Network Working Group                                      D. Harrington
Internet-Draft                                 Huawei Technologies (USA)
Intended status: Informational                          J. Schoenwaelder
Expires: April 14, 2007                  International University Bremen
                                                        October 11, 2006


 Transport Subsystem for the Simple Network Management Protocol (SNMP)
                      draft-ietf-isms-tmsm-04.txt

Status of This Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 14, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document describes a Transport Subsystem, extending the Simple
   Network Management Protocol (SNMP) architecture defined in RFC 3411.
   This document describes a subsystem to contain transport models,
   comparable to other subsystems in the RFC3411 architecture.  As work
   is being done to expand the transport to include secure transport
   such as SSH and TLS, using a subsystem will enable consistent design
   and modularity of such transport models.  This document identifies



Harrington & Schoenwaelder  Expires April 14, 2007              [Page 1]


Internet-Draft          SNMP Transport Subsystem            October 2006


   and discusses some key aspects that need to be considered for any
   transport model for SNMP.

   This memo also defines a portion of the Management Information Base
   (MIB) for managing models in the Transport Subsystem.

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 . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Requirements of a Transport Model  . . . . . . . . . . . . . .  6
     2.1.  Message Security Requirements  . . . . . . . . . . . . . .  6
       2.1.1.  Security Protocol Requirements . . . . . . . . . . . .  6
     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 the Transport Subsystem  . . . . . . . . 21
     3.1.  Command Generator or Notification Originator . . . . . . . 21
     3.2.  Command Responder  . . . . . . . . . . . . . . . . . . . . 22
   4.  Cached Information and References  . . . . . . . . . . . . . . 23
     4.1.  securityStateReference . . . . . . . . . . . . . . . . . . 24
     4.2.  tmStateReference . . . . . . . . . . . . . . . . . . . . . 25
   5.  Abstract Service Interfaces  . . . . . . . . . . . . . . . . . 25
     5.1.  Generating an Outgoing SNMP Message  . . . . . . . . . . . 26
     5.2.  Processing for an Outgoing Message . . . . . . . . . . . . 27
     5.3.  Processing an Incoming SNMP Message  . . . . . . . . . . . 28
       5.3.1.  Processing an Incoming Message . . . . . . . . . . . . 28
       5.3.2.  Prepare Data Elements from Incoming Messages . . . . . 28
       5.3.3.  Processing an Incoming Message . . . . . . . . . . . . 29
   6.  The Transport-Subsystem-MIB Module . . . . . . . . . . . . . . 30
     6.1.  Structure of the MIB Module  . . . . . . . . . . . . . . . 31
       6.1.1.  The tmsmStats Subtree  . . . . . . . . . . . . . . . . 31
     6.2.  Relationship to Other MIB Modules  . . . . . . . . . . . . 31
       6.2.1.  Textual Conventions  . . . . . . . . . . . . . . . . . 31
       6.2.2.  MIB Modules Required for IMPORTS . . . . . . . . . . . 31
     6.3.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . 31
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 36
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 37
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 37
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38



Harrington & Schoenwaelder  Expires April 14, 2007              [Page 2]


Internet-Draft          SNMP Transport Subsystem            October 2006


     10.1. Normative References . . . . . . . . . . . . . . . . . . . 38
     10.2. Informative References . . . . . . . . . . . . . . . . . . 39
   Appendix A.  Parameter Table . . . . . . . . . . . . . . . . . . . 39
     A.1.  ParameterList.csv  . . . . . . . . . . . . . . . . . . . . 39
   Appendix B.  Why tmStateReference? . . . . . . . . . . . . . . . . 41
     B.1.  Define an Abstract Service Interface . . . . . . . . . . . 41
     B.2.  Using an Encapsulating Header  . . . . . . . . . . . . . . 41
     B.3.  Modifying Existing Fields in an SNMP Message . . . . . . . 42
     B.4.  Using a Cache  . . . . . . . . . . . . . . . . . . . . . . 42
   Appendix C.  Open Issues . . . . . . . . . . . . . . . . . . . . . 42
   Appendix D.  Change Log  . . . . . . . . . . . . . . . . . . . . . 42








































Harrington & Schoenwaelder  Expires April 14, 2007              [Page 3]


Internet-Draft          SNMP Transport Subsystem            October 2006


1.  Introduction

   This document describes a Transport Subsystem, extending 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 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 within the document and
   references to where in the document the acronym is defined, for easy
   lookup.
   o  [todo]

1.4.  Motivation

   There are multiple ways to secure one's home or business, 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



Harrington & Schoenwaelder  Expires April 14, 2007              [Page 4]


Internet-Draft          SNMP Transport Subsystem            October 2006


   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 principal and key
   management infrastructure.  Operators have reported that deploying
   another 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
   [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].




