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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                       November 18, 2007
Expires: May 21, 2008


                   Transport Security Model for SNMP
              draft-ietf-isms-transport-security-model-07

Status of This Memo

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   This Internet-Draft will expire on May 21, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

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.




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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  The Internet-Standard Management Framework . . . . . . . .  3
     1.2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  3
     1.3.  Modularity . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.4.  Motivation . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.5.  Constraints  . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  How the Transport Security Model Fits in the Architecture  . .  5
     2.1.  Security Capabilities of this Model  . . . . . . . . . . .  6
       2.1.1.  Threats  . . . . . . . . . . . . . . . . . . . . . . .  6
       2.1.2.  Security Levels  . . . . . . . . . . . . . . . . . . .  7
     2.2.  No Sessions  . . . . . . . . . . . . . . . . . . . . . . .  7
     2.3.  Coexistence  . . . . . . . . . . . . . . . . . . . . . . .  7
     2.4.  Security Parameter Passing . . . . . . . . . . . . . . . .  8
     2.5.  Notifications and Proxy  . . . . . . . . . . . . . . . . .  9
   3.  Cached Information and References  . . . . . . . . . . . . . .  9
     3.1.  tmStateReference . . . . . . . . . . . . . . . . . . . . . 10
     3.2.  securityStateReference . . . . . . . . . . . . . . . . . . 10
   4.  Processing an Outgoing Message . . . . . . . . . . . . . . . . 10
     4.1.  Security Processing for an Outgoing Message  . . . . . . . 10
     4.2.  Elements of Procedure for Outgoing Messages  . . . . . . . 12
   5.  Processing an Incoming SNMP Message  . . . . . . . . . . . . . 12
     5.1.  Security Processing for an Incoming Message  . . . . . . . 12
     5.2.  Elements of Procedure for Incoming Messages  . . . . . . . 13
   6.  MIB Module Overview  . . . . . . . . . . . . . . . . . . . . . 14
     6.1.  Structure of the MIB Module  . . . . . . . . . . . . . . . 14
     6.2.  The tsmStats Subtree . . . . . . . . . . . . . . . . . . . 14
     6.3.  Relationship to Other MIB Modules  . . . . . . . . . . . . 14
       6.3.1.  Relationship to the SNMPv2-MIB . . . . . . . . . . . . 14
       6.3.2.  Relationship to the SNMP-FRAMEWORK-MIB . . . . . . . . 15
       6.3.3.  MIB Modules Required for IMPORTS . . . . . . . . . . . 15
   7.  MIB module definition  . . . . . . . . . . . . . . . . . . . . 15
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
     8.1.  MIB module security  . . . . . . . . . . . . . . . . . . . 19
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 20
     10.2. Informative References . . . . . . . . . . . . . . . . . . 21
   Appendix A.  Notification Tables Configuration . . . . . . . . . . 21
     A.1.  Transport Security Model Processing for Notifications  . . 22
   Appendix B.  Processing Differences between USM and Secure
                Transport . . . . . . . . . . . . . . . . . . . . . . 23
     B.1.  USM and the RFC3411 Architecture . . . . . . . . . . . . . 24
     B.2.  Transport Subsystem and the RFC3411 Architecture . . . . . 24
   Appendix C.  Open Issues . . . . . . . . . . . . . . . . . . . . . 24
   Appendix D.  Change Log  . . . . . . . . . . . . . . . . . . . . . 24




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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 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
   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).

   When a secure Transport Model creates a tmStateReference cache for an



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   incoming message, it will include a tmTransport, tmAddress,
   tmSecurityName and a tmTransportSecurityLevel, and it MAY include
   transport-specific information.  When the Transport Security Model
   sends a message, it will create a cache containing the specified
   transportDomain, transportAddress, securityName, and securityLevel
   parameters.  The Transport Security Model will pass the
   tmStateReference to enable the transport model to extract
   corresponding transport-specific information from the
   tmStateReference cache, in an implementation-dependent manner.

   When the Transport Security Model determines that a cache does not
   yet exist corresponding to the specified transportDomain,
   transportAddress, secuirtyName, and securityLevel parameters, it
   creates one that contains a tmSecurityName and
   tmRequestedSecurityLevel and passes the tmStateReference cache to the
   specified Transport Model.

   The Transport Security Model will determine the security-model-
   independent securityName and securityLevel, and will verify for
   incoming messages that tmTransportSecurityLevel is at least as strong
   as the requested securityLevel.

   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).

   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



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   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.

   Note that the Transport Security Model may work with multiple
   Transport Models, but the isAccessAllowed() application service
   interfaces (ASI) only accepts a value for the Security Model, not for
   Transport Models.  As a result, it is not possible to have different
   access control rules for different Transport Models that use the
   Transport Security Model.

