WDIFF

draft-ietf-isms-tmsm-00.txt --> draft-ietf-isms-tmsm-01.txt

Network Working Group D. Harrington
Internet-Draft Effective Software Futurewei Technologies
Expires: April 17, September 5, 2006 J. Schoenwaelder
International University Bremen
October 14, 2005
March 4, 2006

Transport Mapping Security Model (TMSM) Architectural Extension for the
Simple Network Management Protocol
draft-ietf-isms-tmsm-00.txt (SNMP)
draft-ietf-isms-tmsm-01.txt

Status of this This Memo

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This Internet-Draft will expire on April 17, September 5, 2006.

Abstract

This document describes a Transport Mapping Security Model (TMSM)
subsystem for the Simple Network Management Protocol (SNMP)
architecture defined in RFC 3411. This document identifies and
discusses some key aspects that need to be considered for any
transport-mapping-based security model for SNMP.

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This memo also defines a portion of the Management Information Base
(MIB) for managing the Transport Mapping Security Model Subsystem.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.
1.1. The Internet-Standard Management Framework . . . . . . . . 4
1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Motivation . . 5
3. . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements of a Transport Mapping Security Model . . . . . . 6
3.1.
2.1. Security Requirements . . . . . . . . . . . . . . . . . . 6
3.1.1.
2.1.1. Security Protocol Requirements . . . . . . . . . . . . 6
3.2.
2.2. Session Requirements . . . . . . . . . . . . . . . . . . . 7
3.3.
2.2.1. Session Establishment Requirements . . . . . . . . . . 8
2.2.2. Session Maintenance Requirements . . . . . . . . . . . 8
2.2.3. Message security versus session security . . . . . . . 8
2.3. Architectural Modularity Requirements . . . . . . . . . . 7
3.3.1. 9
2.3.1. USM and the RFC3411 Architecture . . . . . . . . . . . 10
3.3.2. 12
2.3.2. TMSM and the RFC3411 Architecture . . . . . . . . . . 11
3.4. 13
2.4. Passing Messages between Subsystems . . . . . . . . . . . 12
3.5. 15
2.5. Security Parameter Passing Requirement . . . . . . . . . . 13
3.5.1. 16
2.5.1. Define an Abstract Service Interface . . . . . . . . . 14
3.5.2. 17
2.5.2. Using an Encapsulating Header . . . . . . . . . . . . 14
3.5.3. 17
2.5.3. Modifying Existing Fields in an SNMP Message . . . . . 15
3.5.4. 17
2.5.4. Using a Cache . . . . . . . . . . . . . . . . . . . . 15
3.6. 18
2.6. Architectural Requirements for Access Control . . . . . . 15
3.6.1. 18
2.6.1. securityName Binding . . . . . . . . . . . . . . . . . 15
3.6.2. 18
2.6.2. Separation of Authentication and Authorization . . . . 16
3.7. 19
2.7. Requirements for Notifications . . . . . . . . . . . . . . 17
4. 20
3. Scenario Diagrams . . . . . . . . . . . . . . . . . . . . . . 18
4.1. 21
3.1. Command Generator or Notification Originator . . . . . . . 18
4.2. 21
3.2. Command Responder . . . . . . . . . . . . . . . . . . . . 19
5. 22
4. Abstract Service Interfaces . . . . . . . . . . . . . . . . . 20 23
5. TMSM Abstract Service Interfaces . . . . . . . . . . . . . . . 24
6. Integration with the SNMPv3 Message Format . . . . . . . . . . 21 26
6.1. msgVersion . . . . . . . . . . . . . . . . . . . . . . . . 21 26
6.2. msgGlobalData . . . . . . . . . . . . . . . . . . . . . . 21 27
6.3. securityLevel and msgFlags . . . . . . . . . . . . . . . . 22
6.4. 27
7. The tmStateReference for Passing Security Parameters . . . 23
6.5. . . 28
8. securityStateReference Cached Security Data . . . . . . . 23
6.5.1. . . 29
9. Prepare an Outgoing SNMP Message . . . . . . . . . . . 24
6.5.2. . . . . 29
10. Prepare Data Elements from an Incoming SNMP Message . 25
6.6. . . . . 30
11. Notifications . . . . . . . . . . . . . . . . . . . . . . 26
7. . . 31
12. Transport Mapping Security Model Samples . . . . . . . . . . . 26
7.1. 31
12.1. TLS/TCP Transport Mapping Security Model . . . . . . . . . 26
7.1.1. 31
12.1.1. tmStateReference for TLS . . . . . . . . . . . . . . . 26
7.1.2. 32
12.1.2. MPSP for TLS TM-Security Model . . . . . . . . . . . . 27
7.1.3. 32

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12.1.3. MIB Module for TLS Security . . . . . . . . . . . . . 27
7.2. 32
12.2. DTLS/UDP Transport Mapping Security Model . . . . . . . . 27
7.2.1. 32
12.2.1. tmStateReference for DTLS . . . . . . . . . . . . . . 28
7.3. 33
12.3. SASL Transport Mapping Security Model . . . . . . . . . . 29
7.3.1. 34
12.3.1. tmStateReference for SASL DIGEST-MD5 . . . . . . . . 29
8. Security Considerations 34
13. The TMSM MIB Module . . . . . . . . . . . . . . . . . . . 30
9. Acknowledgments . . 35
13.1. Structure of the MIB Module . . . . . . . . . . . . . . . 35
13.1.1. Textual Conventions . . . . . . 30
10. References . . . . . . . . . . . 35
13.1.2. The tmsmStats Subtree . . . . . . . . . . . . . . . 30
10.1. Normative References . 35
13.1.3. The tmsmsSession Subtree . . . . . . . . . . . . . . . 35
13.1.4. The Notifications Subtree . . . 30
10.2. Informative References . . . . . . . . . . . 35
13.2. Relationship to Other MIB Modules . . . . . . . 32

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Appendix A. Questions about msgFlags: . . . . . 36
13.2.1. Relationship to the SNMPv2-MIB . . . . . . . . . 33
A.1. msgFlags versus actual security . . . 36
13.2.2. MIB Modules Required for IMPORTS . . . . . . . . . . 33
A.2. Message security versus session security . 36
14. Definitions . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . 36
15. Implementation Considerations . . . . . . . 35
Intellectual Property and Copyright Statements . . . . . . . . . 42
15.1. Applications that Benefit from Sessions . 36

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1. Introduction

This document describes the Transport Mapping Security Model (TMSM)
architectural extension for the Simple Network Management Protocol
(SNMP) architecture defined in [RFC3411]. This document identifies
and discusses some key aspects . . . . . . . . 42
15.2. Applications that need to be considered for any
transport-mapping-based security model for SNMP.

There are multiple ways to secure one's home or business, but they
largely boil down to a continuum of alternatives. Let's consider
three general approaches. In the first approach, an individual could
buy a gun, learn to use it, and sit on your front porch waiting for
intruders. In the second approach, one could hire an employee with a
gun, schedule the employee, position the employee to guard what you
want protected, hire a second guard to cover if the first gets sick,
and so on. In the third approach, you could hire a security company,
tell them what you want protected, and they could hire employees,
train them, buy the guns, position the guards, schedule the guards,
send a replacement Suffer from Sessions . . . . . . . . . . 43
15.2.1. Troubleshooting . . . . . . . . . . . . . . . . . . . 43
16. Security Considerations . . . . . . . . . . . . . . . . . . . 43
17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
18. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 45
19. References . . . . . . . . . . . . . . . . . . . . . . . . . . 45
19.1. Normative References . . . . . . . . . . . . . . . . . . . 45
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

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1. Introduction

This document describes a Transport Mapping Security Model (TMSM)
subsystem for the Simple Network Management Protocol (SNMP)
architecture defined in [RFC3411]. This document identifies and
discusses some key aspects that need to be considered for any
transport-mapping-based security model for SNMP.

1.1. The Internet-Standard Management Framework

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

Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. MIB objects are generally
accessed through the Simple Network Management Protocol (SNMP).
Objects in the MIB are defined using the mechanisms defined in the
Structure of Management Information (SMI). This memo specifies a MIB
module that is compliant to the SMIv2, which is described in STD 58,
RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
[RFC2580].

1.2. Conventions

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

Some points requiring further WG research and discussion are
identified by [discuss] markers in the text. Some points requiring
further editing by the editors are marked [todo] in the text.

1.3. Motivation

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service being provided.

The User-based Security Model (USM) as defined in [RFC3414] largely
uses the first approach - it provides its own security. It utilizes
existing mechanisms (MD5=the gun), but provides all the coordination.
USM provides for the authentication of a principal, message
encryption, data integrity checking, timeliness checking, etc.

USM was designed to be independent of other existing security
infrastructures. USM therefore requires a separate user and key
management infrastructure. Operators have reported that deploying
another user and key management infrastructure in order to use SNMPv3
is a deterrent to deploying SNMPv3. It is possible but difficult to
define external mechanisms that handle the distribution of keys for
use by the USM approach.

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

A solution based on the third approach might utilize one or more
lower-layer security mechanisms to provide the message-oriented
security services required. These would include authentication of
the sender, encryption, timeliness checking, and data integrity
checking. There are a number of IETF standards available or in
development to address these problems through security layers at the
transport layer or application layer, among them TLS [RFC2246], SASL
[RFC2222], and SSH [RFC4251].

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

This document proposes a Transport Mapping Security Model (TMSM)
subsystem, as an extension of the RFC3411 architecture, that allows
security to be provided by an external protocol connected to the SNMP
engine through an SNMP transport-mapping. Such a TMSM would then
enable the use of existing security mechanisms such as (TLS)
[RFC2246] or SSH [RFC4251] within the RFC3411 architecture.

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

There are a number of challenges to be addressed to map the security you want, with no significant effort on your part other
than identifying
provided by a secure transport into the SNMP architecture so that
SNMP continues to work without any surprises. These challenges are
discussed in detail in this document. For some key issues, design
choices are discussed that may be made to provide a workable solution
that meets operational requirements and verifying fits into the quality SNMP
architecture defined in [RFC3411] .

2. Requirements of the
service being provided.

The User-based a Transport Mapping Security Model (USM) as defined in [RFC3414] largely
uses the first approach - it provides its own security. It utilizes
existing mechanisms (MD5=the gun), but provides all

2.1. Security Requirements

Transport mapping security protocols SHOULD ideally provide the coordination.
USM provides for
protection against the authentication following message-oriented threats [RFC3411]:

1. modification of a principal, information
2. masquerade
3. message
encryption, data integrity checking, timeliness checking, etc.

USM was designed stream modification
4. disclosure

According to be independent [RFC3411], it is not required to protect against denial
of other existing security
infrastructures. USM therefore requires service or traffic analysis.

2.1.1. Security Protocol Requirements

There are a separate user and key
management infrastructure. Operators have reported number of standard protocols that deploying
another user and key management infrastructure in order to could be proposed as
possible solutions within the TMSM framework. Some factors should be
considered when selecting a protocol for use SNMPv3
is within this framework.

Using a protocol in a manner for which it was not designed has
numerous problems. The advertised security characteristics of a reason for not deploying SNMPv3 at this point
protocol may depend on its being used as designed; when used in time. other
ways, it may not deliver the expected security characteristics. It
is
possible but difficult to define external mechanisms recommended that handle any proposed model include a discussion of the
distribution
applicability statement of keys for use by the USM approach. protocols to be used.

A solution based on the second approach might use a USM-compliant
architecture, but combine protocol used for the authentication mechanism with an
external mechanism, such as RADIUS, TMSM framework should ideally require no
modifications to provide the authentication
service. It might be possible to utilize an external protocol. Modifying the protocol to
encrypt may change its
security characteristics in ways that would impact other existing
usages. If a message, to check timeliness, to check data integrity, etc. change is necessary, the change should be an extension
that has no impact on the existing usages. It is difficult to cobble together recommended that

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any proposed model include a number discussion of subcontracted services
and coordinate them however, because it is difficult to build solid
security bindings between the various services, and potential for
gaps in impact on other
usages of the security protocol.

