may vary for different values of contextEngineID and/or contextName. The translation may result in multiple management targets. (2) If appropriate outgoing management target information cannot be found and the notification was an Unconfirmed-Class PDU, processing of the notification is halted. If appropriate outgoing management target information cannot be found and the notification was a Confirmed-Class PDU, the proxy forwarder increments the snmpProxyDrops object, and calls the Dispatcher using the returnResponsePdu abstract service interface. The parameters are: - The messageProcessingModel is the value from the processPdu call. - The securityModel is the value from the processPdu call. - The securityName is the value from the processPdu call. - The securityLevel is the value from the processPdu call. - The contextEngineID is the value from the processPdu call. - The contextName is the value from the processPdu call. Levi, et. al. Standards Track [Page 26] RFC 3413 SNMP Applications December 2002 - The pduVersion is the value from the processPdu call. - The PDU is an undefined and unused value. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value from the processPdu call. - The statusInformation indicates that an error occurred and that a Report message should be generated. Processing of the message stops at this point. Otherwise, (3) The proxy forwarder generates a notification using the procedures described in the preceding section on Notification Originators, with the following exceptions: - The contextEngineID and contextName values from the original received notification are used. - The outgoing management targets previously determined are used. - No filtering mechanisms are applied. - The variable-bindings from the original received notification are used, rather than retrieving variable-bindings from local MIB instrumentation. In particular, no access-control is applied to these variable-bindings, nor to the value of the variable-binding containing snmpTrapOID.0. - If the original notification contains a Confirmed-Class PDU, then any outgoing management targets for which the outgoing SNMP version does not support any PDU types that are both Notification-Class and Confirmed-Class PDUs will not be used when generating the forwarded notifications. - If, for any of the outgoing management targets, the incoming SNMP version and the outgoing SNMP version support different PDU versions, the proxy forwarder may need to perform a translation on the PDU. (A method for performing such a translation is described in [RFC2576].) (4) If the original received notification contains an Unconfirmed-Class PDU, processing of the notification is now completed. Otherwise, the original received notification must contain Confirmed-Class PDU, and processing continues. Levi, et. al. Standards Track [Page 27] RFC 3413 SNMP Applications December 2002 (5) If the forwarded notifications included any Confirmed-Class PDUs, processing continues when the procedures described in the section for Notification Originators determine that either: - None of the generated notifications containing Confirmed-Class PDUs have been successfully acknowledged within the longest of the time intervals, in which case processing of the original notification is halted, or, - At least one of the generated notifications containing Confirmed-Class PDUs is successfully acknowledged, in which case a response to the original received notification containing an Confirmed-Class PDU is generated as described in the following steps. (6) A Response-Class PDU is constructed, using the values of request-id and variable-bindings from the original received Notification-Class PDU, and error-status and error-index values of 0. (7) The Dispatcher is called using the returnResponsePdu abstract service interface. Parameters are: - The messageProcessingModel is the value from the processPdu call. - The securityModel is the value from the processPdu call. - The securityName is the value from the processPdu call. - The securityLevel is the value from the processPdu call. - The contextEngineID is the value from the processPdu call. - The contextName is the value from the processPdu call. - The pduVersion indicates the version of the PDU constructed in step (6) above. - The PDU is the value constructed in step (6) above. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value from the processPdu call. - The statusInformation indicates that no error occurred and that a Response-Class PDU message should be generated. Levi, et. al. Standards Track [Page 28] RFC 3413 SNMP Applications December 2002 4. The Structure of the MIB Modules There are three separate MIB modules described in this document, the management target MIB, the notification MIB, and the proxy MIB. The following sections describe the structure of these three MIB modules. The use of these MIBs by particular types of applications is described later in this document: - The use of the management target MIB and the notification MIB in notification originator applications is described in section 5. - The use of the notification MIB for filtering notifications in notification originator applications is described in section 6. - The use of the management target MIB and the proxy MIB in proxy forwarding applications is described in section 7. 4.1. The Management Target MIB Module The SNMP-TARGET-MIB module contains objects for defining management targets. It consists of two tables and conformance/compliance statements. The first table, the snmpTargetAddrTable, contains information about transport domains and addresses. It also contains an object, snmpTargetAddrTagList, which provides a mechanism for grouping entries. The second table, the snmpTargetParamsTable, contains information about SNMP version and security information to be used when sending messages to particular transport domains and addresses. The Management Target MIB is intended to provide a general-purpose mechanism for specifying transport address, and for specifying parameters of SNMP messages generated by an SNMP entity. It is used within this document for generation of notifications and for proxy forwarding. However, it may be used for other purposes. If another document makes use of this MIB, that document is responsible for specifying how it is used. For example, [RFC2576] uses this MIB for source address validation of SNMPv1 messages. 4.1.1. Tag Lists The snmpTargetAddrTagList object is used for grouping entries in the snmpTargetAddrTable. The value of this object contains a list of tag values which are used to select target addresses to be used for a particular operation. Levi, et. al. Standards Track [Page 29] RFC 3413 SNMP Applications December 2002 A tag value, which may also be used in MIB objects other than snmpTargetAddrTagList, is an arbitrary string of octets, but may not contain a delimiter character. Delimiter characters are defined to be one of the following characters: - An ASCII space character (0x20). - An ASCII TAB character (0x09). - An ASCII carriage return (CR) character (0x0D). - An ASCII line feed (LF) character (0x0A). In addition, a tag value within a tag list may not have a zero length. Generally, a particular MIB object may contain either - a zero-length octet string representing an empty list, or - a single tag value, in which case the value of the MIB object may not contain a delimiter character, or - a list of tag values, separated by single delimiter characters. For a list of tag values, these constraints imply certain restrictions on the value of a MIB object: - There cannot be a leading or trailing delimiter character. - There cannot be multiple adjacent delimiter characters. 4.1.2. Definitions SNMP-TARGET-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, snmpModules, Counter32, Integer32 FROM SNMPv2-SMI TEXTUAL-CONVENTION, TDomain, TAddress, TimeInterval, RowStatus, StorageType, Levi, et. al. Standards Track [Page 30] RFC 3413 SNMP Applications December 2002 TestAndIncr FROM SNMPv2-TC SnmpSecurityModel, SnmpMessageProcessingModel, SnmpSecurityLevel, SnmpAdminString FROM SNMP-FRAMEWORK-MIB MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF; snmpTargetMIB MODULE-IDENTITY LAST-UPDATED "200210140000Z" ORGANIZATION "IETF SNMPv3 Working Group" CONTACT-INFO "WG-email: snmpv3@lists.tislabs.com Subscribe: majordomo@lists.tislabs.com In message body: subscribe snmpv3 Co-Chair: Russ Mundy Network Associates Laboratories Postal: 15204 Omega Drive, Suite 300 Rockville, MD 20850-4601 USA EMail: mundy@tislabs.com Phone: +1 301-947-7107 Co-Chair: David Harrington Enterasys Networks Postal: 35 Industrial Way P. O. Box 5004 Rochester, New Hampshire 03866-5005 USA EMail: dbh@enterasys.com Phone: +1 603-337-2614 Co-editor: David B. Levi Nortel Networks Postal: 3505 Kesterwood Drive Knoxville, Tennessee 37918 EMail: dlevi@nortelnetworks.com Phone: +1 865 686 0432 Co-editor: Paul Meyer Secure Computing Corporation Postal: 2675 Long Lake Road Levi, et. al. Standards Track [Page 31] RFC 3413 SNMP Applications December 2002 Roseville, Minnesota 55113 EMail: paul_meyer@securecomputing.com Phone: +1 651 628 1592 Co-editor: Bob Stewart Retired" DESCRIPTION "This MIB module defines MIB objects which provide mechanisms to remotely configure the parameters used by an SNMP entity for the generation of SNMP messages. Copyright (C) The Internet Society (2002). This version of this MIB module is part of RFC 3413; see the RFC itself for full legal notices. " REVISION "200210140000Z" -- 14 October 2002 DESCRIPTION "Fixed DISPLAY-HINTS for UTF-8 strings, fixed hex value of LF characters, clarified meaning of zero length tag values, improved tag list examples. Published as RFC 3413." REVISION "199808040000Z" -- 4 August 1998 DESCRIPTION "Clarifications, published as RFC 2573." REVISION "199707140000Z" -- 14 July 1997 DESCRIPTION "The initial revision, published as RFC2273." ::= { snmpModules 12 } snmpTargetObjects OBJECT IDENTIFIER ::= { snmpTargetMIB 1 } snmpTargetConformance OBJECT IDENTIFIER ::= { snmpTargetMIB 3 } SnmpTagValue ::= TEXTUAL-CONVENTION DISPLAY-HINT "255t" STATUS current DESCRIPTION "An octet string containing a tag value. Tag values are preferably in human-readable form. To facilitate internationalization, this information is represented using the ISO/IEC IS 10646-1 character set, encoded as an octet string using the UTF-8 character encoding scheme described in RFC 2279. Since additional code points are added by amendments to the 10646 standard from time to time, implementations must be prepared to encounter any code point from 0x00000000 to 0x7fffffff. The use of control codes should be avoided, and certain Levi, et. al. Standards Track [Page 32] RFC 3413 SNMP Applications December 2002 control codes are not allowed as described below. For code points not directly supported by user interface hardware or software, an alternative means of entry and display, such as hexadecimal, may be provided. For information encoded in 7-bit US-ASCII, the UTF-8 representation is identical to the US-ASCII encoding. Note that when this TC is used for an object that is used or envisioned to be used as an index, then a SIZE restriction must be specified so that the number of sub-identifiers for any object instance does not exceed the limit of 128, as defined by [RFC1905]. An object of this type contains a single tag value which is used to select a set of entries in a table. A tag value is an arbitrary string of octets, but may not contain a delimiter character. Delimiter characters are defined to be one of the following: - An ASCII space character (0x20). - An ASCII TAB character (0x09). - An ASCII carriage return (CR) character (0x0D). - An ASCII line feed (LF) character (0x0A). Delimiter characters are used to separate tag values in a tag list. An object of this type may only contain a single tag value, and so delimiter characters are not allowed in a value of this type. Note that a tag value of 0 length means that no tag is defined. In other words, a tag value of 0 length would never match anything in a tag list, and would never select any table entries. Some examples of valid tag values are: - 'acme' - 'router' - 'host' Levi, et. al. Standards Track [Page 33] RFC 3413 SNMP Applications December 2002 The use of a tag value to select table entries is application and MIB specific." SYNTAX OCTET STRING (SIZE (0..255)) SnmpTagList ::= TEXTUAL-CONVENTION DISPLAY-HINT "255t" STATUS current DESCRIPTION "An octet string containing a list of tag values. Tag values are preferably in human-readable form. To facilitate internationalization, this information is represented using the ISO/IEC IS 10646-1 character set, encoded as an octet string using the UTF-8 character encoding scheme described in RFC 2279. Since additional code points are added by amendments to the 10646 standard from time to time, implementations must be prepared to encounter any code point from 0x00000000 to 0x7fffffff. The use of control codes should be avoided, except as described below. For code points not directly supported by user interface hardware or software, an alternative means of entry and display, such as hexadecimal, may be provided. For information encoded in 7-bit US-ASCII, the UTF-8 representation is identical to the US-ASCII encoding. An object of this type contains a list of tag values which are used to select a set of entries in a table. A tag value is an arbitrary string of octets, but may not contain a delimiter character. Delimiter characters are defined to be one of the following: - An ASCII space character (0x20). - An ASCII TAB character (0x09). - An ASCII carriage return (CR) character (0x0D). - An ASCII line feed (LF) character (0x0A). Delimiter characters are used to separate tag values Levi, et. al. Standards Track [Page 34] RFC 3413 SNMP Applications December 2002 in a tag list. Only a single delimiter character may occur between two tag values. A tag value may not have a zero length. These constraints imply certain restrictions on the contents of this object: - There cannot be a leading or trailing delimiter character. - There cannot be multiple adjacent delimiter characters. Some examples of valid tag lists are: - '' -- an empty list - 'acme' -- list of one tag - 'host router bridge' -- list of several tags Note that although a tag value may not have a length of zero, an empty string is still valid. This indicates an empty list (i.e. there are no tag values in the list). The use of the tag list to select table entries is application and MIB specific. Typically, an application will provide one or more tag values, and any entry which contains some combination of these tag values will be selected." SYNTAX OCTET STRING (SIZE (0..255)) -- -- -- The snmpTargetObjects group -- -- snmpTargetSpinLock OBJECT-TYPE SYNTAX TestAndIncr MAX-ACCESS read-write STATUS current DESCRIPTION "This object is used to facilitate modification of table entries in the SNMP-TARGET-MIB module by multiple managers. In particular, it is useful when modifying the value of the snmpTargetAddrTagList object. The procedure for modifying the snmpTargetAddrTagList object is as follows: Levi, et. al. Standards Track [Page 35] RFC 3413 SNMP Applications December 2002 1. Retrieve the value of snmpTargetSpinLock and of snmpTargetAddrTagList. 2. Generate a new value for snmpTargetAddrTagList. 3. Set the value of snmpTargetSpinLock to the retrieved value, and the value of snmpTargetAddrTagList to the new value. If the set fails for the snmpTargetSpinLock object, go back to step 1." ::= { snmpTargetObjects 1 } snmpTargetAddrTable OBJECT-TYPE SYNTAX SEQUENCE OF SnmpTargetAddrEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A table of transport addresses to be used in the generation of SNMP messages." ::= { snmpTargetObjects 2 } snmpTargetAddrEntry OBJECT-TYPE SYNTAX SnmpTargetAddrEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A transport address to be used in the generation of SNMP operations. Entries in the snmpTargetAddrTable are created and deleted using the snmpTargetAddrRowStatus object." INDEX { IMPLIED snmpTargetAddrName } ::= { snmpTargetAddrTable 1 } SnmpTargetAddrEntry ::= SEQUENCE { snmpTargetAddrName SnmpAdminString, snmpTargetAddrTDomain TDomain, snmpTargetAddrTAddress TAddress, snmpTargetAddrTimeout TimeInterval, snmpTargetAddrRetryCount Integer32, snmpTargetAddrTagList SnmpTagList, snmpTargetAddrParams SnmpAdminString, snmpTargetAddrStorageType StorageType, snmpTargetAddrRowStatus RowStatus } snmpTargetAddrName OBJECT-TYPE SYNTAX SnmpAdminString (SIZE(1..32)) Levi, et. al. Standards Track [Page 36] RFC 3413 SNMP Applications December 2002 MAX-ACCESS not-accessible STATUS current DESCRIPTION "The locally arbitrary, but unique identifier associated with this snmpTargetAddrEntry." ::= { snmpTargetAddrEntry 1 } snmpTargetAddrTDomain OBJECT-TYPE SYNTAX TDomain MAX-ACCESS read-create STATUS current DESCRIPTION "This object indicates the transport type of the address contained in the snmpTargetAddrTAddress object." ::= { snmpTargetAddrEntry 2 } snmpTargetAddrTAddress OBJECT-TYPE SYNTAX TAddress MAX-ACCESS read-create STATUS current DESCRIPTION "This object contains a transport address. The format of this address depends on the value of the snmpTargetAddrTDomain object." ::= { snmpTargetAddrEntry 3 } snmpTargetAddrTimeout OBJECT-TYPE SYNTAX TimeInterval MAX-ACCESS read-create STATUS current DESCRIPTION "This object should reflect the expected maximum round trip time for communicating with the transport address defined by this row. When a message is sent to this address, and a response (if one is expected) is not received within this time period, an implementation may assume that the response will not be delivered. Note that the time interval that an application waits for a response may actually be derived from the value of this object. The method for deriving the actual time interval is implementation dependent. One such method is to derive the expected round trip time based on a particular retransmission algorithm and on the number of timeouts which have occurred. The type of message may also be considered when deriving expected round trip times for retransmissions. For example, if a message is being sent with a securityLevel that indicates both Levi, et. al. Standards Track [Page 37] RFC 3413 SNMP Applications December 2002 authentication and privacy, the derived value may be increased to compensate for extra processing time spent during authentication and encryption processing." DEFVAL { 1500 } ::= { snmpTargetAddrEntry 4 } snmpTargetAddrRetryCount OBJECT-TYPE SYNTAX Integer32 (0..255) MAX-ACCESS read-create STATUS current DESCRIPTION "This object specifies a default number of retries to be attempted when a response is not received for a generated message. An application may provide its own retry count, in which case the value of this object is ignored." DEFVAL { 3 } ::= { snmpTargetAddrEntry 5 } snmpTargetAddrTagList OBJECT-TYPE SYNTAX SnmpTagList MAX-ACCESS read-create STATUS current DESCRIPTION "This object contains a list of tag values which are used to select target addresses for a particular operation." DEFVAL { "" } ::= { snmpTargetAddrEntry 6 } snmpTargetAddrParams OBJECT-TYPE SYNTAX SnmpAdminString (SIZE(1..32)) MAX-ACCESS read-create STATUS current DESCRIPTION "The value of this object identifies an entry in the snmpTargetParamsTable. The identified entry contains SNMP parameters to be used when generating messages to be sent to this transport address." ::= { snmpTargetAddrEntry 7 } snmpTargetAddrStorageType OBJECT-TYPE SYNTAX StorageType MAX-ACCESS read-create STATUS current DESCRIPTION "The storage type for this conceptual row. Conceptual rows having the value 'permanent' need not allow write-access to any columnar objects in the row." Levi, et. al. Standards Track [Page 38] RFC 3413 SNMP Applications December 2002 DEFVAL { nonVolatile } ::= { snmpTargetAddrEntry 8 } snmpTargetAddrRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The status of this conceptual row. To create a row in this table, a manager must set this object to either createAndGo(4) or createAndWait(5). Until instances of all corresponding columns are appropriately configured, the value of the corresponding instance of the snmpTargetAddrRowStatus column is 'notReady'. In particular, a newly created row cannot be made active until the corresponding instances of snmpTargetAddrTDomain, snmpTargetAddrTAddress, and snmpTargetAddrParams have all been set. The following objects may not be modified while the value of this object is active(1): - snmpTargetAddrTDomain - snmpTargetAddrTAddress An attempt to set these objects while the value of snmpTargetAddrRowStatus is active(1) will result in an inconsistentValue error." ::= { snmpTargetAddrEntry 9 } snmpTargetParamsTable OBJECT-TYPE SYNTAX SEQUENCE OF SnmpTargetParamsEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A table of SNMP target information to be used in the generation of SNMP messages." ::= { snmpTargetObjects 3 } snmpTargetParamsEntry OBJECT-TYPE SYNTAX SnmpTargetParamsEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A set of SNMP target information. Levi, et. al. Standards Track [Page 39] RFC 3413 SNMP Applications December 2002 Entries in the snmpTargetParamsTable are created and deleted using the snmpTargetParamsRowStatus object." INDEX { IMPLIED snmpTargetParamsName } ::= { snmpTargetParamsTable 1 } SnmpTargetParamsEntry ::= SEQUENCE { snmpTargetParamsName SnmpAdminString, snmpTargetParamsMPModel SnmpMessageProcessingModel, snmpTargetParamsSecurityModel SnmpSecurityModel, snmpTargetParamsSecurityName SnmpAdminString, snmpTargetParamsSecurityLevel SnmpSecurityLevel, snmpTargetParamsStorageType StorageType, snmpTargetParamsRowStatus RowStatus } snmpTargetParamsName OBJECT-TYPE SYNTAX SnmpAdminString (SIZE(1..32)) MAX-ACCESS not-accessible STATUS current DESCRIPTION "The locally arbitrary, but unique identifier associated with this snmpTargetParamsEntry." ::= { snmpTargetParamsEntry 1 } snmpTargetParamsMPModel OBJECT-TYPE SYNTAX SnmpMessageProcessingModel MAX-ACCESS read-create STATUS current DESCRIPTION "The Message Processing Model to be used when generating SNMP messages using this entry." ::= { snmpTargetParamsEntry 2 } snmpTargetParamsSecurityModel OBJECT-TYPE SYNTAX SnmpSecurityModel (1..2147483647) MAX-ACCESS