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rfc:rfc3412

Network Working Group J. Case Request for Comments: 3412 SNMP Research, Inc. STD: 62 D. Harrington Obsoletes: 2572 Enterasys Networks Category: Standards Track R. Presuhn

                                                    BMC Software, Inc.
                                                             B. Wijnen
                                                   Lucent Technologies
                                                         December 2002
             Message Processing and Dispatching for the
             Simple Network Management Protocol (SNMP)

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

 This document describes the Message Processing and Dispatching for
 Simple Network Management Protocol (SNMP) messages within the SNMP
 architecture.  It defines the procedures for dispatching potentially
 multiple versions of SNMP messages to the proper SNMP Message
 Processing Models, and for dispatching PDUs to SNMP applications.
 This document also describes one Message Processing Model - the
 SNMPv3 Message Processing Model.  This document obsoletes RFC 2572.

Case, et al. Standards Track [Page 1] RFC 3412 Message Processing and Dispatching for SNMP December 2002

Table of Contents

 1. Introduction ................................................    3
 2. Overview ....................................................    4
 2.1. The Dispatcher ............................................    5
 2.2. Message Processing Subsystem ..............................    5
 3. Elements of Message Processing and Dispatching ..............    6
 3.1. messageProcessingModel ....................................    6
 3.2. pduVersion ................................................    6
 3.3. pduType ...................................................    7
 3.4. sendPduHandle .............................................    7
 4. Dispatcher Elements of Procedure ............................    7
 4.1. Sending an SNMP Message to the Network ....................    7
 4.1.1. Sending a Request or Notification .......................    8
 4.1.2. Sending a Response to the Network .......................    9
 4.2. Receiving an SNMP Message from the Network ................   11
 4.2.1. Message Dispatching of received SNMP Messages ...........   11
 4.2.2. PDU Dispatching for Incoming Messages ...................   12
 4.2.2.1. Incoming Requests and Notifications ...................   13
 4.2.2.2. Incoming Responses ....................................   14
 4.3. Application Registration for Handling PDU types ...........   15
 4.4. Application Unregistration for Handling PDU Types .........   16
 5. Definitions .................................................   16
 5.1. Definitions for SNMP Message Processing and Dispatching ...   16
 6. The SNMPv3 Message Format ...................................   19
 6.1. msgVersion ................................................   20
 6.2. msgID .....................................................   20
 6.3. msgMaxSize ................................................   21
 6.4. msgFlags ..................................................   21
 6.5. msgSecurityModel ..........................................   24
 6.6. msgSecurityParameters .....................................   24
 6.7. scopedPduData .............................................   24
 6.8. scopedPDU .................................................   24
 6.8.1. contextEngineID .........................................   24
 6.8.2. contextName .............................................   25
 6.8.3. data ....................................................   25
 7. Elements of Procedure for v3MP ..............................   25
 7.1. Prepare an Outgoing SNMP Message ..........................   26
 7.2. Prepare Data Elements from an Incoming SNMP Message .......   32
 8. Intellectual Property .......................................   37
 9. Acknowledgements ............................................   38
 10. Security Considerations ....................................   39
 11. References .................................................   40
 11.1. Normative References .....................................   40
 11.2. Informative References ...................................   41
 12. Editors' Addresses .........................................   42
 13. Full Copyright Statement ...................................   43

Case, et al. Standards Track [Page 2] RFC 3412 Message Processing and Dispatching for SNMP December 2002

1. Introduction

 The Architecture for describing Internet Management Frameworks
 [RFC3411] describes that an SNMP engine is composed of:
    1) a Dispatcher
    2) a Message Processing Subsystem,
    3) a Security Subsystem, and
    4) an Access Control Subsystem.
 Applications make use of the services of these subsystems.
 It is important to understand the SNMP architecture and its
 terminology to understand where the Message Processing Subsystem and
 Dispatcher described in this document fit into the architecture and
 interact with other subsystems within the architecture.  The reader
 is expected to have read and understood the description of the SNMP
 architecture, defined in [RFC3411].
 The Dispatcher in the SNMP engine sends and receives SNMP messages.
 It also dispatches SNMP PDUs to SNMP applications.  When an SNMP
 message needs to be prepared or when data needs to be extracted from
 an SNMP message, the Dispatcher delegates these tasks to a message
 version-specific Message Processing Model within the Message
 Processing Subsystem.
 A Message Processing Model is responsible for processing an SNMP
 version-specific message and for coordinating the interaction with
 the Security Subsystem to ensure proper security is applied to the
 SNMP message being handled.
 Interactions between the Dispatcher, the Message Processing
 Subsystem, and applications are modeled using abstract data elements
 and abstract service interface primitives defined by the SNMP
 architecture.
 Similarly, interactions between the Message Processing Subsystem and
 the Security Subsystem are modeled using abstract data elements and
 abstract service interface primitives as defined by the SNMP
 architecture.
 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 BCP 14, RFC 2119.

Case, et al. Standards Track [Page 3] RFC 3412 Message Processing and Dispatching for SNMP December 2002

2. Overview

 The following illustration depicts the Message Processing in relation
 to SNMP applications, the Security Subsystem and Transport Mappings.
 +-------------------------------------------------------------------+
 | SNMP Entity                                                       |
 |                                                                   |
 | +---------------------------------------------------------------+ |
 | | Applications                                                  | |
 | | +-----------+  +--------------+                               | |
 | | | Command   |  | Notification |                               | |
 | | | Generator |  | Originator   | +-----------+ +--------------+| |
 | | +-----------+  +--------------+ | Proxy     | | Other        || |
 | | +-----------+  +--------------+ | Forwarder | |Application(s)|| |
 | | | Command   |  | Notification | +-----------+ +--------------+| |
 | | | Responder |  | Receiver     |                               | |
 | | +-----------+  +--------------+                               | |
 | +---------------------------------------------------------------+ |
 |        ^                ^               ^           ^             |
 |        |                |               |           |             |
 |        v                v               v           v             |
 |        +--------+-------+---------------+-----------+             |
 |                 ^                                                 |
 |                 |    +---------------------+  +-----------------+ |
 |                 |    | Message Processing  |  | Security        | |
 | Dispatcher      v    | Subsystem           |  | Subsystem       | |
 | +------------------+ |     +------------+  |  |                 | |
 | | PDU Dispatcher   | |  +->| v1MP     * |<--->| +-------------+ | |
 | |                  | |  |  +------------+  |  | | Other       | | |
 | |                  | |  |  +------------+  |  | | Security    | | |
 | |                  | |  +->| v2cMP    * |<--->| | Model       | | |
 | | Message          | |  |  +------------+  |  | +-------------+ | |
 | | Dispatcher  <-------->+                  |  |                 | |
 | |                  | |  |  +------------+  |  | +-------------+ | |
 | |                  | |  +->| v3MP     * |<--->| | User-based  | | |
 | | Transport        | |  |  +------------+  |  | | Security    | | |
 | | Mapping          | |  |  +------------+  |  | | Model       | | |
 | | (e.g., RFC 3417) | |  +->| otherMP  * |<--->| +-------------+ | |
 | +------------------+ |     +------------+  |  |                 | |
 |          ^           +---------------------+  +-----------------+ |
 |          |                                                        |
 +----------|--------------------------------------------------------+
            v
   +------------------+
   |   Network        |           * One or more models may be present.
   +------------------+

Case, et al. Standards Track [Page 4] RFC 3412 Message Processing and Dispatching for SNMP December 2002

2.1. The Dispatcher

 The Dispatcher is a key piece of an SNMP engine.  There is only one
 in an SNMP engine, and its job is to dispatch tasks to the multiple
 version-specific Message Processing Models, and to dispatch PDUs to
 various applications.
 For outgoing messages, an application provides a PDU to be sent, plus
 the data needed to prepare and send the message, and the application
 specifies which version-specific Message Processing Model will be
 used to prepare the message with the desired security processing.
 Once the message is prepared, the Dispatcher sends the message.
 For incoming messages, the Dispatcher determines the SNMP version of
 the incoming message and passes the message to the version-specific
 Message Processing Model to extract the components of the message and
 to coordinate the processing of security services for the message.
 After version-specific processing, the PDU Dispatcher determines
 which application, if any, should receive the PDU for processing and
 forwards it accordingly.
 The Dispatcher, while sending and receiving SNMP messages, collects
 statistics about SNMP messages and the behavior of the SNMP engine in
 managed objects to make them accessible to remote SNMP entities.
 This document defines these managed objects, the MIB module which
 contains them, and how these managed objects might be used to provide
 useful management.

2.2. Message Processing Subsystem

 The SNMP Message Processing Subsystem is the part of an SNMP engine
 which interacts with the Dispatcher to handle the version-specific
 SNMP messages.  It contains one or more Message Processing Models.
 This document describes one Message Processing Model, the SNMPv3
 Message Processing Model, in Section 6.  The SNMPv3 Message
 Processing Model is defined in a separate section to show that
 multiple (independent) Message Processing Models can exist at the
 same time and that such Models can be described in different
 documents.  The SNMPv3 Message Processing Model can be replaced or
 supplemented with other Message Processing Models in the future.  Two
 Message Processing Models which are expected to be developed in the
 future are the SNMPv1 message format [RFC1157] and the SNMPv2c
 message format [RFC1901].  Others may be developed as needed.

