WDIFF

draft-ietf-isms-tmsm-12.txt --> draft-ietf-isms-tmsm-13.txt

Network Working Group D. Harrington
Internet-Draft Huawei Technologies (USA)
Updates: 3411,3412,3414,3417 J. Schoenwaelder
(if approved) Jacobs University Bremen
Intended status: Standards Track February 25, August 27, 2008
Expires: August February 28, 2008 2009

Transport Subsystem for the Simple Network Management Protocol (SNMP)
draft-ietf-isms-tmsm-12
draft-ietf-isms-tmsm-13

Status of This Memo

By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

This Internet-Draft will expire on August February 28, 2008.

Abstract

This document defines a Transport Subsystem, extending the Simple
Network Management Protocol (SNMP) architecture defined in RFC 3411.
This document defines a subsystem to contain Transport Models,
comparable to other subsystems in the RFC3411 architecture. As work
is being done to expand the transport transports to include secure transport transports
such as SSH and TLS, using a subsystem will enable consistent design

Harrington & Schoenwaelder Expires August 28, 2008 [Page 1]

Internet-Draft SNMP Transport Subsystem February 2008
and modularity of such Transport Models. This document identifies
and describes some key aspects that need to be considered for any
Transport Model for SNMP.

Harrington & Schoenwaelder Expires February 28, 2009 [Page 1]

Internet-Draft SNMP Transport Subsystem August 2008

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 4
1.1. The Internet-Standard Management Framework . . . . . . . . 3 4
1.2. Where this Extension Fits Conventions . . . . . . . . . . . . . . . . 3
1.3. Conventions . . . . . . . 4
1.3. Where this Extension Fits . . . . . . . . . . . . . . . . 5 4
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6
3. Requirements of a Transport Model . . . . . . . . . . . . . . 7 8
3.1. Message Security Requirements . . . . . . . . . . . . . . 7 8
3.1.1. Security Protocol Requirements . . . . . . . . . . . . 7 8
3.2. SNMP Requirements . . . . . . . . . . . . . . . . . . . . 8
3.2.1. Architectural Modularity Requirements . . . . . . . . 8 9
3.2.2. Access Control Requirements . . . . . . . . . . . . . 11 12
3.2.3. Security Parameter Passing Requirements . . . . . . . 12
3.2.4. Separation of Authentication and Authorization . . . . 13
3.3. Session Requirements . . . . . . . . . . . . . . . . . . . 14
3.3.1. Session Establishment Requirements Selection . . . . . . . . . . . . . . . . . . 14
3.3.2. Session Establishment Requirements . . . . . . . . . . 15
3.3.3. Session Maintenance Requirements . . . . . . . . . . . 15
3.3.3.
3.3.4. Message security versus session security . . . . . . . 16
4. Scenario Diagrams and the Transport Subsystem . . . . . . . . 17
5. Cached Information and References . . . . . . . . . . . . . . 17
5.1. securityStateReference . . . . . . . . . . . . . . . . . . 18
5.2. tmStateReference . . . . . . . . . . . . . . . . . . . . . 18
6. Abstract Service Interfaces .
5.2.1. Transport information . . . . . . . . . . . . . . . . 19
6.1. sendMessage ASI 18
5.2.2. securityName . . . . . . . . . . . . . . . . . . . . . 19
6.2. Other Outgoing ASIs . .
5.2.3. securityLevel . . . . . . . . . . . . . . . . . 20
6.3. The receiveMessage ASI . . . 20
5.2.4. Session Information . . . . . . . . . . . . . . . 22
6.4. Other Incoming ASIs . . 20
6. Abstract Service Interfaces . . . . . . . . . . . . . . . . . 22
7. Security Considerations 20
6.1. sendMessage ASI . . . . . . . . . . . . . . . . . . . 24
7.1. Coexistence, Security Parameters, and Access Control . . 21
6.2. Changes to RFC3411 Outgoing ASIs . 25
8. IANA Considerations . . . . . . . . . . . . 22
6.2.1. Message Processing Subsystem Primitives . . . . . . . 22
6.2.2. Security Subsystem Primitives . . 26
9. Acknowledgments . . . . . . . . . . 23
6.3. The receiveMessage ASI . . . . . . . . . . . . . 26
10. References . . . . . 25
6.4. Changes to RFC3411 Incoming ASIs . . . . . . . . . . . . . 26
6.4.1. Message Processing Subsystem Primitive . . . . . . . . 26
10.1. Normative References
6.4.2. Security Subsystem Primitive . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . 26
10.2. Informative References . . . . . . . . . . . . . 28
7.1. Coexistence, Security Parameters, and Access Control . . . 29
8. IANA Considerations . . 27
Appendix A. Why tmStateReference? . . . . . . . . . . . . . . . . 28
A.1. Define an Abstract Service Interface . . . 30
9. Acknowledgments . . . . . . . . 28
A.2. Using an Encapsulating Header . . . . . . . . . . . . . . 29
A.3. Modifying Existing Fields in an SNMP Message . 30
10. References . . . . . . 29
A.4. Using a Cache . . . . . . . . . . . . . . . . . . . . 30
10.1. Normative References . . 29 . . . . . . . . . . . . . . . . . 30
10.2. Informative References . . . . . . . . . . . . . . . . . . 31
Appendix A. Why tmStateReference? . . . . . . . . . . . . . . . . 32
A.1. Define an Abstract Service Interface . . . . . . . . . . . 33
A.2. Using an Encapsulating Header . . . . . . . . . . . . . . 33
A.3. Modifying Existing Fields in an SNMP Message . . . . . . . 33

Harrington & Schoenwaelder Expires February 28, 2009 [Page 2]

Internet-Draft SNMP Transport Subsystem August 2008

A.4. Using a Cache . . . . . . . . . . . . . . . . . . . . . . 34
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . . 30 34
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 30 34

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 2] 3]

Internet-Draft SNMP Transport Subsystem February August 2008

1. Introduction

This document defines a Transport Subsystem, extending the Simple
Network Management Protocol (SNMP) architecture defined in [RFC3411].
This document identifies and describes some key aspects that need to
be considered for any Transport Model for SNMP.

1.1. The Internet-Standard Management Framework

For a detailed overview of the documents that describe the current
Internet-Standard Management Framework, please refer to section 7 of
RFC 3410 [RFC3410].

1.2. Where this Extension Fits

It is expected that readers of Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document will have read RFC3410
and RFC3411, and have a general understanding are to be interpreted as described in RFC 2119 [RFC2119].

Non uppercased versions of the functionality
defined keywords should be read as in RFCs 3412-3418.

The "Transport Subsystem" is an additional component for the SNMP
Engine depicted normal
English. They will usually, but not always, be used in RFC3411, section 3.1.

Harrington & Schoenwaelder Expires August a context
relating to compatibility with the RFC3411 architecture or the
subsystem defined here, but which might have no impact on on-the-wire
compatibility. These terms are used as guidance for designers of
proposed IETF models to make the designs compatible with RFC3411
subsystems and Abstract Service Interfaces (see section 3.2).
Implementers are free to implement differently. Some usages of these
lowercase terms are simply normal English usage.

For consistency with SNMP-related specifications, this document
favors terminology as defined in STD62 rather than favoring
terminology that is consistent with non-SNMP specifications that use
different variations of the same terminology. This is consistent
with the IESG decision to not require the SNMPv3 terminology be
modified to match the usage of other non-SNMP specifications when
SNMPv3 was advanced to Full Standard.

1.3. Where this Extension Fits

It is expected that readers of this document will have read RFC3410
and RFC3411, and have a general understanding of the functionality
defined in RFCs 3412-3418.

The "Transport Subsystem" is an additional component for the SNMP
Engine depicted in RFC3411, section 3.1.

Harrington & Schoenwaelder Expires February 28, 2008 2009 [Page 3] 4]

Internet-Draft SNMP Transport Subsystem February August 2008

The following diagram depicts its place in the RFC3411 architecture.:

The transport mappings defined in RFC3417 do not provide lower-layer
security functionality, and thus do not provide transport-specific
security parameters. This document updates RFC3411 and RFC3417 by
defining an architectural extension and modifying the ASIs that
transport mappings
(models) (hereafter called transport models) can use to
pass transport-specific security parameters to other subsystems,
including transport-specific security parameters that are translated
into the transport-independent securityName and securityLevel
parameters

The Transport Security Model [I-D.ietf-isms-transport-security-model]
and the Secure Shell Transport Model [I-D.ietf-isms-secshell] utilize

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 4] 5]

Internet-Draft SNMP Transport Subsystem February August 2008

and the Secure Shell Transport Model [I-D.ietf-isms-secshell] utilize
the Transport Subsystem. The Transport Security Model is an
alternative to the existing SNMPv1 Security Model [RFC3584], the
SNMPv2c Security Model [RFC3584], and the User-based Security Model
[RFC3414]. The Secure Shell Transport Model is an alternative to
existing transport mappings (or models) as described in [RFC3417].

1.3. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document

2. Motivation

Just as there are multiple ways to be interpreted as described in RFC 2119 [RFC2119].