It has been a long-standing requirement that SNMP be able to work
when the network is significant.

A solution based on 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 getting no messages through. There has been
a long debate about whether UDP actually offers better support than
TCP when the third approach might utilize one underlying IP or more

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been recent discussion of whether operators actually use SNMP Transport Mapping Security Model October 2005

lower-layer security mechanisms to provide the message-oriented
security services required. These would include authentication of
the sender, encryption, timeliness checking,
troubleshoot and data integrity
checking. repair unstable networks.

There are a number has been discussion of IETF standards available or in
development ways SNMP could be extended to address these problems through security layers at the
transport layer or application layer, among them TLS [RFC2246], SASL
[RFC2222], and SSH [I-D.ietf-secsh-architecture].

From an operational perspective, it better
support management/monitoring needs when a network is highly desirable to use
security mechanisms that can unify the administrative security
management running just
fine. Use of a TCP transport, for SNMPv3, command line interfaces (CLIs) example, could enable larger
message sizes and more efficient table retrievals.

TMSM models MUST be able to coexist with other
management interfaces. The use of security services provided by
lower layers is protocol models, and
may be designed to utilize either TCP or UDP, depending on the approach commonly used for
transport.

2.2. Session Requirements

Throughout this document, the CLI, and term session is also
the approach being proposed for NETCONF [I-D.ietf-netconf-prot].

This document proposes used. Some underlying
secure transports will have a Transport Mapping Security Model (TMSM), as
an extension notion of session. Some underlying
secure transports might enable the use of channels or other session-
like thing. In this document the RFC3411 architecture, that allows security to be
provided by an external protocol connected term session refers to the SNMP engine through an
association between two SNMP transport-mapping. Such a TMSM would then enable engines, that permits the use secure
transmission of
existing security mechanisms such as (TLS) [RFC2246] one or SSH
[I-D.ietf-secsh-architecture] more SNMP messages within the RFC3411 architecture.

There are a number of Internet security protocols and mechanisms that
are in wide spread use. Many lifetime of them try to provide a generic
infrastructure to be used by many different application layer
protocols. The motivation behind TMSM the
session. How the session is actually established, opened, closed, or
maintained is specific to leverage these protocols
where it seems useful.

There are a number of challenges to be addressed to map the particular security
provided by a secure transport into model.

Sessions are not part of the SNMP architecture so that
SNMP continues to work without any surprises. These challenges are
discussed in detail described in this document. For some key issues, design
choices
[RFC3411], but are discussed that may considered desirable because the cost of
authentication can be made amortized over potentially many transactions.

It is important to provide a workable solution note that meets operational requirements and fits into the SNMP architecture defined described in [RFC3411] .

2. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
does not include a session selector in the Abstract Service
Interfaces, and neither is that done for this
document are 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 be interpreted as described in RFC 2119 [RFC2119].

Some points requiring further WG research and discussion are
identified by [todo] markers in the text. concepts of session-like things of the underlying
protocol), how to behave when a TMSM session cannot be established,

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3. Requirements of a Transport Mapping Security Model

3.1. Security Requirements

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

1. modification of information
2. masquerade
3. message stream modification
4. disclosure

According to [RFC3411], it is not required March 2006

how to protect against denial
of service or traffic analysis.

3.1.1. Security Protocol Requirements

There are close 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 it was not designed has
numerous problems. The advertised security characteristics of a session (and the underlying protocol may depend on its being used as designed; equivalent)
properly, how to behave when used in other
ways, it may not deliver a TMSM session is closed improperly, the expected
session security characteristics. It
is recommended properties, session establishment overhead, and
session maintenance overhead.

To reduce redundancy, this document will discuss aspects that any proposed model include a discussion of the
applicability statement of the protocols are
expected to be used.

A protocol used for the TMSM framework should ideally require no
modifications common to the protocol. Modifying the protocol may change its all TMSM-based security characteristics in ways 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 would impact other existing
usages. If a change is necessary,
maintained for its lifetime. This state information allows for the change should
application of various security services to TMSM-based security
models. Cryptographic keys established at the beginning of the
session SHOULD be an extension used to provide authentication, integrity checking,
and encryption services for data that has no impact on the existing usages. It is recommended that
any proposed model include a discussion of potential impact on other
usages of communicated during the protocol.

It has been
session. The cryptographic protocols used to establish keys for a long-standing requirement
TMSM-based security model session SHOULD ensure that SNMP fresh new
session keys are generated for each session. If each session uses
new session keys, then messages cannot be able replayed from one session
to work
when another. In addition sequence information MAY be maintained in
the network is unstable, session which can be used to enable network troubleshooting prevent the replay and
repair. The UDP approach has been considered to meet that need well,
with an assumption that getting small messages through, even if out reordering of order, is better than gettting no
messages through. There has
been within a long debate about whether UDP actually offers better support
than TCP when the underlying IP 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 lower layers are unstable. There
has been recent discussion
would be on behalf of whether operators actually use SNMP to
troubleshoot and repair unstable networks.

There has been discussion a different securityName, then another session
would be needed. An immediate consequence of ways SNMP could this is that
implementations should be extended 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 better support management/monitoring needs when multiple levels of security,
selectable on a network per-message basis by an SNMP application, because
there is running just 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

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fine. Use March 2006

processing of a TCP transport, for example, could enable larger
message sizes and more efficient table retrievals.

TMSM the messages.

Some TMSM-based security models MUST be able MAY support only specific
authentication and encryption services, such as requiring all
messages to coexist with other protocol models, 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 designed to utilize either TCP or UDP, depending on negotiated once at the
transport.

3.2. Session Requirements

Sessions are not part beginning
of the SNMP architecture, but are considered
desirable because session. But if a message is presented to the cost session with a
security level of authentication can be amortized over
potentially many transactions.

For transports authNoPriv, then that utilize sessions, 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 session should have per-
message basis, a single
user and TMSM-based security level associated model could have a security-
model-specific MIB module with it. If an exchange between
communicating engines would require configurable maxSecurityLevel and a different security level or
would be on behalf
minSecurityLevel objects to identify the range of possible levels. A
session's maxSecurityLevel would identify the maximum security it
could provide, and a different user, then another session created with a minSecurityLevel of
authPriv would be
needed. An immediate consequence 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 is determination.

For security models that implementations
should be able to maintain some reasonable number of concurrent
sessions.

[todo] Say more about how do not support variable security services in
one session, multiple sessions are initiated, how session state
is made visibile 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 on.

3.3. does encrypting unnecessarily.
Designers of security models should consider the tradeoffs for
resource-constrained devices.

2.3. Architectural Modularity Requirements

SNMP version 3 (SNMPv3) is based on a modular architecture (described
in [RFC3411] section 3) to allow the evolution of the SNMP protocol
standards over time, and to minimize side effects between subsystems
when changes are made. This architecture includes a Security
Subsystem which is responsible for realizing security services.

In SNMPv2, there were many problems of side effects between
subsystems caused by the manipulation of MIB objects, especially
those related to authentication and authorization, because many of
the parameters were stored in shared MIB objects, and different

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models and protocols could assign different values to the objects.
Contributors assumed slightly different shades of meaning depending
on the models and protocols being used. As the shared MIB module
design was modified to accommodate a specific model, other models
which used the same MIB objects were broken.

Abstract Service Interfaces (ASIs) were developed to pass model-
independent parameters. The models were required to translate from
their model-dependent formats into a model-independent format,
defined using model-independent semantics, which would not impact
other models.

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Parameters have been provided in the ASIs to pass model-independent
information about the authentication that has been provided. These
parameters include a model-independent identifier of the security
"principal", the security model used to perform the authentication,
and which SNMP-specific security features were applied to the message
(authentication and/or privacy).

The design of a transport mapping security model must abide the goals
of the RFC3411 architecture defined in [RFC3411]. To that end, this
transport mapping security model proposal focuses on a modular
subsystem that can be advanced through the standards process
independently of other proposals, and independent of other subsystems
as much as 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.

[todo]

[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,
with the capability of adding new security mechanisms in the future.
Any transport mapping security model should define one minimum-
compliance mechanism, preferably one which is already widely deployed
within the transport layer security protocol used.

The TMSM subsystem is designed as an architectural extension that
permits additional transport security protocols to be "plugged into"
the RFC3411 architecture, supported by corresponding transport-
security-aware transport mapping models.

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The RFC3411 architecture, and the USM approach, assume that a
security model is called by a message-processing model and will
perform multiple security functions. The TMSM approach performs
similar functions but performs them in different places within the
archtitecture,
architecture, so we need to distinguish the two locations for
security processing.

Transport mapping security is by its very nature a security layer
which is plugged into the RFC3411 architecture between the transport
layer and the message dispatcher. Conceptually, transport mapping
security processing will be called from within the Transport Mapping
functionality of an SNMP engine dispatcher to perform the translation

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of transport security parameters to/from security-model-independent
parameters. This transport mapping security processor will be
referred to in this document as TMSP.

Additional functionality may be performed as part of the message
processing function, i.e. in the security subsystem of the RFC3411
architecture. This document will refer to message processor's
security processor as the MPSP.

Thus a TMSM is composed of both a TPSP and an MPSP.

+------------------------------+ is composed of both a TPSP and an MPSP.

+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v
+-----+ +-----+ +-------+
| UDP | | TCP | . . . | other |
+-----+ +-----+ +-------+
^ ^ ^
| | |
v v v
+-----+ +-----+ +-------+
| SSH | | TLS | . . . | other |
+-----+ +-----+ +-------+ (traditional SNMP agent)
+-------------------------------------------------------------------+
| ^ |
| | |
| Dispatcher v |
| +-------------------+ |
| | Transport | +--------------+ |
| | Mapping |<---> | TMSM | |
| | (e.g., RFC 3417) | | TMSP | |
| | | +--------------+ |

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| | | |
| | | +---------------------+ +----------------+ |
| | | | Message Processing | | Security | |
| | | | Subsystem | | Subsystem | |
| | | | +------------+ | | | |
| | | | +->| v1MP * |<--->| +------------+ | |
| | | | | +------------+ | | | Other | | |
| | | | | +------------+ | | | Security | | |
| | | | +->| v2cMP * |<--->| | Model | | |
| | Message | | | +------------+ | | +------------+ | |
| | Dispatcher <--------->| +------------+ | | +------------+ | |
| | | | +->| v3MP * |<--->| | TMSM | | |
| | | | | +------------+ | | | MPSP | | |
| | PDU Dispatcher | | | +------------+ | | | | | |
| +-------------------+ | +->| otherMP * |<--->| +------------+ | | Network
|
+------------------------------+
^ ^ ^ | +------------+ | |
v v v
+-----+ +-----+ +-------+ | UDP |
| TCP | . . . +---------------------+ +----------------+ |
| v |
| +-------+-------------------------+---------------+ | other
|
+-----+ +-----+ +-------+ ^ ^ ^ |
| |
v v v
+-----+ +-----+ +-------+ | SSH | | TLS
| . . . v v v | other
|
+-----+ +-----+ +-------+ (traditional SNMP agent)
+-------------------------------------------------------------------+ +-------------+ +---------+ +--------------+ +-------------+ | ^
| | COMMAND | | ACCESS | Dispatcher v | NOTIFICATION | +-------------------+ | PROXY | | Transport
| +--------------+ | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | Mapping |<---> FORWARDER | TMSM |
| | application | (e.g., RFC 3417) | | TMSP | applications | | application | |
| +-------------+ +---------+ +--------------+ +-------------+ |
| ^ ^ |
| | | |
| +---------------------+ +----------------+ v v |
| +----------------------------------------------+ |
| | MIB instrumentation | Message Processing SNMP entity |
+-------------------------------------------------------------------+

2.3.1. USM and the RFC3411 Architecture

The following diagrams illustrate the difference in the security
processing done by the USM model and the security processing done by
a TMSM model.

