draft-ietf-isms-tmsm-03.txt   draft-ietf-isms-tmsm-04.txt 
Network Working Group D. Harrington Network Working Group D. Harrington
Internet-Draft Huawei Technologies (USA) Internet-Draft Huawei Technologies (USA)
Intended status: Informational J. Schoenwaelder Intended status: Informational J. Schoenwaelder
Expires: December 25, 2006 International University Bremen Expires: April 14, 2007 International University Bremen
June 23, 2006 October 11, 2006
Transport Mapping Security Model (TMSM) Architectural Extension for the Transport Subsystem for the Simple Network Management Protocol (SNMP)
Simple Network Management Protocol (SNMP) draft-ietf-isms-tmsm-04.txt
draft-ietf-isms-tmsm-03.txt
Status of This Memo Status of This Memo
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This Internet-Draft will expire on December 25, 2006. This Internet-Draft will expire on April 14, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document describes a Transport Mapping Security Model (TMSM) This document describes a Transport Subsystem, extending the Simple
extension for the Simple Network Management Protocol (SNMP) Network Management Protocol (SNMP) architecture defined in RFC 3411.
architecture defined in RFC 3411. This document identifies and This document describes a subsystem to contain transport models,
discusses some key aspects that need to be considered for any comparable to other subsystems in the RFC3411 architecture. As work
transport-mapping-based security model for SNMP. is being done to expand the transport to include secure transport
such as SSH and TLS, using a subsystem will enable consistent design
and modularity of such transport models. This document identifies
and discusses some key aspects that need to be considered for any
transport model for SNMP.
This memo also defines a portion of the Management Information Base This memo also defines a portion of the Management Information Base
(MIB) for managing sessions in the Transport Mapping Security Model (MIB) for managing models in the Transport Subsystem.
extension.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. The Internet-Standard Management Framework . . . . . . . . 4 1.1. The Internet-Standard Management Framework . . . . . . . . 4
1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 5 1.4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements of a Transport Mapping Security Model . . . . . . 6 2. Requirements of a Transport Model . . . . . . . . . . . . . . 6
2.1. Message Security Requirements . . . . . . . . . . . . . . 6 2.1. Message Security Requirements . . . . . . . . . . . . . . 6
2.1.1. Security Protocol Requirements . . . . . . . . . . . . 7 2.1.1. Security Protocol Requirements . . . . . . . . . . . . 6
2.2. SNMP Requirements . . . . . . . . . . . . . . . . . . . . 7 2.2. SNMP Requirements . . . . . . . . . . . . . . . . . . . . 7
2.2.1. Architectural Modularity Requirements . . . . . . . . 7 2.2.1. Architectural Modularity Requirements . . . . . . . . 7
2.2.2. Access Control Requirements . . . . . . . . . . . . . 14 2.2.2. Access Control Requirements . . . . . . . . . . . . . 14
2.2.3. Security Parameter Passing Requirements . . . . . . . 16 2.2.3. Security Parameter Passing Requirements . . . . . . . 16
2.3. Session Requirements . . . . . . . . . . . . . . . . . . . 17 2.3. Session Requirements . . . . . . . . . . . . . . . . . . . 17
2.3.1. Session Establishment Requirements . . . . . . . . . . 18 2.3.1. Session Establishment Requirements . . . . . . . . . . 18
2.3.2. Session Maintenance Requirements . . . . . . . . . . . 19 2.3.2. Session Maintenance Requirements . . . . . . . . . . . 19
2.3.3. Message security versus session security . . . . . . . 19 2.3.3. Message security versus session security . . . . . . . 19
3. Scenario Diagrams for TMSM . . . . . . . . . . . . . . . . . . 21 3. Scenario Diagrams for the Transport Subsystem . . . . . . . . 21
3.1. Command Generator or Notification Originator . . . . . . . 21 3.1. Command Generator or Notification Originator . . . . . . . 21
3.2. Command Responder . . . . . . . . . . . . . . . . . . . . 22 3.2. Command Responder . . . . . . . . . . . . . . . . . . . . 22
4. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 23 4. Cached Information and References . . . . . . . . . . . . . . 23
4.1. SNMPv3 Message Fields . . . . . . . . . . . . . . . . . . 24 4.1. securityStateReference . . . . . . . . . . . . . . . . . . 24
4.1.1. msgGlobalData . . . . . . . . . . . . . . . . . . . . 26 4.2. tmStateReference . . . . . . . . . . . . . . . . . . . . . 25
4.1.2. msgSecurityParameters . . . . . . . . . . . . . . . . 27 5. Abstract Service Interfaces . . . . . . . . . . . . . . . . . 25
5. Cached Information and References . . . . . . . . . . . . . . 27 5.1. Generating an Outgoing SNMP Message . . . . . . . . . . . 26
5.1. tmSessionReference Cached Session Data . . . . . . . . . . 27 5.2. Processing for an Outgoing Message . . . . . . . . . . . . 27
5.2. securityStateReference Cached Security Data . . . . . . . 27 5.3. Processing an Incoming SNMP Message . . . . . . . . . . . 28
6. Abstract Service Interfaces for TMSM . . . . . . . . . . . . . 28 5.3.1. Processing an Incoming Message . . . . . . . . . . . . 28
6.1. Generating an Outgoing SNMP Message . . . . . . . . . . . 29 5.3.2. Prepare Data Elements from Incoming Messages . . . . . 28
6.2. TMSP for an Outgoing Message . . . . . . . . . . . . . . . 30 5.3.3. Processing an Incoming Message . . . . . . . . . . . . 29
6.3. Processing an Incoming SNMP Message . . . . . . . . . . . 30 6. The Transport-Subsystem-MIB Module . . . . . . . . . . . . . . 30
6.3.1. TMSP for an Incoming Message . . . . . . . . . . . . . 30 6.1. Structure of the MIB Module . . . . . . . . . . . . . . . 31
6.3.2. Prepare Data Elements from Incoming Messages . . . . . 31 6.1.1. The tmsmStats Subtree . . . . . . . . . . . . . . . . 31
6.3.3. MPSP for an Incoming Message . . . . . . . . . . . . . 32 6.2. Relationship to Other MIB Modules . . . . . . . . . . . . 31
7. The TMSM MIB Module . . . . . . . . . . . . . . . . . . . . . 33 6.2.1. Textual Conventions . . . . . . . . . . . . . . . . . 31
7.1. Structure of the MIB Module . . . . . . . . . . . . . . . 33 6.2.2. MIB Modules Required for IMPORTS . . . . . . . . . . . 31
7.1.1. The tmsmStats Subtree . . . . . . . . . . . . . . . . 33 6.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 31
7.2. Relationship to Other MIB Modules . . . . . . . . . . . . 33 7. Security Considerations . . . . . . . . . . . . . . . . . . . 36
7.2.1. Textual Conventions . . . . . . . . . . . . . . . . . 33 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
7.2.2. MIB Modules Required for IMPORTS . . . . . . . . . . . 33 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37
7.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 33 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38
8. Security Considerations . . . . . . . . . . . . . . . . . . . 38 10.1. Normative References . . . . . . . . . . . . . . . . . . . 38
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39 10.2. Informative References . . . . . . . . . . . . . . . . . . 39
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 39 Appendix A. Parameter Table . . . . . . . . . . . . . . . . . . . 39
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39 A.1. ParameterList.csv . . . . . . . . . . . . . . . . . . . . 39
11.1. Normative References . . . . . . . . . . . . . . . . . . . 39 Appendix B. Why tmStateReference? . . . . . . . . . . . . . . . . 41
11.2. Informative References . . . . . . . . . . . . . . . . . . 40 B.1. Define an Abstract Service Interface . . . . . . . . . . . 41
Appendix A. Parameter Table . . . . . . . . . . . . . . . . . . . 41 B.2. Using an Encapsulating Header . . . . . . . . . . . . . . 41
A.1. ParameterList.csv . . . . . . . . . . . . . . . . . . . . 41 B.3. Modifying Existing Fields in an SNMP Message . . . . . . . 42
Appendix B. Why tmSessionReference? . . . . . . . . . . . . . . . 42 B.4. Using a Cache . . . . . . . . . . . . . . . . . . . . . . 42
B.1. Define an Abstract Service Interface . . . . . . . . . . . 43 Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . . 42
B.2. Using an Encapsulating Header . . . . . . . . . . . . . . 43 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 42
B.3. Modifying Existing Fields in an SNMP Message . . . . . . . 43
B.4. Using a Cache . . . . . . . . . . . . . . . . . . . . . . 44
Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . . 44
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 44
1. Introduction 1. Introduction
This document describes a Transport Mapping Security Model (TMSM) This document describes a Transport Subsystem, extending the Simple
extension for the Simple Network Management Protocol (SNMP) Network Management Protocol (SNMP) architecture defined in [RFC3411].
architecture defined in [RFC3411]. This document identifies and This document identifies and discusses some key aspects that need to
discusses some key aspects that need to be considered for any be considered for any transport model for SNMP.
transport-mapping-based security 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].
Managed objects are accessed via a virtual information store, termed Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. MIB objects are generally the Management Information Base or MIB. MIB objects are generally
accessed through the Simple Network Management Protocol (SNMP). accessed through the Simple Network Management Protocol (SNMP).
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Some points requiring further WG research and discussion are Some points requiring further WG research and discussion are
identified by [discuss] markers in the text. Some points requiring identified by [discuss] markers in the text. Some points requiring
further editing by the editors are marked [todo] in the text. further editing by the editors are marked [todo] in the text.
1.3. Acronyms 1.3. Acronyms
This section contains a list of acronyms used within the document and This section contains a list of acronyms used within the document and
references to where in the document the acronym is defined, for easy references to where in the document the acronym is defined, for easy
lookup. lookup.
o TMSM - a Transport Mapping Security Model o [todo]
o SMSP - a Security Model Security Processor, the portion of a TMSM
security model that resides in the Message Processing subsystem of
an SNMPv3 engine. See Section 2.2.1
o TMSP - the Transport Mapping Security Processor, the portion of a
TMSM security model that resides in the Transport Mapping section
of the Dispatcher of an SNMPv3 engine. See Section 2.2.1
1.4. Motivation 1.4. Motivation
There are multiple ways to secure one's home or business, in a There are multiple ways to secure one's home or business, in a
continuum of alternatives. Let's consider three general approaches. continuum of alternatives. Let's consider three general approaches.
In the first approach, an individual could buy a gun, learn to use In the first approach, an individual could buy a gun, learn to use
it, and sit on your front porch waiting for intruders. In the second it, and sit on your front porch waiting for intruders. In the second
approach, one could hire an employee with a gun, schedule the approach, one could hire an employee with a gun, schedule the
employee, position the employee to guard what you want protected, employee, position the employee to guard what you want protected,
hire a second guard to cover if the first gets sick, and so on. In hire a second guard to cover if the first gets sick, and so on. In
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transport layer or application layer, among them TLS [RFC4366], SASL transport layer or application layer, among them TLS [RFC4366], SASL
[RFC4422], and SSH [RFC4251]. [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 [I-D.ietf-netconf-ssh]. the approach being proposed for NETCONF [I-D.ietf-netconf-ssh].
This document proposes a Transport Mapping Security Model (TMSM) This document describes a Transport Subsystem extension to the
extension to the RFC3411 architecture, that allows security to be RFC3411 architecture, that allows security to be provided by an
provided by an external protocol connected to the SNMP engine through external protocol connected to the SNMP engine through an SNMP
an SNMP transport-mapping [RFC3417]. Such a TMSM would then enable transport-model [RFC3417]. Such a transport model would then enable
the use of existing security mechanisms such as (TLS) [RFC4366] or the use of existing security mechanisms such as (TLS) [RFC4366] or
SSH [RFC4251] within the RFC3411 architecture. SSH [RFC4251] 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 TMSM is to leverage these protocols protocols. The motivation behind the transport subsystem is to
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
SNMP continues to work without any surprises. These challenges are SNMP continues to work without any surprises. These challenges are
discussed in detail in this document. For some key issues, design discussed in detail in this document. For some key issues, design
choices are discussed that may be made to provide a workable solution choices are discussed that may be made to provide a workable solution
that meets operational requirements and fits into the SNMP that meets operational requirements and fits into the SNMP
architecture defined in [RFC3411]. architecture defined in [RFC3411].