Harrington & Schoenwaelder  Expires April 14, 2007              [Page 5]


Internet-Draft          SNMP Transport Subsystem            October 2006


   This document describes a Transport Subsystem extension to the
   RFC3411 architecture, that allows security to be provided by an
   external protocol connected to the SNMP engine through an SNMP
   transport-model [RFC3417].  Such a transport model 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 the transport subsystem 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 Model

2.1.  Message Security Requirements

   Transport 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 transport subsystem.  Some factors
   should be considered when selecting a protocol.

   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.



Harrington & Schoenwaelder  Expires April 14, 2007              [Page 6]


Internet-Draft          SNMP Transport Subsystem            October 2006


   A transport model should require no modifications to the underlying
   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 transport
   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.

   Transport models MUST be able to coexist with other transport models,
   and may be designed to utilize either TCP or UDP or SCTP.

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 RFC3411 architecture includes a security subsystem for enabling
   different methods of providing security services, a messaging
   subsystem permitting different message versions to be handled by a
   single engine, an application subsystem to support different types of
   application processors, and an access control subsystem for allowing
   multiple approaches to access control.  The RFC3411 architecture does
   not include a subsystem for transport models, despite the fact there
   are multiple transport mappings already defined for SNMP.  This
   document addresses the need for a transport subsystem compatible with
   the RFC3411 architecture.

   In SNMPv2, there were many problems of side effects between
   subsystems caused by the manipulation of MIB objects, especially



Harrington & Schoenwaelder  Expires April 14, 2007              [Page 7]


Internet-Draft          SNMP Transport Subsystem            October 2006


   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 would be 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 subsystem must abide the goals of the
   RFC3411 architecture defined in [RFC3411].  To that end, this
   transport subsystem proposal uses a modular design that will permit
   transport models to be advanced through the standards process
   independently of other transport models, and independent of other
   modular SNMP components as much as possible.

   IETF standards typically require one mandatory to implement solution,
   with the capability of adding new mechanisms in the future.  Part of
   the motivstion of developing transport models is to develop support
   for secure transport protocols, such as a transport model that
   utilizes the Secure Shell protocol.  Any transport model should
   define one minimum-compliance security mechanism, preferably one
   which is already widely used to secure the transport layer protocol.

   The Transport Subsystem permits multiple transport protocols to be
   "plugged into" the RFC3411 architecture, supported by corresponding
   transport models, including models that are security-aware.

   The RFC3411 architecture,and the USM assume that a security model is
   called by a message-processing model and will perform multiple
   security functions within the security subsystem.  A transport model
   that supports a secure transport protocol may perform similar



Harrington & Schoenwaelder  Expires April 14, 2007              [Page 8]


Internet-Draft          SNMP Transport Subsystem            October 2006


   security functions within the transport subsystem.  A transport model
   may perform the translation of transport security parameters to/from
   security-model-independent parameters.  To accommodate this, the ASIs
   for the transport subsystem, the messaging subsystem, and the
   security subsystem will be extended to pass security-model-
   independent values, and a cache of transport-specific information.













































Harrington & Schoenwaelder  Expires April 14, 2007              [Page 9]


Internet-Draft          SNMP Transport Subsystem            October 2006


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



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 10]


Internet-Draft          SNMP Transport Subsystem            October 2006


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
   potentially done by a transport 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.
































Harrington & Schoenwaelder  Expires April 14, 2007             [Page 11]


Internet-Draft          SNMP Transport Subsystem            October 2006


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

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



2.2.1.2.  Transport Subsystem and the RFC3411 Architecture

   With the Transport Subsystem, the order of the steps may differ and
   may be handled by different subsystems:
   1) decrypt the encrypted portions of the message (transport layer)
   2*)  translate parameters to model-independent parameters (transport
      model)
   3) determine the SNMP security model and parameters (messaging model)
   4) decode the ASN.1 (messaging model)
   5) determine which application should get the decrypted portions
      (messaging model)
   7) pass on the decrypted portions with model-independent security
      parameters

   If a message is secured using non-SNMP-specific message security and
   parameters, then the transport model should provide the translation
   from e.g., an SSH user name to the securityName in step 3,





Harrington & Schoenwaelder  Expires April 14, 2007             [Page 12]