The USM security model is encapsulated by the messaging model,
because the messaging model needs to perform the following steps (for
incoming messages)
1) decode the ASN.1 (messaging model)

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2) determine the SNMP security model and parameters (messaging model)
3) decrypt the encrypted portions of the message (security model)
4) translate parameters to model-independent parameters (security
model)
5) determine which application should get the decrypted portions
(messaging model), and
6) pass on the decrypted portions with model-independent parameters.

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

| Security -----------------------------------------------|
| transport layer |
| -----------------------------------------------|
^
|
v
--------------------------------------------------
| -----------------------------------------------|
| Subsystem | transport mapping | Subsystem
| -----------------------------------------------|
| ^
| |
| v
| +------------+ --------------------------------------------- |
| --------------------- ------------------ |
| SNMP messaging <--> | decryption + | |
| +->| v1MP * |<--->| +------------+ | translation | |
| --------------------- ------------------ |
| ^
| +------------+ |
| v
| Other --------------------- ------------------ |
| | SNMP applications | <--> | access control | |
| +------------+ --------------------- ------------------ |

| --------------------------------------------- |

2.3.2. TMSM and the RFC3411 Architecture

In the TMSM approach, the order of the steps differ and may be
handled by different subsystems:

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| | | | +->| v2cMP * |<--->| | Model | | |
| | Message | | | +------------+ | | +------------+ | |
| | Dispatcher <--------->| +------------+ | | +------------+ | |
| | | | +->| v3MP * |<--->| | March 2006

1) decrypt the encrypted portions of the message (transport layer)
2) determine the SNMP security model and parameters (transport
mapping)
3*) translate parameters to model-independent parameters (transport
mapping)
4) decode the ASN.1 (messaging model)
5) determine which application should get the decrypted portions
(messaging model)
6*) translate parameters to model-independent parameters (security
model)
7) pass on the decrypted portions with model-independent security
parameters

This is largely based on having non-SNMP-specific message security
and parameters. The transport mapping model might provide the
translation from e.g., an SSH user name to the securityName in step
3, OR the SSH user might be passed to the messaging model to pass to
a TMSM | | | security model to do the translation in step 6, if the WG
decides all translations should use the same translation table (e.g.,
the USM MIB).

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| -----------------------------------------------|
| ------------------ |
| transport layer <--> | decryption | +-------------------+ | +->| otherMP * |<--->| +------------+
| ------------------ |
| -----------------------------------------------|
^
| +------------+ |
v
--------------------------------------------------
| -----------------------------------------------|
| ------------------ |
| transport mapping <--> | +---------------------+ +----------------+ translation* | | v
| ------------------ | +-------+-------------------------+---------------+
| -----------------------------------------------|
| ^ ^ ^ |
| | |
| |
| v v v |
| +-------------+ +---------+ +--------------+ +-------------+ |
| | COMMAND
| --------------------------------------------- | ACCESS
| ------------------ | NOTIFICATION
| SNMP messaging <--> | PROXY translation* | |
| ------------------ | RESPONDER |<->| CONTROL |<->| ORIGINATOR
| --------------------- ------------------ | FORWARDER
| ^
| |
| application v
| --------------------- ------------------ |
| | SNMP applications | <--> | application | |
| +-------------+ +---------+ +--------------+ +-------------+ |
| ^ ^ |
| | | |
| v v access control | | +----------------------------------------------+
| --------------------- ------------------ |

| MIB instrumentation --------------------------------------------- |

2.4. Passing Messages between Subsystems

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
mappings of two SNMP engines. One transport mapping security model
instance encrypts all messages, and the other transport mapping
security model instance decrypts the messages.

After the transport layer tunnel is established, then SNMP messages
can conceptually be sent through the tunnel from one SNMP entity |
+-------------------------------------------------------------------+

3.3.1. USM message
dispatcher to another SNMP message dispatcher. Once the tunnel is

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established, multiple SNMP messages may be able to be passed through
the same tunnel.

Within an engine, outgoing SNMP messages are passed unencrypted from
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 Architecture

The following diagrams illustrate section 4 describes primitives to describe the difference in abstract
service interfaces used to conceptually pass information between the
various subsystems, models and applications within the architecture.

The security
processing done by parameters include a model-independent identifier of the USM
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 processing done by 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 model.

The USM 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 model is encapsulated by capabilities, or can this be handled in
the messaging model,
because TMSP, given the messaging model needs to perform model-independent (and message-version-
independent) parameters? Are there any security services provided by
the following steps (for MPSP for an outgoing message?

[discuss] For incoming messages)
1) decode messages, is there security functionality that
can only be handled after the ASN.1 (messaging model)
2) determine message version is known, such as the SNMP
comparison of transport security model capabilities and parameters (messaging model)
3) decrypt the encrypted portions of the message (security model)
4) translate parameters msgFlags? Does
that functionality need to model-independent parameters (security
model)
5) determine which application should get know the decrypted portions
(messaging model), transport address and
6) pass on session or
just the decrypted portions with model-independent parameters.

The USM approach uses 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 parameters. the dispatcher, and
between the dispatcher and the message processing model. If there is

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| -----------------------------------------------|
| transport layer |
| -----------------------------------------------|
^
|
v
--------------------------------------------------
| -----------------------------------------------|
| | transport mapping |
| -----------------------------------------------|
| ^
| |
| v
| --------------------------------------------- |
| --------------------- ------------------ |
| SNMP messaging <--> | decryption + | |
| | translation | |
| --------------------- ------------------ |
| ^
| |
| v
| --------------------- ------------------ |
| | March 2006

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 applications | <--> | access control | |
| --------------------- ------------------ |

| --------------------------------------------- |

3.3.2. message,
3. the TMSM and could utilize fields already defined in the RFC3411 Architecture

In existing
SNMPv3 message, or
4. the TMSM approach, could pass the order 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 steps differ services provided and may be
handled by different subsystems:
1) decrypt the encrypted portions of abstract data
elements that are to be passed when the message (transport layer)
2) determine services are invoked.
Defining additional ASIs to pass the SNMP security model and parameters (transport
mapping)
3*) translate parameters to model-independent parameters (transport
mapping)
4) decode transport
information from the ASN.1 (messaging model)
5) determine which application should get transport mapping to a messaging security model
has the decrypted portions
(messaging model)
6*) translate parameters advantage of being consistent with existing RFC3411/3412
practice, and helps to model-independent parameters (security
model)
7) ensure that any TMSM proposals pass on the decrypted portions with model-independent security
parameters

This is largely based on having non-SNMP-specific message security
necessary data, and do not cause side effects by creating model-
specific dependencies between itself and parameters. The transport mapping model might provide 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

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translation message to pass necessary
information from e.g., an SSH user name the TMSP to the securityName dispatcher and then to a messaging
security model. The message header would be included in step
3, OR the SSH user might
wholeMessage ASI parameter, and would be passed to removed by a corresponding
messaging model. This would imply the (one and only) messaging model
dispatcher would need to pass be modified to determine which SNMP message
version was involved, and a TMSM security new message processing model would need
to do the translation in step 6, if the WG
decides all translations should use the same translation table (e.g.,
the USM MIB).

| -----------------------------------------------|
| ------------------ |
| transport layer <--> | decryption | |
| ------------------ |
| -----------------------------------------------|
^
|
v
--------------------------------------------------
| -----------------------------------------------|
| ------------------ |
| transport mapping <--> | translation* | |
| ------------------ |
| -----------------------------------------------|
| ^
| |
| v
| --------------------------------------------- |
| ------------------ |
| SNMP messaging <--> | translation* | |
| ------------------ |
| --------------------- ------------------ |
| ^
| |
| v
| --------------------- ------------------ |
| | SNMP applications | <--> | access control | |
| --------------------- ------------------ |

| --------------------------------------------- |

3.4. Passing Messages between Subsystems

RFC3411 defines ASIs be developed that describe knew how to extract the passing of messages between
subsystem within an engine, header from the message
and pass it to the parameters MPSP.

2.5.3. Modifying Existing Fields in an SNMP Message

[RFC3412] describes the SNMPv3 message, which are expected contains fields to
be passed between the subsystems. The ASIs generally pass model-
independent information.

A
security related parameters. The TMSM model will establish could use these fields in an encrypted tunnel
SNMPv3 message, or comparable fields in other message formats to pass
information between the transport mapping security models in different
SNMP engines, and to pass information between a transport mapping
security model and a corresponding messaging security model.

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mappings of two SNMP engines. One transport mapping security model
instance encrypts all messages, and March 2006

If the other transport mapping
security model instance decrypts fields in an incoming SNMPv3 message are changed by the messages.

After TMSP
before passing it to the transport layer tunnel is established, MPSP, then SNMP messages
can conceptually be sent through the tunnel from one SNMP 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 another SNMP the
transport layer. This would require an intimate knowledge of the
message dispatcher. Once format and message versions so the tunnel is
established, multiple SNMP messages 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 able
multiple TM-security caches, a cache ID would need to be passed
through
the same tunnel.

Within an engine, outgoing SNMP messages are passed unencrypted from ASI so the message dispatcher MPSP knows which cache of information to
consult.

The cache reference could be thought of as an additional parameter in
the transport mapping, and incoming
messages are passed unencrypted from ASIs between the transport mapping to and the
message dispatcher.

3.5. Security Parameter Passing Requirement messaging security
model. The RFC3411 section 4 describes primitives to describe the abstract
service interfaces used ASIs would not need to conceptually pass information between the
various subsystems, models and applications within be changed since the architecture.

The security
SNMPv3 WG expected that additional parameters include a model-independent identifier could be passed for
value-add features 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 implementations.

This approach does create dependencies between 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 TPSP
and a corresponding specific parameters are not all carried 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

For SNMP message, and can be determined from the transport layer by access control to function properly, the
transport mapping, before security mechanism
must establish a securityModel identifier, a securityLevel, and a
securityName, which is the security model independent identifier for
a principal. The SNMPv3 message processing begins.

[todo] For outgoing messages, it is necessary architecture subsystem
relies on a security model, such as USM, to have an MPSP because
it is the MPSP play a role in security
that actually creates goes beyond protecting the message from - it scomponent
parts. Does provides a mapping
between the MPSP need USM-specific principal to know the transport address or the
actual transport security capabilities, or a security-model independent
securityName which 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 used for
an outgoing message?

[todo] For incoming messages, is there security functionality that
can only be handled after the message version is known, subsequent processing, such as the
comparison of for
access control.

The TMSM is a two-stage security model, with a transport mapping
security capabilities process (TMSP) and msgFlags? Does
that functionality need to know a message processing security process
(MPSP). Depending on the transport address and session or
just design of the model-independent security parameters (securityName, specific TMSM model, i.e.

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level)? Are there any SNMP-specific parameters that need March 2006

which transport layer protocol is used, different features might be
provided by the TMSP or by the MPSP. For example, the translation
from a mechanism-specific authenticated identity to a securityName
might be done by the TMSP or by the MPSP.

[discuss] It may be possible to define a consistent division of
stages regardless of the transport layer protocol used, and a
consistent division of functionality would be
unpacked from the message for MPSP handling? msgFlags, securityLevel,
etc.? preferred.

The RFC3411 SNMP architecture has no ASI parameters for passing security
information distinguishes between the transport mapping and the dispatcher, messages with no
authentication and
between the dispatcher no privacy (noAuthNoPriv), authentication without
privacy (authNoPriv) and authentication with privacy (authPriv).
Hence, the message processing model. If there is authentication of a need to have transport layer identity plays an MPSP called from the message processing model to,
for example, verify that msgFlags
important role and the transport security are
consistent, then it will must be necessary to pass considered by any TMSM, and user
authentication must be available via the model-independent transport layer security parameters from the TPSP through to the MPSP.

There are four approaches that could be used for passing information
between
protocol.

