draft-ietf-isms-tmsm-12.txt   draft-ietf-isms-tmsm-13.txt 
Network Working Group D. Harrington Network Working Group D. Harrington
Internet-Draft Huawei Technologies (USA) Internet-Draft Huawei Technologies (USA)
Updates: 3411,3412,3414,3417 J. Schoenwaelder Updates: 3411,3412,3414,3417 J. Schoenwaelder
(if approved) Jacobs University Bremen (if approved) Jacobs University Bremen
Intended status: Standards Track February 25, 2008 Intended status: Standards Track August 27, 2008
Expires: August 28, 2008 Expires: February 28, 2009
Transport Subsystem for the Simple Network Management Protocol (SNMP) Transport Subsystem for the Simple Network Management Protocol (SNMP)
draft-ietf-isms-tmsm-12 draft-ietf-isms-tmsm-13
Status of This Memo Status of This Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
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have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
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This Internet-Draft will expire on August 28, 2008. This Internet-Draft will expire on February 28, 2009.
Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract Abstract
This document defines a Transport Subsystem, extending the Simple This document defines a Transport Subsystem, extending the Simple
Network Management Protocol (SNMP) architecture defined in RFC 3411. Network Management Protocol (SNMP) architecture defined in RFC 3411.
This document defines a subsystem to contain Transport Models, This document defines a subsystem to contain Transport Models,
comparable to other subsystems in the RFC3411 architecture. As work comparable to other subsystems in the RFC3411 architecture. As work
is being done to expand the transport to include secure transport is being done to expand the transports to include secure transports
such as SSH and TLS, using a subsystem will enable consistent design such as SSH and TLS, using a subsystem will enable consistent design
and modularity of such Transport Models. This document identifies and modularity of such Transport Models. This document identifies
and describes some key aspects that need to be considered for any and describes some key aspects that need to be considered for any
Transport Model for SNMP. Transport Model for SNMP.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. The Internet-Standard Management Framework . . . . . . . . 3 1.1. The Internet-Standard Management Framework . . . . . . . . 4
1.2. Where this Extension Fits . . . . . . . . . . . . . . . . 3 1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Conventions . . . . . . . . . . . . . . . . . . . . . . . 5 1.3. Where this Extension Fits . . . . . . . . . . . . . . . . 4
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Requirements of a Transport Model . . . . . . . . . . . . . . 7 3. Requirements of a Transport Model . . . . . . . . . . . . . . 8
3.1. Message Security Requirements . . . . . . . . . . . . . . 7 3.1. Message Security Requirements . . . . . . . . . . . . . . 8
3.1.1. Security Protocol Requirements . . . . . . . . . . . . 7 3.1.1. Security Protocol Requirements . . . . . . . . . . . . 8
3.2. SNMP Requirements . . . . . . . . . . . . . . . . . . . . 8 3.2. SNMP Requirements . . . . . . . . . . . . . . . . . . . . 8
3.2.1. Architectural Modularity Requirements . . . . . . . . 8 3.2.1. Architectural Modularity Requirements . . . . . . . . 9
3.2.2. Access Control Requirements . . . . . . . . . . . . . 11 3.2.2. Access Control Requirements . . . . . . . . . . . . . 12
3.2.3. Security Parameter Passing Requirements . . . . . . . 12 3.2.3. Security Parameter Passing Requirements . . . . . . . 12
3.2.4. Separation of Authentication and Authorization . . . . 13 3.2.4. Separation of Authentication and Authorization . . . . 13
3.3. Session Requirements . . . . . . . . . . . . . . . . . . . 14 3.3. Session Requirements . . . . . . . . . . . . . . . . . . . 14
3.3.1. Session Establishment Requirements . . . . . . . . . . 14 3.3.1. Session Selection . . . . . . . . . . . . . . . . . . 14
3.3.2. Session Maintenance Requirements . . . . . . . . . . . 15 3.3.2. Session Establishment Requirements . . . . . . . . . . 15
3.3.3. Message security versus session security . . . . . . . 16 3.3.3. Session Maintenance Requirements . . . . . . . . . . . 15
3.3.4. Message security versus session security . . . . . . . 16
4. Scenario Diagrams and the Transport Subsystem . . . . . . . . 17 4. Scenario Diagrams and the Transport Subsystem . . . . . . . . 17
5. Cached Information and References . . . . . . . . . . . . . . 17 5. Cached Information and References . . . . . . . . . . . . . . 17
5.1. securityStateReference . . . . . . . . . . . . . . . . . . 18 5.1. securityStateReference . . . . . . . . . . . . . . . . . . 18
5.2. tmStateReference . . . . . . . . . . . . . . . . . . . . . 18 5.2. tmStateReference . . . . . . . . . . . . . . . . . . . . . 18
6. Abstract Service Interfaces . . . . . . . . . . . . . . . . . 19 5.2.1. Transport information . . . . . . . . . . . . . . . . 18
6.1. sendMessage ASI . . . . . . . . . . . . . . . . . . . . . 19 5.2.2. securityName . . . . . . . . . . . . . . . . . . . . . 19
6.2. Other Outgoing ASIs . . . . . . . . . . . . . . . . . . . 20 5.2.3. securityLevel . . . . . . . . . . . . . . . . . . . . 20
6.3. The receiveMessage ASI . . . . . . . . . . . . . . . . . . 22 5.2.4. Session Information . . . . . . . . . . . . . . . . . 20
6.4. Other Incoming ASIs . . . . . . . . . . . . . . . . . . . 22 6. Abstract Service Interfaces . . . . . . . . . . . . . . . . . 20
7. Security Considerations . . . . . . . . . . . . . . . . . . . 24 6.1. sendMessage ASI . . . . . . . . . . . . . . . . . . . . . 21
7.1. Coexistence, Security Parameters, and Access Control . . . 25 6.2. Changes to RFC3411 Outgoing ASIs . . . . . . . . . . . . . 22
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 6.2.1. Message Processing Subsystem Primitives . . . . . . . 22
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26 6.2.2. Security Subsystem Primitives . . . . . . . . . . . . 23
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 6.3. The receiveMessage ASI . . . . . . . . . . . . . . . . . . 25
10.1. Normative References . . . . . . . . . . . . . . . . . . . 26 6.4. Changes to RFC3411 Incoming ASIs . . . . . . . . . . . . . 26
10.2. Informative References . . . . . . . . . . . . . . . . . . 27 6.4.1. Message Processing Subsystem Primitive . . . . . . . . 26
Appendix A. Why tmStateReference? . . . . . . . . . . . . . . . . 28 6.4.2. Security Subsystem Primitive . . . . . . . . . . . . . 27
A.1. Define an Abstract Service Interface . . . . . . . . . . . 28 7. Security Considerations . . . . . . . . . . . . . . . . . . . 28
A.2. Using an Encapsulating Header . . . . . . . . . . . . . . 29 7.1. Coexistence, Security Parameters, and Access Control . . . 29
A.3. Modifying Existing Fields in an SNMP Message . . . . . . . 29 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
A.4. Using a Cache . . . . . . . . . . . . . . . . . . . . . . 29 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . . 30 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 30 10.1. Normative References . . . . . . . . . . . . . . . . . . . 30
10.2. Informative References . . . . . . . . . . . . . . . . . . 31
Appendix A. Why tmStateReference? . . . . . . . . . . . . . . . . 32
A.1. Define an Abstract Service Interface . . . . . . . . . . . 33
A.2. Using an Encapsulating Header . . . . . . . . . . . . . . 33
A.3. Modifying Existing Fields in an SNMP Message . . . . . . . 33
A.4. Using a Cache . . . . . . . . . . . . . . . . . . . . . . 34
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . . 34
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction 1. Introduction
This document defines a Transport Subsystem, extending the Simple This document defines a Transport Subsystem, extending the Simple
Network Management Protocol (SNMP) architecture defined in [RFC3411]. Network Management Protocol (SNMP) architecture defined in [RFC3411].
This document identifies and describes some key aspects that need to This document identifies and describes some key aspects that need to
be considered for any Transport Model for SNMP. be considered for any Transport Model for SNMP.
1.1. The Internet-Standard Management Framework 1.1. The Internet-Standard Management Framework
For a detailed overview of the documents that describe the current For a detailed overview of the documents that describe the current
Internet-Standard Management Framework, please refer to section 7 of Internet-Standard Management Framework, please refer to section 7 of
RFC 3410 [RFC3410]. RFC 3410 [RFC3410].
1.2. Where this Extension Fits 1.2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Non uppercased versions of the keywords should be read as in normal
English. They will usually, but not always, be used in a context
relating to compatibility with the RFC3411 architecture or the
subsystem defined here, but which might have no impact on on-the-wire
compatibility. These terms are used as guidance for designers of
proposed IETF models to make the designs compatible with RFC3411
subsystems and Abstract Service Interfaces (see section 3.2).
Implementers are free to implement differently. Some usages of these
lowercase terms are simply normal English usage.
For consistency with SNMP-related specifications, this document
favors terminology as defined in STD62 rather than favoring
terminology that is consistent with non-SNMP specifications that use
different variations of the same terminology. This is consistent
with the IESG decision to not require the SNMPv3 terminology be
modified to match the usage of other non-SNMP specifications when
SNMPv3 was advanced to Full Standard.
1.3. Where this Extension Fits
It is expected that readers of this document will have read RFC3410 It is expected that readers of this document will have read RFC3410
and RFC3411, and have a general understanding of the functionality and RFC3411, and have a general understanding of the functionality
defined in RFCs 3412-3418. defined in RFCs 3412-3418.
The "Transport Subsystem" is an additional component for the SNMP The "Transport Subsystem" is an additional component for the SNMP
Engine depicted in RFC3411, section 3.1. Engine depicted in RFC3411, section 3.1.