Internet-Draft          SNMP Transport Subsystem            October 2006


   | -----------------------------------------------|
   |                            ------------------  |
   |   transport layer     <--> | decryption     |  |
   |                            ------------------  |
   | -----------------------------------------------|
               ^
             |
             v
   --------------------------------------------------
   | -----------------------------------------------|
   |                            ------------------  |
   |  transport model     <--> | translation     |  |
   |                            ------------------  |
   | -----------------------------------------------|
   |         ^
   |         |
   |         v
   | ---------------------------------------------  |
   |                                                |
   |   message  model                               |
   |                                                |
   | -----------------------------------------------|
   |         ^
   |         |
   |         v
   | ---------------------------------------------  |
   |                                                |
   |   security model                               |
   |                                                |
   | -----------------------------------------------|
   |         ^
   |         |
   |         v
   | ---------------------      ------------------  |
   | | SNMP applications | <--> | access control |  |
   | ---------------------      ------------------  |

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



2.2.1.3.  Passing Information between Engines

   A secure transport model will establish an encrypted tunnel between
   the transport models of two SNMP engines.  One transport model
   instance encrypts all messages, and the other transport model
   instance decrypts the messages.




Harrington & Schoenwaelder  Expires April 14, 2007             [Page 13]


Internet-Draft          SNMP Transport Subsystem            October 2006


   After a transport layer tunnel is established, then SNMP messages can
   conceptually be sent through the tunnel from one SNMP engine to
   another SNMP engine.  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, security processing
   must establish a securityModel identifier, a securityLevel, and a
   securityName, which is the security model independent identifier for
   a principal.  The message processing 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 securityName MUST be bound to the mechanism-specific
   authenticated identity, and this mapping MUST be done for incoming
   messages before the security model passes securityName to the message
   processing model via the processIncoming() ASI.  This translation
   from a mechanism-specific authenticated identity to a securityName
   MAY be done by the transport model, and the securityname is then
   provided to the security model to be passed to the message processing
   model..

   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 via 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 transport model that provides security services 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
   transport or security subsystems, to be consistent with the
   modularity of the RFC3411 architecture.  This separation was a



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 14]


Internet-Draft          SNMP Transport Subsystem            October 2006


   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 (in the access control subsystem) MAY require
   authentication by certain securityModels and a minimum securityLevel
   to allow access to the data.

   Transport models that provide secure transport are an enhancement for
   the SNMPv3 privacy and authentication, but they are not a significant
   improvement for the authorization (access control) needs of SNMPv3.
   Only the model-independent parameters for the isAccessAllowed()
   primitive [RFC3411] are provided by the transport and security
   subsystems.

   A transport model must not specify how the securityModel and
   securityName could be dynamically mapped to an access control
   mechanism, such as a VACM-style groupName.  The mapping of
   (securityModel, securityName) to a groupName is a VACM-specific
   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 from the model-independent security parameters to
   an authorization-model-dependent access policy within the access
   control model.

   To provide support for protocols which simultaneously send
   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 transport model or a security model
   and an access control model, just as it is undesirable for a
   transport model to create a dependency between an SNMP message
   version and the security provided by a transport model.







Harrington & Schoenwaelder  Expires April 14, 2007             [Page 15]


Internet-Draft          SNMP Transport Subsystem            October 2006


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 transport model, outgoing SNMP messages are
   passed unencrypted from the message dispatcher to the transport
   model, and incoming messages are passed unencrypted from the
   transport model 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.

   When using a secure transport model, security parameters MAY be
   provided through means other than carrying them in the SNMP message.
   The parameters MAY be provided by SNMP applications for outgoing
   messages, and the parameters for incoming messages MAY be extracted
   from the transport layer by the transport model before the message is
   passed to the message processing subsystem.

   For outgoing messages, even when a secure transport model will
   provide the security services, it is necessary to have an security
   model because it is the security model that actually creates the
   message from its component parts.  Whether there are any security
   services provided by the security model for an outgoing message is
   model-dependent.

   For incoming messages, even when a secure transport model provides
   security services, a security model is necessary because there might
   be some security functionality that can only be provided after the
   message version is known.  The message version is determined by the
   Message Processing model and passed to the security model via the
   processIncoming() ASI.

   The RFC3411 architecture has no ASI parameters for passing security
   information between a transport mapping (a transport model) and the



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 16]


Internet-Draft          SNMP Transport Subsystem            October 2006


   dispatcher, and between the dispatcher and the message processing
   model.

   This document describes a cache mechanism, into which the transport
   model puts information about the transport and security parameters
   applied to a transport connection or an incoming message, and a
   security model MAY extract that information from the cache.  A
   tmStateReference is passed as an extra parameter in the ASIs of the
   transport subsystem and the messaging and security subsystems, to
   identify the relevant cache.

