WDIFF

draft-ietf-isms-tmsm-05.txt --> draft-ietf-isms-tmsm-06.txt

Network Working Group D. Harrington
Internet-Draft Huawei Technologies (USA)
Updates: 3411,3412,3414,3417 J. Schoenwaelder
(if approved) International University Bremen
Intended status: Standards Track J. Schoenwaelder February 5, 2007
Expires: June 16, August 9, 2007 International University Bremen
December 13, 2006

Transport Subsystem for the Simple Network Management Protocol (SNMP)
draft-ietf-isms-tmsm-05
draft-ietf-isms-tmsm-06

Status of This Memo

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This Internet-Draft will expire on June 16, August 9, 2007.

Abstract

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

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and modularity of such Transport Models. This document identifies
and discusses describes some key aspects that need to be considered for any
transport model
Transport Model for SNMP.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 4
1.1. The Internet-Standard Management Framework . . . . . . . . 3 4
1.2. Where this Extension Fits . . . . . . . . . . . . . . . . 4
1.3. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3 6
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 6
3. Requirements of a Transport Model . . . . . . . . . . . . . . 6 8
3.1. Message Security Requirements . . . . . . . . . . . . . . 6 8
3.1.1. Security Protocol Requirements . . . . . . . . . . . . 6 8
3.2. SNMP Requirements . . . . . . . . . . . . . . . . . . . . 7 9
3.2.1. Architectural Modularity Requirements . . . . . . . . 7 9
3.2.2. Access Control Requirements . . . . . . . . . . . . . 11 13
3.2.3. Security Parameter Passing Requirements . . . . . . . 12 14
3.2.4. Separation of Authentication and Authorization . . . . 15
3.3. Session Requirements . . . . . . . . . . . . . . . . . . . 14 16
3.3.1. Session Establishment Requirements . . . . . . . . . . 14 17
3.3.2. Session Maintenance Requirements . . . . . . . . . . . 16 18
3.3.3. Message security versus session security . . . . . . . 16 18
4. Scenario Diagrams for the Transport Subsystem . . . . . . . . 17 19
4.1. Command Generator or Notification Originator . . . . . . . 17 19
4.2. Command Responder . . . . . . . . . . . . . . . . . . . . 18 21
5. Cached Information and References . . . . . . . . . . . . . . 19 22
5.1. securityStateReference . . . . . . . . . . . . . . . . . . 20 23
5.2. tmStateReference . . . . . . . . . . . . . . . . . . . . . 21 24
6. Abstract Service Interfaces . . . . . . . . . . . . . . . . . 21 24
6.1. Generating an Outgoing SNMP Message sendMessage ASI . . . . . . . . . . . 22 . . . . . . . . . . 24
6.2. Processing for an Other Outgoing Message ASIs . . . . . . . . . . . . 23
6.3. Processing an Incoming SNMP Message . . . . . . . 25
6.3. The receiveMessage ASI . . . . 23
6.3.1. Processing an Incoming Message . . . . . . . . . . . . 23
6.3.2. Prepare Data Elements from . . 26
6.4. Other Incoming Messages ASIs . . . . . 23
6.3.3. Processing an Incoming Message . . . . . . . . . . . . 24 . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 25 28
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 29
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26 29
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 29
10.1. Normative References . . . . . . . . . . . . . . . . . . . 26 29
10.2. Informative References . . . . . . . . . . . . . . . . . . 27 30
Appendix A. Parameter Table . . . . . . . . . . . . . . . . . . . 28 31
A.1. ParameterList.csv . . . . . . . . . . . . . . . . . . . . 28 31
Appendix B. Why tmStateReference? . . . . . . . . . . . . . . . . 29 33
B.1. Define an Abstract Service Interface . . . . . . . . . . . 29 33
B.2. Using an Encapsulating Header . . . . . . . . . . . . . . 30 33
B.3. Modifying Existing Fields in an SNMP Message . . . . . . . 30 34
B.4. Using a Cache . . . . . . . . . . . . . . . . . . . . . . 30 34
Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . . 31 34
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 31 35

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1. Introduction

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

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

It is expected that readers of this document are to be interpreted as described will have read RFC3410
and RFC3411, and have a general understanding of the functionality
defined in RFC 2119 [RFC2119].

2. Motivation

There are multiple ways to secure one's home or business, in a
continuum of alternatives. Let's consider three general approaches.
In the first approach, an individual could buy a gun, learn to use
it, and sit on your front porch waiting for intruders. In the second
approach, one could hire an employee with a gun, schedule the
employee, position the employee to guard what you want protected,
hire a second guard to cover if the first gets sick, and so on. In
the third approach, you could hire a security company, tell them what
you want protected, and they could hire employees, train them, buy
the guns, position the guards, schedule the guards, send a
replacement when a guard cannot make it, etc., thus providing the
security you want, with no significant effort on your part other than
identifying requirements and verifying the quality of the service
being provided. RFCs 3412-3418.

The User-based Security Model (USM) as defined in [RFC3414] largely
uses the first approach - it provides its own security. It utilizes
existing mechanisms (SHA=the gun), but provides all the coordination.
USM provides "Transport Subsystem" is an additional component 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 SNMP
Engine depicted in order to use
SNMPv3 is a deterrent to deploying SNMPv3. It is possible but
difficult to define external mechanisms that handle the distribution RFC3411, section 3.1.

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of keys for use by the USM approach.

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

A solution based on the third approach might 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. 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 [RFC4366], SASL
[RFC4422], and SSH [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. February 2007

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 NETCONF [I-D.ietf-netconf-ssh].

This document describes a Transport Subsystem extension to following diagram depicts its place in the RFC3411 architecture.

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This extension allows

The transport mappings defined in RFC3417 do not provide lower-layer
security to be provided by an external protocol
connected to the SNMP engine through an SNMP transport-model
[RFC3417]. Such a transport model would then enable the use of
existing functionality, and thus do not provide transport-specific
security mechanisms such as (TLS) [RFC4366] or SSH [RFC4251]
within the parameters. This document updates 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 RFC3417 by many different application layer
protocols. The motivation behind the
defining an architectural extension and ASIs that transport subsystem is to
leverage these protocols where it seems useful.

There are a number of challenges mappings
(models) can use to be addressed pass transport-specific security parameters to map the
other subsystems, including transport-specific security parameters
translated into the transport-independent securityName and
securityLevel.

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provided by a secure transport into the SNMP architecture so that
SNMP continues to work without any surprises. These challenges February 2007

1.3. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are
discussed to be interpreted as described in detail RFC 2119 [RFC2119].

The key words "must", "must not", "required", "shall", "shall not",
"should", "should not", "recommended", "may", and "optional" in this document. For some key issues, design
choices
document are discussed that may be made not to provide be interpreted as described in RFC2119. They
will usually, but not always, be used in a workable solution
that meets operational requirements and fits into context relating to
compatibility with the SNMP RFC3411 architecture or the subsystem defined in [RFC3411].

