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

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Copyright Notice

   Copyright (C) The Internet Society (2005). (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.

   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
       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
   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 . . . . . . . . . . 36

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
     15.1. 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 when a guard cannot make it, etc., thus providing
   the security you want, with no significant effort on your part other
   than identifying requirements and verifying the quality of the
   service being provided.

   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 Benefit from Sessions  . . . . . . . . . 42
     15.2. Applications that 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

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

   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 when a guard cannot make it, etc., thus providing
   the security you want, with no significant effort on your part other
   than identifying requirements and verifying the quality of the
   service being provided.

   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. 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 provides 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 a principal, message
   the sender, encryption, data integrity checking, timeliness checking, etc.

   USM was designed 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 independent provided by an external protocol connected to the SNMP
   engine through an SNMP transport-mapping.  Such a TMSM would then
   enable the use of other existing security
   infrastructures.  USM therefore requires mechanisms such as (TLS)
   [RFC2246] or SSH [RFC4251] within the RFC3411 architecture.

   There are a separate user number of Internet security protocols and key
   management infrastructure.  Operators have reported mechanisms that deploying
   another user and key management infrastructure
   are in order wide spread use.  Many of them try to use SNMPv3
   is provide a reason for not deploying SNMPv3 at this point in time.  It generic
   infrastructure to be used by many different application layer
   protocols.  The motivation behind TMSM is
   possible but difficult to define external mechanisms that handle the
   distribution leverage these protocols
   where it seems useful.

   There are a number of keys for use by the USM approach.

   A solution based on challenges to be addressed to map the second approach might use security
   provided by a USM-compliant
   architecture, but combine secure transport into the authentication mechanism with an
   external mechanism, such as RADIUS, SNMP architecture so that
   SNMP continues to provide the authentication
   service.  It might work without any surprises.  These challenges are
   discussed in detail in this document.  For some key issues, design
   choices are discussed that may be possible to utilize an external protocol made to
   encrypt provide a message, to check timeliness, workable solution
   that meets operational requirements and fits into the SNMP
   architecture defined in [RFC3411] .

2.  Requirements of a Transport Mapping Security Model

2.1.  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 check data integrity, etc.
   It [RFC3411], it is difficult not required to cobble together protect against denial
   of service or traffic analysis.

2.1.1.  Security Protocol Requirements

   There are a number of subcontracted services
   and coordinate them however, because it is difficult to build solid
   security bindings between standard protocols that could be proposed as
   possible solutions within the various services, and potential TMSM framework.  Some factors should be
   considered when selecting a protocol for
   gaps use within this framework.

   Using a protocol in the a manner for which it was not designed has
   numerous problems.  The advertised security is significant.

   A solution based characteristics of a
   protocol may depend on its being used as designed; when used in other
   ways, it may not deliver the third approach might utilize one or more
   lower-layer security mechanisms to provide the message-oriented expected security services required.  These would characteristics.  It
   is recommended that any proposed model include authentication a discussion of the sender, encryption, timeliness checking, and data integrity
   checking.  There are a number
   applicability statement of IETF standards available or in
   development the protocols to address these problems through security layers at be used.

   A protocol used for the
   transport layer or application layer, among them TLS [RFC2246], SASL
   [RFC2222], and SSH [I-D.ietf-secsh-architecture].

   From an operational perspective, it is highly desirable TMSM framework should ideally require no
   modifications to use
   security mechanisms that can unify the administrative protocol.  Modifying the protocol may change its
   security
   management for SNMPv3, command line interfaces (CLIs) and characteristics in ways that would impact other
   management interfaces.  The use of security services provided by
   lower layers existing
   usages.  If a change is necessary, the approach commonly used for change should be an extension
   that has no impact on the CLI, and existing usages.  It is also
   the approach being recommended that
   any proposed for NETCONF [I-D.ietf-netconf-prot].

   This document proposes model include a Transport Mapping Security Model (TMSM), as
   an extension discussion of potential impact on other
   usages of the RFC3411 architecture, protocol.

   It has been a long-standing requirement that allows security to SNMP be
   provided by an external protocol connected able to work
   when the SNMP engine through network is unstable, to enable network troubleshooting and
   repair.  The UDP approach has been considered to meet that need well,
   with an SNMP transport-mapping.  Such assumption that getting small messages through, even if out
   of order, is better than getting no messages through.  There has been
   a TMSM would then enable long debate about whether UDP actually offers better support than
   TCP when the use of
   existing security mechanisms such as (TLS) [RFC2246] underlying IP or SSH
   [I-D.ietf-secsh-architecture] within the RFC3411 architecture.

   There lower layers are a number unstable.  There has
   been recent discussion of Internet security protocols whether operators actually use SNMP to
   troubleshoot and mechanisms that
   are in wide spread use.  Many repair unstable networks.

   There has been discussion of them try to provide a generic
   infrastructure to ways SNMP could be used by many different application layer
   protocols.  The motivation behind TMSM is extended to leverage these protocols
   where it seems useful.

   There are better
   support management/monitoring needs when a number network is running just
   fine.  Use of challenges a TCP transport, for example, could enable larger
   message sizes and more efficient table retrievals.

   TMSM models MUST be able to coexist with other protocol models, and
   may be addressed designed to map utilize either TCP or UDP, depending on the security
   provided by
   transport.

2.2.  Session Requirements

   Throughout this document, the term session is used.  Some underlying
   secure transports will have a notion of session.  Some underlying
   secure transport into transports might enable the use of channels or other session-
   like thing.  In this document the term session refers to an
   association between two SNMP architecture so engines, that permits the secure
   transmission of one or more SNMP continues messages within the lifetime of the
   session.  How the session is actually established, opened, closed, or
   maintained is specific to work without any surprises.  These challenges a particular security model.

   Sessions are
   discussed in detail not part of the SNMP architecture 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" in this
   document are to be interpreted as described
   does not include a session selector in RFC 2119 [RFC2119].

   Some points requiring further WG research the Abstract Service
   Interfaces, and discussion are
   identified by [todo] markers in neither is that done for this architectural
   extension, so an SNMP application cannot select the text.

3.  Requirements of session except by
   passing 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 unique combination of information
   2.  masquerade
   3.  message stream modification
   4.  disclosure

   According securityName, securityModel, and
   securityLevel.

   All TMSM-based security models should discuss the impact of sessions
   on SNMP usage, including how to [RFC3411], establish/open a TMSM session (i.e.
   how it is not required maps to protect against denial the concepts of service or traffic analysis.

3.1.1.  Security Protocol Requirements

   There are a number session-like things of standard protocols that could be proposed as
   possible solutions within the TMSM framework.  Some factors should be
   considered underlying
   protocol), how to behave 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 TMSM session cannot be established,
   how to close a TMSM 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
   session security properties, session establishment overhead, and
   session maintenance overhead.

   To reduce redundancy, this document will discuss aspects that are
   expected to be common to all TMSM-based security characteristics.  It 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 recommended associated with state information that any proposed model include a discussion is
   maintained for its lifetime.  This state information allows for the
   application of various security services to TMSM-based security
   models.  Cryptographic keys established at the
   applicability statement beginning of the protocols to
   session SHOULD be used.

   A protocol used to provide authentication, integrity checking,
   and encryption services for data that is communicated during the TMSM framework should ideally require no
   modifications
   session.  The cryptographic protocols used to the protocol.  Modifying the protocol may change its establish keys for a
   TMSM-based security characteristics model session SHOULD ensure that fresh new
   session keys are generated for each session.  If each session uses
   new session keys, then messages cannot be replayed from one session
   to another.  In addition sequence information MAY be maintained in ways that would impact other existing
   usages.  If a change is necessary,
   the change should session which can be an extension
   that has no impact on used to prevent the existing usages.  It is recommended that
   any proposed model include a discussion replay and reordering of potential impact
   messages within a session.

   A TMSM session will typically have a single securityName and
   securityLevel associated with it.  If an exchange between
   communicating engines would require a different securityLevel or
   would be on other
   usages behalf of the protocol.

   It has been a long-standing requirement different securityName, then another session
   would be needed.  An immediate consequence of this is that SNMP
   implementations should be able to work
   when the network maintain some reasonable number of
   concurrent sessions.

   For TMSM models, securityName is unstable, to enable network troubleshooting typically specified during session
   setup, and
   repair.  The UDP approach has been considered to meet that need well, associated with an assumption that getting small messages through, even if out the session identifier.

   SNMPv3 was designed to support multiple levels of order, security,
   selectable on a per-message basis by an SNMP application, because
   there is better than gettting no messages through.  There has
   been not much value in using encryption for a long debate about whether UDP actually offers better support
   than TCP when Commander Generator
   to poll for non-sensitive performance data on thousands of interfaces
   every ten minutes; the underlying IP or lower layers are unstable.  There
   has been recent discussion encryption adds significant overhead to
   processing of whether operators actually use SNMP the messages.

   Some TMSM-based security models MAY support only specific
   authentication and encryption services, such as requiring all
   messages to
   troubleshoot be carried using both authentication and repair unstable networks.

   There has been discussion encryption,
   regardless of ways the security level requested by an SNMP could be extended to better
   support management/monitoring needs when application.