2. Requirements of a Transport Mapping Security Model 2. Requirements of a Transport Model
2.1. Message Security Requirements 2.1. Message Security Requirements
Transport mapping security protocols SHOULD ideally provide the Transport security protocols SHOULD ideally provide the protection
protection against the following message-oriented threats [RFC3411]: against the following message-oriented threats [RFC3411]:
1. modification of information 1. modification of information
2. masquerade 2. masquerade
3. message stream modification 3. message stream modification
4. disclosure 4. disclosure
According to [RFC3411], it is not required to protect against denial According to [RFC3411], it is not required to protect against denial
of service or traffic analysis. of service or traffic analysis.
2.1.1. Security Protocol Requirements 2.1.1. 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 TMSM framework. Some factors should be possible solutions within the transport subsystem. Some factors
considered when selecting a protocol for use within this framework. 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 may depend on its being used as designed; when used in other protocol may depend on its being used as designed; when used in other
ways, it may not deliver the expected security characteristics. It ways, it may not deliver the expected security characteristics. It
is recommended that any proposed model include a discussion of the is recommended that any proposed model include a discussion of the
applicability statement of the protocols to be used. applicability statement of the protocols to be used.
A protocol used for the TMSM framework should ideally require no A transport model should require no modifications to the underlying
modifications to the protocol. Modifying the protocol may change its protocol. Modifying the protocol may change its security
security characteristics in ways that would impact other existing characteristics in ways that would impact other existing usages. If
usages. If a change is necessary, the change should be an extension a change is necessary, the change should be an extension that has no
that has no impact on the existing usages. It is recommended that impact on the existing usages. It is recommended that any transport
any proposed model include a discussion of potential impact on other model include a discussion of potential impact on other usages of the
usages of the protocol. protocol.
It has been a long-standing requirement that SNMP be able to work It has been a long-standing requirement that SNMP be able to work
when the network is unstable, to enable network troubleshooting and when the network is unstable, to enable network troubleshooting and
repair. The UDP approach has been considered to meet that need well, repair. The UDP approach has been considered to meet that need well,
with an assumption that getting small messages through, even if out with an assumption that getting small messages through, even if out
of order, is better than getting no messages through. There has been of order, is better than getting no messages through. There has been
a long debate about whether UDP actually offers better support than a long debate about whether UDP actually offers better support than
TCP when the underlying IP or lower layers are unstable. There has TCP when the underlying IP or lower layers are unstable. There has
been recent discussion of whether operators actually use SNMP to been recent discussion of whether operators actually use SNMP to
troubleshoot and repair unstable networks. troubleshoot and repair unstable networks.
There has been discussion of ways SNMP could be extended to better There has been discussion of ways SNMP could be extended to better
support management/monitoring needs when a network is running just support management/monitoring needs when a network is running just
fine. Use of a TCP transport, for example, could enable larger fine. Use of a TCP transport, for example, could enable larger
message sizes and more efficient table retrievals. message sizes and more efficient table retrievals.
TMSM models MUST be able to coexist with other protocol models, and Transport models MUST be able to coexist with other transport models,
may be designed to utilize either TCP or UDP, depending on the and may be designed to utilize either TCP or UDP or SCTP.
transport.
2.2. SNMP Requirements 2.2. SNMP Requirements
2.2.1. Architectural Modularity Requirements 2.2.1. Architectural Modularity Requirements
SNMP version 3 (SNMPv3) is based on a modular architecture (described SNMP version 3 (SNMPv3) is based on a modular architecture (described
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. The architecture includes a Security when changes are made.
Subsystem which is responsible for realizing security services.
The RFC3411 architecture includes a security subsystem for enabling
different methods of providing security services, a messaging
subsystem permitting different message versions to be handled by a
single engine, an application subsystem to support different types of
application processors, and an access control subsystem for allowing
multiple approaches to access control. The RFC3411 architecture does
not include a subsystem for transport models, despite the fact there
are multiple transport mappings already defined for SNMP. This
document addresses the need for a transport subsystem compatible with
the RFC3411 architecture.
In SNMPv2, there were many problems of side effects between In SNMPv2, there were many problems of side effects between
subsystems caused by the manipulation of MIB objects, especially subsystems caused by the manipulation of MIB objects, especially
those related to authentication and authorization, because many of those related to authentication and authorization, because many of
the parameters were stored in shared MIB objects, and different the parameters were stored in shared MIB objects, and different
models and protocols could assign different values to the objects. models and protocols could assign different values to the objects.
Contributors assumed slightly different shades of meaning depending Contributors assumed slightly different shades of meaning depending
on the models and protocols being used. As the shared MIB module on the models and protocols being used. As the shared MIB module
design was modified to accommodate a specific model, other models design was modified to accommodate a specific model, other models
which used the same MIB objects were broken. which used the same MIB objects would be broken.
Abstract Service Interfaces (ASIs) were developed to pass model- Abstract Service Interfaces (ASIs) were developed to pass model-
independent parameters. The models were required to translate from independent parameters. The models were required to translate from
their model-dependent formats into a model-independent format, their model-dependent formats into a model-independent format,
defined using model-independent semantics, which would not impact defined using model-independent semantics, which would not impact
other models. other models.
Parameters have been provided in the ASIs to pass model-independent Parameters have been provided in the ASIs to pass model-independent
information about the authentication that has been provided. These information about the authentication that has been provided. These
parameters include a model-independent identifier of the security parameters include a model-independent identifier of the security
"principal", the security model used to perform the authentication, "principal", the security model used to perform the authentication,
and which SNMP-specific security features were applied to the message and which SNMP-specific security features were applied to the message
(authentication and/or privacy). (authentication and/or privacy).
Parameters have been provided in the ASIs to pass model-independent Parameters have been provided in the ASIs to pass model-independent
transport address information. These parameters utilize the transport address information. These parameters utilize the
TransportType and TransportAddress TransportType and TransportAddress
The design of a transport mapping security model must abide the goals The design of a transport subsystem must abide the goals of the
of the RFC3411 architecture defined in [RFC3411]. To that end, this RFC3411 architecture defined in [RFC3411]. To that end, this
transport mapping security model proposal uses a modular design that transport subsystem proposal uses a modular design that will permit
can be advanced through the standards process independently of other transport models to be advanced through the standards process
proposals, and independent of other modular components as much as independently of other transport models, and independent of other
possible. modular SNMP components as much as possible.
IETF standards typically require one mandatory to implement solution, IETF standards typically require one mandatory to implement solution,
with the capability of adding new security mechanisms in the future. with the capability of adding new mechanisms in the future. Part of
Any transport mapping security model should define one minimum- the motivstion of developing transport models is to develop support
compliance mechanism, preferably one which is already widely deployed for secure transport protocols, such as a transport model that
within the transport layer security protocol used. utilizes the Secure Shell protocol. Any transport model should
define one minimum-compliance security mechanism, preferably one
The TMSM architectural extension permits additional transport which is already widely used to secure the transport layer protocol.
security protocols to be "plugged into" the RFC3411 architecture,
supported by corresponding transport-security-aware transport mapping
models.
The RFC3411 architecture, and the USM approach, assume that a
security model is called by a message-processing model and will
perform multiple security functions. The TMSM approach performs
similar functions but performs them in different places within the
architecture, so we need to distinguish the two locations for
security processing.
Transport mapping security is by its very nature a security layer
which is plugged into the RFC3411 architecture between the transport
layer and the message dispatcher. Conceptually, transport mapping
security processing will be called from within the Transport Mapping
functionality of an SNMP engine dispatcher to perform the translation
of transport security parameters to/from security-model-independent
parameters. This transport mapping security processor will be
referred to in this document as TMSP.
Additional functionality may be performed as part of the message The Transport Subsystem permits multiple transport protocols to be
processing function, i.e., in the security subsystem of the RFC3411 "plugged into" the RFC3411 architecture, supported by corresponding
architecture. This document will refer to security model's security transport models, including models that are security-aware.
processor as the SMSP.
Thus a TMSM is composed of both a TMSP and an SMSP. The RFC3411 architecture,and the USM 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 may perform similar
security functions within the transport subsystem. A transport model
may perform the translation of transport security parameters to/from
security-model-independent parameters. To accommodate this, the ASIs
for the transport subsystem, the messaging subsystem, and the
security subsystem will be extended to pass security-model-
independent values, and a cache of transport-specific information.
+------------------------------+ +------------------------------+
| Network | | Network |
+------------------------------+ +------------------------------+
^ ^ ^ ^ ^ ^
| | | | | |
v v v v v v (traditional SNMP agent)
+-----+ +-----+ +-------+
| UDP | | TCP | . . . | other |
+-----+ +-----+ +-------+
^ ^ ^
| | |
v v v
+-----+ +-----+ +-------+
| SSH | | TLS | . . . | other |
+-----+ +-----+ +-------+ (traditional SNMP agent)
+-------------------------------------------------------------------+ +-------------------------------------------------------------------+
| +--------------------------------------------------+ |
| | Transport Subsystem | |
| | +-----+ +-----+ +-----+ +-----+ +-------+ | |
| | | UDP | | TCP | | SSH | | TLS | . . . | other | | |
| | +-----+ +-----+ +-----+ +-----+ +-------+ | |
| +--------------------------------------------------+ |
| ^ | | ^ |
| | | | | |
| Dispatcher v | | Dispatcher v |
| +-------------------+ | | +-------------------+ +---------------------+ +----------------+ |
| | Transport | +--------------+ |
| | Mapping |<---> | TMSM | |
| | (e.g., RFC 3417) | | TMSP | |
| | | +--------------+ |
| | | |
| | | +---------------------+ +----------------+ |
| | | | Message Processing | | Security | | | | | | Message Processing | | Security | |
| | | | Subsystem | | Subsystem | | | | | | Subsystem | | Subsystem | |
| | | | +------------+ | | | | | | | | +------------+ | | +------------+ | |
| | | | +->| v1MP * |<--->| +------------+ | | | | | | +->| v1MP * |<--->| | USM * | | |
| | | | | +------------+ | | | Other | | | | | | | | +------------+ | | +------------+ | |
| | | | | +------------+ | | | Security | | | | | | | | +------------+ | | +------------+ | |
| | | | +->| v2cMP * |<--->| | Model | | | | | | | +->| v2cMP * |<--->| | Transport* | | |
| | Message | | | +------------+ | | +------------+ | | | | Message | | | +------------+ | | | Security | | |
| | Dispatcher <--------->| +------------+ | | +------------+ | | | | Dispatcher <--------->| +------------+ | | | Model | | |
| | | | +->| v3MP * |<--->| | TMSM | | | | | | | +->| v3MP * |<--->| +------------+ | |
| | | | | +------------+ | | | SMSP | | | | | | | | +------------+ | | +------------+ | |
| | PDU Dispatcher | | | +------------+ | | | | | | | | PDU Dispatcher | | | +------------+ | | | Other * | | |
| +-------------------+ | +->| otherMP * |<--->| +------------+ | | | +-------------------+ | +->| otherMP * |<--->| | Model(s) | | |
| ^ | +------------+ | | | | | ^ | +------------+ | | +------------+ | |
| | +---------------------+ +----------------+ | | | +---------------------+ +----------------+ |
| v | | v |
| +-------+-------------------------+---------------+ | | +-------+-------------------------+---------------+ |
| ^ ^ ^ | | ^ ^ ^ |
| | | | | | | | | |
| v v v | | v v v |
| +-------------+ +---------+ +--------------+ +-------------+ | | +-------------+ +---------+ +--------------+ +-------------+ |
| | COMMAND | | ACCESS | | NOTIFICATION | | PROXY | | | | COMMAND | | ACCESS | | NOTIFICATION | | PROXY | |
| | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | | | | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | |
| | application | | | | applications | | application | | | | application | | | | applications | | application | |
skipping to change at page 10, line 40 skipping to change at page 11, line 8
| ^ ^ | | ^ ^ |
| | | | | | | |
| v v | | v v |
| +----------------------------------------------+ | | +----------------------------------------------+ |
| | MIB instrumentation | SNMP entity | | | MIB instrumentation | SNMP entity |
+-------------------------------------------------------------------+ +-------------------------------------------------------------------+
2.2.1.1. USM and the RFC3411 Architecture 2.2.1.1. USM and the RFC3411 Architecture
The following diagrams illustrate the difference in the security The following diagrams illustrate the difference in the security
processing done by the USM model and the security processing done by processing done by the USM model and the security processing
a TMSM model. potentially done by a transport model.
