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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 5591

Network Working Group                                      D. Harrington
Internet-Draft                                 Huawei Technologies (USA)
Intended status: Standards Track                             W. Hardaker
Expires: April 9, 2009                                      Sparta, Inc.
                                                         October 6, 2008


                   Transport Security Model for SNMP
              draft-ietf-isms-transport-security-model-09

Status of This Memo

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   This Internet-Draft will expire on April 9, 2009.

Abstract

   This memo describes a Transport Security Model for the Simple Network
   Management Protocol.

   This memo also defines a portion of the Management Information Base
   (MIB) for use with network management protocols in TCP/IP based
   internets.  In particular it defines objects for monitoring and
   managing the Transport Security Model for SNMP.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4



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     1.1.  The Internet-Standard Management Framework . . . . . . . .  4
     1.2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  4
     1.3.  Modularity . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.4.  Motivation . . . . . . . . . . . . . . . . . . . . . . . .  6
     1.5.  Constraints  . . . . . . . . . . . . . . . . . . . . . . .  6
   2.  How the Transport Security Model Fits in the Architecture  . .  6
     2.1.  Security Capabilities of this Model  . . . . . . . . . . .  7
       2.1.1.  Threats  . . . . . . . . . . . . . . . . . . . . . . .  7
       2.1.2.  Security Levels  . . . . . . . . . . . . . . . . . . .  8
     2.2.  No Sessions  . . . . . . . . . . . . . . . . . . . . . . .  8
     2.3.  Coexistence  . . . . . . . . . . . . . . . . . . . . . . .  8
     2.4.  Security Parameter Passing . . . . . . . . . . . . . . . . 10
     2.5.  Notifications and Proxy  . . . . . . . . . . . . . . . . . 10
   3.  Cached Information and References  . . . . . . . . . . . . . . 11
     3.1.  securityStateReference . . . . . . . . . . . . . . . . . . 11
     3.2.  tmStateReference . . . . . . . . . . . . . . . . . . . . . 11
       3.2.1.  Transport information  . . . . . . . . . . . . . . . . 12
       3.2.2.  securityName . . . . . . . . . . . . . . . . . . . . . 12
       3.2.3.  securityLevel  . . . . . . . . . . . . . . . . . . . . 13
       3.2.4.  Session Information  . . . . . . . . . . . . . . . . . 14
     3.3.  Transport Security Model Cached Information  . . . . . . . 14
       3.3.1.  tmStateReference . . . . . . . . . . . . . . . . . . . 14
       3.3.2.  securityStateReference . . . . . . . . . . . . . . . . 15
   4.  Processing an Outgoing Message . . . . . . . . . . . . . . . . 15
     4.1.  Security Processing for an Outgoing Message  . . . . . . . 15
     4.2.  Elements of Procedure for Outgoing Messages  . . . . . . . 16
   5.  Processing an Incoming SNMP Message  . . . . . . . . . . . . . 17
     5.1.  Security Processing for an Incoming Message  . . . . . . . 17
     5.2.  Elements of Procedure for Incoming Messages  . . . . . . . 18
   6.  MIB Module Overview  . . . . . . . . . . . . . . . . . . . . . 19
     6.1.  Structure of the MIB Module  . . . . . . . . . . . . . . . 19
     6.2.  The snmpTsmStats Subtree . . . . . . . . . . . . . . . . . 19
     6.3.  The snmpTsmConfiguration Subtree . . . . . . . . . . . . . 19
     6.4.  Relationship to Other MIB Modules  . . . . . . . . . . . . 19
       6.4.1.  Relationship to the SNMPv2-MIB . . . . . . . . . . . . 19
       6.4.2.  Relationship to the SNMP-FRAMEWORK-MIB . . . . . . . . 20
       6.4.3.  MIB Modules Required for IMPORTS . . . . . . . . . . . 20
   7.  MIB module definition  . . . . . . . . . . . . . . . . . . . . 20
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 25
     8.1.  MIB module security  . . . . . . . . . . . . . . . . . . . 25
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 26
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 27
     11.2. Informative References . . . . . . . . . . . . . . . . . . 28
   Appendix A.  Notification Tables Configuration . . . . . . . . . . 28
     A.1.  Transport Security Model Processing for Notifications  . . 30
   Appendix B.  Processing Differences between USM and Secure



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                Transport . . . . . . . . . . . . . . . . . . . . . . 30
     B.1.  USM and the RFC3411 Architecture . . . . . . . . . . . . . 31
     B.2.  Transport Subsystem and the RFC3411 Architecture . . . . . 31
   Appendix C.  Open Issues . . . . . . . . . . . . . . . . . . . . . 32
   Appendix D.  Change Log  . . . . . . . . . . . . . . . . . . . . . 32














































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1.  Introduction

   This memo describes a Transport Security Model for the Simple Network
   Management Protocol, for use with secure Transport Models in the
   Transport Subsystem [I-D.ietf-isms-tmsm].

   This memo also defines a portion of the Management Information Base
   (MIB) for use with network management protocols in TCP/IP based
   internets.  In particular it defines objects for monitoring and
   managing the Transport Security Model for SNMP.

   It is important to understand the SNMP architecture and the
   terminology of the architecture to understand where the Transport
   Security Model described in this memo fits into the architecture and
   interacts with other subsystems and models within the architecture.
   It is expected that reader will have also read and understood RFC3411
   [RFC3411], RFC3412 [RFC3412], RFC3413 [RFC3413], and RFC3418
   [RFC3418].

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

   For consistency with SNMP-related specifications, this document
   favors terminology as defined in STD62 rather than favoring
   terminology that is consistent with non-SNMP specifications that use
   different variations of the same terminology.  This is consistent
   with the IESG decision to not require the SNMPv3 terminology be
   modified to match the usage of other non-SNMP specifications when
   SNMPv3 was advanced to Full Standard.

   Authentication in this document typically refers to the English
   meaning of "serving to prove the authenticity of" the message, not
   data source authentication or peer identity authentication.




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   The terms "manager" and "agent" are not used in this document,
   because in the RFC 3411 architecture, all SNMP entities have the
   capability of acting as either manager or agent or both depending on
   the SNMP applications included in the engine.  Where distinction is
   required, the application names of Command Generator, Command
   Responder, Notification Originator, Notification Receiver, and Proxy
   Forwarder are used.  See "SNMP Applications" [RFC3413] for further
   information.

   While security protocols frequently refer to a user, the terminology
   used in RFC3411 [RFC3411] and in this memo is "principal".  A
   principal is the "who" on whose behalf services are provided or
   processing takes place.  A principal can be, among other things, an
   individual acting in a particular role; a set of individuals, with
   each acting in a particular role; an application or a set of
   applications, or a combination of these within an administrative
   domain.