   Some security models may use an underlying transport that provides a network is running just
   fine.  Use
   per-message requested level of authentication and encryption
   services.  For example, if a TCP transport, session is created as 'authPriv', then
   keys for example, encryption could enable larger
   message sizes and more efficient table retrievals.

   TMSM models MUST still be able negotiated once at the beginning
   of the session.  But if a message is presented to coexist the session with other protocol models, and
   may a
   security level of authNoPriv, then that message could simply be designed to utilize either TCP or UDP, depending
   authenticated and not encrypted within the same transport session.
   Whether this is possible depends on the
   transport.

3.2.  Session Requirements

   Sessions are not part of security model and the SNMP architecture, but are considered
   desirable because secure
   transport used.

   If the cost of authentication can be amortized over
   potentially many transactions.

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

   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.

   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
   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.

   +------------------------------+
   |           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         |                       |
   | |                   |      +--------------+                       |
   | |                   |                                             |
   | |                   | +---------------------+  +----------------+ |
   | |                   | | Message Processing  |  | Security       | |
   | |                   | | Subsystem           |  | Subsystem      | |
   | |                   | |     +------------+  |  |                | |
   | |                   | |  +->| v1MP     * |<--->| +------------+ | |
   | |                   | |  |  +------------+  |  | | Other      | | |
   | |                   | |  |  +------------+  |  | | Security   | | |
   | |                   | |  +->| v2cMP    * |<--->| | Model      | | |
   | | Message           | |  |  +------------+  |  | +------------+ | |
   | | Dispatcher  <--------->|  +------------+  |  | +------------+ | |
   | |                   | |  +->| v3MP     * |<--->| | TMSM       | | |
   | |                   | |  |  +------------+  |  | | MPSP       | | |
   | | PDU Dispatcher    | |  |  +------------+  |  | |            | | |
   | +-------------------+ |  +->| otherMP  * |<--->| +------------+ | |
   |              ^        |     +------------+  |  |                | |
   |              |        +---------------------+  +----------------+ |
   |              v                                                    |
   |      +-------+-------------------------+---------------+          |
   |      ^                                 ^               ^          |
   |      |                                 |               |          |
   |      v                                 v               v          |
   | +-------------+   +---------+   +--------------+  +-------------+ |
   | |   COMMAND   |   | ACCESS  |   | NOTIFICATION |  |    PROXY    | |
   | |  RESPONDER  |<->| CONTROL |<->|  ORIGINATOR  |  |  FORWARDER  | |
   | | application |   |         |   | applications |  | application | |
   | +-------------+   +---------+   +--------------+  +-------------+ |
   |      ^                                 ^                          |
   |      |                                 |                          |
   |      v                                 v                          |
   | +----------------------------------------------+                  |
   | |             MIB instrumentation              |      SNMP entity |
   +-------------------------------------------------------------------+

3.3.1.

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)
   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 (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.

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

   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), and
   6) model)
   6*) translate parameters to model-independent parameters (security
      model)
   7) pass on the decrypted portions with model-independent parameters.

   The USM approach uses SNMP-specific 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).

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

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

3.3.2.  TMSM applications | <--> | access control |  |
   | ---------------------      ------------------  |

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

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 message
   dispatcher to another SNMP message dispatcher.  Once the tunnel is
   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 RFC3411 Architecture

   In transport mapping to the TMSM approach,
   message dispatcher.

2.5.  Security Parameter Passing Requirement

   RFC3411 section 4 describes primitives to describe the order of abstract
   service interfaces used to conceptually pass information between the steps differ
   various subsystems, models and may be
   handled by different subsystems:
   1) decrypt applications within the encrypted portions architecture.

   The security parameters include a model-independent identifier of the message (transport layer)
   2) determine
   security "principal", the SNMP security model and parameters (transport
      mapping)
   3*) translate parameters used to model-independent parameters (transport
      mapping)
   4) decode perform the ASN.1 (messaging model)
   5) determine
   authentication, and which application should get the decrypted portions
      (messaging model)
   6*) translate parameters SNMP-specific security services were
   (should be) applied to model-independent parameters (security
      model)
   7) pass on the decrypted portions with model-independent message (authentication and/or privacy).

   In the RFC3411 architecture, the messaging model must unpack SNMP-
   specific security parameters

   This is largely based on having non-SNMP-specific 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.  The  In the TMSM approach,
   the security-model specific parameters are not all carried in the
   SNMP message, and can be determined from the transport mapping model might provide 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
   translation MPSP that actually creates the message from e.g., an SSH user name its
   component parts.  Does the MPSP need to know the securityName in step
   3, OR transport address or
   the SSH user might actual transport security capabilities, or can this be passed to handled in
   the messaging model to pass to
   a TMSM security model to do TMSP, given the translation in step 6, if model-independent (and message-version-
   independent) parameters?  Are there any security services provided by
   the WG
   decides all translations should use MPSP for an outgoing message?

   [discuss] For incoming messages, is there security functionality that
   can only be handled after the same translation table (e.g., message version is known, such as the USM MIB).

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

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

3.4.  Passing Messages between Subsystems

   RFC3411 defines ASIs security capabilities and msgFlags?  Does
   that describe functionality need to know the passing of messages between
   subsystem within an engine, transport address and session or
   just the model-independent security parameters which are expected (securityName, model,
   level)?  Are there any SNMP-specific parameters that need to be passed between
   unpacked from the subsystems. message for MPSP handling? msgFlags, securityLevel,
   etc.?

   The ASIs generally pass model-
   independent information.

   A TMSM model will establish an encrypted tunnel RFC3411 architecture has no ASI parameters for passing security
   information 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 dispatcher, and
   between the tunnel from one SNMP message dispatcher to another SNMP message dispatcher.  Once and the tunnel message processing model.  If there is
   established, multiple SNMP messages may be able
   a need to be passed through
   the same tunnel.

   Within have an engine, outgoing SNMP messages are passed unencrypted MPSP called from the message dispatcher to the transport mapping, processing model to,
   for example, verify that msgFlags and incoming
   messages are passed unencrypted from the transport mapping security are
   consistent, then it will be necessary to pass the
   message dispatcher.

3.5.  Security Parameter Passing Requirement

   RFC3411 section 4 describes primitives model-independent
   security parameters from the TPSP through to describe the abstract
   service interfaces MPSP.

   There are four approaches that could be used to conceptually pass for passing information
   between the
   various subsystems, models TMSP and applications within an MPSP.
   1.  one could define an ASI to supplement the architecture.

   The security parameters include existing ASIs, or
   2.  the TMSM could add a model-independent identifier header to encapsulate the SNMP message,
   3.  the TMSM could utilize fields already defined in the existing
       SNMPv3 message, or
   4.  the TMSM could pass the information in an implementation-specific
       cache or via a MIB module.

2.5.1.  Define an Abstract Service Interface

   Abstract Service Interfaces (ASIs) [RFC3411] are defined by a set of
   primitives that specify the
   security "principal", services provided and the security model used abstract data
   elements that are to perform be passed when the
   authentication, and which SNMP-specific security services were
   (should be) applied are invoked.
   Defining additional ASIs to pass the message (authentication and/or privacy).

   In the RFC3411 architecture, the messaging model must unpack SNMP-
   specific security parameters and transport
   information from the message before calling transport mapping to a messaging security model to authenticate and decrypt an incoming message,
   perform integrity checking, and translate model-specific security
   parameters into model-independent parameters.  In
   has the advantage of being consistent with existing RFC3411/3412
   practice, and helps to ensure that any TMSM approach, proposals pass the security-model specific parameters are
   necessary data, and do not all carried in the
   SNMP message, cause side effects by creating model-
   specific dependencies between itself and can be determined from the transport layer other models or other
   subsystems other than those that are clearly defined by the
   transport mapping, before the message processing begins.

   [todo] For outgoing messages, it is necessary to have an MPSP because
   it is the MPSP that actually creates ASI.

2.5.2.  Using an Encapsulating Header

   A header could encapsulate the SNMP message to pass necessary
   information from it scomponent
   parts.  Does the MPSP need TMSP to know the transport address or the
   actual transport dispatcher and then to a messaging
   security capabilities, or can this model.  The message header would be handled included in the
   TMSP, given the model-independent (and message-version-independent)
   parameters?  Are there any security services provided by the MPSP for
   an outgoing message?

   [todo] For incoming messages, is there security functionality that
   can only be handled after the message version is known, such as
   wholeMessage ASI parameter, and would be removed by a corresponding
   messaging model.  This would imply the
   comparison of transport security capabilities (one and msgFlags?  Does
   that functionality only) messaging
   dispatcher would need to know the transport address be modified to determine which SNMP message
   version was involved, and session or
   just the model-independent security parameters (securityName, model,
   level)?  Are there any SNMP-specific parameters that a new message processing model would need
   to be
   unpacked developed that knew how to extract the header from the message for MPSP handling? msgFlags, securityLevel,
   etc.?

   The RFC3411 architecture has no ASI parameters for passing
   and pass it to the MPSP.

2.5.3.  Modifying Existing Fields in an SNMP Message

   [RFC3412] describes the SNMPv3 message, which contains fields to pass
   security related parameters.  The TMSM could use these fields in an
   SNMPv3 message, or comparable fields in other message formats to pass
   information between the transport mapping security models in different
   SNMP engines, and the dispatcher, and to pass information between the dispatcher a transport mapping
   security model and the message processing a corresponding messaging security model.