The USM security model is encapsulated by the messaging model, The USM security model is encapsulated by the messaging model,
because the messaging model needs to perform the following steps (for because the messaging model needs to perform the following steps (for
incoming messages) incoming messages)
1) decode the ASN.1 (messaging model) 1) decode the ASN.1 (messaging model)
2) determine the SNMP security model and parameters (messaging model) 2) determine the SNMP security model and parameters (messaging model)
3) decrypt the encrypted portions of the message (security model) 3) decrypt the encrypted portions of the message (security model)
4) translate parameters to model-independent parameters (security 4) translate parameters to model-independent parameters (security
model) model)
5) determine which application should get the decrypted portions 5) determine which application should get the decrypted portions
skipping to change at page 11, line 40 skipping to change at page 12, line 32
| --------------------- ------------------ | | --------------------- ------------------ |
| ^ | ^
| | | |
| v | v
| --------------------- ------------------ | | --------------------- ------------------ |
| | SNMP applications | <--> | access control | | | | SNMP applications | <--> | access control | |
| --------------------- ------------------ | | --------------------- ------------------ |
| --------------------------------------------- | | --------------------------------------------- |
2.2.1.2. TMSM and the RFC3411 Architecture 2.2.1.2. Transport Subsystem and the RFC3411 Architecture
In the TMSM approach, the order of the steps differ and may be With the Transport Subsystem, the order of the steps may differ and
handled by different subsystems: may be handled by different subsystems:
1) decrypt the encrypted portions of the message (transport layer) 1) decrypt the encrypted portions of the message (transport layer)
2) determine the SNMP security model and parameters (transport 2*) translate parameters to model-independent parameters (transport
mapping) model)
3*) translate parameters to model-independent parameters (transport 3) determine the SNMP security model and parameters (messaging model)
mapping)
4) decode the ASN.1 (messaging model) 4) decode the ASN.1 (messaging model)
5) determine which application should get the decrypted portions 5) determine which application should get the decrypted portions
(messaging model) (messaging model)
6*) translate parameters to model-independent parameters (security
model)
7) pass on the decrypted portions with model-independent security 7) pass on the decrypted portions with model-independent security
parameters parameters
This is largely based on having non-SNMP-specific message security If a message is secured using non-SNMP-specific message security and
and parameters. The transport mapping model might provide the parameters, then the transport model should provide the translation
translation from e.g., an SSH user name to the securityName in step from e.g., an SSH user name to the securityName in step 3,
3, OR the SSH user might be passed to the messaging model to pass to
a TMSM security model to do the translation in step 6, if the WG
decides all translations should use the same translation table (e.g.,
the USM MIB).
| -----------------------------------------------| | -----------------------------------------------|
| ------------------ | | ------------------ |
| transport layer <--> | decryption | | | transport layer <--> | decryption | |
| ------------------ | | ------------------ |
| -----------------------------------------------| | -----------------------------------------------|
^ ^
| |
v v
-------------------------------------------------- --------------------------------------------------
| -----------------------------------------------| | -----------------------------------------------|
| ------------------ | | ------------------ |
| transport mapping <--> | translation* | | | transport model <--> | translation | |
| ------------------ | | ------------------ |
| -----------------------------------------------| | -----------------------------------------------|
| ^ | ^
| | | |
| v | v
| --------------------------------------------- | | --------------------------------------------- |
| ------------------ | | |
| SNMP messaging <--> | translation* | | | message model |
| ------------------ | | |
| --------------------- ------------------ | | -----------------------------------------------|
| ^
| |
| v
| --------------------------------------------- |
| |
| security model |
| |
| -----------------------------------------------|
| ^ | ^
| | | |
| v | v
| --------------------- ------------------ | | --------------------- ------------------ |
| | SNMP applications | <--> | access control | | | | SNMP applications | <--> | access control | |
| --------------------- ------------------ | | --------------------- ------------------ |
| --------------------------------------------- | | --------------------------------------------- |
2.2.1.3. Passing Information between Engines 2.2.1.3. Passing Information between Engines
A TMSM model will establish an encrypted tunnel between the transport A secure transport model will establish an encrypted tunnel between
mappings of two SNMP engines. One transport mapping security model the transport models of two SNMP engines. One transport model
instance encrypts all messages, and the other transport mapping instance encrypts all messages, and the other transport model
security model instance decrypts the messages. instance decrypts the messages.
After the transport layer tunnel is established, then SNMP messages After a transport layer tunnel is established, then SNMP messages can
can conceptually be sent through the tunnel from one SNMP message conceptually be sent through the tunnel from one SNMP engine to
dispatcher to another SNMP message dispatcher. Once the tunnel is another SNMP engine. Once the tunnel is established, multiple SNMP
established, multiple SNMP messages may be able to be passed through messages may be able to be passed through the same tunnel.
the same tunnel.
2.2.2. Access Control Requirements 2.2.2. Access Control Requirements
2.2.2.1. securityName Binding 2.2.2.1. securityName Binding
For SNMP access control to function properly, the security mechanism For SNMP access control to function properly, security processing
must establish a securityModel identifier, a securityLevel, and a must establish a securityModel identifier, a securityLevel, and a
securityName, which is the security model independent identifier for securityName, which is the security model independent identifier for
a principal. The SNMPv3 message processing architecture subsystem a principal. The message processing subsystem relies on a security
relies on a security model, such as USM, to play a role in security model, such as USM, to play a role in security that goes beyond
that goes beyond protecting the message - it provides a mapping protecting the message - it provides a mapping between the USM-
between the USM-specific principal to a security-model independent specific principal to a security-model independent securityName which
securityName which can be used for subsequent processing, such as for can be used for subsequent processing, such as for access control.
access control.
The TMSM is a two-stage security model, with a transport mapping
security process (TMSP) and a security model security process (SMSP).
Depending on the design of the specific TMSM model, i.e., which
transport layer protocol is used, different features might be
provided by the TMSP or by the SMSP. For example, the translation
from a mechanism-specific authenticated identity to a securityName
might be done by the TMSP or by the SMSP.
The securityName MUST be bound to the mechanism-specific The securityName MUST be bound to the mechanism-specific
authenticated identity, and this mapping MUST be done before the SMSP authenticated identity, and this mapping MUST be done for incoming
portion of the model passes securityName to the message processing messages before the security model passes securityName to the message
model via the processIncoming() ASI. processing model via the processIncoming() ASI. This translation
from a mechanism-specific authenticated identity to a securityName
The SNMP architecture distinguishes between messages with no MAY be done by the transport model, and the securityname is then
authentication and no privacy (noAuthNoPriv), authentication without provided to the security model to be passed to the message processing
privacy (authNoPriv) and authentication with privacy (authPriv). model..
Hence, the authentication of a transport layer identity plays an
important role and must be considered by any TMSM, and principal
authentication must be available via the transport layer security
protocol.
If the type of authentication provided by the transport layer (e.g. If the type of authentication provided by the transport layer (e.g.
TLS) is considered adequate to secure and/or encrypt the message, but TLS) is considered adequate to secure and/or encrypt the message, but
inadequate to provide the desired granularity of access control (e.g. inadequate to provide the desired granularity of access control (e.g.
user-based), then a second authentication (e.g., one provided by a user-based), then a second authentication (e.g., one provided via a
RADIUS server) may be used to provide the authentication identity RADIUS server) MAY be used to provide the authentication identity
which is bound to the securityName. This approach would require a which is bound to the securityName. This approach would require a
good analysis of the potential for man-in-the-middle attacks or good analysis of the potential for man-in-the-middle attacks or
masquerade possibilities. masquerade possibilities.
2.2.2.2. Separation of Authentication and Authorization 2.2.2.2. Separation of Authentication and Authorization
A TMSM security model should take care to not violate the separation A transport model that provides security services should take care to
of authentication and authorization in the RFC3411 architecture. The not violate the separation of authentication and authorization in the
isAccessAllowed() primitive is used for passing security-model RFC3411 architecture. The isAccessAllowed() primitive is used for
independent parameters between the subsystems of the architecture. passing security-model independent parameters between the subsystems
of the architecture.
Mapping of (securityModel, securityName) to an access control policy Mapping of (securityModel, securityName) to an access control policy
should be handled within the access control subsystem, not the should be handled within the access control subsystem, not the
security subsystem, to be consistent with the modularity of the transport or security subsystems, to be consistent with the
RFC3411 architecture. This separation was a deliberate decision of modularity of the RFC3411 architecture. This separation was a
the SNMPv3 WG, to allow support for authentication protocols which deliberate decision of the SNMPv3 WG, to allow support for
did not provide authorization capabilities, and to support authentication protocols which did not provide authorization
authorization schemes, such as VACM, that do not perform their own capabilities, and to support authorization schemes, such as VACM,
authentication. that do not perform their own authentication.
An authorization model MAY require authentication by certain An authorization model (in the access control subsystem) MAY require
securityModels and a minimum securityLevel to allow access to the authentication by certain securityModels and a minimum securityLevel
data. to allow access to the data.
TMSM is an enhancement for the SNMPv3 privacy and authentication Transport models that provide secure transport are an enhancement for
provisions, but it is not a significant improvement for the the SNMPv3 privacy and authentication, but they are not a significant
authorization needs of SNMPv3. TMSM provides all the model- improvement for the authorization (access control) needs of SNMPv3.
independent parameters for the isAccessAllowed() primitive [RFC3411]. Only the model-independent parameters for the isAccessAllowed()
primitive [RFC3411] are provided by the transport and security
subsystems.
TMSM does not specify how the securityModel and securityName could be A transport model must not specify how the securityModel and
dynamically mapped to a VACM-style groupName. The mapping of securityName could be dynamically mapped to an access control
mechanism, such as a VACM-style groupName. The mapping of
(securityModel, securityName) to a groupName is a VACM-specific (securityModel, securityName) to a groupName is a VACM-specific
mechanism for naming an access control policy, and for tying the mechanism for naming an access control policy, and for tying the
named policy to the addressing capabilities of the data modeling named policy to the addressing capabilities of the data modeling
language (e.g. SMIv2 [RFC2578]), the operations supported, and other language (e.g. SMIv2 [RFC2578]), the operations supported, and other
factors. Providing a binding outside the Access Control subsystem factors. Providing a binding outside the Access Control subsystem
might create dependencies that could make it harder to develop might create dependencies that could make it harder to develop
alternate models of access control, such as one built on UNIX groups alternate models of access control, such as one built on UNIX groups
or Windows domains. The preferred approach is to pass the model- or Windows domains. The preferred approach is to pass the model-
independent security parameters via the isAccessAllowed() ASI, and independent security parameters via the isAccessAllowed() ASI, and
perform the mapping within the access control model. perform the mapping from the model-independent security parameters to
an authorization-model-dependent access policy within the access
control model.
To provide support for protocols which simultaneously send To provide support for protocols which simultaneously send
information for authentication and authorization, such as RADIUS information for authentication and authorization, such as RADIUS
[RFC2865], model-specific authorization information MAY be cached or [RFC2865], model-specific authorization information MAY be cached or
otherwise made available to the access control subsystem, e.g., via a otherwise made available to the access control subsystem, e.g., via a
MIB table similar to the vacmSecurityToGroupTable, so the access MIB table similar to the vacmSecurityToGroupTable, so the access
control subsystem can create an appropriate binding between the control subsystem can create an appropriate binding between the
model-independent securityModel and securityName and a model-specific model-independent securityModel and securityName and a model-specific
access control policy. This may be highly undesirable, however, if access control policy. This may be highly undesirable, however, if
it creates a dependency between a security model and an access it creates a dependency between a transport model or a security model
control model, just as it is undesirable that the TMSM approach and an access control model, just as it is undesirable for a
creates a dependency between an SNMP message version and the security transport model to create a dependency between an SNMP message
provided by a transport mapping. version and the security provided by a transport model.
2.2.3. Security Parameter Passing Requirements 2.2.3. Security Parameter Passing Requirements
RFC3411 section 4 describes primitives to describe the abstract data RFC3411 section 4 describes primitives to describe the abstract data
flows between the various subsystems, models and applications within flows between the various subsystems, models and applications within
the architecture. Abstract Service Interfaces describe the flow of the architecture. Abstract Service Interfaces describe the flow of
data between subsystems within an engine. The ASIs generally pass data between subsystems within an engine. The ASIs generally pass
model-independent information. model-independent information.
Within an engine using a TMSM-based security model, outgoing SNMP Within an engine using a transport model, outgoing SNMP messages are
messages are passed unencrypted from the message dispatcher to the passed unencrypted from the message dispatcher to the transport
transport mapping, and incoming messages are passed unencrypted from model, and incoming messages are passed unencrypted from the
the transport mapping to the message dispatcher. transport model to the message dispatcher.