   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 [RFC2119].

1.3.  Modularity

   The reader is expected to have read and understood the description of
   the SNMP architecture, as defined in [RFC3411], and the architecture
   extension specified in "Transport Subsystem for the Simple Network
   Management Protocol" [I-D.ietf-isms-tmsm], which enables the use of
   external "lower layer transport" protocols to provide message
   security, tied into the SNMP architecture through the Transport
   Subsystem.  The Transport Security Model is designed to work with
   such lower-layer secure Transport Models.

   In keeping with the RFC 3411 design decisions to use self-contained
   documents, this memo includes the elements of procedure plus
   associated MIB objects which are needed for processing the Transport
   Security Model for SNMP.  These MIB objects SHOULD NOT be referenced
   in other documents.  This allows the Transport Security Model to be
   designed and documented as independent and self-contained, having no
   direct impact on other modules, and allowing this module to be
   upgraded and supplemented as the need arises, and to move along the
   standards track on different time-lines from other modules.

   This modularity of specification is not meant to be interpreted as
   imposing any specific requirements on implementation.






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1.4.  Motivation

   This memo describes a Security Model to make use of Transport Models
   that use lower layer secure transports and existing and commonly
   deployed security infrastructures.  This Security Model is designed
   to meet the security and operational needs of network administrators,
   maximize usability in operational environments to achieve high
   deployment success and at the same time minimize implementation and
   deployment costs to minimize the time until deployment is possible.

1.5.  Constraints

   The design of this SNMP Security Model is also influenced by the
   following constraints:

   1.  In times of network stress, the security protocol and its
       underlying security mechanisms SHOULD NOT depend solely upon the
       ready availability of other network services (e.g., Network Time
       Protocol (NTP) or Authentication, Authorization, and Accounting
       (AAA) protocols).

   2.  When the network is not under stress, the Security Model and its
       underlying security mechanisms MAY depend upon the ready
       availability of other network services.

   3.  It may not be possible for the Security Model to determine when
       the network is under stress.

   4.  A Security Model should require no changes to the SNMP
       architecture.

   5.  A Security Model should require no changes to the underlying
       security protocol.

2.  How the Transport Security Model Fits in the Architecture

   The Transport Security Model is designed to fit into the RFC3411
   architecture as a Security Model in the Security Subsystem, and to
   utilize the services of a secure Transport Model.

   A cache, referenced by tmStateReference, is used to pass information
   between the Transport Security Model and a Transport Model, and vice
   versa.  If the Transport Security Model is used with an insecure
   Transport Model, then the cache will not exist or not be populated
   with security parameters, which will cause the Transport Security
   Model to return an error (see section 5.2) If another Security Model
   (eg Community-based Security Model) is used with a secure Transport
   Model, then the cache may be populated but the other Security Model



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   may be unaware of the cache and ignore its contents (eg deriving the
   securityName from the Community name in the message instead of
   deriving it from the tmSecurityName in the tmStateReference cache).

   For incoming messages, a secure Transport Model creates a
   tmStateReference cache including a tmTransport, tmAddress,
   tmSecurityName and a tmTransportSecurityLevel, and it MAY include
   transport-specific information.  The Transport Security Model will
   determine the security-model-independent securityName and
   securityLevel, and will verify that tmTransportSecurityLevel is at
   least as strong as the requested securityLevel.  As with all security
   models, the securityName represents the principal on whose behalf a
   received SNMP message claims to have been generated.  It is not
   possible to assure the specific principal that originated a received
   SNMP message; rather, it is the principal on whose behalf the message
   was originated that is authenticated.

   For outgoing messages, the Transport Security Model creates a cache
   containing the transportDomain, transportAddress, and a
   tmSecurityName and tmRequestedSecurityLevel and passes the
   tmStateReference cache to the specified Transport Model.

   To maintain the RFC3411 modularity, the Transport Model does not know
   which securityModel will be used for an incoming message; the Message
   Processing Model will determine the securityModel to be used, in a
   Message Processing Model dependent manner.

2.1.  Security Capabilities of this Model

2.1.1.  Threats

   The Transport Security Model, when used with suitable secure
   Transport Models, provides protection against the threats identified
   by the RFC 3411 architecture [RFC3411].

   Which threats are addressed depends on the Transport Model.  The
   Transport Security Model does not address any threats itself, but
   delegates that responsibility to a secure Transport Model.

   The Transport Security Model is called a Security Model to be
   compatible with the RFC3411 architecture.  However, this Security
   Model does not provide security mechanisms such as authentication and
   encryption itself, so it SHOULD always be used with a Transport Model
   that provides appropriate security.







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2.1.2.  Security Levels

   The RFC 3411 architecture recognizes three levels of security:

      - without authentication and without privacy (noAuthNoPriv)

      - with authentication but without privacy (authNoPriv)

      - with authentication and with privacy (authPriv)

   The model-independent securityLevel parameter is used to request
   specific levels of security for outgoing messages, and to assert that
   specific levels of security were applied during the transport and
   processing of incoming messages.

   The transport layer algorithms used to provide security SHOULD NOT be
   exposed to the Transport Security Model, as the Transport Security
   Model has no mechanisms by which it can test whether an assertion
   made by a Transport Model is accurate.

   The Transport Security Model trusts that the underlying secure
   transport connection has been properly configured to support security
   characteristics at least as strong as reported in
   tmTransportSecurityLevel.

2.2.  No Sessions

   The Transport Security Model will associate state regarding each
   message and each known remote engine with a combination of
   transportDomain, transportAddress, securityName, securityModel, and
   securityLevel.

   The Transport Security Model does not recognize sessions of any kind,
   although they may be supported by a transport model.

2.3.  Coexistence

   There are two primary factors which determine whether Security Models
   can coexist.  First, there must be a mechanism to select different
   Security Models at run-time.  Second, the processing of one Security
   Model should not impact the processing of another Security Model.

   In the RFC3411 architecture, a Message Processing Model determines
   which Security Model should be called.  As of this writing, IANA has
   registered four Message Processing Models (SNMPv1, SNMPv2c, SNMPv2u/
   SNMPv2*, and SNMPv3) and three other Security Models (SNMPv1,
   SNMPv2c, and the User-based Security Model).




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   The SNMPv1 and SNMPv2c message processing described in RFC3584 (BCP
   74) [RFC3584] always selects the SNMPv1(1) Security Model for an
   SNMPv1 message, or the SNMPv2c(2) Security Model for an SNMPv2c
   message.  Since there is no field in the message format that permits
   specifying a Security Model, RFC3584 message processing does not
   permit the selection of Security Models other than SNMPv1 or SNMPv2.
   Therefore, SNMPv1 or SNMPv2c messages that go through the SNMPv1 or
   SNMPv2 Message Processing Models **as defined in RFC3584** cannot use
   the Transport Security Model.  (This does not mean an SNMPv1 or
   SNMPv2 message cannot use a secure transport model, only that the
   RFC3584 Message Processing Model will not invoke this security
   model.)

