Network Working Group                                      D. Harrington
Internet-Draft                                    Futurewei                                 Huawei Technologies
Expires: November 4, 2006 (USA)
Intended status: Informational                          J. Schoenwaelder
Expires: December 25, 2006               International University Bremen
                                                             May 3,
                                                           June 23, 2006

Transport Mapping Security Model (TMSM) Architectural Extension for the
               Simple Network Management Protocol (SNMP)
                      draft-ietf-isms-tmsm-02.txt
                      draft-ietf-isms-tmsm-03.txt

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document describes a Transport Mapping Security Model (TMSM)
   extension 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 sessions in the Transport Mapping Security Model
   extension.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  The Internet-Standard Management Framework . . . . . . . .  4
     1.2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  4
     1.3.  Acronyms . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.4.  Motivation . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Requirements of a Transport Mapping Security Model . . . . . .  6
     2.1.  Message Security Requirements  . . . . . . . . . . . . . .  6
       2.1.1.  Security Protocol Requirements . . . . . . . . . . . .  7
     2.2.  SNMP Requirements  . . . . . . . . . . . . . . . . . . . .  7
       2.2.1.  Architectural Modularity Requirements  . . . . . . . .  7
       2.2.2.  Access Control Requirements  . . . . . . . . . . . . . 14
       2.2.3.  Security Parameter Passing Requirements  . . . . . . . 16
     2.3.  Session Requirements . . . . . . . . . . . . . . . . . . . 17
       2.3.1.  Session Establishment Requirements . . . . . . . . . . 18
       2.3.2.  Session Maintenance Requirements . . . . . . . . . . . 19
       2.3.3.  Message security versus session security . . . . . . . 19
   3.  Scenario Diagrams for TMSM . . . . . . . . . . . . . . . . . . 21
     3.1.  Command Generator or Notification Originator . . . . . . . 21
     3.2.  Command Responder  . . . . . . . . . . . . . . . . . . . . 22
   4.  Abstract Service Interfaces for TMSM . . .  Message Formats  . . . . . . . . . . 23
     4.1.  Existing Abstract Service Interfaces . . . . . . . . . . . 24
     4.2.  TMSM Abstract Service Interfaces . . 23
     4.1.  SNMPv3 Message Fields  . . . . . . . . . . . 24
   5.  Cached Information and References . . . . . . . 24
       4.1.1.  msgGlobalData  . . . . . . . 26
     5.1.  securityStateReference Cached Security Data . . . . . . . 26
     5.2.  tmStateReference Cached Security Data . . . . . . 26
       4.1.2.  msgSecurityParameters  . . . . 27
   6.  Integration with the SNMPv3 Message Format . . . . . . . . . . 28
     6.1.  msgVersion . . 27
   5.  Cached Information and References  . . . . . . . . . . . . . . 27
     5.1.  tmSessionReference Cached Session Data . . . . . . . . 28
     6.2.  msgGlobalData . . 27
     5.2.  securityStateReference Cached Security Data  . . . . . . . 27
   6.  Abstract Service Interfaces for TMSM . . . . . . . . . . . . . 28
     6.3.  securityLevel and msgFlags . . . . .
     6.1.  Generating an Outgoing SNMP Message  . . . . . . . . . . . 29
   7.  Prepare
     6.2.  TMSP for an Outgoing SNMP Message . . . . . . . . . . . . . . . 29
   8.  Prepare Data Elements from 30
     6.3.  Processing an Incoming SNMP Message  . . . . . 30
   9.  Notifications  . . . . . . . . . . . 30
       6.3.1.  TMSP for an Incoming Message . . . . . . . . . . . . . 30
   10. The TMSM MIB Module  . . .
       6.3.2.  Prepare Data Elements from Incoming Messages . . . . . 31
       6.3.3.  MPSP for an Incoming Message . . . . . . . . . . . . . 31
     10.1. Structure of the 32
   7.  The TMSM MIB Module  . . . . . . . . . . . . . . . 31
       10.1.1. The tmsmNotifications Subtree  . . . . . . . . . . . . 31
       10.1.2. The tmsmStats Subtree . 33
     7.1.  Structure of the MIB Module  . . . . . . . . . . . . . . . 31
       10.1.3. 33
       7.1.1.  The tmsmSession tmsmStats Subtree  . . . . . . . . . . . . . . . 31
     10.2. . 33
     7.2.  Relationship to Other MIB Modules  . . . . . . . . . . . . 31
       10.2.1. 33
       7.2.1.  Textual Conventions  . . . . . . . . . . . . . . . . . 32
       10.2.2. 33
       7.2.2.  MIB Modules Required for IMPORTS . . . . . . . . . . . 32
   11. 33
     7.3.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . . 32
   12. 33
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 39
   13. 38
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 40
   14. 39
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 41
   15. 39
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 41
     15.1. 39
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 41
     15.2. 39
     11.2. Informative References . . . . . . . . . . . . . . . . . . 42 40
   Appendix A.  Parameter Table . . . . . . . . . . . . . . . . . . . 42 41
     A.1.  ParameterList.csv  . . . . . . . . . . . . . . . . . . . . 43 41
   Appendix B.  Why tmSecurityReference? tmSessionReference? . . . . . . . . . . . . . . 44 . 42
     B.1.  Define an Abstract Service Interface . . . . . . . . . . . 44 43
     B.2.  Using an Encapsulating Header  . . . . . . . . . . . . . . 45 43
     B.3.  Modifying Existing Fields in an SNMP Message . . . . . . . 45 43
     B.4.  Using a Cache  . . . . . . . . . . . . . . . . . . . . . . 45 44
   Appendix C.  Open Issues . . . . . . . . . . . . . . . . . . . . . 45 44
   Appendix D.  Change Log  . . . . . . . . . . . . . . . . . . . . . 46
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 46
   Intellectual Property and Copyright Statements . . . . . . . . . . 47 44

1.  Introduction

   This document describes a Transport Mapping Security Model (TMSM)
   extension 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.  Acronyms

   This section contains a list of acronyms used with within the document and
   references to where in the document the acronym is defined, for easy
   lookup.
   o  TMSM - a Transport Mapping Security Model
   o  MPSP  SMSP - s Messaging Processing a Security Model Security Processor, the portion of a TMSM
      security model that resides in the Message Processing
      subsytem subsystem of
      an SNMPv3 engine.  See Section 2.2.1
   o  TMSP - the Transport Mapping Security Processor, the portion of a
      TMSM security model that resides in the Transport Mapping section
      of the Dispatcher of an SNMPv3 engine.  See Section 2.2.1

1.4.  Motivation

   There are multiple ways to secure one's home or business, but they
   largely boil down to in 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.
   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 principal and key
   management infrastructure.  Operators have reported that deploying
   another user principal and key management infrastructure in order to use
   SNMPv3 is a deterrent to deploying SNMPv3.  It is possible but
   difficult to define external mechanisms that handle the distribution
   of keys for use by the USM approach.

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

   A solution based on the third approach might utilize one or more
   lower-layer security mechanisms to provide the message-oriented
   security services required.  These would include authentication of
   the sender, encryption, timeliness checking, and data integrity
   checking.  There are a number of IETF standards available or in
   development to address these problems through security layers at the
   transport layer or application layer, among them TLS [RFC4366], SASL
   [RFC2222],
   [RFC4422], 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)
   extension to the RFC3411 architecture, that allows security to be
   provided by an external protocol connected to the SNMP engine through
   an SNMP transport-mapping [RFC3417].  Such a TMSM would then enable
   the use of existing security mechanisms such as (TLS) [RFC4366] or
   SSH [RFC4251] within the RFC3411 architecture.

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

   There are a number of challenges to be addressed to map the security
   provided by a secure transport into the SNMP architecture so that
   SNMP continues to work without any surprises.  These challenges are
   discussed in detail in this document.  For some key issues, design
   choices are discussed that may be made to provide a workable solution
   that meets operational requirements and fits into the SNMP
   architecture defined in [RFC3411].

2.  Requirements of a Transport Mapping Security Model

2.1.  Message Security Requirements

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

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

   According to [RFC3411], it is not required to protect against denial
   of service or traffic analysis.