The security parameters include a model-independent identifier of the The security parameters include a model-independent identifier of the
security "principal", the security model used to perform the security "principal", the security model used to perform the
authentication, and which SNMP-specific security services were authentication, and which SNMP-specific security services were
(should be) applied to the message (authentication and/or privacy). (should be) applied to the message (authentication and/or privacy).
In the RFC3411 architecture, which reflects the USM security model In the RFC3411 architecture, which reflects the USM security model
design, the messaging model must unpack SNMP-specific security design, the messaging model must 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 authenticate and decrypt an incoming message,
perform integrity checking, and translate model-specific security perform integrity checking, and translate model-specific security
parameters into model-independent parameters. parameters into model-independent parameters.
In the TMSM approach, the security-model specific parameters are not When using a secure transport model, security parameters MAY be
carried in the SNMP message. The parameters are provided by SNMP provided through means other than carrying them in the SNMP message.
applications for outgoing messages, and the parameters for incoming The parameters MAY be provided by SNMP applications for outgoing
messages are extracted from the transport layer by the security- messages, and the parameters for incoming messages MAY be extracted
model-specific transport mapping before the message is passed to the from the transport layer by the transport model before the message is
message processing subsystem. passed to the message processing subsystem.
For outgoing messages, it is necessary to have an SMSP because it is For outgoing messages, even when a secure transport model will
the SMSP that actually creates the message from its component parts. provide the security services, it is necessary to have an security
Whether there are any security services provided by the SMSP for an model because it is the security model that actually creates the
outgoing message is model-dependent. message from its component parts. Whether there are any security
services provided by the security model for an outgoing message is
model-dependent.
For incoming messages, there might be security functionality that can For incoming messages, even when a secure transport model provides
only be handled after the message version is known. The message security services, a security model is necessary because there might
version is determined by the Message Processing model and passed to be some security functionality that can only be provided after the
the SMSP via the processIncoming() ASI. message version is known. The message version is determined by the
Message Processing model and passed to the security model via the
processIncoming() ASI.
The RFC3411 architecture has no ASI parameters for passing security The RFC3411 architecture has no ASI parameters for passing security
information between the transport mapping and the dispatcher, and information between a transport mapping (a transport model) and the
between the dispatcher and the message processing model. If there is dispatcher, and between the dispatcher and the message processing
a need to have an SMSP called from the message processing model to, model.
for example, verify that msgFlags and the transport security are
consistent, then it will be necessary to pass the model-dependent
security parameters from the TMSP through to the SMSP.
This document describes a cache, into which the TMSP puts information This document describes a cache mechanism, into which the transport
about the security applied to an incoming message, and an SMSP model puts information about the transport and security parameters
extracts that information from the cache. Given that there may be applied to a transport connection or an incoming message, and a
multiple TM-security caches, a tmSessionReference is passed as an security model MAY extract that information from the cache. A
extra parameter in the ASIs between the transport mapping and the tmStateReference is passed as an extra parameter in the ASIs of the
messaging security model, so the SMSP knows which cache of transport subsystem and the messaging and security subsystems, to
information to consult. identify the relevant cache.
This approach does create dependencies between a model-specific TMSP This approach of passing a model-independent reference is consistent
and a corresponding specific SMSP. This approach of passing a model- with the securityStateReference cache already being passed around in
independent reference is consistent with the securityStateReference the RFC3411 ASIs. [todo: can we avoid dependencies?]
cache already being passed around in the RFC3411 ASIs.
2.3. Session Requirements 2.3. Session Requirements
Throughout this document, the term session is used. Some underlying Throughout this document, the term session is used. Some underlying
secure transports will have a notion of session. Some underlying secure transports will have a notion of session. Some underlying
secure transports might enable the use of channels or other session- secure transports might enable the use of channels or other session-
like thing. In this document the term session refers to an like thing. In this document the term session refers to an
association between two SNMP engines that permits the secure association between two SNMP engines that permits the secure
transmission of one or more SNMP messages within the lifetime of the transmission of one or more SNMP messages within the lifetime of the
session. How the session is actually established, opened, closed, or session. How the session is actually established, opened, closed, or
maintained is specific to a particular security model. maintained is specific to a particular transport model.
Sessions are not part of the SNMP architecture described in Sessions are not part of the SNMP architecture described in
[RFC3411], but are considered desirable because the cost of [RFC3411], but are considered desirable because the cost of
authentication can be amortized over potentially many transactions. authentication can be amortized over potentially many transactions.
It is important to note that the architecture described in [RFC3411] It is important to note that the architecture described in [RFC3411]
does not include a session selector in the Abstract Service does not include a session selector in the Abstract Service
Interfaces, and neither is that done for this architectural Interfaces, and neither is that done for the transport subsystem, so
extension, so an SNMP application cannot select the session except by an SNMP application cannot select the session except by passing a
passing a unique combination of transport address, securityName, unique combination of transport type, transport address,
securityModel, and securityLevel. securityName, securityModel, and securityLevel.
All TMSM-based security models should discuss the impact of sessions All transport models should discuss the impact of sessions on SNMP
on SNMP usage, including how to establish/open a TMSM session (i.e., usage, including how to establish/open a transport session (i.e., how
how it maps to the concepts of session-like things of the underlying it maps to the concepts of session-like things of the underlying
protocol), how to behave when a TMSM session cannot be established, protocol), how to behave when a session cannot be established, how to
how to close a TMSM session (and the underlying protocol equivalent) close a session properly, how to behave when a session is closed
properly, how to behave when a TMSM session is closed improperly, the improperly, the session security properties, session establishment
session security properties, session establishment overhead, and overhead, and session maintenance overhead.
session maintenance overhead.
To reduce redundancy, this document will discuss aspects that are To reduce redundancy, this document will discuss aspects that are
expected to be common to all TMSM-based security model sessions. expected to be common to all transport model sessions.
2.3.1. Session Establishment Requirements 2.3.1. Session Establishment Requirements
SNMP applications must provide the transport address, securityName, SNMP applications must provide the transport type, transport address,
securityModel, and securityLevel to be used for a session. securityName, securityModel, and securityLevel to be used for a
session.
SNMP Applications typically have no knowledge of whether the session SNMP Applications typically have no knowledge of whether the session
that will be used to carry commands was initially established as a that will be used to carry commands was initially established as a
notification session, or a request-response session, and SHOULD NOT notification session, or a request-response session, and SHOULD NOT
make any assumptions based on knowing the direction of the session. make any assumptions based on knowing the direction of the session.
If an administrator or security model designer wants to differentiate If an administrator or transport model designer wants to
a session established for different purposes, such as a notification differentiate a session established for different purposes, such as a
session versus a request-response session, the application can use notification session versus a request-response session, the
different securityNames or transport addresses (e.g., port 161 vs. application can use different securityNames or transport addresses
port 162) for different purposes. (e.g., port 161 vs. port 162) for different purposes.
An SNMP engine containing an application that initiates An SNMP engine containing an application that initiates
communication, e.g., a Command Generator or Notification Originator, communication, e.g., a Command Generator or Notification Originator,
MUST be able to attempt to establish a session for delivery if a MUST be able to attempt to establish a session for delivery if a
session does not yet exist. If a session cannot be established then session does not yet exist. If a session cannot be established then
the message is discarded. the message is discarded.
Sessions are usually established by the transport mapping security Sessions are usually established by the transport model when no
processor when no appropriate session is found for an outgoing appropriate session is found for an outgoing message, but sessions
message, but sessions may be established in advance to support may be established in advance to support features such as
features such as notifications and call-home. How sessions are notifications. How sessions are established in advance is beyond the
established in advance is beyond the scope of this document. scope of this document.
Sessions are initiated by notification originators when there is no Sessions are initiated by notification originators when there is no
currently established connection that can be used to send the currently established connection that can be used to send the
notification. For a client-server security protocol, this may notification. For a client-server security protocol, this may
require provisioning authentication credentials on the agent, either require provisioning authentication credentials on the agent, either
statically or dynamically, so the client/agent can successfully statically or dynamically, so the client/agent can successfully
authenticate to a notification receiver. authenticate to a notification receiver.
A TMSM-based security model must be able to determine whether a A transport model must be able to determine whether a session does or
session does or does not exist, and must be able to determine which does not exist, and must be able to determine which session has the
session has the appropriate security characteristics (transport appropriate security characteristics (transport type, transport
address, securityName, securityModel, and securityLevel) for an address, securityName, securityModel, and securityLevel) for an
outgoing message. outgoing message. [discuss: does the transport model have insight
into the securityModel?]
A TMSM security model implementation MAY reuse an already established A transport model implementation MAY reuse an already established
session with the appropriate transport address, securityName, session with the appropriate transport type, transport address,
securityModel, and securityLevel characteristics for delivery of a securityName, securityModel, and securityLevel characteristics for
message originated by a different type of application than originally delivery of a message originated by a different type of application
caused the session to be created. For example, an implementation than originally caused the session to be created. For example, an
that has an existing session originally established to receive a implementation that has an existing session originally established to
request may use that session to send an outgoing notification, and receive a request may use that session to send an outgoing
may use a session that was originally established to send a notification, and may use a session that was originally established
notification to send a request. Responses are expected to be to send a notification to send a request. Responses are expected to
returned using the same session that carried the corresponding be returned using the same session that carried the corresponding
request message. Reuse is not required for conformance. request message. Reuse of sessions is not required for conformance.
If a session can be reused for a different type of message, but a If a session can be reused for a different type of message, but a
receiver is not prepared to accept different message types over the receiver is not prepared to accept different message types over the
same session, then the message MAY be dropped by the manager. same session, then the message MAY be dropped by the receiver. This
may strongly affect the usefulness of session reuse.
2.3.2. Session Maintenance Requirements 2.3.2. Session Maintenance Requirements
A TMSM-based security model can tear down sessions as needed. It may A transport model can tear down sessions as needed. It may be
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.
While it is possible for an implementation to automatically tear down While it is possible for an implementation to automatically tear down
each session once an operation has completed, this is not recommended each session once an operation has completed, this is not recommended
for anticipated performance reasons. How an implementation for anticipated performance reasons. How an implementation
determines that an operation has completed, including all potential determines that an operation has completed, including all potential
error paths, is implementation-dependent. error paths, is implementation-dependent.
Implementations should be careful to not tear down a session between Implementations should be careful to not tear down a session between
the time a request is received and the time the response is sent. the time a request is received and the time the response is sent.
The elements of procedure for TMSM-based security models should be The elements of procedure for transport models should be sure to
sure to describe the expected behavior when no session exists for a describe the expected behavior when no session exists for a response.
response. [todo: do we already say that the message should be discarded, or is
that just in the ssh transport model?]
The elements of procedure may discuss when cached information can be The elements of procedure may discuss when cached information can be
discarded, and the timing of cache cleanup may have security discarded, and the timing of cache cleanup may have security
implications, but cache memory management is an implementation issue. implications, but cache memory management is an implementation issue.
If a security model defines MIB module objects to maintain session If a transport model defines MIB module objects to maintain session
state information, then the security model MUST describe what happens state information, then the transport model MUST describe what
to the objects when a related session is torn down, since this will happens to the objects when a related session is torn down, since
impact interoperability of the MIB module. this will impact interoperability of the MIB module.
2.3.3. Message security versus session security 2.3.3. Message security versus session security
A TMSM session is associated with state information that is A transport model session is associated with state information that
maintained for its lifetime. This state information allows for the is maintained for its lifetime. This state information allows for
application of various security services to TMSM-based security the application of various security services to multiple messages.
models. Cryptographic keys established at the beginning of the Cryptographic keys established at the beginning of the session SHOULD
session SHOULD be used to provide authentication, integrity checking, be used to provide authentication, integrity checking, and encryption
and encryption services for data that is communicated during the services for data that is communicated during the session. The
session. The cryptographic protocols used to establish keys for a cryptographic protocols used to establish keys for a transport model
TMSM-based security model session SHOULD ensure that fresh new session SHOULD ensure that fresh new session keys are generated for
session keys are generated for each session. If each session uses each session. If each session uses new session keys, then messages
new session keys, then messages cannot be replayed from one session cannot be replayed from one session to another. In addition sequence
to another. In addition sequence information MAY be maintained in information MAY be maintained in the session which can be used to
the session which can be used to prevent the replay and reordering of prevent the replay and reordering of messages within a session.
messages within a session.