2.4.  Security Parameter Passing

   For outgoing messages, Transport Security Model uses parameters
   provided by the SNMP application to determine if a corresponding
   tmStateReference cache exists, or to create a suitable
   tmStateReference cache.  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, the Transport Model accepts messages from the
   lower layer transport, and records the transport-related information



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   and security-related information, including a tmSecurityName that
   represents the transport-authenticated identity, and a
   tmTransportSecurityLevel that represents the security features
   provided during transport, in a cache referenced by tmStateReference.
   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.

   For the Transport Security Model, these will be translated as needed
   into tmSecurityName and tmRequestedSecurityLevel.

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

3.  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
   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 document describes
   caches, and differentiates the tmStateReference from the
   securityStateReference, but how this is represented internally is an
   implementation decision.

   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 connection, the state information for that relationship
   might also be discarded.





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3.1.  tmStateReference

   For each transport model, information about the transport security
   may be stored in a cache to pass model- and mechanism-specific
   parameters.

   For security reasons, the Transport Security Model REQUIRES that the
   security parameters used for a response are the same as those used
   for the corresponding request, and passes a tmSameSecurity parameter
   in the tmStateReference cache for outgoing messages to indicate that
   the same security MUST be used for the outgoing response as was used
   for the corresponding incoming request.  It is transport-model-
   dependent and implementation-dependent how this is ensured at the
   transport layer.

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

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.  A sample model-specific cache can be found
   in RFC3414 [RFC3414].

   Transport models do not have access to the securityStateReference.
   For the Transport Security Model, it is important to ensure that the
   security parameters used for a request match those used for the
   corresponding response.  The Transport Security Model will
   conceptually add the tmStateReference to the securityStateReference
   cache, so the transport 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.



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   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
               )


  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
               )





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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.

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

   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:












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   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
    )                         -- 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 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 securityName to the value of tmSecurityName from the cache
   referenced by tmStateReference.

   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



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   cache.

   6) The scopedPDU component is extracted from the wholeMsg.

   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, and some statistics.

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 tsmStats Subtree

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

6.3.  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].

6.3.1.  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-
   TRANSPORT-SM-MIB does not duplicate those objects.







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6.3.2.  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-TRANSPORT-SM-MIB.

6.3.3.  MIB Modules Required for IMPORTS

   The following MIB module imports items from [RFC2578] and [RFC2580].

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
       ;

   snmpTsmMIB MODULE-IDENTITY
       LAST-UPDATED "200710140000Z"
       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
                     Germany
                     +49 421 200-3587
                     j.schoenwaelder@iu-bremen.de



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                  Editor:
                     David Harrington
                     Huawei Technologies USA
                     1700 Alma Dr.
                     Plano TX 75075
                     USA
                     +1 603-436-8634
                     ietfdbh@comcast.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 documents.
                        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 (2007). 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     "200710140000Z"
          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-TRANSPORT-SM-MIB
   -- ---------------------------------------------------------- --




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   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 actual securityLevel provided was less than
                    the requested securityLevel.
                   "
       ::= { snmpTsmStats 2 }

   -- -------------------------------------------------------------
   -- 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



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            the SNMP-TRANSPORT-SM-MIB"
       MODULE
           MANDATORY-GROUPS { snmpTsmGroup }
       ::= { snmpTsmCompliances 1 }

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

       ::= { 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.

   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.






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8.1.  MIB module security

   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  snmpTsmInvalidCaches and snmpTsmInadequateSecurityLevels 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

   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.  References

10.1.  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)",
                         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.




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   [RFC3418]             Presuhn, R., "Management Information Base (MIB)
                         for the Simple Network Management Protocol
                         (SNMP)", STD 62, RFC 3418, 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-10 (work
                         in progress), September 2007.

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.

   [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:
      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.



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   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.
         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):







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

   With USM and other Security Models, security processing starts when
   the Message Processing Model decodes portions of the ASN.1 message to
   extract an opaque block of security parameters and header parameters
   that identify which Security Model should process the message to
   perform authentication, decryption, timeliness checking, integrity
   checking, and translation of parameters to model-independent
   parameters.  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.




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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)
   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 model-independent securityName
   in step 2.

Appendix C.  Open Issues

      none.

Appendix D.  Change Log

   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.




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      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.
      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"





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   From -00- to -01-

      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


Author's Address

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

   Phone: +1 603 436 8634
   EMail: dharrington@huawei.com












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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   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, THE IETF TRUST AND
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Acknowledgement

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







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