   The SNMPv2u/SNMPv2* Message Processing Model is a historic artifact
   for which there is no existing IETF specification.

   The SNMPv3 message processing defined in RFC3412 [RFC3412], extracts
   the securityModel from the msgSecurityModel field of an incoming
   SNMPv3Message.  When the extracted value of msgSecurityModel is
   transportSecurityModel(YY), security processing is directed to the
   Transport Security Model.  For an outgoing message to be secured
   using the Transport Security Model, msgSecurityModel should be set to
   transportSecurityModel(YY).

   [-- NOTE to RFC editor: replace YY with actual IANA-assigned number,
   and remove this note. ]

   The Transport Security Model uses its own MIB module for processing
   to maintain independence from other Security Models.  This allows the
   Transport Security Model to coexist with other Security Models, such
   as the User-based Security Model.

   The Transport Security Model may work with multiple Transport Models,
   but the isAccessAllowed() application service interfaces (ASI) does
   not accept a value for the Transport Model.  This security model MAY
   prepend a transport model identifier to securityName (if enabled by
   the snmpTsmConfigurationUsePrefix object), to allow different access
   control policies for identities authenticated by different Transport
   Models that use the Transport Security Model.

   The MIB module defined in this memo allows an administrator to
   configure the Transport Security Model to disable support for
   specific transport models, and to prepend a transport model
   identifier to the securityName.







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2.4.  Security Parameter Passing

   For outgoing messages, the Transport Security Model uses parameters
   provided by the SNMP application to look up or create an entry in the
   SNMP-TSM-MIB.  From such an entry, the Transport Security Model
   creates a tmStateReference.  The wholeMsg and the tmStateReference
   are passed to the appropriate Transport Model through a series of
   ASIs, as described in "Transport Subsystem for the Simple Network
   Management Protocol" [I-D.ietf-isms-tmsm].

   For incoming messages, a transport model accepts messages from the
   lower layer transport, and records the transport-related information
   and security-related information, including a human-readable name
   that represents the transport-authenticated identity, and a
   securityLevel that represents the security features provided during
   transport, in an implementation-dependent manner.  From this
   information, the transport model creates a tmStateReference to pass
   to whichever security model is selected by the Message Processing
   Model.  The wholeMsg and the tmStateReference are passed to the
   appropriate Security Model through a series of ASIs, as described in
   "Transport Subsystem for the Simple Network Management Protocol"
   [I-D.ietf-isms-tmsm].

2.5.  Notifications and Proxy

   The SNMP-TARGET-MIB module [RFC3413] contains objects for defining
   management targets, including transportDomain, transportAddress,
   securityName, securityModel, and securityLevel parameters, for
   applications such as notifications and proxy.  Transport type and
   address are configured in the snmpTargetAddrTable, and the
   securityModel, securityName, and securityLevel parameters are
   configured in the snmpTargetParamsTable.  Note that if
   snmpTsmConfigurationUsePrefix is set to true then the securityName
   value defined in the SNMP-TARGET-MIB must contain the proper
   transport prefix for the configured target to function.

   The default approach is for an administrator to statically configure
   this information to identify the targets authorized to receive
   notifications or perform proxy.

   These parameters are passed to the security model using the
   appropriate ASIs.  The Transport Security Model will use the
   parameters to determine how to create the appropriate
   tmStateReference for the selected transport model.







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3.  Cached Information and References

   When performing SNMP processing, there are two levels of state
   information that may need to be retained: the immediate state linking
   a request-response pair, and potentially longer-term state relating
   to transport and security.

   The RFC3411 architecture uses caches to maintain the short-term
   message state, and uses references in the ASIs to pass this
   information between subsystems.

   This document defines the requirements for a cache to handle the
   longer-term transport state information, using a tmStateReference
   parameter to pass this information between subsystems.

   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.  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 SHOULD also be
   discarded.

   Since the contents of a cache are meaningful only within an
   implementation, and not on-the-wire, the format of the cache and the
   LCD are implementation-specific.

3.1.  securityStateReference

   The securityStateReference parameter is defined in RFC3411.  Its
   primary purpose is to provide a mapping between a request and the
   corresponding response.  This cache is not accessible to Transport
   Models, and an entry is typically only retained for the lifetime of a
   request-response pair of messages.

3.2.  tmStateReference

   For each transport session, information about the transport security
   is stored in a cache.  The tmStateReference parameter is used to pass
   model-specific and mechanism-specific parameters between the
   Transport subsystem and transport-aware Security Models.

   The tmStateReference cache will typically remain valid for the
   duration of the transport session, and hence may be used for several
   messages.

   Since this cache is only used within an implementation, and not on-



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   the-wire, the precise contents and format are implementation-
   dependent.  However, for interoperability between Transport Models
   and transport-aware Security Models, entries in this cache must
   include at least the following fields:

      transportDomain

      transportAddress

      tmSecurityName

      tmRequestedSecurityLevel

      tmTransportSecurityLevel

      tmSameSecurity

      tmSessionID

3.2.1.  Transport information

   Information about the source of an incoming SNMP message is passed up
   from the Transport subsystem as far as the Message Processing
   subsystem.  However these parameters are not included in the
   processIncomingMsg ASI defined in RFC3411, and hence this information
   is not directly available to the Security Model.

   A transport-aware Security Model might wish to take account of the
   transport protocol and originating address when authenticating the
   request, and setting up the authorization parameters.  It is
   therefore necessary for the Transport Model to include this
   information in the tmStateReference cache, so that it is accessible
   to the Security Model.

   o  transportDomain: the transport protocol (and hence the Transport
      Model) used to receive the incoming message

   o  transportAddress: the source of the incoming message.

   Note that the ASIs used for processing an outgoing message all
   include explicit transportDomain and transportAddress parameters.
   These fields within the tmStateReference cache will typically not be
   used for outgoing messages.