2.1.1.  Security Protocol Requirements

   There are a number of standard protocols that could be proposed as
   possible solutions within the TMSM framework.  Some factors should be
   considered when selecting a protocol for use within this framework.

   Using a protocol in a manner for which it was not designed has
   numerous problems.  The advertised security characteristics of a
   protocol may depend on its being used as designed; when used in other
   ways, it may not deliver the expected security characteristics.  It
   is recommended that any proposed model include a discussion of the
   applicability statement of the protocols to be used.

   A protocol used for the TMSM framework should ideally require no
   modifications to the protocol.  Modifying the protocol may change its
   security characteristics in ways that would impact other existing
   usages.  If a change is necessary, the change should be an extension
   that has no impact on the existing usages.  It is recommended that
   any proposed model include a discussion of potential impact on other
   usages of the protocol.

   It has been a long-standing requirement that SNMP be able to work
   when the network is unstable, to enable network troubleshooting and
   repair.  The UDP approach has been considered to meet that need well,
   with an assumption that getting small messages through, even if out
   of order, is better than getting no messages through.  There has been
   a long debate about whether UDP actually offers better support than
   TCP when the underlying IP or lower layers are unstable.  There has
   been recent discussion of whether operators actually use SNMP to
   troubleshoot and repair unstable networks.

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

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

2.2.  SNMP Requirements

2.2.1.  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.  The 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).

   Parameters have been provided in the ASIs to pass model-independent
   transport address information.  These parameters utilize the
   TransportType and TransportAddress

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

   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 architectural extension 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
   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 model's security
   processor as the MPSP. SMSP.

   Thus a TMSM is composed of both a TMSP and an MPSP. SMSP.

   +------------------------------+
   |           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 SMSP       | | |
   | | PDU Dispatcher    | |  |  +------------+  |  | |            | | |
   | +-------------------+ |  +->| otherMP  * |<--->| +------------+ | |
   |              ^        |     +------------+  |  |                | |
   |              |        +---------------------+  +----------------+ |
   |              v                                                    |
   |      +-------+-------------------------+---------------+          |
   |      ^                                 ^               ^          |
   |      |                                 |               |          |
   |      v                                 v               v          |
   | +-------------+   +---------+   +--------------+  +-------------+ |
   | |   COMMAND   |   | ACCESS  |   | NOTIFICATION |  |    PROXY    | |
   | |  RESPONDER  |<->| CONTROL |<->|  ORIGINATOR  |  |  FORWARDER  | |
   | | application |   |         |   | applications |  | application | |
   | +-------------+   +---------+   +--------------+  +-------------+ |
   |      ^                                 ^                          |
   |      |                                 |                          |
   |      v                                 v                          |
   | +----------------------------------------------+                  |
   | |             MIB instrumentation              |      SNMP entity |
   +-------------------------------------------------------------------+

2.2.1.1.  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
      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 |  |
   | ---------------------      ------------------  |

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

2.2.1.2.  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)
   6*)  translate parameters to model-independent parameters (security
      model)
   7) pass on the decrypted portions with model-independent security
      parameters

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

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

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

2.2.1.3.  Passing Information between Engines

   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.

2.2.2.  Access Control Requirements

2.2.2.1.  securityName Binding

   For SNMP access control to function properly, the security mechanism
   must establish a securityModel identifier, a securityLevel, and a
   securityName, which is the security model independent identifier for
   a principal.  The SNMPv3 message processing architecture subsystem
   relies on a security model, such as USM, to play a role in security
   that goes beyond protecting the message - it provides a mapping
   between the USM-specific principal to a security-model independent
   securityName which 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 message processing security model security process
   (MPSP). (SMSP).
   Depending on the design of the specific TMSM model, i.e., which
   transport layer protocol is used, different features might be
   provided by the TMSP or by the MPSP. SMSP.  For example, the translation
   from a mechanism-specific authenticated identity to a securityName
   might be done by the TMSP or by the MPSP. SMSP.

   The securityName MUST be bound to the mechanism-specific
   authenticated identity, and this mapping MUST be done before the MPSP SMSP
   portion of the model passes securityName to the message processing
   model via the processIncoming() ASI.

   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 layer identity plays an
   important role and must be considered by any TMSM, and user principal
   authentication must be available via the transport layer security
   protocol.

   If the type of authentication provided by the transport layer (e.g.
   TLS) is considered adequate to secure and/or encrypt the message, but
   inadequate to provide the desired granularity of access control (e.g.
   user-based), then a second authentication (e.g., one provided by a
   RADIUS server) may be used to provide the authentication identity
   which is bound to the securityName.  This approach would require a
   good analysis of the potential for man-in-the-middle attacks or
   masquerade possibilities.

2.2.2.2.  Separation of Authentication and Authorization

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

   Mapping of (securityModel, securityName) to an access control policy
   should be handled within the access control subsystem, not the
   security subsystem, to be consistent with the modularity of the
   RFC3411 architecture.  This separation was a deliberate decision of
   the SNMPv3 WG, to allow support for authentication protocols which
   did not provide authorization capabilities, and 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 to allow access to the
   data.

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

   TMSM does not specify how the securityModel and securityName could be
   dynamically mapped to a 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 the addressing capabilities of the data modeling
   language (e.g.  SMIv2 [RFC2578]), the operations supported, and other
   factors.  Providing a binding outside 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
   or Windows domains.  The preferred approach is to pass the model-
   independent security parameters via the isAccessAllowed() ASI, and
   perform the mapping within the access control model.

   To provide support for protocols which simultaneously send
   information for authentication and authorization, such as RADIUS
   [RFC2865], model-specific authorization information MAY be cached or
   otherwise made available to the access control subsystem, e.g., via a
   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 model-specific
   access control policy.  This may be highly undesirable, however, if
   it creates a dependency between a security model and an access
   control model, just as it is undesirable that the TMSM approach
   creates a dependency between a TMSP and an MPSP. SNMP message version and the security
   provided by a transport mapping.

2.2.3.  Security Parameter Passing Requirements

   RFC3411 section 4 describes primitives to describe the abstract data
   flows between the various subsystems, models and applications within
   the architecture.  Abstract Service Interfaces describe the flow of
   data between subsystems within an engine.  The ASIs generally pass
   model-independent information.

   Within an engine using a TMSM-based security model, outgoing SNMP
   messages are passed unencrypted from the message dispatcher to the
   transport mapping, and incoming messages are passed unencrypted from
   the transport mapping to the message dispatcher.

   The security parameters include a model-independent identifier of the
   security "principal", the security model used to perform the
   authentication, and which SNMP-specific security services were
   (should be) applied to the message (authentication and/or privacy).

   In the RFC3411 architecture, which reflects the USM security model
   design, the messaging model must unpack SNMP-specific security
   parameters from an incoming message before calling a specific
   security model to authenticate and decrypt an incoming message,
   perform integrity checking, and translate model-specific security
   parameters into model-independent parameters.

   In the TMSM approach, the security-model specific parameters are not
   carried in the SNMP message.  The parameters are provided by SNMP
   applications for outgoing messages, and the parameters for incoming
   messages are extracted from the transport layer by the security-
   model-specific transport mapping before the message is passed to the
   message processing subsystem.

   For outgoing messages, it is necessary to have an MPSP SMSP because it is
   the MPSP SMSP that actually creates the message from its component parts.
   Whether there are any security services provided by the MPSP SMSP for an
   outgoing message is model-dependent.

   For incoming messages, there might be security functionality that can
   only be handled after the message version is known.  The message
   version is determined by the Message Processing model and passed to
   the MPSP SMSP via the processIncoming() ASI.

   The RFC3411 architecture has no ASI parameters for passing security
   information between the transport mapping and the dispatcher, and
   between the dispatcher and the message processing model.  If there is
   a need to have an MPSP SMSP called from the message processing model to,
   for example, verify that msgFlags and the transport security are
   consistent, then it will be necessary to pass the model-dependent
   security parameters from the TMSP through to the MPSP. SMSP.