3. Requirements
here, but which might have no impact on on-the-wire compatibility.
These terms are used as guidance for designers of a Transport Model

3.1. Message Security Requirements

Transport security protocols SHOULD ideally provide proposed IETF
models to make the protection
against the following message-oriented threats [RFC3411]:

1. modification designs compatible with RFC3411 subsystems and
Abstract Service Interfaces (see section 3.2). Implementers are free
to implement differently. Some usages of information these lowercase terms are
simply normal English usage.

2. masquerade
3. message stream modification
4. disclosure

According to [RFC3411], it is not required Motivation

Just as there are multiple ways to protect against denial
of service secure one's home or traffic analysis.

3.1.1. Security Protocol Requirements

There are business, in
a number continuum of standard protocols that could be proposed as
possible solutions within the transport subsystem. Some factors
should be considered when selecting alternatives, there are multiple ways to secure a
network management protocol.

Using 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 protocol in second guard to cover if the first gets
sick, and so on. In the third approach, he could hire a manner for which it was not designed has
numerous problems. The advertised security characteristics of
company, tell them what he wants protected, and they could hire
employees, train them, position the guards, schedule the guards, send
a
protocol may depend replacement when a guard cannot make it, etc., thus providing the
desired security, with no significant effort on its his part other than
identifying requirements and verifying the quality of the service
being used provided.

The User-based Security Model (USM) as designed; when used defined in other
ways, it may not deliver [RFC3414] largely
uses the expected security characteristics. first approach - it provides its own security. It
is recommended that any proposed model include a discussion of the
applicability of the transport model.

A transport model should require no modifications to the underlying
protocol. Modifying the protocol may change its security
characteristics in ways that would impact other utilizes
existing usages. If
a change is necessary, mechanisms (e.g., SHA), but provides all the change should be an extension that has no
impact on coordination.
USM provides for the existing usages. It is recommended that any transport
model include authentication of a discussion principal, message
encryption, data integrity checking, timeliness checking, etc.

USM was designed to be independent of potential impact on other usages of the
protocol.

It has been existing security
infrastructures. USM therefore requires a long-standing requirement separate principal and key
management infrastructure. Operators have reported that SNMP be able deploying
another principal and key management infrastructure in order to work
when the network use
SNMPv3 is unstable, to enable network troubleshooting and
repair. The UDP approach has been considered a deterrent to meet that need well,
with an assumption that getting small messages through, even if out
of order, deploying SNMPv3. It is better than getting no messages through. There has been possible to use

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a long debate about whether UDP actually offers better support than
TCP when February 2007

external mechanisms to handle the underlying IP or lower layers are unstable. There has
been recent discussion distribution of whether operators actually keys for use SNMP to
troubleshoot and repair unstable networks.

There has been discussion of ways SNMP could be extended to better
support management/monitoring needs when a network by
USM. The more important issue is running just
fine. Use of that operators wanted to leverage a TCP transport, for example, could enable larger
message sizes and more efficient table retrievals.

Transport models MUST be able
single user base that wasn't specific to coexist with other transport models,
and may be designed to utilize either TCP or UDP or SCTP.

3.2. SNMP Requirements

3.2.1. Architectural Modularity Requirements

SNMP version 3 (SNMPv3) is SNMP.

A solution based on the second approach might use a modular architecture (described
in [RFC3411] section 3) to allow USM-compliant
architecture, but combine the evolution of authentication mechanism with an
external mechanism, such as RADIUS [RFC2865], to provide the SNMP
authentication service. It might be possible to utilize an external
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, encrypt a messaging
subsystem permitting different message versions message, to be handled by a
single engine, an application subsystem check timeliness, to support different types check data
integrity, etc. It is difficult to cobble together a number of
application processors,
subcontracted services and an access control subsystem for allowing
multiple approaches coordinate them however, because it is
difficult 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 build solid security bindings between the need various
services, and potential for a transport subsystem compatible with gaps in the RFC3411 architecture.

In SNMPv2, there were many problems of side effects between
subsystems caused by security is significant.

A solution based on the manipulation of MIB objects, especially
those related third approach might utilize one or more
lower-layer security mechanisms to provide the message-oriented
security services required. These would include authentication and authorization, because many of
the parameters were stored in shared MIB objects, and different
models sender, encryption, timeliness checking, and protocols could assign different values to the objects.
Contributors assumed slightly different shades data integrity
checking. There are a number of meaning depending
on IETF standards available or in
development to address these problems through security layers at the models
transport layer or application layer, among them TLS [RFC4366], SASL
[RFC4422], and protocols being used. As the shared MIB module
design was modified SSH [RFC4251].

From an operational perspective, it is highly desirable to accommodate a specific model, use
security mechanisms that can unify the administrative security
management for SNMPv3, command line interfaces (CLIs) and other models
which
management interfaces. The use of security services provided by
lower layers is the approach commonly used for the same MIB objects would be broken.

Abstract Service Interfaces (ASIs) were developed to pass model-
independent parameters. The models were required to translate from
their model-dependent formats into CLI, and is also
the approach being proposed for NETCONF [RFC4741].

This document defines a model-independent format,
defined using model-independent semantics, which would not impact
other models.

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Parameters have been provided in the ASIs extension to pass model-independent
information about the authentication that has been provided. These
parameters include a model-independent identifier of the security
"principal", RFC3411
architecture based on the third approach. This extension specifies
how other lower layer protocols with common security model infrastructures
can be used to perform underneath the authentication, SNMP protocol and which SNMP-specific the desired goal of
unified administrative security can be met.

This extension allows security features were applied to the message
(authentication and/or privacy).

Parameters have been be provided in the ASIs by an external protocol
connected to pass model-independent
transport address information. These parameters utilize the
transportDomain and transportAddress

The design of a transport subsystem must abide the goals of the
RFC3411 architecture defined in [RFC3411]. To that end, this
transport subsystem proposal uses a modular design that will permit
transport models to be advanced SNMP engine through an SNMP Transport Model
[RFC3417]. Such a Transport Model would then enable the standards process
independently of other transport models, and independent use of other
modular SNMP components as much
existing security mechanisms such as possible.

IETF standards typically require one mandatory to implement solution,
with (TLS) [RFC4366] or SSH [RFC4251]
within the capability RFC3411 architecture.

There are a number of adding new Internet security protocols and mechanisms that
are in the future. Part of
the motivstion wide spread use. Many of developing transport models is them try to develop support
for secure transport protocols, such as provide a transport model that
utilizes the Secure Shell protocol. Any transport model should
define one minimum-compliance security mechanism, preferably one
which is already widely used generic
infrastructure to secure the transport be used by many different application layer protocol.
protocols. The motivation behind the Transport Subsystem permits multiple transport is to
leverage these protocols where it seems useful.