If the TMSP and an MPSP.
1. one could define an ASI to supplement type of authentication provided by the existing ASIs, transport layer (e.g.
host-based or
2. the TMSM could add a header anonymous) is considered adequate to encapsulate the SNMP message,
3. the TMSM could utilize fields already defined in secure and/or
encrypt the existing
SNMPv3 message, or
4. the TMSM could pass but inadequate to provide the information in an implementation-specific
cache or via desired
granularity of access control (e.g. user-based), a MIB module.

3.5.1. Define an Abstract Service Interface

Abstract Service Interfaces (ASIs) [RFC3411] are defined second
authentication, e.g. one provided by a set of
primitives that specify the services provided and the abstract data
elements that are to AAA server, may be passed when the services are invoked.
Defining additional ASIs used to pass the security and transport
information from
provide the transport mapping authentication identity which is bound to the
securityName. This approach would require a messaging security model
has good analysis of the advantage
potential for man-in-the-middle attacks or masquerade possibilities.

2.6.2. Separation of being consistent with existing RFC3411/3412
practice, Authentication and helps to ensure that any Authorization

A TMSM proposals pass security model should take care to not violate the
necessary data, separation
of authentication and do not cause side effects by creating model-
specific dependencies authorization in the RFC3411 architecture..
The isAccessAllowed() primitive is used for passing security-model
independent parameters between itself and other models or other the subsystems other than those that are clearly defined by an ASI.

3.5.2. Using an Encapsulating Header

A header could encapsulate of the SNMP message architecture.

Mapping of (securityModel, securityName) to pass necessary
information from an access control policy
should be handled within the TMSP to access control subsystem, not the dispatcher and then to a messaging
security model. The message header would subsystem, to be included in consistent with the
wholeMessage ASI parameter, and would be removed by a corresponding
messaging model. modularity of the
RFC3411 architecture. This would imply separation was a deliberate decision of
the (one and only) messaging
dispatcher would need to be modified SNMPv3 WG, to determine allow support for authentication protocols which SNMP message
version was involved,
did not provide authorization capabilities, and a new message processing model would need to be developed support
authorization schemes, such as VACM, that knew how do not perform their own
authentication.

An authorization model MAY require authentication by certain
securityModels and a minimum securityLevel to allow access to extract the header from the message
data.

TMSM is an enhancement for the SNMPv3 privacy and pass authentication
provisions, but it to is not a significant improvement for the MPSP.

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3.5.3. Modifying Existing Fields in an SNMP Message

[RFC3412] describes March 2006

authorization needs of SNMPv3. TMSM provides all the SNMPv3 message, which contains fields to pass
security related parameters. The model-
independent parameters for the isAccessAllowed() primitive [RFC3411].

TMSM does not specify how the securityModel and securityName could use these fields in an
SNMPv3 message, or comparable fields in other message formats be
dynamically mapped to pass
information between transport a VACM-style groupName. The mapping security models in different
SNMP engines, and of
(securityModel, securityName) to pass information between a transport mapping
security model and groupName is a corresponding messaging security model.

If the fields in VACM-specific
mechanism for naming an incoming SNMPv3 message are changed by access control policy, and for tying the TMSP
before passing it
named policy to the MPSP, then the TMSP will need to decode addressing capabilities of the
ASN.1 message, modify data modeling
language (e.g. SMIv2 [RFC2578]), the fields, operations supported, and re-encode the message in ASN.1
before passing other
factors. Providing a binding outside the message on Access Control subsystem
might create dependencies that could make it harder to the message dispatcher develop
alternate models of access control, such as one built on UNIX groups,
Windows domains, XML hierarchies, or task-based controls. The
preferred approach is to pass the
transport layer. This would require an intimate knowledge of model-independent security
parameters via the
message format isAccessAllowed() ASI, and message versions so the TMSP knew which fields
could be modified. This would seriously violate perform the modularity of mapping
within the architecture.

3.5.4. Using a Cache

A cache mechanism could be used, into access control model.

To provide support for protocols which the TMSP puts simultaneously send
information
about the security applied to an incoming message, for authentication and an MPSP
extracts that authorization, such as RADIUS
[RFC2865], model-specific authorization information from the cache. Given that there may MAY be
multiple TM-security caches, cached or
otherwise made available to the access control subsystem, e.g. via a cache ID would need
MIB table similar to be passed
through an ASI the vacmSecurityToGroupTable, so the MPSP knows which cache of information to
consult.

The cache reference could be thought of as access
control subsystem can create an additional parameter in
the ASIs appropriate binding between the transport mapping
model-independent securityModel and the messaging security
model. The RFC3411 ASIs would not need to securityName and a model-specific
access control policy. This may be changed since the
SNMPv3 WG expected highly undesirable, however, if
it creates a dependency between a security model and an access
control model, just as it is undesirable that additional parameters could be passed for
value-add features of specific implementations.

This the TMSM approach does create dependencies
creates a dependency between a model-specific TPSP TMSP and a corresponding specific an MPSP. If a TMSM-model-independent ASI
parameter

2.7. Requirements for Notifications

[todo] cleanup this section

RFC 3430 (SNMP over TCP) suggests that TCP connections are initiated
by notification originators in case there is passed, no currently established
connection that can be used to send the notification. Following this
approach with SSH would require to provision authentication
credentials on the agent so that agents can successfully authenticate
to a notification receiver. There might be consistent with other approaches, like
the
securityStateReference cache already being passed around 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 ASI. section
dealing with sessions? This document will describe a cache-based approach.

3.6. Architectural Requirements for Access Control

3.6.1. securityName Binding

For SNMP access control seems to function properly, the security mechanism
must establish a securityModel identifier, a securityLevel, and a
securityName, which is be the security model independent identifier right place for
a principal. The SNMPv3 message processing architecture subsystem this
discussion.

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relies on a security model, such as USM, to play a role in security
that goes beyond protecting the message - it March 2006

3. Scenario Diagrams

RFC3411 section 4.6 provides a mapping
between the USM-specific principal scenario diagrams to a security-model independent
securityName which can be used for subsequent processing, such as for
access control.

The TMSM illustrate how an
outgoing message is a two-stage security model, with a transport mapping
security process (TMSP) created, and a how an incoming message processing security process
(MPSP). Depending on is
processed. Both diagrams are incomplete, however. In section 4.6.1,
the design of diagram doesn't show the specific TMSM model, i.e.
which transport layer protocol is used, different features might be
provided by ASI for sending an SNMP request to the
network or receiving an SNMP response message from the network. In
section 4.6.2, the diagram doesn't illustrate the interfaces required
to receive an SNMP message from the TMSP network, or by the MPSP. For example, the translation
from a mechanism-specific authenticated identity to a securityName
might be done by send an SNMP
message to the TMSP network.

3.1. Command Generator or by the MPSP.

[todo] It may be possible to define Notification Originator

This diagram from RFC3411 4.6.1 shows how a consistent division of stages
regardless of the transport layer protocol used, and Command Generator or
Notification Originator application [RFC3413]requests that a consistent
division of functionality would PDU be preferred.

The SNMP architecture distinguishes between messages with no
authentication and no privacy (noAuthNoPriv), authentication without
privacy (authNoPriv)
sent, and authentication with privacy (authPriv).
Hence, how the authentication of response is returned (asynchronously) to that
application.

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

3.2. Command Responder

This diagram shows how a transport layer identity plays an
important role and must be considered by any TMSM, and user
authentication must be available via the transport layer security
protocol.

If the type of authentication provided by the transport layer (e.g.
host-based Command Responder or anonymous) is considered adequate to secure and/or
encrypt the message, but inadequate to provide the desired
granularity of access control (e.g. user-based), Notification Receiver
application registers for handling a second
authentication, e.g. one provided by pduType, how a AAA server, may be used to
provide the authentication identity which PDU is bound to the
securityName. This approach would require a good analysis of the
potential for man-in-the-middle attacks or masquerade possibilities.

3.6.2. Separation of Authentication and Authorization

A TMSM security model should take care dispatched
to not violate the separation
of authentication and authorization in the RFC3411 architecture..
The isAccessAllowed() primitive is used for passing security-model
independent parameters between the subsystems of the architecture.

Mapping of (securityModel, securityName) to application after an access control policy
should be handled within the access control subsystem, not the
security subsystem, to be consistent with the modularity of the
RFC3411 architecture. This separation was a deliberate decision of
the SNMPv3 WG, to allow support for authentication protocols which
did not provide authorization capabilities, SNMP message is received, and how the
Response is (asynchronously) send back to support the network.

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authorization schemes, such as VACM, that do not perform their own
authentication.

An authorization model MAY require authentication by certain
securityModels and a minimum securityLevel to allow access to the
data.

TMSM is an enhancement for the SNMPv3 privacy and authentication
provisions, but it is not a significant improvement for the
authorization needs of SNMPv3. TMSM provides all the model-
independent parameters for the isAccessAllowed() primitive [RFC3411].

TMSM does not specify how the securityModel and securityName could be
dynamically mapped March 2006

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

4. Abstract Service Interfaces

The mapping OUT parameters of
(securityModel, securityName) the prepareOutgoingMessage() ASI are used to a groupName is a VACM-specific
mechanism for naming an access control policy,
pass information from the message processing model to the dispatcher

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and for tying on to the
named policy transport mapping:

statusInformation = -- success or errorIndication
prepareOutgoingMessage(
IN transportDomain -- transport domain to be used
IN transportAddress -- transport address to be used
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model to use
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN contextEngineID -- data from/at this entity
IN contextName -- data from/in this context
IN pduVersion -- the addressing capabilities version of the data modeling
language (e.g. SMIv2), PDU
IN PDU -- SNMP Protocol Data Unit
IN expectResponse -- TRUE or FALSE
IN sendPduHandle -- the operations supported, and other factors.
Providing a binding outside handle for matching
-- incoming responses
OUT destTransportDomain -- destination transport domain
OUT destTransportAddress -- destination transport address
OUT outgoingMessage -- the Access Control subsystem might create
dependencies that could make it harder message to develop alternate models send
OUT outgoingMessageLength -- its length
)

5. TMSM Abstract Service Interfaces

A set of
access control, such as one built on UNIX groups, Windows domains,
XML hierarchies, or task-based controls. abstract service interfaces have been defined within this
document to describe the conceptual data flows between the Transport
Mapping Security Models and adjacent components in the system..

The preferred approach SendMessage ASI is used to pass a message from the model-independent security parameters via the
isAccessAllowed() ASI, and perform Dispatcher to
the transport mapping within the access
control model.

To provide support for protocols which simultaneously send
information security model subsystem for authentication and authorization, such as RADIUS,
model-specific authorization information MAY sending.

statusInformation sendMessage(
IN destTransportDomain -- transport domain to be cached or otherwise
made available used
IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the access control subsystem, e.g. via a MIB table
similar message to the vacmSecurityToGroupTable, so the access control
subsystem can create an approrpiate binding between the model-
independent securityModel and securityName and a model-specific
access control policy. This may be highly undesirable, however, if
it creates a dependency between send
IN outgoingMessageLength -- its length
IN tmStateReference --
OUT sessionID
)

The RecvMessage ASI is used to pass a message from the transport
mapping security model and an access
control model, just as it is undesirable that subsystem to the TMSM approach
creates a dependency between a TMSP and an MPSP.

3.7. Requirements for Notifications

[todo] cleanup this section

RFC 3430 (SNMP over TCP) suggests that TCP connections are initiated
by notification originators in case there is no currently established
connection that can Dispatcher.

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statusInformation RecvMessage(
IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to send be used
IN incomingMessage -- the notification. Following this
approach with SSH would require message received
IN incomingMessageLength -- its length
OUT tmStateReference --
OUT sessionID
)

The Transport Mapping Security Model provides the following
primitives to provision authentication
credentials on pass data back and forth between the agent so that agents can successfully authenticate TMSM and specific
TMSM-based security models, which provide the interface to a notification receiver. There might be other approaches, like the
underlying secure transport service. Each TMSM-based security model
should define the security-model-specific elements of procedure for
the establishSession(), closeSession(), TxMessage(), and RxMessage()
interfaces.