The following diagram depicts its place in the RFC3411 architecture.: The following diagram depicts its place in the RFC3411 architecture.:
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| | | Command | | Notification | | Other | | | | | | Command | | Notification | | Other | | |
| | | Responder | | Originator | | | | | | | | Responder | | Originator | | | | |
| | +-------------+ +--------------+ +--------------+ | | | | +-------------+ +--------------+ +--------------+ | |
| +-------------------------------------------------------------+ | | +-------------------------------------------------------------+ |
| | | |
+-------------------------------------------------------------------+ +-------------------------------------------------------------------+
The transport mappings defined in RFC3417 do not provide lower-layer The transport mappings defined in RFC3417 do not provide lower-layer
security functionality, and thus do not provide transport-specific security functionality, and thus do not provide transport-specific
security parameters. This document updates RFC3411 and RFC3417 by security parameters. This document updates RFC3411 and RFC3417 by
defining an architectural extension and ASIs that transport mappings defining an architectural extension and modifying the ASIs that
(models) can use to pass transport-specific security parameters to transport mappings (hereafter called transport models) can use to
other subsystems, including transport-specific security parameters pass transport-specific security parameters to other subsystems,
translated into transport-independent securityName and securityLevel including transport-specific security parameters that are translated
into the transport-independent securityName and securityLevel
parameters parameters
The Transport Security Model [I-D.ietf-isms-transport-security-model] The Transport Security Model [I-D.ietf-isms-transport-security-model]
and the Secure Shell Transport Model [I-D.ietf-isms-secshell] utilize and the Secure Shell Transport Model [I-D.ietf-isms-secshell] utilize
the Transport Subsystem. The Transport Security Model is an the Transport Subsystem. The Transport Security Model is an
alternative to the existing SNMPv1 Security Model [RFC3584], the alternative to the existing SNMPv1 Security Model [RFC3584], the
SNMPv2c Security Model [RFC3584], and the User-based Security Model SNMPv2c Security Model [RFC3584], and the User-based Security Model
[RFC3414]. The Secure Shell Transport Model is an alternative to [RFC3414]. The Secure Shell Transport Model is an alternative to
existing transport mappings (or models) as described in [RFC3417]. existing transport mappings as described in [RFC3417].
1.3. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Non uppercased versions of the keywords should be read as in normal
English. They will usually, but not always, be used in a context
relating to compatibility with the RFC3411 architecture or the
subsystem defined here, but which might have no impact on on-the-wire
compatibility. These terms are used as guidance for designers of
proposed IETF models to make the designs compatible with RFC3411
subsystems and Abstract Service Interfaces (see section 3.2).
Implementers are free to implement differently. Some usages of these
lowercase terms are simply normal English usage.
For consistency with SNMP-related specifications, this document
favors terminology as defined in STD62 rather than favoring
terminology that is consistent with non-SNMP specifications that use
different variations of the same terminology. This is consistent
with the IESG decision to not require the SNMPv3 terminology be
modified to match the usage of other non-SNMP specifications when
SNMPv3 was advanced to Full Standard.
2. Motivation 2. Motivation
Just as there are multiple ways to secure one's home or business, in Just as there are multiple ways to secure one's home or business, in
a continuum of alternatives, there are multiple ways to secure a a continuum of alternatives, there are multiple ways to secure a
network management protocol. Let's consider three general network management protocol. Let's consider three general
approaches. approaches.
In the first approach, an individual could sit on his front porch In the first approach, an individual could sit on his front porch
waiting for intruders. In the second approach, he could hire an waiting for intruders. In the second approach, he could hire an
employee , schedule the employee, position the employee to guard what employee , schedule the employee, position the employee to guard what
he wants protected, hire a second guard to cover if the first gets he wants protected, hire a second guard to cover if the first gets
sick, and so on. In the third approach, he could hire a security sick, and so on. In the third approach, he could hire a security
company, tell them what he wants protected, and they could hire company, tell them what he wants protected, and leave the details to
employees, train them, position the guards, schedule the guards, send them. Considerations of hiring and training employees, positioning
a replacement when a guard cannot make it, etc., thus providing the and scheduling the guards, arranging for cover, etc., are the
desired security, with no significant effort on his part other than responsibility of the security company. The individual therefore
identifying requirements and verifying the quality of the service achieves the desired security, with no significant effort...
being provided.
The User-based Security Model (USM) as defined in [RFC3414] largely The User-based Security Model (USM) as defined in [RFC3414] largely
uses the first approach - it provides its own security. It utilizes uses the first approach - it provides its own security. It utilizes
existing mechanisms (e.g., SHA), but provides all the coordination. existing mechanisms (e.g., SHA), but provides all the coordination.
USM provides for the authentication of a principal, message USM provides for the authentication of a principal, message
encryption, data integrity checking, timeliness checking, etc. encryption, data integrity checking, timeliness checking, etc.
USM was designed to be independent of other existing security USM was designed to be independent of other existing security
infrastructures. USM therefore requires a separate principal and key infrastructures. USM therefore requires a separate principal and key
management infrastructure. Operators have reported that deploying management infrastructure. Operators have reported that deploying
another principal and key management infrastructure in order to use another principal and key management infrastructure in order to use
SNMPv3 is a deterrent to deploying SNMPv3. It is possible to use SNMPv3 is a deterrent to deploying SNMPv3. It is possible to use
external mechanisms to handle the distribution of keys for use by external mechanisms to handle the distribution of keys for use by
USM. The more important issue is that operators wanted to leverage a USM. The more important issue is that operators wanted to leverage
single user base that wasn't specific to SNMP. existing user base infrastructures that were not specific to SNMP.
A solution based on the second approach might use a USM-compliant A USM-compliant architecture might combine the authentication
architecture, but combine the authentication mechanism with an mechanism with an external mechanism, such as RADIUS [RFC2865] to
external mechanism, such as RADIUS [RFC2865], to provide the provide the authentication service. Similarly it might be possible
authentication service. It might be possible to utilize an external to utilize an external protocol to encrypt a message, to check
protocol to encrypt a message, to check timeliness, to check data timeliness, to check data integrity, etc. However this corresponds
integrity, etc. It is difficult to cobble together a number of to the second approach - requiring the coordination of a number of
subcontracted services and coordinate them however, because it is differently subcontracted services. Building solid security between
difficult to build solid security bindings between the various the various services is difficult, and there is a significant
services, and potential for gaps in the security is significant. potential for gaps in security.
A solution based on the third approach might utilize one or more An alternative approach might be to utilize one or more lower-layer
lower-layer security mechanisms to provide the message-oriented security mechanisms to provide the message-oriented security services
security services required. These would include authentication of required. These would include authentication of the sender,
the sender, encryption, timeliness checking, and data integrity encryption, timeliness checking, and data integrity checking. This
checking. There are a number of IETF standards available or in corresponds to the third approach described above. There are a
development to address these problems through security layers at the number of IETF standards available or in development to address these
transport layer or application layer, among them TLS [RFC4346], SASL problems through security layers at the transport layer or
[RFC4422], and SSH [RFC4251]. application layer, among them TLS [RFC5246], SASL [RFC4422], and SSH
[RFC4251]
From an operational perspective, it is highly desirable to use From an operational perspective, it is highly desirable to use
security mechanisms that can unify the administrative security security mechanisms that can unify the administrative security
management for SNMPv3, command line interfaces (CLIs) and other management for SNMPv3, command line interfaces (CLIs) and other
management interfaces. The use of security services provided by management interfaces. The use of security services provided by
lower layers is the approach commonly used for the CLI, and is also lower layers is the approach commonly used for the CLI, and is also
the approach being proposed for NETCONF [RFC4741]. the approach being proposed for other network management protocols,
such as syslog [I-D.ietf-syslog-protocol] and NETCONF [RFC4741].
This document defines a Transport Subsystem extension to the RFC3411 This document defines a Transport Subsystem extension to the RFC3411
architecture based on the third approach. This extension specifies architecture based on the third approach. This extension specifies
how other lower layer protocols with common security infrastructures how other lower layer protocols with common security infrastructures
can be used underneath the SNMP protocol and the desired goal of can be used underneath the SNMP protocol and the desired goal of
unified administrative security can be met. unified administrative security can be met.
This extension allows security to be provided by an external protocol This extension allows security to be provided by an external protocol
connected to the SNMP engine through an SNMP Transport Model connected to the SNMP engine through an SNMP Transport Model
[RFC3417]. Such a Transport Model would then enable the use of [RFC3417]. Such a Transport Model would then enable the use of
existing security mechanisms such as (TLS) [RFC4346] or SSH [RFC4251] existing security mechanisms such as (TLS) [RFC5246] or SSH [RFC4251]
within the RFC3411 architecture. within the RFC3411 architecture.
There are a number of Internet security protocols and mechanisms that There are a number of Internet security protocols and mechanisms that
are in wide spread use. Many of them try to provide a generic are in wide spread use. Many of them try to provide a generic
infrastructure to be used by many different application layer infrastructure to be used by many different application layer
protocols. The motivation behind the Transport Subsystem is to protocols. The motivation behind the Transport Subsystem is to
leverage these protocols where it seems useful. leverage these protocols where it seems useful.
There are a number of challenges to be addressed to map the security There are a number of challenges to be addressed to map the security
provided by a secure transport into the SNMP architecture so that provided by a secure transport into the SNMP architecture so that
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document. For some key issues, design choices are described that document. For some key issues, design choices are described that
might be made to provide a workable solution that meets operational might be made to provide a workable solution that meets operational
requirements and fits into the SNMP architecture defined in requirements and fits into the SNMP architecture defined in
[RFC3411]. [RFC3411].
3. Requirements of a Transport Model 3. Requirements of a Transport Model
3.1. Message Security Requirements 3.1. Message Security Requirements
Transport security protocols SHOULD provide protection against the Transport security protocols SHOULD provide protection against the
following message-oriented threats [RFC3411]: following message-oriented threats:
1. modification of information 1. modification of information
2. masquerade 2. masquerade
3. message stream modification 3. message stream modification
4. disclosure 4. disclosure
These threats are described in section 1.4 of [RFC3411]. It is not These threats are described in section 1.4 of [RFC3411]. It is not
required to protect against denial of service or traffic analysis, required to protect against denial of service or traffic analysis,
but it should not make those threats significantly worse. but it should not make those threats significantly worse.
3.1.1. Security Protocol Requirements 3.1.1. Security Protocol Requirements
There are a number of standard protocols that could be proposed as There are a number of standard protocols that could be proposed as
possible solutions within the Transport Subsystem. Some factors possible solutions within the Transport Subsystem. Some factors
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4. disclosure 4. disclosure
These threats are described in section 1.4 of [RFC3411]. It is not These threats are described in section 1.4 of [RFC3411]. It is not
required to protect against denial of service or traffic analysis, required to protect against denial of service or traffic analysis,
but it should not make those threats significantly worse. but it should not make those threats significantly worse.
3.1.1. Security Protocol Requirements 3.1.1. Security Protocol Requirements
There are a number of standard protocols that could be proposed as There are a number of standard protocols that could be proposed as
possible solutions within the Transport Subsystem. Some factors possible solutions within the Transport Subsystem. Some factors
SHOULD be considered when selecting a protocol. should be considered when selecting a protocol.
Using a protocol in a manner for which it was not designed has Using a protocol in a manner for which it was not designed has
numerous problems. The advertised security characteristics of a numerous problems. The advertised security characteristics of a
protocol might depend on it being used as designed; when used in protocol might depend on it being used as designed; when used in
other ways, it might not deliver the expected security other ways, it might not deliver the expected security
characteristics. It is recommended that any proposed model include a characteristics. It is recommended that any proposed model include a
description of the applicability of the Transport Model. description of the applicability of the Transport Model.