read-create STATUS current DESCRIPTION "The Security Model to be used when generating SNMP messages using this entry. An implementation may choose to return an inconsistentValue error if an attempt is made to set this variable to a value for a security model which the implementation does not support." ::= { snmpTargetParamsEntry 3 } snmpTargetParamsSecurityName OBJECT-TYPE SYNTAX SnmpAdminString Levi, et. al. Standards Track [Page 40] RFC 3413 SNMP Applications December 2002 MAX-ACCESS read-create STATUS current DESCRIPTION "The securityName which identifies the Principal on whose behalf SNMP messages will be generated using this entry." ::= { snmpTargetParamsEntry 4 } snmpTargetParamsSecurityLevel OBJECT-TYPE SYNTAX SnmpSecurityLevel MAX-ACCESS read-create STATUS current DESCRIPTION "The Level of Security to be used when generating SNMP messages using this entry." ::= { snmpTargetParamsEntry 5 } snmpTargetParamsStorageType OBJECT-TYPE SYNTAX StorageType MAX-ACCESS read-create STATUS current DESCRIPTION "The storage type for this conceptual row. Conceptual rows having the value 'permanent' need not allow write-access to any columnar objects in the row." DEFVAL { nonVolatile } ::= { snmpTargetParamsEntry 6 } snmpTargetParamsRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The status of this conceptual row. To create a row in this table, a manager must set this object to either createAndGo(4) or createAndWait(5). Until instances of all corresponding columns are appropriately configured, the value of the corresponding instance of the snmpTargetParamsRowStatus column is 'notReady'. In particular, a newly created row cannot be made active until the corresponding snmpTargetParamsMPModel, snmpTargetParamsSecurityModel, Levi, et. al. Standards Track [Page 41] RFC 3413 SNMP Applications December 2002 snmpTargetParamsSecurityName, and snmpTargetParamsSecurityLevel have all been set. The following objects may not be modified while the value of this object is active(1): - snmpTargetParamsMPModel - snmpTargetParamsSecurityModel - snmpTargetParamsSecurityName - snmpTargetParamsSecurityLevel An attempt to set these objects while the value of snmpTargetParamsRowStatus is active(1) will result in an inconsistentValue error." ::= { snmpTargetParamsEntry 7 } snmpUnavailableContexts OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because the context contained in the message was unavailable." ::= { snmpTargetObjects 4 } snmpUnknownContexts OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because the context contained in the message was unknown." ::= { snmpTargetObjects 5 } -- -- -- Conformance information -- -- snmpTargetCompliances OBJECT IDENTIFIER ::= { snmpTargetConformance 1 } snmpTargetGroups OBJECT IDENTIFIER ::= { snmpTargetConformance 2 } -- -- -- Compliance statements Levi, et. al. Standards Track [Page 42] RFC 3413 SNMP Applications December 2002 -- -- snmpTargetCommandResponderCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for SNMP entities which include a command responder application." MODULE -- This Module MANDATORY-GROUPS { snmpTargetCommandResponderGroup } ::= { snmpTargetCompliances 1 } snmpTargetBasicGroup OBJECT-GROUP OBJECTS { snmpTargetSpinLock, snmpTargetAddrTDomain, snmpTargetAddrTAddress, snmpTargetAddrTagList, snmpTargetAddrParams, snmpTargetAddrStorageType, snmpTargetAddrRowStatus, snmpTargetParamsMPModel, snmpTargetParamsSecurityModel, snmpTargetParamsSecurityName, snmpTargetParamsSecurityLevel, snmpTargetParamsStorageType, snmpTargetParamsRowStatus } STATUS current DESCRIPTION "A collection of objects providing basic remote configuration of management targets." ::= { snmpTargetGroups 1 } snmpTargetResponseGroup OBJECT-GROUP OBJECTS { snmpTargetAddrTimeout, snmpTargetAddrRetryCount } STATUS current DESCRIPTION "A collection of objects providing remote configuration of management targets for applications which generate SNMP messages for which a response message would be expected." ::= { snmpTargetGroups 2 } snmpTargetCommandResponderGroup OBJECT-GROUP Levi, et. al. Standards Track [Page 43] RFC 3413 SNMP Applications December 2002 OBJECTS { snmpUnavailableContexts, snmpUnknownContexts } STATUS current DESCRIPTION "A collection of objects required for command responder applications, used for counting error conditions." ::= { snmpTargetGroups 3 } END 4.2. The Notification MIB Module The SNMP-NOTIFICATION-MIB module contains objects for the remote configuration of the parameters used by an SNMP entity for the generation of notifications. It consists of three tables and conformance/compliance statements. The first table, the snmpNotifyTable, contains entries which select which entries in the snmpTargetAddrTable should be used for generating notifications, and the type of notifications to be generated. The second table, the snmpNotifyFilterProfileTable, sparsely augments the snmpTargetParamsTable with an object which is used to associate a set of filters with a particular management target. The third table, the snmpNotifyFilterTable, defines filters which are used to limit the number of notifications which are generated using particular management targets. 4.2.1. Definitions SNMP-NOTIFICATION-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, snmpModules FROM SNMPv2-SMI RowStatus, StorageType FROM SNMPv2-TC SnmpAdminString FROM SNMP-FRAMEWORK-MIB SnmpTagValue, Levi, et. al. Standards Track [Page 44] RFC 3413 SNMP Applications December 2002 snmpTargetParamsName FROM SNMP-TARGET-MIB MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF; snmpNotificationMIB MODULE-IDENTITY LAST-UPDATED "200210140000Z" ORGANIZATION "IETF SNMPv3 Working Group" CONTACT-INFO "WG-email: snmpv3@lists.tislabs.com Subscribe: majordomo@lists.tislabs.com In message body: subscribe snmpv3 Co-Chair: Russ Mundy Network Associates Laboratories Postal: 15204 Omega Drive, Suite 300 Rockville, MD 20850-4601 USA EMail: mundy@tislabs.com Phone: +1 301-947-7107 Co-Chair: David Harrington Enterasys Networks Postal: 35 Industrial Way P. O. Box 5004 Rochester, New Hampshire 03866-5005 USA EMail: dbh@enterasys.com Phone: +1 603-337-2614 Co-editor: David B. Levi Nortel Networks Postal: 3505 Kesterwood Drive Knoxville, Tennessee 37918 EMail: dlevi@nortelnetworks.com Phone: +1 865 686 0432 Co-editor: Paul Meyer Secure Computing Corporation Postal: 2675 Long Lake Road Roseville, Minnesota 55113 EMail: paul_meyer@securecomputing.com Phone: +1 651 628 1592 Co-editor: Bob Stewart Retired" Levi, et. al. Standards Track [Page 45] RFC 3413 SNMP Applications December 2002 DESCRIPTION "This MIB module defines MIB objects which provide mechanisms to remotely configure the parameters used by an SNMP entity for the generation of notifications. Copyright (C) The Internet Society (2002). This version of this MIB module is part of RFC 3413; see the RFC itself for full legal notices. " REVISION "200210140000Z" -- 14 October 2002 DESCRIPTION "Clarifications, published as RFC 3413." REVISION "199808040000Z" -- 4 August 1998 DESCRIPTION "Clarifications, published as RFC 2573." REVISION "199707140000Z" -- 14 July 1997 DESCRIPTION "The initial revision, published as RFC2273." ::= { snmpModules 13 } snmpNotifyObjects OBJECT IDENTIFIER ::= { snmpNotificationMIB 1 } snmpNotifyConformance OBJECT IDENTIFIER ::= { snmpNotificationMIB 3 } -- -- -- The snmpNotifyObjects group -- -- snmpNotifyTable OBJECT-TYPE SYNTAX SEQUENCE OF SnmpNotifyEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "This table is used to select management targets which should receive notifications, as well as the type of notification which should be sent to each selected management target." ::= { snmpNotifyObjects 1 } snmpNotifyEntry OBJECT-TYPE SYNTAX SnmpNotifyEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "An entry in this table selects a set of management targets which should receive notifications, as well as the type of Levi, et. al. Standards Track [Page 46] RFC 3413 SNMP Applications December 2002 notification which should be sent to each selected management target. Entries in the snmpNotifyTable are created and deleted using the snmpNotifyRowStatus object." INDEX { IMPLIED snmpNotifyName } ::= { snmpNotifyTable 1 } SnmpNotifyEntry ::= SEQUENCE { snmpNotifyName SnmpAdminString, snmpNotifyTag SnmpTagValue, snmpNotifyType INTEGER, snmpNotifyStorageType StorageType, snmpNotifyRowStatus RowStatus } snmpNotifyName OBJECT-TYPE SYNTAX SnmpAdminString (SIZE(1..32)) MAX-ACCESS not-accessible STATUS current DESCRIPTION "The locally arbitrary, but unique identifier associated with this snmpNotifyEntry." ::= { snmpNotifyEntry 1 } snmpNotifyTag OBJECT-TYPE SYNTAX SnmpTagValue MAX-ACCESS read-create STATUS current DESCRIPTION "This object contains a single tag value which is used to select entries in the snmpTargetAddrTable. Any entry in the snmpTargetAddrTable which contains a tag value which is equal to the value of an instance of this object is selected. If this object contains a value of zero length, no entries are selected." DEFVAL { "" } ::= { snmpNotifyEntry 2 } snmpNotifyType OBJECT-TYPE SYNTAX INTEGER { trap(1), inform(2) } MAX-ACCESS read-create STATUS current DESCRIPTION "This object determines the type of notification to Levi, et. al. Standards Track [Page 47] RFC 3413 SNMP Applications December 2002 be generated for entries in the snmpTargetAddrTable selected by the corresponding instance of snmpNotifyTag. This value is only used when generating notifications, and is ignored when using the snmpTargetAddrTable for other purposes. If the value of this object is trap(1), then any messages generated for selected rows will contain Unconfirmed-Class PDUs. If the value of this object is inform(2), then any messages generated for selected rows will contain Confirmed-Class PDUs. Note that if an SNMP entity only supports generation of Unconfirmed-Class PDUs (and not Confirmed-Class PDUs), then this object may be read-only." DEFVAL { trap } ::= { snmpNotifyEntry 3 } snmpNotifyStorageType OBJECT-TYPE SYNTAX StorageType MAX-ACCESS read-create STATUS current DESCRIPTION "The storage type for this conceptual row. Conceptual rows having the value 'permanent' need not allow write-access to any columnar objects in the row." DEFVAL { nonVolatile } ::= { snmpNotifyEntry 4 } snmpNotifyRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The status of this conceptual row. To create a row in this table, a manager must set this object to either createAndGo(4) or createAndWait(5)." ::= { snmpNotifyEntry 5 } snmpNotifyFilterProfileTable OBJECT-TYPE SYNTAX SEQUENCE OF SnmpNotifyFilterProfileEntry MAX-ACCESS not-accessible STATUS current Levi, et. al. Standards Track [Page 48] RFC 3413 SNMP Applications December 2002 DESCRIPTION "This table is used to associate a notification filter profile with a particular set of target parameters." ::= { snmpNotifyObjects 2 } snmpNotifyFilterProfileEntry OBJECT-TYPE SYNTAX SnmpNotifyFilterProfileEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "An entry in this table indicates the name of the filter profile to be used when generating notifications using the corresponding entry in the snmpTargetParamsTable. Entries in the snmpNotifyFilterProfileTable are created and deleted using the snmpNotifyFilterProfileRowStatus object." INDEX { IMPLIED snmpTargetParamsName } ::= { snmpNotifyFilterProfileTable 1 } SnmpNotifyFilterProfileEntry ::= SEQUENCE { snmpNotifyFilterProfileName SnmpAdminString, snmpNotifyFilterProfileStorType StorageType, snmpNotifyFilterProfileRowStatus RowStatus } snmpNotifyFilterProfileName OBJECT-TYPE SYNTAX SnmpAdminString (SIZE(1..32)) MAX-ACCESS read-create STATUS current DESCRIPTION "The name of the filter profile to be used when generating notifications using the corresponding entry in the snmpTargetAddrTable." ::= { snmpNotifyFilterProfileEntry 1 } snmpNotifyFilterProfileStorType OBJECT-TYPE SYNTAX StorageType MAX-ACCESS read-create STATUS current DESCRIPTION "The storage type for this conceptual row. Conceptual rows having the value 'permanent' need not allow write-access to any columnar objects in the row." DEFVAL { nonVolatile } ::= { snmpNotifyFilterProfileEntry 2 } snmpNotifyFilterProfileRowStatus OBJECT-TYPE Levi, et. al. Standards Track [Page 49] RFC 3413 SNMP Applications December 2002 SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The status of this conceptual row. To create a row in this table, a manager must set this object to either createAndGo(4) or createAndWait(5). Until instances of all corresponding columns are appropriately configured, the value of the corresponding instance of the snmpNotifyFilterProfileRowStatus column is 'notReady'. In particular, a newly created row cannot be made active until the corresponding instance of snmpNotifyFilterProfileName has been set." ::= { snmpNotifyFilterProfileEntry 3 } snmpNotifyFilterTable OBJECT-TYPE SYNTAX SEQUENCE OF SnmpNotifyFilterEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "The table of filter profiles. Filter profiles are used to determine whether particular management targets should receive particular notifications. When a notification is generated, it must be compared with the filters associated with each management target which is configured to receive notifications, in order to determine whether it may be sent to each such management target. A more complete discussion of notification filtering can be found in section 6. of [SNMP-APPL]." ::= { snmpNotifyObjects 3 } snmpNotifyFilterEntry OBJECT-TYPE SYNTAX SnmpNotifyFilterEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "An element of a filter profile. Entries in the snmpNotifyFilterTable are created and deleted using the snmpNotifyFilterRowStatus object." Levi, et. al. Standards Track [Page 50] RFC 3413 SNMP Applications December 2002 INDEX { snmpNotifyFilterProfileName, IMPLIED snmpNotifyFilterSubtree } ::= { snmpNotifyFilterTable 1 } SnmpNotifyFilterEntry ::= SEQUENCE { snmpNotifyFilterSubtree OBJECT IDENTIFIER, snmpNotifyFilterMask OCTET STRING, snmpNotifyFilterType INTEGER, snmpNotifyFilterStorageType StorageType, snmpNotifyFilterRowStatus RowStatus } snmpNotifyFilterSubtree OBJECT-TYPE SYNTAX OBJECT IDENTIFIER MAX-ACCESS not-accessible STATUS current DESCRIPTION "The MIB subtree which, when combined with the corresponding instance of snmpNotifyFilterMask, defines a family of subtrees which are included in or excluded from the filter profile." ::= { snmpNotifyFilterEntry 1 } snmpNotifyFilterMask OBJECT-TYPE SYNTAX OCTET STRING (SIZE(0..16)) MAX-ACCESS read-create STATUS current DESCRIPTION "The bit mask which, in combination with the corresponding instance of snmpNotifyFilterSubtree, defines a family of subtrees which are included in or excluded from the filter profile. Each bit of this bit mask corresponds to a sub-identifier of snmpNotifyFilterSubtree, with the most significant bit of the i-th octet of this octet string value (extended if necessary, see below) corresponding to the (8*i - 7)-th sub-identifier, and the least significant bit of the i-th octet of this octet string corresponding to the (8*i)-th sub-identifier, where i is in the range 1 through 16. Each bit of this bit mask specifies whether or not the corresponding sub-identifiers must match when determining if an OBJECT IDENTIFIER matches this family of filter subtrees; a '1' indicates that an exact match must occur; a '0' indicates 'wild card', i.e., any sub-identifier value matches. Levi, et. al. Standards Track [Page 51] RFC 3413 SNMP Applications December 2002 Thus, the OBJECT IDENTIFIER X of an object instance is contained in a family of filter subtrees if, for each sub-identifier of the value of snmpNotifyFilterSubtree, either: the i-th bit of snmpNotifyFilterMask is 0, or the i-th sub-identifier of X is equal to the i-th sub-identifier of the value of snmpNotifyFilterSubtree. If the value of this bit mask is M bits long and there are more than M sub-identifiers in the corresponding instance of snmpNotifyFilterSubtree, then the bit mask is extended with 1's to be the required length. Note that when the value of this object is the zero-length string, this extension rule results in a mask of all-1's being used (i.e., no 'wild card'), and the family of filter subtrees is the one subtree uniquely identified by the corresponding instance of snmpNotifyFilterSubtree." DEFVAL { ''H } ::= { snmpNotifyFilterEntry 2 } snmpNotifyFilterType OBJECT-TYPE SYNTAX INTEGER { included(1), excluded(2) } MAX-ACCESS read-create STATUS current DESCRIPTION "This object indicates whether the family of filter subtrees defined by this entry are included in or excluded from a filter. A more detailed discussion of the use of this object can be found in section 6. of [SNMP-APPL]." DEFVAL { included } ::= { snmpNotifyFilterEntry 3 } snmpNotifyFilterStorageType OBJECT-TYPE SYNTAX StorageType MAX-ACCESS read-create STATUS current DESCRIPTION "The storage type for this conceptual row. Conceptual rows having the value 'permanent' need not Levi, et. al. Standards Track [Page 52] RFC 3413 SNMP Applications December 2002 allow write-access to any columnar objects in the row." DEFVAL { nonVolatile } ::= { snmpNotifyFilterEntry 4 } snmpNotifyFilterRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The status of this conceptual row. To create a row in this table, a manager must set this object to either createAndGo(4) or createAndWait(5)." ::= { snmpNotifyFilterEntry 5 } -- -- -- Conformance information -- -- snmpNotifyCompliances OBJECT IDENTIFIER ::= { snmpNotifyConformance 1 } snmpNotifyGroups OBJECT IDENTIFIER ::= { snmpNotifyConformance 2 } -- -- -- Compliance statements -- -- snmpNotifyBasicCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for minimal SNMP entities which implement only SNMP Unconfirmed-Class notifications and read-create operations on only the snmpTargetAddrTable." MODULE SNMP-TARGET-MIB MANDATORY-GROUPS { snmpTargetBasicGroup } OBJECT snmpTargetParamsMPModel MIN-ACCESS read-only DESCRIPTION "Create/delete/modify access is not required." OBJECT snmpTargetParamsSecurityModel Levi, et. al. Standards Track [Page 53] RFC 3413 SNMP Applications December 2002 MIN-ACCESS read-only DESCRIPTION "Create/delete/modify access is not required." OBJECT snmpTargetParamsSecurityName MIN-ACCESS read-only DESCRIPTION "Create/delete/modify access is not required." OBJECT snmpTargetParamsSecurityLevel MIN-ACCESS read-only DESCRIPTION "Create/delete/modify access is not required." OBJECT snmpTargetParamsStorageType SYNTAX INTEGER { readOnly(5) } MIN-ACCESS read-only DESCRIPTION "Create/delete/modify access is not required. Support of the values other(1), volatile(2), nonVolatile(3), and permanent(4) is not required." OBJECT snmpTargetParamsRowStatus SYNTAX INTEGER { active(1) } MIN-ACCESS read-only DESCRIPTION "Create/delete/modify access to the snmpTargetParamsTable is not required. Support of the values notInService(2), notReady(3), createAndGo(4), createAndWait(5), and destroy(6) is not required." MODULE -- This Module MANDATORY-GROUPS { snmpNotifyGroup } OBJECT snmpNotifyTag MIN-ACCESS read-only DESCRIPTION "Create/delete/modify access is not required." OBJECT snmpNotifyType SYNTAX INTEGER { trap(1) } Levi, et. al. Standards Track [Page 54] RFC 3413 SNMP Applications December 2002 MIN-ACCESS read-only DESCRIPTION "Create/delete/modify access is not required. Support of the value notify(2) is not required." OBJECT snmpNotifyStorageType SYNTAX INTEGER { readOnly(5) } MIN-ACCESS read-only DESCRIPTION "Create/delete/modify access is not required. Support of the values other(1), volatile(2), nonVolatile(3), and permanent(4) is not required." OBJECT snmpNotifyRowStatus SYNTAX INTEGER { active(1) } MIN-ACCESS read-only DESCRIPTION "Create/delete/modify access to the snmpNotifyTable is not required. Support of the values notInService(2), notReady(3), createAndGo(4), createAndWait(5), and destroy(6) is not required." ::= { snmpNotifyCompliances 1 } snmpNotifyBasicFiltersCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for SNMP entities which implement SNMP Unconfirmed-Class notifications with filtering, and read-create operations on all related tables." MODULE SNMP-TARGET-MIB MANDATORY-GROUPS { snmpTargetBasicGroup } MODULE -- This Module MANDATORY-GROUPS { snmpNotifyGroup, snmpNotifyFilterGroup } ::= { snmpNotifyCompliances 2 } snmpNotifyFullCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for SNMP entities which either implement only SNMP Confirmed-Class notifications, or both SNMP Unconfirmed-Class and Confirmed-Class notifications, Levi, et. al. Standards Track [Page 55] RFC 3413 SNMP Applications December 2002 plus filtering and read-create operations on all related tables." MODULE SNMP-TARGET-MIB MANDATORY-GROUPS { snmpTargetBasicGroup, snmpTargetResponseGroup } MODULE -- This Module MANDATORY-GROUPS { snmpNotifyGroup, snmpNotifyFilterGroup } ::= { snmpNotifyCompliances 3 } snmpNotifyGroup OBJECT-GROUP OBJECTS { snmpNotifyTag, snmpNotifyType, snmpNotifyStorageType, snmpNotifyRowStatus } STATUS current DESCRIPTION "A collection of objects for selecting which management targets are used for generating notifications, and the type of notification to be generated for each selected management target." ::= { snmpNotifyGroups 1 } snmpNotifyFilterGroup OBJECT-GROUP OBJECTS { snmpNotifyFilterProfileName, snmpNotifyFilterProfileStorType, snmpNotifyFilterProfileRowStatus, snmpNotifyFilterMask, snmpNotifyFilterType, snmpNotifyFilterStorageType, snmpNotifyFilterRowStatus } STATUS current DESCRIPTION "A collection of objects providing remote configuration of notification filters." ::= { snmpNotifyGroups 2 } END Levi, et. al. Standards Track [Page 56] RFC 3413 SNMP Applications December 2002 4.3. The Proxy MIB Module The SNMP-PROXY-MIB module, which defines MIB objects that provide mechanisms to remotely configure the parameters used by an SNMP entity for proxy forwarding operations, contains a single table. This table, snmpProxyTable, is used to define translations between management targets for use when forwarding messages. 