draft-ietf-isms-tmsm-01.txt   draft-ietf-isms-tmsm-02.txt 
Network Working Group D. Harrington Network Working Group D. Harrington
Internet-Draft Futurewei Technologies Internet-Draft Futurewei Technologies
Expires: September 5, 2006 J. Schoenwaelder Expires: November 4, 2006 J. Schoenwaelder
International University Bremen International University Bremen
March 4, 2006 May 3, 2006
Transport Mapping Security Model (TMSM) Architectural Extension for the Transport Mapping Security Model (TMSM) Architectural Extension for the
Simple Network Management Protocol (SNMP) Simple Network Management Protocol (SNMP)
draft-ietf-isms-tmsm-01.txt draft-ietf-isms-tmsm-02.txt
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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 Mapping Security Model (TMSM)
subsystem for the Simple Network Management Protocol (SNMP) extension for the Simple Network Management Protocol (SNMP)
architecture defined in RFC 3411. This document identifies and architecture defined in RFC 3411. This document identifies and
discusses some key aspects that need to be considered for any discusses some key aspects that need to be considered for any
transport-mapping-based security model for SNMP. transport-mapping-based security 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 the Transport Mapping Security Model Subsystem. (MIB) for managing sessions in the Transport Mapping Security Model
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. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Requirements of a Transport Mapping Security Model . . . . . . 6 2. Requirements of a Transport Mapping Security Model . . . . . . 6
2.1. Security Requirements . . . . . . . . . . . . . . . . . . 6 2.1. Message Security Requirements . . . . . . . . . . . . . . 6
2.1.1. Security Protocol Requirements . . . . . . . . . . . . 6 2.1.1. Security Protocol Requirements . . . . . . . . . . . . 7
2.2. Session Requirements . . . . . . . . . . . . . . . . . . . 7 2.2. SNMP Requirements . . . . . . . . . . . . . . . . . . . . 7
2.2.1. Session Establishment Requirements . . . . . . . . . . 8 2.2.1. Architectural Modularity Requirements . . . . . . . . 7
2.2.2. Session Maintenance Requirements . . . . . . . . . . . 8 2.2.2. Access Control Requirements . . . . . . . . . . . . . 14
2.2.3. Message security versus session security . . . . . . . 8 2.2.3. Security Parameter Passing Requirements . . . . . . . 16
2.3. Architectural Modularity Requirements . . . . . . . . . . 9 2.3. Session Requirements . . . . . . . . . . . . . . . . . . . 17
2.3.1. USM and the RFC3411 Architecture . . . . . . . . . . . 12 2.3.1. Session Establishment Requirements . . . . . . . . . . 18
2.3.2. TMSM and the RFC3411 Architecture . . . . . . . . . . 13 2.3.2. Session Maintenance Requirements . . . . . . . . . . . 19
2.4. Passing Messages between Subsystems . . . . . . . . . . . 15 2.3.3. Message security versus session security . . . . . . . 19
2.5. Security Parameter Passing Requirement . . . . . . . . . . 16 3. Scenario Diagrams for TMSM . . . . . . . . . . . . . . . . . . 21
2.5.1. Define an Abstract Service Interface . . . . . . . . . 17
2.5.2. Using an Encapsulating Header . . . . . . . . . . . . 17
2.5.3. Modifying Existing Fields in an SNMP Message . . . . . 17
2.5.4. Using a Cache . . . . . . . . . . . . . . . . . . . . 18
2.6. Architectural Requirements for Access Control . . . . . . 18
2.6.1. securityName Binding . . . . . . . . . . . . . . . . . 18
2.6.2. Separation of Authentication and Authorization . . . . 19
2.7. Requirements for Notifications . . . . . . . . . . . . . . 20
3. Scenario Diagrams . . . . . . . . . . . . . . . . . . . . . . 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. Abstract Service Interfaces . . . . . . . . . . . . . . . . . 23 4. Abstract Service Interfaces for TMSM . . . . . . . . . . . . . 23
5. TMSM Abstract Service Interfaces . . . . . . . . . . . . . . . 24 4.1. Existing Abstract Service Interfaces . . . . . . . . . . . 24
6. Integration with the SNMPv3 Message Format . . . . . . . . . . 26 4.2. TMSM Abstract Service Interfaces . . . . . . . . . . . . . 24
6.1. msgVersion . . . . . . . . . . . . . . . . . . . . . . . . 26 5. Cached Information and References . . . . . . . . . . . . . . 26
6.2. msgGlobalData . . . . . . . . . . . . . . . . . . . . . . 27 5.1. securityStateReference Cached Security Data . . . . . . . 26
6.3. securityLevel and msgFlags . . . . . . . . . . . . . . . . 27 5.2. tmStateReference Cached Security Data . . . . . . . . . . 27
7. The tmStateReference for Passing Security Parameters . . . . . 28 6. Integration with the SNMPv3 Message Format . . . . . . . . . . 28
8. securityStateReference Cached Security Data . . . . . . . . . 29 6.1. msgVersion . . . . . . . . . . . . . . . . . . . . . . . . 28
9. Prepare an Outgoing SNMP Message . . . . . . . . . . . . . . . 29 6.2. msgGlobalData . . . . . . . . . . . . . . . . . . . . . . 28
10. Prepare Data Elements from an Incoming SNMP Message . . . . . 30 6.3. securityLevel and msgFlags . . . . . . . . . . . . . . . . 29
11. Notifications . . . . . . . . . . . . . . . . . . . . . . . . 31 7. Prepare an Outgoing SNMP Message . . . . . . . . . . . . . . . 29
12. Transport Mapping Security Model Samples . . . . . . . . . . . 31 8. Prepare Data Elements from an Incoming SNMP Message . . . . . 30
12.1. TLS/TCP Transport Mapping Security Model . . . . . . . . . 31 9. Notifications . . . . . . . . . . . . . . . . . . . . . . . . 30
12.1.1. tmStateReference for TLS . . . . . . . . . . . . . . . 32 10. The TMSM MIB Module . . . . . . . . . . . . . . . . . . . . . 31
12.1.2. MPSP for TLS TM-Security Model . . . . . . . . . . . . 32 10.1. Structure of the MIB Module . . . . . . . . . . . . . . . 31
12.1.3. MIB Module for TLS Security . . . . . . . . . . . . . 32 10.1.1. The tmsmNotifications Subtree . . . . . . . . . . . . 31
12.2. DTLS/UDP Transport Mapping Security Model . . . . . . . . 32 10.1.2. The tmsmStats Subtree . . . . . . . . . . . . . . . . 31
12.2.1. tmStateReference for DTLS . . . . . . . . . . . . . . 33 10.1.3. The tmsmSession Subtree . . . . . . . . . . . . . . . 31
12.3. SASL Transport Mapping Security Model . . . . . . . . . . 34 10.2. Relationship to Other MIB Modules . . . . . . . . . . . . 31
12.3.1. tmStateReference for SASL DIGEST-MD5 . . . . . . . . 34 10.2.1. Textual Conventions . . . . . . . . . . . . . . . . . 32
13. The TMSM MIB Module . . . . . . . . . . . . . . . . . . . . . 35 10.2.2. MIB Modules Required for IMPORTS . . . . . . . . . . . 32
13.1. Structure of the MIB Module . . . . . . . . . . . . . . . 35 11. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 32
13.1.1. Textual Conventions . . . . . . . . . . . . . . . . . 35 12. Security Considerations . . . . . . . . . . . . . . . . . . . 39
13.1.2. The tmsmStats Subtree . . . . . . . . . . . . . . . . 35 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40
13.1.3. The tmsmsSession Subtree . . . . . . . . . . . . . . . 35 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 41
13.1.4. The Notifications Subtree . . . . . . . . . . . . . . 35 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 41
13.2. Relationship to Other MIB Modules . . . . . . . . . . . . 36 15.1. Normative References . . . . . . . . . . . . . . . . . . . 41
13.2.1. Relationship to the SNMPv2-MIB . . . . . . . . . . . . 36 15.2. Informative References . . . . . . . . . . . . . . . . . . 42
13.2.2. MIB Modules Required for IMPORTS . . . . . . . . . . . 36 Appendix A. Parameter Table . . . . . . . . . . . . . . . . . . . 42
14. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 36 A.1. ParameterList.csv . . . . . . . . . . . . . . . . . . . . 43
15. Implementation Considerations . . . . . . . . . . . . . . . . 42 Appendix B. Why tmSecurityReference? . . . . . . . . . . . . . . 44
15.1. Applications that Benefit from Sessions . . . . . . . . . 42 B.1. Define an Abstract Service Interface . . . . . . . . . . . 44
15.2. Applications that Suffer from Sessions . . . . . . . . . . 43 B.2. Using an Encapsulating Header . . . . . . . . . . . . . . 45
15.2.1. Troubleshooting . . . . . . . . . . . . . . . . . . . 43 B.3. Modifying Existing Fields in an SNMP Message . . . . . . . 45
16. Security Considerations . . . . . . . . . . . . . . . . . . . 43 B.4. Using a Cache . . . . . . . . . . . . . . . . . . . . . . 45
17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44 Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . . 45
18. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 45 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 46
19. References . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 46
19.1. Normative References . . . . . . . . . . . . . . . . . . . 45 Intellectual Property and Copyright Statements . . . . . . . . . . 47
19.2. Informative References . . . . . . . . . . . . . . . . . . 47
Appendix A. Questions about msgFlags: . . . . . . . . . . . . . . 47
A.1. msgFlags versus actual security . . . . . . . . . . . . . 48
Appendix B. Parameter Table . . . . . . . . . . . . . . . . . . . 49
B.1. ParameterList.csv . . . . . . . . . . . . . . . . . . . . 49
Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . . 50
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 51
Intellectual Property and Copyright Statements . . . . . . . . . . 51
1. Introduction 1. Introduction
This document describes a Transport Mapping Security Model (TMSM) This document describes a Transport Mapping Security Model (TMSM)
subsystem for the Simple Network Management Protocol (SNMP) extension for the Simple Network Management Protocol (SNMP)
architecture defined in [RFC3411]. This document identifies and architecture defined in [RFC3411]. This document identifies and
discusses some key aspects that need to be considered for any discusses some key aspects that need to be considered for any
transport-mapping-based security 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].
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1.2. Conventions 1.2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
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. Motivation 1.3. Acronyms
This section contains a list of acronyms used with the document and
references to where in the document the acronym is defined, for easy
lookup.
o TMSM - a Transport Mapping Security Model
o MPSP - s Messaging Processing Security Processor, the portion of a
TMSM security model that resides in the Message Processing
subsytem 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
There are multiple ways to secure one's home or business, but they There are multiple ways to secure one's home or business, but they
largely boil down to a continuum of alternatives. Let's consider largely boil down to a continuum of alternatives. Let's consider
three general approaches. In the first approach, an individual could three general approaches. In the first approach, an individual could
buy a gun, learn to use it, and sit on your front porch waiting for buy a gun, learn to use it, and sit on your front porch waiting for
intruders. In the second approach, one could hire an employee with a intruders. In the second approach, one could hire an employee with a
gun, schedule the employee, position the employee to guard what you gun, schedule the employee, position the employee to guard what you
want protected, hire a second guard to cover if the first gets sick, want protected, hire a second guard to cover if the first gets sick,
and so on. In the third approach, you could hire a security company, and so on. In the third approach, you could hire a security company,
tell them what you want protected, and they could hire employees, tell them what you want protected, and they could hire employees,
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subcontracted services and coordinate them however, because it is subcontracted services and coordinate them however, because it is
difficult to build solid security bindings between the various difficult to build solid security bindings between the various
services, and potential for gaps in the security is significant. services, and potential for gaps in the security is significant.