   If there is
   a need to have an MPSP called from the fields in an incoming SNMPv3 message processing model to,
   for example, verify that msgFlags and the transport security are
   consistent, then changed by the TMSP
   before passing it will be necessary to pass the model-independent
   security parameters from MPSP, then the TPSP through TMSP will need to decode the MPSP.

   There are four approaches that could be used for passing information
   between
   ASN.1 message, modify the TMSP fields, and an MPSP.
   1.  one could define an ASI re-encode the message in ASN.1
   before passing the message on to supplement the existing ASIs, message dispatcher or
   2.  the TMSM could add a header to encapsulate the SNMP message,
   3.
   transport layer.  This would require an intimate knowledge of the TMSM could utilize
   message format and message versions so the TMSP knew which fields already defined in
   could be modified.  This would seriously violate the existing
       SNMPv3 message, or
   4. modularity of
   the TMSM architecture.

2.5.4.  Using a Cache

   A cache mechanism could pass be used, into which the TMSP puts information in
   about the security applied to an implementation-specific
       cache or via a MIB module.

3.5.1.  Define incoming message, and an Abstract Service Interface

   Abstract Service Interfaces (ASIs) [RFC3411] are defined by a set of
   primitives MPSP
   extracts that specify the services provided and information from the abstract data
   elements cache.  Given that are there may be
   multiple TM-security caches, a cache ID would need to be passed when
   through an ASI so the services are invoked.
   Defining additional ASIs MPSP knows which cache of information to pass
   consult.

   The cache reference could be thought of as an additional parameter in
   the security and transport
   information from ASIs between the transport mapping to a and the messaging security model
   has the advantage of being consistent with existing RFC3411/3412
   practice, and helps
   model.  The RFC3411 ASIs would not need to ensure that any TMSM proposals pass be changed since the
   necessary data, and do not cause side effects by creating model-
   SNMPv3 WG expected that additional parameters could be passed for
   value-add features of specific implementations.

   This approach does create dependencies between itself a model-specific TPSP
   and other models or other
   subsystems other than those that are clearly defined by an ASI.

3.5.2.  Using an Encapsulating Header

   A header could encapsulate a corresponding specific MPSP.  If a TMSM-model-independent ASI
   parameter is passed, this approach would be consistent with the SNMP message to pass necessary
   information from
   securityStateReference cache already being passed around in the TMSP ASI.

   This document will describe a cache-based approach.

2.6.  Architectural Requirements for Access Control

2.6.1.  securityName Binding

   For SNMP access control to function properly, the dispatcher security mechanism
   must establish a securityModel identifier, a securityLevel, and then to a messaging
   securityName, which is the security model. model independent identifier for
   a principal.  The SNMPv3 message header would be included processing architecture subsystem
   relies on a security model, such as USM, to play a role in security
   that goes beyond protecting the
   wholeMessage ASI parameter, and would be removed by message - it provides a corresponding
   messaging model.  This would imply mapping
   between the (one and only) messaging
   dispatcher would need to be modified USM-specific principal to determine a security-model independent
   securityName which SNMP message
   version was involved, can be used for subsequent processing, such as for
   access control.

   The TMSM is a two-stage security model, with a transport mapping
   security process (TMSP) and a new message processing model would need
   to be developed that knew how to extract security process
   (MPSP).  Depending on the header from design of the message
   and pass it to specific TMSM model, i.e.

   which transport layer protocol is used, different features might be
   provided by the TMSP or by the MPSP.

3.5.3.  Modifying Existing Fields in an SNMP Message

   [RFC3412] describes  For example, the SNMPv3 message, which contains fields translation
   from a mechanism-specific authenticated identity to pass
   security related parameters.  The TMSM could use these fields in an
   SNMPv3 message, a securityName
   might be done by the TMSP or comparable fields in other message formats by the MPSP.

   [discuss] It may be possible to pass
   information between define a consistent division of
   stages regardless of the transport mapping security models in different
   SNMP engines, layer protocol used, and to pass information a
   consistent division of functionality would be preferred.

   The SNMP architecture distinguishes between messages with no
   authentication and no privacy (noAuthNoPriv), authentication without
   privacy (authNoPriv) and authentication with privacy (authPriv).
   Hence, the authentication of a transport mapping
   security model layer identity plays an
   important role and a corresponding messaging must be considered by any TMSM, and user
   authentication must be available via the transport layer security model.
   protocol.

   If the fields in an incoming SNMPv3 message are changed type of authentication provided by the TMSP
   before passing it to the MPSP, then the TMSP will need transport layer (e.g.
   host-based or anonymous) is considered adequate to decode secure and/or
   encrypt the
   ASN.1 message, modify the fields, and re-encode the message in ASN.1
   before passing but inadequate to provide the message on desired
   granularity of access control (e.g. user-based), a second
   authentication, e.g. one provided by a AAA server, may be used to
   provide the message dispatcher or authentication identity which is bound to the
   transport layer.
   securityName.  This approach would require an intimate knowledge a good analysis of the
   message format
   potential for man-in-the-middle attacks or masquerade possibilities.

2.6.2.  Separation of Authentication and message versions so Authorization

   A TMSM security model should take care to not violate the TMSP knew which fields
   could 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 an access control policy
   should be handled within the access control subsystem, not the
   security subsystem, to be modified.  This would seriously violate consistent with the modularity of the
   RFC3411 architecture.

3.5.4.  Using  This separation was a Cache

   A cache mechanism could be used, into which the TMSP puts information
   about deliberate decision of
   the security applied SNMPv3 WG, to an incoming message, allow support for authentication protocols which
   did not provide authorization capabilities, and an MPSP
   extracts that information from the cache.  Given to support
   authorization schemes, such as VACM, that there may be
   multiple TM-security caches, do not perform their own
   authentication.

   An authorization model MAY require authentication by certain
   securityModels and a cache ID would need minimum securityLevel to be passed
   through an ASI so the MPSP knows which cache of information allow access to
   consult.

   The cache reference could be thought of as an additional parameter in the ASIs between
   data.

   TMSM is an enhancement for the transport mapping SNMPv3 privacy and the messaging security
   model.  The RFC3411 ASIs would authentication
   provisions, but it is not need to be changed since a significant improvement for the
   SNMPv3 WG expected that additional
   authorization needs of SNMPv3.  TMSM provides all the model-
   independent parameters could be passed for
   value-add features of specific implementations.

   This approach the isAccessAllowed() primitive [RFC3411].

   TMSM does create dependencies between a model-specific TPSP not specify how the securityModel and a corresponding specific MPSP.  If a TMSM-model-independent ASI
   parameter is passed, this approach would securityName could be consistent with the
   securityStateReference cache already being passed around in the ASI.

   This document will describe
   dynamically mapped to a cache-based approach.

3.6.  Architectural Requirements for Access Control

3.6.1.  securityName Binding

   For SNMP VACM-style groupName.  The mapping of
   (securityModel, securityName) to a groupName is a VACM-specific
   mechanism for naming an access control policy, and for tying the
   named policy to function properly, the security mechanism
   must establish a securityModel identifier, a securityLevel, addressing capabilities of the data modeling
   language (e.g.  SMIv2 [RFC2578]), the operations supported, and other
   factors.  Providing a
   securityName, which is binding outside the security model independent identifier for
   a principal.  The SNMPv3 message processing architecture Access Control subsystem
   relies on a security model,
   might create dependencies that could make it harder to develop
   alternate models of access control, such as USM, one built on UNIX groups,
   Windows domains, XML hierarchies, or task-based controls.  The
   preferred approach is to play a role in pass the model-independent security
   that goes beyond protecting
   parameters via the isAccessAllowed() ASI, and perform the message - it provides a mapping
   between
   within the USM-specific principal to a security-model independent
   securityName access control model.

   To provide support for protocols which can be used simultaneously send
   information for subsequent processing, authentication and authorization, such as for RADIUS
   [RFC2865], model-specific authorization information MAY be cached or
   otherwise made available to the access control.

   The TMSM is a two-stage security model, with control subsystem, e.g. via a transport mapping
   security process (TMSP)
   MIB table similar to the vacmSecurityToGroupTable, so the access
   control subsystem can create an appropriate binding between the
   model-independent securityModel and securityName and a message processing model-specific
   access control policy.  This may be highly undesirable, however, if
   it creates a dependency between a security process
   (MPSP).  Depending on the design of the specific TMSM model and an access
   control model, i.e.
   which transport layer protocol just as it is used, different features might be
   provided by the TMSP or by the MPSP.  For example, undesirable that the translation
   from TMSM approach
   creates a mechanism-specific authenticated identity to dependency between a securityName
   might be done by the TMSP or by the and an MPSP.

2.7.  Requirements for Notifications

   [todo] It may 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 be possible used to define a consistent division of stages
   regardless of send the transport layer protocol used, and a consistent
   division of functionality would be preferred.