4.3.1. Definitions SNMP-PROXY-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, snmpModules FROM SNMPv2-SMI RowStatus, StorageType FROM SNMPv2-TC SnmpEngineID, SnmpAdminString FROM SNMP-FRAMEWORK-MIB SnmpTagValue FROM SNMP-TARGET-MIB MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF; snmpProxyMIB MODULE-IDENTITY LAST-UPDATED "200210140000Z" ORGANIZATION "IETF SNMPv3 Working Group" CONTACT-INFO "WG-email: snmpv3@lists.tislabs.com Subscribe: majordomo@lists.tislabs.com In message body: subscribe snmpv3 Co-Chair: Russ Mundy Network Associates Laboratories Postal: 15204 Omega Drive, Suite 300 Rockville, MD 20850-4601 USA EMail: mundy@tislabs.com Phone: +1 301-947-7107 Levi, et. al. Standards Track [Page 57] RFC 3413 SNMP Applications December 2002 Co-Chair: David Harrington Enterasys Networks Postal: 35 Industrial Way P. O. Box 5004 Rochester, New Hampshire 03866-5005 USA EMail: dbh@enterasys.com Phone: +1 603-337-2614 Co-editor: David B. Levi Nortel Networks Postal: 3505 Kesterwood Drive Knoxville, Tennessee 37918 EMail: dlevi@nortelnetworks.com Phone: +1 865 686 0432 Co-editor: Paul Meyer Secure Computing Corporation Postal: 2675 Long Lake Road Roseville, Minnesota 55113 EMail: paul_meyer@securecomputing.com Phone: +1 651 628 1592 Co-editor: Bob Stewart Retired" DESCRIPTION "This MIB module defines MIB objects which provide mechanisms to remotely configure the parameters used by a proxy forwarding application. Copyright (C) The Internet Society (2002). This version of this MIB module is part of RFC 3413; see the RFC itself for full legal notices. " REVISION "200210140000Z" -- 14 October 2002 DESCRIPTION "Clarifications, published as RFC 3413." REVISION "199808040000Z" -- 4 August 1998 DESCRIPTION "Clarifications, published as RFC 2573." REVISION "199707140000Z" -- 14 July 1997 DESCRIPTION "The initial revision, published as RFC2273." ::= { snmpModules 14 } snmpProxyObjects OBJECT IDENTIFIER ::= { snmpProxyMIB 1 } snmpProxyConformance OBJECT IDENTIFIER ::= { snmpProxyMIB 3 } -- Levi, et. al. Standards Track [Page 58] RFC 3413 SNMP Applications December 2002 -- -- The snmpProxyObjects group -- -- snmpProxyTable OBJECT-TYPE SYNTAX SEQUENCE OF SnmpProxyEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "The table of translation parameters used by proxy forwarder applications for forwarding SNMP messages." ::= { snmpProxyObjects 2 } snmpProxyEntry OBJECT-TYPE SYNTAX SnmpProxyEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A set of translation parameters used by a proxy forwarder application for forwarding SNMP messages. Entries in the snmpProxyTable are created and deleted using the snmpProxyRowStatus object." INDEX { IMPLIED snmpProxyName } ::= { snmpProxyTable 1 } SnmpProxyEntry ::= SEQUENCE { snmpProxyName SnmpAdminString, snmpProxyType INTEGER, snmpProxyContextEngineID SnmpEngineID, snmpProxyContextName SnmpAdminString, snmpProxyTargetParamsIn SnmpAdminString, snmpProxySingleTargetOut SnmpAdminString, snmpProxyMultipleTargetOut SnmpTagValue, snmpProxyStorageType StorageType, snmpProxyRowStatus RowStatus } snmpProxyName OBJECT-TYPE SYNTAX SnmpAdminString (SIZE(1..32)) MAX-ACCESS not-accessible STATUS current DESCRIPTION "The locally arbitrary, but unique identifier associated with this snmpProxyEntry." ::= { snmpProxyEntry 1 } Levi, et. al. Standards Track [Page 59] RFC 3413 SNMP Applications December 2002 snmpProxyType OBJECT-TYPE SYNTAX INTEGER { read(1), write(2), trap(3), inform(4) } MAX-ACCESS read-create STATUS current DESCRIPTION "The type of message that may be forwarded using the translation parameters defined by this entry." ::= { snmpProxyEntry 2 } snmpProxyContextEngineID OBJECT-TYPE SYNTAX SnmpEngineID MAX-ACCESS read-create STATUS current DESCRIPTION "The contextEngineID contained in messages that may be forwarded using the translation parameters defined by this entry." ::= { snmpProxyEntry 3 } snmpProxyContextName OBJECT-TYPE SYNTAX SnmpAdminString MAX-ACCESS read-create STATUS current DESCRIPTION "The contextName contained in messages that may be forwarded using the translation parameters defined by this entry. This object is optional, and if not supported, the contextName contained in a message is ignored when selecting an entry in the snmpProxyTable." ::= { snmpProxyEntry 4 } snmpProxyTargetParamsIn OBJECT-TYPE SYNTAX SnmpAdminString MAX-ACCESS read-create STATUS current DESCRIPTION "This object selects an entry in the snmpTargetParamsTable. The selected entry is used to determine which row of the snmpProxyTable to use for forwarding received messages." ::= { snmpProxyEntry 5 } Levi, et. al. Standards Track [Page 60] RFC 3413 SNMP Applications December 2002 snmpProxySingleTargetOut OBJECT-TYPE SYNTAX SnmpAdminString MAX-ACCESS read-create STATUS current DESCRIPTION "This object selects a management target defined in the snmpTargetAddrTable (in the SNMP-TARGET-MIB). The selected target is defined by an entry in the snmpTargetAddrTable whose index value (snmpTargetAddrName) is equal to this object. This object is only used when selection of a single target is required (i.e. when forwarding an incoming read or write request)." ::= { snmpProxyEntry 6 } snmpProxyMultipleTargetOut OBJECT-TYPE SYNTAX SnmpTagValue MAX-ACCESS read-create STATUS current DESCRIPTION "This object selects a set of management targets defined in the snmpTargetAddrTable (in the SNMP-TARGET-MIB). This object is only used when selection of multiple targets is required (i.e. when forwarding an incoming notification)." ::= { snmpProxyEntry 7 } snmpProxyStorageType OBJECT-TYPE SYNTAX StorageType MAX-ACCESS read-create STATUS current DESCRIPTION "The storage type of this conceptual row. Conceptual rows having the value 'permanent' need not allow write-access to any columnar objects in the row." DEFVAL { nonVolatile } ::= { snmpProxyEntry 8 } snmpProxyRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The status of this conceptual row. To create a row in this table, a manager must Levi, et. al. Standards Track [Page 61] RFC 3413 SNMP Applications December 2002 set this object to either createAndGo(4) or createAndWait(5). The following objects may not be modified while the value of this object is active(1): - snmpProxyType - snmpProxyContextEngineID - snmpProxyContextName - snmpProxyTargetParamsIn - snmpProxySingleTargetOut - snmpProxyMultipleTargetOut" ::= { snmpProxyEntry 9 } -- -- -- Conformance information -- -- snmpProxyCompliances OBJECT IDENTIFIER ::= { snmpProxyConformance 1 } snmpProxyGroups OBJECT IDENTIFIER ::= { snmpProxyConformance 2 } -- -- -- Compliance statements -- -- snmpProxyCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for SNMP entities which include a proxy forwarding application." MODULE SNMP-TARGET-MIB MANDATORY-GROUPS { snmpTargetBasicGroup, snmpTargetResponseGroup } MODULE -- This Module MANDATORY-GROUPS { snmpProxyGroup } ::= { snmpProxyCompliances 1 } snmpProxyGroup OBJECT-GROUP OBJECTS { snmpProxyType, snmpProxyContextEngineID, snmpProxyContextName, snmpProxyTargetParamsIn, Levi, et. al. Standards Track [Page 62] RFC 3413 SNMP Applications December 2002 snmpProxySingleTargetOut, snmpProxyMultipleTargetOut, snmpProxyStorageType, snmpProxyRowStatus } STATUS current DESCRIPTION "A collection of objects providing remote configuration of management target translation parameters for use by proxy forwarder applications." ::= { snmpProxyGroups 3 } END 5. Identification of Management Targets in Notification Originators This section describes the mechanisms used by a notification originator application when using the MIB module described in this document to determine the set of management targets to be used when generating a notification. A notification originator uses all active entries in the snmpNotifyTable to find the management targets to be used for generating notifications. Each active entry in this table selects zero or more entries in the snmpTargetAddrTable. When a notification is generated, it is sent to all of the targets specified by the selected snmpTargetAddrTable entries (subject to the application of access control and notification filtering). Any entry in the snmpTargetAddrTable whose snmpTargetAddrTagList object contains a tag value which is equal to a value of snmpNotifyTag is selected by the snmpNotifyEntry which contains that instance of snmpNotifyTag. Note that a particular snmpTargetAddrEntry may be selected by multiple entries in the snmpNotifyTable, resulting in multiple notifications being generated using that snmpTargetAddrEntry (this allows, for example, both traps and informs to be sent to the same target). Each snmpTargetAddrEntry contains a pointer to the snmpTargetParamsTable (snmpTargetAddrParams). This pointer selects a set of SNMP parameters to be used for generating notifications. If the selected entry in the snmpTargetParamsTable does not exist, the management target is not used to generate notifications. The decision as to whether a notification should contain an Unconfirmed-Class or a Confirmed-Class PDU is determined by the value of the snmpNotifyType object. If the value of this object is trap(1), the notification should contain an Unconfirmed-Class PDU. Levi, et. al. Standards Track [Page 63] RFC 3413 SNMP Applications December 2002 If the value of this object is inform(2), then the notification should contain a Confirmed-Class PDU, and the timeout time and number of retries for the notification are the value of snmpTargetAddrTimeout and snmpTargetAddrRetryCount. Note that the exception to these rules is when the snmpTargetParamsMPModel object indicates an SNMP version which supports a different PDU version. In this case, the notification may be sent using a different PDU type ([RFC2576] defines the PDU type in the case where the outgoing SNMP version is SNMPv1). 6. Notification Filtering This section describes the mechanisms used by a notification originator application when using the MIB module described in this document to filter generation of notifications. A notification originator uses the snmpNotifyFilterTable to filter notifications. A notification filter profile may be associated with a particular entry in the snmpTargetParamsTable. The associated filter profile is identified by an entry in the snmpNotifyFilterProfileTable whose index is equal to the index of the entry in the snmpTargetParamsTable. If no such entry exists in the snmpNotifyFilterProfileTable, no filtering is performed for that management target. If such an entry does exist, the value of snmpNotifyFilterProfileName of the entry is compared with the corresponding portion of the index of all active entries in the snmpNotifyFilterTable. All such entries for which this comparison results in an exact match are used for filtering a notification generated using the associated snmpTargetParamsEntry. If no such entries exist, no filtering is performed, and a notification may be sent to the management target. Otherwise, if matching entries do exist, a notification may be sent if the NOTIFICATION-TYPE OBJECT IDENTIFIER of the notification (this is the value of the element of the variable bindings whose name is snmpTrapOID.0, i.e., the second variable binding) is specifically included, and none of the object instances to be included in the variable-bindings of the notification are specifically excluded by the matching entries. Each set of snmpNotifyFilterTable entries is divided into two collections of filter subtrees: the included filter subtrees, and the excluded filter subtrees. The snmpNotifyFilterType object defines the collection to which each matching entry belongs. To determine whether a particular notification name or object instance is excluded by the set of matching entries, compare the Levi, et. al. Standards Track [Page 64] RFC 3413 SNMP Applications December 2002 notification name's or object instance's OBJECT IDENTIFIER with each of the matching entries. For a notification name, if none match, then the notification name is considered excluded, and the notification should not be sent to this management target. For an object instance, if none match, the object instance is considered included, and the notification may be sent to this management target. If one or more match, then the notification name or object instance is included or excluded, according to the value of snmpNotifyFilterType in the entry whose value of snmpNotifyFilterSubtree has the most sub-identifiers. If multiple entries match and have the same number of sub-identifiers, then the value of snmpNotifyFilterType, in the entry among those which match, and whose instance is lexicographically the largest, determines the inclusion or exclusion. A notification name or object instance's OBJECT IDENTIFIER X matches an entry in the snmpNotifyFilterTable when the number of sub- identifiers in X is at least as many as in the value of snmpNotifyFilterSubtree for the entry, and each sub-identifier in the value of snmpNotifyFilterSubtree matches its corresponding sub- identifier in X. Two sub-identifiers match either if the corresponding bit of snmpNotifyFilterMask is zero (the 'wild card' value), or if the two sub-identifiers are equal. 7. Management Target Translation in Proxy Forwarder Applications This section describes the mechanisms used by a proxy forwarder application when using the MIB module described in this document to translate incoming management target information into outgoing management target information for the purpose of forwarding messages. There are actually two mechanisms a proxy forwarder may use, one for forwarding request messages, and one for forwarding notification messages. 7.1. Management Target Translation for Request Forwarding When forwarding request messages, the proxy forwarder will select a single entry in the snmpProxyTable. To select this entry, it will perform the following comparisons: - The snmpProxyType must be read(1) if the request is a Read-Class PDU. The snmpProxyType must be write(2) if the request is a Write-Class PDU. - The contextEngineID must equal the snmpProxyContextEngineID object. - If the snmpProxyContextName object is supported, it must equal the contextName. Levi, et. al. Standards Track [Page 65] RFC 3413 SNMP Applications December 2002 - The snmpProxyTargetParamsIn object identifies an entry in the snmpTargetParamsTable. The messageProcessingModel, security model, securityName, and securityLevel must match the values of snmpTargetParamsMPModel, snmpTargetParamsSecurityModel, snmpTargetParamsSecurityName, and snmpTargetParamsSecurityLevel of the identified entry in the snmpTargetParamsTable. There may be multiple entries in the snmpProxyTable for which these comparisons succeed. The entry whose snmpProxyName has the lexicographically smallest value and for which the comparisons succeed will be selected by the proxy forwarder. The outgoing management target information is identified by the value of the snmpProxySingleTargetOut object of the selected entry. This object identifies an entry in the snmpTargetAddrTable. The identified entry in the snmpTargetAddrTable also contains a reference to the snmpTargetParamsTable (snmpTargetAddrParams). If either the identified entry in the snmpTargetAddrTable does not exist, or the identified entry in the snmpTargetParamsTable does not exist, then this snmpProxyEntry does not identify valid forwarding information, and the proxy forwarder should attempt to identify another row. If there is no entry in the snmpProxyTable for which all of the conditions above may be met, then there is no appropriate forwarding information, and the proxy forwarder should take appropriate actions. Otherwise, The snmpTargetAddrTDomain, snmpTargetAddrTAddress, snmpTargetAddrTimeout, and snmpTargetRetryCount of the identified snmpTargetAddrEntry, and the snmpTargetParamsMPModel, snmpTargetParamsSecurityModel, snmpTargetParamsSecurityName, and snmpTargetParamsSecurityLevel of the identified snmpTargetParamsEntry are used as the destination management target. 7.2. Management Target Translation for Notification Forwarding When forwarding notification messages, the proxy forwarder will select multiple entries in the snmpProxyTable. To select these entries, it will perform the following comparisons: - The snmpProxyType must be trap(3) if the notification is an Unconfirmed-Class PDU. The snmpProxyType must be inform(4) if the request is a Confirmed-Class PDU. - The contextEngineID must equal the snmpProxyContextEngineID object. - If the snmpProxyContextName object is supported, it must equal the contextName. Levi, et. al. Standards Track [Page 66] RFC 3413 SNMP Applications December 2002 - The snmpProxyTargetParamsIn object identifies an entry in the snmpTargetParamsTable. The messageProcessingModel, security model, securityName, and securityLevel must match the values of snmpTargetParamsMPModel, snmpTargetParamsSecurityModel, snmpTargetParamsSecurityName, and snmpTargetParamsSecurityLevel of the identified entry in the snmpTargetParamsTable. All entries for which these conditions are met are selected. The snmpProxyMultipleTargetOut object of each such entry is used to select a set of entries in the snmpTargetAddrTable. Any snmpTargetAddrEntry whose snmpTargetAddrTagList object contains a tag value equal to the value of snmpProxyMultipleTargetOut, and whose snmpTargetAddrParams object references an existing entry in the snmpTargetParamsTable, is selected as a destination for the forwarded notification. 8. Intellectual Property The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 9. Acknowledgments This document is the result of the efforts of the SNMPv3 Working Group. Some special thanks are in order to the following SNMPv3 WG members: Harald Tveit Alvestrand (Maxware) Dave Battle (SNMP Research, Inc.) Alan Beard (Disney Worldwide Services) Paul Berrevoets (SWI Systemware/Halcyon Inc.) Levi, et. al. Standards Track [Page 67] RFC 3413 SNMP Applications December 2002 Martin Bjorklund (Ericsson) Uri Blumenthal (IBM T.J. Watson Research Center) Jeff Case (SNMP Research, Inc.) John Curran (BBN) Mike Daniele (Compaq Computer Corporation) T. Max Devlin (Eltrax Systems) John Flick (Hewlett Packard) Rob Frye (MCI) Wes Hardaker (U.C.Davis, Information Technology - D.C.A.S.) David Harrington (Enterasys Networks) Lauren Heintz (BMC Software, Inc.) N.C. Hien (IBM T.J. Watson Research Center) Michael Kirkham (InterWorking Labs, Inc.) Dave Levi (Nortel Networks) Louis A Mamakos (UUNET Technologies Inc.) Joe Marzot (Nortel Networks) Paul Meyer (Secure Computing Corporation) Keith McCloghrie (Cisco Systems) Bob Moore (IBM) Russ Mundy (TIS Labs at Network Associates) Bob Natale (ACE*COMM Corporation) Mike O'Dell (UUNET Technologies Inc.) Dave Perkins (DeskTalk) Peter Polkinghorne (Brunel University) Randy Presuhn (BMC Software, Inc.) David Reeder (TIS Labs at Network Associates) David Reid (SNMP Research, Inc.) Aleksey Romanov (Quality Quorum) Shawn Routhier (Epilogue) Juergen Schoenwaelder (TU Braunschweig) Bob Stewart (Cisco Systems) Mike Thatcher (Independent Consultant) Bert Wijnen (Lucent Technologies) The document is based on recommendations of the IETF Security and Administrative Framework Evolution for SNMP Advisory Team. Members of that Advisory Team were: David Harrington (Enterasys Networks) Jeff Johnson (Cisco Systems) David Levi (Nortel Networks) John Linn (Openvision) Russ Mundy (Trusted Information Systems) chair Shawn Routhier (Epilogue) Glenn Waters (Nortel) Bert Wijnen (Lucent Technologies) Levi, et. al. Standards Track [Page 68] RFC 3413 SNMP Applications December 2002 As recommended by the Advisory Team and the SNMPv3 Working Group Charter, the design incorporates as much as practical from previous RFCs and drafts. As a result, special thanks are due to the authors of previous designs known as SNMPv2u and SNMPv2*: Jeff Case (SNMP Research, Inc.) David Harrington (Enterasys Networks) David Levi (Nortel Networks) Keith McCloghrie (Cisco Systems) Brian O'Keefe (Hewlett Packard) Marshall T. Rose (Dover Beach Consulting) Jon Saperia (BGS Systems Inc.) Steve Waldbusser (International Network Services) Glenn W. Waters (Bell-Northern Research Ltd.) 10. Security Considerations The SNMP applications described in this document typically have direct access to MIB instrumentation. Thus, it is very important that these applications be strict in their application of access control as described in this document. In addition, there may be some types of notification generator applications which, rather than accessing MIB instrumentation using access control, will obtain MIB information through other means (such as from a command line). The implementors and users of such applications must be responsible for not divulging MIB information that normally would be inaccessible due to access control. Finally, the MIBs described in this document contain potentially sensitive information. A security administrator may wish to limit access to these MIBs. 11. References 11.1 Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2578] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M. and S. Waldbusser, "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999. [RFC2579] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M. and S. Waldbusser, "Textual Conventions for SMIv2", STD 58, RFC 2579, April 1999. Levi, et. al. Standards Track [Page 69] RFC 3413 SNMP Applications December 2002 [RFC2580] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M. and S. Waldbusser, "Conformance Statements for SMIv2", STD 58, RFC 2580, April 1999. [RFC3411] Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for describing Simple Network Management Protocol (SNMP) Management Frameworks", STD 62, RFC 3411, December 2002. [RFC3412] Case, J., Harrington, D., Presuhn, R. and B. Wijnen, "Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3412, December 2002. [RFC3415] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3415, December 2002. [RFC3416] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Protocol Operations for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3416, December 2002. [RFC3418] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Management Information Base (MIB) for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3418, December 2002. 