Case, et al. Standards Track [Page 5] RFC 3412 Message Processing and Dispatching for SNMP December 2002

3. Elements of Message Processing and Dispatching

 See [RFC3411] for the definitions of:
    contextEngineID
    contextName
    scopedPDU
    maxSizeResponseScopedPDU
    securityModel
    securityName
    securityLevel
    messageProcessingModel
 For incoming messages, a version-specific message processing module
 provides these values to the Dispatcher.  For outgoing messages, an
 application provides these values to the Dispatcher.
 For some version-specific processing, the values may be extracted
 from received messages; for other versions, the values may be
 determined by algorithm, or by an implementation-defined mechanism.
 The mechanism by which the value is determined is irrelevant to the
 Dispatcher.
 The following additional or expanded definitions are for use within
 the Dispatcher.

3.1. messageProcessingModel

 The value of messageProcessingModel identifies a Message Processing
 Model.  A Message Processing Model describes the version-specific
 procedures for extracting data from messages, generating messages,
 calling upon a securityModel to apply its security services to
 messages, for converting data from a version-specific message format
 into a generic format usable by the Dispatcher, and for converting
 data from Dispatcher format into a version-specific message format.

3.2. pduVersion

 The value of pduVersion represents a specific version of protocol
 operation and its associated PDU formats, such as SNMPv1 or SNMPv2
 [RFC3416].  The values of pduVersion are specific to the version of
 the PDU contained in a message, and the PDUs processed by
 applications.  The Dispatcher does not use the value of pduVersion
 directly.

Case, et al. Standards Track [Page 6] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 An application specifies the pduVersion when it requests the PDU
 Dispatcher to send a PDU to another SNMP engine.  The Dispatcher
 passes the pduVersion to a Message Processing Model, so it knows how
 to handle the PDU properly.
 For incoming messages, the pduVersion is provided to the Dispatcher
 by a version-specific Message Processing module.  The PDU Dispatcher
 passes the pduVersion to the application so it knows how to handle
 the PDU properly.  For example, a command responder application needs
 to know whether to use [RFC3416] elements of procedure and syntax
 instead of those specified for SNMPv1.

3.3. pduType

 A value of the pduType represents a specific type of protocol
 operation.  The values of the pduType are specific to the version of
 the PDU contained in a message.
 Applications register to support particular pduTypes for particular
 contextEngineIDs.
 For incoming messages, pduType is provided to the Dispatcher by a
 version-specific Message Processing module.  It is subsequently used
 to dispatch the PDU to the application which registered for the
 pduType for the contextEngineID of the associated scopedPDU.

3.4. sendPduHandle

 This handle is generated for coordinating the processing of requests
 and responses between the SNMP engine and an application.  The handle
 must be unique across all version-specific Message Processing Models,
 and is of local significance only.

4. Dispatcher Elements of Procedure

 This section describes the procedures followed by the Dispatcher when
 generating and processing SNMP messages.

4.1. Sending an SNMP Message to the Network

 This section describes the procedure followed by an SNMP engine
 whenever it sends an SNMP message.

Case, et al. Standards Track [Page 7] RFC 3412 Message Processing and Dispatching for SNMP December 2002

4.1.1. Sending a Request or Notification

 The following procedures are followed by the Dispatcher when an
 application wants to send an SNMP PDU to another (remote)
 application, i.e., to initiate a communication by originating a
 message, such as one containing a request or a notification.
 1) The application requests this using the abstract service
    primitive:
    statusInformation =              -- sendPduHandle if success
                                     -- errorIndication if failure
      sendPdu(
      IN   transportDomain           -- transport domain to be used
      IN   transportAddress          -- destination network address
      IN   messageProcessingModel    -- typically, SNMP version
      IN   securityModel             -- Security Model to use
      IN   securityName              -- on behalf of this principal
      IN   securityLevel             -- Level of Security requested
      IN   contextEngineID           -- data from/at this entity
      IN   contextName               -- data from/in this context
      IN   pduVersion                -- the version of the PDU
      IN   PDU                       -- SNMP Protocol Data Unit
      IN   expectResponse            -- TRUE or FALSE
           )
 2) If the messageProcessingModel value does not represent a Message
    Processing Model known to the Dispatcher, then an errorIndication
    (implementation-dependent) is returned to the calling application.
    No further processing is performed.
 3) The Dispatcher generates a sendPduHandle to coordinate subsequent
    processing.

Case, et al. Standards Track [Page 8] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 4) The Message Dispatcher sends the request to the version-specific
    Message Processing module identified by messageProcessingModel
    using the abstract service primitive:
    statusInformation =              -- success or error indication
      prepareOutgoingMessage(
      IN   transportDomain           -- as specified by application
      IN   transportAddress          -- as specified by application
      IN   messageProcessingModel    -- as specified by application
      IN   securityModel             -- as specified by application
      IN   securityName              -- as specified by application
      IN   securityLevel             -- as specified by application
      IN   contextEngineID           -- as specified by application
      IN   contextName               -- as specified by application
      IN   pduVersion                -- as specified by application
      IN   PDU                       -- as specified by application
      IN   expectResponse            -- as specified by application
      IN   sendPduHandle             -- as determined in step 3.
      OUT  destTransportDomain       -- destination transport domain
      OUT  destTransportAddress      -- destination transport address
      OUT  outgoingMessage           -- the message to send
      OUT  outgoingMessageLength     -- the message length
           )
 5) If the statusInformation indicates an error, the errorIndication
    is returned to the calling application.  No further processing is
    performed.
 6) If the statusInformation indicates success, the sendPduHandle is
    returned to the application, and the outgoingMessage is sent.  The
    transport used to send the outgoingMessage is returned via
    destTransportDomain, and the address to which it was sent is
    returned via destTransportAddress.
 Outgoing Message Processing is complete.

4.1.2. Sending a Response to the Network

 The following procedure is followed when an application wants to
 return a response back to the originator of an SNMP Request.

Case, et al. Standards Track [Page 9] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 1) An application can request this using the abstract service
    primitive:
    result =
    returnResponsePdu(
     IN   messageProcessingModel   -- typically, SNMP version
     IN   securityModel            -- Security Model in use
     IN   securityName             -- on behalf of this principal
     IN   securityLevel            -- same as on incoming request
     IN   contextEngineID          -- data from/at this SNMP entity
     IN   contextName              -- data from/in this context
     IN   pduVersion               -- the version of the PDU
     IN   PDU                      -- SNMP Protocol Data Unit
     IN   maxSizeResponseScopedPDU -- maximum size of Response PDU
     IN   stateReference           -- reference to state information
                                   -- as presented with the request
     IN   statusInformation        -- success or errorIndication
     )                             -- (error counter OID and value
                                   -- when errorIndication)
 2) The Message Dispatcher sends the request to the appropriate
    Message Processing Model indicated by the received value of
    messageProcessingModel using the abstract service primitive:
    result =                       -- SUCCESS or errorIndication
     prepareResponseMessage(
     IN   messageProcessingModel   -- specified by application
     IN   securityModel            -- specified by application
     IN   securityName             -- specified by application
     IN   securityLevel            -- specified by application
     IN   contextEngineID          -- specified by application
     IN   contextName              -- specified by application
     IN   pduVersion               -- specified by application
     IN   PDU                      -- specified by application
     IN   maxSizeResponseScopedPDU -- specified by application
     IN   stateReference           -- specified by application
     IN   statusInformation        -- specified by application
     OUT  destTransportDomain      -- destination transport domain
     OUT  destTransportAddress     -- destination transport address
     OUT  outgoingMessage          -- the message to send
     OUT  outgoingMessageLength    -- the message length
          )
 3) If the result is an errorIndication, the errorIndication is
    returned to the calling application.  No further processing is
    performed.

Case, et al. Standards Track [Page 10] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 4) If the result is success, the outgoingMessage is sent.  The
    transport used to send the outgoingMessage is returned via
    destTransportDomain, and the address to which it was sent is
    returned via destTransportAddress.
 Message Processing is complete.

4.2. Receiving an SNMP Message from the Network

 This section describes the procedure followed by an SNMP engine
 whenever it receives an SNMP message.
 Please note, that for the sake of clarity and to prevent the text
 from being even longer and more complicated, some details were
 omitted from the steps below.  In particular, the elements of
 procedure do not always explicitly indicate when state information
 needs to be released.  The general rule is that if state information
 is available when a message is to be "discarded without further
 processing", then the state information must also be released at that
 same time.