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There are a number of challenges to be
"plugged into" addressed to map the RFC3411 architecture, supported security
provided by corresponding a secure transport models, including models into the SNMP architecture so that
SNMP continues to provide interoperability with existing
implementations. These challenges are security-aware.

The RFC3411 architecture,and the USM assume described in detail in this
document. For some key issues, design choices are described that
might be made to provide a security model is
called by a message-processing model workable solution that meets operational
requirements and will perform multiple
security functions within the fits into the SNMP architecture defined in
[RFC3411].

3. Requirements of a Transport Model

3.1. Message Security Requirements

Transport security subsystem. A transport model protocols SHOULD provide protection against the
following message-oriented threats [RFC3411]:

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 supports could be proposed as
possible solutions within the Transport Subsystem. Some factors
SHOULD be considered when selecting a protocol.

Using a secure transport protocol may perform similar in a manner for which it was not designed has
numerous problems. The advertised security functions within characteristics of a
protocol might depend on it being used as designed; when used in
other ways, it might not deliver the transport subsystem. A transport expected security
characteristics. It is recommended that any proposed model
may perform the translation include a
description of transport security parameters to/from
security-model-independent parameters. To accommodate this, the ASIs
for applicability of the transport subsystem, Transport Model.

A Transport Model SHOULD require no modifications to the messaging subsystem, and underlying
protocol. Modifying the protocol might change its security subsystem will
characteristics in ways that would impact other existing usages. If
a change is necessary, the change SHOULD be extended to pass security-model-
independent values, and an extension that has no
impact on the existing usages. Any Transport Model SHOULD include a cache
description of transport-specific information. potential impact on other usages of the protocol.

Transport Models MUST be able to coexist with each other.

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+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v (traditional February 2007

3.2. SNMP agent)
+-------------------------------------------------------------------+
| +--------------------------------------------------+ |
| | Transport Requirements

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 | |
| | +-----+ +-----+ +-----+ +-----+ +-------+ | |
| | | UDP | | TCP | | SSH | | TLS | . . . | other | | |
| | +-----+ +-----+ +-----+ +-----+ +-------+ | |
| +--------------------------------------------------+ |
| ^ |
| | |
| Dispatcher v |
| +-------------------+ +---------------------+ +----------------+ |
| | Transport | | for enabling
different methods of providing security services, a Message
Processing | | Security | |
| | Dispatch | | Subsystem | | permitting different message versions to be
handled by a single engine, Applications(s) to support different
types of application processors, and an Access Control 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 |
+-------------------------------------------------------------------+

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allowing multiple approaches to access control. The RFC3411
architecture does not include a subsystem for Transport Subsystem December 2006

3.2.1.1. USM and Models,
despite the RFC3411 Architecture

The following diagrams illustrate fact there are multiple transport mappings already
defined for SNMP. This document addresses the difference in need for a Transport
Subsystem compatible with the security
processing RFC3411 architecture. As work is being
done by to expand the USM model transport to include secure transport such as SSH
and the security processing
potentially done by TLS, using a transport model.

The USM security model is encapsulated by the messaging model,
because the messaging model needs to perform the following steps (for
incoming messages)
1) decode the ASN.1 (messaging model)
2) determine the SNMP security model subsystem will enable consistent design and parameters (messaging model)
3) decrypt the encrypted portions
modularity of the message (security model)
4) translate parameters to model-independent parameters (security
model)
5) determine which application should get the decrypted portions
(messaging model), and
6) pass on the decrypted portions with model-independent parameters. such Transport Models.

The USM approach uses SNMP-specific message security and parameters.

3.2.1.2. design of this Transport Subsystem and accepts the RFC3411 Architecture

With goals of the
RFC3411 architecture defined in section 1.5 of [RFC3411]. This
Transport Subsystem, Subsystem uses a modular design that will permit Transport
Models to be advanced through the order standards process independently of the steps may differ
other Transport Models, and
may be handled by different subsystems:
1) decrypt the encrypted portions independent of the message (transport layer)
2*) translate parameters to model-independent parameters (transport
model)
3) determine the other modular SNMP security model and parameters (transport model)
4) decode the ASN.1 (messaging model)
5) determine which application should get
components as much as possible.

Parameters have been added to the decrypted portions
(messaging model)
7) ASIs to pass on the decrypted portions with model-independent security
parameters

If a message is secured using non-SNMP-specific message security and
parameters, then the
transport model should provide the translation
from the authenticated identity (e.g., an SSH user name) address information.

IETF standards typically require one mandatory to implement solution,
with the
securityName capability of adding new mechanisms in step 3.

3.2.1.3. Passing Information between Engines

A secure transport model will establish an encrypted tunnel between the transport models future. Part of two SNMP engines. One transport model
instance encrypts all messages, and
the other transport model
instance decrypts motivation of developing Transport Models is to develop support
for secure transport protocols, such as a Transport Model that
utilizes the messages.

After Secure Shell protocol. Any Transport Model SHOULD
define one minimum-compliance security mechanism, such as
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 layer tunnel 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 established, then called by a Message Processing Model and will

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conceptually Transport Subsystem February 2007

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 sent through described (not shown), and the tunnel from one 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 Mode, the
Transport Security Model, is defined in

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].

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+------------------------------+
| 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 engine to entity |
+-------------------------------------------------------------------+

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another SNMP engine. Once the tunnel is established, multiple SNMP
messages may be able to be passed through the same tunnel.

3.2.2. Access Control Requirements

3.2.2.1. securityName Binding

For SNMP access control to function properly, security processing
must establish a securityModel identifier, a securityLevel, February 2007

3.2.1.1. Processing Differences between USM and a
securityName, which Secure Transport

USM and secure transports differ is the security model independent identifier for
a 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 USM-
specific principal to a security-model independent securityName which
can be used for subsequent processing, such as for access control.

The securityName MUST be bound to the mechanism-specific
authenticated identity, order and this mapping MUST be done for incoming
messages before
responsibilities within the security model passes securityName to RFC3411 architecture. While the message
processing model via steps
are the processIncoming() ASI. This translation
from a mechanism-specific authenticated identity to same, they occur in a securityName
MAY different order, and may be done by
different subsystems. The following lists illustrate the transport model, difference
in the flow and the securityname is then
provided to responsibility for different processing steps for
incoming messages when using USM and when using a secure transport.
(Note that these lists are simplified for illustrative purposes, and
do not represent all details of processing. Transport Models must
provide the detailed elements of procedure.)

With USM and other Security Models, security model to be passed to the message processing
model.

If starts when
the type Message Processing Model decodes portions of authentication provided by the transport layer (e.g.
TLS) is considered adequate ASN.1 message to secure and/or encrypt
extract an opaque block of security parameters and header parameters
that identify which Security Model should process the message, but
inadequate message to provide the desired granularity
perform authentication, decryption, timeliness checking, integrity
checking, and translation of access control (e.g.
user-based), then a second authentication (e.g., one provided via a
RADIUS server) MAY be used parameters to provide model-independent
parameters. A secure transport performs those security functions on
the authentication identity
which is bound to message, before the securityName. This approach would require a
good analysis of ASN.1 is decoded.