   This approach of passing a model-independent reference is consistent
   with the securityStateReference cache already being passed around in
   the RFC3411 ASIs. [todo: can we avoid dependencies?]

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 transport 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 the transport subsystem, so
   an SNMP application cannot select the session except by passing a
   unique combination of transport type, transport address,
   securityName, securityModel, and securityLevel.

   All transport models should discuss the impact of sessions on SNMP
   usage, including how to establish/open a transport session (i.e., how
   it maps to the concepts of session-like things of the underlying
   protocol), how to behave when a session cannot be established, how to
   close a session properly, how to behave when a 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 transport model sessions.




Harrington & Schoenwaelder  Expires April 14, 2007             [Page 17]


Internet-Draft          SNMP Transport Subsystem            October 2006


2.3.1.  Session Establishment Requirements

   SNMP applications must provide the transport type, 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 transport model designer wants to
   differentiate a session established for different purposes, such as a
   notification session versus a request-response session, the
   application can use different securityNames or transport addresses
   (e.g., port 161 vs. port 162) for different purposes.

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

   Sessions are usually established by the transport model when no
   appropriate session is found for an outgoing message, but sessions
   may be established in advance to support features such as
   notifications.  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 transport 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 type, transport
   address, securityName, securityModel, and securityLevel) for an
   outgoing message. [discuss: does the transport model have insight
   into the securityModel?]

   A transport model implementation MAY reuse an already established
   session with the appropriate transport type, 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



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 18]


Internet-Draft          SNMP Transport Subsystem            October 2006


   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 of sessions 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 receiver.  This
   may strongly affect the usefulness of session reuse.

2.3.2.  Session Maintenance Requirements

   A transport 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 transport models should be sure to
   describe the expected behavior when no session exists for a response.
   [todo: do we already say that the message should be discarded, or is
   that just in the ssh transport model?]

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

   If a transport model defines MIB module objects to maintain session
   state information, then the transport 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 transport model session is associated with state information that
   is maintained for its lifetime.  This state information allows for
   the application of various security services to multiple messages.
   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



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 19]


Internet-Draft          SNMP Transport Subsystem            October 2006


   cryptographic protocols used to establish keys for a transport 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 transport model session will typically have a single transport
   type, ransport address, securityModel, 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, or to use a different securityModel, 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 transport 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 transport 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 transport 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 transport model and the
   secure transport used.

   If the underlying transport layer security is configurable on a per-
   message basis, a transport model could have a transport-model 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



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 20]


Internet-Draft          SNMP Transport Subsystem            October 2006


   of procedure of the transport model would need to describe the
   procedures to enable this determination. [discuss: this is a feature
   I find questionable.  It can be developed as a feature of a specific
   transport model.  Do we need this discussion here?]

   For transport 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 transport models should consider the trade offs for
   resource-constrained devices.

3.  Scenario Diagrams for the Transport Subsystem

   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.




















Harrington & Schoenwaelder  Expires April 14, 2007             [Page 21]


Internet-Draft          SNMP Transport Subsystem            October 2006


   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.



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 22]


Internet-Draft          SNMP Transport Subsystem            October 2006


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


4.  Cached Information and References

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



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 23]


Internet-Draft          SNMP Transport Subsystem            October 2006


   subsystems.

   There are two levels of state that may need to be maintained: the
   security state in a request-response pair, and potentially long-term
   state relating to transport and security.

   This state is maintained in caches and a Local Configuration
   Datastore (LCD).  To simplify the elements of procedure, the release
   of state information is not always explicitly specified.  As a
   general rule, if state information is available when a message being
   processed gets discarded, the state related to that message should
   also be discarded, and if state information is available when a
   relationship between engines is severed, such as the closing of a
   transport session, the state information for that relationship might
   also be discarded.

   This document differentiates the tmStateReference from the
   securityStateReference.  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 a security or transport model has had an opportunity
   to extract the information it needs.

4.1.  securityStateReference

   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."

   The information saved should include the model-independent parameters
   (transportType, transportAddress, securityName, securityModel, and
   securityLevel), related security parameters, and other information
   needed to imatch the response with the request.  The Message
   Processing Model has the responsibility for explicitly releasing the
   securityStateReference when such data is no longer needed.  The
   securityStateReference cached data may be implicitly released via the



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 24]


Internet-Draft          SNMP Transport Subsystem            October 2006


   generation of a response, or explicitly released by using the
   stateRelease primitive, as described in RFC 3411 section 4.5.1."