11.2 Informative References [RFC1157] Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple Network Management Protocol", STD 15, RFC 1157, May 1990. [RFC1213] McCloghrie, K. and M. Rose, Editors, "Management Information Base for Network Management of TCP/IP-based internets: MIB-II", STD 17, RFC 1213, March 1991. [RFC2576] Frye, R.,Levi, D., Routhier, S. and B. Wijnen, "Coexistence between Version 1, Version 2, and Version 3 of the Internet-standard Network Management Framework", RFC 2576, February 1999. Levi, et. al. Standards Track [Page 70] RFC 3413 SNMP Applications December 2002 Appendix A - Trap Configuration Example This section describes an example configuration for a Notification Generator application which implements the snmpNotifyBasicCompliance level. The example configuration specifies that the Notification Generator should send notifications to 3 separate managers, using authentication and no privacy for the first 2 managers, and using both authentication and privacy for the third manager. The configuration consists of three rows in the snmpTargetAddrTable, two rows in the snmpTargetTable, and two rows in the snmpNotifyTable. * snmpTargetAddrName = "addr1" snmpTargetAddrTDomain = snmpUDPDomain snmpTargetAddrTAddress = 128.1.2.3/162 snmpTargetAddrTagList = "group1" snmpTargetAddrParams = "AuthNoPriv-joe" snmpTargetAddrStorageType = readOnly(5) snmpTargetAddrRowStatus = active(1) * snmpTargetAddrName = "addr2" snmpTargetAddrTDomain = snmpUDPDomain snmpTargetAddrTAddress = 128.2.4.6/162 snmpTargetAddrTagList = "group1" snmpTargetAddrParams = "AuthNoPriv-joe" snmpTargetAddrStorageType = readOnly(5) snmpTargetAddrRowStatus = active(1) * snmpTargetAddrName = "addr3" snmpTargetAddrTDomain = snmpUDPDomain snmpTargetAddrTAddress = 128.1.5.9/162 snmpTargetAddrTagList = "group2" snmpTargetAddrParams = "AuthPriv-bob" snmpTargetAddrStorageType = readOnly(5) snmpTargetAddrRowStatus = active(1) * snmpTargetParamsName = "AuthNoPriv-joe" snmpTargetParamsMPModel = 3 snmpTargetParamsSecurityModel = 3 (USM) snmpTargetParamsSecurityName = "joe" snmpTargetParamsSecurityLevel = authNoPriv(2) snmpTargetParamsStorageType = readOnly(5) snmpTargetParamsRowStatus = active(1) Levi, et. al. Standards Track [Page 71] RFC 3413 SNMP Applications December 2002 * snmpTargetParamsName = "AuthPriv-bob" snmpTargetParamsMPModel = 3 snmpTargetParamsSecurityModel = 3 (USM) snmpTargetParamsSecurityName = "bob" snmpTargetParamsSecurityLevel = authPriv(3) snmpTargetParamsStorageType = readOnly(5) snmpTargetParamsRowStatus = active(1) * snmpNotifyName = "group1" snmpNotifyTag = "group1" snmpNotifyType = trap(1) snmpNotifyStorageType = readOnly(5) snmpNotifyRowStatus = active(1) * snmpNotifyName = "group2" snmpNotifyTag = "group2" snmpNotifyType = trap(1) snmpNotifyStorageType = readOnly(5) snmpNotifyRowStatus = active(1) These entries define two groups of management targets. The first group contains two management targets: first target second target ------------ ------------- messageProcessingModel SNMPv3 SNMPv3 securityModel 3 (USM) 3 (USM) securityName "joe" "joe" securityLevel authNoPriv(2) authNoPriv(2) transportDomain snmpUDPDomain snmpUDPDomain transportAddress 128.1.2.3/162 128.2.4.6/162 And the second group contains a single management target: messageProcessingModel SNMPv3 securityLevel authPriv(3) securityModel 3 (USM) securityName "bob" transportDomain snmpUDPDomain transportAddress 128.1.5.9/162 Levi, et. al. Standards Track [Page 72] RFC 3413 SNMP Applications December 2002 Editors' Addresses David B. Levi Nortel Networks 3505 Kesterwood Drive Knoxville, TN 37918 U.S.A. Phone: +1 865 686 0432 EMail: dlevi@nortelnetworks.com Paul Meyer Secure Computing Corporation 2675 Long Lake Road Roseville, MN 55113 U.S.A. Phone: +1 651 628 1592 EMail: paul_meyer@securecomputing.com Bob Stewart Retired Levi, et. al. Standards Track [Page 73] RFC 3413 SNMP Applications December 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Levi, et. al. Standards Track [Page 74] ======================================================================== Network Working Group U. Blumenthal Request for Comments: 3414 B. Wijnen STD: 62 Lucent Technologies Obsoletes: 2574 December 2002 Category: Standards Track User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3) Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document describes the User-based Security Model (USM) for Simple Network Management Protocol (SNMP) version 3 for use in the SNMP architecture. It defines the Elements of Procedure for providing SNMP message level security. This document also includes a Management Information Base (MIB) for remotely monitoring/managing the configuration parameters for this Security Model. This document obsoletes RFC 2574. Table of Contents 1. Introduction.......................................... 4 1.1. Threats............................................... 4 1.2. Goals and Constraints................................. 6 1.3. Security Services..................................... 6 1.4. Module Organization................................... 7 1.4.1. Timeliness Module..................................... 8 1.4.2. Authentication Protocol............................... 8 1.4.3. Privacy Protocol...................................... 8 1.5. Protection against Message Replay, Delay and Redirection....................................... 9 1.5.1. Authoritative SNMP engine............................. 9 1.5.2. Mechanisms............................................ 9 1.6. Abstract Service Interfaces........................... 11 Blumenthal & Wijnen Standards Track [Page 1] RFC 3414 USM for SNMPv3 December 2002 1.6.1. User-based Security Model Primitives for Authentication.................................... 11 1.6.2. User-based Security Model Primitives for Privacy........................................... 12 2. Elements of the Model................................. 12 2.1. User-based Security Model Users....................... 12 2.2. Replay Protection..................................... 13 2.2.1. msgAuthoritativeEngineID.............................. 14 2.2.2. msgAuthoritativeEngineBoots and msgAuthoritativeEngineTime............................ 14 2.2.3. Time Window........................................... 15 2.3. Time Synchronization.................................. 15 2.4. SNMP Messages Using this Security Model............... 16 2.5. Services provided by the User-based Security Model.... 17 2.5.1. Services for Generating an Outgoing SNMP Message...... 17 2.5.2. Services for Processing an Incoming SNMP Message...... 20 2.6. Key Localization Algorithm............................ 22 3. Elements of Procedure................................. 22 3.1. Generating an Outgoing SNMP Message................... 22 3.2. Processing an Incoming SNMP Message................... 26 4. Discovery............................................. 31 5. Definitions........................................... 32 6. HMAC-MD5-96 Authentication Protocol................... 51 6.1. Mechanisms............................................ 51 6.1.1. Digest Authentication Mechanism....................... 51 6.2. Elements of the Digest Authentication Protocol........ 52 6.2.1. Users................................................. 52 6.2.2. msgAuthoritativeEngineID.............................. 53 6.2.3. SNMP Messages Using this Authentication Protocol...... 53 6.2.4. Services provided by the HMAC-MD5-96 Authentication Module................................. 53 6.2.4.1. Services for Generating an Outgoing SNMP Message...... 53 6.2.4.2. Services for Processing an Incoming SNMP Message...... 54 6.3. Elements of Procedure................................. 55 6.3.1. Processing an Outgoing Message........................ 55 6.3.2. Processing an Incoming Message........................ 56 7. HMAC-SHA-96 Authentication Protocol................... 57 7.1. Mechanisms............................................ 57 7.1.1. Digest Authentication Mechanism....................... 57 7.2. Elements of the HMAC-SHA-96 Authentication Protocol... 58 7.2.1. Users................................................. 58 7.2.2. msgAuthoritativeEngineID.............................. 58 7.2.3. SNMP Messages Using this Authentication Protocol...... 59 7.2.4. Services provided by the HMAC-SHA-96 Authentication Module................................. 59 7.2.4.1. Services for Generating an Outgoing SNMP Message...... 59 7.2.4.2. Services for Processing an Incoming SNMP Message...... 60 7.3. Elements of Procedure................................. 61 Blumenthal & Wijnen Standards Track [Page 2] RFC 3414 USM for SNMPv3 December 2002 7.3.1. Processing an Outgoing Message........................ 61 7.3.2. Processing an Incoming Message........................ 61 8. CBC-DES Symmetric Encryption Protocol................. 63 8.1. Mechanisms............................................ 63 8.1.1. Symmetric Encryption Protocol......................... 63 8.1.1.1. DES key and Initialization Vector..................... 64 8.1.1.2. Data Encryption....................................... 65 8.1.1.3. Data Decryption....................................... 65 8.2. Elements of the DES Privacy Protocol.................. 65 8.2.1. Users................................................. 65 8.2.2. msgAuthoritativeEngineID.............................. 66 8.2.3. SNMP Messages Using this Privacy Protocol............. 66 8.2.4. Services provided by the DES Privacy Module........... 66 8.2.4.1. Services for Encrypting Outgoing Data................. 66 8.2.4.2. Services for Decrypting Incoming Data................. 67 8.3. Elements of Procedure................................. 68 8.3.1. Processing an Outgoing Message........................ 68 8.3.2. Processing an Incoming Message........................ 69 9. Intellectual Property................................. 69 10. Acknowledgements...................................... 70 11. Security Considerations............................... 71 11.1. Recommended Practices................................. 71 11.2. Defining Users........................................ 73 11.3. Conformance........................................... 74 11.4. Use of Reports........................................ 75 11.5. Access to the SNMP-USER-BASED-SM-MIB.................. 75 12. References............................................ 75 A.1. SNMP engine Installation Parameters................... 78 A.2. Password to Key Algorithm............................. 80 A.2.1. Password to Key Sample Code for MD5................... 81 A.2.2. Password to Key Sample Code for SHA................... 82 A.3. Password to Key Sample Results........................ 83 A.3.1. Password to Key Sample Results using MD5.............. 83 A.3.2. Password to Key Sample Results using SHA.............. 83 A.4. Sample encoding of msgSecurityParameters.............. 83 A.5. Sample keyChange Results.............................. 84 A.5.1. Sample keyChange Results using MD5.................... 84 A.5.2. Sample keyChange Results using SHA.................... 85 B. Change Log............................................ 86 Editors' Addresses.................................... 87 Full Copyright Statement.............................. 88 Blumenthal & Wijnen Standards Track [Page 3] RFC 3414 USM for SNMPv3 December 2002 1. Introduction The Architecture for describing Internet Management Frameworks [RFC3411] describes that an SNMP engine is composed of: 1) a Dispatcher, 2) a Message Processing Subsystem, 3) a Security Subsystem, and 4) an Access Control Subsystem. Applications make use of the services of these subsystems. It is important to understand the SNMP architecture and the terminology of the architecture to understand where the Security Model described in this document fits into the architecture and interacts with other subsystems within the architecture. The reader is expected to have read and understood the description of the SNMP architecture, as defined in [RFC3411]. This memo describes the User-based Security Model as it is used within the SNMP Architecture. The main idea is that we use the traditional concept of a user (identified by a userName) with which to associate security information. This memo describes the use of HMAC-MD5-96 and HMAC-SHA-96 as the authentication protocols and the use of CBC-DES as the privacy protocol. The User-based Security Model however allows for other such protocols to be used instead of or concurrent with these protocols. Therefore, the description of HMAC-MD5-96, HMAC-SHA-96 and CBC-DES are in separate sections to reflect their self-contained nature and to indicate that they can be replaced or supplemented in the future. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 1.1. Threats Several of the classical threats to network protocols are applicable to the network management problem and therefore would be applicable to any SNMP Security Model. Other threats are not applicable to the network management problem. This section discusses principal threats, secondary threats, and threats which are of lesser importance. The principal threats against which this SNMP Security Model should provide protection are: Blumenthal & Wijnen Standards Track [Page 4] RFC 3414 USM for SNMPv3 December 2002 - Modification of Information The modification threat is the danger that some unauthorized entity may alter in-transit SNMP messages generated on behalf of an authorized principal in such a way as to effect unauthorized management operations, including falsifying the value of an object. - Masquerade The masquerade threat is the danger that management operations not authorized for some user may be attempted by assuming the identity of another user that has the appropriate authorizations. Two secondary threats are also identified. The Security Model defined in this memo provides limited protection against: - Disclosure The disclosure threat is the danger of eavesdropping on the exchanges between managed agents and a management station. Protecting against this threat may be required as a matter of local policy. - Message Stream Modification The SNMP protocol is typically based upon a connection-less transport service which may operate over any sub-network service. The re-ordering, delay or replay of messages can and does occur through the natural operation of many such sub- network services. The message stream modification threat is the danger that messages may be maliciously re-ordered, delayed or replayed to an extent which is greater than can occur through the natural operation of a sub-network service, in order to effect unauthorized management operations. There are at least two threats that an SNMP Security Model need not protect against. The security protocols defined in this memo do not provide protection against: - Denial of Service This SNMP Security Model does not attempt to address the broad range of attacks by which service on behalf of authorized users is denied. Indeed, such denial-of-service attacks are in many cases indistinguishable from the type of network failures with which any viable network management protocol must cope as a matter of course. - Traffic Analysis This SNMP Security Model does not attempt to address traffic analysis attacks. Indeed, many traffic patterns are predictable - devices may be managed on a regular basis by a relatively small number of management applications - and therefore there is no significant advantage afforded by protecting against traffic analysis. Blumenthal & Wijnen Standards Track [Page 5] RFC 3414 USM for SNMPv3 December 2002 1.2. Goals and Constraints Based on the foregoing account of threats in the SNMP network management environment, the goals of this SNMP Security Model are as follows. 1) Provide for verification that each received SNMP message has not been modified during its transmission through the network. 2) Provide for verification of the identity of the user on whose behalf a received SNMP message claims to have been generated. 3) Provide for detection of received SNMP messages, which request or contain management information, whose time of generation was not recent. 4) Provide, when necessary, that the contents of each received SNMP message are protected from disclosure. In addition to the principal goal of supporting secure network management, the design of this SNMP Security Model is also influenced by the following constraints: 1) When the requirements of effective management in times of network stress are inconsistent with those of security, the design of USM has given preference to the former. 2) Neither the security protocol nor its underlying security mechanisms should depend upon the ready availability of other network services (e.g., Network Time Protocol (NTP) or key management protocols). 3) A security mechanism should entail no changes to the basic SNMP network management philosophy. 1.3. Security Services The security services necessary to support the goals of this SNMP Security Model are as follows: - Data Integrity is the provision of the property that data has not been altered or destroyed in an unauthorized manner, nor have data sequences been altered to an extent greater than can occur non- maliciously. - Data Origin Authentication is the provision of the property that the claimed identity of the user on whose behalf received data was originated is corroborated. Blumenthal & Wijnen Standards Track [Page 6] RFC 3414 USM for SNMPv3 December 2002 - Data Confidentiality is the provision of the property that information is not made available or disclosed to unauthorized individuals, entities, or processes. - Message timeliness and limited replay protection is the provision of the property that a message whose generation time is outside of a specified time window is not accepted. Note that message reordering is not dealt with and can occur in normal conditions too. For the protocols specified in this memo, it is not possible to assure the specific originator of a received SNMP message; rather, it is the user on whose behalf the message was originated that is authenticated. For these protocols, it not possible to obtain data integrity without data origin authentication, nor is it possible to obtain data origin authentication without data integrity. Further, there is no provision for data confidentiality without both data integrity and data origin authentication. The security protocols used in this memo are considered acceptably secure at the time of writing. However, the procedures allow for new authentication and privacy methods to be specified at a future time if the need arises. 1.4. Module Organization The security protocols defined in this memo are split in three different modules and each has its specific responsibilities such that together they realize the goals and security services described above: - The authentication module MUST provide for: - Data Integrity, - Data Origin Authentication, - The timeliness module MUST provide for: - Protection against message delay or replay (to an extent greater than can occur through normal operation). - The privacy module MUST provide for - Protection against disclosure of the message payload. Blumenthal & Wijnen Standards Track [Page 7] RFC 3414 USM for SNMPv3 December 2002 The timeliness module is fixed for the User-based Security Model while there is provision for multiple authentication and/or privacy modules, each of which implements a specific authentication or privacy protocol respectively. 1.4.1. Timeliness Module Section 3 (Elements of Procedure) uses the timeliness values in an SNMP message to do timeliness checking. The timeliness check is only performed if authentication is applied to the message. Since the complete message is checked for integrity, we can assume that the timeliness values in a message that passes the authentication module are trustworthy. 1.4.2. Authentication Protocol Section 6 describes the HMAC-MD5-96 authentication protocol which is the first authentication protocol that MUST be supported with the User-based Security Model. Section 7 describes the HMAC-SHA-96 authentication protocol which is another authentication protocol that SHOULD be supported with the User-based Security Model. In the future additional or replacement authentication protocols may be defined as new needs arise. The User-based Security Model prescribes that, if authentication is used, then the complete message is checked for integrity in the authentication module. For a message to be authenticated, it needs to pass authentication check by the authentication module and the timeliness check which is a fixed part of this User-based Security model. 1.4.3. Privacy Protocol Section 8 describes the CBC-DES Symmetric Encryption Protocol which is the first privacy protocol to be used with the User-based Security Model. In the future additional or replacement privacy protocols may be defined as new needs arise. The User-based Security Model prescribes that the scopedPDU is protected from disclosure when a message is sent with privacy. The User-based Security Model also prescribes that a message needs to be authenticated if privacy is in use. Blumenthal & Wijnen Standards Track [Page 8] RFC 3414 USM for SNMPv3 December 2002 1.5. Protection against Message Replay, Delay and Redirection 1.5.1. Authoritative SNMP Engine In order to protect against message replay, delay and redirection, one of the SNMP engines involved in each communication is designated to be the authoritative SNMP engine. When an SNMP message contains a payload which expects a response (those messages that contain a Confirmed Class PDU [RFC3411]), then the receiver of such messages is authoritative. When an SNMP message contains a payload which does not expect a response (those messages that contain an Unconfirmed Class PDU [RFC3411]), then the sender of such a message is authoritative. 