4.2.1. Message Dispatching of received SNMP Messages

 1) The snmpInPkts counter [RFC3418] is incremented.
 2) The version of the SNMP message is determined in an
    implementation-dependent manner.  If the packet cannot be
    sufficiently parsed to determine the version of the SNMP message,
    then the snmpInASNParseErrs [RFC3418] counter is incremented, and
    the message is discarded without further processing.  If the
    version is not supported, then the snmpInBadVersions [RFC3418]
    counter is incremented, and the message is discarded without
    further processing.
 3) The origin transportDomain and origin transportAddress are
    determined.

Case, et al. Standards Track [Page 11] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 4) The message is passed to the version-specific Message Processing
    Model which returns the abstract data elements required by the
    Dispatcher.  This is performed using the abstract service
    primitive:
    result =                        -- SUCCESS or errorIndication
      prepareDataElements(
      IN   transportDomain          -- origin as determined in step 3.
      IN   transportAddress         -- origin as determined in step 3.
      IN   wholeMsg                 -- as received from the network
      IN   wholeMsgLength           -- as received from the network
      OUT  messageProcessingModel   -- typically, SNMP version
      OUT  securityModel            -- Security Model specified
      OUT  securityName             -- on behalf of this principal
      OUT  securityLevel            -- Level of Security specified
      OUT  contextEngineID          -- data from/at this entity
      OUT  contextName              -- data from/in this context
      OUT  pduVersion               -- the version of the PDU
      OUT  PDU                      -- SNMP Protocol Data Unit
      OUT  pduType                  -- SNMP PDU type
      OUT  sendPduHandle            -- handle for a matched request
      OUT  maxSizeResponseScopedPDU -- maximum size of Response PDU
      OUT  statusInformation        -- success or errorIndication
                                    -- (error counter OID and value
                                    -- when errorIndication)
      OUT  stateReference           -- reference to state information
                                    -- to be used for a possible
           )                        -- Response
 5) If the result is a FAILURE errorIndication, the message is
    discarded without further processing.
 6) At this point, the abstract data elements have been prepared and
    processing continues as described in Section 4.2.2, PDU
    Dispatching for Incoming Messages.

4.2.2. PDU Dispatching for Incoming Messages

 The elements of procedure for the dispatching of PDUs depends on the
 value of sendPduHandle.  If the value of sendPduHandle is <none>,
 then this is a request or notification and the procedures specified
 in Section 4.2.2.1 apply.  If the value of snmpPduHandle is not
 <none>, then this is a response and the procedures specified in
 Section 4.2.2.2 apply.

Case, et al. Standards Track [Page 12] RFC 3412 Message Processing and Dispatching for SNMP December 2002

4.2.2.1. Incoming Requests and Notifications

 The following procedures are followed for the dispatching of PDUs
 when the value of sendPduHandle is <none>, indicating this is a
 request or notification.
 1) The combination of contextEngineID and pduType is used to
    determine which application has registered for this request or
    notification.
 2) If no application has registered for the combination, then:
    a) The snmpUnknownPDUHandlers counter is incremented.
    b) A Response message is generated using the abstract service
       primitive:
       result =                       -- SUCCESS or FAILURE
       prepareResponseMessage(
       IN   messageProcessingModel    -- as provided by MP module
       IN   securityModel             -- as provided by MP module
       IN   securityName              -- as provided by MP module
       IN   securityLevel             -- as provided by MP module
       IN   contextEngineID           -- as provided by MP module
       IN   contextName               -- as provided by MP module
       IN   pduVersion                -- as provided by MP module
       IN   PDU                       -- as provided by MP module
       IN   maxSizeResponseScopedPDU  -- as provided by MP module
       IN   stateReference            -- as provided by MP module
       IN   statusInformation         -- errorIndication plus
                                      -- snmpUnknownPDUHandlers OID
                                      -- value pair.
       OUT  destTransportDomain       -- destination transportDomain
       OUT  destTransportAddress      -- destination transportAddress
       OUT  outgoingMessage           -- the message to send
       OUT  outgoingMessageLength     -- its length
       )
    c) If the result is SUCCESS, then the prepared message is sent to
       the originator of the request as identified by the
       transportDomain and transportAddress.  The transport used to
       send the outgoingMessage is returned via destTransportDomain,
       and the address to which it was sent is returned via
       destTransportAddress.
    d) The incoming message is discarded without further processing.
       Message Processing for this message is complete.

Case, et al. Standards Track [Page 13] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 3) The PDU is dispatched to the application, using the abstract
    service primitive:
    processPdu(                     -- process Request/Notification
      IN   messageProcessingModel   -- as provided by MP module
      IN   securityModel            -- as provided by MP module
      IN   securityName             -- as provided by MP module
      IN   securityLevel            -- as provided by MP module
      IN   contextEngineID          -- as provided by MP module
      IN   contextName              -- as provided by MP module
      IN   pduVersion               -- as provided by MP module
      IN   PDU                      -- as provided by MP module
      IN   maxSizeResponseScopedPDU -- as provided by MP module
      IN   stateReference           -- as provided by MP module
                                    -- needed when sending response
           )
    Message processing for this message is complete.

4.2.2.2. Incoming Responses

 The following procedures are followed for the dispatching of PDUs
 when the value of sendPduHandle is not <none>, indicating this is a
 response.
 1) The value of sendPduHandle is used to determine, in an
    implementation-defined manner, which application is waiting for a
    response associated with this sendPduHandle.
 2) If no waiting application is found, the message is discarded
    without further processing, and the stateReference is released.
    The snmpUnknownPDUHandlers counter is incremented.  Message
    Processing is complete for this message.
 3) Any cached information, including stateReference, about the
    message is discarded.

Case, et al. Standards Track [Page 14] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 4) The response is dispatched to the application using the abstract
    service primitive:
    processResponsePdu(              -- process Response PDU
      IN   messageProcessingModel    -- provided by the MP module
      IN   securityModel             -- provided by the MP module
      IN   securityName              -- provided by the MP module
      IN   securityLevel             -- provided by the MP module
      IN   contextEngineID           -- provided by the MP module
      IN   contextName               -- provided by the MP module
      IN   pduVersion                -- provided by the MP module
      IN   PDU                       -- provided by the MP module
      IN   statusInformation         -- provided by the MP module
      IN   sendPduHandle             -- provided by the MP module
           )
    Message Processing is complete for this message.

4.3. Application Registration for Handling PDU types

 Applications that want to process certain PDUs must register with the
 PDU Dispatcher.  Applications specify the combination of
 contextEngineID and pduType(s) for which they want to take
 responsibility.
 1) An application registers according to the abstract interface
    primitive:
    statusInformation =           -- success or errorIndication
      registerContextEngineID(
      IN   contextEngineID        -- take responsibility for this one
      IN   pduType                -- the pduType(s) to be registered
           )
    Note: Implementations may provide a means of requesting
    registration for simultaneous multiple contextEngineID values,
    e.g., all contextEngineID values, and may also provide a means for
    requesting simultaneous registration for multiple values of the
    pduType.
 2) The parameters may be checked for validity; if they are not, then
    an errorIndication (invalidParameter) is returned to the
    application.
 3) Each combination of contextEngineID and pduType can be registered
    only once.  If another application has already registered for the
    specified combination, then an errorIndication (alreadyRegistered)
    is returned to the application.

Case, et al. Standards Track [Page 15] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 4) Otherwise, the registration is saved so that SNMP PDUs can be
    dispatched to this application.

4.4. Application Unregistration for Handling PDU Types

 Applications that no longer want to process certain PDUs must
 unregister with the PDU Dispatcher.
 1) An application unregisters using the abstract service primitive:
    unregisterContextEngineID(
     IN   contextEngineID        -- give up responsibility for this
     IN   pduType                -- the pduType(s) to be unregistered
          )
    Note: Implementations may provide a means for requesting the
    unregistration for simultaneous multiple contextEngineID values,
    e.g., all contextEngineID values, and may also provide a means for
    requesting simultaneous unregistration for multiple values of
    pduType.
 2) If the contextEngineID and pduType combination has been
    registered, then the registration is deleted.
    If no such registration exists, then the request is ignored.