   The SNMP architecture distinguishes between messages notification.  Following this
   approach with no
   authentication and no privacy (noAuthNoPriv), authentication without
   privacy (authNoPriv) and SSH would require to provision authentication with privacy (authPriv).
   Hence,
   credentials on the authentication of agent so that agents can successfully authenticate
   to a notification receiver.  There might be other approaches, like
   the reuse of manager initiated secure transport layer identity plays an
   important role 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 must text from RFC 3430 into the section
   dealing with sessions?  This seems to be considered by any TMSM, the right place for this
   discussion.

3.  Scenario Diagrams

   RFC3411 section 4.6 provides scenario diagrams to illustrate how an
   outgoing message is created, and user
   authentication must be available via how an incoming message is
   processed.  Both diagrams are incomplete, however.  In section 4.6.1,
   the diagram doesn't show the ASI for sending an SNMP request to the
   network or receiving an SNMP response message from the network.  In
   section 4.6.2, the diagram doesn't illustrate the transport layer security
   protocol.

   If interfaces required
   to receive an SNMP message from the type of authentication provided by network, or to send an SNMP
   message to the transport layer (e.g.
   host-based network.

3.1.  Command Generator or anonymous) Notification Originator

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

   Command           Dispatcher               Message           Security
   Generator            |                     Processing           Model
   |                    |                     Model                    |
   |      sendPdu       |                        |                     |
   |------------------->|                        |                     |
   |                    | prepareOutgoingMessage |                     |
   :                    |----------------------->|                     |
   :                    |                        | generateRequestMsg  |
   :                    |                        |-------------------->|
   :                    |                        |                     |
   :                    |                        |<--------------------|
   :                    |                        |                     |
   :                    |<-----------------------|                     |
   :                    |                        |                     |
   :                    |------------------+     |                     |
   :                    | Send SNMP        |     |                     |
   :                    | Request Message  |     |                     |
   :                    | to provide the desired
   granularity of access control (e.g. user-based), Network       |     |                     |
   :                    |                  v     |                     |
   :                    :                  :     :                     :
   :                    :                  :     :                     :
   :                    :                  :     :                     :
   :                    |                  |     |                     |
   :                    | Receive SNMP     |     |                     |
   :                    | Response Message |     |                     |
   :                    | from Network     |     |                     |
   :                    |<-----------------+     |                     |
   :                    |                        |                     |
   :                    |   prepareDataElements  |                     |
   :                    |----------------------->|                     |
   :                    |                        | processIncomingMsg  |
   :                    |                        |-------------------->|
   :                    |                        |                     |
   :                    |                        |<--------------------|
   :                    |                        |                     |
   :                    |<-----------------------|                     |
   | processResponsePdu |                        |                     |
   |<-------------------|                        |                     |
   |                    |                        |                     |

3.2.  Command Responder

   This diagram shows how a second
   authentication, e.g. one provided by Command Responder or Notification Receiver
   application registers for handling a AAA server, may be used to
   provide the authentication identity which pduType, how a PDU is bound dispatched
   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 application after an SNMP message is received, and Authorization

   A TMSM security model should take care to not violate how the separation
   of authentication and authorization in
   Response is (asynchronously) send back to the RFC3411 architecture.. network.

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

4.  Abstract Service Interfaces

   The isAccessAllowed() primitive is used for passing security-model
   independent OUT parameters between the subsystems of the architecture.

   Mapping of (securityModel, securityName) prepareOutgoingMessage() ASI are used to an access control policy
   should be handled within the access control subsystem, not
   pass information from the
   security subsystem, message processing model 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, dispatcher
   and on to support
   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 the transport mapping:

      statusInformation = -- success or errorIndication
      prepareOutgoingMessage(
      IN transportDomain -- transport domain to allow access be used
      IN transportAddress -- transport address 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 used
      IN messageProcessingModel -- typically, SNMP version
      IN securityModel -- Security Model to a VACM-style groupName.  The mapping use
      IN securityName -- on behalf of
   (securityModel, securityName) to a groupName is a VACM-specific
   mechanism for naming an access control policy, and this principal
      IN securityLevel -- Level of Security requested
      IN contextEngineID -- data from/at this entity
      IN contextName -- data from/in this context
      IN pduVersion -- the version of the PDU
      IN PDU -- SNMP Protocol Data Unit
      IN expectResponse -- TRUE or FALSE
      IN sendPduHandle -- the handle for tying matching
      -- incoming responses
      OUT destTransportDomain -- destination transport domain
      OUT destTransportAddress -- destination transport address
      OUT outgoingMessage -- the
   named policy message to the addressing capabilities send
      OUT outgoingMessageLength -- its length
      )

5.  TMSM Abstract Service Interfaces

   A set of abstract service interfaces have been defined within this
   document to describe the conceptual data modeling
   language (e.g.  SMIv2), flows between the operations supported, Transport
   Mapping Security Models and other factors.
   Providing a binding outside adjacent components in the Access Control subsystem might create
   dependencies that could make it harder to develop alternate models of
   access control, such as one built on UNIX groups, Windows domains,
   XML hierarchies, or task-based controls. 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 message to send
   IN   outgoingMessageLength       -- its length
   IN   tmStateReference                --
   OUT  sessionID
    )

   The RecvMessage ASI is used to pass a MIB table
   similar message from the transport
   mapping security model subsystem to the vacmSecurityToGroupTable, so Dispatcher.

   statusInformation    RecvMessage(
   IN   destTransportDomain           -- transport domain to be used
   IN   destTransportAddress          -- transport address to be used
   IN   incomingMessage                 -- the message received
   IN   incomingMessageLength       -- its length
   OUT   tmStateReference              --
   OUT   sessionID
    )

   The Transport Mapping Security Model provides the access control
   subsystem can create an approrpiate binding following
   primitives to pass data back and forth between the model-
   independent securityModel and securityName TMSM and a model-specific
   access control policy.  This may be highly undesirable, however, if
   it creates a dependency between a specific
   TMSM-based security models, which provide the interface to the
   underlying secure transport service.  Each TMSM-based security model and an access
   control model, just as it is undesirable that
   should define the TMSM approach
   creates a dependency between a TMSP and an MPSP.

3.7.  Requirements security-model-specific elements of procedure 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
   the establishSession(), closeSession(), TxMessage(), and RxMessage()
   interfaces.

   statusInformation    TxMessage(
   IN   destTransportDomain           -- transport domain to be used
   IN   destTransportAddress          -- transport address to send be used
   IN   outgoingMessage                 -- the notification.  Following this
   approach with SSH would require message to provision authentication
   credentials on the agent so that agents can successfully authenticate send
   IN   outgoingMessageLength       -- its length
   IN   tmStateReference          --
   OUT  sessionID
    )

   statusInformation    RxMessage(
   IN   destTransportDomain           -- transport domain to a notification receiver.  There might be other approaches, like
   the reuse of manager initiated secure used
   IN   destTransportAddress          -- 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 address to be used
   IN   incomingMessage                 -- the section
   dealing with sessions?  This seems message to send
   IN   incomingMessageLength       -- its length
   OUT   tmStateReference          --
    )

    statusInformation    establishSession(
   IN   transportDomain            -- transport domain to be used
   IN   transportAddress           -- transport address to be used
   IN   tmStateReference          --
   OUT  sessionID
    )

   statusInformation    closeSession(
   IN   sessionID
    )

6.  Integration with the right place for this
   discussion.

4.  Scenario Diagrams

   RFC3411 SNMPv3 Message Format

   TMSM proposals can use the SNMPv3 message format, defined in RFC3412,
   section 4.6 provides scenario diagrams to illustrate 6.  This section discusses how an
   outgoing the fields could be reused.

6.1.  msgVersion

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

6.2.  msgGlobalData

   The fields msgID and how an incoming message is
   processed.  Both diagrams msgMaxSize are incomplete, however.In section 4.61,
   the diagram doesn't show used identically for the ASI TMSM
   models as for sending an SNMP request to the
   network or receiving an SNMP response message USM model.

   The msgSecurityModel field should be set to a value from the network.  In
   section 4.6.2,
   SnmpSecurityModel enumeration [RFC3411] to identify the diagram doesn't illustrate 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 interfaces
   description of the SnmpSecurityModel TEXTUAL-CONVENTION from RFC3411.

   The msgSecurityParameters field would carry security information
   required
   to receive an SNMP for message from the network, security processing.  It is unclear whether this
   field would be useful or what parameters would be carried to send support
   security, since message security is provided by an external process,
   and msgSecurityParameters are not used by the 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 network.

4.1.  Command Generator or Notification Originator

   This diagram
   specific services provided in USM security from RFC3411 4.6.1 shows how a Command Generator or
   Notification Originator application requests that a PDU be sent, msgSecurityParameters
   still are needed, and how the response is returned (asynchronously) to that application.

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

4.2.  Command Responder 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 diagram shows how a Command Responder or Notification Receiver
   application registers OCTET STRING is not interpreted by the v3MP,
   but is passed to the local implementation of the Security Model
   indicated by the msgSecurityModel field in the message."

   The msgFlags have the same values for handling 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 pduType, TMSM cannot provide the requested securityLevel, the
   model MUST describe a standard behavior that is followed for that
   situation.  If the TMSM cannot provide at least the requested level
   of security, the TMSM MUST discard the request and SHOULD notify the
   message processing model that the request failed.