   If the transport model connection is closed between the time a
   Request is received and a Response message is being prepared, then
   the Response message MAY be discarded.

4.2.  tmStateReference

   For each message or transport session, information about the message
   security is stored in the Local Configuration Datastore (LCD),
   supplemented with a cache, to pass model- and mechanism-specific
   parameters.  The state referenced by tmStateReference may be saved
   across multiple messages, as compared to securityStateReference which
   is only saved for the life of a request-response pair of messages.

   The format of the cache and the LCD are implementation-specific.  For
   ease of explanation, this document defines a MIB module to
   conceptually represent the LCD, but this is not meant to contrain
   implementations from doing it differently.

   It is expected that the LCD will allow lookup based on the
   combination of transportType, transportAddress, securityName,
   securityModel, and securityLevel.  It is expected that the cache
   contain these values or contain pointers/references to entries in the
   LCD.

   It is expected that a transport model may store transport-specific
   parameters in the LCD for subsequent usage.

5.  Abstract Service Interfaces

   [todo: the discussion of ASIs that are not directly related to the
   transport or security models was added to the document because it was
   difficult to understand what information was available at what
   points, and who provided the information.  The presence of this
   expository text can make it hard to find the relevant ASIs for the
   transport subsystem, and can be confusing because it talks about
   things that the transport subsystem should not know about.  This text
   should be reduced.

   Abstract service interfaces have been defined by RFC 3411 to describe
   the conceptual data flows between the various subsystems within an
   SNMP entity.

   To simplify the elements of procedure, the release of state
   information is not always explicitly specified.  As a general rule,
   if state information is available when a message gets discarded, the



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 25]


Internet-Draft          SNMP Transport Subsystem            October 2006


   message-state information should also be released, and if state
   information is available when a session is closed, the session state
   information should also be released.

   An error indication may return an OID and value for an incremented
   counter and a value for securityLevel, and values for contextEngineID
   and contextName for the counter, and the securityStateReference if
   the information is available at the point where the error is
   detected.

5.1.  Generating an Outgoing SNMP Message

   This section describes the procedure followed by an RFC3411-
   compatible system whenever it generates a message containing a
   management operation (such as 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 used
   IN  transportAddress         -- transport address to be used
   IN  messageProcessingModel   -- typically, SNMP version
   IN  securityModel            -- Security Model to use
   IN  securityName             -- on behalf of this principal
   IN  securityLevel            -- Level of Security requested
   IN  contextEngineID          -- data from/at this entity
   IN  contextName              -- data from/in this context
   IN  pduVersion               -- the version of the 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 to send
   OUT  outgoingMessageLength   -- its length
   OUT  tmStateReference
               )

   Note that tmStateReference has been added to this ASI.

   The IN parameters of the prepareOutgoingMessage() ASI are used to
   pass information from the dispatcher (for the application subsystem)
   to the message processing subsystem.

   The abstract service primitive from a Message Processing Model to a
   Security Model to generate the components of a Request message is
   generateRequestMsg().



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 26]


Internet-Draft          SNMP Transport Subsystem            October 2006


   The abstract service primitive from a Message Processing Model to a
   Security Model to generate the components of a Response message is
   generateResponseMsg().

   Upon completion of processing, the Security Model returns
   statusInformation.  If the process was successful, the completed
   message is returned.  If the process was not successful, then an
   errorIndication is returned.

   The OUT parameters of the prepareOutgoingMessage() ASI are used to
   pass information from the message processing model to the dispatcher
   and on to the transport model:

5.2.  Processing for an Outgoing Message

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

   statusInformation =
   sendMessage(
   IN   destTransportDomain           -- transport domain to be used
   IN   destTransportAddress          -- transport address to be used
   IN   outgoingMessage               -- the message to send
   IN   outgoingMessageLength         -- its length
   IN   tmStateReference
    )

   The Transport Subsystem provides the following primitives to pass
   data back and forth between the dispatcher and specific transport
   models, which provide the interface to the underlying secure
   transport service.  Each transport model should define the elements
   of procedure for the openSession() and closeSession() interfaces.

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


   statusInformation =
   closeSession(
   IN   tmStateReference
    )






Harrington & Schoenwaelder  Expires April 14, 2007             [Page 27]


Internet-Draft          SNMP Transport Subsystem            October 2006


5.3.  Processing an Incoming SNMP Message

5.3.1.  Processing an Incoming Message

   If one does not exist, the Transport Model will need to create an
   entry in a Local Configuration Datastore referenced by
   tmStateReference.  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 pass a message from the transport
   subsystem to the Dispatcher.