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the reuse of manager initiated secure March 2006

statusInformation TxMessage(
IN destTransportDomain -- 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
dealing with sessions? This seems domain to be the right place for this
discussion.

4. Scenario Diagrams

RFC3411 section 4.6 provides scenario diagrams to illustrate how an
outgoing message is created, and how an incoming message is
processed. Both diagrams are incomplete, however.In section 4.61,
the diagram doesn't show the ASI for sending an SNMP request used
IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the
network or receiving an SNMP response message from the network. In
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
message
IN outgoingMessageLength -- its length
IN tmStateReference --
OUT sessionID
)

statusInformation RxMessage(
IN destTransportDomain -- transport domain to the network.

4.1. Command Generator or Notification Originator

This diagram from RFC3411 4.6.1 shows how a Command Generator or
Notification Originator application requests that a PDU be sent, and
how used
IN destTransportAddress -- transport address to be used
IN incomingMessage -- the response is returned (asynchronously) message to that application.

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statusInformation establishSession(
IN transportDomain -- transport domain to Network | | |
: | v | |
: : : : :
: : : : :
: : : : :
: | | | |
: | Receive SNMP | | |
: | Response be used
IN transportAddress -- transport address to be used
IN tmStateReference --
OUT sessionID
)

statusInformation closeSession(
IN sessionID
)

6. Integration with the SNMPv3 Message | | |
: | from Network | | |
: |<-----------------+ | |
: | | |
: | prepareDataElements | |
: |----------------------->| |
: | | processIncomingMsg |
: | |-------------------->|
: | | |
: | |<--------------------|
: | | |
: |<-----------------------| |
| processResponsePdu | | |
|<-------------------| | |
| | | |

4.2. Command Responder Format

TMSM proposals can use the SNMPv3 message format, defined in RFC3412,
section 6. This diagram shows section discusses how a Command Responder or Notification Receiver
application registers the fields could be reused.

6.1. msgVersion

For proposals that reuse the SNMPv3 message format, this field should
contain the value 3.

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6.2. msgGlobalData

The fields msgID and msgMaxSize are used identically for handling a pduType, how the TMSM
models as for the USM model.

The msgSecurityModel field should be set to a PDU value from the
SnmpSecurityModel enumeration [RFC3411] to identify the specific TMSM
model. Each standards-track TMSM model should have an enumeration
assigned by IANA. Each enterprise-specific security model should
have an enumeration assigned following instructions in the
description of the SnmpSecurityModel TEXTUAL-CONVENTION from RFC3411.

The msgSecurityParameters field would carry security information
required for message security processing. It is dispatched unclear whether this
field would be useful or what parameters would be carried to support
security, since message security is provided by an external process,
and msgSecurityParameters are not used by the application after access control
subsystem.

RFC3412 defines two primitives, generateRequestMsg() and
processIncomingMsg() which require the specification of an
authoritative SNMP message entity. [discuss] We need to discuss what the
meaning of authoritative would be in a TMSM environment, whether the
specific services provided in USM security from msgSecurityParameters
still are needed, and how the Message Processing model provides this
information to the security model via generateRequestMsg() and
processIncomingMsg() primitives. RFC3412 specifies that "The data in
the msgSecurityParameters field is used exclusively by the Security
Model, and the contents and format of the data is defined by the
Security Model. This OCTET STRING is received, and how not interpreted by the
Response v3MP,
but is (asynchronously) send back passed to the network.

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

5. Abstract Service Interfaces
indicated by the msgSecurityModel field in the message."

The OUT parameters msgFlags have the same values for the TMSM models as for the USM
model. "The authFlag and privFlag fields indicate the securityLevel
that was applied to the message before it was sent on the wire."

6.3. securityLevel and msgFlags

For an outgoing message, msgFlags is the requested security for the
message; if a TMSM cannot provide the requested securityLevel, the
model MUST describe a standard behavior that is followed for that
situation. If the TMSM cannot provide at least the requested level
of security, the prepareOutgoingMessage() ASI are used to
pass information from TMSM MUST discard the request and SHOULD notify the
message processing model to that the dispatcher request failed.

[discuss] how is yet to be determined, and may be model-specific or
implementation-specific.

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and on to March 2006

For an outgoing message, if the TMSM is able to provide stronger than
requested security, that may be acceptable. The transport mapping:

statusInformation = -- success or errorIndication
prepareOutgoingMessage(
IN transportDomain -- transport domain layer
protocol would need to indicate to the receiver what security has
been applied to the actual message. To avoid the need to mess with
the ASN.1 encoding, the SNMPv3 message carries the requested
msgFlags, not the actual securityLevel applied to the message. If a
message format other than SNMPv3 is used, then the new message may
carry the more accurate securityLevel in the SNMP message.

For an incoming message, the receiving TMSM knows what must be used
IN transportAddress -- done
to process the message based on the transport address layer mechanisms. If
the underlying transport security mechanisms for the receiver cannot
provide the matching securityLevel, then the message should follow
the standard behaviors for the transport security mechanism, or be
discarded silently.

Part of the responsibility of the TMSM is to be used
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model ensure that the actual
security provided by the underlying transport layer security
mechanisms is configured to use
IN securityName -- on behalf of this principal
IN meet or exceed the securityLevel -- Level of Security requested
IN contextEngineID -- data from/at this entity
IN contextName -- data from/in this context
IN pduVersion -- required
by the version of msgFlags in the PDU
IN PDU -- SNMP Protocol Data Unit
IN expectResponse -- TRUE or FALSE
IN sendPduHandle -- message. When the MPSP processes the handle for matching
--
incoming responses
OUT destTransportDomain -- destination transport domain
OUT destTransportAddress -- destination transport address
OUT outgoingMessage -- message, it should compare the message msgFlags field to send
OUT outgoingMessageLength -- its length
)

6. Integration with the SNMPv3 Message Format

TMSM proposals can use
securityLevel actually provided for the SNMPv3 message format, defined in RFC3412,
section 6. This seection discusses how by the fields could be reused.

6.1. msgVersion

For proposals that reuse transport
layer security. If they differ, the SNMPv3 message format, this field MPSP should
contain determine whether
the value 3.

6.2. msgGlobalData changed securityLevel is acceptable. If not, it should discard
the message. Depending on the model, the MPSP may issue a reportPDU
with the XXXXXXX model-specific counter.

7. The fields msgID and msgMaxSize are used identically tmStateReference for Passing Security Parameters

A tmStateReference is used to pass data between the TMSM
models 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 for the USM model. being passed in an encapsulating header.

The msgSecurityModel field TMSP may provide only some aspects of security, and leave some
aspects to the MPSP. tmStateReference should be set used to pass any
parameters, in a value from the
SnmpSecurityModel enumeration [RFC3411] model- and mechanism-specific format, that will be
needed to identify coordinate the specific TMSM
model. Each standards-track TMSM model should have an enumeration
assigned by IANA. Each enterprise-specific security model should
have an enumeration assigned following instructions activities of the TMSP and MPSP, and the
parameters subsequently passed in securityStateReference. For
example, the
description TMSP may provide privacy and data integrity and
authentication and authorization policy retrievals, or some subset of
these features, depending on the SnmpSecurityModel TEXTUAL-CONVENTION from RFC3411.

The msgSecurityParameters features available in the transport
mechanisms. A field would carry security information
required 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 processing. It is unclear whether this identity, the session identifier for session based transport
security, and so on.

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field would be useful or what parameters would be carried March 2006

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 support
security, since message the Message Processing Model. The
cached security is provided by an external process,
and msgSecurityParameters are not used data may be implicitly released via the generation of
a response, or explicitly released by using the access control
subsystem.

RFC3412 defines two primitives, generateRequestMsg() and
processIncomingMsg() which require stateRelease
primitive, as described in RFC3411 section 4.5.1."

For the specification of an
authoritative SNMP entity. [todo] We TMSM approach, the TMSP may need to discuss what provide information to
the meaning
of authoritative would be in a TMSM environment, whether message processing model, such as the specific
services provided in USM security from msgSecurityParameters still
are needed, security-model-independent
securityName, securityLevel, and how securityModel parameters, and for
responses, the Message Processing messaging model provides this may need to pass the parameters back
to the TMSP. To differentiate what information needs to be provided
to the security message processing model via generateRequestMsg() by the TMSP, and
processIncomingMsg() primitives. RFC3412 specifies that "The data in vice-versa, this
document will differentiate the msgSecurityParameters field is used exclusively tmStateReference provide by the Security
Model, and TMSP
from the contents securityStateReference provided by the MPSP. An
implementation MAY use one cache and format one reference to serve both
functions, but an implementer must be aware of the data is defined by cache-release
issues to prevent the
Security Model. This OCTET STRING is not interpreted by cache from being released before the v3MP,
but is passed 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
uses the generateResponseMsg() or generateRequestMsg() primitives, to
call the local implementation of MPSP. The message processing model, or the Security Model
indicated by MPSP it calls,
may need to put information into the msgSecurityModel field in tmStateReference cache for use
by the message."

The msgFlags have TMSP, such as:
tmSecurityStateReference - the same values unique identifier for the TMSM models as for cached
information
tmTransportDomain
tmTransportAddress
tmSecurityModel - an indicator of which mechanisms to use
tmSecurityName - a model-specific identifier of the USM
model. "The authFlag security
principal
tmSecurityLevel - an indicator of which security services are
requested
and privFlag fields indicate the securityLevel
that was applied may contain additional information such as

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tmSessionID
tmSessionKey
tmSessionMsgID

According to RFC3411, section 4.1.1, the message before it was sent on application provides the wire."

6.3. securityLevel
transportDomain and msgFlags

For an outgoing message, msgFlags is transportAddress to the requested security for PDU dispatcher via the
message; if a TMSM cannot provide
sendPDU() primitive. If we permit multiple sessions per
transportAddress, then we would need to define how session
identifiers get passed from the requested securityLevel, application to the
model MUST describe a standard behavior PDU dispatcher
(and then to the MP model).

The SNMP over TCP Transport Mapping document [RFC3430] says that is followed TCP
connections can be recreated dynamically or kept for future use and
actually leaves all that
situation. If the TMSM cannot provide at least the requested level
of security, the TMSM MUST discard to the request transport mapping.

[discuss] we might define a new transportDomain and SHOULD notify the
message processing model that transportAddress,
which includes the request failed.

[todo] how is yet to be determined, address and may be model-specific or
implementation-specific. session identifier. For an outgoing message, if the TMSM is able situations
where a session has not yet been established, we could pass a 0x0000
session identifier (or whatever) to provide stronger than
requested security, indicate that may a session should be acceptable. The transport layer
protocol would need to indicate to
established. Well, this won't work with the receiver what security has
been applied current TAddress
definitions and is probably too ugly to do.

We might have a MIB module that records the actual message. To avoid session information for
subsequent use by the need to mess with applications and other subsystems, or it might
be passed in the ASN.1 encoding, tmStateReference cache. For notifications, I assume
the SNMPv3 message carries notification tables would be a place to find the requested
msgFlags, address,
but I'm not the actual securityLevel applied sure how to identify the message. If a
message format other than SNMPv3 is used, then presumably-dynamic session
identifiers. The MIB module could identify whether the new message may
carry session was
initiated by the more accurate securityLevel 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. Message

For an incoming message, the receiving TMSM knows what must be done
to process the message based on the transport layer mechanisms. If
the underlying TMSP will need to put information from
the transport security mechanisms for used into the receiver cannot
provide tmStateReference so the matching securityLevel, then MPSP
can extract the message should follow information and add it conceptually to the
securityStateReference.

The tmStateReference cache will likely contain at least the following
information:
tmStateReference - a unique identifier for the cached information

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tmSecurityStateReference - the standard behaviors unique identifier for the transport security mechanism, or be
discarded silently.