A TMSM session will typically have a single transport address, A transport model session will typically have a single transport
securityName and securityLevel associated with it. If an exchange type, ransport address, securityModel, securityName and securityLevel
between communicating engines would require a different securityLevel associated with it. If an exchange between communicating engines
or would be on behalf of a different securityName, then another would require a different securityLevel or would be on behalf of a
session would be needed. An immediate consequence of this is that different securityName, or to use a different securityModel, then
implementations should be able to maintain some reasonable number of another session would be needed. An immediate consequence of this is
concurrent sessions. that implementations should be able to maintain some reasonable
number of concurrent sessions.
For TMSM models, securityName is typically specified during session For transport models, securityName is typically specified during
setup, and associated with the session identifier. session setup, and associated with the session identifier.
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
there is not much value in using encryption for a Commander Generator there is not much value in using encryption for a Commander Generator
to poll for non-sensitive performance data on thousands of interfaces to poll for non-sensitive performance data on thousands of interfaces
every ten minutes; the encryption adds significant overhead to every ten minutes; the encryption adds significant overhead to
processing of the messages. processing of the messages.
Some TMSM-based security models MAY support only specific Some transport models MAY support only specific authentication and
authentication and encryption services, such as requiring all encryption services, such as requiring all messages to be carried
messages to be carried using both authentication and encryption, using both authentication and encryption, regardless of the security
regardless of the security level requested by an SNMP application. level requested by an SNMP application.
Some security models may use an underlying transport that provides a Some transport models may use an underlying transport that provides a
per-message requested level of authentication and encryption per-message requested level of authentication and encryption
services. For example, if a session is created as 'authPriv', then services. For example, if a session is created as 'authPriv', then
keys for encryption could still be negotiated once at the beginning keys for encryption could still be negotiated once at the beginning
of the session. But if a message is presented to the session with a of the session. But if a message is presented to the session with a
security level of authNoPriv, then that message could simply be security level of authNoPriv, then that message could simply be
authenticated and not encrypted within the same transport session. authenticated and not encrypted within the same transport session.
Whether this is possible depends on the security model and the secure Whether this is possible depends on the transport model and the
transport used. secure transport used.
If the underlying transport layer security was configurable on a per- If the underlying transport layer security is configurable on a per-
message basis, a TMSM-based security model could have a security- message basis, a transport model could have a transport-model MIB
model-specific MIB module with configurable maxSecurityLevel and a module with configurable maxSecurityLevel and a minSecurityLevel
minSecurityLevel objects to identify the range of possible levels. A objects to identify the range of possible levels. A session's
session's maxSecurityLevel would identify the maximum security it maxSecurityLevel would identify the maximum security it could
could provide, and a session created with a minSecurityLevel of provide, and a session created with a minSecurityLevel of authPriv
authPriv would reject an attempt to send an authNoPriv message. The would reject an attempt to send an authNoPriv message. The elements
elements of procedure of the security model would need to describe of procedure of the transport model would need to describe the
the procedures to enable this determination. procedures to enable this determination. [discuss: this is a feature
I find questionable. It can be developed as a feature of a specific
transport model. Do we need this discussion here?]
For security models that do not support variable security services in For transport models that do not support variable security services
one session, multiple sessions could be established with different in one session, multiple sessions could be established with different
security levels, and for every packet the SNMP engine could select security levels, and for every packet the SNMP engine could select
the appropriate session based on the requested securityLevel. Some the appropriate session based on the requested securityLevel. Some
SNMP entities are resource-constrained. Adding sessions increases SNMP entities are resource-constrained. Adding sessions increases
the need for resources, but so does encrypting unnecessarily. the need for resources, but so does encrypting unnecessarily.
Designers of security models should consider the trade offs for Designers of transport models should consider the trade offs for
resource-constrained devices. resource-constrained devices.
3. Scenario Diagrams for TMSM 3. Scenario Diagrams for the Transport Subsystem
RFC3411 section 4.6 provides scenario diagrams to illustrate how an RFC3411 section 4.6 provides scenario diagrams to illustrate how an
outgoing message is created, and how an incoming message is outgoing message is created, and how an incoming message is
processed. Both diagrams are incomplete, however. In section 4.6.1, processed. Both diagrams are incomplete, however. In section 4.6.1,
the diagram doesn't show the ASI for sending an SNMP request to the the diagram doesn't show the ASI for sending an SNMP request to the
network or receiving an SNMP response message from the network. In network or receiving an SNMP response message from the network. In
section 4.6.2, the diagram doesn't illustrate the interfaces required section 4.6.2, the diagram doesn't illustrate the interfaces required
to receive an SNMP message from the network, or to send an SNMP to receive an SNMP message from the network, or to send an SNMP
message to the network. message to the network.
skipping to change at page 23, line 47 skipping to change at page 23, line 47
: | |<-------------------| : | |<-------------------|
: | | | : | | |
: |<-------------------| | : |<-------------------| |
: | | | : | | |
: |--------------+ | | : |--------------+ | |
: | Send SNMP | | | : | Send SNMP | | |
: | Message | | | : | Message | | |
: | to Network | | | : | to Network | | |
: | v | | : | v | |
4. Message Formats 4. Cached Information and References
The syntax of an SNMP message using this Security Model adheres to
the message format defined in the version-specific Message Processing
Model document (for example [RFC3412]). At the time of this writing,
there are three defined message formats - SNMPv1, SNMPv2c, and
SNMPv3. SNMPv1 and SNMPv2c have been declared Historic, so this memo
only deals with SNMPv3 messages.
The processing is compatible with the RFC 3412 primitives,
generateRequestMsg() and processIncomingMsg(), that show the data
flow between the Message Processor and the SMSP.
4.1. SNMPv3 Message Fields
The SNMPv3Message SEQUENCE is defined in [RFC3412] and [RFC3416].
SNMPv3MessageSyntax DEFINITIONS IMPLICIT TAGS ::= BEGIN
SNMPv3Message ::= SEQUENCE {
-- identify the layout of the SNMPv3Message
-- this element is in same position as in SNMPv1
-- and SNMPv2c, allowing recognition
-- the value 3 is used for snmpv3
msgVersion INTEGER ( 0 .. 2147483647 ),
-- administrative parameters
msgGlobalData HeaderData,
-- security model-specific parameters
-- format defined by Security Model
msgSecurityParameters OCTET STRING,
msgData ScopedPduData
}
HeaderData ::= SEQUENCE {
msgID INTEGER (0..2147483647),
msgMaxSize INTEGER (484..2147483647),
msgFlags OCTET STRING (SIZE(1)),
-- .... ...1 authFlag
-- .... ..1. privFlag
-- .... .1.. reportableFlag
-- Please observe:
-- .... ..00 is OK, means noAuthNoPriv
-- .... ..01 is OK, means authNoPriv
-- .... ..10 reserved, MUST NOT be used.
-- .... ..11 is OK, means authPriv
msgSecurityModel INTEGER (1..2147483647)
}
ScopedPduData ::= CHOICE {
plaintext ScopedPDU,
encryptedPDU OCTET STRING -- encrypted scopedPDU value
}
ScopedPDU ::= SEQUENCE {
contextEngineID OCTET STRING,
contextName OCTET STRING,
data ANY -- e.g., PDUs as defined in [RFC3416]
}
END
The following describes how any TMSM model SHOULD treat certain
fields in the message:
4.1.1. msgGlobalData
msgGlobalData is opaque to a TMSM security model. The values are set
by the Message Processing model (e.g., SNMPv3 Message Processing),
and SHOULD NOT be modified by a TMSM security model.
The msgSecurityModel field should be set by the Message Processing
model to a value from the SnmpSecurityModel enumeration [RFC3411] to
identify the specific TMSM model. Each standards-track TMSM model
should have an enumeration assigned by IANA. Each enterprise-
specific security model should have an enumeration assigned following
instructions in the description of the SnmpSecurityModel TEXTUAL-
CONVENTION from RFC3411.
The msgFlags have the same values for a TMSM model as for the USM
model.
4.1.1.1. securityLevel and msgFlags
For an outgoing message, msgFlags is the requested security for the
message; if a TMSM cannot provide the requested securityLevel, the
model MUST describe a standard behavior that is followed for that
situation. If the TMSM cannot provide at least the requested level
of security, the TMSM MUST discard the request and SHOULD notify the
message processing model that the request failed.
For an outgoing message, if the TMSM is able to provide stronger than
requested security, that may be acceptable. The transport layer
protocol would need to indicate to the receiver what security has
been applied to the actual message. To avoid the need to mess with
the ASN.1 encoding, the SNMPv3 message carries the requested
msgFlags, not the actual securityLevel applied to the message. If a
message format other than SNMPv3 is used, then the new message may
carry the more accurate securityLevel in the SNMP message.
For an incoming message, the receiving TMSM knows what must be done
to process the message based on the transport layer mechanisms. If
the underlying transport security mechanisms for the receiver cannot
provide the matching securityLevel, then the message should follow
the standard behaviors for the transport security mechanism, or be
discarded silently.
Part of the responsibility of the TMSM is to ensure that the actual
security provided by the underlying transport layer security
mechanisms is configured to meet or exceed the securityLevel required
by the msgFlags in the SNMP message. When the SMSP processes the
incoming message, it should compare the msgFlags field to the
securityLevel actually provided for the message by the transport
layer security. If they differ, the SMSP should determine whether
the changed securityLevel is acceptable. If not, it should discard
the message. Depending on the model, the SMSP may issue a reportPDU
with a model-specific counter.
4.1.2. msgSecurityParameters
The field msgSecurityParameters carries model-dependent security
information between engines. When a security model does not utilize
this field, its value MUST be the BER serialization of a zero-length
OCTET STRING, to prevent its being used in a manner that could be
damaging, such as for carrying a virus or worm.
RFC3412 defines two primitives, generateRequestMsg() and
processIncomingMsg() which require the specification of an
authoritative SNMP entity. The meaning of authoritative is model
dependent.
5. Cached Information and References
he RFC3411 architecture uses caches to store dynamic model-specific The RFC3411 architecture uses caches to store dynamic model-specific
information, and uses references in the ASIs to indicate in a model- information, and uses references in the ASIs to indicate in a model-
independent manner which cached information must flow between independent manner which cached information must flow between
subsystems. For most TMSM models, there are two levels of state that subsystems.
need to be maintained: the session state, and the message security
state.
5.1. tmSessionReference Cached Session Data
The tmSessionReference is used to pass references to the appropriate There are two levels of state that may need to be maintained: the
session information between the TMSP and SMSP through the ASIs. security state in a request-response pair, and potentially long-term
state relating to transport and security.
The TMSP may provide only some aspects of security, and leave some This state is maintained in caches and a Local Configuration
aspects to the SMSP. tmSessionReference should be used to pass any Datastore (LCD). To simplify the elements of procedure, the release
parameters, in a model- and mechanism-specific format, that will be of state information is not always explicitly specified. As a
needed to coordinate the activities of the TMSP and SMSP, plus the general rule, if state information is available when a message being
parameters subsequently passed in securityStateReference. 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.
The security model has the responsibility for explicitly releasing This document differentiates the tmStateReference from the
the complete tmSessionReference and possibly deleting the associated securityStateReference. This document does not specify an
LCD information when the session is destroyed. implementation strategy, only an abstract discussion of the data that
must flow between subsystems. An implementation MAY use one cache
and one reference to serve both functions, but an implementer must be
aware of the cache-release issues to prevent the cache from being
released before a security or transport model has had an opportunity
to extract the information it needs.
5.2. securityStateReference Cached Security Data 4.1. securityStateReference
From RFC3411: "For each message received, the Security Model caches From RFC3411: "For each message received, the Security Model caches
the state information such that a Response message can be generated the state information such that a Response message can be generated
using the same security information, even if the Local Configuration using the same security information, even if the Local Configuration
Datastore is altered between the time of the incoming request and the Datastore is altered between the time of the incoming request and the
outgoing response. outgoing response.
A Message Processing Model has the responsibility for explicitly A Message Processing Model has the responsibility for explicitly
releasing the cached data if such data is no longer needed. To releasing the cached data if such data is no longer needed. To
enable this, an abstract securityStateReference data element is enable this, an abstract securityStateReference data element is
passed from the Security Model to the Message Processing Model. The passed from the Security Model to the Message Processing Model. The
cached security data may be implicitly released via the generation of cached security data may be implicitly released via the generation of
a response, or explicitly released by using the stateRelease a response, or explicitly released by using the stateRelease
primitive, as described in RFC3411 section 4.5.1." primitive, as described in RFC3411 section 4.5.1."