5. Definitions

5.1. Definitions for SNMP Message Processing and Dispatching

 SNMP-MPD-MIB DEFINITIONS ::= BEGIN
 IMPORTS
     MODULE-COMPLIANCE, OBJECT-GROUP         FROM SNMPv2-CONF
     MODULE-IDENTITY, OBJECT-TYPE,
     snmpModules, Counter32                  FROM SNMPv2-SMI;
 snmpMPDMIB MODULE-IDENTITY
     LAST-UPDATED "200210140000Z"
     ORGANIZATION "SNMPv3 Working Group"
     CONTACT-INFO "WG-EMail:   snmpv3@lists.tislabs.com
                   Subscribe:  snmpv3-request@lists.tislabs.com
                   Co-Chair:   Russ Mundy
                               Network Associates Laboratories
                   postal:     15204 Omega Drive, Suite 300
                               Rockville, MD 20850-4601
                               USA

Case, et al. Standards Track [Page 16] RFC 3412 Message Processing and Dispatching for SNMP December 2002

                   EMail:      mundy@tislabs.com
                   phone:      +1 301-947-7107
                   Co-Chair &
                   Co-editor:  David Harrington
                               Enterasys Networks
                   postal:     35 Industrial Way
                               P. O. Box 5005
                               Rochester NH 03866-5005
                               USA
                   EMail:      dbh@enterasys.com
                   phone:      +1 603-337-2614
                   Co-editor:  Jeffrey Case
                               SNMP Research, Inc.
                   postal:     3001 Kimberlin Heights Road
                               Knoxville, TN 37920-9716
                               USA
                   EMail:      case@snmp.com
                   phone:      +1 423-573-1434
                   Co-editor:  Randy Presuhn
                               BMC Software, Inc.
                   postal:     2141 North First Street
                               San Jose, CA 95131
                               USA
                   EMail:      randy_presuhn@bmc.com
                   phone:      +1 408-546-1006
                   Co-editor:  Bert Wijnen
                               Lucent Technologies
                   postal:     Schagen 33
                               3461 GL Linschoten
                               Netherlands
                   EMail:      bwijnen@lucent.com
                   phone:      +31 348-680-485
                  "
     DESCRIPTION  "The MIB for Message Processing and Dispatching
                   Copyright (C) The Internet Society (2002). This
                   version of this MIB module is part of RFC 3412;
                   see the RFC itself for full legal notices.
                  "
     REVISION     "200210140000Z"            -- 14 October 2002
     DESCRIPTION  "Updated addresses, published as RFC 3412."
     REVISION     "199905041636Z"            -- 4 May 1999
     DESCRIPTION  "Updated addresses, published as RFC 2572."

Case, et al. Standards Track [Page 17] RFC 3412 Message Processing and Dispatching for SNMP December 2002

     REVISION     "199709300000Z"            -- 30 September 1997
     DESCRIPTION  "Original version, published as RFC 2272."
     ::= { snmpModules 11 }
  1. - Administrative assignments * snmpMPDAdmin OBJECT IDENTIFIER ::= { snmpMPDMIB 1 } snmpMPDMIBObjects OBJECT IDENTIFIER ::= { snmpMPDMIB 2 } snmpMPDMIBConformance OBJECT IDENTIFIER ::= { snmpMPDMIB 3 } – Statistics for SNMP Messages * snmpMPDStats OBJECT IDENTIFIER ::= { snmpMPDMIBObjects 1 } snmpUnknownSecurityModels OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because they referenced a securityModel that was not known to or supported by the SNMP engine. " ::= { snmpMPDStats 1 } snmpInvalidMsgs OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because there were invalid or inconsistent components in the SNMP message. " ::= { snmpMPDStats 2 } snmpUnknownPDUHandlers OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The total number of packets received by the SNMP engine which were dropped because the PDU contained in the packet could not be passed to an application responsible for handling the pduType, e.g. no SNMP application had registered for the proper combination of the contextEngineID and the pduType. " ::= { snmpMPDStats 3 } Case, et al. Standards Track [Page 18] RFC 3412 Message Processing and Dispatching for SNMP December 2002 – Conformance information
 snmpMPDMIBCompliances OBJECT IDENTIFIER ::= {snmpMPDMIBConformance 1}
 snmpMPDMIBGroups      OBJECT IDENTIFIER ::= {snmpMPDMIBConformance 2}
  1. - Compliance statements
 snmpMPDCompliance MODULE-COMPLIANCE
     STATUS       current
     DESCRIPTION "The compliance statement for SNMP entities which
                  implement the SNMP-MPD-MIB.
                 "
     MODULE    -- this module
         MANDATORY-GROUPS { snmpMPDGroup }
     ::= { snmpMPDMIBCompliances 1 }
 snmpMPDGroup OBJECT-GROUP
     OBJECTS {
               snmpUnknownSecurityModels,
               snmpInvalidMsgs,
               snmpUnknownPDUHandlers
             }
     STATUS       current
     DESCRIPTION "A collection of objects providing for remote
                  monitoring of the SNMP Message Processing and
                  Dispatching process.
                 "
     ::= { snmpMPDMIBGroups 1 }
 END

6. The SNMPv3 Message Format

 This section defines the SNMPv3 message format and the corresponding
 SNMP version 3 Message Processing Model (v3MP).
 SNMPv3MessageSyntax DEFINITIONS IMPLICIT TAGS ::= BEGIN
     SNMPv3Message ::= SEQUENCE {
         -- identify the layout of the SNMPv3Message
         -- this element is in same position as in SNMPv1
         -- and SNMPv2c, allowing recognition
         -- the value 3 is used for snmpv3
         msgVersion INTEGER ( 0 .. 2147483647 ),
         -- administrative parameters
         msgGlobalData HeaderData,
         -- security model-specific parameters
         -- format defined by Security Model

Case, et al. Standards Track [Page 19] RFC 3412 Message Processing and Dispatching for SNMP December 2002

         msgSecurityParameters OCTET STRING,
         msgData  ScopedPduData
     }
     HeaderData ::= SEQUENCE {
         msgID      INTEGER (0..2147483647),
         msgMaxSize INTEGER (484..2147483647),
         msgFlags   OCTET STRING (SIZE(1)),
                    --  .... ...1   authFlag
                    --  .... ..1.   privFlag
                    --  .... .1..   reportableFlag
                    --              Please observe:
                    --  .... ..00   is OK, means noAuthNoPriv
                    --  .... ..01   is OK, means authNoPriv
                    --  .... ..10   reserved, MUST NOT be used.
                    --  .... ..11   is OK, means authPriv
         msgSecurityModel INTEGER (1..2147483647)
     }
     ScopedPduData ::= CHOICE {
         plaintext    ScopedPDU,
         encryptedPDU OCTET STRING  -- encrypted scopedPDU value
     }
     ScopedPDU ::= SEQUENCE {
         contextEngineID  OCTET STRING,
         contextName      OCTET STRING,
         data             ANY -- e.g., PDUs as defined in [RFC3416]
     }
 END

6.1. msgVersion

 The msgVersion field is set to snmpv3(3) and identifies the message
 as an SNMP version 3 Message.

6.2. msgID

 The msgID is used between two SNMP entities to coordinate request
 messages and responses, and by the v3MP to coordinate the processing
 of the message by different subsystem models within the architecture.
 Values for msgID SHOULD be generated in a manner that avoids re-use
 of any outstanding values.  Doing so provides protection against some
 replay attacks.  One possible implementation strategy would be to use
 the low-order bits of snmpEngineBoots [RFC3411] as the high-order

Case, et al. Standards Track [Page 20] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 portion of the msgID value and a monotonically increasing integer for
 the low-order portion of msgID.
 Note that the request-id in a PDU may be used by SNMP applications to
 identify the PDU; the msgID is used by the engine to identify the
 message which carries a PDU.  The engine needs to identify the
 message even if decryption of the PDU (and request-id) fails.  No
 assumption should be made that the value of the msgID and the value
 of the request-id are equivalent.
 The value of the msgID field for a response takes the value of the
 msgID field from the message to which it is a response.  By use of
 the msgID value, an engine can distinguish the (potentially multiple)
 outstanding requests, and thereby correlate incoming responses with
 outstanding requests.  In cases where an unreliable datagram service
 is used, the msgID also provides a simple means of identifying
 messages duplicated by the network.  If a request is retransmitted, a
 new msgID value SHOULD be used for each retransmission.

6.3. msgMaxSize

 The msgMaxSize field of the message conveys the maximum message size
 supported by the sender of the message, i.e., the maximum message
 size that the sender can accept when another SNMP engine sends an
 SNMP message (be it a response or any other message) to the sender of
 this message on the transport in use for this message.
 When an SNMP message is being generated, the msgMaxSize is provided
 by the SNMP engine which generates the message.  At the receiving
 SNMP engine, the msgMaxSize is used to determine the maximum message
 size the sender can accommodate.