3.2.2.  securityName

   There are actually three distinct "identities" that can be identified
   during the processing of an SNMP request over a secure transport:



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   o  transport principal: the transport-authenticated identity, on
      whose behalf the secure transport connection was (or should be)
      established.  This value is transport-, mechanism- and
      implementation- specific, and is only used within a given
      Transport Model.

   o  tmSecurityName: a human-readable name (in snmpAdminString format)
      representing this transport identity.  This value is transport-
      and implementation-specific, and is only used (directly) by the
      Transport and Security Models.

   o  securityName: a human-readable name (in snmpAdminString format)
      representing the SNMP principal in a model-independent manner.
      Depending on configuration this value may be prefixed by a
      transport domain specific prefix followed by a ':' (ASCII 0x3a) to
      help distinguish between securityNames from different secure
      transports.

   o  Note that the transport principal may or may not be the same as
      the tmSecurityName.  Similarly, the tmSecurityName may or may not
      be the same as the securityName as seen by the Application and
      Access Control subsystems.  In particular, a non-transport-aware
      Security Model will ignore tmSecurityName completely when
      determining the SNMP securityName.

   o  However it is important that the mapping between the transport
      principal and the SNMP securityName (for transport-aware Security
      Models) is consistent and predictable, to allow configuration of
      suitable access control and the establishment of transport
      connections.

3.2.3.  securityLevel

   There are two distinct issues relating to security level as applied
   to secure transports.  For clarity, these are handled by separate
   fields in the tmStateReference cache:

   o  tmTransportSecurityLevel: an indication from the Transport Model
      of the level of security offered by this session.  The Security
      Model can use this to ensure that incoming messages were suitably
      protected before acting on them.

   o  tmRequestedSecurityLevel: an indication from the Security Model of
      the level of security required to be provided by the transport
      protocol.  The Transport Model can use this to ensure that
      outgoing messages will not be sent over an insufficiently secure
      session.




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3.2.4.  Session Information

   For security reasons, if a secure transport session is closed between
   the time a request message is received and the corresponding response
   message is sent, then the response message SHOULD be discarded, even
   if a new session has been established.  The SNMPv3 WG decided that
   this should be a SHOULD architecturally, and it is a security-model-
   specific decision whether to REQUIRE this.

   When processing an outgoing message, if tmSameSecurity is true, then
   the tmSessionID MUST match the current transport session, otherwise
   the message MUST be discarded, and the dispatcher notified that
   sending the message failed.

   o  tmSameSecurity: this flag is used by a transport-aware Security
      Model to indicate whether the Transport Model MUST enforce this
      restriction.

   o  tmSessionID: in order to verify whether the session has changed,
      the Transport Model must be able to compare the session used to
      receive the original request with the one to be used to send the
      response.  This typically requires some form of session
      identifier.  This value is only ever used by the Transport Model,
      so the format and interpretation of this field are model-specific
      and implementation-dependent.

3.3.  Transport Security Model Cached Information

   The Transport Security Model has specific responsibilities regarding
   the cached information.

3.3.1.  tmStateReference

   For each transport model, model- and mechanism-specific parameters
   for the transport security need to be stored in a local configuration
   datastore.

   To enable a security model to correlate the identity used by specific
   transport-model and the model-independent identity referenced by
   applications, a mapping is provided in the MIB module defined in this
   memo.

   The Transport Security Model REQUIRES that the security parameters
   used for a response are the same as those used for the corresponding
   request.  It is transport-model-dependent and implementation-
   dependent how this is ensured at the transport layer.





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3.3.2.  securityStateReference

   The securityStateReference parameter is defined in RFC3411.  Its
   primary purpose is to provide a mapping between a request and the
   corresponding response.  The Transport Security Model will
   conceptually add the tmStateReference to the securityStateReference
   cache, so the security model can map transport-specific security
   parameters for a request to its corresponding response.  How the
   tmStateReference is added to the securityStateReference is
   implementation-specific.

4.  Processing an Outgoing Message

   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.

4.1.  Security Processing for an Outgoing Message

   This section describes the procedure followed by the Transport
   Security Model.

   The parameters needed for generating a message are supplied to the
   Security Model by the Message Processing Model via the
   generateRequestMsg() or the generateResponseMsg() ASI.  The Transport
   Subsystem architectural extension has added the transportDomain,
   transportAddress, and tmStateReference parameters to the original
   RFC3411 ASIs.

    statusInformation =                -- success or errorIndication
          generateRequestMsg(
          IN   messageProcessingModel  -- typically, SNMP version
          IN   globalData              -- message header, admin data
          IN   maxMessageSize          -- of the sending SNMP entity
          IN   transportDomain         -- (NEW) specified by application
          IN   transportAddress        -- (NEW) specified by application
          IN   securityModel           -- for the outgoing message
          IN   securityEngineID        -- authoritative SNMP entity
          IN   securityName            -- on behalf of this principal
          IN   securityLevel           -- Level of Security requested
          IN   scopedPDU               -- message (plaintext) payload
          OUT  securityParameters      -- filled in by Security Module
          OUT  wholeMsg                -- complete generated message
          OUT  wholeMsgLength          -- length of generated message
          OUT  tmStateReference        -- (NEW)  transport info
               )



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  statusInformation = -- success or errorIndication
          generateResponseMsg(
          IN   messageProcessingModel  -- typically, SNMP version
          IN   globalData              -- message header, admin data
          IN   maxMessageSize          -- of the sending SNMP entity
          IN   transportDomain         -- (NEW) specified by application
          IN   transportAddress        -- (NEW) specified by application
          IN   securityModel           -- for the outgoing message
          IN   securityEngineID        -- authoritative SNMP entity
          IN   securityName            -- on behalf of this principal
          IN   securityLevel           -- Level of Security requested
          IN   scopedPDU               -- message (plaintext) payload
          IN   securityStateReference  -- reference to security state
                                       -- information from original
                                       -- request
          OUT  securityParameters      -- filled in by Security Module
          OUT  wholeMsg                -- complete generated message
          OUT  wholeMsgLength          -- length of generated message
          OUT  tmStateReference        -- (NEW) transport info
               )

4.2.  Elements of Procedure for Outgoing Messages

   1) If there is a securityStateReference, then this is a response
   message.  Extract transportDomain, transportAddress, securityName,
   securityLevel, securityModel, and tmStateReference from the
   securityStateReference cache.  Set the tmRequestedSecurityLevel to
   the value of the extracted securityLevel.  The cachedSecurityData for
   this message can now be discarded.  Set the tmSameSecurity parameter
   in the tmStateReference cache to true.  Note that the securityName
   extracted from the cache will not contain any transport domain
   prefix.

   2) If there is no securityStateReference create a tmStateReference
   cache with tmRequestedSecurityLevel set to the value of
   securityLevel, tmSameSecurity set to false, and tmSecurityName and
   tmTransportIdentity to:

   a.  If the snmpTsmConfigurationUsePrefix object is set to false, then
       set the tmSecurityName set to the value of securityName.

   b.  If the snmpTsmConfigurationUsePrefix object is set to true then
       use the transportDomain to look up its transport prefix in an
       implementation dependent way.  (The transport prefix will likely
       be described in the transport domain object's DESCRIPTION for a
       given transportDomain.)  Strip this prefix and the ':' (ASCII
       0x3a) off of the securityName and place the results in the
       tmSecurityName value.  If the securityName does not begin with



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       the necessary prefix followed by a ':' (ASCII 0x3a) then
       snmpTsmInvalidPrefix counter is incremented and an error
       indication is returned to the calling module.  If the prefix
       look-up using the transportDomain fails for any reason then the
       snmpTsmInvalidPrefixDomain counter is incremented and an error
       indication is returned to the calling module.