   This document describes a cache, into which the TMSP puts information
   about the security applied to an incoming message, and an MPSP SMSP
   extracts that information from the cache.  Given that there may be
   multiple TM-security caches, a tmStateReference tmSessionReference is passed as an
   extra parameter in the ASIs between the transport mapping and the
   messaging security model.so model, so the MPSP SMSP knows which cache of
   information to consult.

   This approach does create dependencies between a model-specific TMSP
   and a corresponding specific MPSP. SMSP.  This approach of passing a model-
   independent reference is consistent with the securityStateReference
   cache already being passed around in the RFC3411 ASIs.

2.3.  Session Requirements

   Throughout this document, the term session is used.  Some underlying
   secure transports will have a notion of session.  Some underlying
   secure transports might enable the use of channels or other session-
   like thing.  In this document the term session refers to an
   association between two SNMP engines that permits the secure
   transmission of one or more SNMP messages within the lifetime of the
   session.  How the session is actually established, opened, closed, or
   maintained is specific to a particular security model.

   Sessions are not part of the SNMP architecture described in
   [RFC3411], but are considered desirable because the cost of
   authentication can be amortized over potentially many transactions.

   It is important to note that the architecture described in [RFC3411]
   does not include a session selector in the Abstract Service
   Interfaces, and neither is that done for this architectural
   extension, so an SNMP application cannot select the session except by
   passing a unique combination of transport address, securityName,
   securityModel, and securityLevel.

   All TMSM-based security models should discuss the impact of sessions
   on SNMP usage, including how to establish/open a TMSM session (i.e.,
   how it maps to the concepts of session-like things of the underlying
   protocol), how to behave when a TMSM session cannot be established,
   how to close a TMSM session (and the underlying protocol equivalent)
   properly, how to behave when a TMSM session is closed improperly, the
   session security properties, session establishment overhead, and
   session maintenance overhead.

   To reduce redundancy, this document will discuss aspects that are
   expected to be common to all TMSM-based security model sessions.

2.3.1.  Session Establishment Requirements

   SNMP applications must provide the transport address, securityName,
   securityModel, and securityLevel to be used for a session.

   SNMP Applications typically have no knowledge of whether the session
   that will be used to carry commands was initially established as a
   notification session, or a request-response session, and SHOULD NOT
   make any assumptions based on knowing the direction of the session.
   If an administrator or security model designer wants to differentiate
   a session established for different purposes, such as a notification
   session versus a request-response session, the application can use
   different securityNames or transport addresses (e.g., port 161 vs vs.
   port 162) for different purposes.

   An SNMP engine containing an application that initiates
   communication, e.g., a Command Generator or Notification Originator,
   MUST be able to attempt to establish a session for delivery if a
   session does not yet exist.  If a session cannot be established then
   the message is discarded.

   Sessions are usually established by the transport mapping security
   processor when no appropriate session is found for an outgoing
   message, but sessions may be established in advance to support
   features such as notifications and call-home.  How sessions are
   established in advance is beyond the scope of this document.

   Sessions are initiated by notification originators when there is no
   currently established connection that can be used to send the
   notification.  For a client-server security protocol, this may
   require provisioning authentication credentials on the agent, either
   statically or dynamically, so the client/agent can successfully
   authenticate to a notification receiver.

   A TMSM-based security model must be able to determine whether a
   session does or does not exist, and must be able to determine which
   session has the appropriate security characteristics (transport
   address, securityName, securityModel, and securityLevel) for an
   outgoing message.

   A TMSM security model implementation MAY reuse an already established
   session with the appropriate transport address, securityName,
   securityModel, and securityLevel characteristics for delivery of a
   message originated by a different type of application than originally
   caused the session to be created.  For example, an implementation
   that has an existing session originally established to receive a
   request may use that session to send an outgoing notification, and
   may use a session that was originally established to send a
   notification to send a request.  Responses are expected to be
   returned using the same session that carried the corresponding
   request message.  Reuse is not required for conformance.

   If a session can be reused for a different type of message, but a
   receiver is not prepared to accept different message types over the
   same session, then the message MAY be dropped by the manager.

2.3.2.  Session Maintenance Requirements

   A TMSM-based security model can tear down sessions as needed.  It may
   be necessary for some implementations to tear down sessions as the
   result of resource constraints, for example.

   The decision to tear down a session is implementation-dependent.
   While it is possible for an implementation to automatically tear down
   each session once an operation has completed, this is not recommended
   for anticipated performance reasons.  How an implementation
   determines that an operation has completed, including all potential
   error paths, is implementation-dependent.

   Implementations should be careful to not tear down a session between
   the time a request is received and the time the response is sent.
   The elements of procedure for TMSM-based security models should be
   sure to describe the expected behavior when no session exists for a
   response.

   The elements of procedure may discuss when cached information can be
   discarded, and the timing of cache cleanup may have security
   implications, but cache memory management is an implementation issue.

   If a security model defines MIB module objects to maintain session
   state information, then the security model MUST describe what happens
   to the objects when a related session is torn down, since this will
   impact interoperability of the MIB module.

2.3.3.  Message security versus session security

   A TMSM session is associated with state information that is
   maintained for its lifetime.  This state information allows for the
   application of various security services to TMSM-based security
   models.  Cryptographic keys established at the beginning of the
   session SHOULD be used to provide authentication, integrity checking,
   and encryption services for data that is communicated during the
   session.  The cryptographic protocols used to establish keys for a
   TMSM-based security model session SHOULD ensure that fresh new
   session keys are generated for each session.  If each session uses
   new session keys, then messages cannot be replayed from one session
   to another.  In addition sequence information MAY be maintained in
   the session which can be used to prevent the replay and reordering of
   messages within a session.

   A TMSM session will typically have a single transport address,
   securityName and securityLevel associated with it.  If an exchange
   between communicating engines would require a different securityLevel
   or would be on behalf of a different securityName, then another
   session would be needed.  An immediate consequence of this is that
   implementations should be able to maintain some reasonable number of
   concurrent sessions.

   For TMSM models, securityName is typically specified during session
   setup, and associated with the session identifier.

   SNMPv3 was designed to support multiple levels of security,
   selectable on a per-message basis by an SNMP application, because
   there is not much value in using encryption for a Commander Generator
   to poll for non-sensitive performance data on thousands of interfaces
   every ten minutes; the encryption adds significant overhead to
   processing of the messages.

   Some TMSM-based security models MAY support only specific
   authentication and encryption services, such as requiring all
   messages to be carried using both authentication and encryption,
   regardless of the security level requested by an SNMP application.

   Some security models may use an underlying transport that provides a
   per-message requested level of authentication and encryption
   services.  For example, if a session is created as 'authPriv', then
   keys for encryption could still be negotiated once at the beginning
   of the session.  But if a message is presented to the session with a
   security level of authNoPriv, then that message could simply be
   authenticated and not encrypted within the same transport session.
   Whether this is possible depends on the security model and the secure
   transport used.

   If the underlying transport layer security was configurable on a per-
   message basis, a TMSM-based security model could have a security-
   model-specific MIB module with configurable maxSecurityLevel and a
   minSecurityLevel objects to identify the range of possible levels.  A
   session's maxSecurityLevel would identify the maximum security it
   could provide, and a session created with a minSecurityLevel of
   authPriv would reject an attempt to send an authNoPriv message.  The
   elements of procedure of the security model would need to describe
   the procedures to enable this determination.

   For security models that do not support variable security services in
   one session, multiple sessions could be established with different
   security levels, and for every packet the SNMP engine could select
   the appropriate session based on the requested securityLevel.  Some
   SNMP entities are resource-constrained.  Adding sessions increases
   the need for resources, but so does encrypting unnecessarily.
   Designers of security models should consider the trade offs for
   resource-constrained devices.

3.  Scenario Diagrams for TMSM

   RFC3411 section 4.6 provides scenario diagrams to illustrate how an
   outgoing message is created, and 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 interfaces required
   to receive an SNMP message from the network, or to send an SNMP
   message to the network.

3.1.  Command Generator or 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 returned (asynchronously) to that
   application.