For the TMSM approach, the TMSP may need to provide the information The information saved should include the model-independent parameters
to be stored in the securityStateReference to the message processing (transportType, transportAddress, securityName, securityModel, and
model. such as the security-model-independent securityName, securityLevel), related security parameters, and other information
securityLevel, and securityModel parameters, and the transport needed to imatch the response with the request. The Message
address, and transport type. For responses, the messaging model may Processing Model has the responsibility for explicitly releasing the
need to pass the parameters back to the TMSP. securityStateReference when such data is no longer needed. The
securityStateReference cached data may be implicitly released via the
generation of a response, or explicitly released by using the
stateRelease primitive, as described in RFC 3411 section 4.5.1."
This document will differentiate the tmSessionReference provided by If the transport model connection is closed between the time a
the TMSP to the SMSP, from the securityStateReference provided by the Request is received and a Response message is being prepared, then
SMSP to the Dispatcher. This document does not specify an the Response message MAY be discarded.
implementation strategy, only an abstract discussion of the data that
must flow between subsystems. An implementation MAY use one cache
and one reference to serve both functions, but an implementer must be
aware of the cache-release issues to prevent the cache from being
released before the transport mapping has had an opportunity to
extract the information it needs.
6. Abstract Service Interfaces for TMSM 4.2. tmStateReference
For each message or transport session, information about the message
security is stored in the Local Configuration Datastore (LCD),
supplemented with a cache, to pass model- and mechanism-specific
parameters. The state referenced by tmStateReference may be saved
across multiple messages, as compared to securityStateReference which
is only saved for the life of a request-response pair of messages.
The format of the cache and the LCD are implementation-specific. For
ease of explanation, this document defines a MIB module to
conceptually represent the LCD, but this is not meant to contrain
implementations from doing it differently.
It is expected that the LCD will allow lookup based on the
combination of transportType, transportAddress, securityName,
securityModel, and securityLevel. It is expected that the cache
contain these values or contain pointers/references to entries in the
LCD.
It is expected that a transport model may store transport-specific
parameters in the LCD for subsequent usage.
5. Abstract Service Interfaces
[todo: the discussion of ASIs that are not directly related to the
transport or security models was added to the document because it was
difficult to understand what information was available at what
points, and who provided the information. The presence of this
expository text can make it hard to find the relevant ASIs for the
transport subsystem, and can be confusing because it talks about
things that the transport subsystem should not know about. This text
should be reduced.
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. TMSM security models use some of these conceptual data SNMP entity.
flows when communicating between subsystems, such as the dispatcher
and the Message Processing Subsystem.
To simplify the elements of procedure, the release of state To simplify the elements of procedure, the release of state
information is not always explicitly specified. As a general rule, information is not always explicitly specified. As a general rule,
if state information is available when a message gets discarded, the if state information is available when a message gets discarded, the
message-state information should also be released, and if state message-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. information should also be released.
An error indication may return an OID and value for an incremented An error indication may return an OID and value for an incremented
counter and a value for securityLevel, and values for contextEngineID counter and a value for securityLevel, and values for contextEngineID
and contextName for the counter, and the securityStateReference if and contextName for the counter, and the securityStateReference if
the information is available at the point where the error is the information is available at the point where the error is
detected. detected.
6.1. Generating an Outgoing SNMP Message 5.1. Generating an Outgoing SNMP Message
This section describes the procedure followed by an RFC3411- This section describes the procedure followed by an RFC3411-
compatible system whenever it generates a message containing a compatible system whenever it generates a message containing a
management operation (such as a request, a response, a notification, management operation (such as a request, a response, a notification,
or a report) on behalf of a user. or a report) on behalf of a user.
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
skipping to change at page 29, line 31 skipping to change at page 26, line 40
IN contextName -- data from/in this context IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit IN PDU -- SNMP Protocol Data Unit
IN expectResponse -- TRUE or FALSE IN expectResponse -- TRUE or FALSE
IN sendPduHandle -- the handle for matching IN sendPduHandle -- the handle for matching
incoming responses incoming responses
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 tmSessionReference OUT tmStateReference
) )
Note that tmSessionReference has been added to this ASI. Note that tmStateReference has been added to this ASI.
The IN parameters of the prepareOutgoingMessage() ASI are used to The IN parameters of the prepareOutgoingMessage() ASI are used to
pass information from the dispatcher (for the application subsystem) pass information from the dispatcher (for the application subsystem)
to the message processing subsystem. to the message processing subsystem.
The abstract service primitive from a Message Processing Model to a The abstract service primitive from a Message Processing Model to a
Security Model to generate the components of a Request message is Security Model to generate the components of a Request message is
generateRequestMsg(). generateRequestMsg().
The abstract service primitive from a Message Processing Model to a The abstract service primitive from a Message Processing Model to a
Security Model to generate the components of a Response message is Security Model to generate the components of a Response message is
generateResponseMsg(). generateResponseMsg().
Upon completion of the SMSP processing, the Security model returns Upon completion of processing, the Security Model returns
statusInformation. If the process was successful, the completed statusInformation. If the process was successful, the completed
message is returned. If the process was not successful, then an message is returned. If the process was not successful, then an
errorIndication is returned. errorIndication is returned.
The OUT parameters of the prepareOutgoingMessage() ASI are used to The OUT parameters of the prepareOutgoingMessage() ASI are used to
pass information from the message processing model to the dispatcher pass information from the message processing model to the dispatcher
and on to the transport mapping: and on to the transport model:
6.2. TMSP for an Outgoing Message 5.2. Processing for an Outgoing Message
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 mapping for sending. the appropriate transport model for sending.
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 tmSessionReference IN tmStateReference
) )
The Transport Mapping Security Model provides the following The Transport Subsystem provides the following primitives to pass
primitives to pass data back and forth between the TMSM and specific data back and forth between the dispatcher and specific transport
TMSM-based security models, which provide the interface to the models, which provide the interface to the underlying secure
underlying secure transport service. Each TMSM-based security model transport service. Each transport model should define the elements
should define the security-model-specific elements of procedure for of procedure for the openSession() and closeSession() interfaces.
the openSession() and closeSession() interfaces.
statusInformation = statusInformation =
openSession( openSession(
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 tmSessionReference IN tmStateReference
) )
statusInformation = statusInformation =
closeSession( closeSession(
IN tmSessionReference IN tmStateReference
) )
6.3. Processing an Incoming SNMP Message 5.3. Processing an Incoming SNMP Message
6.3.1. TMSP for an Incoming Message 5.3.1. Processing an Incoming Message
If one does not exist, the TMSP will need to create an entry in a If one does not exist, the Transport Model will need to create an
Local Configuration Datastore referenced by tmSessionReference. This entry in a Local Configuration Datastore referenced by
information will include transportDomain, transportAddress, the tmStateReference. This information will include transportDomain,
securityModel, the securityLevel, and the securityName, plus any transportAddress, the securityModel, the securityLevel, and the
model or mechanism-specific details. How this information is securityName, plus any model or mechanism-specific details. How this
determined is model-specific. information is determined is model-specific.
The recvMessage ASI is used to pass a message from the transport The recvMessage ASI is used to pass a message from the transport
mapping to the Dispatcher. subsystem to the Dispatcher.
statusInformation = statusInformation =
recvMessage( recvMessage(
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 incomingMessage -- the message received IN incomingMessage -- the message received
IN incomingMessageLength -- its length IN incomingMessageLength -- its length
IN tmSessionReference IN tmStateReference
) )
6.3.2. Prepare Data Elements from Incoming Messages 5.3.2. Prepare Data Elements from Incoming Messages
The abstract service primitive from the Dispatcher to a Message The abstract service primitive from the Dispatcher to a Message
Processing Model for a received message is: Processing Model for a received message is:
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 tmSessionReference -- from the transport mapping IN tmStateReference -- 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
OUT securityName -- on behalf of this principal OUT securityName -- on behalf of this principal
OUT securityLevel -- Level of Security requested OUT securityLevel -- Level of Security requested
OUT contextEngineID -- data from/at this entity OUT contextEngineID -- data from/at this entity
OUT contextName -- data from/in this context OUT contextName -- data from/in this context
OUT pduVersion -- the version of the PDU OUT pduVersion -- the version of the PDU
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
) )
Note that tmSessionReference has been added to this ASI. Note that tmStateReference has been added to this ASI.
6.3.3. MPSP for an Incoming Message 5.3.3. Processing an Incoming Message
This section describes the procedure followed by the SMSP whenever it This section describes the procedure followed by the Security Model
receives an incoming message containing a management operation on whenever it receives an incoming message containing a management
behalf of a user from a Message Processing model. operation on behalf of a user from a Message Processing model.
The Message Processing Model extracts some information from the The Message Processing Model extracts some information from the
wholeMsg. The abstract service primitive from a Message Processing wholeMsg. The abstract service primitive from a Message Processing
Model to the Security Subsystem for a received message is:: Model to the Security Subsystem for a received message is::
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 tmSessionReference -- from the transport mapping IN tmStateReference -- 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
1) The securityEngineID is set to a value in a model-specific manner. 1) The securityEngineID is set to a value in a model-specific manner.
If the securityEngineID is not utilized by the specific model, then If the securityEngineID is not utilized by the specific model, then
it should be set to the local snmpEngineID, to satisfy the SNMPv3 it should be set to the local snmpEngineID, to satisfy the SNMPv3
message processing model in RFC 3412 section 7.2 13a). message processing model in RFC 3412 section 7.2 13a).
2) Extract the value of securityName from the Local Configuration 2) Extract the value of securityName from the Local Configuration
Datastore entry referenced by tmSessionReference. Datastore entry referenced by tmStateReference.
3) The scopedPDU component is extracted from the wholeMsg. 3) The scopedPDU component is extracted from the wholeMsg.
4) The maxSizeResponseScopedPDU is calculated. This is the maximum 4) The maxSizeResponseScopedPDU is calculated. This is the maximum
size allowed for a scopedPDU for a possible Response message. size allowed for a scopedPDU for a possible Response message.
5)The security data is cached as cachedSecurityData, so that a 5)The security data is cached as cachedSecurityData, so that a
possible response to this message can and will use the same security possible response to this message can and will use the same security
parameters. Then securityStateReference is set for subsequent parameters. Then securityStateReference is set for subsequent
reference to this cached data. reference to this cached data.
4) The statusInformation is set to success and a return is made to 4) The statusInformation is set to success and a return is made to
the calling module passing back the OUT parameters as specified in the calling module passing back the OUT parameters as specified in
the processIncomingMsg primitive. the processIncomingMsg primitive.
7. The TMSM MIB Module 6. The Transport-Subsystem-MIB Module
This memo defines a portion of the Management Information Base (MIB) This memo defines a portion of the Management Information Base (MIB)
for statistics in the Transport Mapping Security Model extension. for statistics in the Transport Subsystem.
7.1. Structure of the MIB Module 6.1. Structure of the MIB Module
Objects in this MIB module are arranged into subtrees. Each subtree Objects in this MIB module are arranged into subtrees. Each subtree
is organized as a set of related objects. The overall structure and is organized as a set of related objects. The overall structure and
assignment of objects to their subtrees, and the intended purpose of assignment of objects to their subtrees, and the intended purpose of
each subtree, is shown below. each subtree, is shown below.
7.1.1. The tmsmStats Subtree 6.1.1. The tmsmStats Subtree
This subtree contains security-model-independent counters which are This subtree contains security-model-independent counters which are
applicable to all security models based on the .Transport Mapping applicable to all security models based on the .Transport Subsystem.
Security Model extension. This subtree provides information for This subtree provides information for identifying fault conditions
identifying fault conditions and performance degradation. and performance degradation.
7.2. Relationship to Other MIB Modules 6.2. Relationship to Other MIB Modules
Some management objects defined in other MIB modules are applicable Some management objects defined in other MIB modules are applicable
to an entity implementing this MIB. In particular, it is assumed to an entity implementing this MIB. In particular, it is assumed
that an entity implementing the TMSM-MIB module will also implement that an entity implementing the Transport-Subsystem-MIB module will
the SNMPv2-MIB [RFC3418]. also implement the SNMPv2-MIB [RFC3418].