A Transport Model SHOULD require no modifications to the underlying A Transport Model SHOULD NOT require modifications to the underlying
protocol. Modifying the protocol might change its security protocol. Modifying the protocol might change its security
characteristics in ways that would impact other existing usages. If characteristics in ways that could impact other existing usages. If
a change is necessary, the change SHOULD be an extension that has no a change is necessary, the change SHOULD be an extension that has no
impact on the existing usages. Any Transport Model SHOULD include a impact on the existing usages. Any Transport Model SHOULD include a
description of potential impact on other usages of the protocol. description of potential impact on other usages of the protocol.
Transport Models MUST be able to coexist with each other. Since multiple transport models can exist simultaneously within the
transport subsystem, transport models MUST be able to coexist with
each other.
3.2. SNMP Requirements 3.2. SNMP Requirements
3.2.1. Architectural Modularity Requirements 3.2.1. Architectural Modularity Requirements
SNMP version 3 (SNMPv3) is based on a modular architecture (defined SNMP version 3 (SNMPv3) is based on a modular architecture (defined
in [RFC3411] section 3) to allow the evolution of the SNMP protocol in [RFC3411] section 3) to allow the evolution of the SNMP protocol
standards over time, and to minimize side effects between subsystems standards over time, and to minimize side effects between subsystems
when changes are made. when changes are made.
The RFC3411 architecture includes a Security Subsystem for enabling The RFC3411 architecture includes a Message Processing Subsystem
different methods of providing security services, a Message permitting different message versions to be handled by a single
Processing Subsystem permitting different message versions to be engine, a Security Subsystem for enabling different methods of
handled by a single engine, Applications(s) to support different providing security services, Applications(s) to support different
types of application processors, and an Access Control Subsystem for types of application processors, and an Access Control Subsystem for
allowing multiple approaches to access control. The RFC3411 allowing multiple approaches to access control. The RFC3411
architecture does not include a subsystem for Transport Models, architecture does not include a subsystem for Transport Models,
despite the fact there are multiple transport mappings already despite the fact there are multiple transport mappings already
defined for SNMP. This document addresses the need for a Transport defined for SNMP. This document describes a Transport Subsystem that
Subsystem compatible with the RFC3411 architecture. As work is being is compatible with the RFC3411 architecture. As work is being done
done to expand the transport to include secure transport such as SSH to use secure transports such as SSH and TLS, using a subsystem will
and TLS, using a subsystem will enable consistent design and enable consistent design and modularity of such Transport Models.
modularity of such Transport Models.
The design of this Transport Subsystem accepts the goals of the The design of this Transport Subsystem accepts the goals of the
RFC3411 architecture defined in section 1.5 of [RFC3411]. This RFC3411 architecture defined in section 1.5 of [RFC3411]. This
Transport Subsystem uses a modular design that will permit Transport Transport Subsystem uses a modular design that permits Transport
Models to be advanced through the standards process independently of Models to be "plugged into" the RFC3411 architecture, supported by
other Transport Models, and independent of other modular SNMP corresponding Transport Models (which may or may not be security-
components as much as possible. aware). Such Transport Models would be independent of other modular
SNMP components as much as possible. This design also permits
Parameters have been added to the ASIs to pass model-independent Transport Models to be advanced through the standards process
transport address information. independently of other Transport Models.
IETF standards typically require one mandatory to implement solution,
with the capability of adding new mechanisms in the future. Part of
the motivation of developing Transport Models is to develop support
for secure transport protocols, such as a Transport Model that
utilizes the Secure Shell protocol. Any 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 protocols to be
"plugged into" the RFC3411 architecture, supported by corresponding
Transport Models, including models that are security-aware.
The RFC3411 architecture and the Security Subsystem assume that a
Security Model is called by a Message Processing Model and will
perform multiple security functions within the Security Subsystem. A
Transport Model that supports a secure transport protocol might
perform similar security functions within the Transport Subsystem. A
Transport Model might perform the translation of transport security
parameters to/from security-model-independent parameters.
To accommodate this, an implementation-specific cache of transport- To encourage a basic level of interoperability, IETF standards
specific information will be described (not shown), and the data typically require one mandatory-to-implement solution, with the
flows between the Transport Subsystem and the Transport Dispatch, capability of adding new mechanisms in the future. Any Transport
between the Message Dispatch and the Message Processing Subsystem, Model SHOULD define one minimum-compliance security mechanism, but
and between the Message Processing Subsystem and the Security should also be able to support additional existing and new
Subsystem will be extended to pass security-model-independent values. mechanisms.
New Security Models may also be defined that understand how to work
with the modified ASIs and the cache. One such Security Model, the
Transport Security Model, is defined in
[I-D.ietf-isms-transport-security-model]
The following diagram depicts the SNMPv3 architecture including the The following diagram depicts the SNMPv3 architecture including the
new Transport Subsystem defined in this document, and a new Transport new Transport Subsystem defined in this document, and a new Transport
Security Model defined in [I-D.ietf-isms-transport-security-model]. Security Model defined in [I-D.ietf-isms-transport-security-model].
+------------------------------+ +------------------------------+
| Network | | Network |
+------------------------------+ +------------------------------+
^ ^ ^ ^ ^ ^
| | | | | |
skipping to change at page 11, line 5 skipping to change at page 11, line 5
| | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | | | | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | |
| | application | | | | applications | | application | | | | application | | | | applications | | application | |
| +-------------+ +---------+ +--------------+ +-------------+ | | +-------------+ +---------+ +--------------+ +-------------+ |
| ^ ^ | | ^ ^ |
| | | | | | | |
| v v | | v v |
| +----------------------------------------------+ | | +----------------------------------------------+ |
| | MIB instrumentation | SNMP entity | | | MIB instrumentation | SNMP entity |
+-------------------------------------------------------------------+ +-------------------------------------------------------------------+
3.2.1.1. Processing Differences between USM and Secure Transport 3.2.1.1. Changes to the RFC3411 Architecture
USM and secure transports differ in the processing order and The RFC3411 architecture and the Security Subsystem assume that a
responsibilities within the RFC3411 architecture. While the steps Security Model is called by a Message Processing Model and will
are the same, they occur in a different order, and may be done by perform multiple security functions within the Security Subsystem. A
different subsystems. With USM and some other Security Models, Transport Model that supports a secure transport protocol might
security processing starts when the Message Processing Model decodes perform similar security functions within the Transport Subsystem,
portions of the encoded message to extract security parameters and including the translation of transport security parameters to/from
header parameters that identify which Security Model should process security-model-independent parameters.
the message to perform authentication, decryption, timeliness
checking, integrity checking, and translation of parameters to model-
independent parameters. A secure transport performs those security
functions on the message, before the message is decoded.
3.2.1.2. Passing Information between Engines To accommodate this, an implementation-specific cache of transport-
specific information will be described (not shown), and the data
flows on this path will be extended to pass security-model-
independent values. This document amends some of the ASIs defined in
RFC 3411, and these changes are covered in section 6.
New Security Models may be defined that understand how to work with
these modified ASIs and the transport-information cache. One such
Security Model, the Transport Security Model, is defined in
[I-D.ietf-isms-transport-security-model].
3.2.1.2. Changes to RFC3411 processing
The introduction of secure transports also affects the
responsibilities and order of processing within the RFC3411
architecture. While the steps are the same, they may occur in a
different order, and may be done by different subsystems. With the
existing RFC3411 architecture, security processing starts when the
Message Processing Model decodes portions of the encoded message to
extract parameters that identify which Security Model should handle
the security-related tasks.
A secure transport performs those security functions on the message,
*before* the message is decoded. Note that some of these functions
might then be repeated by the selected Security Model.
3.2.1.3. Passing Information between SNMP Engines
A secure Transport Model will establish an authenticated and/or A secure Transport Model will establish an authenticated and/or
encrypted tunnel between the Transport Models of two SNMP engines. encrypted tunnel between the Transport Models of two SNMP engines.
After a transport layer tunnel is established, then SNMP messages can After a transport layer tunnel is established, then SNMP messages can
be sent through the tunnel from one SNMP engine to the other SNMP be sent through the tunnel from one SNMP engine to the other.
engine. Transport Models MAY support sending multiple SNMP messages Transport Models MAY support sending multiple SNMP messages through
through the same tunnel. the same tunnel.
3.2.2. Access Control Requirements 3.2.2. Access Control Requirements
RFC3411 made some design decisions related to the support of an RFC3411 made some design decisions related to the support of an
Access Control Subsystem. These include establishing and passing in Access Control Subsystem. These include establishing and passing in
a model-independent manner the securityModel, securityName and a model-independent manner the securityModel, securityName and
securityLevel parameters, and separating message authentication from securityLevel parameters, and separating message authentication from
data access authorization. data access authorization.
3.2.2.1. securityName and securityLevel Mapping 3.2.2.1. securityName and securityLevel Mapping
skipping to change at page 12, line 14 skipping to change at page 12, line 40
identity, and this mapping must be done for incoming messages by the identity, and this mapping must be done for incoming messages by the
Security Model before it passes securityName to the Message Security Model before it passes securityName to the Message
Processing Model via the processIncoming ASI. Processing Model via the processIncoming ASI.
A Security Model is also responsible to specify, via the A Security Model is also responsible to specify, via the
securityLevel parameter, whether incoming messages have been securityLevel parameter, whether incoming messages have been
authenticated and/or encrypted, and to ensure that outgoing messages authenticated and/or encrypted, and to ensure that outgoing messages
are authenticated and/or encrypted based on the value of are authenticated and/or encrypted based on the value of
securityLevel. securityLevel.
A translation from a mechanism-specific identity to a securityName The introduction of a secure transport protocol means that the
might be done by a Transport Model, and the proposed securityName and translation from a mechanism-specific identity to a tmSecurityName
a proposed securityLevel might then be made available to a Security and tmSecurityLevel will be done by a Transport Model. A Security
Model via the tmStateReference. A Security Model may have multiple Model may have multiple sources for determining the principal and
sources for determining the principal and desired security services, desired security services, and a particular Security Model may or may
and a particular Security Model may or may not utilize the not utilize the tmSecurityName mapping and tmSecurityLevel proposed
securityName mapping and securityLevel made available by the by the Transport Model when deciding the value of the securityName
Transport Model when deciding the value of the securityName and and securityLevel to be passed to the Message Processing Model.
securityLevel to be passed to the Message Processing Model.
3.2.3. Security Parameter Passing Requirements 3.2.3. Security Parameter Passing Requirements
RFC3411 section 4 describes abstract data flows between the
subsystems, models and applications within the architecture.