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

5.3.2.  Prepare Data Elements from Incoming Messages

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
























Harrington & Schoenwaelder  Expires April 14, 2007             [Page 28]


Internet-Draft          SNMP Transport Subsystem            October 2006


   result =                       -- SUCCESS or errorIndication
   prepareDataElements(
   IN   transportDomain           -- origin transport domain
   IN   transportAddress          -- origin transport address
   IN   wholeMsg                  -- as received from the network
   IN   wholeMsgLength            -- as received from the network
   IN   tmStateReference        -- from the transport model
   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 version of the 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 state information
                                  -- to be used for possible Response
   )


   Note that tmStateReference has been added to this ASI.

5.3.3.  Processing an Incoming Message

   This section describes the procedure followed by the Security Model
   whenever it 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
   wholeMsg.  The abstract service primitive from a Message Processing
   Model to the Security Subsystem for a received message is::















Harrington & Schoenwaelder  Expires April 14, 2007             [Page 29]


Internet-Draft          SNMP Transport Subsystem            October 2006


   statusInformation =  -- errorIndication or success
                            -- error counter OID/value if error
   processIncomingMsg(
   IN   messageProcessingModel    -- typically, SNMP version
   IN   maxMessageSize            -- of the sending SNMP entity
   IN   securityParameters        -- for the received message
   IN   securityModel             -- for the received message
   IN   securityLevel             -- Level of Security
   IN   wholeMsg                  -- as received on the wire
   IN   wholeMsgLength            -- length as received on the wire
   IN   tmStateReference        -- from the transport model
   OUT  securityEngineID          -- authoritative SNMP entity
   OUT  securityName              -- identification of the principal
   OUT  scopedPDU,                -- message (plaintext) payload
   OUT  maxSizeResponseScopedPDU  -- maximum size sender can handle
   OUT  securityStateReference    -- reference to security state
    )                         -- information, needed for response

   1) The securityEngineID is set to a value in a model-specific manner.
   If the securityEngineID is not utilized by the specific model, then
   it should be set to the local snmpEngineID, to satisfy the SNMPv3
   message processing model in RFC 3412 section 7.2 13a).

   2) Extract the value of securityName from the Local Configuration
   Datastore entry referenced by tmStateReference.

   3) The scopedPDU component is extracted from the wholeMsg.

   4) The maxSizeResponseScopedPDU is calculated.  This is the maximum
   size allowed for a scopedPDU for a possible Response message.

   5)The security data is cached as cachedSecurityData, so that a
   possible response to this message can and will use the same security
   parameters.  Then securityStateReference is set for subsequent
   reference to this cached data.

   4) The statusInformation is set to success and a return is made to
   the calling module passing back the OUT parameters as specified in
   the processIncomingMsg primitive.

6.  The Transport-Subsystem-MIB Module

   This memo defines a portion of the Management Information Base (MIB)
   for statistics in the Transport Subsystem.







Harrington & Schoenwaelder  Expires April 14, 2007             [Page 30]


Internet-Draft          SNMP Transport Subsystem            October 2006


6.1.  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.

6.1.1.  The tmsmStats Subtree

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

6.2.  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 Transport-Subsystem-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 transport models within the transport
   subsystem.  This MIB module is designed to be transport-model
   independent and security-model independent, and contains objects
   useful for managing common aspects of any transport model.  Specific
   transport models may define a MIB module to contain transport-model
   dependent information.

6.2.1.  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

6.2.2.  MIB Modules Required for IMPORTS

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

6.3.  Definitions

  Transport-Subsystem-MIB DEFINITIONS ::= BEGIN

  IMPORTS
      MODULE-IDENTITY, OBJECT-TYPE,
      mib-2, Integer32, Unsigned32, Gauge32
        FROM SNMPv2-SMI
      TestAndIncr, StorageType, RowStatus



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 31]


Internet-Draft          SNMP Transport Subsystem            October 2006


        FROM SNMPv2-TC
      MODULE-COMPLIANCE, OBJECT-GROUP
        FROM SNMPv2-CONF
      SnmpSecurityModel,
      SnmpAdminString,  SnmpSecurityLevel, SnmpEngineID
         FROM SNMP-FRAMEWORK-MIB
      TransportAddress, TransportAddressType
        FROM TRANSPORT-ADDRESS-MIB
      ;

  tmsMIB MODULE-IDENTITY
      LAST-UPDATED "200610060000Z"
      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 Subsystem 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.