Non uppercased versions of the keywords should be read as in normal
English. They will usually, but not always, be used in a context
relating to compatibility with the RFC3411 architecture or the
subsystem defined here, but which might have no impact on on-the-wire
compatibility. These terms are used as guidance for designers of
proposed IETF models to make the designs compatible with RFC3411
subsystems and Abstract Service Interfaces (see section 3.2).
Implementers are free to implement differently. Some usages of these
lowercase terms are simply normal English usage.

2. Motivation

Just as there are multiple ways to secure one's home or business, secure one's home or business, in
a continuum of alternatives, there are multiple ways to secure a
network management protocol. Let's consider three general
approaches.

In the first approach, an individual could sit on his front porch
waiting for intruders. In the second approach, he could hire an
employee , schedule the employee, position the employee to guard what
he wants protected, hire a second guard to cover if the first gets
sick, and so on. In the third approach, he could hire a security
company, tell them what he wants protected, and they could hire
employees, train them, position leave the guards, schedule details to
them. Considerations of hiring and training employees, positioning
and scheduling the guards, send
a replacement when a guard cannot make it, arranging for cover, etc., thus providing are the
responsibility of the security company. The individual therefore
achieves the desired security, with no significant effort on his part other than
identifying requirements and verifying the quality of the service
being provided.

Harrington & Schoenwaelder Expires August 28, 2008 [Page 5]

Internet-Draft SNMP Transport Subsystem February 2008 effort...

The User-based Security Model (USM) as defined in [RFC3414] largely
uses the first approach - it provides its own security. It utilizes
existing mechanisms (e.g., SHA), but provides all the coordination.
USM provides for the authentication of a principal, message
encryption, data integrity checking, timeliness checking, etc.

USM was designed to be independent of other existing security
infrastructures. USM therefore requires a separate principal and key
management infrastructure. Operators have reported that deploying
another principal and key management infrastructure in order to use
SNMPv3 is a deterrent to deploying SNMPv3. It is possible to use
external mechanisms to handle the distribution of keys for use by
USM. The more important issue is that operators wanted to leverage a
single
existing user base infrastructures that wasn't were not specific to SNMP.

A solution based on the second approach might use a USM-compliant
architecture, but architecture might combine the authentication
mechanism with an external mechanism, such as RADIUS [RFC2865], [RFC2865] to
provide the authentication service. It Similarly it might be possible
to utilize an external protocol to encrypt a message, to check
timeliness, to check data integrity, etc. It is difficult However this corresponds
to cobble together a number of
subcontracted services and coordinate them however, because it is
difficult to build the second approach - requiring the coordination of a number of
differently subcontracted services. Building solid security bindings between
the various
services, services is difficult, and there is a significant

Harrington & Schoenwaelder Expires February 28, 2009 [Page 6]

Internet-Draft SNMP Transport Subsystem August 2008

potential for gaps in the security is significant.

A solution based on the third security.

An alternative approach might be to utilize one or more lower-layer
security mechanisms to provide the message-oriented security services
required. These would include authentication of the sender,
encryption, timeliness checking, and data integrity checking. This
corresponds to the third approach described above. There are a
number of IETF standards available or in development to address these
problems through security layers at the transport layer or
application layer, among them TLS [RFC4346], [RFC5246], SASL [RFC4422], and SSH [RFC4251].
[RFC4251]

From an operational perspective, it is highly desirable to use
security mechanisms that can unify the administrative security
management for SNMPv3, command line interfaces (CLIs) and other
management interfaces. The use of security services provided by
lower layers is the approach commonly used for the CLI, and is also
the approach being proposed for other network management protocols,
such as syslog [I-D.ietf-syslog-protocol] and NETCONF [RFC4741].

This document defines a Transport Subsystem extension to the RFC3411
architecture based on the third approach. This extension specifies
how other lower layer protocols with common security infrastructures
can be used underneath the SNMP protocol and the desired goal of
unified administrative security can be met.

This extension allows security to be provided by an external protocol

Harrington & Schoenwaelder Expires August 28, 2008 [Page 6]

Internet-Draft SNMP Transport Subsystem February 2008
connected to the SNMP engine through an SNMP Transport Model
[RFC3417]. Such a Transport Model would then enable the use of
existing security mechanisms such as (TLS) [RFC4346] [RFC5246] or SSH [RFC4251]
within the RFC3411 architecture.

There are a number of Internet security protocols and mechanisms that
are in wide spread use. Many of them try to provide a generic
infrastructure to be used by many different application layer
protocols. The motivation behind the Transport Subsystem is to
leverage these protocols where it seems useful.

There are a number of challenges to be addressed to map the security
provided by a secure transport into the SNMP architecture so that
SNMP continues to provide interoperability with existing
implementations. These challenges are described in detail in this
document. For some key issues, design choices are described that
might be made to provide a workable solution that meets operational
requirements and fits into the SNMP architecture defined in
[RFC3411].

Harrington & Schoenwaelder Expires February 28, 2009 [Page 7]

Internet-Draft SNMP Transport Subsystem August 2008

3. Requirements of a Transport Model

3.1. Message Security Requirements

Transport security protocols SHOULD provide protection against the
following message-oriented threats [RFC3411]: threats:

1. modification of information

2. masquerade

3. message stream modification

4. disclosure

These threats are described in section 1.4 of [RFC3411]. It is not
required to protect against denial of service or traffic analysis,
but it should not make those threats significantly worse.

3.1.1. Security Protocol Requirements

There are a number of standard protocols that could be proposed as
possible solutions within the Transport Subsystem. Some factors
SHOULD
should be considered when selecting a protocol.

Using a protocol in a manner for which it was not designed has
numerous problems. The advertised security characteristics of a
protocol might depend on it being used as designed; when used in
other ways, it might not deliver the expected security
characteristics. It is recommended that any proposed model include a
description of the applicability of the Transport Model.

Harrington & Schoenwaelder Expires August 28, 2008 [Page 7]

Internet-Draft SNMP Transport Subsystem February 2008

A Transport Model SHOULD NOT require no modifications to the underlying
protocol. Modifying the protocol might change its security
characteristics in ways that would could impact other existing usages. If
a change is necessary, the change SHOULD be an extension that has no
impact on the existing usages. Any Transport Model SHOULD include a
description of potential impact on other usages of the protocol.

Transport Models

Since multiple transport models can exist simultaneously within the
transport subsystem, transport models MUST be able to coexist with
each other.

3.2. SNMP Requirements

Harrington & Schoenwaelder Expires February 28, 2009 [Page 8]

Internet-Draft SNMP Transport Subsystem August 2008

3.2.1. Architectural Modularity Requirements

SNMP version 3 (SNMPv3) is based on a modular architecture (defined
in [RFC3411] section 3) to allow the evolution of the SNMP protocol
standards over time, and to minimize side effects between subsystems
when changes are made.

The RFC3411 architecture includes a Security Subsystem for enabling
different methods of providing security services, a Message Processing Subsystem
permitting different message versions to be handled by a single
engine, a Security Subsystem for enabling different methods of
providing security services, Applications(s) to support different
types of application processors, and an Access Control Subsystem for
allowing multiple approaches to access control. The RFC3411
architecture does not include a subsystem for Transport Models,
despite the fact there are multiple transport mappings already
defined for SNMP. This document addresses the need for describes a Transport Subsystem that
is compatible with the RFC3411 architecture. As work is being done
to expand the transport to include use secure transport transports such as SSH and TLS, using a subsystem will
enable consistent design and modularity of such Transport Models.

The design of this Transport Subsystem accepts the goals of the
RFC3411 architecture defined in section 1.5 of [RFC3411]. This
Transport Subsystem uses a modular design that will permit permits Transport
Models to be advanced through "plugged into" the standards process independently of
other RFC3411 architecture, supported by
corresponding Transport Models, and Models (which may or may not be security-
aware). Such Transport Models would be independent of other modular
SNMP components as much as possible.

Parameters have been added This design also permits
Transport Models to be advanced through the ASIs to pass model-independent
transport address information. standards process
independently of other Transport Models.

To encourage a basic level of interoperability, IETF standards
typically require one mandatory to implement mandatory-to-implement solution, with the
capability of adding new mechanisms in the future. Part of
the motivation of developing Transport Models is to develop support
for secure transport protocols, such as a Transport Model that
utilizes the Secure Shell protocol. Any Any Transport
Model SHOULD define one minimum-compliance security mechanism, such as

Harrington & Schoenwaelder Expires August 28, 2008 [Page 8]

Internet-Draft SNMP Transport Subsystem February 2008

certificates, to ensure a basic level of interoperability, but
should also be able to support additional existing and new
mechanisms.

The Transport Subsystem permits multiple transport protocols to be
"plugged into" the RFC3411 architecture, supported by corresponding
Transport Models, including models that are security-aware.

The RFC3411 architecture and the Security Subsystem assume that a
Security Model is called by a Message Processing Model and will
perform multiple security functions within the Security Subsystem. A
Transport Model that supports a secure transport protocol might
perform similar security functions within the Transport Subsystem. A
Transport Model might perform the translation of transport security
parameters to/from security-model-independent parameters.