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

3.2.  Command Responder

   This diagram shows how a Command Responder or Notification Receiver
   application registers for handling a pduType, how a PDU is dispatched
   to the application after an SNMP message is received, and how the
   Response is (asynchronously) send back to 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      |     |                    |
   :                         | to Network   |     |                    |
   :                         |              v     |                    |

4.  Abstract Service Interfaces for TMSM

4.1.  Existing Abstract Service Interfaces  Message Formats

   The OUT parameters syntax of the prepareOutgoingMessage() ASI are used an SNMP message using this Security Model adheres to
   pass information from
   the message format defined in the version-specific Message Processing
   Model document (for example [RFC3412]).  At the time of this writing,
   there are three defined message formats - SNMPv1, SNMPv2c, and
   SNMPv3.  SNMPv1 and SNMPv2c have been declared Historic, so this memo
   only deals with SNMPv3 messages.

   The processing model to is compatible with the dispatcher RFC 3412 primitives,
   generateRequestMsg() and on to processIncomingMsg(), that show the transport mapping:

   statusInformation = data
   flow between the Message Processor and the SMSP.

4.1.  SNMPv3 Message Fields

   The SNMPv3Message SEQUENCE is defined in [RFC3412] and [RFC3416].

   SNMPv3MessageSyntax DEFINITIONS IMPLICIT TAGS ::= BEGIN

          SNMPv3Message ::= SEQUENCE {
              -- success or errorIndication
   prepareOutgoingMessage(
   IN  transportDomain identify the layout of the SNMPv3Message
              -- transport domain to be used
   IN  transportAddress this element is in same position as in SNMPv1
              -- transport address to be and SNMPv2c, allowing recognition
              -- the value 3 is used
   IN  messageProcessingModel for snmpv3
              msgVersion INTEGER ( 0 .. 2147483647 ),
              -- typically, SNMP version
   IN  securityModel administrative parameters
              msgGlobalData HeaderData,
              -- security model-specific parameters
              -- format defined by Security Model to use
   IN  securityName
              msgSecurityParameters OCTET STRING,
              msgData  ScopedPduData
          }

          HeaderData ::= SEQUENCE {
              msgID      INTEGER (0..2147483647),
              msgMaxSize INTEGER (484..2147483647),

              msgFlags   OCTET STRING (SIZE(1)),
                         -- on behalf of this principal
   IN  securityLevel  .... ...1   authFlag
                         -- Level of Security requested
   IN  contextEngineID  .... ..1.   privFlag
                         -- data from/at this entity
   IN  contextName  .... .1..   reportableFlag
                         -- data from/in this context
   IN  pduVersion               -- the version of the PDU
   IN  PDU                      -- SNMP Protocol Data Unit
   IN  expectResponse              Please observe:
                         -- TRUE or FALSE
   IN  sendPduHandle  .... ..00   is OK, means noAuthNoPriv
                         -- the handle for matching
                                   incoming responses
   OUT  destTransportDomain  .... ..01   is OK, means authNoPriv
                         -- destination transport domain
   OUT  destTransportAddress  .... ..10   reserved, MUST NOT be used.
                         -- destination transport address
   OUT  outgoingMessage  .... ..11   is OK, means authPriv

              msgSecurityModel INTEGER (1..2147483647)
          }

          ScopedPduData ::= CHOICE {
              plaintext    ScopedPDU,
              encryptedPDU OCTET STRING  -- the message to send
   OUT  outgoingMessageLength encrypted scopedPDU value
          }

          ScopedPDU ::= SEQUENCE {
              contextEngineID  OCTET STRING,
              contextName      OCTET STRING,
              data             ANY -- its length
               )

4.2.  TMSM Abstract Service Interfaces

   A set of abstract service interfaces have been e.g., PDUs as defined within this
   document to describe the conceptual data flows between the Transport
   Mapping Security Models and adjacent components in the system. [RFC3416]
          }
      END

   The sendMessage ASI following describes how any TMSM model SHOULD treat certain
   fields in the message:

4.1.1.  msgGlobalData

   msgGlobalData is used opaque to pass a message from the Dispatcher to TMSM security model.  The values are set
   by the transport mapping for sending.

   statusInformation =
   sendMessage(
   IN   destTransportDomain           -- transport domain to Message Processing model (e.g., SNMPv3 Message Processing),
   and SHOULD NOT be used
   IN   destTransportAddress          -- transport address to modified by a TMSM security model.

   The msgSecurityModel field should be used
   IN   outgoingMessage               -- set by the message to send
   IN   outgoingMessageLength         -- its length
   IN   tmStateReference
   OUT  sessionID
    )

   The recvMessage ASI is used Message Processing
   model to pass a message value from the transport
   mapping to the Dispatcher.

   statusInformation =
   recvMessage(
   IN   destTransportDomain           -- transport domain to be used
   IN   destTransportAddress          -- transport address SnmpSecurityModel enumeration [RFC3411] to be used
   IN   incomingMessage               -- the message received
   IN   incomingMessageLength         -- its length
   OUT   tmStateReference
   OUT   sessionID
    )

   The Transport Mapping Security Model provides
   identify the specific TMSM model.  Each standards-track TMSM model
   should have an enumeration assigned by IANA.  Each enterprise-
   specific security model should have an enumeration assigned following
   primitives to pass data back and forth between
   instructions in the description of the SnmpSecurityModel TEXTUAL-
   CONVENTION from RFC3411.

   The msgFlags have the same values for a TMSM model as for the USM
   model.

4.1.1.1.  securityLevel and specific
   TMSM-based msgFlags

   For an outgoing message, msgFlags is the requested security models, which for the
   message; if a TMSM cannot provide the interface to requested securityLevel, the
   underlying secure transport service.  Each TMSM-based security
   model
   should define MUST describe a standard behavior that is followed for that
   situation.  If the security-model-specific elements TMSM cannot provide at least the requested level
   of procedure for security, the TMSM MUST discard the openSession(), closeSession(), txMessage(), request and rxMessage()
   interfaces.

   statusInformation =
   txMessage(
   IN   destTransportDomain           -- transport domain SHOULD notify the
   message processing model that the request failed.

   For an outgoing message, if the TMSM is able to provide stronger than
   requested security, that may be used
   IN   destTransportAddress          -- acceptable.  The transport address layer
   protocol would need to be used
   IN   outgoingMessage               -- the message indicate to send
   IN   outgoingMessageLength         -- its length
   IN   tmStateReference
   OUT  sessionID
    )

   statusInformation =
   rxMessage(
   IN   destTransportDomain           -- transport domain the receiver what security has
   been applied to be used
   IN   destTransportAddress          -- transport address the actual message.  To avoid the need to be used
   IN   incomingMessage               -- mess with
   the ASN.1 encoding, the SNMPv3 message carries the requested
   msgFlags, not the actual securityLevel applied to send
   IN   incomingMessageLength         -- its length
   OUT   tmStateReference
    )

    statusInformation =
   openSession(
   IN   transportDomain              -- transport domain to be used
   IN   transportAddress             -- the message.  If a
   message format other than SNMPv3 is used, then the new message may
   carry the more accurate securityLevel in the SNMP message.

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

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

4.1.2.  msgSecurityParameters

   The field msgSecurityParameters carries model-dependent security
   information between engines.  When a security model does not utilize
   this field, its value MUST be the BER serialization of a zero-length
   OCTET STRING, to prevent its being used
   IN   tmStateReference
   OUT  sessionID
    )

   statusInformation =
   closeSession(
   IN   sessionID
    ) in a manner that could be
   damaging, such as for carrying a virus or worm.

   RFC3412 defines two primitives, generateRequestMsg() and
   processIncomingMsg() which require the specification of an
   authoritative SNMP entity.  The meaning of authoritative is model
   dependent.

5.  Cached Information and References

   The

   he RFC3411 architecture uses caches to store dynamic model-specific
   information, and uses references in the ASIs to indicate in a model-
   independent manner which cached information must flow between
   subsytems.

5.1.  securityStateReference Cached Security Data

   From RFC3411:
   subsystems.  For most TMSM models, there are two levels of state that
   need to be maintained: the session state, and the message security
   state.