Abstract Service Interfaces describe the flow of data, passing model-
independent information between subsystems within an engine. The
RFC3411 architecture has no ASI parameters for passing security
information between the Transport Subsystem and the dispatcher, or
between the dispatcher and the Message Processing Model. This
document defines or modifies ASIs for this purpose.
A Message Processing Model might unpack SNMP-specific security A Message Processing Model might unpack SNMP-specific security
parameters from an incoming message before calling a specific parameters from an incoming message before calling a specific
Security Model to authenticate and decrypt an incoming message, Security Model to handle the security-related processing of the
perform integrity checking, and translate security-model-specific message. When using a secure Transport Model, some security
parameters into model-independent parameters. When using a secure parameters might be extracted from the transport layer by the
Transport Model, some security parameters might be provided through Security Model before the message is passed to the Message Processing
means other than carrying them in the SNMP message; some of the Subsystem..
parameters for incoming messages might be extracted from the
transport layer by the Transport Model before the message is passed
to the Message Processing Subsystem.
This document describes a cache mechanism (see Section 5), into which This document describes a cache mechanism (see Section 5), into which
the Transport Model puts information about the transport and security the Transport Model puts information about the transport and security
parameters applied to a transport connection or an incoming message, parameters applied to a transport connection or an incoming message,
and a Security Model may extract that information from the cache. A and a Security Model may extract that information from the cache. A
tmStateReference is passed as an extra parameter in the ASIs of the tmStateReference is passed as an extra parameter in the ASIs between
Transport Subsystem and the Message Processing and Security the Transport Subsystem, the Message Processing and Security
Subsystems, to identify the relevant cache. This approach of passing Subsystems, to identify the relevant cache. This approach of passing
a model-independent reference is consistent with the a model-independent reference is consistent with the
securityStateReference cache already being passed around in the securityStateReference cache already being passed around in the
RFC3411 ASIs. RFC3411 ASIs.
For outgoing messages, even when a secure Transport Model will
provide the security services, a Message Processing Model might have
a Security Model actually create the message from its component
parts. Whether there are any security services provided by the
Security Model for an outgoing message is security-model-dependent.
For incoming messages, even when a secure Transport Model provides
security services, a Security Model might provide some security
functionality that can only be provided after the message version or
other parameters are extracted from the message.
3.2.4. Separation of Authentication and Authorization 3.2.4. Separation of Authentication and Authorization
The RFC3411 architecture defines a separation of authentication and The RFC3411 architecture defines a separation of authentication and
the authorization to access and/or modify MIB data. A set of model- the authorization to access and/or modify MIB data. A set of model-
independent parameters (securityModel, securityName, and independent parameters (securityModel, securityName, and
securityLevel) are passed between the Security Subsystem, the securityLevel) are passed between the Security Subsystem, the
applications, and the Access Control Subsystem. applications, and the Access Control Subsystem.
This separation was a deliberate decision of the SNMPv3 WG, to allow This separation was a deliberate decision of the SNMPv3 WG, to allow
support for authentication protocols which did not provide data support for authentication protocols which do not provide data access
access authorization capabilities, and to support data access authorization capabilities, and to support data access authorization
authorization schemes, such as VACM, that do not perform their own schemes, such as VACM, that do not perform their own authentication.
authentication. This decision also permits different types of data
access policies, such as one built on UNIX groups or Windows domains.
The VACM approach is based on administrator-defined groups of users.
A Message Processing Model determines which Security Model is used, A Message Processing Model determines which Security Model is used,
either based on the message version, e.g., SNMPv1 and SNMPv2c, and either based on the message version, e.g., SNMPv1 and SNMPv2c, and
possibly by a value specified in the message, e.g., SNMPv3. possibly by a value specified in the message, (e.g. msgSecurityModel
field in SNMPv3).
The Security Model makes the decision which securityName and The Security Model makes the decision which securityName and
securityLevel values are passed as model-independent parameters to an securityLevel values are passed as model-independent parameters to an
application, which then passes them via the isAccessAllowed ASI to application, which then passes them via the isAccessAllowed ASI to
the Access Control Subsystem. the Access Control Subsystem.
An Access Control Model performs the mapping from the model- An Access Control Model performs the mapping from the model-
independent security parameters to a policy within the Access Control independent security parameters to a policy within the Access Control
Model that is access-control-model-dependent. Model that is access-control-model-dependent.
A Transport Model does not know which securityModel will be used for A Transport Model does not know which Security Model will be used for
an incoming message, so a Transport Model cannot know how the an incoming message, so cannot know how the securityName and
securityName and securityLevel parameters are determined. A securityLevel parameters will be determined. It can propose an
Transport Model can provide a mapping from a transport-specific authenticated identity (via the tmSecurityName field), but there is
identity and provide candidate values for the securityName and no guarantee that this value will be used by the Security Model. For
securityLevel, but there is no guarantee the transport-provided example, non-transport-aware Security Models will typically determine
values will be used by the Security Model. the securityName (and securityLevel) based on the contents of the
SNMP message itself. Such Security Models will simply not know that
For example, the SNMPv1 Message Processing Model described in RFC3584 the tmStateReference cache exists..
always selects the SNMPv1 Security Model. This is true even if the
SNMPv1 message was protected in transit using a secure Transport
Model, such as one based on SSH or TLS. The SNMPv1 Security Model
does not know the tmStateReference exists.
3.3. Session Requirements Further, even if the Transport Model can influence the choice of
securityName, it cannot directly determine the authorization allowed
to this identity. If two different Transport Model each authenticate
a transport principal, that are then both mapped to the same
securityName, then these two identities will typically be afforded
exactly the same authorization by the Access Control Model.
Some secure transports might have a notion of sessions, while other The only way for the Access Control Model to differentiate between
secure transports might provide channels or other session-like identities based on the underlying Transport Model, would be for such
mechanism. Throughout this document, the term session is used in a transport-authenticated identities to be mapped to distinct
broad sense to cover sessions, channels, and session-like mechanisms. securityNames. How and if this is done is Security-Model-dependent.
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.
Sessions are not part of the SNMP architecture defined in [RFC3411], 3.3. Session Requirements
but are considered desirable because the cost of authentication can
be amortized over potentially many transactions.
The architecture defined in [RFC3411] does not include a session Some secure transports have a notion of sessions, while other secure
selector in the Abstract Service Interfaces, and neither is that done transports provide channels or other session-like mechanism.
for the Transport Subsystem, so an SNMP application has no mechanism Throughout this document, the term session is used in a broad sense
to select a session using the ASIs except by passing a unique to cover transport sessions, transport channels, and other transport-
combination of transportDomain, transportAddress, securityName, and layer session-like mechanisms. Transport-layer sessions that can
securityLevel. Implementers, of course, might provide non-standard secure multiple SNMP messages within the lifetime of the session are
mechanisms to select sessions. The transportDomain and considered desirable because the cost of authentication can be
transportAddress identify the transport connection to a remote amortized over potentially many transactions. How a transport
network node; the securityName identifies which security principal to session is actually established, opened, closed, or maintained is
communicate with at that address (e.g., different NMS applications), specific to a particular Transport Model.
and the securityLevel might permit selection of different sets of
security properties for different purposes (e.g., encrypted SETs vs.
non-encrypted GETs).
To reduce redundancy, this document describes aspects that are To reduce redundancy, this document describes aspects that are
expected to be common to all Transport Model sessions. expected to be common to all Transport Model sessions.
3.3.1. Session Establishment Requirements 3.3.1. Session Selection
SNMP has no mechanism to specify a transport session using the ASIs The architecture defined in [RFC3411] and the Transport Subsystem
except by passing a unique combination transportDomain, defined in this document do not support SNMP sessions or include a
transportAddress, securityName, and securityLevel to be used to session selector in the Abstract Service Interfaces. The Transport
identify a session in a transport-independent manner. SNMP Subsystem does not have access to the pduType, so cannot select a
applications provide the transportDomain, transportAddress, given session for particular types of traffic. However certain
securityName, and securityLevel to be used to create a session. parameters of these ASIs might be used to guide the selection of the
appropriate transport session to use for a given request.
For an outgoing message, securityLevel is the requested security for The transportDomain and transportAddress identify the transport
the message, passed in the ASIs. If the Transport Model cannot connection to a remote network node. Elements of the transport
provide at least the requested level of security, the Transport Model address (such as the port number) can be used to select different
SHOULD discard the message and notify the dispatcher that sessions for particular request types. For example, UDP ports 161
establishing a session and sending the message failed. and 162 have typically been used to separate SNMP notifications from
other request/response traffic.
A Transport Model determines whether an appropriate session exists The securityName identifies which security principal to communicate
(transportDomain, transportAddress, securityName, and securityLevel) with at that address (e.g., different NMS applications), and the
for an outgoing message. If an appropriate session does not yet securityLevel might permit selection of different sets of security
exist, the Transport Model attempts to establish a session for properties for different purposes (e.g., encrypted SETs vs. non-
delivery . If a session cannot be established then the message is encrypted GETs).
discarded and the dispatcher should be notified that sending the
message failed. In summary, a unique combination of transportDomain,
transportAddress, securityName, and securityLevel could serve to
identify a given transport session. Different values for any of
these parameters would imply the use of a different session.
However, because the handling of transport sessions is specific to
each transport model, some transport models MAY restrict the
applicability of these parameters for selecting an associated
transport session.
Implementations SHOULD be able to maintain some reasonable number of
concurrent sessions, and MAY provide non-standard internal mechanisms
to select sessions.
3.3.2. Session Establishment Requirements
SNMP applications provide the transportDomain, transportAddress,
securityName, and securityLevel to be used to create a new session.
If the Transport Model cannot provide at least the requested level of
security, the Transport Model SHOULD discard the message and SHOULD
notify the dispatcher that establishing a session and sending the
message failed. Similarly, if the session cannot be established,
then the message should be discarded and the dispatcher notified.
Transport session establishment might require provisioning Transport session establishment might require provisioning
authentication credentials at an engine, either statically or authentication credentials at an engine, either statically or
dynamically. How this is done is dependent on the transport model dynamically. How this is done is dependent on the transport model
and the implementation. and the implementation.
The Transport Subsystem has no knowledge of pduType, so cannot 3.3.3. Session Maintenance Requirements
distinguish between a session created to carry different pduTypes.
To differentiate a session established for different purposes, such
as a notification session versus a request-response session, an
application can use different securityNames or transport addresses.
For example, in SNMPv1, UDP ports 161 and 162 were used to
differentiate types of traffic. New transport models may define a
single well-known port for all traffic types. Administrators might
choose to define one port for SNMP request-response traffic, but
configure notifications to be sent to a different port.
3.3.2. Session Maintenance Requirements
A Transport Model can tear down sessions as needed. It might be A Transport Model can tear down sessions as needed. It might be
necessary for some implementations to tear down sessions as the necessary for some implementations to tear down sessions as the
result of resource constraints, for example. result of resource constraints, for example.