A solution based on the third approach might utilize one or more A solution based on the third approach might utilize one or more
lower-layer security mechanisms to provide the message-oriented lower-layer security mechanisms to provide the message-oriented
security services required. These would include authentication of security services required. These would include authentication of
the sender, encryption, timeliness checking, and data integrity the sender, encryption, timeliness checking, and data integrity
checking. There are a number of IETF standards available or in checking. There are a number of IETF standards available or in
development to address these problems through security layers at the development to address these problems through security layers at the
transport layer or application layer, among them TLS [RFC2246], SASL transport layer or application layer, among them TLS [RFC4366], SASL
[RFC2222], and SSH [RFC4251]. [RFC2222], 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 proposes a Transport Mapping Security Model (TMSM)
subsystem, as an extension of the RFC3411 architecture, that allows extension to the RFC3411 architecture, that allows security to be
security to be provided by an external protocol connected to the SNMP provided by an external protocol connected to the SNMP engine through
engine through an SNMP transport-mapping. Such a TMSM would then an SNMP transport-mapping [RFC3417]. Such a TMSM would then enable
enable the use of existing security mechanisms such as (TLS) the use of existing security mechanisms such as (TLS) [RFC4366] or
[RFC2246] 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 TMSM is to leverage these protocols
where it seems useful. 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 Mapping Security Model
2.1. Security Requirements 2.1. Message Security Requirements
Transport mapping security protocols SHOULD ideally provide the Transport mapping security protocols SHOULD ideally provide the
protection against the following message-oriented threats [RFC3411]: protection 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
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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 TMSM models MUST be able to coexist with other protocol models, and
may be designed to utilize either TCP or UDP, depending on the may be designed to utilize either TCP or UDP, depending on the
transport. transport.
2.2. Session Requirements 2.2. SNMP Requirements
Throughout this document, the term session is used. Some underlying
secure transports will have a notion of session. Some underlying
secure transports might enable the use of channels or other session-
like thing. In this document the term session refers to an
association between two SNMP engines, that permits the secure
transmission of one or more SNMP messages within the lifetime of the
session. How the session is actually established, opened, closed, or
maintained is specific to a particular security model.
Sessions are not part of the SNMP architecture described in
[RFC3411], but are considered desirable because the cost of
authentication can be amortized over potentially many transactions.
It is important to note that the architecture described in [RFC3411]
does not include a session selector in the Abstract Service
Interfaces, and neither is that done for this architectural
extension, so an SNMP application cannot select the session except by
passing a unique combination of securityName, securityModel, and
securityLevel.
All TMSM-based security models should discuss the impact of sessions
on SNMP usage, including how to establish/open a TMSM session (i.e.
how it maps to the concepts of session-like things of the underlying
protocol), how to behave when a TMSM session cannot be established,
how to close a TMSM session (and the underlying protocol equivalent)
properly, how to behave when a TMSM session is closed improperly, the
session security properties, session establishment overhead, and
session maintenance overhead.
To reduce redundancy, this document will discuss aspects that are
expected to be common to all TMSM-based security model sessions.
2.2.1. Session Establishment Requirements
[todo] contributions welcome.
2.2.2. Session Maintenance Requirements
[todo] contributions welcome.
2.2.3. Message security versus session security
A TMSM session is associated with state information that is
maintained for its lifetime. This state information allows for the
application of various security services to TMSM-based security
models. Cryptographic keys established at the beginning of the
session SHOULD be used to provide authentication, integrity checking,
and encryption services for data that is communicated during the
session. The cryptographic protocols used to establish keys for a
TMSM-based security model session SHOULD ensure that fresh new
session keys are generated for each session. If each session uses
new session keys, then messages cannot be replayed from one session
to another. In addition sequence information MAY be maintained in
the session which can be used to prevent the replay and reordering of
messages within a session.
A TMSM session will typically have a single securityName and
securityLevel associated with it. If an exchange between
communicating engines would require a different securityLevel or
would be on behalf of a different securityName, then another session
would be needed. An immediate consequence of this is that
implementations should be able to maintain some reasonable number of
concurrent sessions.
For TMSM models, securityName is typically specified during session
setup, and associated with the session identifier.
SNMPv3 was designed to support multiple levels of security,
selectable on a per-message basis by an SNMP application, because
there is not much value in using encryption for a Commander Generator
to poll for non-sensitive performance data on thousands of interfaces
every ten minutes; the encryption adds significant overhead to
processing of the messages.
Some TMSM-based security models MAY support only specific
authentication and encryption services, such as requiring all
messages to be carried using both authentication and encryption,
regardless of the security level requested by an SNMP application.
Some security models may use an underlying transport that provides a
per-message requested level of authentication and encryption
services. For example, if a session is created as 'authPriv', then
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
security level of authNoPriv, then that message could simply be
authenticated and not encrypted within the same transport session.
Whether this is possible depends on the security model and the secure
transport used.
If the underlying transport layer security was configurable on a per-
message basis, a TMSM-based security model could have a security-
model-specific MIB module with configurable maxSecurityLevel and a
minSecurityLevel objects to identify the range of possible levels. A
session's maxSecurityLevel would identify the maximum security it
could provide, and a session created with a minSecurityLevel of
authPriv would reject an attempt to send an authNoPriv message. The
elements of procedure of the security model would need to describe
the procedures to enable this determination.
For security models that do not support variable security services in
one session, multiple sessions could be established, with different
security levels, and for every packet the SNMP engine could select
the appropriate session based on the requested securityLevel. Some
SNMP entities are resource-constrained. Adding sessions increases
the need for resources, but so does encrypting unnecessarily.
Designers of security models should consider the tradeoffs for
resource-constrained devices.
2.3. 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. This architecture includes a Security when changes are made. The architecture includes a Security
Subsystem which is responsible for realizing security services. Subsystem which is responsible for realizing security services.
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
skipping to change at page 10, line 23 skipping to change at page 8, line 29
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
transport address information. These parameters utilize the
TransportType and TransportAddress
The design of a transport mapping security model must abide the goals The design of a transport mapping security model must abide the goals
of the RFC3411 architecture defined in [RFC3411]. To that end, this of the RFC3411 architecture defined in [RFC3411]. To that end, this
transport mapping security model proposal focuses on a modular transport mapping security model proposal uses a modular design that
subsystem that can be advanced through the standards process can be advanced through the standards process independently of other
independently of other proposals, and independent of other subsystems proposals, and independent of other modular components as much as
as much as possible. possible.
There has been some discussion of maintaining multiple sessions for
different security levels or for different applications. The ability
to have an application select different sessions or connections on a
per-message basis would likely require a modification to the SNMP
architecture to provide new ASIs, which is out of scope for this
document.
[discuss] I am not sure whether the previous paragraph is still
correct - I think we need to solve at least some of the session
problem space.
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 security mechanisms in the future.
Any transport mapping security model should define one minimum- Any transport mapping security model should define one minimum-
compliance mechanism, preferably one which is already widely deployed compliance mechanism, preferably one which is already widely deployed
within the transport layer security protocol used. within the transport layer security protocol used.
The TMSM subsystem is designed as an architectural extension that The TMSM architectural extension permits additional transport
permits additional transport security protocols to be "plugged into" security protocols to be "plugged into" the RFC3411 architecture,
the RFC3411 architecture, supported by corresponding transport- supported by corresponding transport-security-aware transport mapping
security-aware transport mapping models. models.
The RFC3411 architecture, and the USM approach, assume that a The RFC3411 architecture, and the USM approach, assume that a
security model is called by a message-processing model and will security model is called by a message-processing model and will
perform multiple security functions. The TMSM approach performs perform multiple security functions. The TMSM approach performs
similar functions but performs them in different places within the similar functions but performs them in different places within the
architecture, so we need to distinguish the two locations for architecture, so we need to distinguish the two locations for
security processing. security processing.
Transport mapping security is by its very nature a security layer Transport mapping security is by its very nature a security layer
which is plugged into the RFC3411 architecture between the transport which is plugged into the RFC3411 architecture between the transport
layer and the message dispatcher. Conceptually, transport mapping layer and the message dispatcher. Conceptually, transport mapping
security processing will be called from within the Transport Mapping security processing will be called from within the Transport Mapping
functionality of an SNMP engine dispatcher to perform the translation functionality of an SNMP engine dispatcher to perform the translation
of transport security parameters to/from security-model-independent of transport security parameters to/from security-model-independent
parameters. This transport mapping security processor will be parameters. This transport mapping security processor will be
referred to in this document as TMSP. referred to in this document as TMSP.
Additional functionality may be performed as part of the message Additional functionality may be performed as part of the message
processing function, i.e. in the security subsystem of the RFC3411 processing function, i.e., in the security subsystem of the RFC3411
architecture. This document will refer to message processor's architecture. This document will refer to message processor's
security processor as the MPSP. security processor as the MPSP.
Thus a TMSM is composed of both a TPSP and an MPSP. Thus a TMSM is composed of both a TMSP and an MPSP.
+------------------------------+ +------------------------------+
| Network | | Network |
+------------------------------+ +------------------------------+
^ ^ ^ ^ ^ ^
| | | | | |
v v v v v v
+-----+ +-----+ +-------+ +-----+ +-----+ +-------+
| UDP | | TCP | . . . | other | | UDP | | TCP | . . . | other |
+-----+ +-----+ +-------+ +-----+ +-----+ +-------+
skipping to change at page 12, line 38 skipping to change at page 10, line 37
| | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | | | | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | |
| | application | | | | applications | | application | | | | application | | | | applications | | application | |
| +-------------+ +---------+ +--------------+ +-------------+ | | +-------------+ +---------+ +--------------+ +-------------+ |
| ^ ^ | | ^ ^ |
| | | | | | | |
| v v | | v v |
| +----------------------------------------------+ | | +----------------------------------------------+ |
| | MIB instrumentation | SNMP entity | | | MIB instrumentation | SNMP entity |
+-------------------------------------------------------------------+ +-------------------------------------------------------------------+
2.3.1. 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 done by
a TMSM model. a TMSM 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)
skipping to change at page 13, line 41 skipping to change at page 11, line 40
| --------------------- ------------------ | | --------------------- ------------------ |
| ^ | ^
| | | |
| v | v
| --------------------- ------------------ | | --------------------- ------------------ |
| | SNMP applications | <--> | access control | | | | SNMP applications | <--> | access control | |
| --------------------- ------------------ | | --------------------- ------------------ |
| --------------------------------------------- | | --------------------------------------------- |
2.3.2. TMSM and the RFC3411 Architecture 2.2.1.2. TMSM and the RFC3411 Architecture
In the TMSM approach, the order of the steps differ and may be In the TMSM approach, the order of the steps differ and may be
handled by different subsystems: 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) determine the SNMP security model and parameters (transport
mapping) mapping)
3*) translate parameters to model-independent parameters (transport 3*) translate parameters to model-independent parameters (transport
mapping) 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 6*) translate parameters to model-independent parameters (security
model) model)
skipping to change at page 15, line 36 skipping to change at page 13, line 36
| --------------------- ------------------ | | --------------------- ------------------ |
| ^ | ^
| | | |
| v | v
| --------------------- ------------------ | | --------------------- ------------------ |
| | SNMP applications | <--> | access control | | | | SNMP applications | <--> | access control | |
| --------------------- ------------------ | | --------------------- ------------------ |
| --------------------------------------------- | | --------------------------------------------- |
2.4. Passing Messages between Subsystems 2.2.1.3. Passing Information between Engines
RFC3411 defines ASIs that describe the passing of messages between
subsystem within an engine, and the parameters which are expected to
be passed between the subsystems. The ASIs generally pass model-
independent information.
A TMSM model will establish an encrypted tunnel between the transport A TMSM model will establish an encrypted tunnel between the transport
mappings of two SNMP engines. One transport mapping security model mappings of two SNMP engines. One transport mapping security model
instance encrypts all messages, and the other transport mapping instance encrypts all messages, and the other transport mapping
security model instance decrypts the messages. security model instance decrypts the messages.