Step 6 cannot occur until after decryption occurs. Step 6 and beyond
are the potential same for man-in-the-middle attacks or
masquerade possibilities.

3.2.2.2. Separation of Authentication USM and Authorization

A transport model that provides security services should take care to
not violate the separation of authentication a secure transport.

3.2.1.1.1. USM and authorization in the RFC3411 architecture. The isAccessAllowed() primitive is used for
passing security-model independent parameters between Architecture

1) decode the subsystems
of ASN.1 header (Message Processing Model)
2) determine the architecture.

Mapping of (securityModel, securityName) SNMP Security Model and parameters (Message
Processing Model)
3) verify securityLevel. [Security Model]
4) translate parameters to an access control policy
should be handled within model-independent parameters (Security
Model)
5) authenticate and decrypt message. [Security Model]
6) determine the access control subsystem, not pduType in the
transport or security subsystems, to be consistent with decrypted portions (Message
Processing Model), and
7) pass on the
modularity of decrypted portions with model-independent parameters.

3.2.1.2. Transport Subsystem and the RFC3411 architecture. This separation was a
deliberate decision of the SNMPv3 WG, Architecture

1) authenticate and decrypt message. [Transport Model]
2) translate parameters to allow support for
authentication protocols which did not provide authorization model-independent parameters (Transport
Model)
3) decode the ASN.1 header (Message Processing Model)
4) determine the SNMP Security Model and parameters (Message
Processing Model)

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capabilities, and to support authorization schemes, such as VACM,
that do not perform their own authentication.

An authorization model (in February 2007

5) verify securityLevel [Security Model]
6) determine the access control subsystem) MAY require
authentication by certain securityModels pduType in the decrypted portions (Message
Processing Model), and
7) pass on the decrypted portions with model-independent security
parameters

If a minimum securityLevel
to allow access to message is secured using a secure transport layer, then the data.
Transport models that Model should provide the translation from the authenticated
identity (e.g., an SSH user name) to the securityName in step 3.

3.2.1.3. Passing Information between Engines

A secure transport are Transport Model will establish an enhancement for authenticated and/or
encrypted tunnel between the SNMPv3 privacy and authentication, but they are not Transport Models of two SNMP engines.
After a significant
improvement for transport layer tunnel is established, then SNMP messages can
be sent through the authorization (access control) needs of SNMPv3.
Only tunnel from one SNMP engine to the model-independent parameters for other SNMP
engine. Transport Models MAY support sending multiple SNMP messages
through the isAccessAllowed()
primitive [RFC3411] are provided by same tunnel.

3.2.2. Access Control Requirements

RFC3411 made some design decisions related to the transport support of an
Access Control Subsystem. These include a securityName and security
subsystems.

A transport model must not specify how
securityLevel mapping, the securityModel separation of Authentication and
Authorization, and the passing of model-independent security
parameters.

3.2.2.1. securityName could be dynamically mapped to an and securityLevel Mapping

For SNMP access control
mechanism, to function properly, Security Models MUST
establish a securityLevel and a securityName, which is the security-
model-independent identifier for a 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 VACM-style groupName. The
mapping of
(securityModel, securityName) between the security-model-specific principal to a groupName is a VACM-specific
mechanism security-
model independent securityName which can be used for subsequent
processing, such as for naming an access control policy, control.

The securityName MUST be mapped from the mechanism-specific
authenticated identity, and this mapping must be done for tying incoming
messages before the
named policy Security Model passes securityName to the addressing capabilities of Message
Processing Model via the data modeling
language (e.g. SMIv2 [RFC2578]), processIncoming ASI. This translation from
a mechanism-specific authenticated identity to a securityName might
be done by the operations supported, Transport Model, and other
factors. Providing a binding outside the Access Control subsystem
might create dependencies that could make it harder to develop
alternate models of access control, such as one built on UNIX groups
or Windows domains. The preferred approach securityName is then provided
to pass the model-
independent security parameters Security Model via the isAccessAllowed() ASI, and
perform tmStateReference to be passed to the mapping from
Message Processing Model.

If the model-independent security parameters type of authentication provided by the transport layer (e.g.,

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TLS) is considered adequate to secure and/or encrypt the message, but
inadequate to
an authorization-model-dependent access policy within provide the desired granularity of access control model.

To provide support for protocols which simultaneously send
information for
(e.g., user-based), then a second authentication and authorization, such as (e.g., one provided
via a RADIUS
[RFC2865], model-specific authorization information server) MAY be cached or
otherwise made available used to provide the access control subsystem, e.g., via a
MIB table similar authentication
identity which is mapped to the vacmSecurityToGroupTable, so the access
control subsystem can create an appropriate binding between the
model-independent securityModel and securityName and a model-specific
access control policy. securityName. This may be highly undesirable, however, if
it creates a dependency between a transport model or a security model
and an access control model, just as it is undesirable for a
transport model to create approach would
require a dependency between an SNMP message
version and good analysis of the security provided by a transport model. potential for man-in-the-middle
attacks or masquerade possibilities.

3.2.3. Security Parameter Passing Requirements

RFC3411 section 4 describes primitives to describe the abstract data flows between the various
subsystems, models and applications within the architecture.
Abstract Service Interfaces describe the flow of

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data data, passing model-
independent information between subsystems within an engine. The ASIs generally pass
model-independent information.

Within an engine using a transport model, outgoing SNMP messages are
passed unencrypted from the message dispatcher to
RFC3411 architecture has no ASI parameters for passing security
information between the transport
model, Transport Subsystem and incoming messages are passed unencrypted from the
transport model to dispatcher, or
between the message dispatcher. dispatcher and the Message Processing Model. This
document defines or modifies ASIs for this purpose.

The security parameters include a model-independent identifier of the
security "principal", "principal" (the securityName), the security model Security Model used to
perform the authentication, and which SNMP-specific security authentication and privacy
services were (should be) applied to the message (authentication and/or privacy).

In the RFC3411 architecture, which reflects the USM security model
design, the messaging model must (securityLevel).

A Message Processing Model might unpack SNMP-specific security
parameters from an incoming message before calling a specific
security model
Security Model to authenticate and decrypt an incoming message,
perform integrity checking, and translate model-specific security security-model-specific
parameters into model-independent parameters. When using a secure transport model,
Transport Model, security parameters MAY might be provided through means
other than carrying them in the SNMP message.
The parameters MAY be provided by SNMP applications for outgoing
messages, and message; the parameters for
incoming messages MAY might be extracted from the transport layer by the transport model
Transport Model before the message is passed to the message processing subsystem. Message
Processing 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 the
Transport Subsystem and the Message Processing and Security
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 Transport Model will
provide the security services, it is necessary to a Message Processing Model might have an security
model because it is the security model that

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a Security Model actually creates create the message from its component
parts. Whether there are any security services provided by the security model
Security Model for an outgoing message is
model-dependent. security-model-dependent.
For incoming messages, even when a secure transport model Transport Model provides
security services, a security model is necessary because there Security Model might
be provide some security
functionality that can only be provided after the message version is known. or
other parameters are extracted from the message.