6.4. msgFlags

 The msgFlags field of the message contains several bit fields which
 control processing of the message.
 The reportableFlag is a secondary aid in determining whether a Report
 PDU MUST be sent.  It is only used in cases where the PDU portion of
 a message cannot be decoded, due to, for example, an incorrect
 encryption key.  If the PDU can be decoded, the PDU type forms the
 basis for decisions on sending Report PDUs.
 When the reportableFlag is used, if its value is one, a Report PDU
 MUST be returned to the sender under those conditions which can cause
 the generation of Report PDUs.  Similarly, when the reportableFlag is
 used and its value is zero, then a Report PDU MUST NOT be sent.  The
 reportableFlag MUST always be zero when the message contains a PDU

Case, et al. Standards Track [Page 21] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 from the Unconfirmed Class, such as a Report PDU, a response-type PDU
 (such as a Response PDU), or an unacknowledged notification-type PDU
 (such as an SNMPv2-trap PDU).  The reportableFlag MUST always be one
 for a PDU from the Confirmed Class, including request-type PDUs (such
 as a Get PDU) and acknowledged notification-type PDUs (such as an
 Inform PDU).
 If the reportableFlag is set to one for a message containing a PDU
 from the Unconfirmed Class, such as a Report PDU, a response-type PDU
 (such as a Response PDU), or an unacknowledged notification-type PDU
 (such as an SNMPv2-trap PDU), then the receiver of that message MUST
 process it as though the reportableFlag had been set to zero.
 If the reportableFlag is set to zero for a message containing a
 request-type PDU (such as a Get PDU) or an acknowledged
 notification-type PDU (such as an Inform PDU), then the receiver of
 that message MUST process it as though the reportableFlag had been
 set to one.
 Report PDUs are generated directly by the SNMPv3 Message Processing
 Model, and support engine-to-engine communications, but may be passed
 to applications for processing.
 An SNMP engine that receives a reportPDU may use it to determine what
 kind of problem was detected by the remote SNMP engine.  It can do so
 based on the error counter included as the first (and only) varBind
 of the reportPDU.  Based on the detected error, the SNMP engine may
 try to send a corrected SNMP message.  If that is not possible, it
 may pass an indication of the error to the application on whose
 behalf the failed SNMP request was issued.
 The authFlag and privFlag portions of the msgFlags field are set by
 the sender to indicate the securityLevel that was applied to the
 message before it was sent on the wire.  The receiver of the message
 MUST apply the same securityLevel when the message is received and
 the contents are being processed.
 There are three securityLevels, namely noAuthNoPriv, which is less
 than authNoPriv, which is in turn less than authPriv.  See the SNMP
 architecture document [RFC3411] for details about the securityLevel.
 a) authFlag
    If the authFlag is set to one, then the securityModel used by the
    SNMP engine which sent the message MUST identify the securityName
    on whose behalf the SNMP message was generated and MUST provide,
    in a securityModel-specific manner, sufficient data for the
    receiver of the message to be able to authenticate that

Case, et al. Standards Track [Page 22] RFC 3412 Message Processing and Dispatching for SNMP December 2002

    identification.  In general, this authentication will allow the
    receiver to determine with reasonable certainty that the message
    was:
  1. sent on behalf of the principal associated with the

securityName,

  1. was not redirected,
  1. was not modified in transit, and
  1. was not replayed.
    If the authFlag is zero, then the securityModel used by the SNMP
    engine which sent the message MUST identify the securityName on
    whose behalf the SNMP message was generated but it does not need
    to provide sufficient data for the receiver of the message to
    authenticate the identification, as there is no need to
    authenticate the message in this case.
 b) privFlag
    If the privFlag is set, then the securityModel used by the SNMP
    engine which sent the message MUST also protect the scopedPDU in
    an SNMP message from disclosure, i.e., it MUST encrypt/decrypt the
    scopedPDU.  If the privFlag is zero, then the securityModel in use
    does not need to protect the data from disclosure.
    It is an explicit requirement of the SNMP architecture that if
    privacy is selected, then authentication is also required.  That
    means that if the privFlag is set, then the authFlag MUST also be
    set to one.
    The combination of the authFlag and the privFlag comprises a Level
    of Security as follows:
       authFlag zero, privFlag zero -> securityLevel is noAuthNoPriv
       authFlag zero, privFlag one  -> invalid combination, see below
       authFlag one,  privFlag zero -> securityLevel is authNoPriv
       authFlag one,  privFlag one  -> securityLevel is authPriv
 The elements of procedure (see below) describe the action to be taken
 when the invalid combination of authFlag equal to zero and privFlag
 equal to one is encountered.
 The remaining bits in msgFlags are reserved, and MUST be set to zero
 when sending a message and SHOULD be ignored when receiving a
 message.

Case, et al. Standards Track [Page 23] RFC 3412 Message Processing and Dispatching for SNMP December 2002

6.5. msgSecurityModel

 The v3MP supports the concurrent existence of multiple Security
 Models to provide security services for SNMPv3 messages.  The
 msgSecurityModel field in an SNMPv3 Message identifies which Security
 Model was used by the sender to generate the message and therefore
 which securityModel MUST be used by the receiver to perform security
 processing for the message.  The mapping to the appropriate
 securityModel implementation within an SNMP engine is accomplished in
 an implementation-dependent manner.

6.6. msgSecurityParameters

 The msgSecurityParameters field of the SNMPv3 Message is used for
 communication between the Security Model modules in the sending and
 receiving SNMP engines.  The data in the msgSecurityParameters field
 is used exclusively by the Security Model, and the contents and
 format of the data is defined by the Security Model.  This OCTET
 STRING is not interpreted by the v3MP, but is passed to the local
 implementation of the Security Model indicated by the
 msgSecurityModel field in the message.

6.7. scopedPduData

 The scopedPduData field represents either the plain text scopedPDU if
 the privFlag in the msgFlags is zero, or it represents an
 encryptedPDU (encoded as an OCTET STRING) which MUST be decrypted by
 the securityModel in use to produce a plaintext scopedPDU.

6.8. scopedPDU

 The scopedPDU contains information to identify an administratively
 unique context and a PDU.  The object identifiers in the PDU refer to
 managed objects which are (expected to be) accessible within the
 specified context.

6.8.1. contextEngineID

 The contextEngineID in the SNMPv3 message uniquely identifies, within
 an administrative domain, an SNMP entity that may realize an instance
 of a context with a particular contextName.
 For incoming messages, the contextEngineID is used in conjunction
 with the pduType to determine to which application the scopedPDU will
 be sent for processing.
 For outgoing messages, the v3MP sets the contextEngineID to the value
 provided by the application in the request for a message to be sent.

Case, et al. Standards Track [Page 24] RFC 3412 Message Processing and Dispatching for SNMP December 2002

6.8.2. contextName

 The contextName field in an SNMPv3 message, in conjunction with the
 contextEngineID field, identifies the particular context associated
 with the management information contained in the PDU portion of the
 message.  The contextName is unique within the SNMP entity specified
 by the contextEngineID, which may realize the managed objects
 referenced within the PDU.  An application which originates a message
 provides the value for the contextName field and this value may be
 used during processing by an application at the receiving SNMP
 Engine.

6.8.3. data

 The data field of the SNMPv3 Message contains the PDU.  Among other
 things, the PDU contains the PDU type that is used by the v3MP to
 determine the type of the incoming SNMP message.  The v3MP specifies
 that the PDU MUST be one of those specified in [RFC3416].

7. Elements of Procedure for v3MP

 This section describes the procedures followed by an SNMP engine when
 generating and processing SNMP messages according to the SNMPv3
 Message Processing Model.
 Please note, that for the sake of clarity and to prevent the text
 from being even longer and more complicated, some details were
 omitted from the steps below.
    a) Some steps specify that when some error conditions are
       encountered when processing a received message, a message
       containing a Report PDU is generated and the received message
       is discarded without further processing.  However, a Report-PDU
       MUST NOT be generated unless the PDU causing generation of the
       Report PDU can be determined to be a member of the Confirmed
       Class, or the reportableFlag is set to one and the PDU class
       cannot be determined.
    b) The elements of procedure do not always explicitly indicate
       when state information needs to be released.  The general rule
       is that if state information is available when a message is to
       be "discarded without further processing", then the state
       information should also be released at that same time.

Case, et al. Standards Track [Page 25] RFC 3412 Message Processing and Dispatching for SNMP December 2002

7.1. Prepare an Outgoing SNMP Message

 This section describes the procedure followed to prepare an SNMPv3
 message from the data elements passed by the Message Dispatcher.
 1) The Message Dispatcher may request that an SNMPv3 message
    containing a Read Class, Write Class, or Notification Class PDU be
    prepared for sending.
    a) It makes such a request according to the abstract service
       primitive:
       statusInformation =           -- success or errorIndication
         prepareOutgoingMessage(
         IN   transportDomain        -- requested transport domain
         IN   transportAddress       -- requested destination address
         IN   messageProcessingModel -- typically, SNMP version
         IN   securityModel          -- Security Model to use
         IN   securityName           -- on behalf of this principal
         IN   securityLevel          -- Level of Security requested
         IN   contextEngineID        -- data from/at this entity
         IN   contextName            -- data from/in this context
         IN   pduVersion             -- version of the PDU *
         IN   PDU                    -- SNMP Protocol Data Unit
         IN   expectResponse         -- TRUE or FALSE *
         IN   sendPduHandle          -- the handle for matching
                                     -- incoming responses
         OUT  destTransportDomain    -- destination transport domain
         OUT  destTransportAddress   -- destination transport address
         OUT  outgoingMessage        -- the message to send
         OUT  outgoingMessageLength  -- the length of the message
         )
  • The SNMPv3 Message Processing Model does not use the values of

expectResponse or pduVersion.

    b) A unique msgID is generated.  The number used for msgID should
       not have been used recently, and MUST NOT be the same as was
       used for any outstanding request.
 2) The Message Dispatcher may request that an SNMPv3 message
    containing a Response Class or Internal Class PDU be prepared for
    sending.