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 32]


Internet-Draft          SNMP Transport Subsystem            October 2006


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

         REVISION     "200610060000Z"         -- 20 April 2006
         DESCRIPTION  "The initial version, published in RFC XXXX.
  -- NOTE to RFC editor: replace XXXX with actual RFC number
  --                     for this document and remove this note
                      "

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

  -- ---------------------------------------------------------- --
  -- subtrees in the Transport-Subsystem-MIB
  -- ---------------------------------------------------------- --

  tmsNotifications OBJECT IDENTIFIER ::= { tmsMIB 0 }
  tmsObjects       OBJECT IDENTIFIER ::= { tmsMIB 1 }
  tmsConformance   OBJECT IDENTIFIER ::= { tmsMIB 2 }

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

  -- Textual Conventions

  SnmpTransportModel ::= TEXTUAL-CONVENTION
      STATUS       current
      DESCRIPTION "An identifier that uniquely identifies a
                   Transport Model of the Transport Subsystem within
                   the SNMP Management Architecture.

                   The values for transportModel are allocated as
                   follows:

                   - The zero value does not identify any particular
                     transport model.

                   - Values between 1 and 255, inclusive, are reserved
                     for standards-track Transport Models and are
                     managed by the Internet Assigned Numbers Authority
                     (IANA).
                   - Values greater than 255 are allocated to
                     enterprise-specific Transport Models.  An
                     enterprise-specific transportModel value is defined
                     to be:



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 33]


Internet-Draft          SNMP Transport Subsystem            October 2006


                     enterpriseID * 256 + transport model within
                     enterprise

                     For example, the fourth Transport Model defined by
                     the enterprise whose enterpriseID is 1 would be
                     260.

                   This scheme for allocation of transportModel
                   values allows for a maximum of 255 standards-
                   based Transport Models, and for a maximum of
                   256 Transport Models per enterprise.

                   It is believed that the assignment of new
                   transportModel values will be rare in practice
                   because the larger the number of simultaneously
                   utilized Transport Models, the larger the
                   chance that interoperability will suffer.
                   Consequently, it is believed that such a range
                   will be sufficient.  In the unlikely event that
                   the standards committee finds this number to be
                   insufficient over time, an enterprise number
                   can be allocated to obtain an additional 256
                   possible values.

                   Note that the most significant bit must be zero;
                   hence, there are 23 bits allocated for various
                   organizations to design and define non-standard
                   transportModels.  This limits the ability to
                   define new proprietary implementations of Transport
                   Models to the first 8,388,608 enterprises.

                   It is worthwhile to note that, in its encoded
                   form, the transportModel value will normally
                   require only a single byte since, in practice,
                   the leftmost bits will be zero for most messages
                   and sign extension is suppressed by the encoding
                   rules.

                   As of this writing, there are several values
                   of transportModel defined for use with SNMP or
                   reserved for use with supporting MIB objects.
                   They are as follows:

                       0  reserved for 'any'
                       1  reserved for UDP
                       2  reserved for TCP
                       3  SSH Transport Model
                  "



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 34]


Internet-Draft          SNMP Transport Subsystem            October 2006


      SYNTAX       INTEGER(0 .. 2147483647)

  -- Notifications for the Transport Subsystem

  -- Statistics for the Transport Subsystem


  tmsStats         OBJECT IDENTIFIER ::= { tmsObjects 1 }


  -- -------------------------------------------------------------
  -- Conformance Information
  -- -------------------------------------------------------------

  tmsGroups OBJECT IDENTIFIER ::= { tmsConformance 1 }

  tmsCompliances OBJECT IDENTIFIER ::= { tmsConformance 2 }

  -- -------------------------------------------------------------
  -- Units of conformance
  -- -------------------------------------------------------------
  tmsGroup OBJECT-GROUP
      OBJECTS {

      }
      STATUS      current
      DESCRIPTION "A collection of objects for maintaining session
                   information of an SNMP engine which implements the
                   Transport subsystem.
                  "

      ::= { tmsGroups 2 }

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

  tmsCompliance MODULE-COMPLIANCE
      STATUS      current
      DESCRIPTION
          "The compliance statement for SNMP engines that support the
          Transport-Subsystem-MIB"
      MODULE
          MANDATORY-GROUPS { tmsGroup }
      ::= { tmsCompliances 1 }

  END




Harrington & Schoenwaelder  Expires April 14, 2007             [Page 35]


Internet-Draft          SNMP Transport Subsystem            October 2006


7.  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.

   It is considered desirable by some industry segments that SNMP
   transport 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 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.