5.1.  tmSessionReference Cached Session Data

   The tmSessionReference is used to pass references to the appropriate
   session information between the TMSP and SMSP through the ASIs.

   The TMSP may provide only some aspects of security, and leave some
   aspects to the SMSP. tmSessionReference should be used to pass any
   parameters, in a model- and mechanism-specific format, that will be
   needed to coordinate the activities of the TMSP and SMSP, plus the
   parameters subsequently passed in securityStateReference.

   The security model has the responsibility for explicitly releasing
   the complete tmSessionReference and possibly deleting the associated
   LCD information when the session is destroyed.

5.2.  securityStateReference Cached Security Data

   From RFC3411: "For each message received, the Security Model caches
   the state information such that a Response message can be generated
   using the same security information, even if the Local Configuration
   Datastore is altered between the time of the incoming request and the
   outgoing response.

   A Message Processing Model has the responsibility for explicitly
   releasing the cached data if such data is no longer needed.  To
   enable this, an abstract securityStateReference data element is
   passed from the Security Model to the Message Processing Model.  The
   cached security data may be implicitly released via the generation of
   a response, or explicitly released by using the stateRelease
   primitive, as described in RFC3411 section 4.5.1."

   For the TMSM approach, the TMSP may need to provide the information
   to be stored in the securityStateReference to the message processing
   model. such as the security-model-independent securityName,
   securityLevel, and securityModel parameters. parameters, and the transport
   address, and transport type.  For responses, the messaging model may
   need to pass the parameters back to the TMSP.

   This document will differentiate the tmStateReference tmSessionReference provided by
   the TMSP to the MPSP, SMSP, from the securityStateReference provided by the
   MPSP
   SMSP to the Dispatcher.  This document does not specify an
   implementation strategy, only an abstract discussion of the data that
   must flow between subsystems.  An implementation MAY use one cache
   and one reference to serve both functions, but an implementer must be
   aware of the cache-release issues to prevent the cache from being
   released before the transport mapping has had an opportunity to
   extract the information it needs.

5.2.  tmStateReference Cached Security Data

   A tmStateReference is used

6.  Abstract Service Interfaces for TMSM

   Abstract service interfaces have been defined by RFC 3411 to pass describe
   the conceptual data flows between the TMSP and the
   MPSP, similar to the securityStateReference described in RFC3412.  A
   reference to this cache can be envisioned as being appended to the
   ASIs various subsystems within an
   SNMP entity.  TMSM security models use some of these conceptual data
   flows when communicating between subsystems, such as the TM dispatcher
   and the MP.

   The TMSP may provide only some aspects Message Processing Subsystem.

   To simplify the elements of security, and leave some
   aspects to procedure, the MPSP. tmStateReference release of state
   information is not always explicitly specified.  As a general rule,
   if state information is available when a message gets discarded, the
   message-state information should also be used to pass any
   parameters, in a model- released, and mechanism-specific format, that will be
   needed to coordinate the activities of the TMSP and MPSP, plus the
   parameters subsequently passed in securityStateReference.  For
   example, if state
   information is available when a session is closed, the TMSP session state
   information should also be released.

   An error indication may provide privacy return an OID and data integrity value for an incremented
   counter and
   authentication a value for securityLevel, and authorization policy retrievals, or some subset of
   these features, depending on the features available in the transport
   mechanisms.  A field in tmStateReference should identify which
   services were provided values for contextEngineID
   and contextName for each received message by the TMSP, the
   securityLevel applied to counter, and the received message, securityStateReference if
   the model-specific
   security identity, information is available at the session identifier for session based transport
   security, and so on.

6.  Integration with point where the SNMPv3 error is
   detected.

6.1.  Generating an Outgoing SNMP Message Format

   TMSM proposals can use the SNMPv3 message format, defined in RFC3412,
   section 6.

   This section discusses how the fields could be reused.

6.1.  msgVersion

   For proposals that reuse describes the SNMPv3 procedure followed by an RFC3411-
   compatible system whenever it generates a message format, this field should
   contain the value 3.

6.2.  msgGlobalData

   The fields msgID and msgMaxSize are used identically for the TMSM
   models containing a
   management operation (such as for the USM model.

   The msgSecurityModel field should a request, a response, a notification,
   or a report) on behalf of a user.

   statusInformation =          -- success or errorIndication
   prepareOutgoingMessage(
   IN  transportDomain          -- transport domain to be set used
   IN  transportAddress         -- transport address to a value from the
   SnmpSecurityModel enumeration [RFC3411] be used
   IN  messageProcessingModel   -- typically, SNMP version
   IN  securityModel            -- Security Model to identify the specific TMSM
   model.  Each standards-track TMSM model should have an enumeration
   assigned by IANA.  Each enterprise-specific security model should
   have an enumeration assigned following instructions in 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
   description version of the SnmpSecurityModel TEXTUAL-CONVENTION from RFC3411.

   The msgSecurityParameters field would carry security information
   required PDU
   IN  PDU                      -- SNMP Protocol Data Unit
   IN  expectResponse           -- TRUE or FALSE
   IN  sendPduHandle            -- the handle for matching
                                   incoming responses
   OUT  destTransportDomain     -- destination transport domain
   OUT  destTransportAddress    -- destination transport address
   OUT  outgoingMessage         -- the message security processing.  It is unclear whether to send
   OUT  outgoingMessageLength   -- its length
   OUT  tmSessionReference
               )

   Note that tmSessionReference has been added to this
   field would be useful or what ASI.

   The IN parameters would be carried to support
   security, since message security is provided by an external process,
   and msgSecurityParameters of the prepareOutgoingMessage() ASI are not used by to
   pass information from the access control
   subsystem.

   RFC3412 defines two primitives, generateRequestMsg() and
   processIncomingMsg() which require dispatcher (for the specification of an
   authoritative SNMP entity. [discuss] We need application subsystem)
   to discuss what the
   meaning of authoritative would be in a TMSM environment, whether the
   specific services provided in USM security message processing subsystem.

   The abstract service primitive from msgSecurityParameters
   still are needed, and how the a Message Processing model provides this
   information Model to the security model via generateRequestMsg() and
   processIncomingMsg() primitives.  RFC3412 specifies that "The data in
   the msgSecurityParameters field is used exclusively by the a
   Security
   Model, and Model to generate the contents and format components of the data is defined by the
   Security Model.  This OCTET STRING is not interpreted by the v3MP,
   but a Request message is passed
   generateRequestMsg().

   The abstract service primitive from a Message Processing Model to the local implementation of the a
   Security Model
   indicated by the msgSecurityModel field in the message."

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

6.3.  securityLevel and msgFlags

   For an outgoing message, msgFlags is
   generateResponseMsg().

   Upon completion of the requested security for SMSP processing, the
   message; if a TMSM cannot provide Security model returns
   statusInformation.  If the requested securityLevel, process was successful, the
   model MUST describe a standard behavior that completed
   message is followed for that
   situation. returned.  If the TMSM cannot provide at least the requested level process was not successful, then an
   errorIndication is returned.

   The OUT parameters of security, the TMSM MUST discard the request and SHOULD notify prepareOutgoingMessage() ASI are used to
   pass information from the message processing model that the request failed.

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

   For an outgoing message, if on to the TMSM transport mapping:

6.2.  TMSP for an Outgoing Message

   The sendMessage ASI is able used to pass a message from the Dispatcher to
   the appropriate transport mapping for sending.

   statusInformation =
   sendMessage(
   IN   destTransportDomain           -- transport domain to provide stronger than
   requested security, that may be acceptable.  The used
   IN   destTransportAddress          -- transport layer
   protocol would need address to indicate be used
   IN   outgoingMessage               -- the message to send
   IN   outgoingMessageLength         -- its length
   IN   tmSessionReference
    )

   The Transport Mapping Security Model provides the receiver what security has
   been applied following
   primitives to pass data back and forth between the actual message.  To avoid TMSM and specific
   TMSM-based security models, which provide the need interface to mess with the ASN.1 encoding,
   underlying secure transport service.  Each TMSM-based security model
   should define the SNMPv3 message carries security-model-specific elements of procedure for
   the requested
   msgFlags, openSession() and closeSession() interfaces.

    statusInformation =
   openSession(
   IN   transportDomain              -- transport domain to be used
   IN   transportAddress             -- transport address to be used
   IN   tmSessionReference
    )

   statusInformation =
   closeSession(
   IN   tmSessionReference
    )

6.3.  Processing an Incoming SNMP Message

6.3.1.  TMSP for an Incoming Message

   If one does not exist, the actual securityLevel applied TMSP will need to create an entry in a
   Local Configuration Datastore referenced by tmSessionReference.  This
   information will include transportDomain, transportAddress, the
   securityModel, the securityLevel, and the securityName, plus any
   model or mechanism-specific details.  How this information is
   determined is model-specific.