1.5.2. Mechanisms The following mechanisms are used: 1) To protect against the threat of message delay or replay (to an extent greater than can occur through normal operation), a set of timeliness indicators (for the authoritative SNMP engine) are included in each message generated. An SNMP engine evaluates the timeliness indicators to determine if a received message is recent. An SNMP engine may evaluate the timeliness indicators to ensure that a received message is at least as recent as the last message it received from the same source. A non-authoritative SNMP engine uses received authentic messages to advance its notion of the timeliness indicators at the remote authoritative source. An SNMP engine MUST also use a mechanism to match incoming Responses to outstanding Requests and it MUST drop any Responses that do not match an outstanding request. For example, a msgID can be inserted in every message to cater for this functionality. These mechanisms provide for the detection of authenticated messages whose time of generation was not recent. This protection against the threat of message delay or replay does not imply nor provide any protection against unauthorized deletion or suppression of messages. Also, an SNMP engine may not be able to detect message reordering if all the messages involved are sent within the Time Window interval. Other mechanisms defined independently of the security protocol can also be used to detect the re-ordering replay, deletion, or suppression of messages containing Set operations (e.g., the MIB variable snmpSetSerialNo [RFC3418]). Blumenthal & Wijnen Standards Track [Page 9] RFC 3414 USM for SNMPv3 December 2002 2) Verification that a message sent to/from one authoritative SNMP engine cannot be replayed to/as-if-from another authoritative SNMP engine. Included in each message is an identifier unique to the authoritative SNMP engine associated with the sender or intended recipient of the message. A message containing an Unconfirmed Class PDU sent by an authoritative SNMP engine to one non-authoritative SNMP engine can potentially be replayed to another non-authoritative SNMP engine. The latter non-authoritative SNMP engine might (if it knows about the same userName with the same secrets at the authoritative SNMP engine) as a result update its notion of timeliness indicators of the authoritative SNMP engine, but that is not considered a threat. In this case, A Report or Response message will be discarded by the Message Processing Model, because there should not be an outstanding Request message. A Trap will possibly be accepted. Again, that is not considered a threat, because the communication was authenticated and timely. It is as if the authoritative SNMP engine was configured to start sending Traps to the second SNMP engine, which theoretically can happen without the knowledge of the second SNMP engine anyway. Anyway, the second SNMP engine may not expect to receive this Trap, but is allowed to see the management information contained in it. 3) Detection of messages which were not recently generated. A set of time indicators are included in the message, indicating the time of generation. Messages without recent time indicators are not considered authentic. In addition, an SNMP engine MUST drop any Responses that do not match an outstanding request. This however is the responsibility of the Message Processing Model. This memo allows the same user to be defined on multiple SNMP engines. Each SNMP engine maintains a value, snmpEngineID, which uniquely identifies the SNMP engine. This value is included in each message sent to/from the SNMP engine that is authoritative (see section 1.5.1). On receipt of a message, an authoritative SNMP engine checks the value to ensure that it is the intended recipient, and a non-authoritative SNMP engine uses the value to ensure that the message is processed using the correct state information. Each SNMP engine maintains two values, snmpEngineBoots and snmpEngineTime, which taken together provide an indication of time at that SNMP engine. Both of these values are included in an authenticated message sent to/received from that SNMP engine. On receipt, the values are checked to ensure that the indicated Blumenthal & Wijnen Standards Track [Page 10] RFC 3414 USM for SNMPv3 December 2002 timeliness value is within a Time Window of the current time. The Time Window represents an administrative upper bound on acceptable delivery delay for protocol messages. For an SNMP engine to generate a message which an authoritative SNMP engine will accept as authentic, and to verify that a message received from that authoritative SNMP engine is authentic, such an SNMP engine must first achieve timeliness synchronization with the authoritative SNMP engine. See section 2.3. 1.6. Abstract Service Interfaces Abstract service interfaces have been defined to describe the conceptual interfaces between the various subsystems within an SNMP entity. Similarly a set of abstract service interfaces have been defined within the User-based Security Model (USM) to describe the conceptual interfaces between the generic USM services and the self-contained authentication and privacy services. These abstract service interfaces are defined by a set of primitives that define the services provided and the abstract data elements that must be passed when the services are invoked. This section lists the primitives that have been defined for the User-based Security Model. 1.6.1. User-based Security Model Primitives for Authentication The User-based Security Model provides the following internal primitives to pass data back and forth between the Security Model itself and the authentication service: statusInformation = authenticateOutgoingMsg( IN authKey -- secret key for authentication IN wholeMsg -- unauthenticated complete message OUT authenticatedWholeMsg -- complete authenticated message ) statusInformation = authenticateIncomingMsg( IN authKey -- secret key for authentication IN authParameters -- as received on the wire IN wholeMsg -- as received on the wire OUT authenticatedWholeMsg -- complete authenticated message ) Blumenthal & Wijnen Standards Track [Page 11] RFC 3414 USM for SNMPv3 December 2002 1.6.2. User-based Security Model Primitives for Privacy The User-based Security Model provides the following internal primitives to pass data back and forth between the Security Model itself and the privacy service: statusInformation = encryptData( IN encryptKey -- secret key for encryption IN dataToEncrypt -- data to encrypt (scopedPDU) OUT encryptedData -- encrypted data (encryptedPDU) OUT privParameters -- filled in by service provider ) statusInformation = decryptData( IN decryptKey -- secret key for decrypting IN privParameters -- as received on the wire IN encryptedData -- encrypted data (encryptedPDU) OUT decryptedData -- decrypted data (scopedPDU) ) 2. Elements of the Model This section contains definitions required to realize the security model defined by this memo. 2.1. User-based Security Model Users Management operations using this Security Model make use of a defined set of user identities. For any user on whose behalf management operations are authorized at a particular SNMP engine, that SNMP engine must have knowledge of that user. An SNMP engine that wishes to communicate with another SNMP engine must also have knowledge of a user known to that engine, including knowledge of the applicable attributes of that user. A user and its attributes are defined as follows: userName A string representing the name of the user. securityName A human-readable string representing the user in a format that is Security Model independent. There is a one-to-one relationship between userName and securityName. Blumenthal & Wijnen Standards Track [Page 12] RFC 3414 USM for SNMPv3 December 2002 authProtocol An indication of whether messages sent on behalf of this user can be authenticated, and if so, the type of authentication protocol which is used. Two such protocols are defined in this memo: - the HMAC-MD5-96 authentication protocol. - the HMAC-SHA-96 authentication protocol. authKey If messages sent on behalf of this user can be authenticated, the (private) authentication key for use with the authentication protocol. Note that a user's authentication key will normally be different at different authoritative SNMP engines. The authKey is not accessible via SNMP. The length requirements of the authKey are defined by the authProtocol in use. authKeyChange and authOwnKeyChange The only way to remotely update the authentication key. Does that in a secure manner, so that the update can be completed without the need to employ privacy protection. privProtocol An indication of whether messages sent on behalf of this user can be protected from disclosure, and if so, the type of privacy protocol which is used. One such protocol is defined in this memo: the CBC-DES Symmetric Encryption Protocol. privKey If messages sent on behalf of this user can be en/decrypted, the (private) privacy key for use with the privacy protocol. Note that a user's privacy key will normally be different at different authoritative SNMP engines. The privKey is not accessible via SNMP. The length requirements of the privKey are defined by the privProtocol in use. privKeyChange and privOwnKeyChange The only way to remotely update the encryption key. Does that in a secure manner, so that the update can be completed without the need to employ privacy protection. 2.2. Replay Protection Each SNMP engine maintains three objects: - snmpEngineID, which (at least within an administrative domain) uniquely and unambiguously identifies an SNMP engine. Blumenthal & Wijnen Standards Track [Page 13] RFC 3414 USM for SNMPv3 December 2002 - snmpEngineBoots, which is a count of the number of times the SNMP engine has re-booted/re-initialized since snmpEngineID was last configured; and, - snmpEngineTime, which is the number of seconds since the snmpEngineBoots counter was last incremented. Each SNMP engine is always authoritative with respect to these objects in its own SNMP entity. It is the responsibility of a non- authoritative SNMP engine to synchronize with the authoritative SNMP engine, as appropriate. An authoritative SNMP engine is required to maintain the values of its snmpEngineID and snmpEngineBoots in non-volatile storage. 2.2.1. msgAuthoritativeEngineID The msgAuthoritativeEngineID value contained in an authenticated message is used to defeat attacks in which messages from one SNMP engine to another SNMP engine are replayed to a different SNMP engine. It represents the snmpEngineID at the authoritative SNMP engine involved in the exchange of the message. When an authoritative SNMP engine is first installed, it sets its local value of snmpEngineID according to a enterprise-specific algorithm (see the definition of the Textual Convention for SnmpEngineID in the SNMP Architecture document [RFC3411]). 2.2.2. msgAuthoritativeEngineBoots and msgAuthoritativeEngineTime The msgAuthoritativeEngineBoots and msgAuthoritativeEngineTime values contained in an authenticated message are used to defeat attacks in which messages are replayed when they are no longer valid. They represent the snmpEngineBoots and snmpEngineTime values at the authoritative SNMP engine involved in the exchange of the message. Through use of snmpEngineBoots and snmpEngineTime, there is no requirement for an SNMP engine to have a non-volatile clock which ticks (i.e., increases with the passage of time) even when the SNMP engine is powered off. Rather, each time an SNMP engine re-boots, it retrieves, increments, and then stores snmpEngineBoots in non-volatile storage, and resets snmpEngineTime to zero. When an SNMP engine is first installed, it sets its local values of snmpEngineBoots and snmpEngineTime to zero. If snmpEngineTime ever reaches its maximum value (2147483647), then snmpEngineBoots is incremented as if the SNMP engine has re-booted and snmpEngineTime is reset to zero and starts incrementing again. Blumenthal & Wijnen Standards Track [Page 14] RFC 3414 USM for SNMPv3 December 2002 Each time an authoritative SNMP engine re-boots, any SNMP engines holding that authoritative SNMP engine's values of snmpEngineBoots and snmpEngineTime need to re-synchronize prior to sending correctly authenticated messages to that authoritative SNMP engine (see Section 2.3 for (re-)synchronization procedures). Note, however, that the procedures do provide for a notification to be accepted as authentic by a receiving SNMP engine, when sent by an authoritative SNMP engine which has re-booted since the receiving SNMP engine last (re- )synchronized. If an authoritative SNMP engine is ever unable to determine its latest snmpEngineBoots value, then it must set its snmpEngineBoots value to 2147483647. Whenever the local value of snmpEngineBoots has the value 2147483647 it latches at that value and an authenticated message always causes an notInTimeWindow authentication failure. In order to reset an SNMP engine whose snmpEngineBoots value has reached the value 2147483647, manual intervention is required. The engine must be physically visited and re-configured, either with a new snmpEngineID value, or with new secret values for the authentication and privacy protocols of all users known to that SNMP engine. Note that even if an SNMP engine re-boots once a second that it would still take approximately 68 years before the max value of 2147483647 would be reached. 2.2.3. Time Window The Time Window is a value that specifies the window of time in which a message generated on behalf of any user is valid. This memo specifies that the same value of the Time Window, 150 seconds, is used for all users. 2.3. Time Synchronization Time synchronization, required by a non-authoritative SNMP engine in order to proceed with authentic communications, has occurred when the non-authoritative SNMP engine has obtained a local notion of the authoritative SNMP engine's values of snmpEngineBoots and snmpEngineTime from the authoritative SNMP engine. These values must be (and remain) within the authoritative SNMP engine's Time Window. So the local notion of the authoritative SNMP engine's values must be kept loosely synchronized with the values stored at the authoritative SNMP engine. In addition to keeping a local copy of snmpEngineBoots and snmpEngineTime from the authoritative SNMP engine, a non-authoritative SNMP engine must also keep one Blumenthal & Wijnen Standards Track [Page 15] RFC 3414 USM for SNMPv3 December 2002 local variable, latestReceivedEngineTime. This value records the highest value of snmpEngineTime that was received by the non-authoritative SNMP engine from the authoritative SNMP engine and is used to eliminate the possibility of replaying messages that would prevent the non-authoritative SNMP engine's notion of the snmpEngineTime from advancing. A non-authoritative SNMP engine must keep local notions of these values (snmpEngineBoots, snmpEngineTime and latestReceivedEngineTime) for each authoritative SNMP engine with which it wishes to communicate. Since each authoritative SNMP engine is uniquely and unambiguously identified by its value of snmpEngineID, the non-authoritative SNMP engine may use this value as a key in order to cache its local notions of these values. Time synchronization occurs as part of the procedures of receiving an SNMP message (Section 3.2, step 7b). As such, no explicit time synchronization procedure is required by a non-authoritative SNMP engine. Note, that whenever the local value of snmpEngineID is changed (e.g., through discovery) or when secure communications are first established with an authoritative SNMP engine, the local values of snmpEngineBoots and latestReceivedEngineTime should be set to zero. This will cause the time synchronization to occur when the next authentic message is received. 2.4. SNMP Messages Using this Security Model The syntax of an SNMP message using this Security Model adheres to the message format defined in the version-specific Message Processing Model document (for example [RFC3412]). The field msgSecurityParameters in SNMPv3 messages has a data type of OCTET STRING. Its value is the BER serialization of the following ASN.1 sequence: USMSecurityParametersSyntax DEFINITIONS IMPLICIT TAGS ::= BEGIN UsmSecurityParameters ::= SEQUENCE { -- global User-based security parameters msgAuthoritativeEngineID OCTET STRING, msgAuthoritativeEngineBoots INTEGER (0..2147483647), msgAuthoritativeEngineTime INTEGER (0..2147483647), msgUserName OCTET STRING (SIZE(0..32)), -- authentication protocol specific parameters msgAuthenticationParameters OCTET STRING, -- privacy protocol specific parameters msgPrivacyParameters OCTET STRING Blumenthal & Wijnen Standards Track [Page 16] RFC 3414 USM for SNMPv3 December 2002 } END The fields of this sequence are: - The msgAuthoritativeEngineID specifies the snmpEngineID of the authoritative SNMP engine involved in the exchange of the message. - The msgAuthoritativeEngineBoots specifies the snmpEngineBoots value at the authoritative SNMP engine involved in the exchange of the message. - The msgAuthoritativeEngineTime specifies the snmpEngineTime value at the authoritative SNMP engine involved in the exchange of the message. - The msgUserName specifies the user (principal) on whose behalf the message is being exchanged. Note that a zero-length userName will not match any user, but it can be used for snmpEngineID discovery. - The msgAuthenticationParameters are defined by the authentication protocol in use for the message, as defined by the usmUserAuthProtocol column in the user's entry in the usmUserTable. - The msgPrivacyParameters are defined by the privacy protocol in use for the message, as defined by the usmUserPrivProtocol column in the user's entry in the usmUserTable). See appendix A.4 for an example of the BER encoding of field msgSecurityParameters. 2.5. Services provided by the User-based Security Model This section describes the services provided by the User-based Security Model with their inputs and outputs. The services are described as primitives of an abstract service interface and the inputs and outputs are described as abstract data elements as they are passed in these abstract service primitives. 2.5.1. Services for Generating an Outgoing SNMP Message When the Message Processing (MP) Subsystem invokes the User-based Security module to secure an outgoing SNMP message, it must use the appropriate service as provided by the Security module. These two services are provided: Blumenthal & Wijnen Standards Track [Page 17] RFC 3414 USM for SNMPv3 December 2002 1) A service to generate a Request message. The abstract service primitive is: statusInformation = -- success or errorIndication generateRequestMsg( IN messageProcessingModel -- typically, SNMP version IN globalData -- message header, admin data IN maxMessageSize -- of the sending SNMP entity IN securityModel -- for the outgoing message IN securityEngineID -- authoritative SNMP entity IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN scopedPDU -- message (plaintext) payload OUT securityParameters -- filled in by Security Module OUT wholeMsg -- complete generated message OUT wholeMsgLength -- length of generated message ) 2) A service to generate a Response message. The abstract service primitive is: statusInformation = -- success or errorIndication generateResponseMsg( IN messageProcessingModel -- typically, SNMP version IN globalData -- message header, admin data IN maxMessageSize -- of the sending SNMP entity IN securityModel -- for the outgoing message IN securityEngineID -- authoritative SNMP entity IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN scopedPDU -- message (plaintext) payload IN securityStateReference -- reference to security state -- information from original -- request OUT securityParameters -- filled in by Security Module OUT wholeMsg -- complete generated message OUT wholeMsgLength -- length of generated message ) The abstract data elements passed as parameters in the abstract service primitives are as follows: statusInformation An indication of whether the encoding and securing of the message was successful. If not it is an indication of the problem. Blumenthal & Wijnen Standards Track [Page 18] RFC 3414 USM for SNMPv3 December 2002 messageProcessingModel The SNMP version number for the message to be generated. This data is not used by the User-based Security module. globalData The message header (i.e., its administrative information). This data is not used by the User-based Security module. maxMessageSize The maximum message size as included in the message. This data is not used by the User-based Security module. securityParameters These are the security parameters. They will be filled in by the User-based Security module. securityModel The securityModel in use. Should be User-based Security Model. This data is not used by the User-based Security module. securityName Together with the snmpEngineID it identifies a row in the usmUserTablethat is to be used for securing the message. The securityName has a format that is independent of the Security Model. In case of a response this parameter is ignored and the value from the cache is used. securityLevel The Level of Security from which the User-based Security module determines if the message needs to be protected from disclosure and if the message needs to be authenticated. securityEngineID The snmpEngineID of the authoritative SNMP engine to which a dateRequest message is to be sent. In case of a response it is implied to be the processing SNMP engine's snmpEngineID and so if it is specified, then it is ignored. scopedPDU The message payload. The data is opaque as far as the User-based Security Model is concerned. securityStateReference A handle/reference to cachedSecurityData to be used when securing an outgoing Response message. This is the exact same handle/reference as it was generated by the User-based Security module when processing the incoming Request message to which this is the Response message. Blumenthal & Wijnen Standards Track [Page 19] RFC 3414 USM for SNMPv3 December 2002 wholeMsg The fully encoded and secured message ready for sending on the wire. wholeMsgLength The length of the encoded and secured message (wholeMsg). Upon completion of the process, the User-based Security module returns statusInformation. If the process was successful, the completed message with privacy and authentication applied if such was requested by the specified securityLevel is returned. If the process was not successful, then an errorIndication is returned. 