To accommodate this, an implementation-specific cache of transport-
specific information will be described (not shown), and the data
flows between the Transport Subsystem and the Transport Dispatch,
between the Message Dispatch and the Message Processing Subsystem,
and between the Message Processing Subsystem and the Security
Subsystem will be extended to pass security-model-independent values.
New Security Models may also be defined that understand how to work
with the modified ASIs and the cache. One such Security Model, the
Transport Security Model, is defined in
[I-D.ietf-isms-transport-security-model]

The following diagram depicts the SNMPv3 architecture including the
new Transport Subsystem defined in this document, and a new Transport
Security Model defined in [I-D.ietf-isms-transport-security-model].

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 9]

Internet-Draft SNMP Transport Subsystem February August 2008

+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v
+-------------------------------------------------------------------+
| +--------------------------------------------------+ |
| | Transport Subsystem | |
| | +-----+ +-----+ +-----+ +-----+ +-------+ | |
| | | UDP | | TCP | | SSH | | TLS | . . . | other | | |
| | +-----+ +-----+ +-----+ +-----+ +-------+ | |
| +--------------------------------------------------+ |
| ^ |
| | |
| Dispatcher v |
| +-------------------+ +---------------------+ +----------------+ |
| | Transport | | Message Processing | | Security | |
| | Dispatch | | Subsystem | | Subsystem | |
| | | | +------------+ | | +------------+ | |
| | | | +->| v1MP |<--->| | USM | | |
| | | | | +------------+ | | +------------+ | |
| | | | | +------------+ | | +------------+ | |
| | | | +->| v2cMP |<--->| | Transport | | |
| | Message | | | +------------+ | | | Security | | |
| | Dispatch <--------->| +------------+ | | | Model | | |
| | | | +->| v3MP |<--->| +------------+ | |
| | | | | +------------+ | | +------------+ | |
| | PDU Dispatch | | | +------------+ | | | Other | | |
| +-------------------+ | +->| otherMP |<--->| | Model(s) | | |
| ^ | +------------+ | | +------------+ | |
| | +---------------------+ +----------------+ |
| v |
| +-------+-------------------------+---------------+ |
| ^ ^ ^ |
| | | | |
| v v v |
| +-------------+ +---------+ +--------------+ +-------------+ |
| | COMMAND | | ACCESS | | NOTIFICATION | | PROXY | |
| | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | |
| | application | | | | applications | | application | |
| +-------------+ +---------+ +--------------+ +-------------+ |
| ^ ^ |
| | | |
| v v |
| +----------------------------------------------+ |
| | MIB instrumentation | SNMP entity |
+-------------------------------------------------------------------+

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 10]

Internet-Draft SNMP Transport Subsystem February August 2008

3.2.1.1. Processing Differences between USM and Secure Transport

USM and secure transports differ in the processing order and
responsibilities within Changes to the RFC3411 architecture. While the steps
are the same, they occur in a different order, Architecture

The RFC3411 architecture and the Security Subsystem assume that a
Security Model is called by a Message Processing Model and will
perform multiple security functions within the Security Subsystem. A
Transport Model that supports a secure transport protocol might
perform similar security functions within the Transport Subsystem,
including the translation of transport security parameters to/from
security-model-independent parameters.

To accommodate this, an implementation-specific cache of transport-
specific information will be described (not shown), and the data
flows on this path will be extended to pass security-model-
independent values. This document amends some of the ASIs defined in
RFC 3411, and these changes are covered in section 6.

New Security Models may be defined that understand how to work with
these modified ASIs and the transport-information cache. One such
Security Model, the Transport Security Model, is defined in
[I-D.ietf-isms-transport-security-model].

3.2.1.2. Changes to RFC3411 processing

The introduction of secure transports also affects the
responsibilities and order of processing within the RFC3411
architecture. While the steps are the same, they may occur in a
different order, and may be done by different subsystems. With USM and some other Security Models, the
existing RFC3411 architecture, security processing starts when the
Message Processing Model decodes portions of the encoded message to
extract security parameters and
header parameters that identify which Security Model should process handle
the message to perform authentication, decryption, timeliness
checking, integrity checking, and translation of parameters to model-
independent parameters. security-related tasks.

A secure transport performs those security functions on the message, before
*before* the message is decoded.

3.2.1.2. Note that some of these functions
might then be repeated by the selected Security Model.

3.2.1.3. Passing Information between SNMP Engines

A secure Transport Model will establish an authenticated and/or
encrypted tunnel between the Transport Models of two SNMP engines.
After a transport layer tunnel is established, then SNMP messages can
be sent through the tunnel from one SNMP engine to the other SNMP
engine. other.
Transport Models MAY support sending multiple SNMP messages through
the same tunnel.

Harrington & Schoenwaelder Expires February 28, 2009 [Page 11]

Internet-Draft SNMP Transport Subsystem August 2008

3.2.2. Access Control Requirements

RFC3411 made some design decisions related to the support of an
Access Control Subsystem. These include establishing and passing in
a model-independent manner the securityModel, securityName and
securityLevel parameters, and separating message authentication from
data access authorization.

3.2.2.1. securityName and securityLevel Mapping

SNMP data access controls are expected to work on the basis of who
can perform what operations on which subsets of data, and based on
the security services that will be provided to secure the data in
transit. The securityModel and securityLevel parameters establish
the protections for transit - whether authentication and privacy
services will be or have been applied to the message. The
securityName is a model-independent identifier of the security
"principal",

The Message Processing Subsystem relies on a Security Model, such as
USM, to play a role in security that goes beyond protecting the
message - it provides a mapping between the security-model-specific
principal for an incoming message to a security-model independent
securityName which can be used for subsequent processing, such as for
access control. The securityName is mapped from a mechanism-specific

Harrington & Schoenwaelder Expires August 28, 2008 [Page 11]

Internet-Draft SNMP Transport Subsystem February 2008
identity, and this mapping must be done for incoming messages by the
Security Model before it passes securityName to the Message
Processing Model via the processIncoming ASI.

A Security Model is also responsible to specify, via the
securityLevel parameter, whether incoming messages have been
authenticated and/or encrypted, and to ensure that outgoing messages
are authenticated and/or encrypted based on the value of
securityLevel.

A translation from a mechanism-specific identity to

The introduction of a securityName
might secure transport protocol means that the
translation from a mechanism-specific identity to a tmSecurityName
and tmSecurityLevel will be done by a Transport Model, and the proposed securityName and
a proposed securityLevel might then be made available to a Security
Model via the tmStateReference. Model. A Security
Model may have multiple sources for determining the principal and
desired security services, and a particular Security Model may or may
not utilize the
securityName tmSecurityName mapping and securityLevel made available tmSecurityLevel proposed
by the Transport Model when deciding the value of the securityName
and securityLevel to be passed to the Message Processing Model.

3.2.3. Security Parameter Passing Requirements

RFC3411 section 4 describes abstract data flows between the
subsystems, models and applications within the architecture.
Abstract Service Interfaces describe the flow of data, passing model-
independent information between subsystems within an engine. The
RFC3411 architecture has no ASI parameters for passing security
information between the Transport Subsystem and the dispatcher, or
between the dispatcher and the Message Processing Model. This
document defines or modifies ASIs for this purpose.

A Message Processing Model might unpack SNMP-specific security
parameters from an incoming message before calling a specific

Harrington & Schoenwaelder Expires February 28, 2009 [Page 12]

Internet-Draft SNMP Transport Subsystem August 2008

Security Model to authenticate and decrypt an incoming message,
perform integrity checking, and translate security-model-specific
parameters into model-independent parameters. handle the security-related processing of the
message. When using a secure Transport Model, some security
parameters might be provided through
means other than carrying them in the SNMP message; some of the
parameters for incoming messages might be extracted from the transport layer by the Transport
Security Model before the message is passed to the Message Processing Subsystem.
Subsystem..

This document describes a cache mechanism (see Section 5), into which
the Transport Model puts information about the transport and security
parameters applied to a transport connection or an incoming message,
and a Security Model may extract that information from the cache. A
tmStateReference is passed as an extra parameter in the ASIs of between
the Transport Subsystem and Subsystem, the Message Processing and Security

Harrington & Schoenwaelder Expires August 28, 2008 [Page 12]

Internet-Draft SNMP Transport Subsystem February 2008
Subsystems, to identify the relevant cache. This approach of passing
a model-independent reference is consistent with the
securityStateReference cache already being passed around in the
RFC3411 ASIs.

For outgoing messages, even when a secure Transport Model will
provide the security services, a Message Processing Model might have

3.2.4. Separation of Authentication and Authorization

The RFC3411 architecture defines a Security Model actually create separation of authentication and
the message from its component
parts. Whether there authorization to access and/or modify MIB data. A set of model-
independent parameters (securityModel, securityName, and
securityLevel) are any security services provided by the
Security Model for an outgoing message is security-model-dependent.
For incoming messages, even when a secure Transport Model provides
security services, a Security Model might provide some security
functionality that can only be provided after the message version or
other parameters are extracted from the message.

3.2.4. Separation of Authentication and Authorization

The RFC3411 architecture defines a separation of authentication and
the authorization to access and/or modify MIB data. A set of model-
independent parameters (securityModel, securityName, and
securityLevel) are passed between passed between the Security Subsystem, the
applications, and the Access Control Subsystem.