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

   For an outgoing message, if the TMSM is able to provide stronger than
   requested security, that may be acceptable.  The transport layer
   protocol would need to indicate to the receiver what security has
   been applied to the actual message.  To avoid the need to mess with
   the ASN.1 encoding, the SNMPv3 message carries the requested
   msgFlags, not the actual securityLevel applied to the message.  If a PDU
   message format other than SNMPv3 is dispatched used, then the new message may
   carry the more accurate securityLevel in the SNMP message.

   For an incoming message, the receiving TMSM knows what must be done
   to process the application after an SNMP message is received, and how based on the
   Response transport layer mechanisms.  If
   the underlying transport security mechanisms for the receiver cannot
   provide the matching securityLevel, then the message should follow
   the standard behaviors for the transport security mechanism, or be
   discarded silently.

   Part of the responsibility of the TMSM is (asynchronously) send back to ensure that the network.

   Command               Dispatcher            Message          Security
   Responder                 |                 Processing          Model
   |                         |                 Model                   |
   |                         |                    |                    |
   | registerContextEngineID |                    |                    |
   |------------------------>|                    |                    |
   |<------------------------|              |     |                    |
   |                         | Receive SNMP |     |                    |
   :                         | Message      |     |                    |
   :                         | from Network |     |                    |
   :                         |<-------------+     |                    |
   :                         |                    |                    |
   :                         |prepareDataElements |                    |
   :                         |------------------->|                    |
   :                         |                    | processIncomingMsg |
   :                         |                    |------------------->|
   :                         |                    |                    |
   :                         |                    |<-------------------|
   :                         |                    |                    |
   :                         |<-------------------|                    |
   |     processPdu          |                    |                    |
   |<------------------------|                    |                    |
   |                         |                    |                    |
   :                         :                    :                    :
   :                         :                    :                    :
   |    returnResponsePdu    |                    |                    |
   |------------------------>|                    |                    |
   :                         | prepareResponseMsg |                    |
   :                         |------------------->|                    |
   :                         |                    |generateResponseMsg |
   :                         |                    |------------------->|
   :                         |                    |                    |
   :                         |                    |<-------------------|
   :                         |                    |                    |
   :                         |<-------------------|                    |
   :                         |                    |                    |
   :                         |--------------+     |                    |
   :                         | Send SNMP    |     |                    |
   :                         | Message      |     |                    |
   :                         | actual
   security provided by the underlying transport layer security
   mechanisms is configured to Network   |     |                    |
   :                         |              v     |                    |

5.  Abstract Service Interfaces

   The OUT parameters of meet or exceed the prepareOutgoingMessage() ASI are used securityLevel required
   by the msgFlags in the SNMP message.  When the MPSP processes the
   incoming message, it should compare the msgFlags field to
   pass information from the
   securityLevel actually provided for the message processing model to by the dispatcher
   and 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 to the transport mapping:

      statusInformation = -- success or errorIndication
      prepareOutgoingMessage(
      IN transportDomain -- transport domain to be model, the MPSP may issue a reportPDU
   with the XXXXXXX model-specific counter.

7.  The tmStateReference for Passing Security Parameters

   A tmStateReference is used
      IN transportAddress -- transport address to pass data between the TMSP and the
   MPSP, similar to the securityStateReference described in RFC3412.
   This can be used
      IN messageProcessingModel -- typically, SNMP version
      IN securityModel -- Security Model envisioned as being appended to use
      IN securityName -- on behalf of this principal
      IN securityLevel -- Level of Security requested
      IN contextEngineID -- data from/at this entity
      IN contextName -- data from/in this context
      IN pduVersion -- the version of ASIs between the PDU
      IN PDU -- SNMP Protocol Data Unit
      IN expectResponse -- TRUE or FALSE
      IN sendPduHandle -- TM
   and the handle for matching
      -- incoming responses
      OUT destTransportDomain -- destination transport domain
      OUT destTransportAddress -- destination transport address
      OUT outgoingMessage -- MP or as being passed in an encapsulating header.

   The TMSP may provide only some aspects of security, and leave some
   aspects to the message MPSP. tmStateReference should be used to pass any
   parameters, in a model- and mechanism-specific format, that will be
   needed to send
      OUT outgoingMessageLength -- its length
      )

6.  Integration with coordinate the SNMPv3 Message Format

   TMSM proposals can use activities of the SNMPv3 message format, defined in RFC3412,
   section 6.  This seection discusses how TMSP and MPSP, and the fields could be reused.

6.1.  msgVersion
   parameters subsequently passed in securityStateReference.  For proposals that reuse the SNMPv3 message format, this field should
   contain
   example, the value 3.

6.2.  msgGlobalData

   The fields msgID TMSP may provide privacy and msgMaxSize are used identically for data integrity and
   authentication and authorization policy retrievals, or some subset of
   these features, depending on the TMSM
   models as for features available in the USM model.

   The msgSecurityModel transport
   mechanisms.  A field in tmStateReference should be set to a value from identify which
   services were provided for each received message by the
   SnmpSecurityModel enumeration [RFC3411] TMSP, the
   securityLevel applied to identify the specific TMSM
   model.  Each standards-track TMSM model should have an enumeration
   assigned by IANA.  Each enterprise-specific received message, the model-specific
   security model should
   have an enumeration assigned following instructions in identity, the
   description session identifier for session based transport
   security, and so on.

8.  securityStateReference Cached Security Data

   From RFC3411: "For each message received, the Security Model caches
   the state information such that a Response message can be generated
   using the same security information, even if the Local Configuration
   Datastore is altered between the time of the SnmpSecurityModel TEXTUAL-CONVENTION 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 RFC3411. the Security Model to the Message Processing Model.  The msgSecurityParameters field would carry security information
   required for message
   cached security processing.  It is unclear whether this
   field would data may be useful implicitly released via the generation of
   a response, or what parameters would be carried to support
   security, since message security is provided by an external process,
   and msgSecurityParameters are not used 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 cache from being released before the transport
   mapping has had an opportunity to extract the information it needs.

9.  Prepare an Outgoing SNMP Message

   Following RFC3412, section 7.1, the SNMPv3 message processing model
   uses the generateResponseMsg() or generateRequestMsg() primitives, to
   call the
   Security Model.  This OCTET STRING is not interpreted by MPSP.  The message processing model, or the v3MP,
   but is passed MPSP it calls,
   may need to put information into the local implementation of the Security Model
   indicated tmStateReference cache for use
   by the msgSecurityModel field in 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
      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 standard behaviors
   securityStateReference.

   The tmStateReference cache will likely contain at least the following
   information:
      tmStateReference - a unique identifier for the transport security mechanism, or be
   discarded silently.

   Part of cached information
      tmSecurityStateReference - the responsibility of unique identifier for the TMSM is cached
      information
      tmTransportDomain
      tmTransportAddress
      tmSecurityModel - an indicator of which mechanisms to ensure that use
      tmSecurityName - a model-specific identifier of the actual security provided by the underlying transport layer
      principal
      tmSecurityLevel - an indicator of which security
   mechanisms is configured to meet or exceed the securityLevel required
   by the msgFlags in services are
      requested
      tmAuthProtocol
      tmPrivProtocol
   and may contain additional information such as
      tmSessionID
      tmSessionKey
      tmSessionMsgID

11.  Notifications

   For notifications, if the SNMP message.  When cache has been released and then session
   closed, then the MPSP processes the
   incoming message, it should compare will request the msgFlags field TMSP to establish a session,
   populate the
   securityLevel actually provided for the message by cache, and pass the transport
   layer security.  If they differ, securityStateReference to the MPSP should MPSP.

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

12.  Transport Mapping Security Model Samples

   There are a number of standard protocols that could be proposed as
   possible solutions within the changed securityLevel is acceptable.  If not, it TMSM framework.  Some factors should discard
   the message.  Depending on the model, the MPSP may issue be
   considered when selecting a protocol for use within this framework.

   Using a protocol in a reportPDU
   with the XXXXXXX model-specific counter.

6.4.  The tmStateReference manner for Passing Security Parameters

   A tmStateReference which is used to pass data between the TMSP and the
   MPSP, similar to the securityStateReference described in RFC3412.
   This can be envisioned as was not designed has
   numerous problems.  The advertised security characteristics of a
   protocol may depend on its being appended to the ASIs between the TM
   and the MP or used as being passed designed; when used in an encapsulating header.

   The TMSP other
   ways, it may provide only some aspects not deliver the expected security characteristics.  It
   is recommended that any proposed model include a discussion of security, and leave some
   aspects to the MPSP. tmStateReference should be used
   applicability statement of the protocols to pass any
   parameters, 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 a model- and mechanism-specific format, that [RFC3430].

   TLS/TCP will be
   needed to coordinate create an association between the activities TMSM of the TMSP and MPSP, one SNMP
   entity and the
   parameters subsequently passed in securityStateReference.  For
   example, the TMSP 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
   integrity are optional features available in the transport
   mechanisms.  A field TLS.  The TLS TMSP MUST provide
   authentication if auth is requested in tmStateReference should identify which
   services were provided for each received the 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.

   A Message Processing Model has the responsibility for explicitly
   releasing memory management.