2.5.2. Services for Processing an Incoming SNMP Message When the Message Processing (MP) Subsystem invokes the User-based Security module to verify proper security of an incoming message, it must use the service provided for an incoming message. The abstract service primitive is: statusInformation = -- errorIndication or success -- error counter OID/value if error processIncomingMsg( IN messageProcessingModel -- typically, SNMP version IN maxMessageSize -- of the sending SNMP entity IN securityParameters -- for the received message IN securityModel -- for the received message IN securityLevel -- Level of Security IN wholeMsg -- as received on the wire IN wholeMsgLength -- length as received on the wire OUT securityEngineID -- authoritative SNMP entity OUT securityName -- identification of the principal OUT scopedPDU, -- message (plaintext) payload OUT maxSizeResponseScopedPDU -- maximum size of the Response PDU OUT securityStateReference -- reference to security state ) -- information, needed for response The abstract data elements passed as parameters in the abstract service primitives are as follows: statusInformation An indication of whether the process was successful or not. If not, then the statusInformation includes the OID and the value of the error counter that was incremented. messageProcessingModel The SNMP version number as received in the message. This data is not used by the User-based Security module. Blumenthal & Wijnen Standards Track [Page 20] RFC 3414 USM for SNMPv3 December 2002 maxMessageSize The maximum message size as included in the message. The User-bas User-based Security module uses this value to calculate the maxSizeResponseScopedPDU. securityParameters These are the security parameters as received in the message. securityModel The securityModel in use. Should be the User-based Security Model. This data is not used by the User-based Security module. securityLevel The Level of Security from which the User-based Security module determines if the message needs to be protected from disclosure and if the message needs to be authenticated. wholeMsg The whole message as it was received. wholeMsgLength The length of the message as it was received (wholeMsg). securityEngineID The snmpEngineID that was extracted from the field msgAuthoritativeEngineID and that was used to lookup the secrets in the usmUserTable. securityName The security name representing the user on whose behalf the message was received. The securityName has a format that is independent of the Security Model. scopedPDU The message payload. The data is opaque as far as the User-based Security Model is concerned. maxSizeResponseScopedPDU The maximum size of a scopedPDU to be included in a possible Response message. The User-based Security module calculates this size based on the msgMaxSize (as received in the message) and the space required for the message header (including the securityParameters) for such a Response message. securityStateReference A handle/reference to cachedSecurityData to be used when securing an outgoing Response message. When the Message Processing Subsystem calls the User-based Security module to generate a Blumenthal & Wijnen Standards Track [Page 21] RFC 3414 USM for SNMPv3 December 2002 response to this incoming message it must pass this handle/reference. Upon completion of the process, the User-based Security module returns statusInformation and, if the process was successful, the additional data elements for further processing of the message. If the process was not successful, then an errorIndication, possibly with a OID and value pair of an error counter that was incremented. 2.6. Key Localization Algorithm. A localized key is a secret key shared between a user U and one authoritative SNMP engine E. Even though a user may have only one password and therefore one key for the whole network, the actual secrets shared between the user and each authoritative SNMP engine will be different. This is achieved by key localization [Localized- key]. First, if a user uses a password, then the user's password is converted into a key Ku using one of the two algorithms described in Appendices A.2.1 and A.2.2. To convert key Ku into a localized key Kul of user U at the authoritative SNMP engine E, one appends the snmpEngineID of the authoritative SNMP engine to the key Ku and then appends the key Ku to the result, thus enveloping the snmpEngineID within the two copies of user's key Ku. Then one runs a secure hash function (which one depends on the authentication protocol defined for this user U at authoritative SNMP engine E; this document defines two authentication protocols with their associated algorithms based on MD5 and SHA). The output of the hash-function is the localized key Kul for user U at the authoritative SNMP engine E. 3. Elements of Procedure This section describes the security related procedures followed by an SNMP engine when processing SNMP messages according to the User-based Security Model. 3.1. Generating an Outgoing SNMP Message This section describes the procedure followed by an SNMP engine whenever it generates a message containing a management operation (like a request, a response, a notification, or a report) on behalf of a user, with a particular securityLevel. Blumenthal & Wijnen Standards Track [Page 22] RFC 3414 USM for SNMPv3 December 2002 1) a) If any securityStateReference is passed (Response or Report message), then information concerning the user is extracted from the cachedSecurityData. The cachedSecurityData can now be discarded. The securityEngineID is set to the local snmpEngineID. The securityLevel is set to the value specified by the calling module. Otherwise, b) based on the securityName, information concerning the user at the destination snmpEngineID, specified by the securityEngineID, is extracted from the Local Configuration Datastore (LCD, usmUserTable). If information about the user is absent from the LCD, then an error indication (unknownSecurityName) is returned to the calling module. 2) If the securityLevel specifies that the message is to be protected from disclosure, but the user does not support both an authentication and a privacy protocol then the message cannot be sent. An error indication (unsupportedSecurityLevel) is returned to the calling module. 3) If the securityLevel specifies that the message is to be authenticated, but the user does not support an authentication protocol, then the message cannot be sent. An error indication (unsupportedSecurityLevel) is returned to the calling module. 4) a) If the securityLevel specifies that the message is to be protected from disclosure, then the octet sequence representing the serialized scopedPDU is encrypted according to the user's privacy protocol. To do so a call is made to the privacy module that implements the user's privacy protocol according to the abstract primitive: statusInformation = -- success or failure encryptData( IN encryptKey -- user's localized privKey IN dataToEncrypt -- serialized scopedPDU OUT encryptedData -- serialized encryptedPDU OUT privParameters -- serialized privacy parameters ) statusInformation indicates if the encryption process was successful or not. encryptKey the user's localized private privKey is the secret key that can be used by the encryption algorithm. Blumenthal & Wijnen Standards Track [Page 23] RFC 3414 USM for SNMPv3 December 2002 dataToEncrypt the serialized scopedPDU is the data to be encrypted. encryptedData the encryptedPDU represents the encrypted scopedPDU, encoded as an OCTET STRING. privParameters the privacy parameters, encoded as an OCTET STRING. If the privacy module returns failure, then the message cannot be sent and an error indication (encryptionError) is returned to the calling module. If the privacy module returns success, then the returned privParameters are put into the msgPrivacyParameters field of the securityParameters and the encryptedPDU serves as the payload of the message being prepared. Otherwise, b) If the securityLevel specifies that the message is not to be be protected from disclosure, then a zero-length OCTET STRING is encoded into the msgPrivacyParameters field of the securityParameters and the plaintext scopedPDU serves as the payload of the message being prepared. 5) The securityEngineID is encoded as an OCTET STRING into the msgAuthoritativeEngineID field of the securityParameters. Note that an empty (zero length) securityEngineID is OK for a Request message, because that will cause the remote (authoritative) SNMP engine to return a Report PDU with the proper securityEngineID included in the msgAuthoritativeEngineID in the securityParameters of that returned Report PDU. 6) a) If the securityLevel specifies that the message is to be authenticated, then the current values of snmpEngineBoots and snmpEngineTime corresponding to the securityEngineID from the LCD are used. Otherwise, b) If this is a Response or Report message, then the current value of snmpEngineBoots and snmpEngineTime corresponding to the local snmpEngineID from the LCD are used. Blumenthal & Wijnen Standards Track [Page 24] RFC 3414 USM for SNMPv3 December 2002 Otherwise, c) If this is a Request message, then a zero value is used for both snmpEngineBoots and snmpEngineTime. This zero value gets used if snmpEngineID is empty. The values are encoded as INTEGER respectively into the msgAuthoritativeEngineBoots and msgAuthoritativeEngineTime fields of the securityParameters. 7) The userName is encoded as an OCTET STRING into the msgUserName field of the securityParameters. 8) a) If the securityLevel specifies that the message is to be authenticated, the message is authenticated according to the user's authentication protocol. To do so a call is made to the authentication module that implements the user's authentication protocol according to the abstract service primitive: statusInformation = authenticateOutgoingMsg( IN authKey -- the user's localized authKey IN wholeMsg -- unauthenticated message OUT authenticatedWholeMsg -- authenticated complete message ) statusInformation indicates if authentication was successful or not. authKey the user's localized private authKey is the secret key that can be used by the authentication algorithm. wholeMsg the complete serialized message to be authenticated. authenticatedWholeMsg the same as the input given to the authenticateOutgoingMsg service, but with msgAuthenticationParameters properly filled in. If the authentication module returns failure, then the message cannot be sent and an error indication (authenticationFailure) is returned to the calling module. Blumenthal & Wijnen Standards Track [Page 25] RFC 3414 USM for SNMPv3 December 2002 If the authentication module returns success, then the msgAuthenticationParameters field is put into the securityParameters and the authenticatedWholeMsg represents the serialization of the authenticated message being prepared. Otherwise, b) If the securityLevel specifies that the message is not to be authenticated then a zero-length OCTET STRING is encoded into the msgAuthenticationParameters field of the securityParameters. The wholeMsg is now serialized and then represents the unauthenticated message being prepared. 9) The completed message with its length is returned to the calling module with the statusInformation set to success. 3.2. Processing an Incoming SNMP Message This section describes the procedure followed by an SNMP engine whenever it receives a message containing a management operation on behalf of a user, with a particular securityLevel. To simplify the elements of procedure, the release of state information is not always explicitly specified. As a general rule, if state information is available when a message gets discarded, the state information should also be released. Also, an error indication can return an OID and value for an incremented counter and optionally a value for securityLevel, and values for contextEngineID or contextName for the counter. In addition, the securityStateReference data is returned if any such information is available at the point where the error is detected. 1) If the received securityParameters is not the serialization (according to the conventions of [RFC3417]) of an OCTET STRING formatted according to the UsmSecurityParameters defined in section 2.4, then the snmpInASNParseErrs counter [RFC3418] is incremented, and an error indication (parseError) is returned to the calling module. Note that we return without the OID and value of the incremented counter, because in this case there is not enough information to generate a Report PDU. 2) The values of the security parameter fields are extracted from the securityParameters. The securityEngineID to be returned to the caller is the value of the msgAuthoritativeEngineID field. The cachedSecurityData is prepared and a securityStateReference is prepared to reference this data. Values to be cached are: msgUserName Blumenthal & Wijnen Standards Track [Page 26] RFC 3414 USM for SNMPv3 December 2002 3) If the value of the msgAuthoritativeEngineID field in the securityParameters is unknown then: a) a non-authoritative SNMP engine that performs discovery may optionally create a new entry in its Local Configuration Datastore (LCD) and continue processing; or b) the usmStatsUnknownEngineIDs counter is incremented, and an error indication (unknownEngineID) together with the OID and value of the incremented counter is returned to the calling module. Note in the event that a zero-length, or other illegally sized msgAuthoritativeEngineID is received, b) should be chosen to facilitate engineID discovery. Otherwise the choice between a) and b) is an implementation issue. 4) Information about the value of the msgUserName and msgAuthoritativeEngineID fields is extracted from the Local Configuration Datastore (LCD, usmUserTable). If no information is available for the user, then the usmStatsUnknownUserNames counter is incremented and an error indication (unknownSecurityName) together with the OID and value of the incremented counter is returned to the calling module. 5) If the information about the user indicates that it does not support the securityLevel requested by the caller, then the usmStatsUnsupportedSecLevels counter is incremented and an error indication (unsupportedSecurityLevel) together with the OID and value of the incremented counter is returned to the calling module. 6) If the securityLevel specifies that the message is to be authenticated, then the message is authenticated according to the user's authentication protocol. To do so a call is made to the authentication module that implements the user's authentication protocol according to the abstract service primitive: statusInformation = -- success or failure authenticateIncomingMsg( IN authKey -- the user's localized authKey IN authParameters -- as received on the wire IN wholeMsg -- as received on the wire OUT authenticatedWholeMsg -- checked for authentication ) Blumenthal & Wijnen Standards Track [Page 27] RFC 3414 USM for SNMPv3 December 2002 statusInformation indicates if authentication was successful or not. authKey the user's localized private authKey is the secret key that can be used by the authentication algorithm. wholeMsg the complete serialized message to be authenticated. authenticatedWholeMsg the same as the input given to the authenticateIncomingMsg service, but after authentication has been checked. If the authentication module returns failure, then the message cannot be trusted, so the usmStatsWrongDigests counter is incremented and an error indication (authenticationFailure) together with the OID and value of the incremented counter is returned to the calling module. If the authentication module returns success, then the message is authentic and can be trusted so processing continues. 7) If the securityLevel indicates an authenticated message, then the local values of snmpEngineBoots, snmpEngineTime and latestReceivedEngineTime corresponding to the value of the msgAuthoritativeEngineID field are extracted from the Local Configuration Datastore. a) If the extracted value of msgAuthoritativeEngineID is the same as the value of snmpEngineID of the processing SNMP engine (meaning this is the authoritative SNMP engine), then if any of the following conditions is true, then the message is considered to be outside of the Time Window: - the local value of snmpEngineBoots is 2147483647; - the value of the msgAuthoritativeEngineBoots field differs from the local value of snmpEngineBoots; or, - the value of the msgAuthoritativeEngineTime field differs from the local notion of snmpEngineTime by more than +/- 150 seconds. If the message is considered to be outside of the Time Window then the usmStatsNotInTimeWindows counter is incremented and an error indication (notInTimeWindow) together with the OID, the value of the incremented counter, and an indication that Blumenthal & Wijnen Standards Track [Page 28] RFC 3414 USM for SNMPv3 December 2002 the error must be reported with a securityLevel of authNoPriv, is returned to the calling module b) If the extracted value of msgAuthoritativeEngineID is not the same as the value snmpEngineID of the processing SNMP engine (meaning this is not the authoritative SNMP engine), then: 1) if at least one of the following conditions is true: - the extracted value of the msgAuthoritativeEngineBoots field is greater than the local notion of the value of snmpEngineBoots; or, - the extracted value of the msgAuthoritativeEngineBoots field is equal to the local notion of the value of snmpEngineBoots, and the extracted value of msgAuthoritativeEngineTime field is greater than the value of latestReceivedEngineTime, then the LCD entry corresponding to the extracted value of the msgAuthoritativeEngineID field is updated, by setting: - the local notion of the value of snmpEngineBoots to the value of the msgAuthoritativeEngineBoots field, - the local notion of the value of snmpEngineTime to the value of the msgAuthoritativeEngineTime field, and - the latestReceivedEngineTime to the value of the value of the msgAuthoritativeEngineTime field. 2) if any of the following conditions is true, then the message is considered to be outside of the Time Window: - the local notion of the value of snmpEngineBoots is 2147483647; - the value of the msgAuthoritativeEngineBoots field is less than the local notion of the value of snmpEngineBoots; or, - the value of the msgAuthoritativeEngineBoots field is equal to the local notion of the value of snmpEngineBoots and the value of the msgAuthoritativeEngineTime field is more than 150 seconds less than the local notion of the value of snmpEngineTime. Blumenthal & Wijnen Standards Track [Page 29] RFC 3414 USM for SNMPv3 December 2002 If the message is considered to be outside of the Time Window then an error indication (notInTimeWindow) is returned to the calling module. Note that this means that a too old (possibly replayed) message has been detected and is deemed unauthentic. Note that this procedure allows for the value of msgAuthoritativeEngineBoots in the message to be greater than the local notion of the value of snmpEngineBoots to allow for received messages to be accepted as authentic when received from an authoritative SNMP engine that has re-booted since the receiving SNMP engine last (re-)synchronized. 8) a) If the securityLevel indicates that the message was protected from disclosure, then the OCTET STRING representing the encryptedPDU is decrypted according to the user's privacy protocol to obtain an unencrypted serialized scopedPDU value. To do so a call is made to the privacy module that implements the user's privacy protocol according to the abstract primitive: statusInformation = -- success or failure decryptData( IN decryptKey -- the user's localized privKey IN privParameters -- as received on the wire IN encryptedData -- encryptedPDU as received OUT decryptedData -- serialized decrypted scopedPDU ) statusInformation indicates if the decryption process was successful or not. decryptKey the user's localized private privKey is the secret key that can be used by the decryption algorithm. privParameters the msgPrivacyParameters, encoded as an OCTET STRING. encryptedData the encryptedPDU represents the encrypted scopedPDU, encoded as an OCTET STRING. decryptedData the serialized scopedPDU if decryption is successful. Blumenthal & Wijnen Standards Track [Page 30] RFC 3414 USM for SNMPv3 December 2002 If the privacy module returns failure, then the message can not be processed, so the usmStatsDecryptionErrors counter is incremented and an error indication (decryptionError) together with the OID and value of the incremented counter is returned to the calling module. If the privacy module returns success, then the decrypted scopedPDU is the message payload to be returned to the calling module. Otherwise, b) The scopedPDU component is assumed to be in plain text and is the message payload to be returned to the calling module. 9) The maxSizeResponseScopedPDU is calculated. This is the maximum size allowed for a scopedPDU for a possible Response message. Provision is made for a message header that allows the same securityLevel as the received Request. 10) The securityName for the user is retrieved from the usmUserTable. 11) The security data is cached as cachedSecurityData, so that a possible response to this message can and will use the same authentication and privacy secrets. Information to be saved/cached is as follows: msgUserName, usmUserAuthProtocol, usmUserAuthKey usmUserPrivProtocol, usmUserPrivKey 12) The statusInformation is set to success and a return is made to the calling module passing back the OUT parameters as specified in the processIncomingMsg primitive. 4. Discovery The User-based Security Model requires that a discovery process obtains sufficient information about other SNMP engines in order to communicate with them. Discovery requires an non-authoritative SNMP engine to learn the authoritative SNMP engine's snmpEngineID value before communication may proceed. This may be accomplished by generating a Request message with a securityLevel of noAuthNoPriv, a msgUserName of zero-length, a msgAuthoritativeEngineID value of zero length, and the varBindList left empty. The response to this message will be a Report message containing the snmpEngineID of the authoritative SNMP engine as the value of the msgAuthoritativeEngineID field within the msgSecurityParameters Blumenthal & Wijnen Standards Track [Page 31] RFC 3414 USM for SNMPv3 December 2002 field. It contains a Report PDU with the usmStatsUnknownEngineIDs counter in the varBindList. If authenticated communication is required, then the discovery process should also establish time synchronization with the authoritative SNMP engine. This may be accomplished by sending an authenticated Request message with the value of msgAuthoritativeEngineID set to the newly learned snmpEngineID and with the values of msgAuthoritativeEngineBoots and msgAuthoritativeEngineTime set to zero. For an authenticated Request message, a valid userName must be used in the msgUserName field. The response to this authenticated message will be a Report message containing the up to date values of the authoritative SNMP engine's snmpEngineBoots and snmpEngineTime as the value of the msgAuthoritativeEngineBoots and msgAuthoritativeEngineTime fields respectively. It also contains the usmStatsNotInTimeWindows counter in the varBindList of the Report PDU. The time synchronization then happens automatically as part of the procedures in section 3.2 step 7b. See also section 2.3. 