The decision to tear down a session is implementation-dependent. The decision to tear down a session is implementation-dependent. How
While it is possible for an implementation to automatically tear down an implementation determines that an operation has completed is
each session once an operation has completed, this is not recommended implementation-dependent. While it is possible to tear down each
for anticipated performance reasons. How an implementation transport session after processing for each message has completed,
determines that an operation has completed, including all potential this is not recommended for performance reasons.
error paths, is implementation-dependent.
The elements of procedure describe when cached information can be The elements of procedure describe when cached information can be
discarded, in some circumstances, and the timing of cache cleanup discarded, and the timing of cache cleanup might have security
might have security implications, but cache memory management is an implications, but cache memory management is an implementation issue.
implementation issue.
If a Transport Model defines MIB module objects to maintain session If a Transport Model defines MIB module objects to maintain session
state information, then the Transport Model MUST define what SHOULD state information, then the Transport Model MUST define what SHOULD
happen to the objects when a related session is torn down, since this happen to the objects when a related session is torn down, since this
will impact interoperability of the MIB module. will impact interoperability of the MIB module.
3.3.3. Message security versus session security 3.3.4. Message security versus session security
A Transport Model session is associated with state information that A Transport Model session is associated with state information that
is maintained for its lifetime. This state information allows for is maintained for its lifetime. This state information allows for
the application of various security services to multiple messages. the application of various security services to multiple messages.
Cryptographic keys associated with the transport session SHOULD be Cryptographic keys associated with the transport session SHOULD be
used to provide authentication, integrity checking, and encryption used to provide authentication, integrity checking, and encryption
services, as needed, for data that is communicated during the services, as needed, for data that is communicated during the
session. The cryptographic protocols used to establish keys for a session. The cryptographic protocols used to establish keys for a
Transport Model session SHOULD ensure that fresh new session keys are Transport Model session SHOULD ensure that fresh new session keys are
generated for each session. In addition sequence information might generated for each session. This would ensure that a cross-session
be maintained in the session which can be used to prevent the replay replay attack would be unsuccessful; that is, an attacker could not
and reordering of messages within a session. If each session uses take a message observed on one session, and successfully replay this
new keys, then a cross-session replay attack will be unsuccessful; on another session.
that is, an attacker cannot successfully replay on one session a
message he observed from another session. A good security protocol
will also 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 have a single transportDomain, A good security protocol would also protect against replay attacks
transportAddress, securityName and securityLevel associated with it. within a session; that is, an attacker could not take a message
If an exchange between communicating engines requires a different observed on a session, and successfully replay this later in the same
securityLevel or is on behalf of a different securityName, then session. One approach would be to use sequence information within
another session would be needed. An immediate consequence of this is the protocol, allowing the participants to detect if messages were
that implementations SHOULD be able to maintain some reasonable replayed or reordered within a session.
number of concurrent sessions.
For Transport Models, securityName should be specified during session Note that if a secure transport session is closed between the time a
setup, and associated with the session identifier. request message is received, and the corresponding response message
is sent, then the response message SHOULD be discarded, even if a new
session has been established. The SNMPv3 WG decided that this should
be a SHOULD architecturally, and it is a security-model-specific
decision whether to REQUIRE this.
SNMPv3 was designed to support multiple levels of security, SNMPv3 was designed to support multiple levels of security,
selectable on a per-message basis by an SNMP application, because, selectable on a per-message basis by an SNMP application, because,
for example, there is not much value in using encryption for a for example, there is not much value in using encryption for a
Commander Generator to poll for potentially non-sensitive performance Commander Generator to poll for potentially non-sensitive performance
data on thousands of interfaces every ten minutes; the encryption data on thousands of interfaces every ten minutes; the encryption
might add significant overhead to processing of the messages. might add significant overhead to processing of the messages.
Some Transport Models might support only specific authentication and Some Transport Models might support only specific authentication and
encryption services, such as requiring all messages to be carried encryption services, such as requiring all messages to be carried
using both authentication and encryption, regardless of the security using both authentication and encryption, regardless of the security
level requested by an SNMP application. A Transport Model may level requested by an SNMP application. A Transport Model MAY
upgrade the requested security level, i.e. noAuthNoPriv and upgrade the security level requested by a transport-aware security
authNoPriv MAY be sent over an authenticated and encrypted session. model, i.e. noAuthNoPriv and authNoPriv might be sent over an
authenticated and encrypted session.
4. Scenario Diagrams and the Transport Subsystem 4. Scenario Diagrams and the Transport Subsystem
RFC3411 section 4.6.1 and 4.6.2 provide scenario diagrams to RFC3411 section 4.6.1 and 4.6.2 provide scenario diagrams to
illustrate how an outgoing message is created, and how an incoming illustrate how an outgoing message is created, and how an incoming
message is processed. RFC3411 does not define ASIs for "Send SNMP message is processed. RFC3411 does not define ASIs for "Send SNMP
Request Message to Network" or "Receive SNMP Response Message from Request Message to Network" or "Receive SNMP Response Message from
Network", and does not define ASIs for "Receive SNMP Message from Network", and does not define ASIs for "Receive SNMP Message from
Network" or "Send SNMP message to Network". Network" or "Send SNMP message to Network".
This document defines a sendMessage ASI to send SNMP messages to the This document defines a sendMessage ASI to send SNMP messages to the
network, regardless of pduType, and a receiveMessage ASI to receive network, and a receiveMessage ASI to receive SNMP messages from the
SNMP messages from the network, regardless of pduType. network, regardless of pduType.
5. Cached Information and References 5. Cached Information and References
The RFC3411 architecture uses caches to store dynamic model-specific When performing SNMP processing, there are two levels of state
information, and uses references in the ASIs to indicate in a model- information that may need to be retained: the immediate state linking
independent manner which cached information flows between subsystems. a request-response pair, and potentially longer-term state relating
to transport and security.
There are two levels of state that might need to be maintained: the The RFC3411 architecture uses caches to maintain the short-term
security state in a request-response pair, and potentially long-term message state, and uses references in the ASIs to pass this
state relating to transport and security. information between subsystems.
This state is maintained in caches. To simplify the elements of This document defines the requirements for a cache to handle the
procedure, the release of state information is not always explicitly longer-term transport state information, using a tmStateReference
specified. As a general rule, if state information is available when parameter to pass this information between subsystems.
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 To simplify the elements of procedure, the release of state
securityStateReference. This document does not specify an information is not always explicitly specified. As a general rule,
implementation strategy, only an abstract description of the data if state information is available when a message being processed gets
that flows between subsystems. An implementation might use one cache discarded, the state related to that message SHOULD also be
and one reference to serve both functions, but an implementer must be discarded. If state information is available when a relationship
aware of the cache-release issues to prevent the cache from being between engines is severed, such as the closing of a transport
released before a security or Transport Model has had an opportunity session, the state information for that relationship SHOULD also be
to extract the information it needs. discarded.
Since the contents of a cache are meaningful only within an
implementation, and not on-the-wire, the format of the cache and the
LCD are implementation-specific.
5.1. securityStateReference 5.1. securityStateReference
The securityStateReference parameter is defined in RFC3411. The securityStateReference parameter is defined in RFC3411. Its
securityStateReference is not accessible to models of the Transport primary purpose is to provide a mapping between a request and the
Subsystem. corresponding response. This cache is not accessible to Transport
Models, and an entry is typically only retained for the lifetime of a
request-response pair of messages.
5.2. tmStateReference 5.2. tmStateReference
For each transport session, information about the message security is For each transport session, information about the transport security
stored in a cache to pass model- and mechanism-specific parameters. is stored in a cache. The tmStateReference parameter is used to pass
The state referenced by tmStateReference may be saved across multiple model-specific and mechanism-specific parameters between the
messages, in a Local Configuration Datastore (LCD), as compared to Transport subsystem and transport-aware Security Models.
securityStateReference which is usually only saved for the life of a
request-response pair of messages. The tmStateReference cache will typically remain valid for the
duration of the transport session, and hence may be used for several
messages.
Since this cache is only used within an implementation, and not on-
the-wire, the precise contents and format are implementation-
dependent. However, for interoperability between Transport Models
and transport-aware Security Models, entries in this cache must
include at least the following fields:
transportDomain
transportAddress
tmSecurityName
tmRequestedSecurityLevel
tmTransportSecurityLevel
tmSameSecurity
tmSessionID
5.2.1. Transport information
Information about the source of an incoming SNMP message is passed up
from the Transport subsystem as far as the Message Processing
subsystem. However these parameters are not included in the
processIncomingMsg ASI defined in RFC3411, and hence this information
is not directly available to the Security Model.
A transport-aware Security Model might wish to take account of the
transport protocol and originating address when authenticating the
request, and setting up the authorization parameters. It is
therefore necessary for the Transport Model to include this
information in the tmStateReference cache, so that it is accessible
to the Security Model.
o transportDomain: the transport protocol (and hence the Transport
Model) used to receive the incoming message
o transportAddress: the source of the incoming message.
Note that the ASIs used for processing an outgoing message all
include explicit transportDomain and transportAddress parameters.
These fields within the tmStateReference cache will typically not be
used for outgoing messages.
5.2.2. securityName
There are actually three distinct "identities" that can be identified
during the processing of an SNMP request over a secure transport:
o transport principal: the transport-authenticated identity, on
whose behalf the secure transport connection was (or should be)
established. This value is transport-, mechanism- and
implementation- specific, and is only used within a given
Transport Model.
o tmSecurityName: a human-readable name (in snmpAdminString format)
representing this transport identity. This value is transport-
and implementation-specific, and is only used (directly) by the
Transport and Security Models.
o securityName: a human-readable name (in snmpAdminString format)
representing the SNMP principal in a model-independent manner.
o Note that the transport principal may or may not be the same as
the tmSecurityName. Similarly, the tmSecurityName may or may not
be the same as the securityName as seen by the Application and
Access Control subsystems. In particular, a non-transport-aware
Security Model will ignore tmSecurityName completely when
determining the SNMP securityName.
o However it is important that the mapping between the transport
principal and the SNMP securityName (for transport-aware Security
Models) is consistent and predictable, to allow configuration of
suitable access control and the establishment of transport
connections.
5.2.3. securityLevel
There are two distinct issues relating to security level as applied
to secure transports. For clarity, these are handled by separate
fields in the tmStateReference cache:
o tmTransportSecurityLevel: an indication from the Transport Model
of the level of security offered by this session. The Security
Model can use this to ensure that incoming messages were suitably
protected before acting on them.
o tmRequestedSecurityLevel: an indication from the Security Model of
the level of security required to be provided by the transport
protocol. The Transport Model can use this to ensure that
outgoing messages will not be sent over an insufficiently secure
session.