After the transport layer tunnel is established, then SNMP messages After the transport layer tunnel is established, then SNMP messages
can conceptually be sent through the tunnel from one SNMP message can conceptually be sent through the tunnel from one SNMP message
dispatcher to another SNMP message dispatcher. Once the tunnel is dispatcher to another SNMP message dispatcher. Once the tunnel is
established, multiple SNMP messages may be able to be passed through established, multiple SNMP messages may be able to be passed through
the same tunnel. the same tunnel.
Within an engine, outgoing SNMP messages are passed unencrypted from 2.2.2. Access Control Requirements
the message dispatcher to the transport mapping, and incoming
messages are passed unencrypted from the transport mapping to the
message dispatcher.
2.5. Security Parameter Passing Requirement
RFC3411 section 4 describes primitives to describe the abstract
service interfaces used to conceptually pass information between the
various subsystems, models and applications within the architecture.
The security parameters include a model-independent identifier of the
security "principal", the security model used to perform the
authentication, and which SNMP-specific security services were
(should be) applied to the message (authentication and/or privacy).
In the RFC3411 architecture, the messaging model must unpack SNMP-
specific security parameters from the message before calling a
security model to authenticate and decrypt an incoming message,
perform integrity checking, and translate model-specific security
parameters into model-independent parameters. In the TMSM approach,
the security-model specific parameters are not all carried in the
SNMP message, and can be determined from the transport layer by the
transport mapping, before the message processing begins.
[discuss] For outgoing messages, it is necessary to have an MPSP
because it is the MPSP that actually creates the message from its
component parts. Does the MPSP need to know the transport address or
the actual transport security capabilities, or can this be handled in
the TMSP, given the model-independent (and message-version-
independent) parameters? Are there any security services provided by
the MPSP for an outgoing message?
[discuss] For incoming messages, is there security functionality that
can only be handled after the message version is known, such as the
comparison of transport security capabilities and msgFlags? Does
that functionality need to know the transport address and session or
just the model-independent security parameters (securityName, model,
level)? Are there any SNMP-specific parameters that need to be
unpacked from the message for MPSP handling? msgFlags, securityLevel,
etc.?
The RFC3411 architecture has no ASI parameters for passing security
information between the transport mapping and the dispatcher, and
between the dispatcher and the message processing model. If there is
a need to have an MPSP called from the message processing model to,
for example, verify that msgFlags and the transport security are
consistent, then it will be necessary to pass the model-independent
security parameters from the TPSP through to the MPSP.
There are four approaches that could be used for passing information
between the TMSP and an MPSP.
1. one could define an ASI to supplement the existing ASIs, or
2. the TMSM could add a header to encapsulate the SNMP message,
3. the TMSM could utilize fields already defined in the existing
SNMPv3 message, or
4. the TMSM could pass the information in an implementation-specific
cache or via a MIB module.
2.5.1. Define an Abstract Service Interface
Abstract Service Interfaces (ASIs) [RFC3411] are defined by a set of
primitives that specify the services provided and the abstract data
elements that are to be passed when the services are invoked.
Defining additional ASIs to pass the security and transport
information from the transport mapping to a messaging security model
has the advantage of being consistent with existing RFC3411/3412
practice, and helps to ensure that any TMSM proposals pass the
necessary data, and do not cause side effects by creating model-
specific dependencies between itself and other models or other
subsystems other than those that are clearly defined by an ASI.
2.5.2. Using an Encapsulating Header
A header could encapsulate the SNMP message to pass necessary
information from the TMSP to the dispatcher and then to a messaging
security model. The message header would be included in the
wholeMessage ASI parameter, and would be removed by a corresponding
messaging model. This would imply the (one and only) messaging
dispatcher would need to be modified to determine which SNMP message
version was involved, and a new message processing model would need
to be developed that knew how to extract the header from the message
and pass it to the MPSP.
2.5.3. Modifying Existing Fields in an SNMP Message
[RFC3412] describes the SNMPv3 message, which contains fields to pass
security related parameters. The TMSM could use these fields in an
SNMPv3 message, or comparable fields in other message formats to pass
information between transport mapping security models in different
SNMP engines, and to pass information between a transport mapping
security model and a corresponding messaging security model.
If the fields in an incoming SNMPv3 message are changed by the TMSP
before passing it to the MPSP, then the TMSP will need to decode the
ASN.1 message, modify the fields, and re-encode the message in ASN.1
before passing the message on to the message dispatcher or to the
transport layer. This would require an intimate knowledge of the
message format and message versions so the TMSP knew which fields
could be modified. This would seriously violate the modularity of
the architecture.
2.5.4. Using a Cache
A cache mechanism could be used, into which the TMSP puts information
about the security applied to an incoming message, and an MPSP
extracts that information from the cache. Given that there may be
multiple TM-security caches, a cache ID would need to be passed
through an ASI so the MPSP knows which cache of information to
consult.
The cache reference could be thought of as an additional parameter in
the ASIs between the transport mapping and the messaging security
model. The RFC3411 ASIs would not need to be changed since the
SNMPv3 WG expected that additional parameters could be passed for
value-add features of specific implementations.
This approach does create dependencies between a model-specific TPSP
and a corresponding specific MPSP. If a TMSM-model-independent ASI
parameter is passed, this approach would be consistent with the
securityStateReference cache already being passed around in the ASI.
This document will describe a cache-based approach.
2.6. Architectural Requirements for Access Control
2.6.1. 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, the security mechanism
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 SNMPv3 message processing architecture subsystem
relies on a security model, such as USM, to play a role in security relies on a security model, such as USM, to play a role in security
that goes beyond protecting the message - it provides a mapping that goes beyond protecting the message - it provides a mapping
between the USM-specific principal to a security-model independent between the USM-specific principal to a security-model independent
securityName which can be used for subsequent processing, such as for securityName which 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 The TMSM is a two-stage security model, with a transport mapping
security process (TMSP) and a message processing security process security process (TMSP) and a message processing security process
(MPSP). Depending on the design of the specific TMSM model, i.e. (MPSP). Depending on the design of the specific TMSM model, i.e.,
which transport layer protocol is used, different features might be which transport layer protocol is used, different features might be
provided by the TMSP or by the MPSP. For example, the translation provided by the TMSP or by the MPSP. For example, the translation
from a mechanism-specific authenticated identity to a securityName from a mechanism-specific authenticated identity to a securityName
might be done by the TMSP or by the MPSP. might be done by the TMSP or by the MPSP.
[discuss] It may be possible to define a consistent division of The securityName MUST be bound to the mechanism-specific
stages regardless of the transport layer protocol used, and a authenticated identity, and this mapping MUST be done before the MPSP
consistent division of functionality would be preferred. portion of the model passes securityName to the message processing
model via the processIncoming() ASI.
The SNMP architecture distinguishes between messages with no The SNMP architecture distinguishes between messages with no
authentication and no privacy (noAuthNoPriv), authentication without authentication and no privacy (noAuthNoPriv), authentication without
privacy (authNoPriv) and authentication with privacy (authPriv). privacy (authNoPriv) and authentication with privacy (authPriv).
Hence, the authentication of a transport layer identity plays an Hence, the authentication of a transport layer identity plays an
important role and must be considered by any TMSM, and user important role and must be considered by any TMSM, and user
authentication must be available via the transport layer security authentication must be available via the transport layer security
protocol. 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.
host-based or anonymous) is considered adequate to secure and/or TLS) is considered adequate to secure and/or encrypt the message, but
encrypt the message, but inadequate to provide the desired inadequate to provide the desired granularity of access control (e.g.
granularity of access control (e.g. user-based), a second user-based), then a second authentication (e.g., one provided by a
authentication, e.g. one provided by a AAA server, may be used to RADIUS server) may be used to provide the authentication identity
provide the authentication identity which is bound to the which is bound to the securityName. This approach would require a
securityName. This approach would require a good analysis of the good analysis of the potential for man-in-the-middle attacks or
potential for man-in-the-middle attacks or masquerade possibilities. masquerade possibilities.
2.6.2. 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 TMSM security model should take care to not violate the separation
of authentication and authorization in the RFC3411 architecture.. of authentication and authorization in the RFC3411 architecture. The
The isAccessAllowed() primitive is used for passing security-model isAccessAllowed() primitive is used for passing security-model
independent parameters between the subsystems of the architecture. 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 security subsystem, to be consistent with the modularity of the
RFC3411 architecture. This separation was a deliberate decision of RFC3411 architecture. This separation was a deliberate decision of
the SNMPv3 WG, to allow support for authentication protocols which the SNMPv3 WG, to allow support for authentication protocols which
did not provide authorization capabilities, and to support did not provide authorization capabilities, and to support
authorization schemes, such as VACM, that do not perform their own authorization schemes, such as VACM, that do not perform their own
authentication. authentication.
skipping to change at page 20, line 15 skipping to change at page 15, line 33
independent parameters for the isAccessAllowed() primitive [RFC3411]. independent parameters for the isAccessAllowed() primitive [RFC3411].
TMSM does not specify how the securityModel and securityName could be TMSM does not specify how the securityModel and securityName could be
dynamically mapped to a VACM-style groupName. The mapping of dynamically mapped to 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
Windows domains, XML hierarchies, or task-based controls. The or Windows domains. The preferred approach is to pass the model-
preferred approach is to pass the model-independent security independent security parameters via the isAccessAllowed() ASI, and
parameters via the isAccessAllowed() ASI, and perform the mapping perform the mapping within the access control model.
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 security model and an access
control model, just as it is undesirable that the TMSM approach control model, just as it is undesirable that the TMSM approach
creates a dependency between a TMSP and an MPSP. creates a dependency between a TMSP and an MPSP.
2.7. Requirements for Notifications 2.2.3. Security Parameter Passing Requirements
[todo] cleanup this section RFC3411 section 4 describes primitives to describe the abstract data
flows between the various subsystems, models and applications within
the architecture. Abstract Service Interfaces describe the flow of
data between subsystems within an engine. The ASIs generally pass
model-independent information.
RFC 3430 (SNMP over TCP) suggests that TCP connections are initiated Within an engine using a TMSM-based security model, outgoing SNMP
by notification originators in case there is no currently established messages are passed unencrypted from the message dispatcher to the
connection that can be used to send the notification. Following this transport mapping, and incoming messages are passed unencrypted from
approach with SSH would require to provision authentication the transport mapping to the message dispatcher.
credentials on the agent so that agents can successfully authenticate
to a notification receiver. There might be other approaches, like
the reuse of manager initiated secure transport connections for
notifications. There is some text in Appendix A in RFC 3430 which
captures some of these discussions when RFC 3430 was written.
[todo] merge this text and text from RFC 3430 into the section The security parameters include a model-independent identifier of the
dealing with sessions? This seems to be the right place for this security "principal", the security model used to perform the
discussion. authentication, and which SNMP-specific security services were
(should be) applied to the message (authentication and/or privacy).
3. Scenario Diagrams In the RFC3411 architecture, which reflects the USM security model
design, the messaging model must unpack SNMP-specific security
parameters from an incoming message before calling a specific
security model to authenticate and decrypt an incoming message,
perform integrity checking, and translate model-specific security
parameters into model-independent parameters.
In the TMSM approach, the security-model specific parameters are not
carried in the SNMP message. The parameters are provided by SNMP
applications for outgoing messages, and the parameters for incoming
messages are extracted from the transport layer by the security-
model-specific transport mapping before the message is passed to the
message processing subsystem.
For outgoing messages, it is necessary to have an MPSP because it is
the MPSP that actually creates the message from its component parts.
Whether there are any security services provided by the MPSP for an
outgoing message is model-dependent.