Case, et al. Standards Track [Page 26] RFC 3412 Message Processing and Dispatching for SNMP December 2002

    a) It makes such a request according to the abstract service
       primitive:
       result =                       -- SUCCESS or FAILURE
       prepareResponseMessage(
        IN   messageProcessingModel   -- typically, SNMP version
        IN   securityModel            -- same as on incoming request
        IN   securityName             -- same as on incoming request
        IN   securityLevel            -- same as on incoming request
        IN   contextEngineID          -- data from/at this SNMP entity
        IN   contextName              -- data from/in this context
        IN   pduVersion               -- version of the PDU
        IN   PDU                      -- SNMP Protocol Data Unit
        IN   maxSizeResponseScopedPDU -- maximum size sender can
                                      -- accept
        IN   stateReference           -- reference to state
                                      -- information presented with
                                      -- the request
        IN   statusInformation        -- success or errorIndication
                                      -- error counter OID and value
                                      -- when errorIndication
        OUT  destTransportDomain      -- destination transport domain
        OUT  destTransportAddress     -- destination transport address
        OUT  outgoingMessage          -- the message to send
        OUT  outgoingMessageLength    -- the length of the message
        )
    b) The cached information for the original request is retrieved
       via the stateReference, including:
  1. msgID,
  2. contextEngineID,
  3. contextName,
  4. securityModel,
  5. securityName,
  6. securityLevel,
  7. securityStateReference,
  8. reportableFlag,
  9. transportDomain, and
  10. transportAddress.
       The SNMPv3 Message Processing Model does not allow cached data
       to be overridden, except by error indications as detailed in
       (3) below.

Case, et al. Standards Track [Page 27] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 3) If statusInformation contains values for an OID/value combination
    (potentially also containing a securityLevel value,
    contextEngineID value, or contextName value), then:
    a) If a PDU is provided, it is the PDU from the original request.
       If possible, extract the request-id and pduType.
    b) If the pduType is determined to not be a member of the
       Confirmed Class, or if the reportableFlag is zero and the
       pduType cannot be determined, then the original message is
       discarded, and no further processing is done.  A result of
       FAILURE is returned.  SNMPv3 Message Processing is complete.
    c) A Report PDU is prepared:
       1) the varBindList is set to contain the OID and value from the
          statusInformation.
       2) error-status is set to 0.
       3) error-index is set to 0.
       4) request-id is set to the value extracted in step b).
          Otherwise, request-id is set to 0.
    d) The errorIndication in statusInformation may be accompanied by
       a securityLevel value, a contextEngineID value, or a
       contextName value.
       1) If statusInformation contains a value for securityLevel,
          then securityLevel is set to that value, otherwise it is set
          to noAuthNoPriv.
       2) If statusInformation contains a value for contextEngineID,
          then contextEngineID is set to that value, otherwise it is
          set to the value of this entity's snmpEngineID.
       3) If statusInformation contains a value for contextName, then
          contextName is set to that value, otherwise it is set to the
          default context of "" (zero-length string).
    e) PDU is set to refer to the new Report-PDU.  The old PDU is
       discarded.
    f) Processing continues with step 6) below.

Case, et al. Standards Track [Page 28] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 4) If the contextEngineID is not yet determined, then the
    contextEngineID is determined, in an implementation-dependent
    manner, possibly using the transportDomain and transportAddress.
 5) If the contextName is not yet determined, the contextName is set
    to the default context.
 6) A scopedPDU is prepared from the contextEngineID, contextName, and
    PDU.
 7) msgGlobalData is constructed as follows:
    a) The msgVersion field is set to snmpv3(3).
    b) msgID is set as determined in step 1 or 2 above.
    c) msgMaxSize is set to an implementation-dependent value.
    d) msgFlags are set as follows:
  1. If securityLevel specifies noAuthNoPriv, then authFlag and

privFlag are both set to zero.

  1. If securityLevel specifies authNoPriv, then authFlag is set

to one and privFlag is set to zero.

  1. If securityLevel specifies authPriv, then authFlag is set to

one and privFlag is set to one.

  1. If the PDU is from the Unconfirmed Class, then the

reportableFlag is set to zero.

  1. If the PDU is from the Confirmed Class then the

reportableFlag is set to one.

  1. All other msgFlags bits are set to zero.
    e) msgSecurityModel is set to the value of securityModel.

Case, et al. Standards Track [Page 29] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 8) If the PDU is from the Response Class or the Internal Class, then:
    a) The specified Security Model is called to generate the message
       according to the primitive:
       statusInformation =
         generateResponseMsg(
         IN   messageProcessingModel -- SNMPv3 Message Processing
                                     -- Model
         IN   globalData             -- msgGlobalData from step 7
         IN   maxMessageSize         -- from msgMaxSize (step 7c)
         IN   securityModel          -- as determined in step 7e
         IN   securityEngineID       -- the value of snmpEngineID
         IN   securityName           -- on behalf of this principal
         IN   securityLevel          -- for the outgoing message
         IN   scopedPDU              -- as prepared in step 6)
         IN   securityStateReference -- as determined in step 2
         OUT  securityParameters     -- filled in by Security Module
         OUT  wholeMsg               -- complete generated message
         OUT  wholeMsgLength         -- length of generated message
         )
       If, upon return from the Security Model, the statusInformation
       includes an errorIndication, then any cached information about
       the outstanding request message is discarded, and an
       errorIndication is returned, so it can be returned to the
       calling application.  SNMPv3 Message Processing is complete.
    b) A SUCCESS result is returned.  SNMPv3 Message Processing is
       complete.
 9) If the PDU is from the Confirmed Class or the Notification Class,
    then:
    a) If the PDU is from the Unconfirmed Class, then securityEngineID
       is set to the value of this entity's snmpEngineID.
       Otherwise, the snmpEngineID of the target entity is determined,
       in an implementation-dependent manner, possibly using
       transportDomain and transportAddress.  The value of the
       securityEngineID is set to the value of the target entity's
       snmpEngineID.

Case, et al. Standards Track [Page 30] RFC 3412 Message Processing and Dispatching for SNMP December 2002

    b) The specified Security Model is called to generate the message
       according to the primitive:
       statusInformation =
        generateRequestMsg(
        IN  messageProcessingModel -- SNMPv3 Message Processing Model
        IN  globalData             -- msgGlobalData, from step 7
        IN  maxMessageSize         -- from msgMaxSize in step 7 c)
        IN  securityModel          -- as provided by caller
        IN  securityEngineID       -- authoritative SNMP entity
                                   -- from step 9 a)
        IN  securityName           -- as provided by caller
        IN  securityLevel          -- as provided by caller
        IN  scopedPDU              -- as prepared in step 6
        OUT securityParameters     -- filled in by Security Module
        OUT wholeMsg               -- complete generated message
        OUT wholeMsgLength         -- length of the generated message
        )
       If, upon return from the Security Model, the statusInformation
       includes an errorIndication, then the message is discarded, and
       the errorIndication is returned, so it can be returned to the
       calling application, and no further processing is done.  SNMPv3
       Message Processing is complete.
    c) If the PDU is from the Confirmed Class, information about the
       outgoing message is cached, and an implementation-specific
       stateReference is created.  Information to be cached includes
       the values of:
  1. sendPduHandle
  2. msgID
  3. snmpEngineID
  4. securityModel
  5. securityName
  6. securityLevel
  7. contextEngineID
  8. contextName
    d) A SUCCESS result is returned.  SNMPv3 Message Processing is
       complete.

Case, et al. Standards Track [Page 31] RFC 3412 Message Processing and Dispatching for SNMP December 2002

7.2. Prepare Data Elements from an Incoming SNMP Message

 This section describes the procedure followed to extract data from an
 SNMPv3 message, and to prepare the data elements required for further
 processing of the message by the Message Dispatcher.
 1)  The message is passed in from the Message Dispatcher according to
     the abstract service primitive:
     result =                       -- SUCCESS or errorIndication
       prepareDataElements(
       IN  transportDomain          -- origin transport domain
       IN  transportAddress         -- origin transport address
       IN  wholeMsg                 -- as received from the network
       IN  wholeMsgLength           -- as received from the network
       OUT messageProcessingModel   -- typically, SNMP version
       OUT securityModel            -- Security Model to use
       OUT securityName             -- on behalf of this principal
       OUT securityLevel            -- Level of Security requested
       OUT contextEngineID          -- data from/at this entity
       OUT contextName              -- data from/in this context
       OUT pduVersion               -- version of the PDU
       OUT PDU                      -- SNMP Protocol Data Unit
       OUT pduType                  -- SNMP PDU type
       OUT sendPduHandle            -- handle for matched request
       OUT maxSizeResponseScopedPDU -- maximum size sender can accept
       OUT statusInformation        -- success or errorIndication
                                    -- error counter OID and value
                                    -- when errorIndication
       OUT stateReference           -- reference to state information
                                    -- to be used for a possible
       )                            -- Response
 2)  If the received message is not the serialization (according to
     the conventions of [RFC3417]) of an SNMPv3Message value, then the
     snmpInASNParseErrs counter [RFC3418] is incremented, the message
     is discarded without further processing, and a FAILURE result is
     returned.  SNMPv3 Message Processing is complete.
 3)  The values for msgVersion, msgID, msgMaxSize, msgFlags,
     msgSecurityModel, msgSecurityParameters, and msgData are
     extracted from the message.
 4)  If the value of the msgSecurityModel component does not match a
     supported securityModel, then the snmpUnknownSecurityModels
     counter is incremented, the message is discarded without further
     processing, and a FAILURE result is returned.  SNMPv3 Message
     Processing is complete.