   The tmStateReference cache:
      tmStateReference
      tmSecurityStateReference
      tmTransportDomain = TCP/IPv4
      tmTransportAddress = x.x.x.x:y
      tmSecurityModel - TLS TMSM
      tmSecurityName = "dbharrington"
      tmSecurityLevel = "authPriv"

12.1.2.  MPSP for TLS TM-Security Model

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

12.1.3.  MIB Module for TLS Security

   Each security model should use its own MIB module, rather than
   utilizing the cached data if such data is no longer needed.  To
   enable this, an abstract securityStateReference data element USM MIB, to eliminate dependencies on a model that
   could be replaced some day.  See RFC3411 section 4.1.1.

   The TLS MIB module needs to provide the mapping from model-specific
   identity to a model independent securityName.

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

12.2.  DTLS/UDP  Transport Mapping Security Model

   DTLS has been proposed as a UDP-based TLS.  Transport Layer Security
   (TLS) [RFC2246] traditionally requires a connection-oriented
   transport and is
   passed from the usually used over TCP.  Datagram Transport Layer
   Security Model (DTLS) [I-D.rescorla-dtls] provides security services
   equivalent to TLS for connection-less transports such as UDP.

   DTLS provides all the Message Processing Model.  The
   cached security data may be implicitly released via the generation services needed from an SNMP
   architectural point of view.  Although it is possible to derive a response, or explicitly released by using the stateRelease
   primitive, as described in RFC3411 section 4.5.1."

   For
   securityName from the TMSM approach, public key certificates (e.g. the TMSP may need 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 the security-model-independent
   securityName, securityLevel, and securityModel parameters, and for
   responses, the messaging model may need Secure Remote Password with TLS
   [I-D.ietf-tls-srp].  A similar option would be to pass the parameters back use Kerberos
   authentication with TLS as defined in [RFC2712].

   It is important to stress that the TMSP.  To differentiate what information needs to authentication exchange must be provided
   to the message processing model by
   integrated into the TMSP, and vice-versa, 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
   document will differentiate the tmStateReference provide by the TMSP
   from the securityStateReference provided by the MPSP.  An
   implementation MAY use one cache and one reference choice seems to serve both
   functions, but an implementor must be aware of
   problematic until the cache-release
   issues mechanism to prevent the cache from being released before cryptographically bind SASL into
   the transport
   mapping TLS mechanism has had been defined.

   DTLS will create an opportunity to extract association between the information it needs.

6.5.1.  Prepare an Outgoing TMSM of one SNMP Message

   Following RFC3412, section 7.1, entity
   and the SNMPv3 message processing 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
   uses
   MUST provide authentication if auth is requested in the generateResponseMsg() or generateRequestMsg() primitives, to
   call securityLevel
   of the MPSP.  The SNMP message processing model, or request (RFC3412 4.1.1).  The TLS TM-security
   model MUST specify that the MPSP it calls,
   may need to put information into messages be encrypted if priv is
   requested in the tmStateReference cache for use
   by securityLevel parameter of the TMSP, such as:
      tmSecurityStateReference - SNMP message request
   (RFC3412 4.1.1).

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

12.2.1.  tmStateReference for the cached
      information
      tmTransportDomain
      tmTransportAddress
      tmSecurityModel - an indicator of which mechanisms to use
      tmSecurityName - DTLS

   DTLS has been suggested as a model-specific identifier of the security
      principal
      tmSecurityLevel - possible secure transport.  It is not
   clear whether DTLS is a reasonable choice for SNMP interactions.  It
   is mentioned here only as an indicator example.

   Upon establishment of which security services are
      requested
   and may contain additional information such as
      tmSessionID
      tmSessionKey
      tmSessionMsgID

   According to RFC3411, section 4.1.1, the application provides the
   transportDomain and transportAddress to the PDU dispatcher via a DTLS session, the
   sendPDU() primitive.  If we permit multiple sessions per
   transportAddress, then we would need to define how session
   identifiers get passed from TMSP will cache the application state
   information.  A unique tmStateReference will be passed to the PDU dispatcher
   (and then
   corresponding MPSP.  The MPSP will pass the securityStateReference to
   the MP model). Message Processing Model for memory management.

   The SNMP over TCP tmStateReference cache:

      tmStateReference
      tmSecurityStateReference
      tmTransportDomain = UDP/IPv4
      tmTransportAddress = x.x.x.x:y
      tmSecurityModel - DTLS TMSM
      tmSecurityName = "dbharrington"
      tmSecurityLevel = "authPriv"

12.3.  SASL Transport Mapping document [RFC3430] says that TCP
   connections can be recreated dynamically or kept for future use Security Model

   The Simple Authentication and
   actually leaves all that to the transport mapping.

   [todo] we might define Security Layer (SASL) [RFC2222]
   provides a new transportDomain and transportAddress,
   which includes the address hook for authentication and session identifier.  For situations
   where a session has not yet been established, we could pass a 0x0000
   session identifier (or whatever) security mechanisms to indicate that a session should be
   established.  Well, this won't work with the current TAddress
   definitions and is probably too ugly to do.

   We might have used
   in application protocols.  SASL supports a MIB module that records number of authentication
   and security mechanisms, among them Kerberos via the session information for
   subsequent GSSAPI mechanism
   [RFC4121].

   This sample will use by the applications and other subsytems, or DIGEST-MD5 because it might
   be passed in the tmStateReference cache.  For notifications, I assume
   the supports authentication,
   integrity checking, and confidentiality.

   DIGEST-MD5 supports auth, auth with integrity, and auth with
   confidentiality.  Since SNMPv3 notification tables would be a place assumes integrity checking is part of
   authentication, if msgFlags is set to find authNoPriv, the address,
   but I'm not sure how qop-value
   should be set to identify auth-int; if msgFlags is authPriv, then qop-value
   should be auth-conf.

   Realm is optional, but can be utilized by the presumably-dynamic session
   identifiers.  The MIB module securityModel if
   desired.  SNMP does not use this value, but a TMSM could identify whether map the session was
   initiated by
   realm into SNMP processing in various ways.  For example, realm and
   username could be concatenated to be the remote engine securityName value, e.g.
   helpdesk::username", or initiated by the current engine,
   and possibly assigned a purpose (incoming request/response or
   outgoing notifications).  First we need realm could be used to decide whether specify a
   groupName to handle
   notifications and requests use 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 an Incoming SNMP Message

   For an incoming message, the TMSP will need VACM access control.  This would be similar
   to put information from having the transport mechanisms used into securityName-to-group mapping done by the external AAA
   server.

12.3.1.  tmStateReference so the MPSP
   can extract the information and add it conceptually to the
   securityStateReference. for SASL  DIGEST-MD5

   The tmStateReference cache will likely contain at least the following
   information: cache:
      tmStateReference - a unique identifier for the cached information
      tmSecurityStateReference - the unique identifier for the cached
      information
      tmTransportDomain = TCP/IPv4
      tmTransportAddress = x.x.x.x:y
      tmSecurityModel - an indicator of which mechanisms to use SASL TMSM
      tmSecurityName - = username
      tmSecurityLevel = [auth-conf]
      tmAuthProtocol = md5-sess
      tmPrivProtocol = 3des
      tmServicesProvided          mutual authentication,
         reauthentication,
         integrity,
         encryption
      tmParameters = "realm=helpdesk, serv-type=SNMP

13.  The TMSM MIB Module

   This memo defines a model-specific identifier portion of the security
      principal
      tmSecurityLevel - an indicator Management Information Base (MIB)
   for managing the Transport Mapping Security Model Subsystem.

13.1.  Structure of which security services the MIB Module

   Objects in this MIB module are
      requested
      tmAuthProtocol
      tmPrivProtocol
   and may contain additional information such arranged into subtrees.  Each subtree
   is organized as
      tmSessionID
      tmSessionKey
      tmSessionMsgID

6.6.  Notifications

   For notifications, if the cache has been released a set of related objects.  The overall structure and then session
   closed, then the MPSP will request the TMSP
   assignment of objects to establish a session,
   populate the cache, their subtrees, and pass the securityStateReference intended purpose of
   each subtree, is shown below.

13.1.1.  Textual Conventions

   Generic and Common Textual Conventions used in this 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 MPSP.

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

7.  Transport .Transport Mapping
   Security Model Samples

   There Subsystem.

   This subtree provides information for identifying fault conditions
   and performance degradation.

13.1.3.  The tmsmsSession Subtree

   This subtree contains security-model-independent information about
   sessions which are a number of standard protocols that could be proposed as
   possible solutions within applicable to all security models based on the TMSM framework.  Some factors should be
   considered when selecting a protocol
   Transport Mapping Security Model Subsystem.

   This subtree provides information for use within this framework.

   Using a protocol in a manner managing sessions for which is was not designed has
   numerous problems.  The advertised any
   security characteristics model based on the Transport Mapping Security Model
   Subsystem.

13.1.4.  The Notifications Subtree

   This subtree contains notifications to alert other entities to events
   which could alter the operational behavior of the entity in a
   protocol may depend on its being used as designed; when used network
   utilizing the SAMPLE Protocol.

13.2.  Relationship to Other MIB Modules

   Some management objects defined in other
   ways, it may not deliver the expected security characteristics.  It MIB modules are applicable
   to an entity implementing this MIB.  In particular, it is recommended assumed
   that any proposed model include a discussion of an entity implementing the
   applicability statement of TMSM-MIB module will also implement
   the protocols SNMPv2-MIB [RFC3418].