For incoming messages, there might be security functionality that can
only be handled after the message version is known. The message
version is determined by the Message Processing model and passed to
the MPSP via the processIncoming() ASI.
The RFC3411 architecture has no ASI parameters for passing security
information between the transport mapping and the dispatcher, and
between the dispatcher and the message processing model. If there is
a need to have an MPSP called from the message processing model to,
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 MPSP.
This document describes a cache, into which the TMSP puts information
about the security applied to an incoming message, and an MPSP
extracts that information from the cache. Given that there may be
multiple TM-security caches, a tmStateReference is passed as an extra
parameter in the ASIs between the transport mapping and the messaging
security model.so the MPSP knows which cache of information to
consult.
This approach does create dependencies between a model-specific TMSP
and a corresponding specific MPSP. This approach of passing a model-
independent reference is consistent with the securityStateReference
cache already being passed around in the RFC3411 ASIs.
2.3. Session Requirements
Throughout this document, the term session is used. Some underlying
secure transports will have a notion of session. Some underlying
secure transports might enable the use of channels or other session-
like thing. In this document the term session refers to an
association between two SNMP engines that permits the secure
transmission of one or more SNMP messages within the lifetime of the
session. How the session is actually established, opened, closed, or
maintained is specific to a particular security model.
Sessions are not part of the SNMP architecture described in
[RFC3411], but are considered desirable because the cost of
authentication can be amortized over potentially many transactions.
It is important to note that the architecture described in [RFC3411]
does not include a session selector in the Abstract Service
Interfaces, and neither is that done for this architectural
extension, so an SNMP application cannot select the session except by
passing a unique combination of securityName, securityModel, and
securityLevel.
All TMSM-based security models should discuss the impact of sessions
on SNMP usage, including how to establish/open a TMSM session (i.e.,
how it maps to the concepts of session-like things of the underlying
protocol), how to behave when a TMSM session cannot be established,
how to close a TMSM session (and the underlying protocol equivalent)
properly, how to behave when a TMSM session is closed improperly, the
session security properties, session establishment overhead, and
session maintenance overhead.
To reduce redundancy, this document will discuss aspects that are
expected to be common to all TMSM-based security model sessions.
2.3.1. Session Establishment Requirements
SNMP applications must provide the transport address, securityName,
securityModel, and securityLevel to be used for a session.
SNMP Applications typically have no knowledge of whether the session
that will be used to carry commands was initially established as a
notification session, or a request-response session, and SHOULD NOT
make any assumptions based on knowing the direction of the session.
If an administrator or security model designer wants to differentiate
a session established for different purposes, such as a notification
session versus a request-response session, the application can use
different securityNames or transport addresses (e.g., port 161 vs
port 162) for different purposes.
An SNMP engine containing an application that initiates
communication, e.g., a Command Generator or Notification Originator,
MUST be able to attempt to establish a session for delivery if a
session does not yet exist. If a session cannot be established then
the message is discarded.
Sessions are usually established by the transport mapping security
processor when no appropriate session is found for an outgoing
message, but sessions may be established in advance to support
features such as notifications and call-home. How sessions are
established in advance is beyond the scope of this document.
Sessions are initiated by notification originators when there is no
currently established connection that can be used to send the
notification. For a client-server security protocol, this may
require provisioning authentication credentials on the agent, either
statically or dynamically, so the client/agent can successfully
authenticate to a notification receiver.
A TMSM-based security model must be able to determine whether a
session does or does not exist, and must be able to determine which
session has the appropriate security characteristics (transport
address, securityName, securityModel, and securityLevel) for an
outgoing message.
A TMSM security model implementation MAY reuse an already established
session with the appropriate transport address, securityName,
securityModel, and securityLevel characteristics for delivery of a
message originated by a different type of application than originally
caused the session to be created. For example, an implementation
that has an existing session originally established to receive a
request may use that session to send an outgoing notification, and
may use a session that was originally established to send a
notification to send a request. Responses are expected to be
returned using the same session that carried the corresponding
request message. Reuse is not required for conformance.
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
same session, then the message MAY be dropped by the manager.
2.3.2. Session Maintenance Requirements
A TMSM-based security model can tear down sessions as needed. It may
be necessary for some implementations to tear down sessions as the
result of resource constraints, for example.
The decision to tear down a session is implementation-dependent.
While it is possible for an implementation to automatically tear down
each session once an operation has completed, this is not recommended
for anticipated performance reasons. How an implementation
determines that an operation has completed, including all potential
error paths, is implementation-dependent.
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 elements of procedure for TMSM-based security models should be
sure to describe the expected behavior when no session exists for a
response.
The elements of procedure may discuss when cached information can be
discarded, and the timing of cache cleanup may have security
implications, but cache memory management is an implementation issue.
If a security model defines MIB module objects to maintain session
state information, then the security model MUST describe what happens
to the objects when a related session is torn down, since this will
impact interoperability of the MIB module.
2.3.3. Message security versus session security
A TMSM session is associated with state information that is
maintained for its lifetime. This state information allows for the
application of various security services to TMSM-based security
models. Cryptographic keys established at the beginning of the
session SHOULD be used to provide authentication, integrity checking,
and encryption services for data that is communicated during the
session. The cryptographic protocols used to establish keys for a
TMSM-based security model session SHOULD ensure that fresh new
session keys are generated for each session. If each session uses
new session keys, then messages cannot be replayed from one session
to another. In addition sequence information MAY be maintained in
the session which can be used to prevent the replay and reordering of
messages within a session.
A TMSM session will typically have a single transport address,
securityName and securityLevel associated with it. If an exchange
between communicating engines would require a different securityLevel
or would be on behalf of a different securityName, then another
session would be needed. An immediate consequence of this is that
implementations should be able to maintain some reasonable number of
concurrent sessions.
For TMSM models, securityName is typically specified during session
setup, and associated with the session identifier.
SNMPv3 was designed to support multiple levels of security,
selectable on a per-message basis by an SNMP application, because
there is not much value in using encryption for a Commander Generator
to poll for non-sensitive performance data on thousands of interfaces
every ten minutes; the encryption adds significant overhead to
processing of the messages.
Some TMSM-based security models MAY support only specific
authentication and encryption services, such as requiring all
messages to be carried using both authentication and encryption,
regardless of the security level requested by an SNMP application.
Some security models may use an underlying transport that provides a
per-message requested level of authentication and encryption
services. For example, if a session is created as 'authPriv', then
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
security level of authNoPriv, then that message could simply be
authenticated and not encrypted within the same transport session.
Whether this is possible depends on the security model and the secure
transport used.
If the underlying transport layer security was configurable on a per-
message basis, a TMSM-based security model could have a security-
model-specific MIB module with configurable maxSecurityLevel and a
minSecurityLevel objects to identify the range of possible levels. A
session's maxSecurityLevel would identify the maximum security it
could provide, and a session created with a minSecurityLevel of
authPriv would reject an attempt to send an authNoPriv message. The
elements of procedure of the security model would need to describe
the procedures to enable this determination.
For security models that do not support variable security services in
one session, multiple sessions could be established with different
security levels, and for every packet the SNMP engine could select
the appropriate session based on the requested securityLevel. Some
SNMP entities are resource-constrained. Adding sessions increases
the need for resources, but so does encrypting unnecessarily.
Designers of security models should consider the trade offs for
resource-constrained devices.
3. Scenario Diagrams for TMSM
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. Abstract Service Interfaces 4. Abstract Service Interfaces for TMSM
4.1. Existing Abstract Service Interfaces
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 mapping:
statusInformation = -- success or errorIndication statusInformation = -- success or errorIndication
prepareOutgoingMessage( prepareOutgoingMessage(
IN transportDomain -- transport domain to be used IN transportDomain -- transport domain to be used
IN transportAddress -- transport address to be used IN transportAddress -- transport address to be used
IN messageProcessingModel -- typically, SNMP version IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model to use IN securityModel -- Security Model to use
IN securityName -- on behalf of this principal IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested IN securityLevel -- Level of Security requested
IN contextEngineID -- data from/at this entity IN contextEngineID -- data from/at this entity
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
) )
5. TMSM Abstract Service Interfaces 4.2. TMSM Abstract Service Interfaces
A set of abstract service interfaces have been defined within this A set of abstract service interfaces have been defined within this
document to describe the conceptual data flows between the Transport document to describe the conceptual data flows between the Transport
Mapping Security Models and adjacent components in the system.. Mapping Security Models and adjacent components in the system.
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 transport mapping security model subsystem for sending. the transport mapping for sending.
statusInformation sendMessage( statusInformation =
sendMessage(
IN destTransportDomain -- transport domain to be used IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the message to send IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length IN outgoingMessageLength -- its length
IN tmStateReference -- IN tmStateReference
OUT sessionID OUT sessionID
) )
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 security model subsystem to the Dispatcher. mapping to the Dispatcher.
statusInformation RecvMessage( statusInformation =
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
OUT tmStateReference -- OUT tmStateReference
OUT sessionID OUT sessionID
) )
The Transport Mapping Security Model provides the following The Transport Mapping Security Model provides the following
primitives to pass data back and forth between the TMSM and specific primitives to pass data back and forth between the TMSM and specific
TMSM-based security models, which provide the interface to the TMSM-based security models, which provide the interface to the
underlying secure transport service. Each TMSM-based security model underlying secure transport service. Each TMSM-based security model
should define the security-model-specific elements of procedure for should define the security-model-specific elements of procedure for
the establishSession(), closeSession(), TxMessage(), and RxMessage() the openSession(), closeSession(), txMessage(), and rxMessage()
interfaces. interfaces.
statusInformation TxMessage( statusInformation =
txMessage(
IN destTransportDomain -- transport domain to be used IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the message to send IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length IN outgoingMessageLength -- its length
IN tmStateReference -- IN tmStateReference
OUT sessionID OUT sessionID
) )
statusInformation RxMessage( statusInformation =
rxMessage(
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 to send IN incomingMessage -- the message to send
IN incomingMessageLength -- its length IN incomingMessageLength -- its length
OUT tmStateReference -- OUT tmStateReference
) )
statusInformation establishSession( statusInformation =
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 tmStateReference -- IN tmStateReference
OUT sessionID OUT sessionID
) )
statusInformation closeSession( statusInformation =
closeSession(
IN sessionID IN sessionID
) )
5. Cached Information and References
The RFC3411 architecture uses caches to store dynamic model-specific
information, and uses references in the ASIs to indicate in a model-
independent manner which cached information must flow between
subsytems.
5.1. securityStateReference Cached Security Data
From RFC3411: "For each message received, the Security Model caches
the state information such that a Response message can be generated
using the same security information, even if the Local Configuration
Datastore is altered between the time of the incoming request and the
outgoing response.
A Message Processing Model has the responsibility for explicitly
releasing the cached data if such data is no longer needed. To
enable this, an abstract securityStateReference data element is
passed from the Security Model to the Message Processing Model. The
cached security data may be implicitly released via the generation of
a response, or explicitly released by using the stateRelease
primitive, as described in RFC3411 section 4.5.1."
For the TMSM approach, the TMSP may need to provide the information
to be stored in the securityStateReference to the message processing
model. such as the security-model-independent securityName,
securityLevel, and securityModel parameters. For responses, the
messaging model may need to pass the parameters back to the TMSP.
This document will differentiate the tmStateReference provided by the
TMSP to the MPSP, from the securityStateReference provided by the
MPSP to the Dispatcher. This document does not specify an
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.
5.2. tmStateReference Cached Security Data
A tmStateReference is used to pass data between the TMSP and the
MPSP, similar to the securityStateReference described in RFC3412. A
reference to this cache can be envisioned as being appended to the
ASIs between the TM and the MP.