Case, et al. Standards Track [Page 32] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 5)  The securityLevel is determined from the authFlag and the
     privFlag bits of the msgFlags component as follows:
     a) If the authFlag is not set and the privFlag is not set, then
        securityLevel is set to noAuthNoPriv.
     b) If the authFlag is set and the privFlag is not set, then
        securityLevel is set to authNoPriv.
     c) If the authFlag is set and the privFlag is set, then
        securityLevel is set to authPriv.
     d) If the authFlag is not set and privFlag is set, then the
        snmpInvalidMsgs counter is incremented, the message is
        discarded without further processing, and a FAILURE result is
        returned.  SNMPv3 Message Processing is complete.
     e) Any other bits in the msgFlags are ignored.
 6)  The security module implementing the Security Model as specified
     by the securityModel component is called for authentication and
     privacy services.  This is done according to the abstract service
     primitive:
     statusInformation =            -- errorIndication or success
                                    -- error counter OID and
                                    -- value if error
       processIncomingMsg(
       IN  messageProcessingModel   -- SNMPv3 Message Processing Model
       IN  maxMessageSize           -- of the sending SNMP entity
       IN  securityParameters       -- for the received message
       IN  securityModel            -- for the received message
       IN  securityLevel            -- Level of Security
       IN  wholeMsg                 -- as received on the wire
       IN  wholeMsgLength           -- length as received on the wire
       OUT securityEngineID         -- authoritative SNMP entity
       OUT securityName             -- identification of the principal
       OUT scopedPDU,               -- message (plaintext) payload
       OUT maxSizeResponseScopedPDU -- maximum size sender can accept
       OUT securityStateReference   -- reference to security state
       )                            -- information, needed for
                                    -- response
     If an errorIndication is returned by the security module, then:
     a) If statusInformation contains values for an OID/value pair,
        then generation of a Report PDU is attempted (see step 3 in
        section 7.1).

Case, et al. Standards Track [Page 33] RFC 3412 Message Processing and Dispatching for SNMP December 2002

        1) If the scopedPDU has been returned from processIncomingMsg,
           then determine contextEngineID, contextName, and PDU.
        2) Information about the message is cached and a
           stateReference is created (implementation-specific).
           Information to be cached includes the values of:
                        msgVersion,
                        msgID,
                        securityLevel,
                        msgFlags,
                        msgMaxSize,
                        securityModel,
                        maxSizeResponseScopedPDU,
                        securityStateReference
        3) Request that a Report-PDU be prepared and sent, according
           to the abstract service primitive:
           result =                     -- SUCCESS or FAILURE
           returnResponsePdu(
           IN  messageProcessingModel   -- SNMPv3(3)
           IN  securityModel            -- same as on incoming request
           IN  securityName             -- from processIncomingMsg
           IN  securityLevel            -- same as on incoming request
           IN  contextEngineID          -- from step 6 a) 1)
           IN  contextName              -- from step 6 a) 1)
           IN  pduVersion               -- SNMPv2-PDU
           IN  PDU                      -- from step 6 a) 1)
           IN  maxSizeResponseScopedPDU -- from processIncomingMsg
           IN  stateReference           -- from step 6 a) 2)
           IN  statusInformation        -- from processIncomingMsg
           )
     b) The incoming message is discarded without further processing,
        and a FAILURE result is returned.  SNMPv3 Message Processing
        is complete.
 7)  The scopedPDU is parsed to extract the contextEngineID, the
     contextName and the PDU.  If any parse error occurs, then the
     snmpInASNParseErrs counter [RFC3418] is incremented, the security
     state information is discarded, the message is discarded without
     further processing, and a FAILURE result is returned.  SNMPv3
     Message Processing is complete.  Treating an unknown PDU type is
     treated as a parse error is an implementation option.

Case, et al. Standards Track [Page 34] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 8)  The pduVersion is determined in an implementation-dependent
     manner.  For SNMPv3, the pduVersion would be an SNMPv2-PDU.
 9)  The pduType is determined, in an implementation-dependent manner.
     For [RFC3416], the pduTypes include:
  1. GetRequest-PDU,
  2. GetNextRequest-PDU,
  3. GetBulkRequest-PDU,
  4. SetRequest-PDU,
  5. InformRequest-PDU,
  6. SNMPv2-Trap-PDU,
  7. Response-PDU,
  8. Report-PDU.
 10) If the pduType is from the Response Class or the Internal Class,
     then:
     a) The value of the msgID component is used to find the cached
        information for a corresponding outstanding Request message.
        If no such outstanding Request message is found, then the
        security state information is discarded, the message is
        discarded without further processing, and a FAILURE result is
        returned.  SNMPv3 Message Processing is complete.
     b) sendPduHandle is retrieved from the cached information.
     Otherwise, sendPduHandle is set to <none>, an implementation
     defined value.
 11) If the pduType is from the Internal Class, then:
     a) statusInformation is created using the contents of the
        Report-PDU, in an implementation-dependent manner.  This
        statusInformation will be forwarded to the application
        associated with the sendPduHandle.
     b) The cached data for the outstanding message, referred to by
        stateReference, is retrieved.  If the securityModel or
        securityLevel values differ from the cached ones, it is
        important to recognize that Internal Class PDUs delivered at
        the security level of noAuthNoPriv open a window of
        opportunity for spoofing or replay attacks.  If the receiver
        of such messages is aware of these risks, the use of such
        unauthenticated messages is acceptable and may provide a
        useful function for discovering engine IDs or for detecting
        misconfiguration at remote nodes.

Case, et al. Standards Track [Page 35] RFC 3412 Message Processing and Dispatching for SNMP December 2002

        When the securityModel or securityLevel values differ from the
        cached ones, an implementation may retain the cached
        information about the outstanding Request message, in
        anticipation of the possibility that the Internal Class PDU
        received might be illegitimate.  Otherwise, any cached
        information about the outstanding Request message is
        discarded.
     c) The security state information for this incoming message is
        discarded.
     d) stateReference is set to <none>.
     e) A SUCCESS result is returned.  SNMPv3 Message Processing is
        complete.
 12) If the pduType is from the Response Class, then:
     a) The cached data for the outstanding request, referred to by
        stateReference, is retrieved, including:
  1. snmpEngineID
  2. securityModel
  3. securityName
  4. securityLevel
  5. contextEngineID
  6. contextName
     b) If the values extracted from the incoming message differ from
        the cached data, then any cached information about the
        outstanding Request message is discarded, the incoming message
        is discarded without further processing, and a FAILURE result
        is returned.  SNMPv3 Message Processing is complete.
        When the securityModel or securityLevel values differ from the
        cached ones, an implementation may retain the cached
        information about the outstanding Request message, in
        anticipation of the possibility that the Response Class PDU
        received might be illegitimate.
     c) Otherwise, any cached information about the outstanding
        Request message is discarded, and the stateReference is set to
        <none>.
     d) A SUCCESS result is returned.  SNMPv3 Message Processing is
        complete.
 13) If the pduType is from the Confirmed Class, then:

Case, et al. Standards Track [Page 36] RFC 3412 Message Processing and Dispatching for SNMP December 2002

     a) If the value of securityEngineID is not equal to the value of
        snmpEngineID, then the security state information is
        discarded, any cached information about this message is
        discarded, the incoming message is discarded without further
        processing, and a FAILURE result is returned.  SNMPv3 Message
        Processing is complete.
     b) Information about the message is cached and a stateReference
        is created (implementation-specific).  Information to be
        cached includes the values of:
              msgVersion,
              msgID,
              securityLevel,
              msgFlags,
              msgMaxSize,
              securityModel,
              maxSizeResponseScopedPDU,
              securityStateReference
     c) A SUCCESS result is returned.  SNMPv3 Message Processing is
        complete.
 14) If the pduType is from the Unconfirmed Class, then a SUCCESS
     result is returned.  SNMPv3 Message Processing is complete.

8. Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 intellectual property or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; neither does it represent that it
 has made any effort to identify any such rights.  Information on the
 IETF's procedures with respect to rights in standards-track and
 standards-related documentation can be found in BCP-11.  Copies of
 claims of rights made available for publication and any assurances of
 licenses to be made available, or the result of an attempt made to
 obtain a general license or permission for the use of such
 proprietary rights by implementors or users of this specification can
 be obtained from the IETF Secretariat.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights which may cover technology that may be required to practice
 this standard.  Please address the information to the IETF Executive
 Director.