This separation was a deliberate decision of the SNMPv3 WG, to allow
support for authentication protocols which did do not provide data access
authorization capabilities, and to support data access authorization
schemes, such as VACM, that do not perform their own authentication. This decision also permits different types of data
access policies, such as one built on UNIX groups or Windows domains.
The VACM approach is based on administrator-defined groups of users.

A Message Processing Model determines which Security Model is used,
either based on the message version, e.g., SNMPv1 and SNMPv2c, and
possibly by a value specified in the message, e.g., SNMPv3. (e.g. msgSecurityModel
field in SNMPv3).

The Security Model makes the decision which securityName and
securityLevel values are passed as model-independent parameters to an
application, which then passes them via the isAccessAllowed ASI to
the Access Control Subsystem.

An Access Control Model performs the mapping from the model-
independent security parameters to a policy within the Access Control
Model that is access-control-model-dependent.

A Transport Model does not know which securityModel Security Model will be used for
an incoming message, so a Transport Model cannot know how the securityName and
securityLevel parameters are will be determined. A
Transport Model It can provide a mapping from a transport-specific propose an
authenticated identity (via the tmSecurityName field), but there is

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 13]

Internet-Draft SNMP Transport Subsystem February August 2008

identity and provide candidate values for the securityName and
securityLevel, but there is

no guarantee the transport-provided
values that this value will be used by the Security Model. For
example, the SNMPv1 Message Processing Model described in RFC3584
always selects the SNMPv1 non-transport-aware Security Model. This is true even if Models will typically determine
the
SNMPv1 message was protected in transit using a secure Transport
Model, such as one securityName (and securityLevel) based on SSH or TLS. The SNMPv1 the contents of the
SNMP message itself. Such Security Model
does Models will simply not know that
the tmStateReference exists.

3.3. Session Requirements

Some secure transports might have a notion cache exists..

Further, even if the Transport Model can influence the choice of sessions, while other
secure transports might provide channels or other session-like
mechanism. Throughout this document,
securityName, it cannot directly determine the term session is used in a
broad sense authorization allowed
to cover sessions, channels, and session-like mechanisms.
Session refers to an association between this identity. If two SNMP engines different Transport Model each authenticate
a transport principal, that
permits are then both mapped to the same
securityName, then these two identities will typically be afforded
exactly the same authorization by the Access Control Model.

The only way for the Access Control Model to differentiate between
identities based on the transmission underlying Transport Model, would be for such
transport-authenticated identities to be mapped to distinct
securityNames. How and if this is done is Security-Model-dependent.

3.3. Session Requirements

Some secure transports have a notion of one sessions, while other secure
transports provide channels or more other session-like mechanism.
Throughout this document, the term session is used in a broad sense
to cover transport sessions, transport channels, and other transport-
layer session-like mechanisms. Transport-layer sessions that can
secure multiple SNMP messages within the lifetime of the session. How session are
considered desirable because the cost of authentication can be
amortized over potentially many transactions. How a transport
session is actually established, opened, closed, or maintained is
specific to a particular Transport Model.

Sessions are not part of the SNMP architecture defined in [RFC3411],
but

To reduce redundancy, this document describes aspects that are considered desirable because the cost of authentication can
expected to be amortized over potentially many transactions. common to all Transport Model sessions.

3.3.1. Session Selection

The architecture defined in [RFC3411] does and the Transport Subsystem
defined in this document do not support SNMP sessions or include a
session selector in the Abstract Service Interfaces, and neither is that done
for the Interfaces. The Transport Subsystem, so an SNMP application has no mechanism
Subsystem does not have access to the pduType, so cannot select a
given session using the ASIs except by passing a unique
combination for particular types of transportDomain, transportAddress, securityName, and
securityLevel. Implementers, traffic. However certain
parameters of course, these ASIs might provide non-standard
mechanisms be used to select sessions. The transportDomain and
transportAddress identify guide the selection of the
appropriate transport session to use for a given request.

The transportDomain and transportAddress identify the transport
connection to a remote network node; node. Elements of the transport
address (such as the port number) can be used to select different
sessions for particular request types. For example, UDP ports 161

Harrington & Schoenwaelder Expires February 28, 2009 [Page 14]

Internet-Draft SNMP Transport Subsystem August 2008

and 162 have typically been used to separate SNMP notifications from
other request/response traffic.

The securityName identifies which security principal to communicate
with at that address (e.g., different NMS applications), and the
securityLevel might permit selection of different sets of security
properties for different purposes (e.g., encrypted SETs vs.
non-encrypted non-
encrypted GETs).

To reduce redundancy, this document describes aspects that are
expected to be common to all Transport Model sessions.

3.3.1. Session Establishment Requirements

SNMP has no mechanism to specify a transport session using the ASIs
except by passing

In summary, a unique combination of transportDomain,
transportAddress, securityName, and securityLevel could serve to be used to

Harrington & Schoenwaelder Expires August 28, 2008 [Page 14]

Internet-Draft SNMP Transport Subsystem February 2008
identify a session in given transport session. Different values for any of
these parameters would imply the use of a transport-independent manner. different session.

However, because the handling of transport sessions is specific to
each transport model, some transport models MAY restrict the
applicability of these parameters for selecting an associated
transport session.

Implementations SHOULD be able to maintain some reasonable number of
concurrent sessions, and MAY provide non-standard internal mechanisms
to select sessions.

3.3.2. Session Establishment Requirements

SNMP applications provide the transportDomain, transportAddress,
securityName, and securityLevel to be used to create a new session.

For an outgoing message, securityLevel is the requested security for
the message, passed in the ASIs.

If the Transport Model cannot provide at least the requested level of
security, the Transport Model SHOULD discard the message and SHOULD
notify the dispatcher that establishing a session and sending the
message failed.

A Transport Model determines whether an appropriate session exists
(transportDomain, transportAddress, securityName, and securityLevel)
for an outgoing message. If an appropriate session does not yet
exist, Similarly, if the Transport Model attempts to establish a session for
delivery . If a session cannot be established established,
then the message is should be discarded and the dispatcher should be notified that sending the
message failed. notified.

Transport session establishment might require provisioning
authentication credentials at an engine, either statically or
dynamically. How this is done is dependent on the transport model
and the implementation.

The Transport Subsystem has no knowledge of pduType, so cannot
distinguish between a session created to carry different pduTypes.
To differentiate a session established for different purposes, such
as a notification session versus a request-response session, an
application can use different securityNames or transport addresses.
For example, in SNMPv1, UDP ports 161 and 162 were used to
differentiate types of traffic. New transport models may define a
single well-known port for all traffic types. Administrators might
choose to define one port for SNMP request-response traffic, but
configure notifications to be sent to a different port.

3.3.2.

3.3.3. Session Maintenance Requirements

A Transport Model can tear down sessions as needed. It might be
necessary for some implementations to tear down sessions as the
result of resource constraints, for example.

The decision to tear down a session is implementation-dependent. How
an implementation determines that an operation has completed is
implementation-dependent. While it is possible for an implementation to automatically tear down each

Harrington & Schoenwaelder Expires February 28, 2009 [Page 15]

Internet-Draft SNMP Transport Subsystem August 2008

transport session once an operation after processing for each message has completed,
this is not recommended for anticipated performance reasons. How an implementation
determines that an operation has completed, including all potential
error paths, is implementation-dependent.

The elements of procedure describe when cached information can be

Harrington & Schoenwaelder Expires August 28, 2008 [Page 15]

Internet-Draft SNMP Transport Subsystem February 2008
discarded, in some circumstances, and the timing of cache cleanup might have security
implications, but cache memory management is an implementation issue.

If a Transport Model defines MIB module objects to maintain session
state information, then the Transport Model MUST define what SHOULD
happen to the objects when a related session is torn down, since this
will impact interoperability of the MIB module.

3.3.3.

3.3.4. Message security versus session security

A Transport Model session is associated with state information that
is maintained for its lifetime. This state information allows for
the application of various security services to multiple messages.
Cryptographic keys associated with the transport session SHOULD be
used to provide authentication, integrity checking, and encryption
services, as needed, for data that is communicated during the
session. The cryptographic protocols used to establish keys for a
Transport Model session SHOULD ensure that fresh new session keys are
generated for each session. In addition sequence information might
be maintained in the session which can be used to prevent the replay
and reordering of messages within a session. If each session uses
new keys, then This would ensure that a cross-session
replay attack will would be unsuccessful; that is, an attacker cannot successfully replay on one session could not
take a message he observed from on one session, and successfully replay this
on another session.

A good security protocol
will would also protect against replay attacks _within_
within a session; that is, an attacker cannot successfully replay could not take a message
observed earlier on a session, and successfully replay this later in the same
session.

A Transport Model session will have One approach would be to use sequence information within
the protocol, allowing the participants to detect if messages were
replayed or reordered within a single transportDomain,
transportAddress, securityName and securityLevel associated with it.
If an exchange between communicating engines requires session.