The TMSP may provide only some aspects of security, and leave some
aspects to the MPSP. tmStateReference should be used to pass any
parameters, in a model- and mechanism-specific format, that will be
needed to coordinate the activities of the TMSP and MPSP, plus the
parameters subsequently passed in securityStateReference. For
example, the TMSP may provide privacy and data integrity and
authentication and authorization policy retrievals, or some subset of
these features, depending on the features available in the transport
mechanisms. A field in tmStateReference should identify which
services were provided for each received message by the TMSP, the
securityLevel applied to the received message, the model-specific
security identity, the session identifier for session based transport
security, and so on.
6. Integration with the SNMPv3 Message Format 6. Integration with the SNMPv3 Message Format
TMSM proposals can use the SNMPv3 message format, defined in RFC3412, TMSM proposals can use the SNMPv3 message format, defined in RFC3412,
section 6. This section discusses how the fields could be reused. section 6. This section discusses how the fields could be reused.
6.1. msgVersion 6.1. msgVersion
For proposals that reuse the SNMPv3 message format, this field should For proposals that reuse the SNMPv3 message format, this field should
contain the value 3. contain the value 3.
skipping to change at page 28, line 32 skipping to change at page 29, line 44
security provided by the underlying transport layer security security provided by the underlying transport layer security
mechanisms is configured to meet or exceed the securityLevel required mechanisms is configured to meet or exceed the securityLevel required
by the msgFlags in the SNMP message. When the MPSP processes the by the msgFlags in the SNMP message. When the MPSP processes the
incoming message, it should compare the msgFlags field to the incoming message, it should compare the msgFlags field to the
securityLevel actually provided for the message by the transport securityLevel actually provided for the message by the transport
layer security. If they differ, the MPSP should determine whether layer security. If they differ, the MPSP should determine whether
the changed securityLevel is acceptable. If not, it should discard the changed securityLevel is acceptable. If not, it should discard
the message. Depending on the model, the MPSP may issue a reportPDU the message. Depending on the model, the MPSP may issue a reportPDU
with the XXXXXXX model-specific counter. with the XXXXXXX model-specific counter.
7. The tmStateReference for Passing Security Parameters 7. Prepare an Outgoing SNMP Message
A tmStateReference is used to pass data between the TMSP and the
MPSP, similar to the securityStateReference described in RFC3412.
This can be envisioned as being appended to the ASIs between the TM
and the MP or as being passed in an encapsulating header.
The TMSP may provide only some aspects of security, and leave some
aspects to the MPSP. tmStateReference should be used to pass any
parameters, in a model- and mechanism-specific format, that will be
needed to coordinate the activities of the TMSP and MPSP, and the
parameters subsequently passed in securityStateReference. For
example, the TMSP may provide privacy and data integrity and
authentication and authorization policy retrievals, or some subset of
these features, depending on the features available in the transport
mechanisms. A field in tmStateReference should identify which
services were provided for each received message by the TMSP, the
securityLevel applied to the received message, the model-specific
security identity, the session identifier for session based transport
security, and so on.
8. securityStateReference Cached Security Data
From RFC3411: "For each message received, the Security Model caches
the state information such that a Response message can be generated
using the same security information, even if the Local Configuration
Datastore is altered between the time of the incoming request and the
outgoing response.
A Message Processing Model has the responsibility for explicitly
releasing the cached data if such data is no longer needed. To
enable this, an abstract securityStateReference data element is
passed from the Security Model to the Message Processing Model. The
cached security data may be implicitly released via the generation of
a response, or explicitly released by using the stateRelease
primitive, as described in RFC3411 section 4.5.1."
For the TMSM approach, the TMSP may need to provide information to
the message processing model, such as the security-model-independent
securityName, securityLevel, and securityModel parameters, and for
responses, the messaging model may need to pass the parameters back
to the TMSP. To differentiate what information needs to be provided
to the message processing model by the TMSP, and vice-versa, this
document will differentiate the tmStateReference provide by the TMSP
from the securityStateReference provided by the MPSP. 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.
9. Prepare an Outgoing SNMP Message
Following RFC3412, section 7.1, the SNMPv3 message processing model Following RFC3412, section 7.1, the SNMPv3 message processing model
uses the generateResponseMsg() or generateRequestMsg() primitives, to uses the generateResponseMsg() or generateRequestMsg() primitives, to
call the MPSP. The message processing model, or the MPSP it calls, call the MPSP. The message processing model, or the MPSP it calls,
may need to put information into the tmStateReference cache for use may need to put information into the tmStateReference cache for use
by the TMSP, such as: by the TMSP, such as:
tmSecurityStateReference - the unique identifier for the cached tmSecurityStateReference - the unique identifier for the cached
information information
tmTransportDomain tmTransportDomain
tmTransportAddress tmTransportAddress
tmSecurityModel - an indicator of which mechanisms to use tmSecurityModel - an indicator of which mechanisms to use
tmSecurityName - a model-specific identifier of the security tmSecurityName - a model-specific identifier of the security
principal principal
tmSecurityLevel - an indicator of which security services are tmSecurityLevel - an indicator of which security services are
requested requested
and may contain additional information such as A tmStateReference cache may contain additional information such as
tmSessionID tmSessionID
tmSessionKey tmSessionKey
tmSessionMsgID tmSessionMsgID
According to RFC3411, section 4.1.1, the application provides the 8. Prepare Data Elements from an Incoming SNMP Message
transportDomain and transportAddress to the PDU dispatcher via the
sendPDU() primitive. If we permit multiple sessions per
transportAddress, then we would need to define how session
identifiers get passed from the application to the PDU dispatcher
(and then to the MP model).
The SNMP over TCP Transport Mapping document [RFC3430] says that TCP
connections can be recreated dynamically or kept for future use and
actually leaves all that to the transport mapping.
[discuss] we might define a new transportDomain and transportAddress,
which includes the address and session identifier. For situations
where a session has not yet been established, we could pass a 0x0000
session identifier (or whatever) to indicate that a session should be
established. Well, this won't work with the current TAddress
definitions and is probably too ugly to do.
We might have a MIB module that records the session information for
subsequent use by the applications and other subsystems, or it might
be passed in the tmStateReference cache. For notifications, I assume
the SNMPv3 notification tables would be a place to find the address,
but I'm not sure how to identify the presumably-dynamic session
identifiers. The MIB module could identify whether the session was
initiated by the remote engine or initiated by the current engine,
and possibly assigned a purpose (incoming request/response or
outgoing notifications). First we need to decide whether to handle
notifications and requests in one or two (or more) sessions, which
might depend on the transport protocol we choose (the same problem
netconf faced).
10. Prepare Data Elements from an Incoming SNMP Message
For an incoming message, the TMSP will need to put information from For an incoming message, the TMSP will need to put information from
the transport mechanisms used into the tmStateReference so the MPSP the transport mechanisms used into the tmStateReference so the MPSP
can extract the information and add it conceptually to the can extract the information and add it conceptually to the
securityStateReference. securityStateReference.
The tmStateReference cache will likely contain at least the following The tmStateReference cache will likely contain at least the following
information: information:
tmStateReference - a unique identifier for the cached information tmStateReference - a unique identifier for the cached information
tmSecurityStateReference - the unique identifier for the cached tmSecurityStateReference - the unique identifier for the cached
skipping to change at page 31, line 20 skipping to change at page 30, line 45
principal principal
tmSecurityLevel - an indicator of which security services are tmSecurityLevel - an indicator of which security services are
requested requested
tmAuthProtocol tmAuthProtocol
tmPrivProtocol tmPrivProtocol
and may contain additional information such as and may contain additional information such as
tmSessionID tmSessionID
tmSessionKey tmSessionKey
tmSessionMsgID tmSessionMsgID
11. Notifications 9. Notifications
For notifications, if the cache has been released and then session For notifications, if the cache has been released and then session
closed, then the MPSP will request the TMSP to establish a session, closed, then the MPSP will request the TMSP to establish a session,
populate the cache, and pass the securityStateReference to the MPSP. populate the cache, and pass the securityStateReference to the MPSP.
[discuss] We need to determine what state needs to be saved here. [discuss] We need to determine what state needs to be saved here.
12. Transport Mapping Security Model Samples 10. The TMSM MIB Module
There are a number of standard protocols that could be proposed as
possible solutions within the TMSM framework. Some factors should be
considered when selecting a protocol for use within this framework.
Using a protocol in a manner for which is was not designed has
numerous problems. The advertised security characteristics of a
protocol may depend on its being used as designed; when used in other
ways, it may not deliver the expected security characteristics. It
is recommended that any proposed model include a discussion of the
applicability statement of the protocols to be used.
12.1. TLS/TCP Transport Mapping Security Model
SNMP supports multiple transports. The preferred transport for SNMP
over IP is UDP [RFC3417]. An experimental transport for SNMP over
TCP is defined in [RFC3430].
TLS/TCP will create an association between the TMSM of one SNMP
entity and the TMSM of another SNMP entity. The created "tunnel" may
provide encryption and data integrity. Both encryption and data
integrity are optional features in TLS. The TLS TMSP MUST provide
authentication if auth is requested in the securityLevel of the SNMP
message request (RFC3412 4.1.1). The TLS TM-security model MUST
specify that the messages be encrypted if priv is requested in the
securityLevel parameter of the SNMP message request (RFC3412 4.1.1).
The TLS TM-security model MUST support the TLS Handshake Protocol
with mutual authentication.
12.1.1. tmStateReference for TLS
Upon establishment of a TLS session, the TMSP will cache the state
information. A unique tmStateReference will be passed to the
corresponding MPSP. The MPSP will pass the securityStateReference to
the Message Processing Model for memory management.
The tmStateReference cache:
tmStateReference
tmSecurityStateReference
tmTransportDomain = TCP/IPv4
tmTransportAddress = x.x.x.x:y
tmSecurityModel - TLS TMSM
tmSecurityName = "dbharrington"
tmSecurityLevel = "authPriv"
12.1.2. MPSP for TLS TM-Security Model
messageProcessingModel = SNMPv3
securityModel = TLS TMSM
securityName = tmSecurityName
securityLevel = msgSecurityLevel
12.1.3. MIB Module for TLS Security
Each security model should use its own MIB module, rather than
utilizing the USM MIB, to eliminate dependencies on a model that
could be replaced some day. See RFC3411 section 4.1.1.
The TLS MIB module needs to provide the mapping from model-specific
identity to a model independent securityName.
[todo] Module needs to be worked out once things become stable...
12.2. DTLS/UDP Transport Mapping Security Model
DTLS has been proposed as a UDP-based TLS. Transport Layer Security
(TLS) [RFC2246] traditionally requires a connection-oriented
transport and is usually used over TCP. Datagram Transport Layer
Security (DTLS) [I-D.rescorla-dtls] provides security services
equivalent to TLS for connection-less transports such as UDP.
DTLS provides all the security services needed from an SNMP
architectural point of view. Although it is possible to derive a
securityName from the public key certificates (e.g. the subject
field), this approach requires installing certificates on all SNMP
entities, leading to a certificate management problem which does not
integrate well with established AAA systems. [discuss] why does this
not integrate well with existing AAA systems?
Another option is to run an authentication exchange which is
integrated with TLS, such as Secure Remote Password with TLS
[I-D.ietf-tls-srp]. A similar option would be to use Kerberos
authentication with TLS as defined in [RFC2712].
It is important to stress that the authentication exchange must be
integrated into the TLS mechanism to prevent man-in-the-middle
attacks. While SASL [RFC2222] is often used on top of a TLS
encrypted channel to authenticate users, this choice seems to be
problematic until the mechanism to cryptographically bind SASL into
the TLS mechanism has been defined.