5. Definitions SNMP-USER-BASED-SM-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, OBJECT-IDENTITY, snmpModules, Counter32 FROM SNMPv2-SMI TEXTUAL-CONVENTION, TestAndIncr, RowStatus, RowPointer, StorageType, AutonomousType FROM SNMPv2-TC MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF SnmpAdminString, SnmpEngineID, snmpAuthProtocols, snmpPrivProtocols FROM SNMP-FRAMEWORK-MIB; snmpUsmMIB MODULE-IDENTITY LAST-UPDATED "200210160000Z" -- 16 Oct 2002, midnight ORGANIZATION "SNMPv3 Working Group" CONTACT-INFO "WG-email: snmpv3@lists.tislabs.com Subscribe: majordomo@lists.tislabs.com In msg body: subscribe snmpv3 Chair: Russ Mundy Network Associates Laboratories postal: 15204 Omega Drive, Suite 300 Rockville, MD 20850-4601 USA email: mundy@tislabs.com Blumenthal & Wijnen Standards Track [Page 32] RFC 3414 USM for SNMPv3 December 2002 phone: +1 301-947-7107 Co-Chair: David Harrington Enterasys Networks Postal: 35 Industrial Way P. O. Box 5004 Rochester, New Hampshire 03866-5005 USA EMail: dbh@enterasys.com Phone: +1 603-337-2614 Co-editor Uri Blumenthal Lucent Technologies postal: 67 Whippany Rd. Whippany, NJ 07981 USA email: uri@lucent.com phone: +1-973-386-2163 Co-editor: Bert Wijnen Lucent Technologies postal: Schagen 33 3461 GL Linschoten Netherlands email: bwijnen@lucent.com phone: +31-348-480-685 " DESCRIPTION "The management information definitions for the SNMP User-based Security Model. Copyright (C) The Internet Society (2002). This version of this MIB module is part of RFC 3414; see the RFC itself for full legal notices. " -- Revision history REVISION "200210160000Z" -- 16 Oct 2002, midnight DESCRIPTION "Changes in this revision: - Updated references and contact info. - Clarification to usmUserCloneFrom DESCRIPTION clause - Fixed 'command responder' into 'command generator' in last para of DESCRIPTION clause of usmUserTable. This revision published as RFC3414. " REVISION "199901200000Z" -- 20 Jan 1999, midnight DESCRIPTION "Clarifications, published as RFC2574" Blumenthal & Wijnen Standards Track [Page 33] RFC 3414 USM for SNMPv3 December 2002 REVISION "199711200000Z" -- 20 Nov 1997, midnight DESCRIPTION "Initial version, published as RFC2274" ::= { snmpModules 15 } -- Administrative assignments **************************************** usmMIBObjects OBJECT IDENTIFIER ::= { snmpUsmMIB 1 } usmMIBConformance OBJECT IDENTIFIER ::= { snmpUsmMIB 2 } -- Identification of Authentication and Privacy Protocols ************ usmNoAuthProtocol OBJECT-IDENTITY STATUS current DESCRIPTION "No Authentication Protocol." ::= { snmpAuthProtocols 1 } usmHMACMD5AuthProtocol OBJECT-IDENTITY STATUS current DESCRIPTION "The HMAC-MD5-96 Digest Authentication Protocol." REFERENCE "- H. Krawczyk, M. Bellare, R. Canetti HMAC: Keyed-Hashing for Message Authentication, RFC2104, Feb 1997. - Rivest, R., Message Digest Algorithm MD5, RFC1321. " ::= { snmpAuthProtocols 2 } usmHMACSHAAuthProtocol OBJECT-IDENTITY STATUS current DESCRIPTION "The HMAC-SHA-96 Digest Authentication Protocol." REFERENCE "- H. Krawczyk, M. Bellare, R. Canetti, HMAC: Keyed-Hashing for Message Authentication, RFC2104, Feb 1997. - Secure Hash Algorithm. NIST FIPS 180-1. " ::= { snmpAuthProtocols 3 } usmNoPrivProtocol OBJECT-IDENTITY STATUS current DESCRIPTION "No Privacy Protocol." ::= { snmpPrivProtocols 1 } usmDESPrivProtocol OBJECT-IDENTITY STATUS current DESCRIPTION "The CBC-DES Symmetric Encryption Protocol." REFERENCE "- Data Encryption Standard, National Institute of Standards and Technology. Federal Information Processing Standard (FIPS) Publication 46-1. Blumenthal & Wijnen Standards Track [Page 34] RFC 3414 USM for SNMPv3 December 2002 Supersedes FIPS Publication 46, (January, 1977; reaffirmed January, 1988). - Data Encryption Algorithm, American National Standards Institute. ANSI X3.92-1981, (December, 1980). - DES Modes of Operation, National Institute of Standards and Technology. Federal Information Processing Standard (FIPS) Publication 81, (December, 1980). - Data Encryption Algorithm - Modes of Operation, American National Standards Institute. ANSI X3.106-1983, (May 1983). " ::= { snmpPrivProtocols 2 } -- Textual Conventions *********************************************** KeyChange ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "Every definition of an object with this syntax must identify a protocol P, a secret key K, and a hash algorithm H that produces output of L octets. The object's value is a manager-generated, partially-random value which, when modified, causes the value of the secret key K, to be modified via a one-way function. The value of an instance of this object is the concatenation of two components: first a 'random' component and then a 'delta' component. The lengths of the random and delta components are given by the corresponding value of the protocol P; if P requires K to be a fixed length, the length of both the random and delta components is that fixed length; if P allows the length of K to be variable up to a particular maximum length, the length of the random component is that maximum length and the length of the delta component is any length less than or equal to that maximum length. For example, usmHMACMD5AuthProtocol requires K to be a fixed length of 16 octets and L - of 16 octets. usmHMACSHAAuthProtocol requires K to be a fixed length of 20 octets and L - of 20 octets. Other protocols may define other sizes, as deemed appropriate. Blumenthal & Wijnen Standards Track [Page 35] RFC 3414 USM for SNMPv3 December 2002 When a requester wants to change the old key K to a new key keyNew on a remote entity, the 'random' component is obtained from either a true random generator, or from a pseudorandom generator, and the 'delta' component is computed as follows: - a temporary variable is initialized to the existing value of K; - if the length of the keyNew is greater than L octets, then: - the random component is appended to the value of the temporary variable, and the result is input to the the hash algorithm H to produce a digest value, and the temporary variable is set to this digest value; - the value of the temporary variable is XOR-ed with the first (next) L-octets (16 octets in case of MD5) of the keyNew to produce the first (next) L-octets (16 octets in case of MD5) of the 'delta' component. - the above two steps are repeated until the unused portion of the keyNew component is L octets or less, - the random component is appended to the value of the temporary variable, and the result is input to the hash algorithm H to produce a digest value; - this digest value, truncated if necessary to be the same length as the unused portion of the keyNew, is XOR-ed with the unused portion of the keyNew to produce the (final portion of the) 'delta' component. For example, using MD5 as the hash algorithm H: iterations = (lenOfDelta - 1)/16; /* integer division */ temp = keyOld; for (i = 0; i < iterations; i++) { temp = MD5 (temp || random); delta[i*16 .. (i*16)+15] = temp XOR keyNew[i*16 .. (i*16)+15]; } temp = MD5 (temp || random); delta[i*16 .. lenOfDelta-1] = temp XOR keyNew[i*16 .. lenOfDelta-1]; The 'random' and 'delta' components are then concatenated as described above, and the resulting octet string is sent to the recipient as the new value of an instance of this object. At the receiver side, when an instance of this object is set to a new value, then a new value of K is computed as follows: Blumenthal & Wijnen Standards Track [Page 36] RFC 3414 USM for SNMPv3 December 2002 - a temporary variable is initialized to the existing value of K; - if the length of the delta component is greater than L octets, then: - the random component is appended to the value of the temporary variable, and the result is input to the hash algorithm H to produce a digest value, and the temporary variable is set to this digest value; - the value of the temporary variable is XOR-ed with the first (next) L-octets (16 octets in case of MD5) of the delta component to produce the first (next) L-octets (16 octets in case of MD5) of the new value of K. - the above two steps are repeated until the unused portion of the delta component is L octets or less, - the random component is appended to the value of the temporary variable, and the result is input to the hash algorithm H to produce a digest value; - this digest value, truncated if necessary to be the same length as the unused portion of the delta component, is XOR-ed with the unused portion of the delta component to produce the (final portion of the) new value of K. For example, using MD5 as the hash algorithm H: iterations = (lenOfDelta - 1)/16; /* integer division */ temp = keyOld; for (i = 0; i < iterations; i++) { temp = MD5 (temp || random); keyNew[i*16 .. (i*16)+15] = temp XOR delta[i*16 .. (i*16)+15]; } temp = MD5 (temp || random); keyNew[i*16 .. lenOfDelta-1] = temp XOR delta[i*16 .. lenOfDelta-1]; The value of an object with this syntax, whenever it is retrieved by the management protocol, is always the zero length string. Note that the keyOld and keyNew are the localized keys. Note that it is probably wise that when an SNMP entity sends a SetRequest to change a key, that it keeps a copy of the old key until it has confirmed that the key change actually succeeded. " SYNTAX OCTET STRING Blumenthal & Wijnen Standards Track [Page 37] RFC 3414 USM for SNMPv3 December 2002 -- Statistics for the User-based Security Model ********************** usmStats OBJECT IDENTIFIER ::= { usmMIBObjects 1 } usmStatsUnsupportedSecLevels OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because they requested a securityLevel that was unknown to the SNMP engine or otherwise unavailable. " ::= { usmStats 1 } usmStatsNotInTimeWindows OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because they appeared outside of the authoritative SNMP engine's window. " ::= { usmStats 2 } usmStatsUnknownUserNames OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because they referenced a user that was not known to the SNMP engine. " ::= { usmStats 3 } usmStatsUnknownEngineIDs OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because they referenced an snmpEngineID that was not known to the SNMP engine. " ::= { usmStats 4 } usmStatsWrongDigests OBJECT-TYPE Blumenthal & Wijnen Standards Track [Page 38] RFC 3414 USM for SNMPv3 December 2002 SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because they didn't contain the expected digest value. " ::= { usmStats 5 } usmStatsDecryptionErrors OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because they could not be decrypted. " ::= { usmStats 6 } -- The usmUser Group ************************************************ usmUser OBJECT IDENTIFIER ::= { usmMIBObjects 2 } usmUserSpinLock OBJECT-TYPE SYNTAX TestAndIncr MAX-ACCESS read-write STATUS current DESCRIPTION "An advisory lock used to allow several cooperating Command Generator Applications to coordinate their use of facilities to alter secrets in the usmUserTable. " ::= { usmUser 1 } -- The table of valid users for the User-based Security Model ******** usmUserTable OBJECT-TYPE SYNTAX SEQUENCE OF UsmUserEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "The table of users configured in the SNMP engine's Local Configuration Datastore (LCD). To create a new user (i.e., to instantiate a new conceptual row in this table), it is recommended to follow this procedure: 1) GET(usmUserSpinLock.0) and save in sValue. Blumenthal & Wijnen Standards Track [Page 39] RFC 3414 USM for SNMPv3 December 2002 2) SET(usmUserSpinLock.0=sValue, usmUserCloneFrom=templateUser, usmUserStatus=createAndWait) You should use a template user to clone from which has the proper auth/priv protocol defined. If the new user is to use privacy: 3) generate the keyChange value based on the secret privKey of the clone-from user and the secret key to be used for the new user. Let us call this pkcValue. 4) GET(usmUserSpinLock.0) and save in sValue. 5) SET(usmUserSpinLock.0=sValue, usmUserPrivKeyChange=pkcValue usmUserPublic=randomValue1) 6) GET(usmUserPulic) and check it has randomValue1. If not, repeat steps 4-6. If the new user will never use privacy: 7) SET(usmUserPrivProtocol=usmNoPrivProtocol) If the new user is to use authentication: 8) generate the keyChange value based on the secret authKey of the clone-from user and the secret key to be used for the new user. Let us call this akcValue. 9) GET(usmUserSpinLock.0) and save in sValue. 10) SET(usmUserSpinLock.0=sValue, usmUserAuthKeyChange=akcValue usmUserPublic=randomValue2) 11) GET(usmUserPulic) and check it has randomValue2. If not, repeat steps 9-11. If the new user will never use authentication: 12) SET(usmUserAuthProtocol=usmNoAuthProtocol) Finally, activate the new user: 13) SET(usmUserStatus=active) The new user should now be available and ready to be used for SNMPv3 communication. Note however that access to MIB data must be provided via configuration of the SNMP-VIEW-BASED-ACM-MIB. Blumenthal & Wijnen Standards Track [Page 40] RFC 3414 USM for SNMPv3 December 2002 The use of usmUserSpinlock is to avoid conflicts with another SNMP command generator application which may also be acting on the usmUserTable. " ::= { usmUser 2 } usmUserEntry OBJECT-TYPE SYNTAX UsmUserEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A user configured in the SNMP engine's Local Configuration Datastore (LCD) for the User-based Security Model. " INDEX { usmUserEngineID, usmUserName } ::= { usmUserTable 1 } UsmUserEntry ::= SEQUENCE { usmUserEngineID SnmpEngineID, usmUserName SnmpAdminString, usmUserSecurityName SnmpAdminString, usmUserCloneFrom RowPointer, usmUserAuthProtocol AutonomousType, usmUserAuthKeyChange KeyChange, usmUserOwnAuthKeyChange KeyChange, usmUserPrivProtocol AutonomousType, usmUserPrivKeyChange KeyChange, usmUserOwnPrivKeyChange KeyChange, usmUserPublic OCTET STRING, usmUserStorageType StorageType, usmUserStatus RowStatus } usmUserEngineID OBJECT-TYPE SYNTAX SnmpEngineID MAX-ACCESS not-accessible STATUS current DESCRIPTION "An SNMP engine's administratively-unique identifier. In a simple agent, this value is always that agent's own snmpEngineID value. The value can also take the value of the snmpEngineID of a remote SNMP engine with which this user can communicate. Blumenthal & Wijnen Standards Track [Page 41] RFC 3414 USM for SNMPv3 December 2002 " ::= { usmUserEntry 1 } usmUserName OBJECT-TYPE SYNTAX SnmpAdminString (SIZE(1..32)) MAX-ACCESS not-accessible STATUS current DESCRIPTION "A human readable string representing the name of the user. This is the (User-based Security) Model dependent security ID. " ::= { usmUserEntry 2 } usmUserSecurityName OBJECT-TYPE SYNTAX SnmpAdminString MAX-ACCESS read-only STATUS current DESCRIPTION "A human readable string representing the user in Security Model independent format. The default transformation of the User-based Security Model dependent security ID to the securityName and vice versa is the identity function so that the securityName is the same as the userName. " ::= { usmUserEntry 3 } usmUserCloneFrom OBJECT-TYPE SYNTAX RowPointer MAX-ACCESS read-create STATUS current DESCRIPTION "A pointer to another conceptual row in this usmUserTable. The user in this other conceptual row is called the clone-from user. When a new user is created (i.e., a new conceptual row is instantiated in this table), the privacy and authentication parameters of the new user must be cloned from its clone-from user. These parameters are: - authentication protocol (usmUserAuthProtocol) - privacy protocol (usmUserPrivProtocol) They will be copied regardless of what the current value is. Cloning also causes the initial values of the secret authentication key (authKey) and the secret encryption Blumenthal & Wijnen Standards Track [Page 42] RFC 3414 USM for SNMPv3 December 2002 key (privKey) of the new user to be set to the same values as the corresponding secrets of the clone-from user to allow the KeyChange process to occur as required during user creation. The first time an instance of this object is set by a management operation (either at or after its instantiation), the cloning process is invoked. Subsequent writes are successful but invoke no action to be taken by the receiver. The cloning process fails with an 'inconsistentName' error if the conceptual row representing the clone-from user does not exist or is not in an active state when the cloning process is invoked. When this object is read, the ZeroDotZero OID is returned. " ::= { usmUserEntry 4 } usmUserAuthProtocol OBJECT-TYPE SYNTAX AutonomousType MAX-ACCESS read-create STATUS current DESCRIPTION "An indication of whether messages sent on behalf of this user to/from the SNMP engine identified by usmUserEngineID, can be authenticated, and if so, the type of authentication protocol which is used. An instance of this object is created concurrently with the creation of any other object instance for the same user (i.e., as part of the processing of the set operation which creates the first object instance in the same conceptual row). If an initial set operation (i.e. at row creation time) tries to set a value for an unknown or unsupported protocol, then a 'wrongValue' error must be returned. The value will be overwritten/set when a set operation is performed on the corresponding instance of usmUserCloneFrom. Once instantiated, the value of such an instance of this object can only be changed via a set operation to the value of the usmNoAuthProtocol. If a set operation tries to change the value of an Blumenthal & Wijnen Standards Track [Page 43] RFC 3414 USM for SNMPv3 December 2002 existing instance of this object to any value other than usmNoAuthProtocol, then an 'inconsistentValue' error must be returned. If a set operation tries to set the value to the usmNoAuthProtocol while the usmUserPrivProtocol value in the same row is not equal to usmNoPrivProtocol, then an 'inconsistentValue' error must be returned. That means that an SNMP command generator application must first ensure that the usmUserPrivProtocol is set to the usmNoPrivProtocol value before it can set the usmUserAuthProtocol value to usmNoAuthProtocol. " DEFVAL { usmNoAuthProtocol } ::= { usmUserEntry 5 } usmUserAuthKeyChange OBJECT-TYPE SYNTAX KeyChange -- typically (SIZE (0 | 32)) for HMACMD5 -- typically (SIZE (0 | 40)) for HMACSHA MAX-ACCESS read-create STATUS current DESCRIPTION "An object, which when modified, causes the secret authentication key used for messages sent on behalf of this user to/from the SNMP engine identified by usmUserEngineID, to be modified via a one-way function. The associated protocol is the usmUserAuthProtocol. The associated secret key is the user's secret authentication key (authKey). The associated hash algorithm is the algorithm used by the user's usmUserAuthProtocol. When creating a new user, it is an 'inconsistentName' error for a set operation to refer to this object unless it is previously or concurrently initialized through a set operation on the corresponding instance of usmUserCloneFrom. When the value of the corresponding usmUserAuthProtocol is usmNoAuthProtocol, then a set is successful, but effectively is a no-op. When this object is read, the zero-length (empty) string is returned. The recommended way to do a key change is as follows: Blumenthal & Wijnen Standards Track [Page 44] RFC 3414 USM for SNMPv3 December 2002 1) GET(usmUserSpinLock.0) and save in sValue. 