Note that if a different
securityLevel or secure transport session is on behalf of closed between the time a different securityName, then
another session would be needed. An immediate consequence of this
request message is
that implementations received, and the corresponding response message
is sent, then the response message SHOULD be able to maintain some reasonable
number of concurrent sessions.

For Transport Models, securityName discarded, even if a new
session has been established. The SNMPv3 WG decided that this should
be specified during session
setup, a SHOULD architecturally, and associated with the session identifier. it is a security-model-specific
decision whether to REQUIRE this.

SNMPv3 was designed to support multiple levels of security,
selectable on a per-message basis by an SNMP application, because,
for example, there is not much value in using encryption for a
Commander Generator to poll for potentially non-sensitive performance
data on thousands of interfaces every ten minutes; the encryption
might add significant overhead to processing of the messages.

Some Transport Models might support only specific authentication and

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 16]

Internet-Draft SNMP Transport Subsystem February August 2008

Some Transport Models might support only specific authentication and
encryption services, such as requiring all messages to be carried
using both authentication and encryption, regardless of the security
level requested by an SNMP application. A Transport Model may MAY
upgrade the security level requested by a transport-aware security level,
model, i.e. noAuthNoPriv and authNoPriv MAY might be sent over an
authenticated and encrypted session.

4. Scenario Diagrams and the Transport Subsystem

RFC3411 section 4.6.1 and 4.6.2 provide scenario diagrams to
illustrate how an outgoing message is created, and how an incoming
message is processed. RFC3411 does not define ASIs for "Send SNMP
Request Message to Network" or "Receive SNMP Response Message from
Network", and does not define ASIs for "Receive SNMP Message from
Network" or "Send SNMP message to Network".

This document defines a sendMessage ASI to send SNMP messages to the
network, regardless of pduType, and a receiveMessage ASI to receive SNMP messages from the
network, regardless of pduType.

5. Cached Information and References

The RFC3411 architecture uses caches to store dynamic model-specific
information, and uses references in the ASIs to indicate in a model-
independent manner which cached information flows between subsystems.

There

When performing SNMP processing, there are two levels of state
information that might may need to be maintained: retained: the
security immediate state in linking
a request-response pair, and potentially long-term longer-term state relating
to transport and security.

The RFC3411 architecture uses caches to maintain the short-term
message state, and uses references in the ASIs to pass this
information between subsystems.

This document defines the requirements for a cache to handle the
longer-term transport state is maintained in caches. information, using a tmStateReference
parameter to pass this information between subsystems.

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 being processed gets
discarded, the state related to that message should SHOULD also be discarded, and if
discarded. If state information is available when a relationship
between engines is severed, such as the closing of a transport
session, the state information for that relationship might SHOULD also be
discarded.

This document differentiates the tmStateReference from

Since the
securityStateReference. This document does not specify an
implementation strategy, contents of a cache are meaningful only within an abstract description
implementation, and not on-the-wire, the format of the data
that flows between subsystems. An implementation might use one cache and one reference to serve both functions, but an implementer must be
aware of the cache-release issues to prevent the cache from being
released before a security or Transport Model has had an opportunity
to extract the information it needs.
LCD are implementation-specific.

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 17]

Internet-Draft SNMP Transport Subsystem February August 2008

5.1. securityStateReference

The securityStateReference parameter is defined in RFC3411.
securityStateReference Its
primary purpose is to provide a mapping between a request and the
corresponding response. This cache is not accessible to models of the Transport
Subsystem.
Models, and an entry is typically only retained for the lifetime of a
request-response pair of messages.

5.2. tmStateReference

For each transport session, information about the message transport security
is stored in a cache cache. The tmStateReference parameter is used to pass model-
model-specific and mechanism-specific parameters. parameters between the
Transport subsystem and transport-aware Security Models.

The state referenced by tmStateReference may be saved across multiple
messages, in a Local Configuration Datastore (LCD), as compared to
securityStateReference which is usually only saved cache will typically remain valid for the life
duration of a
request-response pair of messages.

For security reasons, if a secure transport session is closed between the time a request message is received transport session, and the corresponding response
message is sent, then the response message SHOULD hence may be discarded, even
if a new session has been established. The SNMPv3 WG decided that used for several
messages.

Since this should be a SHOULD architecturally, and it cache is a security-model-
specific decision whether to REQUIRE this.

Since a transport model does not know whether a message contains a
response, only used within an implementation, and transport session information is transport-model-
specific, not on-
the-wire, the tmStateReference contains two pieces of information precise contents and format are implementation-
dependent. However, for
performing the request-response transport session pairing.

Each interoperability between Transport Models
and transport-aware Security Model that supports the tmStateReference cache SHOULD
pass a tmSameSecurity parameter Models, entries in the tmStateReference this cache for
outgoing messages to indicate whether the same security parameters
MUST be used for must
include at least the outgoing following fields:

transportDomain

transportAddress

tmSecurityName

tmRequestedSecurityLevel

tmTransportSecurityLevel

tmSameSecurity

tmSessionID

5.2.1. Transport information

Information about the source of an incoming SNMP message is passed up
from the Transport subsystem as was used far as the Message Processing
subsystem. However these parameters are not included in the
processIncomingMsg ASI defined in RFC3411, and hence this information
is not directly available to the Security Model.

A transport-aware Security Model might wish to take account of the

Harrington & Schoenwaelder Expires February 28, 2009 [Page 18]

Internet-Draft SNMP Transport Subsystem August 2008

transport protocol and originating address when authenticating the
request, and setting up the authorization parameters. It is
therefore necessary for the
corresponding Transport Model to include this
information in the tmStateReference cache, so that it is accessible
to the Security Model.

o transportDomain: the transport protocol (and hence the Transport
Model) used to receive the incoming message

o transportAddress: the source of the incoming message.

Each transport model

Note that supports sessions the ASIs used for processing an outgoing message all
include explicit transportDomain and supports transportAddress parameters.
These fields within the tmStateReference cache SHOULD include will typically not be
used for outgoing messages.

5.2.2. securityName

There are actually three distinct "identities" that can be identified
during the processing of an SNMP request over a transport-specific session
identifier secure transport:

o transport principal: the transport-authenticated identity, on
whose behalf the secure transport connection was (or should be)
established. This value is transport-, mechanism- and
implementation- specific, and is only used within a given
Transport Model.

o tmSecurityName: a human-readable name (in snmpAdminString format)
representing this transport identity. This value is transport-
and implementation-specific, and is only used (directly) by the
Transport and Security Models.

o securityName: a human-readable name (in snmpAdminString format)
representing the SNMP principal in a model-independent manner.

o Note that the cache for transport principal may or may not be the same as
the tmSecurityName. Similarly, the tmSecurityName may or may not
be the same as the securityName as seen by the Application and
Access Control subsystems. In particular, a non-transport-aware
Security Model will ignore tmSecurityName completely when
determining the SNMP securityName.

o However it is important that the mapping between the transport
principal and the SNMP securityName (for transport-aware Security
Models) is consistent and predictable, to allow configuration of
suitable access control and the establishment of transport
connections.

Harrington & Schoenwaelder Expires February 28, 2009 [Page 19]

Internet-Draft SNMP Transport Subsystem August 2008

5.2.3. securityLevel

There are two distinct issues relating to security level as applied
to secure transports. For clarity, these are handled by separate
fields in the tmStateReference cache:

o tmTransportSecurityLevel: an indication from the Transport Model
of the level of security offered by this session. The Security
Model can use this to ensure that incoming message, so messages were suitably
protected before acting on them.

o tmRequestedSecurityLevel: an indication from the Security Model of
the level of security required to be provided by the transport
protocol. The Transport Model can use this to ensure that
outgoing messages will not be sent over an insufficiently secure
session.

5.2.4. Session Information

For security reasons, if a
security model requests tmSameSecurity, the transport model can
determine whether the current existing secure transport session is closed between
the same
as time a request message is received and the transport session used for corresponding response
message is sent, then the incoming request. response message SHOULD be discarded, even
if a new session has been established. The SNMPv3 WG decided that
this should be a SHOULD architecturally, and it is a security-model-
specific decision whether to REQUIRE this.

When processing an outgoing message, if the tmSameSecurity
requirement is indicated by the security model, but the session
identified in true, then
the tmStateReference does not tmSessionID MUST match the current
established transport session, i.e., it is not the same transport session, then otherwise
the message MUST be discarded, and the dispatcher
should be notified the that
sending of the message failed.

Since

o tmSameSecurity: this flag is used by a transport-aware Security
Model to indicate whether the contents Transport Model MUST enforce this
restriction.

o tmSessionID: in order to verify whether the session has changed,
the Transport Model must be able to compare the session used to
receive the original request with the one to be used to send the
response. This typically requires some form of a cache are meaningful session
identifier. This value is only within an

Harrington & Schoenwaelder Expires August 28, 2008 [Page 18]

Internet-Draft SNMP ever used by the Transport Subsystem February 2008

implementation, and not on-the-wire, Model,
so the format of the cache and the
LCD interpretation of this field are implementation-specific. model-specific
and implementation-dependent.