This MIB module is expected to be used with the MIB modules defined This MIB module is expected to be used with the MIB modules defined
for managing specific security models that are based on the TMSM for managing specific transport models within the transport
extension. This MIB module is designed to be security-model subsystem. This MIB module is designed to be transport-model
independent, and contains objects useful for managing common aspects independent and security-model independent, and contains objects
of any TMSM-based security model. Specific security models may useful for managing common aspects of any transport model. Specific
define a MIB module to contain security-model-dependent information. transport models may define a MIB module to contain transport-model
dependent information.
7.2.1. Textual Conventions 6.2.1. Textual Conventions
Generic and Common Textual Conventions used in this document can be Generic and Common Textual Conventions used in this document can be
found summarized at http://www.ops.ietf.org/mib-common-tcs.html found summarized at http://www.ops.ietf.org/mib-common-tcs.html
7.2.2. MIB Modules Required for IMPORTS 6.2.2. MIB Modules Required for IMPORTS
The. following MIB module imports items from [RFC2578], [RFC2579], The. following MIB module imports items from [RFC2578], [RFC2579],
[RFC2580], [RFC3411], and [RFC3419] [RFC2580], [RFC3411], and [RFC3419]
7.3. Definitions 6.3. Definitions
Transport-Subsystem-MIB DEFINITIONS ::= BEGIN
TMSM-MIB DEFINITIONS ::= BEGIN
IMPORTS IMPORTS
MODULE-IDENTITY, OBJECT-TYPE, MODULE-IDENTITY, OBJECT-TYPE,
mib-2, Integer32, Unsigned32, Gauge32 mib-2, Integer32, Unsigned32, Gauge32
FROM SNMPv2-SMI FROM SNMPv2-SMI
TestAndIncr, StorageType, RowStatus TestAndIncr, StorageType, RowStatus
FROM SNMPv2-TC FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP MODULE-COMPLIANCE, OBJECT-GROUP
FROM SNMPv2-CONF FROM SNMPv2-CONF
SnmpSecurityModel, SnmpSecurityModel,
SnmpAdminString, SnmpSecurityLevel, SnmpEngineID SnmpAdminString, SnmpSecurityLevel, SnmpEngineID
FROM SNMP-FRAMEWORK-MIB FROM SNMP-FRAMEWORK-MIB
TransportAddress, TransportAddressType TransportAddress, TransportAddressType
FROM TRANSPORT-ADDRESS-MIB FROM TRANSPORT-ADDRESS-MIB
; ;
tmsmMIB MODULE-IDENTITY tmsMIB MODULE-IDENTITY
LAST-UPDATED "200604200000Z" LAST-UPDATED "200610060000Z"
ORGANIZATION "ISMS Working Group" ORGANIZATION "ISMS Working Group"
CONTACT-INFO "WG-EMail: isms@lists.ietf.org CONTACT-INFO "WG-EMail: isms@lists.ietf.org
Subscribe: isms-request@lists.ietf.org Subscribe: isms-request@lists.ietf.org
Chairs: Chairs:
Juergen Quittek Juergen Quittek
NEC Europe Ltd. NEC Europe Ltd.
Network Laboratories Network Laboratories
Kurfuersten-Anlage 36 Kurfuersten-Anlage 36
69115 Heidelberg 69115 Heidelberg
skipping to change at page 35, line 4 skipping to change at page 32, line 47
Editor: Editor:
David Harrington David Harrington
FutureWei Technologies FutureWei Technologies
1700 Alma Drive, Suite 100 1700 Alma Drive, Suite 100
Plano, Texas 75075 Plano, Texas 75075
USA USA
+1 603-436-8634 +1 603-436-8634
dharrington@huawei.com dharrington@huawei.com
" "
DESCRIPTION "The Transport Mapping Security Model DESCRIPTION "The Transport Subsystem MIB Module
MIB Module
Copyright (C) The Internet Society (2006). This Copyright (C) The Internet Society (2006). This
version of this MIB module is part of RFC XXXX; version of this MIB module is part of RFC XXXX;
see the RFC itself for full legal notices. see the RFC itself for full legal notices.
-- NOTE to RFC editor: replace XXXX with actual RFC number -- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and remove this note -- for this document and remove this note
" "
DESCRIPTION "The initial version, published in RFC XXXX. DESCRIPTION "The initial version, published in RFC XXXX.
-- NOTE to RFC editor: replace XXXX with actual RFC number -- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and remove this note -- for this document and remove this note
" "
::= { mib-2 xxxx } ::= { mib-2 xxxx }
-- RFC Ed.: replace xxxx with IANA-assigned number and -- RFC Ed.: replace xxxx with IANA-assigned number and
skipping to change at page 35, line 23 skipping to change at page 33, line 18
DESCRIPTION "The initial version, published in RFC XXXX. DESCRIPTION "The initial version, published in RFC XXXX.
-- NOTE to RFC editor: replace XXXX with actual RFC number -- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and remove this note -- for this document and remove this note
" "
::= { mib-2 xxxx } ::= { mib-2 xxxx }
-- RFC Ed.: replace xxxx with IANA-assigned number and -- RFC Ed.: replace xxxx with IANA-assigned number and
-- remove this note -- remove this note
-- ---------------------------------------------------------- -- -- ---------------------------------------------------------- --
-- subtrees in the TMSM-MIB -- subtrees in the Transport-Subsystem-MIB
-- ---------------------------------------------------------- -- -- ---------------------------------------------------------- --
tmsmNotifications OBJECT IDENTIFIER ::= { tmsmMIB 0 } tmsNotifications OBJECT IDENTIFIER ::= { tmsMIB 0 }
tmsmObjects OBJECT IDENTIFIER ::= { tmsmMIB 1 } tmsObjects OBJECT IDENTIFIER ::= { tmsMIB 1 }
tmsmConformance OBJECT IDENTIFIER ::= { tmsmMIB 2 } tmsConformance OBJECT IDENTIFIER ::= { tmsMIB 2 }
-- ------------------------------------------------------------- -- -------------------------------------------------------------
-- Objects -- Objects
-- ------------------------------------------------------------- -- -------------------------------------------------------------
-- Textual Conventions -- Textual Conventions
-- Notifications for the Transport Model Security Model extension SnmpTransportModel ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "An identifier that uniquely identifies a
Transport Model of the Transport Subsystem within
the SNMP Management Architecture.
-- Statistics for the Transport Model Security Model extension The values for transportModel are allocated as
follows:
tmsmStats OBJECT IDENTIFIER ::= { tmsmObjects 1 } - The zero value does not identify any particular
transport model.
tmsmSessionOpenErrors OBJECT-TYPE - Values between 1 and 255, inclusive, are reserved
SYNTAX Counter32 for standards-track Transport Models and are
MAX-ACCESS read-only managed by the Internet Assigned Numbers Authority
STATUS current (IANA).
DESCRIPTION "The number of times an openSession() request - Values greater than 255 are allocated to
failed to open a Session. enterprise-specific Transport Models. An
" enterprise-specific transportModel value is defined
::= { tmsmStats 1 } to be:
tmsmSessionNoAvailableSessions OBJECT-TYPE enterpriseID * 256 + transport model within
SYNTAX Counter32 enterprise
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of times a Response message
was dropped because the corresponding
session was no longer available.
"
::= { tmsmStats 2 }
-- The tmsmSession Group For example, the fourth Transport Model defined by
the enterprise whose enterpriseID is 1 would be
260.
tmsmSession OBJECT IDENTIFIER ::= { tmsmObjects 2 } This scheme for allocation of transportModel
values allows for a maximum of 255 standards-
based Transport Models, and for a maximum of
256 Transport Models per enterprise.
tmsmSessionCurrent OBJECT-TYPE It is believed that the assignment of new
SYNTAX Gauge32 transportModel values will be rare in practice
MAX-ACCESS read-only because the larger the number of simultaneously
STATUS current utilized Transport Models, the larger the
DESCRIPTION "The current number of open sessions. chance that interoperability will suffer.
" Consequently, it is believed that such a range
::= { tmsmSession 1 } will be sufficient. In the unlikely event that
the standards committee finds this number to be
insufficient over time, an enterprise number
can be allocated to obtain an additional 256
possible values.
tmsmSessionMaxSupported OBJECT-TYPE Note that the most significant bit must be zero;
SYNTAX Unsigned32 hence, there are 23 bits allocated for various
MAX-ACCESS read-only organizations to design and define non-standard
STATUS current transportModels. This limits the ability to
DESCRIPTION "The maximum number of open sessions supported. define new proprietary implementations of Transport
The value zero indicates the maximum is dynamic. Models to the first 8,388,608 enterprises.
"
::= { tmsmSession 2 }
tmsmSessionOpenErrors OBJECT-TYPE It is worthwhile to note that, in its encoded
SYNTAX Counter32 form, the transportModel value will normally
MAX-ACCESS read-only require only a single byte since, in practice,
STATUS current the leftmost bits will be zero for most messages
DESCRIPTION "The number of times an openSession() request and sign extension is suppressed by the encoding
failed to open a Session. rules.
"
::= { tmsmSession 3 }
tmsmSessionSecurityLevelNotAvailableErrors OBJECT-TYPE As of this writing, there are several values
SYNTAX Counter32 of transportModel defined for use with SNMP or
MAX-ACCESS read-only reserved for use with supporting MIB objects.
STATUS current They are as follows:
DESCRIPTION "The number of times an outgoing message was
discarded because a requested securityLevel could not 0 reserved for 'any'
provided. 1 reserved for UDP
2 reserved for TCP
3 SSH Transport Model
" "
::= { tmsmSession 4 } SYNTAX INTEGER(0 .. 2147483647)
-- Notifications for the Transport Subsystem
-- Statistics for the Transport Subsystem
tmsStats OBJECT IDENTIFIER ::= { tmsObjects 1 }
-- ------------------------------------------------------------- -- -------------------------------------------------------------
-- tmsmMIB - Conformance Information -- Conformance Information
-- ------------------------------------------------------------- -- -------------------------------------------------------------
tmsmGroups OBJECT IDENTIFIER ::= { tmsmConformance 1 } tmsGroups OBJECT IDENTIFIER ::= { tmsConformance 1 }
tmsmCompliances OBJECT IDENTIFIER ::= { tmsmConformance 2 } tmsCompliances OBJECT IDENTIFIER ::= { tmsConformance 2 }
-- ------------------------------------------------------------- -- -------------------------------------------------------------
-- Units of conformance -- Units of conformance
-- ------------------------------------------------------------- -- -------------------------------------------------------------
tmsmGroup OBJECT-GROUP tmsGroup OBJECT-GROUP
OBJECTS { OBJECTS {
tmsmSessionOpenErrors,
tmsmSessionSecurityLevelNotAvailableErrors,
tmsmSessionCurrent,
tmsmSessionMaxSupported,
} }
STATUS current STATUS current
DESCRIPTION "A collection of objects for maintaining session DESCRIPTION "A collection of objects for maintaining session
information of an SNMP engine which implements the information of an SNMP engine which implements the
TMSM architectural extension. Transport subsystem.
" "
::= { tmsmGroups 2 } ::= { tmsGroups 2 }
-- ------------------------------------------------------------- -- -------------------------------------------------------------
-- Compliance statements -- Compliance statements
-- ------------------------------------------------------------- -- -------------------------------------------------------------
tmsmCompliance MODULE-COMPLIANCE tmsCompliance MODULE-COMPLIANCE
STATUS current STATUS current
DESCRIPTION DESCRIPTION
"The compliance statement for SNMP engines that support the "The compliance statement for SNMP engines that support the
TMSM-MIB" Transport-Subsystem-MIB"
MODULE MODULE
MANDATORY-GROUPS { tmsmGroup } MANDATORY-GROUPS { tmsGroup }
::= { tmsmCompliances 1 } ::= { tmsCompliances 1 }
END END
8. Security Considerations 7. Security Considerations
This document describes an architectural approach and multiple This document describes an architectural approach and multiple
proposed configurations that would permit SNMP to utilize transport proposed configurations that would permit SNMP to utilize transport
layer security services. Each section containing a proposal should layer security services. Each section containing a proposal should
discuss the security considerations of that approach. discuss the security considerations.
It is considered desirable by some industry segments that SNMP It is considered desirable by some industry segments that SNMP
security 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.
Perfect forward secrecy guarantees that compromise of long term Perfect forward secrecy guarantees that compromise of long term
secret keys does not result in disclosure of past session keys. secret keys does not result in disclosure of past session keys.