DTLS will create an association between the TMSM of one SNMP entity
and the TMSM of another SNMP entity. The created "tunnel" may
provide encryption and data integrity. Both encryption and data
integrity are optional features in DTLS. The DTLS TM-security model
MUST provide authentication if auth is requested in the securityLevel
of the SNMP message request (RFC3412 4.1.1). The TLS TM-security
model MUST specify that the messages be encrypted if priv is
requested in the securityLevel parameter of the SNMP message request
(RFC3412 4.1.1).
The DTLS TM-security model MUST support the TLS Handshake Protocol
with mutual authentication.
12.2.1. tmStateReference for DTLS
DTLS has been suggested as a possible secure transport. It is not
clear whether DTLS is a reasonable choice for SNMP interactions. It
is mentioned here only as an example.
Upon establishment of a DTLS session, the TMSP will cache the state
information. A unique tmStateReference will be passed to the
corresponding MPSP. The MPSP will pass the securityStateReference to
the Message Processing Model for memory management.
The tmStateReference cache:
tmStateReference
tmSecurityStateReference
tmTransportDomain = UDP/IPv4
tmTransportAddress = x.x.x.x:y
tmSecurityModel - DTLS TMSM
tmSecurityName = "dbharrington"
tmSecurityLevel = "authPriv"
12.3. SASL Transport Mapping Security Model
The Simple Authentication and Security Layer (SASL) [RFC2222]
provides a hook for authentication and security mechanisms to be used
in application protocols. SASL supports a number of authentication
and security mechanisms, among them Kerberos via the GSSAPI mechanism
[RFC4121].
This sample will use DIGEST-MD5 because it supports authentication,
integrity checking, and confidentiality.
DIGEST-MD5 supports auth, auth with integrity, and auth with
confidentiality. Since SNMPv3 assumes integrity checking is part of
authentication, if msgFlags is set to authNoPriv, the qop-value
should be set to auth-int; if msgFlags is authPriv, then qop-value
should be auth-conf.
Realm is optional, but can be utilized by the securityModel if
desired. SNMP does not use this value, but a TMSM could map the
realm into SNMP processing in various ways. For example, realm and
username could be concatenated to be the securityName value, e.g.
helpdesk::username", or the realm could be used to specify a
groupName to use in the VACM access control. This would be similar
to having the securityName-to-group mapping done by the external AAA
server.
12.3.1. tmStateReference for SASL DIGEST-MD5
The tmStateReference cache:
tmStateReference
tmSecurityStateReference
tmTransportDomain = TCP/IPv4
tmTransportAddress = x.x.x.x:y
tmSecurityModel - SASL TMSM
tmSecurityName = username
tmSecurityLevel = [auth-conf]
tmAuthProtocol = md5-sess
tmPrivProtocol = 3des
tmServicesProvided mutual authentication,
reauthentication,
integrity,
encryption
tmParameters = "realm=helpdesk, serv-type=SNMP
13. The TMSM 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 managing the Transport Mapping Security Model Subsystem. for managing sessions in the Transport Mapping Security Model
extension.
13.1. Structure of the MIB Module 10.1. 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.
13.1.1. Textual Conventions 10.1.1. The tmsmNotifications Subtree
Generic and Common Textual Conventions used in this document can be This subtree contains notifications to alert other entities to events
found summarized at http://www.ops.ietf.org/mib-common-tcs.html that are applicable to all security models based on the Transport
Mapping Security Model extension.
13.1.2. The tmsmStats Subtree 10.1.2. 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 Mapping
Security Model Subsystem. Security Model extension. This subtree provides information for
identifying fault conditions and performance degradation.
This subtree provides information for identifying fault conditions
and performance degradation.
13.1.3. The tmsmsSession Subtree 10.1.3. The tmsmSession Subtree
This subtree contains security-model-independent information about This subtree contains security-model-independent information about
sessions which are applicable to all security models based on the sessions which are applicable to all security models based on the
Transport Mapping Security Model Subsystem. Transport Mapping Security Model extension.
This subtree provides information for managing sessions for any
security model based on the Transport Mapping Security Model
Subsystem.
13.1.4. The Notifications Subtree
This subtree contains notifications to alert other entities to events
which could alter the operational behavior of the entity in a network
utilizing the SAMPLE Protocol.
13.2. Relationship to Other MIB Modules 10.2. 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 TMSM-MIB module will also implement
the SNMPv2-MIB [RFC3418]. 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 security models that are based on the TMSM
subsystem. This MIB module is designed to be security-model extension. This MIB module is designed to be security-model
independent, and conatins objects useful for managing common aspects independent, and contains objects useful for managing common aspects
of any TMSM-based security model. Specific security models may of any TMSM-based security model. Specific security models may
define a MIB module to contain security-model-dependent information. define a MIB module to contain security-model-dependent information.
13.2.1. Relationship to the SNMPv2-MIB 10.2.1. Textual Conventions
The 'system' subtree in the SNMPv2-MIB [RFC3418] is defined as being Generic and Common Textual Conventions used in this document can be
mandatory for all systems, and the objects apply to the entity as a found summarized at http://www.ops.ietf.org/mib-common-tcs.html
whole. The 'system' subtree provides identification of the
management entity and certain other system-wide data. The TMSM-MIB
utilizes, but does not dupicate, some of those objects. [todo] do we
actually use any of the objects, since we don't have any elements of
procedure?
13.2.2. MIB Modules Required for IMPORTS 10.2.2. 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]
14. Definitions 11. Definitions
TMSM-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 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 tmsmMIB MODULE-IDENTITY
LAST-UPDATED "200602270000Z" LAST-UPDATED "200604200000Z"
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 37, line 33 skipping to change at page 33, line 12
Juergen Schoenwaelder Juergen Schoenwaelder
International University Bremen International University Bremen
Campus Ring 1 Campus Ring 1
28725 Bremen 28725 Bremen
Germany Germany
+49 421 200-3587 +49 421 200-3587
j.schoenwaelder@iu-bremen.de j.schoenwaelder@iu-bremen.de
Editor: Editor:
David Harrington David Harrington
Effective Software FutureWei Technologies
50 Harding Rd 1700 Alma Drive, Suite 100
Portsmouth, New Hampshire 03801 Plano, Texas 75075
USA USA
+1 603-436-8634 +1 603-436-8634
ietfdbh@comcast.net dharrington@huawei.com
" "
DESCRIPTION "The Transport Mapping Security Model DESCRIPTION "The Transport Mapping Security Model
Subsystem MIB MIB
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
" "
REVISION "200602270000Z" -- 27 February 2006 REVISION "200604200000Z" -- 20 April 2006
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 TMSM-MIB
skipping to change at page 38, line 25 skipping to change at page 33, line 51
-- ---------------------------------------------------------- -- -- ---------------------------------------------------------- --
tmsmNotifications OBJECT IDENTIFIER ::= { tmsmMIB 0 } tmsmNotifications OBJECT IDENTIFIER ::= { tmsmMIB 0 }
tmsmObjects OBJECT IDENTIFIER ::= { tmsmMIB 1 } tmsmObjects OBJECT IDENTIFIER ::= { tmsmMIB 1 }
tmsmConformance OBJECT IDENTIFIER ::= { tmsmMIB 2 } tmsmConformance OBJECT IDENTIFIER ::= { tmsmMIB 2 }
-- ------------------------------------------------------------- -- -------------------------------------------------------------
-- Objects -- Objects
-- ------------------------------------------------------------- -- -------------------------------------------------------------
-- Statistics for the Transport Model Security Model Subsystem -- Textual Conventions
SessionIndex ::= TEXTUAL-CONVENTION
DISPLAY-HINT "d"
STATUS current
DESCRIPTION
"A unique value, greater than zero, identifying a transport
mapping security model session. The value must remain
constant for the duration of a session. New values should
be assigned in such a way that reuse of recently used
values is avoided."
SYNTAX Integer (1..2147483647)
SessionIndexOrZero TEXTUAL-CONVENTION
DISPLAY-HINT "d"
STATUS current
DESCRIPTION
"This extension of the TmsmSessionId permits the additional
value zero. The meaning of the value zero is object-specific
and must therefore be defined as part of the description of
any object which uses this syntax. Examples of the usage of
zero might include situations where a session was unknown
or where none or all sessions need to be referenced."
SYNTAX Integer (0..2147483647)
-- Notifications for the Transport Model Security Model extension
-- Statistics for the Transport Model Security Model extension
tmsmStats OBJECT IDENTIFIER ::= { tmsmObjects 1 } tmsmStats OBJECT IDENTIFIER ::= { tmsmObjects 1 }
-- [discuss] do we need any tmsm stats? tmsmSessionOpenErrors OBJECT-TYPE
-- these should be for interoperability, not local debug. SYNTAX Counter32
-- we could probably track session establishment failures MAX-ACCESS read-only
-- although this really belongs in an SSH-MIB, not TMSM-MIB STATUS current
DESCRIPTION "The number of times an openSession() request
failed to open a Session.
"
::= { tmsmStats 1 }
-- The tmsmSession Group -- The tmsmSession Group
tmsmSession OBJECT IDENTIFIER ::= { tmsmObjects 2 } tmsmSession OBJECT IDENTIFIER ::= { tmsmObjects 2 }
tmsmSessionSpinLock OBJECT-TYPE tmsmSessionSpinLock OBJECT-TYPE
SYNTAX TestAndIncr SYNTAX TestAndIncr
MAX-ACCESS read-write MAX-ACCESS read-write
STATUS current STATUS current
DESCRIPTION "An advisory lock used to allow several cooperating DESCRIPTION "An advisory lock used to allow several cooperating
TMSM security models to coordinate their TMSM security models to coordinate their
use of facilities to create sessions in the use of facilities to create sessions in the
tmsmSessionTable. tmsmSessionTable.
" "
::= { tmsmSession 1 } ::= { tmsmSession 1 }
tmsmSessionCurrent OBJECT-TYPE tmsmSessionCurrent OBJECT-TYPE
SYNTAX Gauge32 SYNTAX Gauge32
MAX-ACCESS read-only MAX-ACCESS read-only
STATUS current STATUS current
DESCRIPTION "The current number of established sessions. DESCRIPTION "The current number of open sessions.
" "
::= { tmsmSession 2 } ::= { tmsmSession 2 }
tmsmSessionMaxSupported OBJECT-TYPE tmsmSessionMaxSupported OBJECT-TYPE
SYNTAX Unsigned32 SYNTAX Unsigned32
MAX-ACCESS read-only MAX-ACCESS read-only
STATUS current STATUS current
DESCRIPTION "The maximum number of open sessions allowed. DESCRIPTION "The maximum number of open sessions supported.
The value zero indicates the maximum is dynamic.
" "
::= { tmsmSession 3 } ::= { tmsmSession 3 }
tmsmSessionOpenErrors OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of times an openSession() request
failed to open a Session.
"
::= { tmsmSession 4 }
tmsmSessionSecurityLevelNotAvailableErrors OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of times an outgoing message was
discarded because a requested securityLevel could not
provided.
"
::= { tmsmSession 5 }
tmsmSessionTable OBJECT-TYPE tmsmSessionTable OBJECT-TYPE
SYNTAX SEQUENCE OF TmsmSessionEntry SYNTAX SEQUENCE OF TmsmSessionEntry
MAX-ACCESS not-accessible MAX-ACCESS not-accessible
STATUS current STATUS current
DESCRIPTION "The table of currently available sessions configured DESCRIPTION "The table of currently available sessions configured
in the SNMP engine's Local Configuration Datastore in the SNMP engine's Local Configuration Datastore
(LCD). (LCD).
Sessions are created as needed, and do not persist Sessions are created as needed, and do not persist
across network management system reboots. across network management system reboots.