3.2.4. Separation of Authentication and Authorization

The message version RFC3411 architecture defines a separation of authentication and
authorization (access control), and a Transport Model that provides
security services should take care to not violate this separation. A
Transport Model must not specify how the securityModel and
securityName could be dynamically mapped to an access control
mechanism, such as a VACM-style groupName.

The RECOMMENDED approach is determined by to pass the
Message Processing model model-independent security
parameters via the isAccessAllowed ASI, and passed to perform the mapping from
the model-independent security model via parameters to an access-control-model-
dependent policy within the
processIncoming() ASI. Access Control Model. The RFC3411 architecture has no
isAccessAllowed ASI parameters is used for passing the securityModel,
securityName, and securityLevel parameters that are independent of
any specific security
information between model and any specific access control model to
the Access Control Subsystem.

The mapping of (securityModel, securityName, securityLevel) to an
access-control-model-specific policy should be handled within a transport
specific access control model. This mapping (a transport model) and should not be done in
the
dispatcher, and between Transport or Security Subsystems, to be consistent with the dispatcher and
modularity of the message processing
model. RFC3411 architecture. This document describes separation was a cache mechanism, into which
deliberate decision of the transport
model puts information about SNMPv3 WG, to allow support for
authentication protocols which did not provide authorization (access
control) capabilities, and to support authorization schemes, such as
VACM, that do not perform their own authentication.

The View-based Access Control Model uses the transport securityModel and security parameters

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applied the
securityName as inputs to check for access rights. It determines the
groupName as a transport connection or an incoming message, function of securityModel and securityName. Providing
a
security model MAY extract binding outside the Access Control Subsystem might create
dependencies that could make it harder to develop alternate models of
access control, such as one built on UNIX groups or Windows domains.

To provide support for protocols which simultaneously send
information from for authentication and authorization (access control),
such as RADIUS [RFC2865], access-control-model-specific information
might be cached or otherwise made available to the Access Control
Subsystem, e.g., via a MIB table similar to the cache. A
tmStateReference is passed as an extra parameter in

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vacmSecurityToGroupTable, so the ASIs of Access Control Subsystem can create
an appropriate binding between the
transport subsystem access-control-model-independent
securityModel and the messaging securityName and security subsystems, to
identify the relevant cache. an access-control-model-specific
policy. This approach of passing would be highly undesirable, however, if it creates a model-independent reference is consistent
with the securityStateReference cache already being passed around in
the RFC3411 ASIs.
dependency between a Transport Model or a Security Model and an
Access Control Model.

3.3. Session Requirements

Some secure transports may might have a notion of sessions, while other
secure transports might provide channels or other session-like thing.
mechanism. Throughout this document, the term session is used in a
broad sense to cover sessions, channels, and session-like things. mechanisms.
Session refers to an association between two SNMP engines that
permits the transmission of one or more SNMP messages within the
lifetime of the session. How the session is actually established,
opened, closed, or maintained is specific to a particular transport model. Transport
Model.

Sessions are not part of the SNMP architecture described defined in [RFC3411],
but are considered desirable because the cost of authentication can
be amortized over potentially many transactions.

It is important to note that the

The architecture described defined in [RFC3411] does not include a session
selector in the Abstract Service Interfaces, and neither is that done
for the transport subsystem, Transport Subsystem, so an SNMP application cannot has no mechanism
to select the a session using the ASIs except by passing a unique
combination of transport type, transport address, transportDomain, transportAddress, securityName,
securityModel, and securityLevel.

All Implementers, of course, might
provide non-standard mechanisms to select sessions. The
transportDomain and transportAddress identify the transport models
connection to a remote network node; the securityName identifies
which security principal to communicate with at that address (e.g.,
different NMS applications), and the securityModel and securityLevel
might permit selection of different sets of security properties for
different purposes (e.g., encrypted SETs vs. non-encrypted GETs).

All Transport Models should discuss the impact of sessions on SNMP
usage, including how to establish/open a transport session (i.e., how
it maps to the concepts of session-like things mechanisms of the underlying
protocol), how to behave when a session cannot be established, how to
close a session properly, how to behave when a session is closed
improperly, the session security properties, session establishment
overhead, and session maintenance overhead.

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

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3.3.1. Session Establishment Requirements

SNMP applications must provide the transport type, transport address, transportDomain, transportAddress,
securityName, securityModel, and securityLevel to be used for a
session.

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SNMP Applications typically might have no knowledge of whether the session that
will be used to carry commands was initially established as a
notification session, or a request-response session, and SHOULD NOT
make any assumptions based on knowing the direction of the session.
If an administrator or transport model Transport Model designer wants to
differentiate a session established for different purposes, such as a
notification session versus a request-response session, the
application can use different securityNames or transport addresses
(e.g., port 161 vs. port 162) for different purposes.

An SNMP engine containing an application that initiates
communication, e.g., a Command Generator or Notification Originator,
MUST
must be able to attempt to establish a session for delivery if a
session does not yet exist. If a session cannot be established then
the message is discarded.

Sessions are usually established by the transport model Transport Model when no
appropriate session is found for an outgoing message, but sessions
may
might be established in advance to support features such as
notifications. How sessions are established in advance is beyond the
scope of this document.

Sessions are initiated by notification originators when there is no
currently established connection that can be used to send the
notification. For a client-server security protocol, this may might
require provisioning authentication credentials on the agent, either
statically or dynamically, so the client/agent can successfully
authenticate to a notification receiver.

A transport model Transport Model must be able to determine whether a session does or
does not exist, and must be able to determine which session has the
appropriate security characteristics (transport type, transport
address, (transportDomain,
transportAddress, securityName, securityModel, and securityLevel) for
an outgoing message.

A transport model Transport Model implementation MAY reuse an already established
session with the appropriate transport type, transport address, transportDomain, transportAddress,
securityName, securityModel, and securityLevel characteristics for
delivery of a message originated by containing a different type of application pduType than originally
caused the session to be created. For example, an implementation
that has an existing session originally established to receive a
request may MAY use that session to send an outgoing notification, and may

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MAY use a session that was originally established to send a
notification to send a request. Responses are expected to SHOULD be returned using
the same session that carried the corresponding request message.
Reuse of sessions is not required for conformance.

If a session can be reused for a different type of message, pduType, but a

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not prepared to accept different message types pduTypes over the same session, then
the message MAY be dropped by the receiver. This
may strongly affect the usefulness of session reuse, and transport
models should define a standard behavior for this circumstance.