   3) Fill in the securityParameters with a zero-length OCTET STRING
   ('0400').

   4) Combine the message parts into a wholeMsg and calculate
   wholeMsgLength.

   5) The wholeMsg, wholeMsgLength, securityParameters and
   tmStateReference are returned to the calling Message Processing Model
   with the statusInformation set to success.

5.  Processing an Incoming SNMP Message

   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.  Security Processing for an Incoming Message

   This section describes the procedure followed by the Transport
   Security Model whenever it receives an incoming message from a
   Message Processing Model.  The ASI from a Message Processing Model to
   the Security Subsystem for a received message is:

   statusInformation =  -- errorIndication or success
                            -- error counter OID/value if error
   processIncomingMsg(
   IN   messageProcessingModel    -- typically, SNMP version
   IN   maxMessageSize            -- from the received message
   IN   securityParameters        -- from the received message
   IN   securityModel             -- from the received message
   IN   securityLevel             -- from the received message
   IN   wholeMsg                  -- as received on the wire
   IN   wholeMsgLength            -- length as received on the wire
   IN   tmStateReference          -- (NEW) 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



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    )                         -- information, needed for response

5.2.  Elements of Procedure for Incoming Messages

   1) Set the securityEngineID to the local snmpEngineID.

   2) If tmStateReference does not refer to a cache containing values
   for transportDomain, tmSecurityName and tmTransportSecurityLevel,
   then the snmpTsmInvalidCaches counter is incremented, an error
   indication is returned to the calling module, and Security Model
   processing stops for this message.

   3) Set the securityName:

   a.  If the snmpTsmConfigurationUsePrefix object is set false, copy
       the tmSecurityName to securityName.

   b.  If the snmpTsmConfigurationUsePrefix object is set to true then
       use the transportDomain to look up the needed transport prefix in
       an implementation dependent way.  (The transport prefix will
       likely be described in the transport domain object's DESCRIPTION
       clause for a given transportDomain.)  Set the securityName to the
       concatenation of the transport's prefix, the colon character
       (':', ASCII 0x3a) and the tmSecurityName.  If the prefix look-up
       using the transportDomain fails for any reason then the
       snmpTsmInvalidPrefixDomain counter is incremented and an error
       indication is returned to the calling module.

   4) Compare the value of tmTransportSecurityLevel in the
   tmStateReference cache to the value of the securityLevel parameter
   passed in the processIncomingMsg ASI.  If securityLevel specifies
   privacy (Priv), and tmTransportSecurityLevel specifies no privacy
   (noPriv), or securityLevel specifies authentication (auth) and
   tmTransportSecurityLevel specifies no authentication (noAuth) was
   provided by the Transport Model, then the
   snmpTsmInadequateSecurityLevels counter is incremented, and an error
   indication (unsupportedSecurityLevel) together with the OID and value
   of the incremented counter is returned to the calling module.
   Transport Security Model processing stops for this message.

   5)The security data is cached as cachedSecurityData, so that a
   possible response to this message will use the same security
   parameters.  Then securityStateReference is set for subsequent
   reference to this cached data.  For Transport Security Model, the
   securityStateReference includes a reference to the tmStateReference
   cache.

   6) The scopedPDU component is extracted from the wholeMsg.



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

   8) 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 ASI.

6.  MIB Module Overview

   This MIB module provides management of the Transport Security Model.
   It defines some needed textual conventions, some statistics, and a
   configuration scalar for use by the Transport Security Model.

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.

6.2.  The snmpTsmStats Subtree

   This subtree contains counters specific to the Transport Security
   Model, that provide information for identifying fault conditions.

6.3.  The snmpTsmConfiguration Subtree

   This subtree contains configuration objects that enable
   administrators to specify if they want securityNames derived from
   transports to begin with a transport specific prefix string.

6.4.  Relationship to Other MIB Modules

   Some management objects defined in other MIB modules are applicable
   to an entity implementing the Transport Security Model.  In
   particular, it is assumed that an entity implementing the Transport
   Security Model will implement the SNMPv2-MIB [RFC3418] and the SNMP-
   FRAMEWORK-MIB [RFC3411].

6.4.1.  Relationship to the SNMPv2-MIB

   The 'system' group in the SNMPv2-MIB [RFC3418] is defined as being
   mandatory for all systems, and the objects apply to the entity as a
   whole.  The 'system' group provides identification of the management
   entity and certain other system-wide data.  The snmpInASNParseErrs
   counter is incremented during the elements of procedure.  The SNMP-
   TSM-MIB does not duplicate those objects.




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6.4.2.  Relationship to the SNMP-FRAMEWORK-MIB

   The SNMP-FRAMEWORK-MIB provides definitions for the concepts of
   SnmpEngineID, enumeration of Message Processing Models, Security
   Models and Security Levels, and object definitions for snmpEngineID
   These are important for implementing the Transport Security Model,
   but are not needed to implement the SNMP-TSM-MIB.

6.4.3.  MIB Modules Required for IMPORTS

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

7.  MIB module definition


 SNMP-TSM-MIB DEFINITIONS ::= BEGIN

 IMPORTS
     MODULE-IDENTITY, OBJECT-TYPE,
     mib-2, Counter32
       FROM SNMPv2-SMI
     MODULE-COMPLIANCE, OBJECT-GROUP
       FROM SNMPv2-CONF
     TruthValue
        FROM SNMPv2-TC
     ;

 snmpTsmMIB MODULE-IDENTITY
     LAST-UPDATED "200807100000Z"
     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
                     Jacobs University Bremen
                     Campus Ring 1
                     28725 Bremen



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                     Germany
                     +49 421 200-3587
                     j.schoenwaelder@iu-bremen.de

                   Editor:
                     David Harrington
                     Huawei Technologies USA
                     1700 Alma Dr.
                     Plano TX 75075
                     USA
                     +1 603-436-8634
                     ietfdbh@comcast.net

                     Wes Hardaker
                     Sparta, Inc.
                     P.O. Box 382
                     Davis, CA  95617
                     USA
                     +1 530 792 1913
                     ietf@hardakers.net
                  "
     DESCRIPTION "The Transport Security Model MIB

                  In keeping with the RFC 3411 design decisions
                  to use self-contained documents, the RFC which
                  contains the definition of this MIB module also
                  includes the elements of procedure which are
                  needed for processing the Transport Security
                  Model for SNMP. These MIB objects
                  SHOULD NOT be modified via other subsystems
                  or models defined in other document..
                  This allows the Transport Security Model
                  for SNMP to be designed and documented as
                  independent and self- contained, having no
                  direct impact on other modules, and this
                  allows this module to be upgraded and
                  supplemented as the need arises, and to
                  move along the standards track on different
                  time-lines from other modules.