" "
::= { tmsmSession 4 } ::= { tmsmSession 6 }
tmsmSessionEntry OBJECT-TYPE tmsmSessionEntry OBJECT-TYPE
SYNTAX TmsmSessionEntry SYNTAX TmsmSessionEntry
MAX-ACCESS not-accessible MAX-ACCESS not-accessible
STATUS current STATUS current
DESCRIPTION "A session configured in the SNMP engine's Local DESCRIPTION "A session configured in the SNMP engine's Local
Configuration Datastore (LCD) for Transport Mapping Configuration Datastore (LCD) for Transport Mapping
Security Models. Security Models.
" "
INDEX { tmsmSessionID } INDEX { tmsmSessionID }
::= { tmsmSessionTable 1 } ::= { tmsmSessionTable 1 }
TmsmSessionEntry ::= SEQUENCE TmsmSessionEntry ::= SEQUENCE
{ {
tmsmSessionID Integer32, tmsmSessionID SessionIndex,
tmsmSessionTransport TransportAddressType, tmsmSessionTransport TransportAddressType,
tmsmSessionAddress TransportAddress, tmsmSessionAddress TransportAddress,
tmsmSessionSecurityModel SnmpSecurityModel, tmsmSessionSecurityModel SnmpSecurityModel,
tmsmSessionSecurityName SnmpAdminString, tmsmSessionSecurityName SnmpAdminString,
tmsmSessionSecurityLevel SnmpSecurityLevel, tmsmSessionSecurityLevel SnmpSecurityLevel,
tmsmSessionEngineID SnmpEngineID tmsmSessionEngineID SnmpEngineID
} }
tmsmSessionID OBJECT-TYPE tmsmSessionID OBJECT-TYPE
SYNTAX Integer32 (1..65535) SYNTAX SessionIndex
MAX-ACCESS not-accessible MAX-ACCESS not-accessible
STATUS current STATUS current
DESCRIPTION "A locally-unique identifier for a session. DESCRIPTION "A locally-unique identifier for a session.
" "
::= { tmsmSessionEntry 1 } ::= { tmsmSessionEntry 1 }
tmsmSessionTransport OBJECT-TYPE tmsmSessionTransport OBJECT-TYPE
SYNTAX TransportAddressType SYNTAX TransportAddressType
MAX-ACCESS read-only MAX-ACCESS read-only
STATUS current STATUS current
skipping to change at page 40, line 43 skipping to change at page 37, line 25
STATUS current STATUS current
DESCRIPTION "The Security Model associated with this session." DESCRIPTION "The Security Model associated with this session."
::= { tmsmSessionEntry 4 } ::= { tmsmSessionEntry 4 }
tmsmSessionSecurityName OBJECT-TYPE tmsmSessionSecurityName OBJECT-TYPE
SYNTAX SnmpAdminString SYNTAX SnmpAdminString
MAX-ACCESS read-only MAX-ACCESS read-only
STATUS current STATUS current
DESCRIPTION "A human readable string representing the principal DESCRIPTION "A human readable string representing the principal
in Security Model independent format. in Security Model independent format.
The default transformation of the Secure Shell
Security Model dependent security ID to the
securityName
and vice versa is the identity function so that the
securityName is the same as the SSH user name.
" "
::= { tmsmSessionEntry 5 } ::= { tmsmSessionEntry 5 }
tmsmSessionSecurityLevel OBJECT-TYPE tmsmSessionSecurityLevel OBJECT-TYPE
SYNTAX SnmpSecurityLevel SYNTAX SnmpSecurityLevel
MAX-ACCESS read-only MAX-ACCESS read-only
STATUS current STATUS current
DESCRIPTION "The Level of Security at which SNMP messages can be DESCRIPTION "The Level of Security at which SNMP messages can be
sent using this session, in particular, one of: sent using this session, in particular, one of:
noAuthNoPriv - without authentication and noAuthNoPriv - without authentication and
without privacy, without privacy,
authNoPriv - with authentication but authNoPriv - with authentication but
skipping to change at page 41, line 43 skipping to change at page 38, line 19
tmsmGroups OBJECT IDENTIFIER ::= { tmsmConformance 1 } tmsmGroups OBJECT IDENTIFIER ::= { tmsmConformance 1 }
tmsmCompliances OBJECT IDENTIFIER ::= { tmsmConformance 2 } tmsmCompliances OBJECT IDENTIFIER ::= { tmsmConformance 2 }
-- ------------------------------------------------------------- -- -------------------------------------------------------------
-- Units of conformance -- Units of conformance
-- ------------------------------------------------------------- -- -------------------------------------------------------------
tmsmGroup OBJECT-GROUP tmsmGroup OBJECT-GROUP
OBJECTS { OBJECTS {
tmsmSessionOpenErrors,
tmsmSessionSecurityLevelNotAvailableErrors,
tmsmSessionCurrent, tmsmSessionCurrent,
tmsmSessionMaxSupported, tmsmSessionMaxSupported,
tmsmSessionTransport, tmsmSessionTransport,
tmsmSessionAddress, tmsmSessionAddress,
tmsmSessionSecurityModel, tmsmSessionSecurityModel,
tmsmSessionSecurityName, tmsmSessionSecurityName,
tmsmSessionSecurityLevel, tmsmSessionSecurityLevel,
tmsmSessionEngineID, tmsmSessionEngineID,
tmsmSessionSpinLock tmsmSessionSpinLock
} }
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
SNMP Secure Shell Security Model. TMSM architectural extension.
" "
::= { tmsmGroups 2 } ::= { tmsmGroups 2 }
-- ------------------------------------------------------------- -- -------------------------------------------------------------
-- Compliance statements -- Compliance statements
-- ------------------------------------------------------------- -- -------------------------------------------------------------
tmsmCompliance MODULE-COMPLIANCE tmsmCompliance MODULE-COMPLIANCE
STATUS current STATUS current
skipping to change at page 42, line 25 skipping to change at page 39, line 4
-- ------------------------------------------------------------- -- -------------------------------------------------------------
tmsmCompliance MODULE-COMPLIANCE tmsmCompliance 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" TMSM-MIB"
MODULE MODULE
MANDATORY-GROUPS { tmsmGroup } MANDATORY-GROUPS { tmsmGroup }
::= { tmsmCompliances 1 } ::= { tmsmCompliances 1 }
END END
15. Implementation Considerations 12. Security Considerations
15.1. Applications that Benefit from Sessions
[todo] contributions welcome.
There has been discussion of ways SNMP could be extended to better
support management/monitoring needs when a network is running just
fine. Use of a TCP transport, for example, could enable larger
message sizes and more efficient table retrievals.
Discussing how to improve SNMP once you have less strict message size
constraints is beyond the scope of this document, or that of TMSM-
based security models. Applications utilizing TMSM-based security
models may want to take advantage of the increased message sizes by
sending larger requests and utilizing existing SNMP operations (e.g.
getbulk) effectively. However, doing so might have negative impacts
on existing SNMP management and the networks that contain them.
15.2. Applications that Suffer from Sessions
[todo] contributions welcome.
15.2.1. Troubleshooting
It has been a long-standing requirement that SNMP be able to work
when the network is unstable, to enable network troubleshooting and
repair. The UDP approach has been considered to meet that need well,
with an assumption that getting small messages through, even if out
of order, is better than gettting no messages through. There has
been a long debate about whether UDP actually offers better support
than TCP when the underlying IP or lower layers are unstable. There
has been recent discussion of whether operators actually use SNMP to
troubleshoot and repair unstable networks.
The need to establish a session before using SNMP to troubleshoot a
device may prove problematic in practice. TMSM-based security models
should include discussion of how troubleshooting applications might
be impacted by the use of the specific security model, and recommend
workarounds.
This document RECOMMENDS that all TMSM-based security models include
a fallback approach, triggered by multiple failed attempts to
establish sessions. The default fallback should be to utilize the
IETF-Standard USM security model to send a notification, so an
administrator can attempt to manually correct the problem.
16. 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] discuss the security considerations of that approach.
expand as needed.
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 security 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 a number of management objects defined in this MIB module There are a number of management objects defined in this MIB module
with a MAX-ACCESS clause of read-write and/or read-create. Such with a MAX-ACCESS clause of read-write and/or read-create. Such
objects may be considered sensitive or vulnerable in some network objects may be considered sensitive or vulnerable in some network
environments. The support for SET operations in a non-secure environments. The support for SET operations in a non-secure
environment without proper protection can have a negative effect on environment without proper protection can have a negative effect on
network operations. These are the tables and objects and their network operations. These are the tables and objects and their
sensitivity/vulnerability: sensitivity/vulnerability:
o [todo] list the tables and objects and state why they are o [discuss] Should it be possible for a manager to create or modify
rows in the session table? If so, then we may need the rowstatus
object. If the session table is read-only then we can probably
eliminate the rowstatus. If the tabel is not read-only, then we
need to list the tables and objects and state why they are
sensitive. sensitive.
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.
Some of the readable objects in this MIB module (i.e., objects with a Some of the readable objects in this MIB module (i.e., objects with a
MAX-ACCESS other than not-accessible) may be considered sensitive or MAX-ACCESS other than not-accessible) may be considered sensitive or
skipping to change at page 44, line 22 skipping to change at page 40, line 4
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.
Some of the readable objects in this MIB module (i.e., objects with a Some of the readable objects in this MIB module (i.e., objects with a
MAX-ACCESS other than not-accessible) may be considered sensitive or MAX-ACCESS other than not-accessible) may be considered sensitive or
vulnerable in some network environments. It is thus important to vulnerable in some network environments. It is thus important to
control even GET and/or NOTIFY access to these objects and possibly control even GET and/or NOTIFY access to these objects and possibly
to even encrypt the values of these objects when sending them over to even encrypt the values of these objects when sending them over
the network via SNMP. These are the tables and objects and their the network via SNMP. These are the tables and objects and their
sensitivity/vulnerability: sensitivity/vulnerability:
o [todo] list the tables and objects and state why they are o [todo] list the tables and objects and state why they are
sensitive. sensitive.
[discuss] how do we modify this section for an SNMP/SSH or other
transport mapping security model? If the security model provides for
securityName/Level/Model then some of the normal boilerplate is not
true.
SNMP versions prior to SNMPv3 did not include adequate security. SNMP versions prior to SNMPv3 did not include adequate security.
Even if the network itself is secure (for example by using IPSec), Even if the network itself is secure (for example by using IPSec),
even then, there is no control as to who on the secure network is even then, there is no control as to who on the secure network is
allowed to access and GET/SET (read/change/create/delete) the objects allowed to access and GET/SET (read/change/create/delete) the objects
in this MIB module. in this MIB module.
It is RECOMMENDED that implementers consider the security features as It is RECOMMENDED that implementers consider the security features as
provided by the SNMPv3 framework (see [RFC3410], section 8), provided by the SNMPv3 framework (see [RFC3410], section 8),
including full support for the SNMPv3 cryptographic mechanisms (for including full support for the SNMPv3 cryptographic mechanisms (for
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.
17. IANA Considerations 13. IANA Considerations
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 } tmsmMIB { 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.
[discuss] How do we add a new TransportType? [discuss] How do we add a new TransportType?
18. Acknowledgments 14. 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
19. References 15. References
19.1. Normative References 15.1. 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.
[RFC2222] Myers, J., "Simple Authentication and Security Layer [RFC2222] Myers, J., "Simple Authentication and Security Layer
(SASL)", RFC 2222, October 1997. (SASL)", RFC 2222, October 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", [RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
RFC 2246, January 1999. and T. Wright, "Transport Layer Security (TLS)
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
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999. Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J. [RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Textual Conventions for SMIv2", Schoenwaelder, Ed., "Textual Conventions for SMIv2",
STD 58, RFC 2579, April 1999. STD 58, RFC 2579, April 1999.
[RFC2580] McCloghrie, K., Perkins, D., and J. Schoenwaelder, [RFC2580] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
skipping to change at page 46, line 46 skipping to change at page 42, line 27
Management Protocol (SNMP)", STD 62, RFC 3417, Management Protocol (SNMP)", STD 62, RFC 3417,
December 2002. December 2002.