5.2.4. Session Information
For security reasons, if a secure transport session is closed between For security reasons, if a secure transport session is closed between
the time a request message is received and the corresponding response the time a request message is received and the corresponding response
message is sent, then the response message SHOULD be discarded, even message is sent, then the response message SHOULD be discarded, even
if a new session has been established. The SNMPv3 WG decided that if a new session has been established. The SNMPv3 WG decided that
this should be a SHOULD architecturally, and it is a security-model- this should be a SHOULD architecturally, and it is a security-model-
specific decision whether to REQUIRE this. specific decision whether to REQUIRE this.
Since a transport model does not know whether a message contains a When processing an outgoing message, if tmSameSecurity is true, then
response, and transport session information is transport-model- the tmSessionID MUST match the current transport session, otherwise
specific, the tmStateReference contains two pieces of information for the message MUST be discarded, and the dispatcher notified that
performing the request-response transport session pairing. sending the message failed.
Each Security Model that supports the tmStateReference cache SHOULD
pass a tmSameSecurity parameter in the tmStateReference cache for
outgoing messages to indicate whether the same security parameters
MUST be used for the outgoing message as was used for the
corresponding incoming message.
Each transport model that supports sessions and supports the
tmStateReference cache SHOULD include a transport-specific session
identifier in the cache for an incoming message, so that if a
security model requests tmSameSecurity, the transport model can
determine whether the current existing transport session is the same
as the transport session used for the incoming request.
When processing an outgoing message, if the tmSameSecurity o tmSameSecurity: this flag is used by a transport-aware Security
requirement is indicated by the security model, but the session Model to indicate whether the Transport Model MUST enforce this
identified in the tmStateReference does not match the current restriction.
established transport session, i.e., it is not the same transport
session, then the message MUST be discarded, and the dispatcher
should be notified the sending of the message failed.
Since the contents of a cache are meaningful only within an o tmSessionID: in order to verify whether the session has changed,
implementation, and not on-the-wire, the format of the cache and the the Transport Model must be able to compare the session used to
LCD are implementation-specific. receive the original request with the one to be used to send the
response. This typically requires some form of session
identifier. This value is only ever used by the Transport Model,
so the format and interpretation of this field are model-specific
and implementation-dependent.
6. Abstract Service Interfaces 6. Abstract Service Interfaces
Abstract service interfaces have been defined by RFC 3411 to describe Abstract service interfaces have been defined by RFC 3411 to describe
the conceptual data flows between the various subsystems within an the conceptual data flows between the various subsystems within an
SNMP entity, and to help keep the subsystems independent of each SNMP entity, and to help keep the subsystems independent of each
other except for the common parameters. other except for the common parameters.
This document introduces a couple of new ASIs to define the interface
between the Transport and Dispatcher Subsystems, and extends some of
the ASIs defined in RFC3411 to include transport-related information.
This document follows the example of RFC3411 regarding the release of This document follows the example of RFC3411 regarding the release of
state information, and regarding error indications. state information, and regarding error indications.
1) The release of state information is not always explicitly 1) The release of state information is not always explicitly
specified in a transport model. As a general rule, if state specified in a transport model. As a general rule, if state
information is available when a message gets discarded, the message- information is available when a message gets discarded, the message-
state information should also be released, and if state information state information should also be released, and if state information
is available when a session is closed, the session state information is available when a session is closed, the session state information
should also be released. Note that keeping sensitive security should also be released. Note that keeping sensitive security
information longer than necessary might introduce potential information longer than necessary might introduce potential
vulnerabilities to an implementation. vulnerabilities to an implementation.
2) An error indication in statusInformation may include an OID and 2)An error indication in statusInformation will typically include the
value for an incremented counter and a value for securityLevel, and OID and value for an incremented error counter. This may be
values for contextEngineID and contextName for the counter, and the accompanied by values for contextEngineID and contextName for this
securityStateReference if the information is available at the point counter, a value for securityLevel, and the appropriate state
where the error is detected. reference if the information is available at the point where the
error is detected.
6.1. sendMessage ASI 6.1. sendMessage ASI
The sendMessage ASI is used to pass a message from the Dispatcher to The sendMessage ASI is used to pass a message from the Dispatcher to
the appropriate Transport Model for sending. the appropriate Transport Model for sending.
In the diagram in section 4.6.1 of RFC 3411, the sendMessage ASI In the diagram in section 4.6.1 of RFC 3411, the sendMessage ASI
replaces the text "Send SNMP Request Message to Network". In section defined in this document replaces the text "Send SNMP Request Message
4.6.2, the sendMessage ASI replaces the text "Send SNMP Message to to Network". In section 4.6.2, the sendMessage ASI replaces the text
Network" "Send SNMP Message to Network"
If present and valid, the tmStateReference refers to a cache If present and valid, the tmStateReference refers to a cache
containing transport-model-specific parameters for the transport and containing transport-model-specific parameters for the transport and
transport security. How the information in the cache is used is transport security. How the information in the cache is used is
transport-model-dependent and implementation-dependent. How a transport-model-dependent and implementation-dependent. How a
tmStateReference is determined to be present and valid is tmStateReference is determined to be present and valid is
implementation-dependent. implementation-dependent.
This may sound underspecified, but a transport model might be This may sound underspecified, but a transport model might be
something like SNMP over UDP over IPv6, where no security is something like SNMP over UDP over IPv6, where no security is
skipping to change at page 20, line 15 skipping to change at page 22, line 14
statusInformation = statusInformation =
sendMessage( sendMessage(
IN destTransportDomain -- transport domain to be used IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the message to send IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length IN outgoingMessageLength -- its length
IN tmStateReference -- reference to transport state IN tmStateReference -- reference to transport state
) )
6.2. Other Outgoing ASIs 6.2. Changes to RFC3411 Outgoing ASIs
A tmStateReference parameter has been added to the [DISCUSS: this section has been significantly rewritten and
prepareOutgoingMessage, prepareResponseMessage, generateRequestMsg, reorganized. This needs to be checked thoroughly to verify no
and generateResponseMsg ASIs as an OUT parameter. The technical changes have been introduced in the editorial changes.]
transportDomain and transportAddress parameters have been added to
the generateRequestMsg, and generateResponseMsg ASIs as IN parameters Additional parameters have been added to the ASIs defined in RFC3411,
(not shown). concerned with communication between the Dispatcher and Message
Processing subsystems, and between the Message Processing and
Security Subsystems.
6.2.1. Message Processing Subsystem Primitives
A tmStateReference parameter has been added as an OUT parameter to
the prepareOutgoingMessage and prepareResponseMessage ASIs. This is
passed from Message Processing Subsystem to the dispatcher, and from
there to the Transport Subsystem.
How or if the Message Processing Subsystem modifies or utilizes the
contents of the cache is message-processing-model specific.
statusInformation = -- success or errorIndication statusInformation = -- success or errorIndication
prepareOutgoingMessage( prepareOutgoingMessage(
IN transportDomain -- transport domain to be used IN transportDomain -- transport domain to be used
IN transportAddress -- transport address to be used IN transportAddress -- transport address to be used
IN messageProcessingModel -- typically, SNMP version IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model to use IN securityModel -- Security Model to use
IN securityName -- on behalf of this principal IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested IN securityLevel -- Level of Security requested
IN contextEngineID -- data from/at this entity IN contextEngineID -- data from/at this entity
skipping to change at page 21, line 26 skipping to change at page 23, line 49
-- as presented with the request -- as presented with the request
IN statusInformation -- success or errorIndication IN statusInformation -- success or errorIndication
-- error counter OID/value if error -- error counter OID/value if error
OUT destTransportDomain -- destination transport domain OUT destTransportDomain -- destination transport domain
OUT destTransportAddress -- destination transport address OUT destTransportAddress -- destination transport address
OUT outgoingMessage -- the message to send OUT outgoingMessage -- the message to send
OUT outgoingMessageLength -- its length OUT outgoingMessageLength -- its length
OUT tmStateReference -- (NEW) reference to transport state OUT tmStateReference -- (NEW) reference to transport state
) )
The tmStateReference parameter of generateRequestMsg or 6.2.2. Security Subsystem Primitives
generateResponseMsg is passed in the OUT parameters of the Security
Subsystem to the Message Processing Subsystem. If a cache exists for
a session identifiable from transportDomain, transportAddress,
securityModel, securityName, and securityLevel, then an appropriate
Security Model might create a tmStateReference to the cache and pass
that as an OUT parameter.
If one does not exist, the Security Model might create a cache transportDomain and transportAddress parameters have been added as IN
referenced by tmStateReference. This information might include parameters to the generateOutgoingMessage and generateResponseMessage
transportDomain, transportAddress, the securityLevel, and the ASIs, and a tmStateReference parameter has been added as an OUT
securityName, plus any model or mechanism-specific details. The parameter. The transportDomain and transportAddress parameters will
contents of the cache may be incomplete until the Transport Model has have been passed into the Message Processing Subsystem from the
established a session. What information is passed, and how this dispatcher, and are passed on to the Security Subsystem. The
information is determined, is implementation and security-model- tmStateReference parameter will be passed from the Security Subsystem
specific. back to the Message Processing Subsystem, and on to the dispatcher
and Transport subsystems.
The prepareOutgoingMessage ASI passes tmStateReference from the If a cache exists for a session identifiable from the
Message Processing Subsystem to the dispatcher. How or if the transportDomain, transportAddress, tmSecurityName and requested
Message Processing Subsystem modifies or utilizes the contents of the securityLevel, then a transport-aware Security Model might create a
cache is message-processing-model-specific. tmStateReference parameter to this cache, and pass that as an OUT
parameter.
This may sound underspecified, but a message processing model might statusInformation =
have access to all the information from the cache and from the generateRequestMessage(
message, and an application might specify a Security Model such as IN transportDomain -- (NEW) destination transport domain
USM to authenticate and secure the SNMP message, but also specify a IN transportAddress -- (NEW) destination transport address
secure transport such as that provided by the SSH Transport Model to IN messageProcessingModel -- typically, SNMP version
send the message to its destination. IN globalData -- message header, admin data
IN maxMessageSize -- of the sending SNMP entity
IN securityModel -- for the outgoing message
IN securityEngineID -- authoritative SNMP entity
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN scopedPDU -- message (plaintext) payload
OUT securityParameters -- filled in by Security Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of generated message
OUT tmStateReference -- (NEW) reference to transport state
)
)
statusInformation =
generateResponseMessage(
IN transportDomain -- (NEW) destination transport domain
IN transportAddress -- (NEW) destination transport address
IN messageProcessingModel -- SNMPv3 Message Processing
-- Model
IN globalData -- msgGlobalData from step 7
IN maxMessageSize -- from msgMaxSize (step 7c)
IN securityModel -- as determined in step 7e
IN securityEngineID -- the value of snmpEngineID
IN securityName -- on behalf of this principal
IN securityLevel -- for the outgoing message
IN scopedPDU -- as prepared in step 6)
IN securityStateReference -- as determined in step 2
OUT securityParameters -- filled in by Security Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of generated message
OUT tmStateReference -- (NEW) reference to transport state
)
)
6.3. The receiveMessage ASI 6.3. The receiveMessage ASI
If one does not exist, the Transport Model might create a cache When a message is received on a given transport session, if a cache
referenced by tmStateReference. If present, this information might does not already exist for that session, the Transport Model might
include transportDomain, transportAddress, securityLevel, and create one, referenced by tmStateReference. The contents of this
securityName, plus model or mechanism-specific details. How this cache are discussed in section 5. How this information is determined
information is determined is implementation and transport-model- is implementation- and transport-model-specific.
specific.