   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.




Harrington & Schoenwaelder  Expires April 14, 2007             [Page 36]


Internet-Draft          SNMP Transport Subsystem            October 2006


8.  IANA Considerations

   IANA is requested to create a new registry in the Simple Network
   Management Protocol (SNMP) Number Spaces for SnmpTransportModels, as
   described in the Transport-Subsystem-MIB defined in this document.
   Values 0 through 255 are IANA-assigned by Standards Action, as
   defined in RFC2434.  Values above 255 are assigned by Hierarchical
   allocation, using the algorithm defined in the definition of the
   SnmpTransportModels TEXTUAL-CONVENTION in the Transport-Subsystem-MIB
   in this document.

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


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

   Transport-Subsystem-MIB        { 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.



9.  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

10.  References






Harrington & Schoenwaelder  Expires April 14, 2007             [Page 37]


Internet-Draft          SNMP Transport Subsystem            October 2006


10.1.  Normative References

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



Harrington & Schoenwaelder  Expires April 14, 2007             [Page 38]


Internet-Draft          SNMP Transport Subsystem            October 2006


              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.

10.2.  Informative References

   [RFC3410]               Case, J., Mundy, R., Partain, D., and B.
                           Stewart, "Introduction and Applicability
                           Statements for Internet-Standard Management
                           Framework", RFC 3410, December 2002.

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

   [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,,,




Harrington & Schoenwaelder  Expires April 14, 2007             [Page 39]


Internet-Draft          SNMP Transport Subsystem            October 2006


   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




Harrington & Schoenwaelder  Expires April 14, 2007             [Page 40]


Internet-Draft          SNMP Transport Subsystem            October 2006


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

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

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

Appendix B.  Why tmStateReference?

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

   There are four approaches that could be used for passing information
   between the Transport Model and an Security Model.

   1.  one could define an ASI to supplement the existing ASIs, or
   2.  one could add a header to encapsulate the SNMP message,
   3.  one could utilize fields already defined in the existing SNMPv3
       message, or
   4.  one 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 subsystem to security subsystem has
   the advantage of being consistent with existing RFC3411/3412
   practice, and helps to ensure that any transport model 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 Transport Model 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 Security Model.





Harrington & Schoenwaelder  Expires April 14, 2007             [Page 41]


Internet-Draft          SNMP Transport Subsystem            October 2006


B.3.  Modifying Existing Fields in an SNMP Message

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

   If the fields in an incoming SNMPv3 message are changed by the
   Transport Model before passing it to the Security Model, then the
   Transport Model 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 Transport Model 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 Transport Model puts
   information about the security applied to an incoming message, and an
   Security Model extracts that information from the cache.  Given that
   there may be multiple TM-security caches, a tmStateReference is
   passed as an extra parameter in the ASIs between the transport
   subsystem and the security subsystem, so the Security Model knows
   which cache of information to consult.

   This approach does create dependencies between a specific Transport
   Model and a corresponding specific Security Model.  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 -03- to -04-

      changed title from Transport Mapping Security Model Architectural
      Extension to Transport Subsystem
      modified the abstract and introduction





Harrington & Schoenwaelder  Expires April 14, 2007             [Page 42]


Internet-Draft          SNMP Transport Subsystem            October 2006


      changed TMSM to TMS
      changed MPSP to simply Security Model
      changed SMSP to simply Security Model
      changed TMSP to Transport Model
      removed MPSP and TMSP and SMSP from Acronyms section
      modified diagrams
      removed most references to dispatcher functionality
      worked to remove dependencies between transport and security
      models.
      defined snmpTransportModel enumeration similar to
      snmpSecurityModel, etc.
      eliminated all reference to SNMPv3 msgXXXX fields
      changed tmSessionReference back to tmStateReference

   Changes from revision -02- to -03-

   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 TMS and MIB
      security issues





Harrington & Schoenwaelder  Expires April 14, 2007             [Page 43]


Internet-Draft          SNMP Transport Subsystem            October 2006


   o  reorganized slightly to better separate requirements from proposed
      solution.  This probably needs additional work.
   o  removed section with sample protocols and sample
      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 tmSessionReference for DTLS that revealed
      lower layer info.
   o  Added TMS-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
   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









Harrington & Schoenwaelder  Expires April 14, 2007             [Page 44]


Internet-Draft          SNMP Transport Subsystem            October 2006


Full Copyright Statement

   Copyright (C) The Internet Society (2006).

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

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

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.

Acknowledgement

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).







Harrington & Schoenwaelder  Expires April 14, 2007             [Page 45]