[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.
[RFC3430] Schoenwaelder, J., "Simple Network Management Protocol
Over Transmission Control Protocol Transport Mapping",
RFC 3430, 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.
[I-D.rescorla-dtls] 15.2. Informative References
Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", draft-rescorla-dtls-05 (work in progress),
June 2005.
19.2. Informative References
[RFC2712] Medvinsky, A. and M. Hur, "Addition of Kerberos Cipher
Suites to Transport Layer Security (TLS)", RFC 2712,
October 1999.
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart, [RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet- "Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002. Standard Management Framework", RFC 3410, December 2002.
[RFC3413] Levi, D., Meyer, P., and B. Stewart, "Simple Network [RFC3413] Levi, D., Meyer, P., and B. Stewart, "Simple Network
Management Protocol (SNMP) Applications", STD 62, Management Protocol (SNMP) Applications", STD 62,
RFC 3413, December 2002. RFC 3413, December 2002.
[RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
Version 5 Generic Security Service Application Program
Interface (GSS-API) Mechanism: Version 2", RFC 4121,
July 2005.
[I-D.ietf-netconf-ssh] [I-D.ietf-netconf-ssh]
Wasserman, M. and T. Goddard, "Using the NETCONF Wasserman, M. and T. Goddard, "Using the NETCONF
Configuration Protocol over Secure Shell (SSH)", Configuration Protocol over Secure Shell (SSH)",
draft-ietf-netconf-ssh-05 (work in progress), draft-ietf-netconf-ssh-06 (work in progress), March 2006.
October 2005.
[I-D.ietf-tls-srp]
Taylor, D., "Using SRP for TLS Authentication",
draft-ietf-tls-srp-10 (work in progress), October 2005.
Appendix A. Questions about msgFlags:
[discuss] many of these questions can be resolved by deciding whether
the TMSP or MPSP provides the service of comparing msgFlags (from
inside the message) to actual capabilities of the transport layer
security (external to the message). It may however be necessary to
provide this service for two slightly different purposes depending on
whether the message is outgoing (and may need to be checked by the
TMSP when a new transport session might be created) or the message is
incoming ( the capabilities of the transport layer session are
already known, but msgFlags has not been unpacked yet at the TMSP, so
the comparison must be done at the MPSP). Of course, we really only
need to compare the authflag and the privflag, i.e. the
securityLevel, so if we pass the securityLevel between the two
stages, then they each have the info they need to do their respective
comparisons.
There have been a large number of questions about msgFlags in the
TMSM approach, mostly concerning the msgFlags value and the actual
security provided, and whether msgFlags can be used to initiate per-
message or per-session security.
A.1. msgFlags versus actual security
Using IPSEC, SSH, or SSL/TLS to provide security services "below" the
SNMP message, the use of securityName and securityLevel will differ
from the USM/VACM approach to SNMP access control. VACM uses the
"securityName" and the "securityLevel" to determine if access is
allowed. With the SNMPv3 message and USM security model, both
securityLevel and securityName are contained in every SNMPv3 message.
Any proposal for a security model using IPSEC, SSH, or SSL/TLS needs
to specify how this info is made available to the SNMPv3 message
processing, and how it is used.
One specific case to consider is the relationship between the
msgFlags of an SNMPv3 message, and the actual services provided by
the lower layer security. For example, if a session is set up with
encryption, is the priv bit always (or never) set in the msgFlags
field, and is the PDU never (or always) encrypted? Do msgFlags have
to match the security services provided by the lower layer, or are
the msgFlags ignored and the values from the lower layer used?
Is the securityLevel looked at before the security model gets to
it.? No. the security model has two parts - the TMSP and the
MPSP. The securityLevel is looked at by the TMSP before it gets
to the MPSP, but both are parts of the same security model.
Would it be legal for the security model to ignore the incoming
flags and change them before passing them back up? If it changed
them, it wouldn't necessarily be ignoring them. The TMSP should
pass both an actual securityLevel applied to the message, and the
msgFlags in the SNMP message to the MPSP for consideration related
to access control.. The msgFlags parameter in the SNMP message is
never changed when processing an incoming message.
Would it be legal for the security model to ignore the outgoing
flags and change them before passing them out? no; because the two
stages are parts of the same security model, either the MPSP
should recognize that a securityLevel cannot be met or exceeded,
and reject the message during the message-build phase, or the TMSP
should determine if it is possible to honor the request. It is
possible to apply an increased securityLevel for an outgoing
request, but the procedure to do so must be spelled out clearly in
the model design.
The security model MUST check the incoming security level flags to
make sure they matched the transport session setup. and if not
drop the message. Yes, mostly. Depending on the model, either
the TMSP or the MPSP MUST verify that the actual processing met or
exceeded the securityLevel requested by the msgFlags and that it
is acceptable to the specific-model processing (or operator
configuration) for this different securityLevel to be applied to
the message. This is also true (especially) for outgoing
messages.
You might legally be able to have a authNoPriv message that is
actually encrypted via the transport (but not the other way around
of course). Yes, a TMSM could define that as the behavior (or
permit an operator to specify that is acceptable behavior) when a
requested securityLevel cannot be provided, but a stronger
securityLevel can be provided.
Appendix B. Parameter Table Appendix A. Parameter Table
Following is a CSV-formatted matrix useful for tracking data flows Following is a CSV formatted matrix useful for tracking data flows
into and out of the dispatcher, message, and security subsystems. into and out of the dispatcher, message, and security subsystems.
Import this into your favorite spreadsheet or other CSV-compatible Import this into your favorite spreadsheet or other CSV compatible
application. You wil need to remove lines feeds from the second and application. You will need to remove lines feeds from the second and
thrid lines, which needed to be wrapped to fit into RFC limits. third lines, which needed to be wrapped to fit into RFC limits.
B.1. ParameterList.csv A.1. ParameterList.csv
,Dispatcher,,,,Messaging,,,Security,, ,Dispatcher,,,,Messaging,,,Security,,
,sendPDU,returnResponse,processPDU,processResponse ,sendPdu,returnResponse,processPdu,processResponse
,prepareOutgoingMessage,prepareResponseMessage,prepareDataElements ,prepareOutgoingMessage,prepareResponseMessage,prepareDataElements
,generateRequest,processIncoming,generateResponse ,generateRequest,processIncoming,generateResponse
transportDomain,In,,,,In,,In,,, transportDomain,In,,,,In,,In,,,
transportAddress,In,,,,In,,In,,, transportAddress,In,,,,In,,In,,,
destTransportDomain,,,,,Out,Out,,,, destTransportDomain,,,,,Out,Out,,,,
destTransportAddress,,,,,Out,Out,,,, destTransportAddress,,,,,Out,Out,,,,
skipping to change at page 50, line 46 skipping to change at page 44, line 22
scopedPDU,,,,,,,,In,Out,In scopedPDU,,,,,,,,In,Out,In
securityParameters,,,,,,,,Out,,Out securityParameters,,,,,,,,Out,,Out
securityStateReference,,,,,,,,,Out,In securityStateReference,,,,,,,,,Out,In
pduType,,,,,,,Out,,, pduType,,,,,,,Out,,,
tmStateReference,,,,,,Out,In,,In, tmStateReference,,,,,,Out,In,,In,
Appendix B. Why tmSecurityReference?
This appendix considers why a cache-based approach was selected for
passing parameters. This section may be removed from subsequent
revisions fo the document.
There are four approaches that could be used for passing information
between the TMSP and an MPSP.
1. one could define an ASI to supplement the existing ASIs, or
2. the TMSM could add a header to encapsulate the SNMP message,
3. the TMSM could utilize fields already defined in the existing
SNMPv3 message, or
4. the TMSM could pass the information in an implementation-specific
cache or via a MIB module.
B.1. Define an Abstract Service Interface
Abstract Service Interfaces (ASIs) [RFC3411] are defined by a set of
primitives that specify the services provided and the abstract data
elements that are to be passed when the services are invoked.
Defining additional ASIs to pass the security and transport
information from the transport mapping to a messaging security model
has the advantage of being consistent with existing RFC3411/3412
practice, and helps to ensure that any TMSM proposals pass the
necessary data, and do not cause side effects by creating model-
specific dependencies between itself and other models or other
subsystems other than those that are clearly defined by an ASI.
B.2. Using an Encapsulating Header
A header could encapsulate the SNMP message to pass necessary
information from the TMSP to the dispatcher and then to a messaging
security model. The message header would be included in the
wholeMessage ASI parameter, and would be removed by a corresponding
messaging model. This would imply the (one and only) messaging
dispatcher would need to be modified to determine which SNMP message
version was involved, and a new message processing model would need
to be developed that knew how to extract the header from the message
and pass it to the MPSP.
B.3. Modifying Existing Fields in an SNMP Message
[RFC3412] describes the SNMPv3 message, which contains fields to pass
security related parameters. The TMSM could use these fields in an
SNMPv3 message, or comparable fields in other message formats to pass
information between transport mapping security models in different
SNMP engines, and to pass information between a transport mapping
security model and a corresponding messaging security model.
If the fields in an incoming SNMPv3 message are changed by the TMSP
before passing it to the MPSP, then the TMSP will need to decode the
ASN.1 message, modify the fields, and re-encode the message in ASN.1
before passing the message on to the message dispatcher or to the
transport layer. This would require an intimate knowledge of the
message format and message versions so the TMSP knew which fields
could be modified. This would seriously violate the modularity of
the architecture.
B.4. Using a Cache
This document describes a cache, into which the TMSP puts information
about the security applied to an incoming message, and an MPSP
extracts that information from the cache. Given that there may be
multiple TM-security caches, a tmStateReference is passed as an extra
parameter in the ASIs between the transport mapping and the messaging
security model.so the MPSP knows which cache of information to
consult.
This approach does create dependencies between a model-specific TMSP
and a corresponding specific MPSP. This approach of passing a model-
independent reference is consistent with the 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 revison -00- Changes from revision -01- to -02-
changed SSH references from I-Ds to RFCs
removed parameters from tmState Reference for DTLS that revealed o wrote text for session establishment requirements section.
o wrote text for session maintenance requirements section.
o removed section on relation to SNMPv2-MIB
o updated MIB module to pass smilint
o Added Structure of the MIB module, and other expected MIB-related
sections.
o updated author address
o corrected spelling
o removed msgFlags appendix
o Removed section on implementation considerations.
o started modifying the security boilerplate to address TMSM and MIB
security issues
o reorganized slightly to better separate requirements from proposed
solution. This probably needs additional work.
o removed section with sample protocols and sample tmStateReference.
o Added section for acronyms
o moved section comparing parameter passing techniques to appendix.
o Removed section on notification requirements.
Changes from revision -00-
o changed SSH references from I-Ds to RFCs
o removed parameters from tmStateReference for DTLS that revealed
lower layer info. lower layer info.
Added TMSM-MIB module o Added TMSM-MIB module
Added Internet-Standard Management Framework boilerplate o Added Internet-Standard Management Framework boilerplate
Added Structure of the MIB Module o Added Structure of the MIB Module
Added MIB security considerations boilerplate (to be completed) o Added MIB security considerations boilerplate (to be completed)
Added IANA Considerations o Added IANA Considerations
Added ASI Parameter table o Added ASI Parameter table
Added discussion of Sessions o Added discussion of Sessions
Added Open issues and Change Log o Added Open issues and Change Log
Rearranged sections o Rearranged sections
Authors' Addresses Authors' Addresses
David Harrington David Harrington
Futurewei Technologies Futurewei Technologies
1700 Alma Dr. Suite 100 1700 Alma Dr. Suite 100
Plano, TX 75075 Plano, TX 75075
USA USA
Phone: +1 603 436 8634 Phone: +1 603 436 8634
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