3.3.2. Session Maintenance Requirements

A transport model Transport Model can tear down sessions as needed. It may 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.
While it is possible for an implementation to automatically tear down
each session once an operation 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 may discuss describe when cached information can be
discarded, in some circumstances, and the timing of cache cleanup may
might have security implications, but cache memory management is an
implementation issue.

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

3.3.3. Message security versus session security

A transport model 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 established at the beginning of the session SHOULD
be used to provide authentication, integrity checking, and encryption
services for data that is communicated during the session. The
cryptographic protocols used to establish keys for a transport model Transport Model
session SHOULD ensure that fresh new session keys are generated for
each session. If each session uses new session keys, then messages
cannot be replayed from one session to another. In addition sequence information MAY 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 a
cross-session replay attack will be unsuccessful; that is, an
attacker cannot successfully replay on one session a message he
observed from another session. A transport model good security protocol will also

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protect against replay attacks _within_ a session; that is, an
attacker cannot successfully replay a message observed earlier in the
same session.

A Transport Model session will typically have a single transport
type, transport address, transportDomain,
transportAddress, securityModel, securityName and securityLevel
associated with it. If an exchange between communicating engines
requires a different securityLevel or is on behalf of a different
securityName, or uses a different securityModel, then another session
would be needed. An immediate

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implementations should SHOULD be able to maintain some reasonable number of
concurrent sessions.

For transport models, Transport Models, securityName is typically should be specified during session
setup, and associated with the session identifier.

SNMPv3 was designed to support multiple levels of security,
selectable on a per-message basis by an SNMP application, because 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 may
might add significant overhead to processing of the messages.

Some transport models MAY 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 Transport Model may
upgrade the requested security level, i.e. noAuth/noPriv noAuthNoPriv and auth/
noPriv
authNoPriv MAY be sent over an authenticated and encrypted session.

4. Scenario Diagrams for the Transport Subsystem

RFC3411 section 4.6 provides scenario diagrams to illustrate how an
outgoing message is created, and how an incoming message is
processed. Both diagrams are incomplete, however. In section 4.6.1,
the diagram doesn't show the an ASI for sending an SNMP request to the
network or for receiving an SNMP response message from the network.
In section 4.6.2, the diagram doesn't illustrate show the interfaces required ASIs to receive an
SNMP message from the network, or to send an SNMP message to the
network.

4.1. Command Generator or Notification Originator

This diagram from RFC3411 4.6.1 shows how a Command Generator or
Notification Originator application [RFC3413] requests that a PDU be
sent, and how the response is returned (asynchronously) to that
application.

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

Command Dispatcher Message Security
Generator | Processing Model
| | Model |
| sendPdu | | |
|------------------->| | |
| | prepareOutgoingMessage | |
: |----------------------->| |
: | | generateRequestMsg |
: | |-------------------->|
: | | |
: | |<--------------------|
: | | |
: |<-----------------------| |
: | | |
: |------------------+ | |
: | Send SNMP | | |
: | Request Message | | |
: | to Network | | |
: | v | |
: : : : :
: : : : :
: : : : :
: | | | |
: | Receive SNMP | | |
: | Response Message | | |
: | from Network | | |
: |<-----------------+ | |
: | | |
: | prepareDataElements | |
: |----------------------->| |
: | | processIncomingMsg |
: | |-------------------->|
: | | |
: | |<--------------------|
: | | |
: |<-----------------------| |
| processResponsePdu | | |
|<-------------------| | |
| | | |

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4.2. Command Responder

This diagram shows how a Command Responder or Notification Receiver
application registers for handling a pduType, how a PDU is dispatched
to the application after an SNMP message is received, and how the
Response is (asynchronously) send sent back to the network.

This document defines the sendMessage and receiveMessage ASIs for
this purpose.

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Command Dispatcher Message Security
Responder | Processing Model
| | Model |
| | | |
| registerContextEngineID | | |
|------------------------>| | |
|<------------------------| | | |
| | Receive SNMP | | |
: | Message | | |
: | from Network | | |
: |<-------------+ | |
: | | |
: |prepareDataElements | |
: |------------------->| |
: | | processIncomingMsg |
: | |------------------->|
: | | |
: | |<-------------------|
: | | |
: |<-------------------| |
| processPdu | | |
|<------------------------| | |
| | | |
: : : :
: : : :
| returnResponsePdu | | |
|------------------------>| | |
: | prepareResponseMsg | |
: |------------------->| |
: | |generateResponseMsg |
: | |------------------->|
: | | |
: | |<-------------------|
: | | |
: |<-------------------| |
: | | |
: |--------------+ | |
: | Send SNMP | | |
: | Message | | |
: | to Network | | |
: | v | |

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 must flow flows between subsystems.

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subsystems. February 2007

There are two levels of state that may might need to be maintained: the
security state in a request-response pair, and potentially long-term
state relating to transport and security.

This state is maintained in caches. 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 also be discarded, and 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 also be discarded.

This document differentiates the tmStateReference from the
securityStateReference. This document does not specify an
implementation strategy, only an abstract discussion description of the data
that
must flow flows between subsystems. An implementation MAY 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 Transport Model has had an opportunity
to extract the information it needs.

5.1. securityStateReference

From RFC3411: "For each message received, the Security Model caches
the state information such that a Response message can be generated
using the same security information, even if the Local Configuration
Datastore is altered between the time of the incoming request and the
outgoing response.

A Message Processing Model has the responsibility for explicitly
releasing the cached data if such data is no longer needed. response." To enable this, an abstract
securityStateReference data element element, defined in RFC3411 section
A.1.5, is passed from the Security Model to the Message Processing
Model.

The
cached security data may be implicitly released via the generation of
a response, or explicitly released by using the stateRelease
primitive, as described in RFC3411 section 4.5.1."

The information saved should include the model-independent parameters
(transportDomain, transportAddress, securityName, securityModel, and
securityLevel), related security parameters, and other information
needed to imatch match the response with the request. The related security
parameters may include transport-specific security information.

The Message Processing Model has the responsibility for explicitly
releasing the securityStateReference when such data is no longer
needed. The securityStateReference cached data may be implicitly
released via the generation of a response, or explicitly released by
using the

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If the transport model Transport Model connection is closed between the time a
Request is received and a Response message is being prepared, then
the Response message MAY be discarded.

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5.2. tmStateReference

For each message or transport session, information about the message
security is stored in a cache, which may inlcude include model- and
mechanism-specific parameters. The tmStateReference is passed
between subsystems to provide a handle for the cache. A transport
model Transport
Model may store transport-specific parameters in the cache for
subsequent usage. Since the contents of a cache are meaningful only
within an implementation, and not on-the-wire, the format of the
cache is implementation-specific.