   The recvMessage ASI is used to the message.  If pass a message format other than SNMPv3 is used, then the new message may
   carry the more accurate securityLevel in from the SNMP message.

   For an incoming message, transport
   mapping to the receiving TMSM knows what must Dispatcher.

   statusInformation =
   recvMessage(
   IN   destTransportDomain           -- transport domain to be done used
   IN   destTransportAddress          -- transport address to process be used
   IN   incomingMessage               -- the message based on received
   IN   incomingMessageLength         -- its length
   IN   tmSessionReference
    )

6.3.2.  Prepare Data Elements from Incoming Messages

   The abstract service primitive from the Dispatcher to a Message
   Processing Model for a received message is:

   result =                       -- SUCCESS or errorIndication
   prepareDataElements(
   IN   transportDomain           -- origin transport layer mechanisms.  If
   the underlying domain
   IN   transportAddress          -- origin transport security mechanisms for the receiver cannot
   provide the matching securityLevel, then address
   IN   wholeMsg                  -- as received from the message should follow network
   IN   wholeMsgLength            -- as received from the standard behaviors for network
   IN   tmSessionReference          -- from the transport security mechanism, or be
   discarded silently.

   Part mapping
   OUT  messageProcessingModel    -- typically, SNMP version
   OUT  securityModel             -- Security Model to use
   OUT  securityName              -- on behalf of this principal
   OUT  securityLevel             -- Level of Security requested
   OUT  contextEngineID           -- data from/at this entity
   OUT  contextName               -- data from/in this context
   OUT  pduVersion                -- the responsibility version of the TMSM is PDU
   OUT  PDU                       -- SNMP Protocol Data Unit
   OUT  pduType                   -- SNMP PDU type
   OUT  sendPduHandle             -- handle for matched request
   OUT  maxSizeResponseScopedPDU  -- maximum size sender can accept
   OUT  statusInformation         -- success or errorIndication
                                  -- error counter OID/value if error
   OUT  stateReference            -- reference to ensure that the actual
   security provided by the underlying transport layer security
   mechanisms is configured state information
                                  -- to be used for possible Response
   )

   Note that tmSessionReference has been added to meet or exceed this ASI.

6.3.3.  MPSP for an Incoming Message

   This section describes the securityLevel required procedure followed by the msgFlags in the SNMP message.  When the MPSP processes the
   incoming message, SMSP whenever it should compare
   receives an incoming message containing a management operation on
   behalf of a user from a Message Processing model.

   The Message Processing Model extracts some information from the msgFlags field
   wholeMsg.  The abstract service primitive from a Message Processing
   Model to the
   securityLevel actually provided Security Subsystem for the a received message by is::

   statusInformation =  -- errorIndication or success
                            -- error counter OID/value if error
   processIncomingMsg(
   IN   messageProcessingModel    -- typically, SNMP version
   IN   maxMessageSize            -- of the transport
   layer security.  If they differ, sending SNMP entity
   IN   securityParameters        -- for the MPSP should determine whether received message
   IN   securityModel             -- for the changed received message
   IN   securityLevel is acceptable.  If not, it should discard
   the message.  Depending             -- Level of Security
   IN   wholeMsg                  -- as received on the model, wire
   IN   wholeMsgLength            -- length as received on the MPSP may issue a reportPDU
   with wire
   IN   tmSessionReference          -- from the XXXXXXX model-specific counter.

7.  Prepare an Outgoing transport mapping
   OUT  securityEngineID          -- authoritative SNMP Message

   Following RFC3412, section 7.1, the SNMPv3 message processing model
   uses the generateResponseMsg() or generateRequestMsg() primitives, to
   call entity
   OUT  securityName              -- identification of the MPSP.  The principal
   OUT  scopedPDU,                -- message processing model, or the MPSP it calls,
   may need (plaintext) payload
   OUT  maxSizeResponseScopedPDU  -- maximum size sender can handle
   OUT  securityStateReference    -- reference to put information into the tmStateReference cache for use
   by the TMSP, such as:

      tmSecurityStateReference - the unique identifier security state
    )                         -- information, needed for the cached
      information
      tmTransportDomain
      tmTransportAddress
      tmSecurityModel - an indicator of which mechanisms response

   1) The securityEngineID is set to use
      tmSecurityName - a value in a model-specific identifier of manner.
   If the security
      principal
      tmSecurityLevel - an indicator of which security services are
      requested
   A tmStateReference cache may contain additional information such as
      tmSessionID
      tmSessionKey
      tmSessionMsgID

8.  Prepare Data Elements from an Incoming SNMP Message

   For an incoming message, securityEngineID is not utilized by the TMSP will need specific model, then
   it should be set to put information from the transport mechanisms used into local snmpEngineID, to satisfy the tmStateReference so SNMPv3
   message processing model in RFC 3412 section 7.2 13a).

   2) Extract the MPSP
   can extract value of securityName from the information and add it conceptually to Local Configuration
   Datastore entry referenced by tmSessionReference.

   3) The scopedPDU component is extracted from the
   securityStateReference. wholeMsg.

   4) The tmStateReference cache will likely contain at least maxSizeResponseScopedPDU is calculated.  This is the following
   information:
      tmStateReference - a unique identifier maximum
   size allowed for the cached information
      tmSecurityStateReference - the unique identifier a scopedPDU for the cached
      information
      tmTransportDomain
      tmTransportAddress
      tmSecurityModel - an indicator of which mechanisms to use
      tmSecurityName - a model-specific identifier of the security
      principal
      tmSecurityLevel - an indicator of which possible Response message.

   5)The security services are
      requested
      tmAuthProtocol
      tmPrivProtocol
   and may contain additional information such data is cached as
      tmSessionID
      tmSessionKey
      tmSessionMsgID

9.  Notifications

   For notifications, if the cache has been released cachedSecurityData, so that a
   possible response to this message can and then session
   closed, then the MPSP will request use the TMSP same security
   parameters.  Then securityStateReference is set for subsequent
   reference to establish this cached data.

   4) The statusInformation is set to success and a session,
   populate return is made to
   the cache, and pass calling module passing back the securityStateReference to OUT parameters as specified in
   the MPSP.

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

10. processIncomingMsg primitive.

7.  The TMSM MIB Module

   This memo defines a portion of the Management Information Base (MIB)
   for managing sessions statistics in the Transport Mapping Security Model extension.

10.1.

7.1.  Structure of the MIB Module

   Objects in this MIB module are arranged into subtrees.  Each subtree
   is organized as a set of related objects.  The overall structure and
   assignment of objects to their subtrees, and the intended purpose of
   each subtree, is shown below.

10.1.1.  The tmsmNotifications Subtree

   This subtree contains notifications to alert other entities to events
   that are applicable to all security models based on the Transport
   Mapping Security Model extension.

10.1.2.

7.1.1.  The tmsmStats Subtree

   This subtree contains security-model-independent counters which are
   applicable to all security models based on the .Transport Mapping
   Security Model extension.  This subtree provides information for
   identifying fault conditions and performance degradation.

10.1.3.  The tmsmSession Subtree

   This subtree contains security-model-independent information about
   sessions which are applicable to all security models based on the
   Transport Mapping Security Model extension.

10.2.

7.2.  Relationship to Other MIB Modules

   Some management objects defined in other MIB modules are applicable
   to an entity implementing this MIB.  In particular, it is assumed
   that an entity implementing the TMSM-MIB module will also implement
   the SNMPv2-MIB [RFC3418].