                  Copyright (C) The IETF Trust (2008). This
                  version of this MIB module is part of RFC XXXX;
                  see the RFC itself for full legal notices.
 -- NOTE to RFC editor: replace XXXX with actual RFC number
 --                     for this document and remove this note
                 "

     REVISION    "200807100000Z"



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     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 SNMP-TSM-MIB
 -- ---------------------------------------------------------- --

 snmpTsmNotifications OBJECT IDENTIFIER ::= { snmpTsmMIB 0 }
 snmpTsmMIBObjects    OBJECT IDENTIFIER ::= { snmpTsmMIB 1 }
 snmpTsmConformance   OBJECT IDENTIFIER ::= { snmpTsmMIB 2 }

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

 -- Statistics for the Transport Security Model


 snmpTsmStats         OBJECT IDENTIFIER ::= { snmpTsmMIBObjects 1 }

 snmpTsmInvalidCaches OBJECT-TYPE
     SYNTAX       Counter32
     MAX-ACCESS   read-only
     STATUS       current
     DESCRIPTION "The number of messages dropped because the
                  tmStateReference referred to an invalid cache.
                 "
     ::= { snmpTsmStats 1 }

 snmpTsmInadequateSecurityLevels OBJECT-TYPE
     SYNTAX       Counter32
     MAX-ACCESS   read-only
     STATUS       current
     DESCRIPTION "The number of incoming messages dropped because
                  the securityLevel asserted by the transport model was
                  less than the securityLevel requested by the
                  application.
                 "
     ::= { snmpTsmStats 2 }

 snmpTsmInvalidDomains OBJECT-TYPE
     SYNTAX       Counter32



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     MAX-ACCESS   read-only
     STATUS       current
     DESCRIPTION "The number of messages dropped because the
                  specified transport domain is not supported or is
                  disabled.
                 "
     ::= { snmpTsmStats 3 }

 snmpTsmInvalidPrefixDomain OBJECT-TYPE
     SYNTAX       Counter32
     MAX-ACCESS   read-only
     STATUS       current
     DESCRIPTION "The number of messages dropped because
                  snmpTsmConfigurationUsePrefix was set to true and
                  there is no known prefix for the specified transport
                  domain.
                 "
     ::= { snmpTsmStats 4 }

 snmpTsmInvalidPrefix OBJECT-TYPE
     SYNTAX       Counter32
     MAX-ACCESS   read-only
     STATUS       current
     DESCRIPTION "The number of messages dropped because
                  the securityName associated with an outgoing message
                  did not contain a valid transport domain prefix.
                 "
     ::= { snmpTsmStats 5 }


 -- -------------------------------------------------------------
 -- Configuration
 -- -------------------------------------------------------------

 -- Configuration for the Transport Security Model


 snmpTsmConfiguration   OBJECT IDENTIFIER ::= { snmpTsmMIBObjects 2 }

 snmpTsmConfigurationUsePrefix OBJECT-TYPE
     SYNTAX      TruthValue
     MAX-ACCESS  read-write
     STATUS      current
     DESCRIPTION "If this object is set to true then securityNames
                  passing to and from the application will contain a
                  transport domain specific prefix. If set to true then
                  the prefix will be added by the TSM to the
                  securityName for incoming messages and removed from



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                  the securityName for outgoing messages. The resulting
                  securityName, when prefixed, will begin with the
                  transport specific prefix, followed by a ':'
                  character (ASCII 0x3a). The transport specific prefix
                  should be defined within the transport domain's
                  object definition.
                 "
     DEFVAL { false }
     ::= { snmpTsmConfiguration 1 }

 -- -------------------------------------------------------------
 -- snmpTsmMIB - Conformance Information
 -- -------------------------------------------------------------

 snmpTsmCompliances OBJECT IDENTIFIER ::= { snmpTsmConformance 1 }

 snmpTsmGroups      OBJECT IDENTIFIER ::= { snmpTsmConformance 2 }

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

 snmpTsmCompliance MODULE-COMPLIANCE
     STATUS      current
     DESCRIPTION "The compliance statement for SNMP engines that support
                  the SNMP-TSM-MIB
                 "
     MODULE
         MANDATORY-GROUPS { snmpTsmGroup }
     ::= { snmpTsmCompliances 1 }

 -- -------------------------------------------------------------
 -- Units of conformance
 -- -------------------------------------------------------------
 snmpTsmGroup OBJECT-GROUP
     OBJECTS {
         snmpTsmInvalidCaches,
         snmpTsmInadequateSecurityLevels,
         snmpTsmInvalidDomains,
         snmpTsmInvalidPrefixDomain,
         snmpTsmInvalidPrefix,
         snmpTsmConfigurationUsePrefix
     }
     STATUS      current
     DESCRIPTION "A collection of objects for maintaining
                  information of an SNMP engine which implements
                  the SNMP Transport Security Model.
                 "



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     ::= { snmpTsmGroups 2 }


 END


8.  Security Considerations

   This document describes a Security Model that permits SNMP to utilize
   security services provided through an SNMP Transport Model.  The
   Transport Security Model relies on Transport Models for mutual
   authentication, binding of keys, confidentiality and integrity.  The
   security threats and how those threats are mitigated should be
   covered in detail in the specification of the Transport Model and the
   underlying secure transport.

   Transport Security Model relies on a Transport Model to provide an
   authenticated principal for mapping to securityName, and an assertion
   of tmTransportSecurityLevel.  New transport models SHOULD provide a
   transport domain prefix to allow operators to distinguish between
   identities whose authentication is coordinated by different transport
   models.  This should preferably be specified in the transport domain
   object's DESCRIPTION clause.  The prefix MUST be added and removed
   appropriately by the Transport Security Model if the administrator
   has set snmpTsmConfigurationUsePrefix to true and MUST NOT be added
   and removed if snmpTsmConfigurationUsePrefix is set to false.

   The Transport Security Model is called a Security Model to be
   compatible with the RFC3411 architecture.  However, this Security
   Model provides no security itself.  It SHOULD always be used with a
   Transport Model that provides security, but this is a run-time
   decision of the operator or management application, or a
   configuration decision of an operator.