Case, et al. Standards Track [Page 37] RFC 3412 Message Processing and Dispatching for SNMP December 2002

9. Acknowledgements

 This document is the result of the efforts of the SNMPv3 Working
 Group.  Some special thanks are in order to the following SNMPv3 WG
 members:
    Harald Tveit Alvestrand (Maxware)
    Dave Battle (SNMP Research, Inc.)
    Alan Beard (Disney Worldwide Services)
    Paul Berrevoets (SWI Systemware/Halcyon Inc.)
    Martin Bjorklund (Ericsson)
    Uri Blumenthal (IBM T. J. Watson Research Center)
    Jeff Case (SNMP Research, Inc.)
    John Curran (BBN)
    Mike Daniele (Compaq Computer Corporation)
    T. Max Devlin (Eltrax Systems)
    John Flick (Hewlett Packard)
    Rob Frye (MCI)
    Wes Hardaker (U.C.Davis, Information Technology - D.C.A.S.)
    David Harrington (Cabletron Systems Inc.)
    Lauren Heintz (BMC Software, Inc.)
    N.C. Hien (IBM T. J. Watson Research Center)
    Michael Kirkham (InterWorking Labs, Inc.)
    Dave Levi (SNMP Research, Inc.)
    Louis A Mamakos (UUNET Technologies Inc.)
    Joe Marzot (Nortel Networks)
    Paul Meyer (Secure Computing Corporation)
    Keith McCloghrie (Cisco Systems)
    Bob Moore (IBM)
    Russ Mundy (TIS Labs at Network Associates)
    Bob Natale (ACE*COMM Corporation)
    Mike O'Dell (UUNET Technologies Inc.)
    Dave Perkins (DeskTalk)
    Peter Polkinghorne (Brunel University)
    Randy Presuhn (BMC Software, Inc.)
    David Reeder (TIS Labs at Network Associates)
    David Reid (SNMP Research, Inc.)
    Aleksey Romanov (Quality Quorum)
    Shawn Routhier (Epilogue)
    Juergen Schoenwaelder (TU Braunschweig)
    Bob Stewart (Cisco Systems)
    Mike Thatcher (Independent Consultant)
    Bert Wijnen (IBM T. J. Watson Research Center)

Case, et al. Standards Track [Page 38] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 The document is based on recommendations of the IETF Security and
 Administrative Framework Evolution for SNMP Advisory Team.  Members
 of that Advisory Team were:
    David Harrington (Cabletron Systems Inc.)
    Jeff Johnson (Cisco Systems)
    David Levi (SNMP Research Inc.)
    John Linn (Openvision)
    Russ Mundy (Trusted Information Systems) chair
    Shawn Routhier (Epilogue)
    Glenn Waters (Nortel)
    Bert Wijnen (IBM T. J. Watson Research Center)
 As recommended by the Advisory Team and the SNMPv3 Working Group
 Charter, the design incorporates as much as practical from previous
 RFCs and drafts.  As a result, special thanks are due to the authors
 of previous designs known as SNMPv2u and SNMPv2*:
    Jeff Case (SNMP Research, Inc.)
    David Harrington (Cabletron Systems Inc.)
    David Levi (SNMP Research, Inc.)
    Keith McCloghrie (Cisco Systems)
    Brian O'Keefe (Hewlett Packard)
    Marshall T. Rose (Dover Beach Consulting)
    Jon Saperia (BGS Systems Inc.)
    Steve Waldbusser (International Network Services)
    Glenn W. Waters (Bell-Northern Research Ltd.)

10. Security Considerations

 The Dispatcher coordinates the processing of messages to provide a
 level of security for management messages and to direct the SNMP PDUs
 to the proper SNMP application(s).
 A Message Processing Model, and in particular the v3MP defined in
 this document, interacts as part of the Message Processing with
 Security Models in the Security Subsystem via the abstract service
 interface primitives defined in [RFC3411] and elaborated above.
 The level of security actually provided is primarily determined by
 the specific Security Model implementation(s) and the specific SNMP
 application implementation(s) incorporated into this framework.
 Applications have access to data which is not secured.  Applications
 should take reasonable steps to protect the data from disclosure, and
 when they send data across the network, they should obey the
 securityLevel and call upon the services of an Access Control Model
 as they apply access control.

Case, et al. Standards Track [Page 39] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 The values for the msgID element used in communication between SNMP
 entities MUST be chosen to avoid replay attacks.  The values do not
 need to be unpredictable; it is sufficient that they not repeat.
 When exchanges are carried out over an insecure network, there is an
 open opportunity for a third party to spoof or replay messages when
 any message of an exchange is given at the security level of
 noAuthNoPriv.  For most exchanges, all messages exist at the same
 security level.  In the case where the final message is an Internal
 Class PDU, this message may be delivered at a level of noAuthNoPriv
 or authNoPriv, independent of the security level of the preceding
 messages.  Internal Class PDUs delivered at the level of authNoPriv
 are not considered to pose a security hazard.  Internal Class PDUs
 delivered at the security level of noAuthNoPriv open a window of
 opportunity for spoofing or replay attacks.  If the receiver of such
 messages is aware of these risks, the use of such unauthenticated
 messages is acceptable and may provide a useful function for
 discovering engine IDs or for detecting misconfiguration at remote
 nodes.
 This document also contains a MIB definition module.  None of the
 objects defined is writable, and the information they represent is
 not deemed to be particularly sensitive.  However, if they are deemed
 sensitive in a particular environment, access to them should be
 restricted through the use of appropriately configured Security and
 Access Control models.

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., Perkins, D., Schoenwaelder, J., Case, J.,
             Rose, M. and S. Waldbusser, "Structure of Management
             Information Version 2 (SMIv2)", STD 58, RFC 2578, April
             1999.
 [RFC2580]   McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
             Rose, M. and S. Waldbusser, "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.

Case, et al. Standards Track [Page 40] RFC 3412 Message Processing and Dispatching for SNMP December 2002

 [RFC3413]   Levi, D., Meyer, P. and B. Stewart, "Simple Network
             Management Protocol (SNMP) Applications", STD 62, RFC
             3413, December 2002.
 [RFC3414]   Blumenthal, U. and B. Wijnen, "The User-Based Security
             Model (USM) for Version 3 of the Simple Network
             Management Protocol (SNMPv3)", STD 62, RFC 3414, December
             2002.
 [RFC3415]   Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based
             Access Control Model (VACM) for the Simple Network
             Management Protocol (SNMP)", STD 62, RFC 3415, December
             2002.
 [RFC3416]   Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
             Waldbusser, "Version 2 of the Protocol Operations for the
             Simple Network Management Protocol (SNMP)", STD 62, RFC
             3416, December 2002.
 [RFC3417]   Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
             Waldbusser, "Transport Mappings for the Simple Network
             Management Protocol (SNMP)", STD 62, RFC 3417, December
             2002.
 [RFC3418]   Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
             Waldbusser, "Management Information Base (MIB) for the
             Simple Network Management Protocol (SNMP)", STD 62, RFC
             3418, December 2002.

11.2. Informative References

 [RFC1901]   Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
             "Introduction to Community-based SNMPv2", RFC 1901,
             January 1996.
 [RFC2028]   Hovey, R. and S. Bradner, "The Organizations Involved in
             the IETF Standards Process", BCP 11, RFC 2028, October
             1996.
 [RFC2576]   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",
             RFC 2576, March 2000.
 [RFC3410]   Case, J., Mundy, R., Partain, D. and B. Stewart,
             "Introduction and Applicability Statements for Internet-
             Standard Management Framework", RFC 3410, December 2002.

Case, et al. Standards Track [Page 41] RFC 3412 Message Processing and Dispatching for SNMP December 2002

12. Editors' Addresses

 Jeffrey Case
 SNMP Research, Inc.
 3001 Kimberlin Heights Road
 Knoxville, TN 37920-9716
 USA
 Phone: +1 423-573-1434
 EMail: case@snmp.com
 David Harrington
 Enterasys Networks
 35 Industrial Way
 Post Office Box 5005
 Rochester, NH 03866-5005
 USA
 Phone: +1 603-337-2614
 EMail: dbh@enterasys.com
 Randy Presuhn
 BMC Software, Inc.
 2141 North First Street
 San Jose, CA 95131
 USA
 Phone: +1 408-546-1006
 EMail: randy_presuhn@bmc.com
 Bert Wijnen
 Lucent Technologies
 Schagen 33
 3461 GL Linschoten
 Netherlands
 Phone: +31 348-680-485
 EMail: bwijnen@lucent.com

Case, et al. Standards Track [Page 42] RFC 3412 Message Processing and Dispatching for SNMP December 2002

13. Full Copyright Statement

 Copyright (C) The Internet Society (2002).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Case, et al. Standards Track [Page 43]

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