   This MIB module is expected to be used with the MIB modules defined
   for managing specific security models that are based on the TMSM
   extension.  This MIB module is designed to be security-model
   independent, and contains objects useful for managing common aspects
   of any TMSM-based security model.  Specific security models may
   define a MIB module to contain security-model-dependent information.

10.2.1.

7.2.1.  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

10.2.2.

7.2.2.  MIB Modules Required for IMPORTS

   The

   The. following MIB module imports items from [RFC2578], [RFC2579],
   [RFC2580], [RFC3411], and [RFC3419]

11.

7.3.  Definitions

   TMSM-MIB DEFINITIONS ::= BEGIN
   IMPORTS
       MODULE-IDENTITY, OBJECT-TYPE,
       mib-2, Integer32, Unsigned32, Gauge32
         FROM SNMPv2-SMI
       TestAndIncr, StorageType, RowStatus
         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 "200604200000Z"
       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
                     FutureWei Technologies
                     1700 Alma Drive, Suite 100
                     Plano, Texas 75075
                     USA
                     +1 603-436-8634
                     dharrington@huawei.com
                       "
          DESCRIPTION  "The Transport Mapping Security Model
                                    MIB Module

                        Copyright (C) The Internet Society (2006). This
                        version of this MIB module is part of RFC XXXX;
                        see the RFC itself for full legal notices.
   -- NOTE to RFC editor: replace XXXX with actual RFC number
   --                     for this document and remove this note
                       "
          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 TMSM-MIB
   -- ---------------------------------------------------------- --

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

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

   -- Textual Conventions
   SessionIndex ::= TEXTUAL-CONVENTION
       DISPLAY-HINT "d"
       STATUS       current
       DESCRIPTION
           "A unique value, greater than zero, identifying a transport
            mapping security model session. The value must remain
            constant for the duration of a session. New values should
            be assigned in such a way that reuse of recently used
            values is avoided."
       SYNTAX Integer (1..2147483647)

   SessionIndexOrZero TEXTUAL-CONVENTION
       DISPLAY-HINT "d"
       STATUS       current
       DESCRIPTION
           "This extension of the TmsmSessionId permits the additional
            value zero. The meaning of the value zero is object-specific
            and must therefore be defined as part of the description of
            any object which uses this syntax. Examples of the usage of
            zero might include situations where a session was unknown
            or where none or all sessions need to be referenced."
       SYNTAX Integer (0..2147483647)

   -- Notifications for the Transport Model Security Model extension

   -- Statistics for the Transport Model Security Model extension

   tmsmStats         OBJECT IDENTIFIER ::= { tmsmObjects 1 }

   tmsmSessionOpenErrors  OBJECT-TYPE
       SYNTAX       Counter32
       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION "The number of times an openSession() request
                  failed to open a Session.
                   "
       ::= { tmsmStats 1 }

   -- 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 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 open sessions.
                   " tmsmMIB 0 }
   tmsmObjects       OBJECT IDENTIFIER ::= { tmsmSession tmsmMIB 1 }
   tmsmConformance   OBJECT IDENTIFIER ::= { tmsmMIB 2 }

   tmsmSessionMaxSupported  OBJECT-TYPE
       SYNTAX       Unsigned32
       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION "The maximum number of open sessions supported.
                    The value zero indicates

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

   -- Textual Conventions

   -- Notifications for the maximum is dynamic.
                   " Transport Model Security Model extension

   -- Statistics for the Transport Model Security Model extension

   tmsmStats         OBJECT IDENTIFIER ::= { tmsmSession 3 tmsmObjects 1 }

   tmsmSessionOpenErrors  OBJECT-TYPE
       SYNTAX       Counter32
       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION "The number of times an openSession() request
                  failed to open a Session.
                   "
       ::= { tmsmSession 4 tmsmStats 1 }

   tmsmSessionSecurityLevelNotAvailableErrors

   tmsmSessionNoAvailableSessions  OBJECT-TYPE
       SYNTAX       Counter32
       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION "The number of times an outgoing a Response message
                  was
                  discarded dropped because a requested securityLevel could not
                  provided.
                   "
       ::= { tmsmSession 5 }

   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 6 }

   tmsmSessionEntry     OBJECT-TYPE
       SYNTAX       TmsmSessionEntry
       MAX-ACCESS   not-accessible
       STATUS       current
       DESCRIPTION "A corresponding
                  session configured in the SNMP engine's Local
                    Configuration Datastore (LCD) for Transport Mapping
                    Security Models.

                   "
       INDEX       { tmsmSessionID }
       ::= { tmsmSessionTable 1 }

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

    tmsmSessionID  OBJECT-TYPE
       SYNTAX       SessionIndex
       MAX-ACCESS   not-accessible
       STATUS       current
       DESCRIPTION "A locally-unique identifier for a session. was no longer available.
                   "
       ::= { tmsmSessionEntry 1 tmsmStats 2 }

    tmsmSessionTransport  OBJECT-TYPE
       SYNTAX       TransportAddressType
       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION "The transport domain associated with this session.
                   "

   -- The tmsmSession Group

   tmsmSession          OBJECT IDENTIFIER ::= { tmsmSessionEntry tmsmObjects 2 }
    tmsmSessionAddress

   tmsmSessionCurrent  OBJECT-TYPE
       SYNTAX       TransportAddress       Gauge32
       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION "The transport address associated with this session. current number of open sessions.
                   "
       ::= { tmsmSessionEntry 3 tmsmSession 1 }

   tmsmSessionSecurityModel

   tmsmSessionMaxSupported  OBJECT-TYPE
       SYNTAX       SnmpSecurityModel       Unsigned32
       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 maximum number of open sessions supported.
                    The value zero indicates the principal
                    in Security Model independent format. maximum is dynamic.
                   "
       ::= { tmsmSessionEntry 5 tmsmSession 2 }

   tmsmSessionSecurityLevel

   tmsmSessionOpenErrors  OBJECT-TYPE
       SYNTAX      SnmpSecurityLevel       Counter32
       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION "The Level number of Security 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. times an openSession() request
                  failed to open a Session.
                   "
       DEFVAL      { authPriv }
       ::= { tmsmSessionEntry 6 tmsmSession 3 }

   tmsmSessionEngineID

   tmsmSessionSecurityLevelNotAvailableErrors  OBJECT-TYPE
       SYNTAX       SnmpEngineID       Counter32
       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION "The administratively-unique identifier for the
                    remote SNMP engine associated with this session. number of times an outgoing message was
                  discarded because a requested securityLevel could not
                  provided.
                   "
       ::= { tmsmSessionEntry 7 tmsmSession 4 }

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

   tmsmGroups OBJECT IDENTIFIER ::= { tmsmConformance 1 }

   tmsmCompliances OBJECT IDENTIFIER ::= { tmsmConformance 2 }

   -- -------------------------------------------------------------
   -- Units of conformance
   -- -------------------------------------------------------------
   tmsmGroup OBJECT-GROUP
       OBJECTS {
           tmsmSessionOpenErrors,
           tmsmSessionSecurityLevelNotAvailableErrors,
           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
                    TMSM architectural extension.
                   "

       ::= { 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

12.

8.  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 security considerations of that approach.

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

   There are a number of management objects defined in this MIB module
   with a MAX-ACCESS clause of read-write and/or read-create.  Such
   objects may be considered sensitive or vulnerable in some network
   environments.  The support for SET operations in a non-secure
   environment without proper protection can have a negative effect on
   network operations.  These are the tables and objects and their
   sensitivity/vulnerability:
   o  [discuss] Should it be possible for a manager to create or modify
      rows in the session table?  If so, then we may need the rowstatus
      object.  If the session table is read-only then we can probably
      eliminate the rowstatus.  If approach and multiple
   proposed configurations that would permit SNMP to utilize transport
   layer security services.  Each section containing a proposal should
   discuss the tabel security considerations of that approach.

   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.
   Perfect forward secrecy guarantees that compromise of long term
   secret keys does not read-only, then we
      need to list the tables and objects and state why they are
      sensitive. result in disclosure of past session keys.