The state referenced by tmStateReference may might be saved in a Local
Configuration Datastore (LCD) to make it available across multiple
messages, as compared to securityStateReference which is designed to
be saved only for the life of a request-response pair of messages.
It is expected that an LCD will allow lookup based on the combination
of transportDomain, transportAddress, securityName, securityModel,
and securityLevel, and that the cache contain these values to
reference entries in the LCD.

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.

To simplify entity, and to help keep the elements subsystems independent of procedure, each
other except for the common parameters.

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.
specified in a transport model. As a general rule, if state
information is available when a message gets discarded, the
message-state 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.

2) An error indication in statusInformation may return include an OID and
value for an incremented counter and a value for securityLevel, and
values for contextEngineID and contextName for the counter, and the
securityStateReference 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.

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6.1. Generating an Outgoing February 2007

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 keep in mind that a transport
model might be something like SNMP Message

This section describes the procedure followed by an RFC3411-
compatible system whenever over UDP over IPv6, where no
security is provided, so it generates might have no mechanisms for utilizing a
securityName and securityLevel.

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

6.2. Other Outgoing ASIs

A tmStateReference parameter has been added to the
prepareOutgoingMessage, generateRequestMsg, and generateResponseMsg
ASIs as a request, a response, a notification,
or a report) on behalf of a user. an OUT parameter.

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
)

Note that tmStateReference has been added to this ASI.

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The IN parameters tmStateReference parameter of generateRequestMsg or
generateResponseMsg is passed in the prepareOutgoingMessage() ASI are used to
pass information from the dispatcher (from return parameters of the application subsystem)
Security Subsystem to the message processing subsystem.

The abstract service primitive from a Message Processing Model to Subsystem. If a
Security Model to generate the components of cache
exists for a Request message is
generateRequestMsg().

The abstract service primitive session identifiable from a Message Processing Model to a transportDomain,
transportAddress, securityModel, securityName, and securityLevel,
then an appropriate Security Model might create a tmStateReference to generate
the components of a Response message is
generateResponseMsg().

Upon completion of processing, cache and pass that as an OUT parameter.

If one does not exist, the Security Model returns
statusInformation. If might create a cache
referenced by tmStateReference. This information might include
transportDomain, transportAddress, the process was successful, securityModel, the completed
message is returned. If
securityLevel, and the process was not successful, then an
errorIndication is returned.

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specific details. The OUT parameters contents of the prepareOutgoingMessage() ASI are used to
pass cache may be incomplete until
the Transport Model has established a session. What information is
passed, and how this information is determined, is implementation and
security-model-specific.

The prepareOutgoingMessage ASI passes tmStateReference from the message processing model
Message Processing Subsystem to the dispatcher
and on to dispatcher. How or if the transport model:

6.2. Processing for an Outgoing
Message

The sendMessage ASI Processing Subsystem modifies or utilizes the contents of the
cache is used to pass message-processing-model-specific.

This may sound underspecified, but keep in mind that a message
processing model might have access to all the information from the Dispatcher to
cache and from the appropriate transport model for sending.

statusInformation =
sendMessage(
IN destTransportDomain -- transport domain message, and have no need to be used
IN destTransportAddress -- call a Security Model
to do any processing; an application might choose a Security Model
such as USM to authenticate and secure the SNMP message, but also
utilize a secure transport address such as that provided by the SSH Transport
Model to be used
IN outgoingMessage -- send the message to send
IN outgoingMessageLength -- its length
IN tmStateReference -- reference to transport state
) destination.

6.3. Processing an Incoming SNMP Message

6.3.1. Processing an Incoming Message The receiveMessage ASI

If one does not exist, the Transport Model will need to might create an
entry in a Local Configuration Datastore cache
referenced by tmStateReference. This If present, this information will might
include transportDomain, transportAddress, the securityModel, the securityLevel, and the
securityName, plus any model or mechanism-specific details. How this
information is determined is model-specific. implementation and transport-model-
specific.

This may sound underspecified, but keep in mind that 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.

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

statusInformation =
recvMessage(
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
)

6.3.2. Prepare Data Elements from

6.4. Other Incoming Messages

The abstract service primitive from ASIs

To support the Transport Subsystem, the tmStateReference is added to
the prepareDataElements ASI (from the Dispatcher to a the Message
Processing Subsystem), and to the processIncomingMsg ASI (from the
Message Processing Subsystem to the Security Model for Subsystem). How
or if a received message is:

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tmStateReference is message-processing-model-dependent and security-
model-dependent.

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 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
)

Note that tmStateReference has been added to this ASI.

6.3.3. Processing an Incoming Message

This section describes the procedure followed by the Security Model
whenever it receives an incoming message containing a management
operation on behalf of a user from a Message Processing model.

The Message Processing Model extracts some information from the
wholeMsg. The abstract service primitive from a Message Processing
Model to the Security Subsystem for a received message is:

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statusInformation = -- errorIndication or success
-- error counter OID/value if error
processIncomingMsg(
IN messageProcessingModel -- typically, SNMP version
IN maxMessageSize -- of the sending SNMP entity
IN securityParameters -- for the received message
IN securityModel -- for the received message
IN securityLevel -- Level of Security
IN wholeMsg -- as received on the wire
IN wholeMsgLength -- length as received on the wire
IN tmStateReference -- (NEW) from the transport model 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 securityEngineID is set to a value in a model-specific manner.
If the securityEngineID tmStateReference parameter of prepareDataElements is not utilized by passed from
the specific model, then
it should be set dispatcher to the local snmpEngineID, to satisfy Message Processing Subsystem. How or if the SNMPv3
message processing model in RFC 3412 section 7.2 13a).

2) Extract
Message Processing Subsystem modifies or utilizes the value contents of securityName from the Local Configuration
Datastore entry referenced by tmStateReference.

3) The scopedPDU component
cache is extracted message-processing-model-specific.

The processIncomingMessage ASI passes tmStateReference from the wholeMsg.

4) The maxSizeResponseScopedPDU is calculated. This
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 maximum
size allowed for a scopedPDU for a possible Response message.

5) The security data cache is cached as cachedSecurityData, so security-
model-specific.

This may sound underspecified, but keep in mind that a
possible response to this message can
processing model might have access to all the information from the
cache and will use from the same security
parameters. Then securityStateReference is set for subsequent
reference message, and have no need to this cached data.

6) call a Security Model
to do any processing. The statusInformation Message Processing Model might determine
that the USM Security Model is set specified in an SNMPv3 message header;
the USM Security Model has no need of values in the tmStateReference
cache to success authenticate and a return is made to
the calling module passing back secure the OUT parameters SNMP message, but an application
might have chosen to use a secure transport such as specified in that provided by
the processIncomingMsg primitive. SSH Transport Model to send the message to its destination.

7. Security Considerations

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

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It is considered desirable by some industry segments that SNMP

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transport models 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. The
editors recommend 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 each proposed transport model include user. Otherwise an engine that has multiple
transports open might be "tricked" into sending a
discussion in its security considerations of whether perfect forward
security is appropriate for the transport model.