6. Abstract Service Interfaces

Abstract service interfaces have been defined by RFC 3411 to describe
the conceptual data flows between the various subsystems within an
SNMP entity, and to help keep the subsystems independent of each

Harrington & Schoenwaelder Expires February 28, 2009 [Page 20]

Internet-Draft SNMP Transport Subsystem August 2008

other except for the common parameters.

This document introduces a couple of new ASIs to define the interface
between the Transport and Dispatcher Subsystems, and extends some of
the ASIs defined in RFC3411 to include transport-related information.

This document follows the example of RFC3411 regarding the release of
state information, and regarding error indications.

1) The release of state information is not always explicitly
specified in a transport model. As a general rule, if state
information is available when a message gets discarded, the message-
state information should also be released, and if state information
is available when a session is closed, the session state information
should also be released. Note that keeping sensitive security
information longer than necessary might introduce potential
vulnerabilities to an implementation.

2) An

2)An error indication in statusInformation may will typically include an the
OID and value for an incremented counter and a value for securityLevel, and error counter. This may be
accompanied by values for contextEngineID and contextName for the this
counter, a value for securityLevel, and the
securityStateReference appropriate state
reference if the information is available at the point where the
error is detected.

6.1. sendMessage ASI

The sendMessage ASI is used to pass a message from the Dispatcher to
the appropriate Transport Model for sending.

In the diagram in section 4.6.1 of RFC 3411, the sendMessage ASI
defined in this document replaces the text "Send SNMP Request Message
to Network". In section 4.6.2, the sendMessage ASI replaces the text
"Send SNMP Message to Network"

If present and valid, the tmStateReference refers to a cache
containing transport-model-specific parameters for the transport and
transport security. How the information in the cache is used is
transport-model-dependent and implementation-dependent. How a
tmStateReference is determined to be present and valid is
implementation-dependent.

This may sound underspecified, but a transport model might be
something like SNMP over UDP over IPv6, where no security is
provided, so it might have no mechanisms for utilizing a securityName
and securityLevel.

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 19] 21]

Internet-Draft SNMP Transport Subsystem February August 2008

and securityLevel.

statusInformation =
sendMessage(
IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length
IN tmStateReference -- reference to transport state
)

6.2. Other Changes to RFC3411 Outgoing ASIs

A tmStateReference parameter

[DISCUSS: this section has been significantly rewritten and
reorganized. This needs to be checked thoroughly to verify no
technical changes have been introduced in the editorial changes.]

Additional parameters have been added to the
prepareOutgoingMessage, prepareResponseMessage, generateRequestMsg,
and generateResponseMsg ASIs defined in RFC3411,
concerned with communication between the Dispatcher and Message
Processing subsystems, and between the Message Processing and
Security Subsystems.

6.2.1. Message Processing Subsystem Primitives

A tmStateReference parameter has been added as an OUT parameter. The
transportDomain parameter to
the prepareOutgoingMessage and transportAddress parameters have been added prepareResponseMessage ASIs. This is
passed from Message Processing Subsystem to the generateRequestMsg, dispatcher, and generateResponseMsg ASIs as IN parameters
(not shown). from
there to the Transport Subsystem.

How or if the Message Processing Subsystem modifies or utilizes the
contents of the cache is message-processing-model specific.

Harrington & Schoenwaelder Expires February 28, 2009 [Page 22]

Internet-Draft SNMP Transport Subsystem August 2008

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
OUT tmStateReference -- (NEW) reference to transport state
)

Harrington & Schoenwaelder Expires August 28, 2008 [Page 20]

Internet-Draft SNMP Transport Subsystem February 2008

statusInformation = -- success or errorIndication
prepareResponseMessage(
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 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
OUT tmStateReference -- (NEW) reference to transport state
)

The

6.2.2. Security Subsystem Primitives

transportDomain and transportAddress parameters have been added as IN
parameters to the generateOutgoingMessage and generateResponseMessage

Harrington & Schoenwaelder Expires February 28, 2009 [Page 23]

Internet-Draft SNMP Transport Subsystem August 2008

ASIs, and a tmStateReference parameter of generateRequestMsg or
generateResponseMsg is passed in the has been added as an OUT
parameter. The transportDomain and transportAddress parameters of will
have been passed into the Message Processing Subsystem from the
dispatcher, and are passed on to the Security Subsystem. The
tmStateReference parameter will be passed from the Security Subsystem
back to the Message Processing Subsystem, and on to the Message Processing Subsystem. dispatcher
and Transport subsystems.

If a cache exists for a session identifiable from the
transportDomain, transportAddress,
securityModel, securityName, tmSecurityName and requested
securityLevel, then an appropriate a transport-aware Security Model might create a
tmStateReference parameter to the cache this cache, and pass that as an OUT
parameter.

If one does not exist, the Security Model might create a cache
referenced by tmStateReference. This information might include
transportDomain, transportAddress, the securityLevel, and the
securityName, plus any model or mechanism-specific details. The
contents

statusInformation =
generateRequestMessage(
IN transportDomain -- (NEW) destination transport domain
IN transportAddress -- (NEW) destination transport address
IN messageProcessingModel -- typically, SNMP version
IN globalData -- message header, admin data
IN maxMessageSize -- of the cache may be incomplete until sending SNMP entity
IN securityModel -- for the Transport Model has
established a session. What information is passed, and how outgoing message
IN securityEngineID -- authoritative SNMP entity
IN securityName -- on behalf of this
information is determined, is implementation and security-model-
specific.

The prepareOutgoingMessage ASI passes tmStateReference from the
Message Processing Subsystem to the dispatcher. How or if the
Message Processing Subsystem modifies or utilizes the contents principal
IN securityLevel -- Level of the
cache is message-processing-model-specific.

This may sound underspecified, but a Security requested
IN scopedPDU -- message processing model might
have access to all the information from the cache and from the
message, and an application might specify a (plaintext) payload
OUT securityParameters -- filled in by Security Model such as
USM Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of generated message
OUT tmStateReference -- (NEW) reference to authenticate and secure the SNMP message, but also specify a transport state
)
)

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 21] 24]

Internet-Draft SNMP Transport Subsystem February August 2008

secure

statusInformation =
generateResponseMessage(
IN transportDomain -- (NEW) destination transport such domain
IN transportAddress -- (NEW) destination transport address
IN messageProcessingModel -- SNMPv3 Message Processing
-- Model
IN globalData -- msgGlobalData from step 7
IN maxMessageSize -- from msgMaxSize (step 7c)
IN securityModel -- as that provided by determined in step 7e
IN securityEngineID -- the SSH Transport Model to
send 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
OUT tmStateReference -- (NEW) reference to its destination. transport state
)

)

6.3. The receiveMessage ASI

If one

When a message is received on a given transport session, if a cache
does not exist, already exist for that session, the Transport Model might
create a cache one, referenced by tmStateReference. If present, The contents of this information might
include transportDomain, transportAddress, securityLevel, and
securityName, plus model or mechanism-specific details.
cache are discussed in section 5. How this information is determined
is implementation implementation- and transport-model-
specific. transport-model-specific.

In the diagram in section 4.6.1 of RFC 3411, the receiveMessage ASI
replaces the text "Receive SNMP Response Message from Network". In
section 4.6.2, the receiveMessage ASI replaces the text "Receive SNMP
Message from Network"

This may sound underspecified, but a transport model might be
something like SNMP over UDP over IPv6, where no security is
provided, so it might have no mechanisms for determining a
securityName and securityLevel.

The Transport Model does not know the securityModel for an incoming
message; this will be determined by the Message Processing Model in a
message-processing-model-dependent manner.

The receiveMessage ASI is used to pass a message from the Transport
Subsystem to the Dispatcher.

Harrington & Schoenwaelder Expires February 28, 2009 [Page 25]

Internet-Draft SNMP Transport Subsystem August 2008

statusInformation =
receiveMessage(
IN transportDomain -- origin transport domain
IN transportAddress -- origin transport address
IN incomingMessage -- the message received
IN incomingMessageLength -- its length
IN tmStateReference -- reference to transport state
)

6.4. Other Changes to RFC3411 Incoming ASIs

To support the Transport Subsystem,

The tmStateReference parameter has also been added to some of the
incoming ASIs defined in RFC3411. How or if a Message Processing
Model or Security Model uses tmStateReference is added message-processing-
and security-model-specific.

This may sound underspecified, but a message processing model might
have access to all the prepareDataElements ASI (from information from the Dispatcher to cache and from the
message. The Message Processing Subsystem), Model might determine that the USM
Security Model is specified in an SNMPv3 message header; the USM
Security Model has no need of values in the tmStateReference cache to
authenticate and secure the SNMP message, but an application might
have specified to use a secure transport such as that provided by the
SSH Transport Model to send the processIncomingMsg ASI (from the message to its destination.

6.4.1. Message Processing Subsystem Primitive

The tmStateReference parameter of prepareDataElements is passed from
the dispatcher to the Security Model Subsystem). Message Processing Subsystem. How or if a the
Message Processing Model Subsystem modifies or Security Model uses
tmStateReference utilizes the contents of the
cache is message-processing-model-dependent and security-
model-dependent. message-processing-model-specific.