   This MIB module is expected to be used.

7.1.  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 used with the MIB modules defined in [RFC3430].

   TLS/TCP will create an association between
   for managing specific security models that are based on the TMSM of one SNMP
   entity
   subsystem.  This MIB module is designed to be security-model
   independent, and the TMSM conatins objects useful for managing common aspects
   of another SNMP entity.  The created "tunnel" any TMSM-based security model.  Specific security models may
   provide encryption and data integrity.  Both encryption and data
   integrity are optional features in TLS.
   define a MIB module to contain security-model-dependent information.

13.2.1.  Relationship to the SNMPv2-MIB

   The TLS TMSP MUST provide
   authentication if auth is requested 'system' subtree in the securityLevel of SNMPv2-MIB [RFC3418] is defined as being
   mandatory for all systems, and the SNMP
   message request (RFC3412 4.1.1).  The TLS TM-security model MUST
   specify that objects apply to the messages be encrypted if priv is requested in entity as a
   whole.  The 'system' subtree provides identification of the
   securityLevel parameter
   management entity and certain other system-wide data.  The TMSM-MIB
   utilizes, but does not dupicate, some of those objects. [todo] do we
   actually use any of the SNMP message request (RFC3412 4.1.1). objects, since we don't have any elements of
   procedure?

13.2.2.  MIB Modules Required for IMPORTS

   The following MIB module imports items from [RFC2578], [RFC2579],
   [RFC2580], [RFC3411], and [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
         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 TLS TM-security model MUST support Internet Society (2006). This
                        version of this MIB module is part of RFC XXXX;
                        see the TLS Handshake Protocol RFC itself for full legal notices.
   -- NOTE to RFC editor: replace XXXX with mutual authentication.

7.1.1.  tmStateReference actual RFC number
   --                     for TLS

   Upon establishment of a TLS session, the TMSP will cache the state
   information.  A unique tmStateReference will be passed this document and remove this note
                       "

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

   -- NOTE to RFC editor: replace XXXX with actual RFC number
   --                     for this document and remove this note
                       "

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

   -- ---------------------------------------------------------- --
   -- subtrees in the
   corresponding MPSP.  The MPSP will pass the securityStateReference to TMSM-MIB
   -- ---------------------------------------------------------- --

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

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

   -- Statistics for the Message Processing Transport Model Security Model Subsystem

   tmsmStats         OBJECT IDENTIFIER ::= { tmsmObjects 1 }

   -- [discuss] do we need any tmsm stats?
   -- these should be for memory management.

   The tmStateReference cache:

      tmStateReference
      tmSecurityStateReference
      tmTransportDomain = TCP/IPv4
      tmTransportAddress = x.x.x.x:y
      tmSecurityModel - TLS TMSM
      tmSecurityName = "dbharrington"
      tmSecurityLevel = "authPriv"
      tmAuthProtocol = Handshake MD5
      tmPrivProtocol = Handshake DES
      tmSessionID = Handshake interoperability, not local debug.
   -- we could probably track session identifier
      tmSessionKey = Handshake peer certificate
      tmSessionMasterSecret = master secret
      tmSessionParameters = compression method, cipher spec, is-
      resumable

7.1.2.  MPSP for TLS TM-Security Model

      messageProcessingModel = SNMPv3
      securityModel = TLS establishment failures
   -- although this really belongs in an SSH-MIB, not TMSM-MIB

   -- The tmsmSession Group

   tmsmSession          OBJECT IDENTIFIER ::= { tmsmObjects 2 }

   tmsmSessionSpinLock  OBJECT-TYPE
       SYNTAX       TestAndIncr
       MAX-ACCESS   read-write
       STATUS       current
       DESCRIPTION "An advisory lock used to allow several cooperating
                    TMSM
      securityName = tmSecurityName
      securityLevel = msgSecurityLevel

7.1.3.  MIB Module security models to coordinate their
                    use of facilities to create sessions in the
                    tmsmSessionTable.
                   "
       ::= { tmsmSession 1 }

   tmsmSessionCurrent  OBJECT-TYPE
       SYNTAX       Gauge32
       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION "The current number of established sessions.
                   "
       ::= { tmsmSession 2 }

   tmsmSessionMaxSupported  OBJECT-TYPE
       SYNTAX       Unsigned32
       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION "The maximum number of 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 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 SNMP engine's Local
                    Configuration Datastore (LCD) for TLS Transport Mapping
                    Security

   Each security model should use its own MIB module, rather than
   utilizing the USM MIB, to eliminate dependencies on Models.
                   "
       INDEX       { tmsmSessionID }
       ::= { tmsmSessionTable 1 }

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

    tmsmSessionID  OBJECT-TYPE
       SYNTAX       Integer32 (1..65535)
       MAX-ACCESS   not-accessible
       STATUS       current
       DESCRIPTION "A locally-unique identifier for a model that
   could be replaced some day.  See RFC3411 section 4.1.1.

   The TLS MIB module needs to provide 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 mapping from model-specific
   identity to a model independent securityName.

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

7.2.  DTLS/UDP  Transport Mapping principal
                    in Security Model

   DTLS has been proposed as a UDP-based TLS.  Transport Layer independent format.

                    The default transformation of the Secure Shell
                    Security
   (TLS) [RFC2246] traditionally requires a connection-oriented
   transport Model dependent security ID to the
                    securityName
                    and vice versa is usually used over TCP.  Datagram Transport Layer the identity function so that the
                    securityName is the same as the SSH user name.
                   "
       ::= { tmsmSessionEntry 5 }
   tmsmSessionSecurityLevel OBJECT-TYPE
       SYNTAX      SnmpSecurityLevel
       MAX-ACCESS   read-only
       STATUS       current
        DESCRIPTION "The Level of Security (DTLS) [I-D.rescorla-dtls] provides security services
   equivalent to TLS at which SNMP messages can be
                    sent using this session, in particular, one of:

                      noAuthNoPriv - 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 for connection-less transports such as UDP.

   DTLS provides all the security services needed
                    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
       }
       STATUS      current
       DESCRIPTION "A collection of objects for maintaining session
                    information of an SNMP engine which implements the
                    SNMP Secure Shell Security Model.
                   "

       ::= { tmsmGroups 2 }

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

   tmsmCompliance MODULE-COMPLIANCE
       STATUS      current
       DESCRIPTION
           "The compliance statement for SNMP engines that support the
           TMSM-MIB"
       MODULE
           MANDATORY-GROUPS { tmsmGroup }
       ::= { tmsmCompliances 1 }

   END

15.  Implementation Considerations

15.1.  Applications that Benefit from an Sessions

   [todo] contributions welcome.

   There has been discussion of ways SNMP
   architectural point could be extended to better
   support management/monitoring needs when a network is running just
   fine.  Use of view.  Although it a TCP transport, for example, could enable larger
   message sizes and more efficient table retrievals.

   Discussing how to improve SNMP once you have less strict message size
   constraints is possible beyond the scope of this document, or that of TMSM-
   based security models.  Applications utilizing TMSM-based security
   models may want to derive a
   securityName from take advantage of the public key certificates increased message sizes by
   sending larger requests and utilizing existing SNMP operations (e.g. the subject
   field), this approach requires installing certificates
   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. and the networks that contain them.

15.2.  Applications that Suffer from Sessions

   [todo] why does this not
   integrate well with existing AAA systems?
   Another option contributions welcome.

15.2.1.  Troubleshooting

   It has been a long-standing requirement that SNMP be able to work
   when the network is unstable, to run enable network troubleshooting and
   repair.  The UDP approach has been considered to meet that need well,
   with an authentication exchange which assumption that getting small messages through, even if out
   of order, is
   integrated with TLS, such as Secure Remote Password with TLS
   [I-D.ietf-tls-srp].  A similar option would be to better than gettting no messages through.  There has
   been a long debate about whether UDP actually offers better support
   than TCP when the underlying IP or lower layers are unstable.  There
   has been recent discussion of whether operators actually use Kerberos
   authentication with TLS as defined in [RFC2712].

   It is important SNMP to stress that the authentication exchange must
   troubleshoot and repair unstable networks.

   The need to establish a session before using SNMP to troubleshoot a
   device may prove problematic in practice.  TMSM-based security models
   should include discussion of how troubleshooting applications might
   be
   integrated into impacted by the TLS mechanism to prevent man-in-the-middle
   attacks.  While SASL [RFC2222] is often used on top use of the specific security model, and recommend
   workarounds.

   This document RECOMMENDS that all TMSM-based security models include
   a TLS
   encrypted channel to authenticate users, this choice seems fallback approach, triggered by multiple failed attempts to
   establish sessions.  The default fallback should be
   problematic until the mechanism to cryptographically bind SASL into utilize the TLS mechanism has been defined.

   DTLS will create
   IETF-Standard USM security model to send a notification, so an association between
   administrator can attempt to manually correct the TMSM of one SNMP entity 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 TMSM security considerations of another that approach. [discuss]
   expand as needed.

   It is considered desirable by some industry segments that SNMP entity.  The created "tunnel" may
   provide encryption and data integrity.  Both
   security models should utilize transport layer security that
   addresses perfect forward secrecy at least for encryption and data
   integrity are optional features in DTLS.  The DTLS TM-security model
   MUST provide authentication if auth is requested keys.
   Perfect forward secrecy guarantees that compromise of long term
   secret keys does not result in the securityLevel disclosure of past session keys.