2) generate the keyChange value based on the old (existing) secret key and the new secret key, let us call this kcValue. If you do the key change on behalf of another user: 3) SET(usmUserSpinLock.0=sValue, usmUserAuthKeyChange=kcValue usmUserPublic=randomValue) If you do the key change for yourself: 4) SET(usmUserSpinLock.0=sValue, usmUserOwnAuthKeyChange=kcValue usmUserPublic=randomValue) If you get a response with error-status of noError, then the SET succeeded and the new key is active. If you do not get a response, then you can issue a GET(usmUserPublic) and check if the value is equal to the randomValue you did send in the SET. If so, then the key change succeeded and the new key is active (probably the response got lost). If not, then the SET request probably never reached the target and so you can start over with the procedure above. " DEFVAL { ''H } -- the empty string ::= { usmUserEntry 6 } usmUserOwnAuthKeyChange OBJECT-TYPE SYNTAX KeyChange -- typically (SIZE (0 | 32)) for HMACMD5 -- typically (SIZE (0 | 40)) for HMACSHA MAX-ACCESS read-create STATUS current DESCRIPTION "Behaves exactly as usmUserAuthKeyChange, with one notable difference: in order for the set operation to succeed, the usmUserName of the operation requester must match the usmUserName that indexes the row which is targeted by this operation. In addition, the USM security model must be used for this operation. The idea here is that access to this column can be public, since it will only allow a user to change his own secret authentication key (authKey). Note that this can only be done once the row is active. Blumenthal & Wijnen Standards Track [Page 45] RFC 3414 USM for SNMPv3 December 2002 When a set is received and the usmUserName of the requester is not the same as the umsUserName that indexes the row which is targeted by this operation, then a 'noAccess' error must be returned. When a set is received and the security model in use is not USM, then a 'noAccess' error must be returned. " DEFVAL { ''H } -- the empty string ::= { usmUserEntry 7 } usmUserPrivProtocol OBJECT-TYPE SYNTAX AutonomousType MAX-ACCESS read-create STATUS current DESCRIPTION "An indication of whether messages sent on behalf of this user to/from the SNMP engine identified by usmUserEngineID, can be protected from disclosure, and if so, the type of privacy protocol which is used. An instance of this object is created concurrently with the creation of any other object instance for the same user (i.e., as part of the processing of the set operation which creates the first object instance in the same conceptual row). If an initial set operation (i.e. at row creation time) tries to set a value for an unknown or unsupported protocol, then a 'wrongValue' error must be returned. The value will be overwritten/set when a set operation is performed on the corresponding instance of usmUserCloneFrom. Once instantiated, the value of such an instance of this object can only be changed via a set operation to the value of the usmNoPrivProtocol. If a set operation tries to change the value of an existing instance of this object to any value other than usmNoPrivProtocol, then an 'inconsistentValue' error must be returned. Note that if any privacy protocol is used, then you must also use an authentication protocol. In other words, if usmUserPrivProtocol is set to anything else than usmNoPrivProtocol, then the corresponding instance of usmUserAuthProtocol cannot have a value of Blumenthal & Wijnen Standards Track [Page 46] RFC 3414 USM for SNMPv3 December 2002 usmNoAuthProtocol. If it does, then an 'inconsistentValue' error must be returned. " DEFVAL { usmNoPrivProtocol } ::= { usmUserEntry 8 } usmUserPrivKeyChange OBJECT-TYPE SYNTAX KeyChange -- typically (SIZE (0 | 32)) for DES MAX-ACCESS read-create STATUS current DESCRIPTION "An object, which when modified, causes the secret encryption key used for messages sent on behalf of this user to/from the SNMP engine identified by usmUserEngineID, to be modified via a one-way function. The associated protocol is the usmUserPrivProtocol. The associated secret key is the user's secret privacy key (privKey). The associated hash algorithm is the algorithm used by the user's usmUserAuthProtocol. When creating a new user, it is an 'inconsistentName' error for a set operation to refer to this object unless it is previously or concurrently initialized through a set operation on the corresponding instance of usmUserCloneFrom. When the value of the corresponding usmUserPrivProtocol is usmNoPrivProtocol, then a set is successful, but effectively is a no-op. When this object is read, the zero-length (empty) string is returned. See the description clause of usmUserAuthKeyChange for a recommended procedure to do a key change. " DEFVAL { ''H } -- the empty string ::= { usmUserEntry 9 } usmUserOwnPrivKeyChange OBJECT-TYPE SYNTAX KeyChange -- typically (SIZE (0 | 32)) for DES MAX-ACCESS read-create STATUS current DESCRIPTION "Behaves exactly as usmUserPrivKeyChange, with one notable difference: in order for the Set operation to succeed, the usmUserName of the operation requester must match the usmUserName that indexes Blumenthal & Wijnen Standards Track [Page 47] RFC 3414 USM for SNMPv3 December 2002 the row which is targeted by this operation. In addition, the USM security model must be used for this operation. The idea here is that access to this column can be public, since it will only allow a user to change his own secret privacy key (privKey). Note that this can only be done once the row is active. When a set is received and the usmUserName of the requester is not the same as the umsUserName that indexes the row which is targeted by this operation, then a 'noAccess' error must be returned. When a set is received and the security model in use is not USM, then a 'noAccess' error must be returned. " DEFVAL { ''H } -- the empty string ::= { usmUserEntry 10 } usmUserPublic OBJECT-TYPE SYNTAX OCTET STRING (SIZE(0..32)) MAX-ACCESS read-create STATUS current DESCRIPTION "A publicly-readable value which can be written as part of the procedure for changing a user's secret authentication and/or privacy key, and later read to determine whether the change of the secret was effected. " DEFVAL { ''H } -- the empty string ::= { usmUserEntry 11 } usmUserStorageType OBJECT-TYPE SYNTAX StorageType MAX-ACCESS read-create STATUS current DESCRIPTION "The storage type for this conceptual row. Conceptual rows having the value 'permanent' must allow write-access at a minimum to: - usmUserAuthKeyChange, usmUserOwnAuthKeyChange and usmUserPublic for a user who employs authentication, and - usmUserPrivKeyChange, usmUserOwnPrivKeyChange and usmUserPublic for a user who employs privacy. Blumenthal & Wijnen Standards Track [Page 48] RFC 3414 USM for SNMPv3 December 2002 Note that any user who employs authentication or privacy must allow its secret(s) to be updated and thus cannot be 'readOnly'. If an initial set operation tries to set the value to 'readOnly' for a user who employs authentication or privacy, then an 'inconsistentValue' error must be returned. Note that if the value has been previously set (implicit or explicit) to any value, then the rules as defined in the StorageType Textual Convention apply. It is an implementation issue to decide if a SET for a readOnly or permanent row is accepted at all. In some contexts this may make sense, in others it may not. If a SET for a readOnly or permanent row is not accepted at all, then a 'wrongValue' error must be returned. " DEFVAL { nonVolatile } ::= { usmUserEntry 12 } usmUserStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The status of this conceptual row. Until instances of all corresponding columns are appropriately configured, the value of the corresponding instance of the usmUserStatus column is 'notReady'. In particular, a newly created row for a user who employs authentication, cannot be made active until the corresponding usmUserCloneFrom and usmUserAuthKeyChange have been set. Further, a newly created row for a user who also employs privacy, cannot be made active until the usmUserPrivKeyChange has been set. The RowStatus TC [RFC2579] requires that this DESCRIPTION clause states under which circumstances other objects in this row can be modified: The value of this object has no effect on whether other objects in this conceptual row can be modified, except for usmUserOwnAuthKeyChange and usmUserOwnPrivKeyChange. For these 2 objects, the Blumenthal & Wijnen Standards Track [Page 49] RFC 3414 USM for SNMPv3 December 2002 value of usmUserStatus MUST be active. " ::= { usmUserEntry 13 } -- Conformance Information ******************************************* usmMIBCompliances OBJECT IDENTIFIER ::= { usmMIBConformance 1 } usmMIBGroups OBJECT IDENTIFIER ::= { usmMIBConformance 2 } -- Compliance statements usmMIBCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for SNMP engines which implement the SNMP-USER-BASED-SM-MIB. " MODULE -- this module MANDATORY-GROUPS { usmMIBBasicGroup } OBJECT usmUserAuthProtocol MIN-ACCESS read-only DESCRIPTION "Write access is not required." OBJECT usmUserPrivProtocol MIN-ACCESS read-only DESCRIPTION "Write access is not required." ::= { usmMIBCompliances 1 } -- Units of compliance usmMIBBasicGroup OBJECT-GROUP OBJECTS { usmStatsUnsupportedSecLevels, usmStatsNotInTimeWindows, usmStatsUnknownUserNames, usmStatsUnknownEngineIDs, usmStatsWrongDigests, usmStatsDecryptionErrors, usmUserSpinLock, usmUserSecurityName, usmUserCloneFrom, usmUserAuthProtocol, usmUserAuthKeyChange, usmUserOwnAuthKeyChange, usmUserPrivProtocol, usmUserPrivKeyChange, usmUserOwnPrivKeyChange, Blumenthal & Wijnen Standards Track [Page 50] RFC 3414 USM for SNMPv3 December 2002 usmUserPublic, usmUserStorageType, usmUserStatus } STATUS current DESCRIPTION "A collection of objects providing for configuration of an SNMP engine which implements the SNMP User-based Security Model. " ::= { usmMIBGroups 1 } END 6. HMAC-MD5-96 Authentication Protocol This section describes the HMAC-MD5-96 authentication protocol. This authentication protocol is the first defined for the User-based Security Model. It uses MD5 hash-function which is described in [RFC1321], in HMAC mode described in [RFC2104], truncating the output to 96 bits. This protocol is identified by usmHMACMD5AuthProtocol. Over time, other authentication protocols may be defined either as a replacement of this protocol or in addition to this protocol. 6.1. Mechanisms - In support of data integrity, a message digest algorithm is required. A digest is calculated over an appropriate portion of an SNMP message and included as part of the message sent to the recipient. - In support of data origin authentication and data integrity, a secret value is prepended to SNMP message prior to computing the digest; the calculated digest is partially inserted into the SNMP message prior to transmission, and the prepended value is not transmitted. The secret value is shared by all SNMP engines authorized to originate messages on behalf of the appropriate user. 6.1.1. Digest Authentication Mechanism The Digest Authentication Mechanism defined in this memo provides for: - verification of the integrity of a received message, i.e., the message received is the message sent. Blumenthal & Wijnen Standards Track [Page 51] RFC 3414 USM for SNMPv3 December 2002 The integrity of the message is protected by computing a digest over an appropriate portion of the message. The digest is computed by the originator of the message, transmitted with the message, and verified by the recipient of the message. - verification of the user on whose behalf the message was generated. A secret value known only to SNMP engines authorized to generate messages on behalf of a user is used in HMAC mode (see [RFC2104]). It also recommends the hash-function output used as Message Authentication Code, to be truncated. This protocol uses the MD5 [RFC1321] message digest algorithm. A 128-bit MD5 digest is calculated in a special (HMAC) way over the designated portion of an SNMP message and the first 96 bits of this digest is included as part of the message sent to the recipient. The size of the digest carried in a message is 12 octets. The size of the private authentication key (the secret) is 16 octets. For the details see section 6.3. 6.2. Elements of the Digest Authentication Protocol This section contains definitions required to realize the authentication module defined in this section of this memo. 6.2.1. Users Authentication using this authentication protocol makes use of a defined set of userNames. For any user on whose behalf a message must be authenticated at a particular SNMP engine, that SNMP engine must have knowledge of that user. An SNMP engine that wishes to communicate with another SNMP engine must also have knowledge of a user known to that engine, including knowledge of the applicable attributes of that user. A user and its attributes are defined as follows: A string representing the name of the user. A user's secret key to be used when calculating a digest. It MUST be 16 octets long for MD5. Blumenthal & Wijnen Standards Track [Page 52] RFC 3414 USM for SNMPv3 December 2002 6.2.2. msgAuthoritativeEngineID The msgAuthoritativeEngineID value contained in an authenticated message specifies the authoritative SNMP engine for that particular message (see the definition of SnmpEngineID in the SNMP Architecture document [RFC3411]). The user's (private) authentication key is normally different at each authoritative SNMP engine and so the snmpEngineID is used to select the proper key for the authentication process. 6.2.3. SNMP Messages Using this Authentication Protocol Messages using this authentication protocol carry a msgAuthenticationParameters field as part of the msgSecurityParameters. For this protocol, the msgAuthenticationParameters field is the serialized OCTET STRING representing the first 12 octets of the HMAC-MD5-96 output done over the wholeMsg. The digest is calculated over the wholeMsg so if a message is authenticated, that also means that all the fields in the message are intact and have not been tampered with. 6.2.4. Services provided by the HMAC-MD5-96 Authentication Module This section describes the inputs and outputs that the HMAC-MD5-96 Authentication module expects and produces when the User-based Security module calls the HMAC-MD5-96 Authentication module for services. 6.2.4.1. Services for Generating an Outgoing SNMP Message The HMAC-MD5-96 authentication protocol assumes that the selection of the authKey is done by the caller and that the caller passes the secret key to be used. Upon completion the authentication module returns statusInformation and, if the message digest was correctly calculated, the wholeMsg with the digest inserted at the proper place. The abstract service primitive is: statusInformation = -- success or failure authenticateOutgoingMsg( IN authKey -- secret key for authentication IN wholeMsg -- unauthenticated complete message OUT authenticatedWholeMsg -- complete authenticated message ) Blumenthal & Wijnen Standards Track [Page 53] RFC 3414 USM for SNMPv3 December 2002 The abstract data elements are: statusInformation An indication of whether the authentication process was successful. If not it is an indication of the problem. authKey The secret key to be used by the authentication algorithm. The length of this key MUST be 16 octets. wholeMsg The message to be authenticated. authenticatedWholeMsg The authenticated message (including inserted digest) on output. Note, that authParameters field is filled by the authentication module and this module and this field should be already present in the wholeMsg before the Message Authentication Code (MAC) is generated. 6.2.4.2. Services for Processing an Incoming SNMP Message The HMAC-MD5-96 authentication protocol assumes that the selection of the authKey is done by the caller and that the caller passes the secret key to be used. Upon completion the authentication module returns statusInformation and, if the message digest was correctly calculated, the wholeMsg as it was processed. The abstract service primitive is: statusInformation = -- success or failure authenticateIncomingMsg( IN authKey -- secret key for authentication IN authParameters -- as received on the wire IN wholeMsg -- as received on the wire OUT authenticatedWholeMsg -- complete authenticated message ) The abstract data elements are: statusInformation An indication of whether the authentication process was successful. If not it is an indication of the problem. authKey The secret key to be used by the authentication algorithm. The length of this key MUST be 16 octets. Blumenthal & Wijnen Standards Track [Page 54] RFC 3414 USM for SNMPv3 December 2002 authParameters The authParameters from the incoming message. wholeMsg The message to be authenticated on input and the authenticated message on output. authenticatedWholeMsg The whole message after the authentication check is complete. 6.3. Elements of Procedure This section describes the procedures for the HMAC-MD5-96 authentication protocol. 6.3.1. Processing an Outgoing Message This section describes the procedure followed by an SNMP engine whenever it must authenticate an outgoing message using the usmHMACMD5AuthProtocol. 1) The msgAuthenticationParameters field is set to the serialization, according to the rules in [RFC3417], of an OCTET STRING containing 12 zero octets. 2) From the secret authKey, two keys K1 and K2 are derived: a) extend the authKey to 64 octets by appending 48 zero octets; save it as extendedAuthKey b) obtain IPAD by replicating the octet 0x36 64 times; c) obtain K1 by XORing extendedAuthKey with IPAD; d) obtain OPAD by replicating the octet 0x5C 64 times; e) obtain K2 by XORing extendedAuthKey with OPAD. 3) Prepend K1 to the wholeMsg and calculate MD5 digest over it according to [RFC1321]. 4) Prepend K2 to the result of the step 4 and calculate MD5 digest over it according to [RFC1321]. Take the first 12 octets of the final digest - this is Message Authentication Code (MAC). 5) Replace the msgAuthenticationParameters field with MAC obtained in the step 4. Blumenthal & Wijnen Standards Track [Page 55] RFC 3414 USM for SNMPv3 December 2002 6) The authenticatedWholeMsg is then returned to the caller together with statusInformation indicating success. 6.3.2. Processing an Incoming Message This section describes the procedure followed by an SNMP engine whenever it must authenticate an incoming message using the usmHMACMD5AuthProtocol. 1) If the digest received in the msgAuthenticationParameters field is not 12 octets long, then an failure and an errorIndication (authenticationError) is returned to the calling module. 2) The MAC received in the msgAuthenticationParameters field is saved. 3) The digest in the msgAuthenticationParameters field is replaced by the 12 zero octets. 4) From the secret authKey, two keys K1 and K2 are derived: a) extend the authKey to 64 octets by appending 48 zero octets; save it as extendedAuthKey b) obtain IPAD by replicating the octet 0x36 64 times; c) obtain K1 by XORing extendedAuthKey with IPAD; d) obtain OPAD by replicating the octet 0x5C 64 times; e) obtain K2 by XORing extendedAuthKey with OPAD. 5) The MAC is calculated over the wholeMsg: a) prepend K1 to the wholeMsg and calculate the MD5 digest over it; b) prepend K2 to the result of step 5.a and calculate the MD5 digest over it; c) first 12 octets of the result of step 5.b is the MAC. The msgAuthenticationParameters field is replaced with the MAC value that was saved in step 2. Blumenthal & Wijnen Standards Track [Page 56] RFC 3414 USM for SNMPv3 December 2002 6) Then the newly calculated MAC is compared with the MAC saved in step 2. If they do not match, then an failure and an errorIndication (authenticationFailure) is returned to the calling module. 7) The authenticatedWholeMsg and statusInformation indicating success are then returned to the caller. 7. HMAC-SHA-96 Authentication Protocol This section describes the HMAC-SHA-96 authentication protocol. This protocol uses the SHA hash-function which is described in [SHA-NIST], in HMAC mode described in [RFC2104], truncating the output to 96 bits. This protocol is identified by usmHMACSHAAuthProtocol. Over time, other authentication protocols may be defined either as a replacement of this protocol or in addition to this protocol. 7.1. Mechanisms - In support of data integrity, a message digest algorithm is required. A digest is calculated over an appropriate portion of an SNMP message and included as part of the message sent to the recipient. - In support of data origin authentication and data integrity, a secret value is prepended to the SNMP message prior to computing the digest; the calculated digest is then partially inserted into the message prior to transmission. The prepended secret is not transmitted. The secret value is shared by all SNMP engines authorized to originate messages on behalf of the appropriate user. 7.1.1. Digest Authentication Mechanism The Digest Authentication Mechanism defined in this memo provides for: - verification of the integrity of a received message, i.e., the message received is the message sent. The integrity of the message is protected by computing a digest over an appropriate portion of the message. The digest is computed by the originator of the message, transmitted with the message, and verified by the recipient of the message. Blumenthal & Wijnen Standards Track [Page 57] RFC 3414 USM for SNMPv3 December 2002 - verification of the user on whose behalf the message was generated. A secret value known only to SNMP engines authorized to generate messages on behalf of a user is used in HMAC mode (see [RFC2104]). It also recommends the hash-function output used as Message Authentication Code, to be truncated. This mechanism uses the SHA [SHA-NIST] message digest algorithm. A 160-bit SHA digest is calculated in a special (HMAC) way over the designated portion of an SNMP message and the first 96 bits of this digest is included as part of the message sent to the recipient. The size of the digest carried in a message is 12 octets. The size of the private authentication key (the secret) is 20 octets. For the details see section 7.3. 7.2. Elements of the HMAC-SHA-96 Authentication Protocol This section contains definitions required to realize the authentication module defined in this section of this memo. 7.2.1. Users Authentication using this authentication protocol makes use of a defined set of userNames. For any user on whose behalf a message must be authenticated at a particular SNMP engine, that SNMP engine must have knowledge of that user. An SNMP engine that wishes to communicate with another SNMP engine must also have knowledge of a user known to that engine, including knowledge of the applicable attributes of that user. A user and its attributes are defined as follows: A string representing the name of the user. A user's secret key to be used when calculating a digest. It MUST be 20 octets long for SHA. 7.2.2. msgAuthoritativeEngineID The msgAuthoritativeEngineID value contained in an authenticated message specifies the authoritative SNMP engine for that particular message (see the definition of SnmpEngineID in the SNMP Architecture document [RFC3411]). The user's (private) authentication key is normally different at each authoritative SNMP engine and so the snmpEngineID is used to select the proper key for the authentication process. Blumenthal & Wijnen Standards Track [Page 58] RFC 3414 USM for SNMPv3 December 2002 7.2.3. SNMP Messages Using this Authentication Protocol Messages using this authentication protocol carry a msgAuthenticationParameters field as part of the msgSecurityParameters. For this protocol, the msgAuthenticationParameters field is the serialized OCTET STRING representing the first 12 octets of HMAC-SHA-96 output done over the wholeMsg. The digest is calculated over the wholeMsg so if a message is authenticated, that also means that all the fields in the message are intact and have not been tampered with. 7.2.4. Services Provided by the HMAC-SHA-96 Authentication Module This section describes the inputs and outputs that the HMAC-SHA-96 Authentication module expects and produces when the User-based Security module calls the HMAC-SHA-96 Authentication module for services. 7.2.4.1. Services for Generating an Outgoing SNMP Message HMAC-SHA-96 authentication protocol assumes that the selection of the authKey is done by the caller and that the caller passes the secret key to be used. Upon comple