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 22] 26]

Internet-Draft SNMP Transport Subsystem February August 2008

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
IN tmStateReference -- (NEW) from the Transport Model
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
)

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

6.4.2. Security
IN wholeMsg -- as received on the wire
IN wholeMsgLength -- length as received on the wire
IN tmStateReference -- (NEW) from the Transport Model
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

The tmStateReference parameter of prepareDataElements is passed from
the dispatcher to the Message Processing Subsystem. How or if the
Message Processing Subsystem modifies or utilizes the contents of the
cache is message-processing-model-specific.

Harrington & Schoenwaelder Expires August 28, 2008 [Page 23]

Internet-Draft SNMP Transport Subsystem February 2008 Primitive

The processIncomingMessage ASI passes tmStateReference from the
Message Processing Subsystem to the Security Subsystem.

If tmStateReference is present and valid, an appropriate Security
Model might utilize the information in the cache. How or if the
Security Subsystem utilizes the information in the cache is security-
model-specific.

This may sound underspecified, but a message processing model might
have access to all the information from the cache and from the
message. The Message Processing Model might determine that utilize the USM
Security Model is specified information in an SNMPv3 message header; the USM cache. How or if the
Security Model has no need of values Subsystem utilizes the information in the tmStateReference cache to
authenticate and secure is security-
model-specific.

Harrington & Schoenwaelder Expires February 28, 2009 [Page 27]

Internet-Draft SNMP Transport Subsystem August 2008

statusInformation = -- errorIndication or success
-- error counter OID/value if error
processIncomingMsg(
IN messageProcessingModel -- typically, SNMP version
IN maxMessageSize -- of the sending SNMP message, but an application might
have specified to use a secure transport such entity
IN securityParameters -- for the received message
IN securityModel -- for the received message
IN securityLevel -- Level of Security
IN wholeMsg -- as that provided by received on the wire
IN wholeMsgLength -- length as received on the wire
IN tmStateReference -- (NEW) from the
SSH Transport Model to send
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 its destination. security state
) -- information, needed for response

7. Security Considerations

This document defines an architectural approach that permits SNMP to
utilize transport layer security services. Each proposed Transport
Model should discuss the security considerations of the Transport
Model.

It is considered desirable by some industry segments that SNMP
Transport Models should utilize transport layer security that
addresses perfect forward secrecy at least for encryption keys.
Perfect forward secrecy guarantees that compromise of long term
secret keys does not result in disclosure of past session keys. Each
proposed Transport Model should include a discussion in its security
considerations of whether perfect forward security is appropriate for
the Transport Model.

Since the cache and LCD will contain security-related parameters,
implementers should store this information (in memory or in
persistent storage) in a manner to protect it from unauthorized
disclosure and/or modification.

Care must be taken to ensure that a SNMP engine is sending packets
out over a transport using credentials that are legal for that engine
to use on behalf of that user. Otherwise an engine that has multiple
transports open might be "tricked" into sending a message through the
wrong transport.

A Security Model may have multiple sources from which to define the
securityName and securityLevel. The use of a secure Transport Model
does not imply that the securityName and securityLevel chosen by the
Security Model represent the transport-authenticated identity or the

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 24] 28]

Internet-Draft SNMP Transport Subsystem February August 2008

Security Model represent the transport-authenticated identity or the
transport-provided security services. The securityModel,
securityName, and securityLevel parameters are a related set, and an
administrator should understand how the specified securityModel
selects the corresponding securityName and securityLevel.

7.1. Coexistence, Security Parameters, and Access Control

In the RFC3411 architecture, the Message Processing Model makes the
decision about which Security Model to use. The architectural change
described by this document does not alter that.

The architecture change described by this document does however,
allow SNMP to support two different approaches to security - message-
driven security and transport-driven security. With message-driven
security, SNMP provides its own security, and passes security
parameters within the SNMP message; with transport-driven security,
SNMP depends on an external entity to provide security during
transport by "wrapping" the SNMP message.

Security models defined before the Transport Security Model (i.e.,
SNMPv1, SNMPv2c, and USM) do not support transport-based security,
and only have access to the security parameters contained within the
SNMP message. They do not know about the security parameters
associated with a secure transport. As a result, the Access Control
Subsystem bases its decisions on the security parameters extracted
from the SNMP message, not on transport-based security parameters.

Implications of coexistence of older security models with secure
transport models are known. The securityName used for access control
decisions represents an SNMP-authenticated identity, not the
transport-authenticated identity. (I can transport-authenticate as
guest and then simply use a community name for root, or a USM non-
authenticated identity.)

o An SNMPv1 message will always be paired with an SNMPv1 Security
Model (per RFC3584), regardless of the transport mapping or
transport model used, and access controls will be based on the
community name.

o An SNMPv2c message will always be paired with an SNMPv2c Security
Model (per RFC3584), regardless of the transport mapping or
transport model used, and access controls will be based on the
community name.

o An SNMPv3 message will always be paired with the securityModel
specified in the msgSecurityParameters field of the message (per
RFC3412), regardless of the transport mapping or transport model

Harrington & Schoenwaelder Expires February 28, 2009 [Page 29]

Internet-Draft SNMP Transport Subsystem August 2008

used. If the SNMPv3 message specifies the User-based Security
Model (USM), access controls will be based on the USM user. If
the SNMPv3 message specifies the Transport Security Model (TSM),
access controls will be based on the principal authenticated by

Harrington & Schoenwaelder Expires August 28, 2008 [Page 25]

Internet-Draft SNMP Transport Subsystem February 2008
the transport.

8. IANA Considerations

This document requires no action by IANA.

9. Acknowledgments

The Integrated Security for SNMP WG would like to thank the following
people for their contributions to the process:

The authors of submitted Security Model proposals: Chris Elliot, Wes
Hardaker, David Harrington, Keith McCloghrie, Kaushik Narayan, David
Perkins, Joseph Salowey, and Juergen Schoenwaelder.

The members of the Protocol Evaluation Team: Uri Blumenthal,
Lakshminath Dondeti, Randy Presuhn, and Eric Rescorla.

WG members who performed detailed reviews: Jeffrey Hutzelman, Bert
Wijnen, Tom Petch.

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.

[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.

[RFC3414] Blumenthal, U. and B.

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 26] 30]

Internet-Draft SNMP Transport Subsystem February August 2008

(SNMP)", STD 62, RFC 3412,
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.

[RFC3417] Presuhn, R., "Transport
Mappings for the Simple
Network Management Protocol
(SNMP)", STD 62, RFC 3417,
December 2002.

10.2. Informative References

[RFC2865] Rigney, C., Willens, S.,
Rubens, A., and W. Simpson,
"Remote Authentication Dial
In User Service (RADIUS)",
RFC 2865, 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.

[RFC3584] 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",
BCP 74, RFC 3584,
August 2003.

[RFC4346]

[RFC5246] Dierks, T. and E. Rescorla,
"The Transport Layer
Security (TLS) Protocol
Version 1.1", 1.2", RFC 4346,
April 2006.

[RFC4422] Melnikov, A. and K.
Zeilenga, "Simple
Authentication and Security 5246,
August 2008.

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 27] 31]

Internet-Draft SNMP Transport Subsystem February August 2008

[RFC4422] Melnikov, A. and K.
Zeilenga, "Simple
Authentication and Security
Layer (SASL)", RFC 4422,
June 2006.

[RFC4251] Ylonen, T. and C. Lonvick,
"The Secure Shell (SSH)
Protocol Architecture",
RFC 4251, January 2006.

[RFC4741] Enns, R., "NETCONF
Configuration Protocol",
RFC 4741, December 2006.

[I-D.ietf-isms-transport-security-model] Harrington, D., "Transport
Security Model for SNMP", d
raft-ietf-isms-transport-
security-model-07
security-model-08 (work in
progress), November 2007. July 2008.

[I-D.ietf-isms-secshell] Harrington, D. and J.
Salowey, "Secure Shell
Transport Model for SNMP",
draft-ietf-isms-secshell-09
draft-ietf-isms-secshell-11
(work in progress),
July 2008.

[I-D.ietf-syslog-protocol] Gerhards, R., "The syslog
Protocol", draft-ietf-
syslog-protocol-23 (work in
progress),
November September 2007.

Appendix A. Why tmStateReference?

This appendix considers why a cache-based approach was selected for
passing parameters.

There are four approaches that could be used for passing information
between the Transport Model and a Security Model.

1. one could define an ASI to supplement the existing ASIs, or

2. one could add a header to encapsulate the SNMP message,

3. one could utilize fields already defined in the existing SNMPv3
message, or

Harrington & Schoenwaelder Expires February 28, 2009 [Page 32]

Internet-Draft SNMP Transport Subsystem August 2008

4. one could pass the information in an implementation-specific
cache or via a MIB module.

A.1. Define an Abstract Service Interface

Abstract Service Interfaces (ASIs) are defined by a set of primitives
that specify the services provided and the abstract data elements
that are to be passed when the services are invoked. Defining
additional ASIs to pass the security and transport information from
the Transport Subsystem to Security Subsystem has the advantage of
being consistent with existing RFC3411/3412 practice, and helps to

Harrington & Schoenwaelder Expires August 28, 2008 [Page 28]

Internet-Draft SNMP Transport Subsystem February 2008
ensure that any Transport Model proposals pass the necessary data,
and do not cause side effects by creating model-specific dependencies
between itself and other models or other subsystems other than those
that are clearly defined by an ASI.