Part of the responsibility cached
information
tmTransportDomain
tmTransportAddress
tmSecurityModel - an indicator of the TMSM is to ensure that the actual
security provided by the underlying transport layer security which mechanisms is configured to meet or exceed the securityLevel required
by the msgFlags in the SNMP message. When the MPSP processes the
incoming message, it should compare the msgFlags field to the
securityLevel actually provided for the message by the transport
layer security. If they differ, the MPSP should determine whether
the changed securityLevel is acceptable. If not, it should discard
the message. Depending on the model, the MPSP may issue use
tmSecurityName - a reportPDU
with the XXXXXXX model-specific counter.

6.4. The tmStateReference for Passing Security Parameters

A tmStateReference is used to pass data between identifier of the TMSP security
principal
tmSecurityLevel - an indicator of which security services are
requested
tmAuthProtocol
tmPrivProtocol
and the
MPSP, similar to the securityStateReference described in RFC3412.
This can be envisioned may contain additional information such as being appended to the ASIs between
tmSessionID
tmSessionKey
tmSessionMsgID

11. Notifications

For notifications, if the TM cache has been released and then session
closed, then the MPSP will request the MP or as being passed in an encapsulating header.

The TMSP may provide only some aspects of security, to establish a session,
populate the cache, and leave some
aspects pass the securityStateReference to the MPSP. tmStateReference should be used

[discuss] We need to pass any
parameters, in determine what state needs to be saved here.

12. Transport Mapping Security Model Samples

There are a model- and mechanism-specific format, number of standard protocols that will could be
needed to coordinate proposed as
possible solutions within the activities 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 TMSP and MPSP, and
applicability statement of the
parameters subsequently passed 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 securityStateReference. For
example, [RFC3430].

TLS/TCP will create an association between the TMSP TMSM of one SNMP
entity and the TMSM of another SNMP entity. The created "tunnel" may
provide privacy encryption and data integrity and
authentication integrity. Both encryption and authorization policy retrievals, or some subset of
these features, depending on the data

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integrity are optional features available in TLS. The TLS TMSP MUST provide
authentication if auth is requested in the transport
mechanisms. A field in tmStateReference should identify which
services were provided for each received securityLevel of the SNMP
message by request (RFC3412 4.1.1). The TLS TM-security model MUST
specify that the TMSP, messages be encrypted if priv is requested in the
securityLevel applied to the received message, parameter of the model-specific
security identity, SNMP message request (RFC3412 4.1.1).

The TLS TM-security model MUST support the session identifier TLS Handshake Protocol
with mutual authentication.

12.1.1. tmStateReference for session based transport
security, and so on.

6.5. securityStateReference Cached Security Data

From RFC3411: "For each message received, TLS

Upon establishment of a TLS session, the Security Model caches TMSP will cache the state information such that a Response message can
information. A unique tmStateReference will be generated
using the same security information, even if the Local Configuration
Datastore is altered between passed to the time of
corresponding MPSP. The MPSP will pass the incoming request and securityStateReference to
the
outgoing response.

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 Message Processing Model. The
cached security data may mapping from model-specific
identity to a model independent securityName.

[todo] Module needs to be implicitly released via the generation of 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

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a response, or explicitly released by using the stateRelease
primitive, March 2006

Security (DTLS) [I-D.rescorla-dtls] provides security services
equivalent to TLS for connection-less transports such as described in RFC3411 section 4.5.1."

For UDP.

DTLS provides all the TMSM approach, security services needed from an SNMP
architectural point of view. Although it is possible to derive a
securityName from the TMSP may need public key certificates (e.g. the subject
field), this approach requires installing certificates on all SNMP
entities, leading to provide information 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
the message processing model, 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 security-model-independent
securityName, securityLevel, and securityModel parameters, and for
responses, authentication exchange must be
integrated into the messaging model may need TLS mechanism to pass the parameters back prevent man-in-the-middle
attacks. While SASL [RFC2222] is often used on top of a TLS
encrypted channel to the TMSP. To differentiate what information needs authenticate users, this choice seems to be provided
problematic until the mechanism to cryptographically bind SASL into
the message processing model by TLS mechanism has been defined.

DTLS will create an association between the TMSP, TMSM of one SNMP entity
and vice-versa, this
document will differentiate the tmStateReference TMSM of another SNMP entity. The created "tunnel" may
provide by 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 TMSP
from securityLevel
of the securityStateReference provided by SNMP message request (RFC3412 4.1.1). The TLS TM-security
model MUST specify that the MPSP. An
implementation MAY use one cache and one reference to serve both
functions, but an implementor must messages be aware of encrypted if priv is
requested in the cache-release
issues to prevent securityLevel parameter of the cache from being released before SNMP message request
(RFC3412 4.1.1).

The DTLS TM-security model MUST support the transport
mapping TLS Handshake Protocol
with mutual authentication.

12.2.1. tmStateReference for DTLS

DTLS has had an opportunity to extract the information it needs.

6.5.1. Prepare an Outgoing been suggested as a possible secure transport. It is not
clear whether DTLS is a reasonable choice for SNMP Message

Following RFC3412, section 7.1, interactions. It
is mentioned here only as an example.

Upon establishment of a DTLS session, the SNMPv3 message processing model
uses TMSP will cache the generateResponseMsg() or generateRequestMsg() primitives, state
information. A unique tmStateReference will be passed to
call the
corresponding MPSP. The message processing model, or the MPSP it calls,
may need to put information into the tmStateReference cache for use
by MPSP will pass the TMSP, such as:
tmSecurityStateReference - securityStateReference to
the unique identifier Message Processing Model for the cached
information memory management.

The tmStateReference cache:

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tmStateReference
tmSecurityStateReference
tmTransportDomain = UDP/IPv4
tmTransportAddress = x.x.x.x:y
tmSecurityModel - an indicator of which mechanisms to use DTLS TMSM
tmSecurityName - a model-specific identifier of the security
principal = "dbharrington"
tmSecurityLevel - an indicator of which security services are
requested = "authPriv"

12.3. SASL Transport Mapping Security Model

The Simple Authentication and may contain additional information such as
tmSessionID
tmSessionKey
tmSessionMsgID

According to RFC3411, section 4.1.1, the application Security Layer (SASL) [RFC2222]
provides the
transportDomain a hook for authentication and transportAddress security mechanisms to the PDU dispatcher be used
in application protocols. SASL supports a number of authentication
and security mechanisms, among them Kerberos via the
sendPDU() primitive. If we permit multiple sessions per
transportAddress, then we would need 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 define how session
identifiers get passed from authNoPriv, the application qop-value
should be set to the PDU dispatcher
(and auth-int; if msgFlags is authPriv, then to qop-value
should be auth-conf.

Realm is optional, but can be utilized by the MP model).

The securityModel if
desired. SNMP over TCP Transport Mapping document [RFC3430] says that TCP
connections can 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 recreated dynamically concatenated to be the securityName value, e.g.
helpdesk::username", or kept for future the realm could be used to specify a
groupName to use and
actually leaves all that in the VACM access control. This would be similar
to having the transport mapping. 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

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[todo] we might define March 2006

tmServicesProvided mutual authentication,
reauthentication,
integrity,
encryption
tmParameters = "realm=helpdesk, serv-type=SNMP

13. The TMSM MIB Module

This memo defines a new transportDomain and transportAddress,
which includes portion of the address and session identifier. For situations
where a session has not yet been established, we could pass Management Information Base (MIB)
for managing the Transport Mapping Security Model Subsystem.

13.1. Structure of the MIB Module

Objects in this MIB module are arranged into subtrees. Each subtree
is organized as a 0x0000
session identifier (or whatever) set of related objects. The overall structure and
assignment of objects to indicate that a session should be
established. Well, their subtrees, and the intended purpose of
each subtree, is shown below.

13.1.1. Textual Conventions

Generic and Common Textual Conventions used in this won't work with document can be
found summarized at http://www.ops.ietf.org/mib-common-tcs.html

13.1.2. The tmsmStats Subtree

This subtree contains security-model-independent counters which are
applicable to all security models based on the current TAddress
definitions .Transport Mapping
Security Model Subsystem.

This subtree provides information for identifying fault conditions
and is probably too ugly performance degradation.

13.1.3. The tmsmsSession Subtree

This subtree contains security-model-independent information about
sessions which are applicable to do.

We might have a MIB module that records all security models based on the session
Transport Mapping Security Model Subsystem.

This subtree provides information for
subsequent use by the applications and other subsytems, or it might
be passed in the tmStateReference cache. For notifications, I assume managing sessions for any
security model based on the SNMPv3 notification tables would be a place Transport Mapping Security Model
Subsystem.

13.1.4. The Notifications Subtree

This subtree contains notifications to find the address,
but I'm not sure how alert other entities to identify the presumably-dynamic session
identifiers. The MIB module events
which could identify whether alter the session was
initiated by the remote engine or initiated by operational behavior of the current engine,
and possibly assigned entity in a purpose (incoming request/response or
outgoing notifications). First we need to decide whether network

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utilizing the SAMPLE Protocol.

13.2. Relationship to handle
notifications and requests Other MIB Modules

Some management objects defined in one or two (or more) sessions, which
might depend on the transport protocol we choose (the same problem
netconf faced).

6.5.2. Prepare Data Elements from other MIB modules are applicable
to an Incoming SNMP Message

For entity implementing this MIB. In particular, it is assumed
that an incoming message, entity implementing the TMSP TMSM-MIB module will need to put information from also implement
the transport mechanisms SNMPv2-MIB [RFC3418].

This MIB module is expected to be used into the tmStateReference so with the MPSP
can extract MIB modules defined
for managing specific security models that are based on the information TMSM
subsystem. This MIB module is designed to be security-model
independent, and add it conceptually conatins objects useful for managing common aspects
of any TMSM-based security model. Specific security models may
define a MIB module to contain security-model-dependent information.

13.2.1. Relationship to the
securityStateReference. SNMPv2-MIB

The tmStateReference cache will likely contain at least 'system' subtree in the following
information:
tmStateReference - a unique identifier SNMPv2-MIB [RFC3418] is defined as being
mandatory for all systems, and the cached information
tmSecurityStateReference - objects apply to the unique identifier for entity as a
whole. The 'system' subtree provides identification of the cached
information
tmTransportDomain
tmTransportAddress
tmSecurityModel - an indicator
management entity and certain other system-wide data. The TMSM-MIB
utilizes, but does not dupicate, some of which mechanisms to those objects. [todo] do we
actually use
tmSecurityName - a model-specific identifier any of the security
principal
tmSecurityLevel - an indicator objects, since we don't have any elements of which security services are
requested
tmAuthProtocol
tmPrivProtocol
procedure?

13.2.2. MIB Modules Required for IMPORTS

The following MIB module imports items from [RFC2578], [RFC2579],
[RFC2580], [RFC3411], and may contain additional information such as
tmSessionID
tmSessionKey
tmSessionMsgID [RFC3419]

14. Definitions

TMSM-MIB DEFINITIONS ::= BEGIN

IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
mib-2, Integer32, Unsigned32, Gauge32
FROM SNMPv2-SMI
TestAndIncr
FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP
FROM SNMPv2-CONF
SnmpSecurityModel,
SnmpAdminString, SnmpSecurityLevel, SnmpEngineID
FROM SNMP-FRAMEWORK-MIB
TransportAddress, TransportAddressType

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6.6. Notifications

For notifications, if March 2006

FROM TRANSPORT-ADDRESS-MIB
;

tmsmMIB MODULE-IDENTITY
LAST-UPDATED "200602270000Z"
ORGANIZATION "ISMS Working Group"
CONTACT-INFO "WG-EMail: isms@lists.ietf.org
Subscribe: isms-request@lists.ietf.org

Chairs:
Juergen Quittek
NEC Europe Ltd.
Network Laboratories
Kurfuersten-Anlage 36
69115 Heidelberg
Germany
+49 6221 90511-15
quittek@netlab.nec.de

Juergen Schoenwaelder
International University Bremen
Campus Ring 1
28725 Bremen
Germany
+49 421 200-3587
j.schoenwaelder@iu-bremen.de

Editor:
David Harrington
Effective Software
50 Harding Rd
Portsmouth, New Hampshire 03801
USA
+1 603-436-8634
ietfdbh@comcast.net
"
DESCRIPTION "The Transport Mapping Security Model
Subsystem MIB

Copyright (C) The Internet Society (2006). This
version of this MIB module is part of RFC XXXX;
see the cache has been released RFC itself for full legal notices.
-- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and then session
closed, then the MPSP will request the TMSP remove this note
"

REVISION "200602270000Z" -- 27 February 2006
DESCRIPTION "The initial version, published in RFC XXXX.