8.1.  MIB module security

   There are a number of management objects defined in this MIB module
   with a MAX-ACCESS clause of read-write and/or read-create.  Such
   objects may be considered sensitive or vulnerable in some network
   environments.  The support for SET operations in a non-secure
   environment without proper protection can have a negative effect on
   network operations.  These are the tables and objects and their
   sensitivity/vulnerability:

   o  The snmpTsmConfigurationUsePrefix object could be modified
      creating a denial of service or authorizing SNMP messages that
      would not have previously been authorized by an Access Control
      Model (e.g. the VACM).



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   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  snmpTsmInvalidCaches and snmpTsmInadequateSecurityLevels and
      snmpTsmInvalidDomains may make it easier for an attacker to detect
      vulnerabilities.

   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 USM and Transport Security Model 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.

9.  IANA Considerations

   [DISCUSS: should we have default ports for request/response traffic
   and for notifications?]

   IANA is requested to assign:

   1.  an SMI number under mib-2, for the MIB module in this document,

   2.  a value, preferably 4, to identify the Transport Security Model,
       in the Security Models registry at
       http://www.iana.org/assignments/snmp-number-spaces.  This should
       result in the following table of values:







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   Value   Description                         References
   -----   -----------                         ----------
     0     reserved for 'any'                  [RFC3411]
     1     reserved for SNMPv1                 [RFC3411]
     2     reserved for SNMPv2c                [RFC3411]
     3     User-Based Security Model (USM)     [RFC3411]
     YY    Transport Security Model (TSM)      [RFCXXXX]

   -- NOTE to RFC editor: replace XXXX with actual RFC number
   --                     for this document and remove this note
   -- NOTE to RFC editor: replace YY with actual IANA-assigned number,
                          throughout this document and remove this note.

10.  Acknowledgements

   The editors would like to thank Jeffrey Hutzelman for sharing his SSH
   insights, and Dave Shields for an outstanding job wordsmithing the
   existing document to improve organization and clarity.

11.  References

11.1.  Normative References

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

   [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.

   [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)",



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                         STD 62, RFC 3412, December 2002.

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

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

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

   [I-D.ietf-isms-tmsm]  Harrington, D. and J. Schoenwaelder, "Transport
                         Subsystem for the Simple Network Management
                         Protocol (SNMP)", draft-ietf-isms-tmsm-13 (work
                         in progress), August 2008.

11.2.  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.

   [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.

   [RFC3584]             Frye, R., Levi, D., Routhier, S., and B.
                         Wijnen, "Coexistence between Version 1, Version
                         2, and Version 3 of the Internet-standard
                         Network Management Framework", BCP 74,
                         RFC 3584, August 2003.

Appendix A.  Notification Tables Configuration

   The SNMP-TARGET-MIB and SNMP-NOTIFICATION-MIB [RFC3413] are used to
   configure notification originators with the destinations to which
   notifications should be sent.

   Most of the configuration is security-model-independent and
   transport-model-independent.

   The values we will use in the examples for the five model-independent
   security and transport parameters are:



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      transportDomain = snmpSSHDomain

      transportAddress = 192.0.2.1:162

      securityModel = Transport Security Model

      securityName = sampleUser

      securityLevel = authPriv

   The following example will configure the Notification Originator to
   send informs to a Notification Receiver at host 192.0.2.1 port 162
   using the securityName "sampleUser".  The columns marked with a "*"
   are the items that are Security Model or Transport Model specific.

   The configuration for the "sampleUser" settings in the SNMP-VIEW-
   BASED-ACM-MIB objects are not shown here for brevity.  First we
   configure which type of notification should be sent for this taglist
   (toCRTag).  In this example, we choose to send an Inform.
     snmpNotifyTable row:
          snmpNotifyName                 CRNotif
          snmpNotifyTag                  toCRTag
          snmpNotifyType                 inform
          snmpNotifyStorageType          nonVolatile
          snmpNotifyColumnStatus         createAndGo

   Then we configure a transport address to which notifications
   associated with this taglist should be sent, and we specify which
   snmpTargetParamsEntry should be used (toCR) when sending to this
   transport address.
          snmpTargetAddrTable row:
             snmpTargetAddrName              toCRAddr
         *   snmpTargetAddrTDomain           snmpSSHDomain
             snmpTargetAddrTAddress          192.0.2.1:162
             snmpTargetAddrTimeout           1500
             snmpTargetAddrRetryCount        3
             snmpTargetAddrTagList           toCRTag
             snmpTargetAddrParams            toCR   (must match below)
             snmpTargetAddrStorageType       nonVolatile
             snmpTargetAddrColumnStatus      createAndGo


   Then we configure which principal at the host should receive the
   notifications associated with this taglist.  Here we choose
   "sampleUser", who uses the Transport Security Model.






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         snmpTargetParamsTable row:
             snmpTargetParamsName            toCR
             snmpTargetParamsMPModel         SNMPv3
         *   snmpTargetParamsSecurityModel   TransportSecurityModel
             snmpTargetParamsSecurityName    "sampleUser"
             snmpTargetParamsSecurityLevel   authPriv
             snmpTargetParamsStorageType     nonVolatile
             snmpTargetParamsRowStatus       createAndGo


A.1.  Transport Security Model Processing for Notifications

   The Transport Security Model is called using the generateRequestMsg()
   ASI, with the following parameters (* are from the above tables):

    statusInformation =                -- success or errorIndication
          generateRequestMsg(
          IN   messageProcessingModel  -- *snmpTargetParamsMPModel
          IN   globalData              -- message header, admin data
          IN   maxMessageSize          -- of the sending SNMP entity
          IN   transportDomain         -- *snmpTargetAddrTDomain
          IN   transportAddress        -- *snmpTargetAddrTAddress
          IN   securityModel           -- *snmpTargetParamsSecurityModel
          IN   securityEngineID        -- immaterial; TSM will ignore.
          IN   securityName            -- snmpTargetParamsSecurityName
          IN   securityLevel           -- *snmpTargetParamsSecurityLevel
          IN   scopedPDU               -- message (plaintext) payload
          OUT  securityParameters      -- filled in by Security Module
          OUT  wholeMsg                -- complete generated message
          OUT  wholeMsgLength          -- length of generated message
          OUT  tmStateReference        -- reference to transport info
               )

   The Transport Security Model will determine the Transport Model based
   on the snmpTargetAddrTDomain.  The selected Transport Model will
   select the appropriate transport connection using the
   snmpTargetAddrTAddress, snmpTargetParamsSecurityName, and
   snmpTargetParamsSecurityLevel.