A.2. Using an Encapsulating Header

A header could encapsulate the SNMP message to pass necessary
information from the Transport Model to the dispatcher and then to a
Message Processing Model. The message header would be included in
the wholeMessage ASI parameter, and would be removed by a
corresponding Message Processing Model. This would imply the (one
and only) messaging dispatcher would need to be modified to determine
which SNMP message version was involved, and a new Message Processing
Model would need to be developed that knew how to extract the header
from the message and pass it to the Security Model.

A.3. Modifying Existing Fields in an SNMP Message

[RFC3412] defines the SNMPv3 message, which contains fields to pass
security related parameters. The Transport Subsystem could use these
fields in an SNMPv3 message, or comparable fields in other message
formats to pass information between Transport Models in different
SNMP engines, and to pass information between a Transport Model and a
corresponding Message Processing Model.

If the fields in an incoming SNMPv3 message are changed by the
Transport Model before passing it to the Security Model, then the
Transport Model will need to decode the ASN.1 message, modify the
fields, and re-encode the message in ASN.1 before passing the message
on to the message dispatcher or to the transport layer. This would
require an intimate knowledge of the message format and message
versions so the Transport Model knew which fields could be modified.
This would seriously violate the modularity of the architecture.

Harrington & Schoenwaelder Expires February 28, 2009 [Page 33]

Internet-Draft SNMP Transport Subsystem August 2008

A.4. Using a Cache

This document describes a cache, into which the Transport Model puts
information about the security applied to an incoming message, and a
Security Model can extract that information from the cache. Given
that there might be multiple TM-security caches, a tmStateReference
is passed as an extra parameter in the ASIs between the Transport
Subsystem and the Security Subsystem, so the Security Model knows
which cache of information to consult.

This approach does create dependencies between a specific Transport
Model and a corresponding specific Security Model. However, the
approach of passing a model-independent reference to a model-

Harrington & Schoenwaelder Expires August 28, 2008 [Page 29]

Internet-Draft SNMP Transport Subsystem February 2008
dependent cache is consistent with the securityStateReference already
being passed around in the RFC3411 ASIs.

Appendix B. Open Issues

NOTE to RFC editor: If this section is empty, then please remove this
open issues section before publishing this document as an RFC. (If
it is not empty, please send it back to the editor to resolve.

Appendix C. Change Log

NOTE to RFC editor: Please remove this change log before publishing
this document as an RFC.

Changes from -12- to -13-

o moved conventions after Internet Standard framework, for
consistency with related documents.

o editorial changes and reorganization

Changes from -10- to -12-

o clarified relation to other documents.

o clarified relation to older security models.

o moved comparison of TSM and USM to TSM document

Changes from -09- to -10-

Harrington & Schoenwaelder Expires February 28, 2009 [Page 34]

Internet-Draft SNMP Transport Subsystem August 2008

o Pointed to companion documents

o Wordsmithed extensively

o Modified the note about SNMPv3-consistent terminology

o Modified the note about RFC2119 terminology.

o Modified discussion of cryptographic key generation.

o Added security considerations about coexistence with older
security models

o Expanded discussion of same session functionality

o Described how sendMessage and receiveMessage fit into RFC3411
diagrams

o Modified prepareResponseMessage ASI
o

Changes from -08- to -09-

o A question was raised that notifications would not work properly,
but we could never find the circumstances where this was true.

o removed appendix with parameter matrix

o Added a note about terminology, for consistency with SNMPv3 rather
than with RFC2828.

Changes from -07- to -08-

o Identified new parameters in ASIs.

o Added discussion about well-known ports.

Changes from -06- to -07-

o Removed discussion of double authentication

Harrington & Schoenwaelder Expires August 28, 2008 [Page 30]

Internet-Draft SNMP Transport Subsystem February 2008

o Removed all direct and indirect references to pduType by Transport
Subsystem

o Added warning regarding keeping sensitive security information
available longer than needed.

o Removed knowledge of securityStateReference from Transport
Subsystem.

Harrington & Schoenwaelder Expires February 28, 2009 [Page 35]

Internet-Draft SNMP Transport Subsystem August 2008

o Changed transport session identifier to not include securityModel,
since this is not known for incoming messages until the message
processing model.

Changes from revision -05- to -06-

mostly editorial changes

removed some paragraphs considered unnecessary

added Updates to header

modified some text to get the security details right

modified text re: ASIs so they are not API-like

cleaned up some diagrams

cleaned up RFC2119 language

added section numbers to citations to RFC3411

removed gun for political correctness

Changes from revision -04- to -05-

removed all objects from the MIB module.

changed document status to "Standard" rather than the xml2rfc
default of informational.

changed mention of MD5 to SHA

moved addressing style to TDomain and TAddress

modified the diagrams as requested

removed the "layered stack" diagrams that compared USM and a
Transport Model processing

removed discussion of speculative features that might exist in
future Transport Models

removed openSession and closeSession ASIs, since those are model-
dependent

Harrington & Schoenwaelder Expires February 28, 2009 [Page 36]

Internet-Draft SNMP Transport Subsystem August 2008

removed the MIB module

removed the MIB boilerplate intro (this memo defines a SMIv2 MIB
...)

removed IANA considerations related to the now-gone MIB module

removed security considerations related to the MIB module

removed references needed for the MIB module

changed receiveMessage ASI to use origin transport domain/address

updated Parameter CSV appendix

Changes from revision -03- to -04-

Harrington & Schoenwaelder Expires August 28, 2008 [Page 31]

Internet-Draft SNMP Transport Subsystem February 2008

changed title from Transport Mapping Security Model Architectural
Extension to Transport Subsystem

modified the abstract and introduction

changed TMSM to TMS

changed MPSP to simply Security Model

changed SMSP to simply Security Model

changed TMSP to Transport Model

removed MPSP and TMSP and SMSP from Acronyms section

modified diagrams

removed most references to dispatcher functionality

worked to remove dependencies between transport and security
models.

defined snmpTransportModel enumeration similar to
snmpSecurityModel, etc.

eliminated all reference to SNMPv3 msgXXXX fields

changed tmSessionReference back to tmStateReference

Changes from revision -02- to -03-

Harrington & Schoenwaelder Expires February 28, 2009 [Page 37]

Internet-Draft SNMP Transport Subsystem August 2008

o removed session table from MIB module

o removed sessionID from ASIs

o reorganized to put ASI discussions in EOP section, as was done in
SSHSM

o changed user auth to client auth

o changed tmStateReference to tmSessionReference

o modified document to meet consensus positions published by JS

* authoritative is model-specific

* msgSecurityParameters usage is model-specific

* msgFlags vs. securityLevel is model/implementation-specific

* notifications must be able to cause creation of a session

* security considerations must be model-specific

* TDomain and TAddress are model-specific

* MPSP changed to SMSP (Security Model security processing)

Changes from revision -01- to -02-

o wrote text for session establishment requirements section.

o wrote text for session maintenance requirements section.

o removed section on relation to SNMPv2-MIB

o updated MIB module to pass smilint

o Added Structure of the MIB module, and other expected MIB-related
sections.

o updated author address

o corrected spelling

o removed msgFlags appendix

o Removed section on implementation considerations.

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 32] 38]

Internet-Draft SNMP Transport Subsystem February August 2008

o started modifying the security boilerplate to address TMS and MIB
security issues

o reorganized slightly to better separate requirements from proposed
solution. This probably needs additional work.

o removed section with sample protocols and sample
tmSessionReference.

o Added section for acronyms

o moved section comparing parameter passing techniques to appendix.

o Removed section on notification requirements.

Changes from revision -00-

o changed SSH references from I-Ds to RFCs

o removed parameters from tmSessionReference for DTLS that revealed
lower layer info.

o Added TMS-MIB module

o Added Internet-Standard Management Framework boilerplate

o Added Structure of the MIB Module

o Added MIB security considerations boilerplate (to be completed)

o Added IANA Considerations

o Added ASI Parameter table

o Added discussion of Sessions

o Added Open issues and Change Log

o Rearranged sections

Harrington & Schoenwaelder Expires February 28, 2009 [Page 39]

Internet-Draft SNMP Transport Subsystem August 2008

Authors' Addresses

David Harrington
Huawei Technologies (USA)
1700 Alma Dr. Suite 100
Plano, TX 75075
USA

Phone: +1 603 436 8634
EMail: dharrington@huawei.com

Juergen Schoenwaelder
Jacobs University Bremen
Campus Ring 1
28725 Bremen
Germany

Phone: +49 421 200-3587
EMail: j.schoenwaelder@iu-bremen.de

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 33] 40]

Internet-Draft SNMP Transport Subsystem February August 2008

Full Copyright Statement

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.

This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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.

Intellectual Property

The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights 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; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.

Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.

Acknowledgement

Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).

Harrington & Schoenwaelder Expires August February 28, 2008 2009 [Page 34] 41]

----