In the diagram in section 4.6.1 of RFC 3411, the receiveMessage ASI In the diagram in section 4.6.1 of RFC 3411, the receiveMessage ASI
replaces the text "Receive SNMP Response Message from Network". In replaces the text "Receive SNMP Response Message from Network". In
section 4.6.2, the receiveMessage ASI replaces the text "Receive SNMP section 4.6.2, the receiveMessage ASI replaces the text "Receive SNMP
Message from Network" Message from Network"
This may sound underspecified, but a transport model might be This may sound underspecified, but a transport model might be
something like SNMP over UDP over IPv6, where no security is something like SNMP over UDP over IPv6, where no security is
provided, so it might have no mechanisms for determining a provided, so it might have no mechanisms for determining a
securityName and securityLevel. securityName and securityLevel.
skipping to change at page 22, line 42 skipping to change at page 26, line 14
statusInformation = statusInformation =
receiveMessage( receiveMessage(
IN transportDomain -- origin transport domain IN transportDomain -- origin transport domain
IN transportAddress -- origin transport address IN transportAddress -- origin transport address
IN incomingMessage -- the message received IN incomingMessage -- the message received
IN incomingMessageLength -- its length IN incomingMessageLength -- its length
IN tmStateReference -- reference to transport state IN tmStateReference -- reference to transport state
) )
6.4. Other Incoming ASIs 6.4. Changes to RFC3411 Incoming ASIs
To support the Transport Subsystem, the tmStateReference is added to The tmStateReference parameter has also been added to some of the
the prepareDataElements ASI (from the Dispatcher to the Message incoming ASIs defined in RFC3411. How or if a Message Processing
Processing Subsystem), and to the processIncomingMsg ASI (from the Model or Security Model uses tmStateReference is message-processing-
Message Processing Subsystem to the Security Model Subsystem). How and security-model-specific.
or if a Message Processing Model or Security Model uses
tmStateReference is message-processing-model-dependent and security- This may sound underspecified, but a message processing model might
model-dependent. have access to all the information from the cache and from the
message. The Message Processing Model might determine that the USM
Security Model is specified in an SNMPv3 message header; the USM
Security Model has no need of values in the tmStateReference cache to
authenticate and secure the SNMP message, but an application might
have specified to use a secure transport such as that provided by the
SSH Transport Model to send the message to its destination.
6.4.1. Message Processing Subsystem Primitive
The tmStateReference parameter of prepareDataElements is passed from
the dispatcher to the Message Processing Subsystem. How or if the
Message Processing Subsystem modifies or utilizes the contents of the
cache is message-processing-model-specific.
result = -- SUCCESS or errorIndication result = -- SUCCESS or errorIndication
prepareDataElements( prepareDataElements(
IN transportDomain -- origin transport domain IN transportDomain -- origin transport domain
IN transportAddress -- origin transport address IN transportAddress -- origin transport address
IN wholeMsg -- as received from the network IN wholeMsg -- as received from the network
IN wholeMsgLength -- as received from the network IN wholeMsgLength -- as received from the network
IN tmStateReference -- (NEW) from the Transport Model IN tmStateReference -- (NEW) from the Transport Model
OUT messageProcessingModel -- typically, SNMP version OUT messageProcessingModel -- typically, SNMP version
OUT securityModel -- Security Model to use OUT securityModel -- Security Model to use
skipping to change at page 23, line 29 skipping to change at page 27, line 29
OUT PDU -- SNMP Protocol Data Unit OUT PDU -- SNMP Protocol Data Unit
OUT pduType -- SNMP PDU type OUT pduType -- SNMP PDU type
OUT sendPduHandle -- handle for matched request OUT sendPduHandle -- handle for matched request
OUT maxSizeResponseScopedPDU -- maximum size sender can accept OUT maxSizeResponseScopedPDU -- maximum size sender can accept
OUT statusInformation -- success or errorIndication OUT statusInformation -- success or errorIndication
-- error counter OID/value if error -- error counter OID/value if error
OUT stateReference -- reference to state information OUT stateReference -- reference to state information
-- to be used for possible Response -- to be used for possible Response
) )
6.4.2. Security Subsystem Primitive
The processIncomingMessage ASI passes tmStateReference from the
Message Processing Subsystem to the Security Subsystem.
If tmStateReference is present and valid, an appropriate Security
Model might utilize the information in the cache. How or if the
Security Subsystem utilizes the information in the cache is security-
model-specific.
statusInformation = -- errorIndication or success statusInformation = -- errorIndication or success
-- error counter OID/value if error -- error counter OID/value if error
processIncomingMsg( processIncomingMsg(
IN messageProcessingModel -- typically, SNMP version IN messageProcessingModel -- typically, SNMP version
IN maxMessageSize -- of the sending SNMP entity IN maxMessageSize -- of the sending SNMP entity
IN securityParameters -- for the received message IN securityParameters -- for the received message
IN securityModel -- for the received message IN securityModel -- for the received message
IN securityLevel -- Level of Security IN securityLevel -- Level of Security
IN wholeMsg -- as received on the wire IN wholeMsg -- as received on the wire
IN wholeMsgLength -- length as received on the wire IN wholeMsgLength -- length as received on the wire
IN tmStateReference -- (NEW) from the Transport Model IN tmStateReference -- (NEW) from the Transport Model
OUT securityEngineID -- authoritative SNMP entity OUT securityEngineID -- authoritative SNMP entity
OUT securityName -- identification of the principal OUT securityName -- identification of the principal
OUT scopedPDU, -- message (plaintext) payload OUT scopedPDU, -- message (plaintext) payload
OUT maxSizeResponseScopedPDU -- maximum size sender can handle OUT maxSizeResponseScopedPDU -- maximum size sender can handle
OUT securityStateReference -- reference to security state OUT securityStateReference -- reference to security state
) -- information, needed for response ) -- information, needed for response
The tmStateReference parameter of prepareDataElements is passed from
the dispatcher to the Message Processing Subsystem. How or if the
Message Processing Subsystem modifies or utilizes the contents of the
cache is message-processing-model-specific.
The processIncomingMessage ASI passes tmStateReference from the
Message Processing Subsystem to the Security Subsystem.
If tmStateReference is present and valid, an appropriate Security
Model might utilize the information in the cache. How or if the
Security Subsystem utilizes the information in the cache is security-
model-specific.
This may sound underspecified, but a message processing model might
have access to all the information from the cache and from the
message. The Message Processing Model might determine that the USM
Security Model is specified in an SNMPv3 message header; the USM
Security Model has no need of values in the tmStateReference cache to
authenticate and secure the SNMP message, but an application might
have specified to use a secure transport such as that provided by the
SSH Transport Model to send the message to its destination.
7. Security Considerations 7. Security Considerations
This document defines an architectural approach that permits SNMP to This document defines an architectural approach that permits SNMP to
utilize transport layer security services. Each proposed Transport utilize transport layer security services. Each proposed Transport
Model should discuss the security considerations of the Transport Model should discuss the security considerations of the Transport
Model. Model.
It is considered desirable by some industry segments that SNMP It is considered desirable by some industry segments that SNMP
Transport Models should utilize transport layer security that Transport Models should utilize transport layer security that
addresses perfect forward secrecy at least for encryption keys. addresses perfect forward secrecy at least for encryption keys.
skipping to change at page 27, line 44 skipping to change at page 31, line 47
[RFC3584] Frye, R., Levi, D., [RFC3584] Frye, R., Levi, D.,
Routhier, S., and B. Routhier, S., and B.
Wijnen, "Coexistence Wijnen, "Coexistence
between Version 1, Version between Version 1, Version
2, and Version 3 of the 2, and Version 3 of the
Internet-standard Network Internet-standard Network
Management Framework", Management Framework",
BCP 74, RFC 3584, BCP 74, RFC 3584,
August 2003. August 2003.
[RFC4346] Dierks, T. and E. Rescorla, [RFC5246] Dierks, T. and E. Rescorla,
"The Transport Layer "The Transport Layer
Security (TLS) Protocol Security (TLS) Protocol
Version 1.1", RFC 4346, Version 1.2", RFC 5246,
April 2006. August 2008.
[RFC4422] Melnikov, A. and K. [RFC4422] Melnikov, A. and K.
Zeilenga, "Simple Zeilenga, "Simple
Authentication and Security Authentication and Security
Layer (SASL)", RFC 4422, Layer (SASL)", RFC 4422,
June 2006. June 2006.
[RFC4251] Ylonen, T. and C. Lonvick, [RFC4251] Ylonen, T. and C. Lonvick,
"The Secure Shell (SSH) "The Secure Shell (SSH)
Protocol Architecture", Protocol Architecture",
RFC 4251, January 2006. RFC 4251, January 2006.
[RFC4741] Enns, R., "NETCONF [RFC4741] Enns, R., "NETCONF
Configuration Protocol", Configuration Protocol",
RFC 4741, December 2006. RFC 4741, December 2006.
[I-D.ietf-isms-transport-security-model] Harrington, D., "Transport [I-D.ietf-isms-transport-security-model] Harrington, D., "Transport
Security Model for SNMP", d Security Model for SNMP", d
raft-ietf-isms-transport- raft-ietf-isms-transport-
security-model-07 (work in security-model-08 (work in
progress), November 2007. progress), July 2008.
[I-D.ietf-isms-secshell] Harrington, D. and J. [I-D.ietf-isms-secshell] Harrington, D. and J.
Salowey, "Secure Shell Salowey, "Secure Shell
Transport Model for SNMP", Transport Model for SNMP",
draft-ietf-isms-secshell-09 draft-ietf-isms-secshell-11
(work in progress), (work in progress),
November 2007. July 2008.
[I-D.ietf-syslog-protocol] Gerhards, R., "The syslog
Protocol", draft-ietf-
syslog-protocol-23 (work in
progress), September 2007.