Appendix B.  Processing Differences between USM and Secure Transport

   USM and secure transports differ in the processing order and
   responsibilities within the RFC3411 architecture.  While the steps
   are the same, they occur in a different order, and may be done by
   different subsystems.  The following lists illustrate the difference
   in the flow and the responsibility for different processing steps for
   incoming messages when using USM and when using a secure transport.
   (Note that these lists are simplified for illustrative purposes, and



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   do not represent all details of processing.  Transport Models must
   provide the detailed elements of procedure.)

   With USM, SNMPv1, and SNMPv2c Security Models, security processing
   starts when the Message Processing Model decodes portions of the
   ASN.1 message to extract header fields that are used to determine
   which Security Model should process the message to perform
   authentication, decryption, timeliness checking, integrity checking,
   and translation of parameters to model-independent parameters.  By
   comparison, a secure transport performs those security functions on
   the message, before the ASN.1 is decoded.

   Step 6 cannot occur until after decryption occurs.  Step 6 and beyond
   are the same for USM and a secure transport.

B.1.  USM and the RFC3411 Architecture

   1) decode the ASN.1 header (Message Processing Model)

   2) determine the SNMP Security Model and parameters (Message
      Processing Model)

   3) verify securityLevel.  [Security Model]

   4) translate parameters to model-independent parameters (Security
      Model)

   5) authenticate the principal, check message integrity and
      timeliness, and decrypt the message.  [Security Model]

   6) determine the pduType in the decrypted portions (Message
      Processing Model), and

   7) pass on the decrypted portions with model-independent parameters.

B.2.  Transport Subsystem and the RFC3411 Architecture

   1) authenticate the principal, check integrity and timeliness of the
      message, and decrypt the message.  [Transport Model]

   2) translate parameters to model-independent parameters (Transport
      Model)

   3) decode the ASN.1 header (Message Processing Model)







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   4) determine the SNMP Security Model and parameters (Message
      Processing Model)

   5) verify securityLevel [Security Model]

   6) determine the pduType in the decrypted portions (Message
      Processing Model), and

   7) pass on the decrypted portions with model-independent security
      parameters

   If a message is secured using a secure transport layer, then the
   Transport Model should provide the translation from the authenticated
   identity (e.g., an SSH user name) to a human-friendly identifier in
   step 2.  The security model will provide a mapping from that
   identifier to a model-independent securityName.

Appendix C.  Open Issues

      Does TSM need to have a mapping table to handle the translations
      from tmSecurityName to securityName?

      Do we need administratively definable transform selection?

      Do we need to let operators disable support for some transports?

Appendix D.  Change Log

   From -08- to -09-

      Added the transport domain specific prefix adding/removing support
      as agreed to within the ISMS WG.  The implementation is a bit
      different than what was originally discussed and is now housed
      entirely within this document and requires only a string
      allocation in the TM documents.  In the end this form greatly
      reduced the documentation and procedure complexity in most
      documents.

      Added the snmpTsmConfigurationUsePrefix scalar.

      Removed the snmpTsmLCDTable since it is no longer needed.

      Removed the snmpTsmLCDDomainTable since it is not needed with the
      prefix addition replaced the functionality.

   From -07- to -08-





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      Added tables to the MIB module to define a Transport Security
      Model-specific LCD, and updated the Elements of Procedure.  This
      was because references to an abstract LCD sort of owned by both
      the security model and the transport model were found confusing.

      Realized we referred to the MIB module in text as SNMP-TRANSPORT-
      SM-MIB, but SNMP-TSM-MIB in the module.  Changed all occurrences
      of SNMP-TRANSPORT-SM-MIB to SNMP-TSM-MIB, following RFC4181
      guidelines for naming.

      Updated Security Considerations to warn about writable objects,
      and added the new counter to the readable objects list.

      Changed snmpTsmLCDName to snmpTsmLCDTmSecurityName

   From -05- to -06-

      Fixed a bunch of editorial nits

      Fixed the note about terminology consistent with SNMPv3.

      Updated MIB assignment to by rfc4181 compatible

      Replaced tmSameSession with tmSameSecurity to eliminate session-
      matching from the security model.

      Eliminated all reference to the LCD from the Transport Security
      Model; the LCD is now TM-specific.

      Added tmTransportSecurityLevel and tmRequestedSecurityLevel to
      clarify incoming versus outgoing

   From -04- to -05-

      Removed check for empty securityParameters for incoming messages

      Added a note about terminology, for consistency with SNMPv3 rather
      than with RFC2828.

   From -03- to -04-

      Editorial changes requested by Tom Petch, to clarify behavior with
      SNMPv1/v2c

      Added early discussion of how TSM fits into the architecture to
      clarify behavior when RFC3584 security models are co-resident.





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      Editorial changes requested by Bert Wijnen, to eliminate version-
      specific discussions.

      Removed sections on version-specific message formats.

      Removed discussion of SNMPv3 in Motivation section.

      Added discussion of request/response session matching.

   From -02- to -03-

      Editorial changes suggested by Juergen Schoenwaelder

      Capitalized Transport Models, Security Models, and Message
      Processing Models, to be consistent with RFC341x conventions.

      Eliminated some text that duplicated RFC3412, especially in
      Elements of Procedure.

      Changed the encoding of msgSecurityParameters

      Marked the (NEW) fields added to existing ASIs

      Modified text intro discussing relationships to other MIB modules.

   From -01- to -02-

      Changed transportSecurityModel(4) to transportSecurityModel(YY),
      waiting for assignment

      cleaned up elements of procedure [todo]s

      use the same errorIndication as USM for unsupportedSecurityLevel

      fixed syntax of tsmInadequateSecurity counter

      changed the "can and will use" the same security parameters to
      "can use", to allow responses that have different security
      parameters than the request.

      removed "Relationship to the SNMP-FRAMEWORK-MIB"

      cleaned up "MIB Modules Required for IMPORTS"



   From -00- to -01-




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      made the Transport Model not know anything about the Security
      Model.

      modified the elements of procedure sections, given the
      implications of this change.

      simplified elements of procedure, removing most info specified in
      architecture/subsystem definitions.

      rethought the coexistence section

      noted the implications of the Transport Security Model on
      isAccessAllowed()

      modified all text related to the LCD.

      removed most of the MIB (now the TSM has no configuration
      parameters).

      added counters needed to support elements of procedure

      renamed MIB module, and registered under snmpModules

      updated IANA and Security Considerations

      updated references.

      modified the notification configurations.

   From SSHSM-04- to Transport-security-model-00

      added tsmUserTable

      updated Appendix - Notification Tables Configuration

      remove open/closed issue appendices

      changed tmSessionReference to tmStateReference













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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


   Wes Hardaker
   Sparta, Inc.
   P.O. Box 382
   Davis, CA  95617
   US

   Phone: +1 530 792 1913
   EMail: ietf@hardakers.net































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