Since message through the cache and LCD will contain security-related parameters,
they should be kept in protected storage.
wrong 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 Security Model proposals: Chris Elliot, Wes
Hardaker, Dave David Harrington, Keith McCloghrie, Kaushik Narayan, Dave 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 committed to and performed detailed reviews: Jeffrey
Hutzelman

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.

[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management
Information Version 2 (SMIv2)", STD 58,
RFC 2578, April 1999.

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[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.

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[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.
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.

[RFC3413] Levi, D., Meyer, P., and B.
Stewart, "Simple Network

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Management Protocol (SNMP)
Applications", STD 62,
RFC 3413, December 2002.

[RFC4366] Blake-Wilson, S., Nystrom,
M., Hopwood, D., Mikkelsen,
J., and T. Wright,
"Transport Layer Security
(TLS) Extensions",
RFC 4366, April 2006.

[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.

[I-D.ietf-netconf-ssh] Wasserman, M. and T. Goddard, "Using the
NETCONF

[RFC4741] Enns, R., "NETCONF
Configuration Protocol over Secure
Shell (SSH)", draft-ietf-netconf-ssh-06 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-02 (work in
progress), March 2006.

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Appendix A. Parameter Table

Following is a CSV Comma-separated-values (CSV) formatted matrix useful
for tracking data flows into and out of the dispatcher, transport, message, Transport,
Message Processing, and security
subsystems. Security Subsystems. This will be of most
use to designers of models, to understand what information is
available at which points in the processing, following the RFC3411
architecture (and this subsystem). Import this into your favorite
spreadsheet or other CSV compatible application. You will need to
remove lines feeds from the second, third, and fourth lines, which
needed to be wrapped to fit into RFC limits. line lengths.

A.1. ParameterList.csv

,Dispatcher,,,,Messaging,,,Security,,,Transport,

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,sendPDU,returnResponse,processPDU,processResponse,

prepareOutgoingMessage,prepareResponseMessage,prepareDataElements,

generateRequest,processIncoming,generateResponse,

sendMessage,recvMessage

sendMessage,receiveMessage

transportDomain,In,,,,In,,In,,,,,In

transportAddress,In,,,,In,,In,,,,,In

destTransportDomain,,,,,Out,Out,,,,,In,

destTransportAddress,,,,,Out,Out,,,,,In,

messageProcessingModel,In,In,In,In,In,In,Out,In,In,In,,

securityModel,In,In,In,In,In,In,Out,In,In,In,,

securityName,In,In,In,In,In,In,Out,In,Out,In,,

securityLevel,In,In,In,In,In,In,Out,In,In,In,,

contextEngineID,In,In,In,In,In,In,Out,,,,,

contextName,In,In,In,In,In,In,Out,,,,,

expectResponse,In,,,,In,,,,,,,

PDU,In,In,In,In,In,In,Out,,,,,

pduVersion,In,In,In,In,In,In,Out,,,,,

statusInfo,Out,In,,In,,In,Out,Out,Out,Out,,

errorIndication,Out,Out,,,,,Out,,,,,

sendPduHandle,Out,,,In,In,,Out,,,,,

maxSizeResponsePDU,,In,In,,,In,Out,,Out,,,

stateReference,,In,In,,,In,Out,,,,,

wholeMessage,,,,,Out,Out,In,Out,In,Out,In,In

messageLength,,,,,Out,Out,In,Out,In,Out,In,In

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errorIndication,Out,Out,,,,,Out,,,,,

sendPduHandle,Out,,,In,In,,Out,,,,,

maxSizeResponsePDU,,In,In,,,In,Out,,Out,,,

stateReference,,In,In,,,In,Out,,,,,

wholeMessage,,,,,Out,Out,In,Out,In,Out,In,In

messageLength,,,,,Out,Out,In,Out,In,Out,In,In February 2007

maxMessageSize,,,,,,,,In,In,In,,

globalData,,,,,,,,In,,In,,

securityEngineID,,,,,,,,In,Out,In,,

scopedPDU,,,,,,,,In,Out,In,,

securityParameters,,,,,,,,Out,In,Out,,

securityStateReference,,,,,,,,,Out,In,,

pduType,,,,,,,Out,,,,,

tmStateReference,,,,,Out,Out,In,,In,,In,In

Appendix B. Why tmStateReference?

This appendix considers why a cache-based approach was selected for
passing parameters. This section may be removed from subsequent
revisions of the document.

There are four approaches that could be used for passing information
between the Transport Model and an 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
4. one could pass the information in an implementation-specific
cache or via a MIB module.

B.1. Define an Abstract Service Interface

Abstract Service Interfaces (ASIs) [RFC3411] are defined by a set of primitives
that specify the services provided and the abstract data

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that are to be passed when the services are invoked. Defining
additional ASIs to pass the security and transport information from
the transport subsystem Transport Subsystem to security subsystem Security Subsystem has the advantage of
being consistent with existing RFC3411/3412 practice, and helps to
ensure that any transport model Transport Model proposals pass the necessary data,
and do not cause side effects by creating model-
specific model-specific dependencies
between itself and other models or other subsystems other than those
that are clearly defined by an ASI.

B.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
messaging security model.

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Message Processing Model. The message header would be included in
the wholeMessage ASI parameter, and would be removed by a
corresponding messaging model. 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 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.

B.3. Modifying Existing Fields in an SNMP Message

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

B.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 may might be multiple TM-security caches, a tmStateReference
is passed as an extra parameter in the ASIs between the transport
subsystem Transport
Subsystem and the security subsystem, Security Subsystem, so the Security Model knows
which cache of information to consult.

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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-
dependent cache is consistent with the securityStateReference already
being passed around in the RFC3411 ASIs.

Appendix C. 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.

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o MUST responses go back on the same session?
o How should we describe the case where a management system wants to
keep session info available for inspection after a session has
closed? see "Abstract Service Interfaces"
o Do Informs work correctly?
o How does a Transport Model know whether a message is a
notification or a request/response?
o cache contents - do we define this?

Appendix D. Change Log

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

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 Transport Models
removed openSession() openSession and closeSession() closeSession ASIs, since those are
model-dependent model-
dependent
removed the MIB module
removed the MIB boilerplate into 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

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Internet-Draft SNMP Transport Subsystem February 2007

removed references needed for the MIB module
changed recvMessage receiveMessage ASI to use origin transport domain/address
updated Parameter CSV appendix
Changes from revision -03- to -04-

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

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Internet-Draft SNMP Transport Subsystem December 2006
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-

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
o
* 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 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

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Internet-Draft SNMP Transport Subsystem February 2007

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.
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

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Internet-Draft SNMP Transport Subsystem December 2006
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

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

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Juergen Schoenwaelder
International University Bremen
Campus Ring 1
28725 Bremen
Germany

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

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