   There are a number of management objects defined in this MIB module
   with a MAX-ACCESS clause of the SNMP message request (RFC3412 4.1.1).  The TLS TM-security
   model MUST specify that the messages read-write and/or read-create.  Such
   objects may be encrypted if priv is
   requested considered sensitive or vulnerable in the securityLevel parameter of the SNMP message request
   (RFC3412 4.1.1). some network
   environments.  The DTLS TM-security model MUST support the TLS Handshake Protocol
   with mutual authentication.

7.2.1.  tmStateReference for DTLS

   Upon establishment of SET operations in a DTLS session, non-secure
   environment without proper protection can have a negative effect on
   network operations.  These are the TMSP will cache tables and objects and their
   sensitivity/vulnerability:
   o  [todo] list the tables and objects and state
   information.  A unique tmStateReference will be passed to the
   corresponding MPSP.  The MPSP will pass the securityStateReference to
   the Message Processing Model for memory management.

   The tmStateReference cache:
      tmStateReference
      tmSecurityStateReference
      tmTransportDomain = UDP/IPv4
      tmTransportAddress = x.x.x.x:y
      tmSecurityModel - DTLS TMSM
      tmSecurityName = "dbharrington"
      tmSecurityLevel = "authPriv"
      tmAuthProtocol = Handshake MD5
      tmPrivProtocol = Handshake DES
      tmSessionID = Handshake session identifier
      tmSessionKey = Handshake peer certificate
      tmSessionMasterSecret = master secret
      tmSessionParameters = compression method, cipher spec, is-
      resumable
      tmSessionSequence = epoch, sequence

   [todo]
      Need to discuss to what extent DTLS is 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 to
      DTLS?
      More details need to be worked out...

7.3.  SASL Transport Mapping Security Model

   The Simple Authentication and Security Layer (SASL) [RFC2222]
   provides readable objects in this MIB module (i.e., objects with a hook for authentication
   MAX-ACCESS other than not-accessible) may be considered sensitive or
   vulnerable in some network environments.  It is thus important to
   control even GET and/or NOTIFY access to 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. SNMPv3 framework (see [RFC3410], section 8),
   including full support for the SNMPv3 cryptographic mechanisms (for
   authentication and privacy).

   Further, deployment of SNMP does not use this value, but versions prior to SNMPv3 is NOT
   RECOMMENDED.  Instead, it is RECOMMENDED to deploy SNMPv3 and to
   enable cryptographic security.  It is then a TMSM could map customer/operator
   responsibility to ensure that the
   realm into SNMP processing in various ways.  For example, realm and
   username could be concatenated entity giving access to an
   instance of this MIB module is properly configured to give access to be
   the securityName value, e.g.
   helpdesk::username", objects only to those principals (users) that have legitimate
   rights to indeed GET or SET (change/create/delete) them.

17.  IANA Considerations
   The MIB module in this document uses the realm could 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 used removed prior to publication):  the IANA is
   requested to specify assign a
   groupname value for "XXXX" under the 'mib-2' subtree
   and to use record the assignment in the VACM access control.  This would be similar SMI Numbers registry.  When
   the assignment has been made, the RFC Editor is asked to having replace
   "XXXX" (here and in the securityName-to-group mapping done by MIB module) with the external AAA
   server.

7.3.1.  tmStateReference for SASL  DIGEST-MD5

   The tmStateReference cache:
      tmStateReference
      tmSecurityStateReference
      tmTransportDomain = TCP/IPv4
      tmTransportAddress = x.x.x.x:y
      tmSecurityModel - SASL TMSM
      tmSecurityName = username
      tmSecurityLevel = [auth-conf]
      tmAuthProtocol = md5-sess
      tmPrivProtocol = 3des
      tmServicesProvided =
         mutual authentication,
         reauthentication,
         integrity,
         encryption
      tmParameters = "realm=helpdesk, serv-type=SNMP

8.  Security Considerations

   This document describes an architectural approach assigned value and multiple
   proposed configurations that would permit SNMPv3 to utilize transport
   layer security services.  Each section containing
   remove this note.

   [discuss] How do we add a proposal should
   discuss the security considerations of that approach. [todo] expand
   as needed.

   Perfect forward secrecy guarantees that compromise of long term
   secret keys does not result in disclosure of past session keys.

   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 encryption keys.

9. 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.

   [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.

   [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]
              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.
              RFC 3430, December 2002.

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

   [RFC4121]  Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
              Version 5 Generic Security Service Application Program
              Interface (GSS-API) Mechanism: Version 2", RFC 4121,
              July 2005.

   [I-D.ietf-netconf-ssh]
              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
   securityLevel, so if we pass the securityLevel between the two
   stages, then they each have the info they need to do their respective
   comparisons.

   There have been a large number of questions about msgFlags in the
   TMSM approach, mostly concerning the msgFlags value and the actual
   security provided, and whether msgFlags can be used to initiate per-
   message or per-session security.

A.1.  msgFlags versus actual security

   Using IPSEC, SSH, or SSL/TLS to provide security services "below" the
   SNMP message, the use of securityName and securityLevel will differ
   from the USM/VACM approach to SNMP access control.  VACM uses the
   "securityName" and the "securityLevel" to determine if access is
   allowed.  With the SNMPv3 message and USM security model, both
   securityLevel and securityName are contained in every SNMPv3 message.

   Any proposal for a security model using IPSEC, SSH, or SSL/TLS needs
   to specify how this info is made available to the SNMPv3 message
   processing, and how it is used.

   One specific case to consider is the relationship between the
   msgFlags of an SNMPv3 message, and the actual services provided by
   the lower layer security.  For example, if a session is set up with
   encryption, is the priv bit always (or never) set in the msgFlags
   field, and is the PDU never (or always) encrypted?  Do msgFlags have
   to match the security services provided by the lower layer, or are
   the msgFlags ignored and the values from the lower layer used?

      Is the securityLevel looked at before the security model gets to
      it.?  No. the security model has two parts - the TMSP and the
      MPSP.  The securityLevel is looked at by the TMSP before it gets
      to the MPSP, but both are parts of the same security model.
      Would it be legal for the security model to ignore the incoming
      flags and change them before passing them back up?  If it changed
      them, it wouldn't necessarily be ignoring them.  The TMSP should
      pass both an actual securityLevel applied to the message, and the
      msgFlags in the SNMP message to the MPSP for consideration related
      to access control..  The msgFlags parameter in the SNMP message is
      never changed when processing an incoming message.
      Would it be legal for the security model to ignore the outgoing
      flags and change them before passing them out? no; because the two
      stages are parts of the same security model, either the MPSP
      should recognize that a securityLevel cannot be met or exceeded,
      and reject the message during the message-build phase, or the TMSP
      should determine if it is possible to honor the request.  It is
      possible to apply an increased securityLevel for an outgoing
      request, but the procedure to do so must be spelled out clearly in
      the model design.
      The security model MUST check the incoming security level flags to
      make sure they matched the transport session setup. and if not
      drop the message.  Yes, mostly.  Depending on the model, either
      the TMSP or the MPSP MUST verify that the actual processing met or
      exceeded the securityLevel requested by the msgFlags and that it
      is acceptable to the specific-model processing (or operator
      configuration) for this different securityLevel to be applied to
      the message.  This is also true (especially) for outgoing
      messages.
      You might legally be able to have a authNoPriv message that is
      actually encrypted via the transport (but not the other way around
      of course).  Yes, a TMSM could define that as the behavior (or
      permit an operator to specify that is acceptable behavior) when
      should recognize that a
      requested securityLevel cannot be provided, but a stronger
      securityLevel can be provided.

A.2.  Message security versus session security

      For SBSM, met or exceeded,
      and for many TMSM models, securityName is specified reject the message during session setup, and associated with the session identifier.
      Is message-build phase, or the TMSP
      should determine if it is possible for the request (and notification) originator to
      specify per message auth and encryption services, or are they
      "fixed" by honor the transport/session model?
      If a session request.  It is created as 'authPriv', then keys
      possible to apply an increased securityLevel for encryption
      would still an outgoing
      request, but the procedure to 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 stronger
      securityLevel can be provided.

Appendix B.  Parameter Table

   Following is a CSV-formatted matrix useful for tracking data flows
   into and out of the dispatcher, message, and security subsystems.
   Import this into your favorite spreadsheet or other CSV-compatible
   application.  You wil need to
      identify remove lines feeds from the range of possible levels, second and not all messages sent
      via
   thrid lines, which needed to 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
   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

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 session are revealed
      lower layer info.
      Added TMSM-MIB module
      Added Internet-Standard Management Framework boilerplate
      Added Structure of the same level.  A session's
      maxSecurityLevel would identify the maximum MIB Module
      Added MIB security it could
      provide, and a session created with a minSecurityLevel considerations boilerplate (to be completed)
      Added IANA Considerations
      Added ASI Parameter table
      Added discussion of authPriv
      would reject an attempt to send an authNoPriv message. 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

   Copyright (C) The Internet Society (2005). (2006).

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Acknowledgement

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