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-- NOTE to establish a session,
populate the cache, RFC editor: replace XXXX with actual RFC number
-- for this document and pass remove this note
"

::= { mib-2 xxxx }
-- RFC Ed.: replace xxxx with IANA-assigned number and
-- remove this note

-- ---------------------------------------------------------- --
-- subtrees in the securityStateReference to TMSM-MIB
-- ---------------------------------------------------------- --

tmsmNotifications OBJECT IDENTIFIER ::= { tmsmMIB 0 }
tmsmObjects OBJECT IDENTIFIER ::= { tmsmMIB 1 }
tmsmConformance OBJECT IDENTIFIER ::= { tmsmMIB 2 }

-- -------------------------------------------------------------
-- Objects
-- -------------------------------------------------------------

-- Statistics for the MPSP.

[todo] We need to determine what state needs to be saved here.

7. Transport Mapping Model Security Model Samples

There are a number of standard protocols that could be proposed as
possible solutions within the TMSM framework. Some factors Subsystem

tmsmStats OBJECT IDENTIFIER ::= { tmsmObjects 1 }

-- [discuss] do we need any tmsm stats?
-- these should be
considered when selecting a protocol for use within interoperability, not local debug.
-- we could probably track session establishment failures
-- although this framework.

Using a protocol really belongs in a manner for which is was an SSH-MIB, not designed has
numerous problems. TMSM-MIB

-- The advertised security characteristics of a
protocol may depend on its being used as designed; when tmsmSession Group

tmsmSession OBJECT IDENTIFIER ::= { tmsmObjects 2 }

tmsmSessionSpinLock OBJECT-TYPE
SYNTAX TestAndIncr
MAX-ACCESS read-write
STATUS current
DESCRIPTION "An advisory lock used in other
ways, it may not deliver the expected to allow several cooperating
TMSM security characteristics. It
is recommended that any proposed model include a discussion of the
applicability statement models to coordinate their
use of the protocols facilities to be used.

7.1. TLS/TCP create sessions in the
tmsmSessionTable.
"
::= { tmsmSession 1 }

tmsmSessionCurrent OBJECT-TYPE
SYNTAX Gauge32

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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 March 2006

MAX-ACCESS read-only
STATUS current
DESCRIPTION "The current number of one SNMP
entity and the TMSM established sessions.
"
::= { tmsmSession 2 }

tmsmSessionMaxSupported OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The maximum number 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 open sessions allowed.
"
::= { tmsmSession 3 }

tmsmSessionTable OBJECT-TYPE
SYNTAX SEQUENCE OF TmsmSessionEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "The table of currently available sessions configured
in the SNMP
message request (RFC3412 4.1.1). The TLS TM-security model MUST
specify that the messages be encrypted if priv is requested engine's Local Configuration Datastore
(LCD).

Sessions are created as needed, and do not persist
across network management system reboots.
"
::= { tmsmSession 4 }

tmsmSessionEntry OBJECT-TYPE
SYNTAX TmsmSessionEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "A session configured 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.

7.1.1. tmStateReference engine's Local
Configuration Datastore (LCD) for Transport Mapping
Security Models.
"
INDEX { tmsmSessionID }
::= { tmsmSessionTable 1 }

TmsmSessionEntry ::= SEQUENCE
{
tmsmSessionID Integer32,
tmsmSessionTransport TransportAddressType,
tmsmSessionAddress TransportAddress,
tmsmSessionSecurityModel SnmpSecurityModel,
tmsmSessionSecurityName SnmpAdminString,
tmsmSessionSecurityLevel SnmpSecurityLevel,
tmsmSessionEngineID SnmpEngineID

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}

tmsmSessionID OBJECT-TYPE
SYNTAX Integer32 (1..65535)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "A locally-unique identifier for TLS

Upon establishment of a TLS session, session.
"
::= { tmsmSessionEntry 1 }

tmsmSessionTransport OBJECT-TYPE
SYNTAX TransportAddressType
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The transport domain associated with this session.
"
::= { tmsmSessionEntry 2 }

tmsmSessionAddress OBJECT-TYPE
SYNTAX TransportAddress
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The transport address associated with this session.
"
::= { tmsmSessionEntry 3 }

tmsmSessionSecurityModel OBJECT-TYPE
SYNTAX SnmpSecurityModel
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The Security Model associated with this session."
::= { tmsmSessionEntry 4 }

tmsmSessionSecurityName OBJECT-TYPE
SYNTAX SnmpAdminString
MAX-ACCESS read-only
STATUS current
DESCRIPTION "A human readable string representing the TMSP will cache principal
in Security Model independent format.

The default transformation of the state
information. A unique tmStateReference will be passed Secure Shell
Security Model dependent security ID to the
corresponding MPSP. The MPSP will pass
securityName
and vice versa is the securityStateReference to identity function so that the Message Processing Model for memory management.

The tmStateReference cache:
securityName is the same as the SSH user name.
"
::= { tmsmSessionEntry 5 }

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tmStateReference
tmSecurityStateReference
tmTransportDomain = TCP/IPv4
tmTransportAddress = x.x.x.x:y
tmSecurityModel March 2006

tmsmSessionSecurityLevel OBJECT-TYPE
SYNTAX SnmpSecurityLevel
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The Level of Security at which SNMP messages can be
sent using this session, in particular, one of:

noAuthNoPriv - TLS TMSM
tmSecurityName = "dbharrington"
tmSecurityLevel = "authPriv"
tmAuthProtocol = Handshake MD5
tmPrivProtocol = Handshake DES
tmSessionID = Handshake session without authentication and
without privacy,
authNoPriv - with authentication but
without privacy,
authPriv - with authentication and
with privacy.
"
DEFVAL { authPriv }
::= { tmsmSessionEntry 6 }

tmsmSessionEngineID OBJECT-TYPE
SYNTAX SnmpEngineID
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The administratively-unique identifier
tmSessionKey = Handshake peer certificate
tmSessionMasterSecret = master secret
tmSessionParameters = compression method, cipher spec, is-
resumable

7.1.2. MPSP for TLS TM-Security the
remote SNMP engine associated with this session.
"
::= { tmsmSessionEntry 7 }

-- -------------------------------------------------------------
-- tmsmMIB - Conformance Information
-- -------------------------------------------------------------

tmsmGroups OBJECT IDENTIFIER ::= { tmsmConformance 1 }

tmsmCompliances OBJECT IDENTIFIER ::= { tmsmConformance 2 }

-- -------------------------------------------------------------
-- Units of conformance
-- -------------------------------------------------------------
tmsmGroup OBJECT-GROUP
OBJECTS {
tmsmSessionCurrent,
tmsmSessionMaxSupported,
tmsmSessionTransport,
tmsmSessionAddress,
tmsmSessionSecurityModel,
tmsmSessionSecurityName,
tmsmSessionSecurityLevel,
tmsmSessionEngineID,
tmsmSessionSpinLock

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messageProcessingModel = SNMPv3
securityModel = TLS TMSM
securityName = tmSecurityName
securityLevel = msgSecurityLevel

7.1.3. MIB Module March 2006

}
STATUS current
DESCRIPTION "A collection of objects for TLS Security

Each security model should use its own MIB module, rather than
utilizing maintaining session
information of an SNMP engine which implements the USM MIB, to eliminate dependencies on a model
SNMP Secure Shell Security Model.
"

::= { tmsmGroups 2 }

-- -------------------------------------------------------------
-- Compliance statements
-- -------------------------------------------------------------

tmsmCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines that
could be replaced some day. See RFC3411 section 4.1.1.

The TLS MIB module needs to provide support the mapping
TMSM-MIB"
MODULE
MANDATORY-GROUPS { tmsmGroup }
::= { tmsmCompliances 1 }

END

15. Implementation Considerations

15.1. Applications that Benefit from model-specific
identity to a model independent securityName. Sessions

[todo] Module needs to be worked out once things become stable...

7.2. DTLS/UDP Transport Mapping Security Model

DTLS contributions welcome.

There has been proposed as discussion of ways SNMP could be extended to better
support management/monitoring needs when a UDP-based TLS. Transport Layer Security
(TLS) [RFC2246] traditionally requires network is running just
fine. Use of a connection-oriented
transport TCP transport, for example, could enable larger
message sizes and is usually used over TCP. Datagram Transport Layer
Security (DTLS) [I-D.rescorla-dtls] provides security services
equivalent more efficient table retrievals.

Discussing how to TLS for connection-less transports such as UDP.

DTLS provides all the security services needed from an improve SNMP
architectural point of view. Although it once you have less strict message size
constraints is possible to derive a
securityName from the public key certificates (e.g. beyond the subject
field), scope of this approach requires installing certificates 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 all existing SNMP
entities, leading to a certificate management problem which does not
integrate well with established AAA systems. [todo] why does this not
integrate well with existing AAA systems? and the networks that contain them.

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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]. March 2006

15.2. Applications that Suffer from Sessions

[todo] contributions welcome.

15.2.1. Troubleshooting

It is important to stress has been a long-standing requirement that the authentication exchange must SNMP 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 able to be
problematic until work
when the mechanism network is unstable, to cryptographically bind SASL into
the TLS mechanism enable network troubleshooting and
repair. The UDP approach has been defined.

DTLS will create considered to meet that need well,
with 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 assumption that the getting small messages be encrypted through, even if priv out
of order, is
requested in better than gettting no messages through. There has
been a long debate about whether UDP actually offers better support
than TCP when the securityLevel parameter underlying IP or lower layers are unstable. There
has been recent discussion of the whether operators actually use SNMP message request
(RFC3412 4.1.1). to
troubleshoot and repair unstable networks.

The DTLS TM-security model MUST support the TLS Handshake Protocol
with mutual authentication.

7.2.1. tmStateReference for DTLS

Upon establishment of need to establish a DTLS session, 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 TMSP will cache use of the state
information. A unique tmStateReference will 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 passed to utilize the
corresponding MPSP. The MPSP will pass
IETF-Standard USM security model to send a notification, so an
administrator can attempt to manually correct the securityStateReference problem.

16. Security Considerations

This document describes an architectural approach and multiple
proposed configurations that would permit SNMP to utilize transport
layer security services. Each section containing a proposal should
discuss the Message Processing Model security considerations of that approach. [discuss]
expand as needed.

It is considered desirable by some industry segments that SNMP
security models should utilize transport layer security that
addresses perfect forward secrecy at least for memory management.

The tmStateReference cache:
tmStateReference
tmSecurityStateReference
tmTransportDomain = UDP/IPv4
tmTransportAddress = x.x.x.x:y
tmSecurityModel - DTLS TMSM
tmSecurityName = "dbharrington"
tmSecurityLevel = "authPriv"
tmAuthProtocol = Handshake MD5
tmPrivProtocol = Handshake DES
tmSessionID = Handshake session identifier
tmSessionKey = Handshake peer certificate
tmSessionMasterSecret = master encryption keys.
Perfect forward secrecy guarantees that compromise of long term
secret
tmSessionParameters = compression method, cipher spec, is-
resumable keys does not result in disclosure of past session keys.