   There are no management objects defined in this MIB module that have
   a MAX-ACCESS clause of read-write and/or read-create.  So, if this
   MIB module is 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 readable objects in this MIB module (i.e., objects with a
   MAX-ACCESS other than not-accessible) may be considered sensitive or
   vulnerable in some network environments.  It is thus important to
   control even GET and/or NOTIFY access to these objects and possibly
   to even encrypt the values of these objects when sending them over
   the network via SNMP.  These are the tables and objects and their
   sensitivity/vulnerability:
   o  [todo] list the tables and objects and state why they are
      sensitive.

   [discuss] how do we modify this section for an SNMP/SSH or other
   transport mapping security model?  If the security model provides for
   securityName/Level/Model then some of the normal boilerplate is not
   true.

   SNMP versions prior to SNMPv3 did not include adequate security.
   Even if the network itself is secure (for example by using IPSec),
   even then, there is no control as to who on the secure network is
   allowed to access and GET/SET (read/change/create/delete) the objects
   in this MIB module.

   It is RECOMMENDED that implementers consider the security features as
   provided by the SNMPv3 framework (see [RFC3410], section 8),
   including full support for the SNMPv3 cryptographic mechanisms (for
   authentication and privacy).

   Further, deployment of SNMP versions prior to SNMPv3 is NOT
   RECOMMENDED.  Instead, it is RECOMMENDED to deploy SNMPv3 and to
   enable cryptographic security.  It is then a customer/operator
   responsibility to ensure that the SNMP entity giving access to an
   instance of this MIB module is properly configured to give access to
   the objects only to those principals (users) that have legitimate
   rights to indeed GET or SET (change/create/delete) them.

13.

9.  IANA Considerations

   The MIB module in this document uses the following IANA-assigned
   OBJECT IDENTIFIER values recorded in the SMI Numbers registry:

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

   tmsmMIB        { mib-2 XXXX }

   Editor's Note (to be removed prior to publication):  the IANA is
   requested to assign a value for "XXXX" under the 'mib-2' subtree
   and to record the assignment in the SMI Numbers registry.  When
   the assignment has been made, the RFC Editor is asked to replace
   "XXXX" (here and in the MIB module) with the assigned value and to
   remove this note.

   [discuss] How do we add a new TransportType?

14.

10.  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

15.

11.  References

15.1.

11.1.  Normative References

   [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.

   [RFC4366]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
              and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 4366, April 2006.

   [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.

   [RFC3416]  Presuhn, R., "Version 2 of the Protocol Operations for the
              Simple Network Management Protocol (SNMP)", STD 62,
              RFC 3416, 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.

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

15.2.

11.2.  Informative References

   [RFC3410]               Case, J., Mundy, R., Partain, D., and B.
                           Stewart, "Introduction and Applicability
                           Statements for Internet-
              Standard 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.

   [RFC4422]               Melnikov, A. and K. Zeilenga, "Simple
                           Authentication and Security Layer (SASL)",
                           RFC 4422, June 2006.

   [I-D.ietf-netconf-ssh]  Wasserman, M. and T. Goddard, "Using the
                           NETCONF Configuration Protocol over Secure
                           Shell (SSH)", draft-ietf-netconf-ssh-06 (work
                           in progress), March 2006.

Appendix A.  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 will need to remove lines feeds from the second and
   third lines, which needed to be wrapped to fit into RFC limits.

A.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,

   tmSessionReference,,,,,,Out,In,,In,

Appendix B.  Why tmSecurityReference? tmSessionReference?

   This appendix considers why a cache-based approach was selected for
   passing parameters.  This section may be removed from subsequent
   revisions fo of the document.

   There are four approaches that could be used for passing information
   between the TMSP and an MPSP. SMSP.

   1.  one could define an ASI to supplement the existing ASIs, or
   2.  the TMSM could add a header to encapsulate the SNMP message,
   3.  the TMSM could utilize fields already defined in the existing
       SNMPv3 message, or
   4.  the TMSM could pass the information in an implementation-specific
       cache or via a MIB module.

B.1.  Define an Abstract Service Interface

   Abstract Service Interfaces (ASIs) [RFC3411] are defined by a set of
   primitives that specify the services provided and the abstract data
   elements that are to be passed when the services are invoked.
   Defining additional ASIs to pass the security and transport
   information from the transport mapping to a messaging security model
   has the advantage of being consistent with existing RFC3411/3412
   practice, and helps to ensure that any TMSM proposals pass the
   necessary data, and do not cause side effects by creating model-
   specific dependencies between itself and other models or other
   subsystems other than those that are clearly defined by an ASI.

B.2.  Using an Encapsulating Header

   A header could encapsulate the SNMP message to pass necessary
   information from the TMSP to the dispatcher and then to a messaging
   security model.  The message header would be included in the
   wholeMessage ASI parameter, and would be removed by a corresponding
   messaging model.  This would imply the (one and only) messaging
   dispatcher would need to be modified to determine which SNMP message
   version was involved, and a new message processing model would need
   to be developed that knew how to extract the header from the message
   and pass it to the MPSP. SMSP.

B.3.  Modifying Existing Fields in an SNMP Message

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

   If the fields in an incoming SNMPv3 message are changed by the TMSP
   before passing it to the MPSP, SMSP, then the TMSP will need to decode the
   ASN.1 message, modify the fields, and re-encode the message in ASN.1
   before passing the message on to the message dispatcher or to the
   transport layer.  This would require an intimate knowledge of the
   message format and message versions so the TMSP knew which fields
   could be modified.  This would seriously violate the modularity of
   the architecture.

B.4.  Using a Cache

   This document describes a cache, into which the TMSP puts information
   about the security applied to an incoming message, and an MPSP SMSP
   extracts that information from the cache.  Given that there may be
   multiple TM-security caches, a tmStateReference tmSessionReference is passed as an
   extra parameter in the ASIs between the transport mapping and the
   messaging security model.so model, so the MPSP SMSP knows which cache of
   information to consult.

   This approach does create dependencies between a model-specific TMSP
   and a corresponding specific MPSP. SMSP.  This approach of passing a model-
   independent reference is consistent with the securityStateReference
   cache already being passed around in the RFC3411 ASIs.

Appendix C.  Open Issues

Appendix D.  Change Log

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

   Changes from revision -02- to -03-

   o  removed session table from MIB module
   o  removed sessionID from ASIs
   o  reorganized to put ASI discussions in EOP section, as was done in
      SSHSM
   o  changed user auth to client auth
   o  changed tmStateReference to tmSessionReference
   o  modified document to meet consensus positions published by JS
   o
      *  authoritative is model-specific
      *  msgSecurityParameters usage is model-specific
      *  msgFlags vs. securityLevel is model/implementation-specific
      *  notifications must be able to cause creation of a session
      *  security considerations must be model-specific
      *  TDomain and TAddress are model-specific
      *  MPSP changed to SMSP (Security model security processing)

   Changes from revision -01- to -02-

   o  wrote text for session establishment requirements section.
   o  wrote text for session maintenance requirements section.

   o  removed section on relation to SNMPv2-MIB
   o  updated MIB module to pass smilint
   o  Added Structure of the MIB module, and other expected MIB-related
      sections.
   o  updated author address
   o  corrected spelling
   o  removed msgFlags appendix
   o  Removed section on implementation considerations.
   o  started modifying the security boilerplate to address TMSM and MIB
      security issues
   o  reorganized slightly to better separate requirements from proposed
      solution.  This probably needs additional work.
   o  removed section with sample protocols and sample tmStateReference.
      tmSessionReference.
   o  Added section for acronyms
   o  moved section comparing parameter passing techniques to appendix.
   o  Removed section on notification requirements.

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

Authors' Addresses

   David Harrington
   Futurewei
   Huawei Technologies (USA)
   1700 Alma Dr. Suite 100
   Plano, TX 75075
   USA

   Phone: +1 603 436 8634
   EMail: dharrington@huawei.com
   Juergen Schoenwaelder
   International University Bremen
   Campus Ring 1
   28725 Bremen
   Germany

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

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