There are no management objects defined in this MIB module that have There are no management objects defined in this MIB module that have
a MAX-ACCESS clause of read-write and/or read-create. So, if this a MAX-ACCESS clause of read-write and/or read-create. So, if this
MIB module is implemented correctly, then there is no risk that an MIB module is implemented correctly, then there is no risk that an
intruder can alter or create any management objects of this MIB intruder can alter or create any management objects of this MIB
module via direct SNMP SET operations. module via direct SNMP SET operations.
skipping to change at page 39, line 5 skipping to change at page 37, line 5
authentication and privacy). authentication and privacy).
Further, deployment of SNMP versions prior to SNMPv3 is NOT Further, deployment of SNMP versions prior to SNMPv3 is NOT
RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to
enable cryptographic security. It is then a customer/operator enable cryptographic security. It is then a customer/operator
responsibility to ensure that the SNMP entity giving access to an responsibility to ensure that the SNMP entity giving access to an
instance of this MIB module is properly configured to give access to instance of this MIB module is properly configured to give access to
the objects only to those principals (users) that have legitimate the objects only to those principals (users) that have legitimate
rights to indeed GET or SET (change/create/delete) them. rights to indeed GET or SET (change/create/delete) them.
9. IANA Considerations 8. IANA Considerations
IANA is requested to create a new registry in the Simple Network
Management Protocol (SNMP) Number Spaces for SnmpTransportModels, as
described in the Transport-Subsystem-MIB defined in this document.
Values 0 through 255 are IANA-assigned by Standards Action, as
defined in RFC2434. Values above 255 are assigned by Hierarchical
allocation, using the algorithm defined in the definition of the
SnmpTransportModels TEXTUAL-CONVENTION in the Transport-Subsystem-MIB
in this document.
The MIB module in this document uses the following IANA-assigned The MIB module in this document uses the following IANA-assigned
OBJECT IDENTIFIER values recorded in the SMI Numbers registry: OBJECT IDENTIFIER values recorded in the SMI Numbers registry:
Descriptor OBJECT IDENTIFIER value Descriptor OBJECT IDENTIFIER value
---------- ----------------------- ---------- -----------------------
tmsmMIB { mib-2 XXXX } Transport-Subsystem-MIB { mib-2 XXXX }
Editor's Note (to be removed prior to publication): the IANA is Editor's Note (to be removed prior to publication): the IANA is
requested to assign a value for "XXXX" under the 'mib-2' subtree requested to assign a value for "XXXX" under the 'mib-2' subtree
and to record the assignment in the SMI Numbers registry. When and to record the assignment in the SMI Numbers registry. When
the assignment has been made, the RFC Editor is asked to replace the assignment has been made, the RFC Editor is asked to replace
"XXXX" (here and in the MIB module) with the assigned value and to "XXXX" (here and in the MIB module) with the assigned value and to
remove this note. remove this note.
10. Acknowledgments 9. Acknowledgments
The Integrated Security for SNMP WG would like to thank the following The Integrated Security for SNMP WG would like to thank the following
people for their contributions to the process: people for their contributions to the process:
The authors of submitted security model proposals: Chris Elliot, Wes The authors of submitted security model proposals: Chris Elliot, Wes
Hardaker, Dave Harrington, Keith McCloghrie, Kaushik Narayan, Dave Hardaker, Dave Harrington, Keith McCloghrie, Kaushik Narayan, Dave
Perkins, Joseph Salowey, and Juergen Schoenwaelder. Perkins, Joseph Salowey, and Juergen Schoenwaelder.
The members of the Protocol Evaluation Team: Uri Blumenthal, The members of the Protocol Evaluation Team: Uri Blumenthal,
Lakshminath Dondeti, Randy Presuhn, and Eric Rescorla. Lakshminath Dondeti, Randy Presuhn, and Eric Rescorla.
WG members who committed to and performed detailed reviews: Jeffrey WG members who committed to and performed detailed reviews: Jeffrey
Hutzelman Hutzelman
11. References 10. References
11.1. Normative References 10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., [RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS) and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 4366, April 2006. Extensions", RFC 4366, April 2006.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J. [RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information Schoenwaelder, Ed., "Structure of Management Information
skipping to change at page 40, line 49 skipping to change at page 39, line 13
[RFC3418] Presuhn, R., "Management Information Base (MIB) for the [RFC3418] Presuhn, R., "Management Information Base (MIB) for the
Simple Network Management Protocol (SNMP)", STD 62, Simple Network Management Protocol (SNMP)", STD 62,
RFC 3418, December 2002. RFC 3418, December 2002.
[RFC3419] Daniele, M. and J. Schoenwaelder, "Textual Conventions for [RFC3419] Daniele, M. and J. Schoenwaelder, "Textual Conventions for
Transport Addresses", RFC 3419, December 2002. Transport Addresses", RFC 3419, December 2002.
[RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) [RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Protocol Architecture", RFC 4251, January 2006. Protocol Architecture", RFC 4251, January 2006.
11.2. Informative References 10.2. Informative References
[RFC3410] Case, J., Mundy, R., Partain, D., and B. [RFC3410] Case, J., Mundy, R., Partain, D., and B.
Stewart, "Introduction and Applicability Stewart, "Introduction and Applicability
Statements for Internet-Standard Management Statements for Internet-Standard Management
Framework", RFC 3410, December 2002. Framework", RFC 3410, December 2002.
[RFC3413] Levi, D., Meyer, P., and B. Stewart, "Simple [RFC3413] Levi, D., Meyer, P., and B. Stewart, "Simple
Network Management Protocol (SNMP) Network Management Protocol (SNMP)
Applications", STD 62, RFC 3413, Applications", STD 62, RFC 3413,
December 2002. December 2002.
skipping to change at page 42, line 37 skipping to change at page 41, line 4
maxMessageSize,,,,,,,,In,In,In maxMessageSize,,,,,,,,In,In,In
globalData,,,,,,,,In,,In globalData,,,,,,,,In,,In
securityEngineID,,,,,,,,In,Out,In securityEngineID,,,,,,,,In,Out,In
scopedPDU,,,,,,,,In,Out,In scopedPDU,,,,,,,,In,Out,In
securityParameters,,,,,,,,Out,,Out securityParameters,,,,,,,,Out,,Out
securityStateReference,,,,,,,,,Out,In securityStateReference,,,,,,,,,Out,In
pduType,,,,,,,Out,,, pduType,,,,,,,Out,,,
tmSessionReference,,,,,,Out,In,,In, tmStateReference,,,,,,Out,In,,In,
Appendix B. Why tmSessionReference? Appendix B. 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. This section may be removed from subsequent passing parameters. This section may be removed from subsequent
revisions of the document. revisions of the document.
There are four approaches that could be used for passing information There are four approaches that could be used for passing information
between the TMSP and an SMSP. between the Transport Model and an 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
2. the TMSM could add a header to encapsulate the SNMP message, 2. one could add a header to encapsulate the SNMP message,
3. the TMSM could utilize fields already defined in the existing 3. one could utilize fields already defined in the existing SNMPv3
SNMPv3 message, or message, or
4. the TMSM could pass the information in an implementation-specific 4. one could pass the information in an implementation-specific
cache or via a MIB module. cache or via a MIB module.
B.1. Define an Abstract Service Interface B.1. Define an Abstract Service Interface
Abstract Service Interfaces (ASIs) [RFC3411] are defined by a set of Abstract Service Interfaces (ASIs) [RFC3411] are defined by a set of
primitives that specify the services provided and the abstract data primitives that specify the services provided and the abstract data
elements that are to be passed when the services are invoked. elements that are to be passed when the services are invoked.
Defining additional ASIs to pass the security and transport Defining additional ASIs to pass the security and transport
information from the transport mapping to a messaging security model information from the transport subsystem to security subsystem has
has the advantage of being consistent with existing RFC3411/3412 the advantage of being consistent with existing RFC3411/3412
practice, and helps to ensure that any TMSM proposals pass the practice, and helps to ensure that any transport model proposals pass
necessary data, and do not cause side effects by creating model- the necessary data, and do not cause side effects by creating model-
specific dependencies between itself and other models or other specific dependencies between itself and other models or other
subsystems other than those that are clearly defined by an ASI. subsystems other than those that are clearly defined by an ASI.
B.2. Using an Encapsulating Header B.2. Using an Encapsulating Header
A header could encapsulate the SNMP message to pass necessary A header could encapsulate the SNMP message to pass necessary
information from the TMSP to the dispatcher and then to a messaging information from the Transport Model to the dispatcher and then to a
security model. The message header would be included in the messaging security model. The message header would be included in
wholeMessage ASI parameter, and would be removed by a corresponding the wholeMessage ASI parameter, and would be removed by a
messaging model. This would imply the (one and only) messaging corresponding messaging model. This would imply the (one and only)
dispatcher would need to be modified to determine which SNMP message messaging dispatcher would need to be modified to determine which
version was involved, and a new message processing model would need SNMP message version was involved, and a new message processing model
to be developed that knew how to extract the header from the message would need to be developed that knew how to extract the header from
and pass it to the SMSP. the message and pass it to the Security Model.
B.3. Modifying Existing Fields in an SNMP Message B.3. Modifying Existing Fields in an SNMP Message
[RFC3412] describes the SNMPv3 message, which contains fields to pass [RFC3412] describes the SNMPv3 message, which contains fields to pass
security related parameters. The TMSM could use these fields in an security related parameters. The transport subsystem could use these
SNMPv3 message, or comparable fields in other message formats to pass fields in an SNMPv3 message, or comparable fields in other message
information between transport mapping security models in different formats to pass information between transport models in different
SNMP engines, and to pass information between a transport mapping SNMP engines, and to pass information between a transport model and a
security model and a corresponding messaging security model. corresponding messaging security model.
If the fields in an incoming SNMPv3 message are changed by the TMSP If the fields in an incoming SNMPv3 message are changed by the
before passing it to the SMSP, then the TMSP will need to decode the Transport Model before passing it to the Security Model, then the
ASN.1 message, modify the fields, and re-encode the message in ASN.1 Transport Model will need to decode the ASN.1 message, modify the
before passing the message on to the message dispatcher or to the fields, and re-encode the message in ASN.1 before passing the message
transport layer. This would require an intimate knowledge of the on to the message dispatcher or to the transport layer. This would
message format and message versions so the TMSP knew which fields require an intimate knowledge of the message format and message
could be modified. This would seriously violate the modularity of versions so the Transport Model knew which fields could be modified.
the architecture. This would seriously violate the modularity of the architecture.
B.4. Using a Cache B.4. Using a Cache
This document describes a cache, into which the TMSP puts information This document describes a cache, into which the Transport Model puts
about the security applied to an incoming message, and an SMSP information about the security applied to an incoming message, and an
extracts that information from the cache. Given that there may be Security Model extracts that information from the cache. Given that
multiple TM-security caches, a tmSessionReference is passed as an there may be multiple TM-security caches, a tmStateReference is
extra parameter in the ASIs between the transport mapping and the passed as an extra parameter in the ASIs between the transport
messaging security model, so the SMSP knows which cache of subsystem and the security subsystem, so the Security Model knows
information to consult. which cache of information to consult.
This approach does create dependencies between a model-specific TMSP This approach does create dependencies between a specific Transport
and a corresponding specific SMSP. This approach of passing a model- Model and a corresponding specific Security Model. This approach of
independent reference is consistent with the securityStateReference passing a model-independent reference is consistent with the
cache already being passed around in the RFC3411 ASIs. securityStateReference cache already being passed around in the
RFC3411 ASIs.
Appendix C. Open Issues Appendix C. Open Issues
Appendix D. Change Log Appendix D. 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 revision -03- to -04-
changed title from Transport Mapping Security Model Architectural
Extension to Transport Subsystem
modified the abstract and introduction
changed TMSM to TMS
changed MPSP to simply Security Model
changed SMSP to simply Security Model
changed TMSP to Transport Model
removed MPSP and TMSP and SMSP from Acronyms section
modified diagrams
removed most references to dispatcher functionality
worked to remove dependencies between transport and security
models.
defined snmpTransportModel enumeration similar to
snmpSecurityModel, etc.
eliminated all reference to SNMPv3 msgXXXX fields
changed tmSessionReference back to tmStateReference
Changes from revision -02- to -03- 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
o o
skipping to change at page 45, line 4 skipping to change at page 43, line 40
* 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 TMSM 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 TMSM-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
 End of changes. 177 change blocks. 
720 lines changed or deleted 636 lines changed or added

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