Appendix A. Why tmStateReference? Appendix A. Why tmStateReference?
This appendix considers why a cache-based approach was selected for This appendix considers why a cache-based approach was selected for
passing parameters. passing parameters.
There are four approaches that could be used for passing information There are four approaches that could be used for passing information
between the Transport Model and a Security Model. between the Transport Model and a Security Model.
1. one could define an ASI to supplement the existing ASIs, or 1. one could define an ASI to supplement the existing ASIs, or
skipping to change at page 30, line 12 skipping to change at page 34, line 26
Model and a corresponding specific Security Model. However, the Model and a corresponding specific Security Model. However, the
approach of passing a model-independent reference to a model- approach of passing a model-independent reference to a model-
dependent cache is consistent with the securityStateReference already dependent cache is consistent with the securityStateReference already
being passed around in the RFC3411 ASIs. being passed around in the RFC3411 ASIs.
Appendix B. Open Issues Appendix B. Open Issues
NOTE to RFC editor: If this section is empty, then please remove this NOTE to RFC editor: If this section is empty, then please remove this
open issues section before publishing this document as an RFC. (If open issues section before publishing this document as an RFC. (If
it is not empty, please send it back to the editor to resolve. it is not empty, please send it back to the editor to resolve.
o o
Appendix C. Change Log Appendix C. Change Log
NOTE to RFC editor: Please remove this change log before publishing NOTE to RFC editor: Please remove this change log before publishing
this document as an RFC. this document as an RFC.
Changes from -09- to -10- Changes from -12- to -13-
o moved conventions after Internet Standard framework, for
consistency with related documents.
o editorial changes and reorganization
Changes from -10- to -12-
o clarified relation to other documents.
o clarified relation to older security models.
o moved comparison of TSM and USM to TSM document
Changes from -09- to -10-
o Pointed to companion documents o Pointed to companion documents
o Wordsmithed extensively o Wordsmithed extensively
o Modified the note about SNMPv3-consistent terminology o Modified the note about SNMPv3-consistent terminology
o Modified the note about RFC2119 terminology. o Modified the note about RFC2119 terminology.
o Modified discussion of cryptographic key generation. o Modified discussion of cryptographic key generation.
o Added security considerations about coexistence with older o Added security considerations about coexistence with older
security models security models
o Expanded discussion of same session functionality o Expanded discussion of same session functionality
o Described how sendMessage and receiveMessage fit into RFC3411 o Described how sendMessage and receiveMessage fit into RFC3411
diagrams diagrams
o Modified prepareResponseMessage ASI o Modified prepareResponseMessage ASI
o
Changes from -08- to -09- Changes from -08- to -09-
o A question was raised that notifications would not work properly, o A question was raised that notifications would not work properly,
but we could never find the circumstances where this was true. but we could never find the circumstances where this was true.
o removed appendix with parameter matrix o removed appendix with parameter matrix
o Added a note about terminology, for consistency with SNMPv3 rather o Added a note about terminology, for consistency with SNMPv3 rather
than with RFC2828. than with RFC2828.
Changes from -07- to -08- Changes from -07- to -08-
o Identified new parameters in ASIs. o Identified new parameters in ASIs.
o Added discussion about well-known ports. o Added discussion about well-known ports.
Changes from -06- to -07- Changes from -06- to -07-
o Removed discussion of double authentication o Removed discussion of double authentication
o Removed all direct and indirect references to pduType by Transport o Removed all direct and indirect references to pduType by Transport
Subsystem Subsystem
o Added warning regarding keeping sensitive security information o Added warning regarding keeping sensitive security information
available longer than needed. available longer than needed.
o Removed knowledge of securityStateReference from Transport o Removed knowledge of securityStateReference from Transport
Subsystem. Subsystem.
o Changed transport session identifier to not include securityModel, o Changed transport session identifier to not include securityModel,
since this is not known for incoming messages until the message since this is not known for incoming messages until the message
processing model. processing model.
Changes from revision -05- to -06- Changes from revision -05- to -06-
mostly editorial changes mostly editorial changes
removed some paragraphs considered unnecessary removed some paragraphs considered unnecessary
added Updates to header added Updates to header
modified some text to get the security details right modified some text to get the security details right
modified text re: ASIs so they are not API-like modified text re: ASIs so they are not API-like
cleaned up some diagrams cleaned up some diagrams
cleaned up RFC2119 language cleaned up RFC2119 language
added section numbers to citations to RFC3411 added section numbers to citations to RFC3411
removed gun for political correctness removed gun for political correctness
Changes from revision -04- to -05- Changes from revision -04- to -05-
removed all objects from the MIB module. removed all objects from the MIB module.
changed document status to "Standard" rather than the xml2rfc changed document status to "Standard" rather than the xml2rfc
default of informational. default of informational.
changed mention of MD5 to SHA changed mention of MD5 to SHA
moved addressing style to TDomain and TAddress moved addressing style to TDomain and TAddress
modified the diagrams as requested modified the diagrams as requested
removed the "layered stack" diagrams that compared USM and a removed the "layered stack" diagrams that compared USM and a
Transport Model processing Transport Model processing
removed discussion of speculative features that might exist in removed discussion of speculative features that might exist in
future Transport Models future Transport Models
removed openSession and closeSession ASIs, since those are model- removed openSession and closeSession ASIs, since those are model-
dependent dependent
removed the MIB module removed the MIB module
removed the MIB boilerplate intro (this memo defines a SMIv2 MIB removed the MIB boilerplate intro (this memo defines a SMIv2 MIB
...) ...)
removed IANA considerations related to the now-gone MIB module removed IANA considerations related to the now-gone MIB module
removed security considerations related to the MIB module removed security considerations related to the MIB module
removed references needed for the MIB module removed references needed for the MIB module
changed receiveMessage ASI to use origin transport domain/address changed receiveMessage ASI to use origin transport domain/address
updated Parameter CSV appendix updated Parameter CSV appendix
Changes from revision -03- to -04- Changes from revision -03- to -04-
changed title from Transport Mapping Security Model Architectural changed title from Transport Mapping Security Model Architectural
Extension to Transport Subsystem Extension to Transport Subsystem
modified the abstract and introduction modified the abstract and introduction
changed TMSM to TMS changed TMSM to TMS
changed MPSP to simply Security Model changed MPSP to simply Security Model
changed SMSP to simply Security Model changed SMSP to simply Security Model
changed TMSP to Transport Model changed TMSP to Transport Model
removed MPSP and TMSP and SMSP from Acronyms section removed MPSP and TMSP and SMSP from Acronyms section
modified diagrams modified diagrams
removed most references to dispatcher functionality removed most references to dispatcher functionality
worked to remove dependencies between transport and security worked to remove dependencies between transport and security
models. models.
defined snmpTransportModel enumeration similar to defined snmpTransportModel enumeration similar to
snmpSecurityModel, etc. snmpSecurityModel, etc.
eliminated all reference to SNMPv3 msgXXXX fields eliminated all reference to SNMPv3 msgXXXX fields
changed tmSessionReference back to tmStateReference changed tmSessionReference back to tmStateReference
Changes from revision -02- to -03- Changes from revision -02- to -03-
o removed session table from MIB module o removed session table from MIB module
o removed sessionID from ASIs o removed sessionID from ASIs
o reorganized to put ASI discussions in EOP section, as was done in o reorganized to put ASI discussions in EOP section, as was done in
SSHSM SSHSM
o changed user auth to client auth o changed user auth to client auth
o changed tmStateReference to tmSessionReference o changed tmStateReference to tmSessionReference
o modified document to meet consensus positions published by JS o modified document to meet consensus positions published by JS
* authoritative is model-specific * authoritative is model-specific
* msgSecurityParameters usage is model-specific * msgSecurityParameters usage is model-specific
* msgFlags vs. securityLevel is model/implementation-specific * msgFlags vs. securityLevel is model/implementation-specific
* notifications must be able to cause creation of a session * notifications must be able to cause creation of a session
* security considerations must be model-specific * security considerations must be model-specific
* TDomain and TAddress are model-specific * TDomain and TAddress are model-specific
* MPSP changed to SMSP (Security Model security processing) * MPSP changed to SMSP (Security Model security processing)
Changes from revision -01- to -02- Changes from revision -01- to -02-
o wrote text for session establishment requirements section. o wrote text for session establishment requirements section.
o wrote text for session maintenance requirements section. o wrote text for session maintenance requirements section.
o removed section on relation to SNMPv2-MIB o removed section on relation to SNMPv2-MIB
o updated MIB module to pass smilint o updated MIB module to pass smilint
o Added Structure of the MIB module, and other expected MIB-related o Added Structure of the MIB module, and other expected MIB-related
sections. sections.
o updated author address o updated author address
o corrected spelling o corrected spelling
o removed msgFlags appendix o removed msgFlags appendix
o Removed section on implementation considerations. o Removed section on implementation considerations.
o started modifying the security boilerplate to address TMS and MIB o started modifying the security boilerplate to address TMS and MIB
security issues security issues
o reorganized slightly to better separate requirements from proposed o reorganized slightly to better separate requirements from proposed
solution. This probably needs additional work. solution. This probably needs additional work.
o removed section with sample protocols and sample o removed section with sample protocols and sample
tmSessionReference. tmSessionReference.
o Added section for acronyms o Added section for acronyms
o moved section comparing parameter passing techniques to appendix. o moved section comparing parameter passing techniques to appendix.
o Removed section on notification requirements. o Removed section on notification requirements.
Changes from revision -00- Changes from revision -00-
o changed SSH references from I-Ds to RFCs o changed SSH references from I-Ds to RFCs
o removed parameters from tmSessionReference for DTLS that revealed o removed parameters from tmSessionReference for DTLS that revealed
lower layer info. lower layer info.
o Added TMS-MIB module o Added TMS-MIB module
o Added Internet-Standard Management Framework boilerplate o Added Internet-Standard Management Framework boilerplate
o Added Structure of the MIB Module o Added Structure of the MIB Module
o Added MIB security considerations boilerplate (to be completed) o Added MIB security considerations boilerplate (to be completed)
o Added IANA Considerations o Added IANA Considerations
o Added ASI Parameter table o Added ASI Parameter table
o Added discussion of Sessions o Added discussion of Sessions
o Added Open issues and Change Log o Added Open issues and Change Log
o Rearranged sections o Rearranged sections
Authors' Addresses Authors' Addresses
David Harrington David Harrington
Huawei Technologies (USA) Huawei Technologies (USA)
1700 Alma Dr. Suite 100 1700 Alma Dr. Suite 100
Plano, TX 75075 Plano, TX 75075
USA USA
skipping to change at page 34, line 44 skipping to change at line 1791
attempt made to obtain a general license or permission for the use of attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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