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
objects may be considered sensitive or vulnerable in some network
environments. The support for SET operations in a non-secure
environment without proper protection can have a negative effect on

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tmSessionSequence = epoch, sequence March 2006

network operations. These are the tables and objects and their
sensitivity/vulnerability:
o [todo]
Need to discuss to what extent DTLS is list the tables and objects and state why they are
sensitive.

There are no management objects defined in this MIB module that have
a reasonable choice for
SNMP interactions.
What MAX-ACCESS clause of read-write and/or read-create. So, if this
MIB module is the status implemented correctly, then there is no risk that an
intruder can alter or create any management objects of this MIB
module via direct SNMP SET operations.

Some of the work to cryptographically bind SASL readable objects in this MIB module (i.e., objects with a
MAX-ACCESS other than not-accessible) may be considered sensitive or
vulnerable in some network environments. It is thus important to
DTLS?
More details need
control even GET and/or NOTIFY access to be worked out...

7.3. SASL Transport Mapping Security Model

The Simple Authentication and Security Layer (SASL) [RFC2222]
provides a hook for authentication these objects and security mechanisms possibly
to be used
in application protocols. SASL supports a number even encrypt the values of authentication
and security mechanisms, among these objects when sending them Kerberos over
the network via SNMP. These are the GSSAPI
mechanism.

This sample will use DIGEST-MD5 because it supports authentication,
integrity checking, tables and confidentiality.

DIGEST-MD5 supports auth, auth with integrity, objects and auth with
confidentiality. Since their
sensitivity/vulnerability:
o [todo] list the tables and objects and state why they are
sensitive.

SNMP versions prior to SNMPv3 assumes integrity checking is part of
authentication, did not include adequate security.
Even if msgFlags the network itself is set secure (for example by using IPSec),
even then, there is no control as to authNoPriv, who on the qop-value
should be set to auth-int; if msgFlags secure network is authPriv, then qop-value
should be auth-conf.

Realm
allowed to access and GET/SET (read/change/create/delete) the objects
in this MIB module.

It is optional, but can be utilized RECOMMENDED that implementers consider the security features as
provided by the securityModel if
desired. SNMP does not use this value, but a TMSM could map SNMPv3 framework (see [RFC3410], section 8),
including full support for the
realm into SNMP processing in various ways. For example, realm SNMPv3 cryptographic mechanisms (for
authentication and
username could be concatenated privacy).

Further, deployment of SNMP versions prior to be the securityName value, e.g.
helpdesk::username", or the realm could be used SNMPv3 is NOT
RECOMMENDED. Instead, it is RECOMMENDED to specify deploy SNMPv3 and to
enable cryptographic security. It is then a
groupname customer/operator
responsibility to use in ensure that the VACM SNMP entity giving access to an
instance of this MIB module is properly configured to give access control. This would be similar to having the securityName-to-group mapping done by
the external AAA
server.

7.3.1. tmStateReference for SASL DIGEST-MD5

17. IANA Considerations

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tmPrivProtocol = 3des
tmServicesProvided =
mutual authentication,
reauthentication,
integrity,
encryption
tmParameters = "realm=helpdesk, serv-type=SNMP

8. Security Considerations

This March 2006

The MIB module in this document describes an architectural approach and multiple
proposed configurations that would permit SNMPv3 uses the following IANA-assigned
OBJECT IDENTIFIER values recorded in the SMI Numbers registry:

Descriptor OBJECT IDENTIFIER value
---------- -----------------------

tmsmMIB { mib-2 XXXX }

Editor's Note (to be removed prior to utilize transport
layer security services. Each section containing publication): the IANA is
requested to assign a proposal should
discuss value for "XXXX" under the security considerations of that approach. [todo] expand
as needed.

Perfect forward secrecy guarantees that compromise of long term
secret keys does not result 'mib-2' subtree
and to record the assignment in disclosure of past session keys.

It the SMI Numbers registry. When
the assignment has been made, the RFC Editor is considered desirable by some industry segments that SNMP
security models should utilize transport layer security that
addresses perfect forward secrecy at least for encryption keys.

9. asked to replace
"XXXX" (here and in the MIB module) with the assigned value and to
remove this note.

[discuss] How do we add a new TransportType?

18. Acknowledgments

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

The authors of submitted security model proposals: Chris Elliot, Wes
Hardaker, Dave Harrington, Keith McCloghrie, Kaushik Narayan, Dave
Perkins, Joseph Salowey, and Juergen Schoenwaelder.

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

WG members who committed to and performed detailed reviews: Jeffrey
Hutzelman, and Nicolas Williams.

10.
Hutzelman

19. References

10.1.

19.1. Normative References

[RFC1510] Kohl, J. and B. Neuman, "The Kerberos Network
Authentication Service (V5)", RFC 1510, September 1993.

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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2222] Myers, J., "Simple Authentication and Security Layer
(SASL)", RFC 2222, October 1997.

[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.

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

[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Textual Conventions for SMIv2",
STD 58, RFC 2579, April 1999.

[RFC2580] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
"Conformance Statements for SMIv2", STD 58, RFC 2580,
April 1999.

[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.

[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
December 2002.

[RFC3412] Case, J., Harrington, D., Presuhn, R., and B. Wijnen,
"Message Processing and Dispatching for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3412,
December 2002.

[RFC3414] Blumenthal, U. and B. Wijnen, "User-based Security Model
(USM) for version 3 of the Simple Network Management
Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.

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

[RFC3418] Presuhn, R., "Management Information Base (MIB) for the
Simple Network Management Protocol (SNMP)", STD 62,
RFC 3418, December 2002.

[RFC3419] Daniele, M. and J. Schoenwaelder, "Textual Conventions for
Transport Addresses", RFC 3419, December 2002.

[RFC3430] Schoenwaelder, J., "Simple Network Management Protocol
Over Transmission Control Protocol Transport Mapping",
RFC 3430, December 2002.

[I-D.ietf-secsh-architecture]

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

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Internet-Draft SNMP Transport Mapping Security Model October 2005

Ylonen, T. and C. Lonvick, "SSH Protocol Architecture",
draft-ietf-secsh-architecture-22 (work in progress),
March 2005.

[I-D.ietf-secsh-connect]
Lonvick, C. and T. Ylonen, "SSH Connection Protocol",
draft-ietf-secsh-connect-25 (work in progress),
March 2005.

[I-D.ietf-secsh-transport]
Lonvick, C., "SSH Transport Layer Protocol",
draft-ietf-secsh-transport-24 (work in progress),
March 2005.

[I-D.ietf-secsh-userauth]
Lonvick, C. and T. Ylonen, "SSH Authentication Protocol",
draft-ietf-secsh-userauth-27 (work in progress), March 2005. 2006

[I-D.rescorla-dtls]
Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", draft-rescorla-dtls-05 (work in progress),
June 2005.

[I-D.schoenw-snmp-tlsm]
Harrington, D. and J. Schoenwaelder, "Transport Mapping
Security Model (TMSM) for the Simple Network Management
Protocol version 3 (SNMPv3)", draft-schoenw-snmp-tlsm-02
(work in progress), May 2005.

10.2.

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,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.

[RFC3413] Levi, D., Meyer, P., and B. Stewart, "Simple Network
Management Protocol (SNMP) Applications", STD 62,
RFC 3413, December 2002.

[I-D.ietf-netconf-prot]
Enns, R., "NETCONF Configuration Protocol",
draft-ietf-netconf-prot-09 (work in progress),
October 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.

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[I-D.ietf-netconf-ssh]
Wasserman, M. and T. Goddard, "Using the NETCONF
Configuration Protocol over Secure Shell (SSH)",
draft-ietf-netconf-ssh-04 (work in progress), April 2005.

[I-D.ietf-secsh-gsskeyex]
Hutzelman, J., "GSSAPI Authentication and Key Exchange for
the Secure Shell Protocol", draft-ietf-secsh-gsskeyex-10
draft-ietf-netconf-ssh-05 (work in progress), August
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:

[todo]

[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

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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

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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.

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A.2. Message security versus session security

For SBSM, and for many TMSM models, securityName is specified
during session setup, and associated with the session identifier.
Is it possible for March 2006

request, but the request (and notification) originator procedure to
specify per message auth and encryption services, or are they
"fixed" by the transport/session model?
If a session is created as 'authPriv', then keys for encryption
would still do so must be negotiated once at spelled out clearly in
the beginning of model design.
The security model MUST check the session.
But if a message is presented incoming security level flags to
make sure they matched the transport session with a security level
of authNoPriv, then that message could simply be authenticated setup. and if not encrypted. Wouldn't that also have some security benefit, in
that it reduces
drop the encrypted data available to an attacker
gathering packets to try and discover message. Yes, mostly. Depending on the encryption keys?
Some SNMP entities are resource-constrained. Adding sessions
increases model, either
the need for resources, we shouldn't require two
sessions when one can suffice. 2 bytes per session structure and a
compare TMSP or two is much less of a resource burden than two separate
sessions.
It's not just about CPU power of the device but MPSP MUST verify that the percentage of
CPU cycles actual processing met or
exceeded the securityLevel requested by the msgFlags and that are spent on network management. There isn't much
value in using encryption for a performance management system
polling PEs for performance data on thousands of interfaces every
ten minutes, it just adds significant overhead
is acceptable to processing of the packet. Using an encrypted TLS channel for everything may not
work specific-model processing (or operator
configuration) for use cases in performance management wherein we collect
massive amounts of non sensitive data at periodic intervals. Each
SNMP "session" would have this different securityLevel to be applied to negotiate two separate protection
channels (authPriv and authNoPriv) and for every packet the SNMP
engine will use the appropriate channel based on
the desired
securityLevel.
If 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 underlying transport layer security was configurable on a
per-message basis, (but not the other way around
of course). Yes, a TMSM could have define that as the behavior (or
permit an operator to specify that is acceptable behavior) when a MIB module with
configurable maxSecurityLevel and
requested securityLevel cannot be provided, but a minSecurityLevel objects to
identify the range of possible levels, stronger
securityLevel can be provided.

Appendix B. Parameter Table

Following is a CSV-formatted matrix useful for tracking data flows
into and not all messages sent
via that session are out of the same level. A session's
maxSecurityLevel would identify the maximum dispatcher, message, and security it could
provide, subsystems.
Import this into your favorite spreadsheet or other CSV-compatible
application. You wil need to remove lines feeds from the second and a session created with a minSecurityLevel of authPriv
would reject an attempt
thrid lines, which needed to send an authNoPriv message. be wrapped to fit into RFC limits.

B.1. ParameterList.csv

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

,sendPDU,returnResponse,processPDU,processResponse
,prepareOutgoingMessage,prepareResponseMessage,prepareDataElements
,generateRequest,processIncoming,generateResponse

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

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

destTransportDomain,,,,,Out,Out,,,,

destTransportAddress,,,,,Out,Out,,,,

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

securityParameters,,,,,,,,Out,,Out

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

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

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

Appendix C. Open Issues

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Appendix D. Change Log

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

Changes from revison -00-
changed SSH references from I-Ds to RFCs
removed parameters from tmState Reference for DTLS that revealed
lower layer info.
Added TMSM-MIB module
Added Internet-Standard Management Framework boilerplate
Added Structure of the MIB Module
Added MIB security considerations boilerplate (to be completed)
Added IANA Considerations
Added ASI Parameter table
Added discussion of Sessions
Added Open issues and Change Log
Rearranged sections

Authors' Addresses

David Harrington
Effective Software
Harding Rd
Portsmouth NH
Futurewei Technologies
1700 Alma Dr. Suite 100
Plano, TX 75075
USA

Phone: +1 603 436 8634
Email: dbharrington@comcast.net
EMail: dharrington@huawei.com

Juergen Schoenwaelder
International University Bremen
Campus Ring 1
28725 Bremen
Germany

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

Full Copyright Statement

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

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retain all their rights.

This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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found in BCP 78 and BCP 79.

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Acknowledgment

Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

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