Network Working Group J. Case
Request for Comments: 2272 SNMP Research, Inc.
Obsoletes: 2262 D. Harrington
Category: Standards Track Cabletron Systems, Inc.
 R. Presuhn
 BMC Software, Inc.
 B. Wijnen
 IBM T. J. Watson Research
 January 1998
 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 (1998). All Rights Reserved.
IANA Note
 Due to a clerical error in the assignment of the snmpModules in this
 memo, this RFC provides the corrected number assignment for this
 protocol. This memo obsoletes RFC 2262.
Abstract
 This document describes the Message Processing and Dispatching for
 SNMP messages within the SNMP architecture [RFC2271]. 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.
Table of Contents
 1. Introduction ............................................... 2
 2. Overview ................................................... 3
 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 ...................... 7
 4.1.2. Sending a Response to the Network ...................... 9
 4.2. Receiving an SNMP Message from the Network ............... 10
 4.2.1. Message Dispatching of received SNMP Messages .......... 10
 4.2.2. PDU Dispatching for Incoming Messages .................. 11
 4.2.2.1. Incoming Requests and Notifications .................. 12
 4.2.2.2. Incoming Responses ................................... 13
 4.3. Application Registration for Handling PDU types .......... 14
 4.4. Application Unregistration for Handling PDU Types ........ 14
 5. Definitions ................................................ 15
 5.1. Definitions for SNMP Message Processing and Dispatching .. 15
 6. The SNMPv3 Message Format .................................. 18
 6.1. msgVersion ............................................... 19
 6.2. msgID .................................................... 19
 6.3. msgMaxSize ............................................... 19
 6.4. msgFlags ................................................. 20
 6.5. msgSecurityModel ......................................... 22
 6.6. msgSecurityParameters .................................... 22
 6.7. scopedPduData ............................................ 22
 6.8. scopedPDU ................................................ 22
 6.8.1. contextEngineID ........................................ 22
 6.8.2. contextName ............................................ 23
 6.8.3. data ................................................... 23
 7. Elements of Procedure for v3MP ............................. 23
 7.1. Prepare an Outgoing SNMP Message ......................... 24
 7.2. Prepare Data Elements from an Incoming SNMP Message ...... 29
 8. Intellectual Property ...................................... 34
 9. Acknowledgements ........................................... 35
 10. Security Considerations ................................... 36
 11. References ................................................ 36
 12. Editors' Addresses ........................................ 38
 13. Full Copyright Statement .................................. 39
1. Introduction
 The Architecture for describing Internet Management Frameworks
 [RFC2271] 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 [RFC2271].
 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 responsibile for processing a 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 modelled 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 modelled 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 RFC 2119.
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 RFC1906) | | +->| otherMP * |<--->| +-------------+ | |
 | +------------------+ | +------------+ | | | |
 | ^ +---------------------+ +-----------------+ |
 | | |
 +----------|--------------------------------------------------------+
 v
 +------------------+
 | Network |
 +------------------+
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.
3. Elements of Message Processing and Dispatching
 See [RFC2271] 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
 [RFC1905]. 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.
 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, 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 [RFC1905] elements of procedure and syntax instead of
 those specified for SNMPv1.
3.3. pduType
 A value of pduType represents a specific type of protocol operation.
 The values of 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.
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 trap.
 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.
 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 -- the version of the PDU
 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 via
 the transport specified by the transportDomain to the address
 specified by the transportAddress.
 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.
 1) An application can request this using the abstract service
 primitive:
 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.
 4) If the result is success, the outgoingMessage is sent over the
 transport specified by the transportDomain to the address
 specified by the transportAddress.
 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 [RFC1907] 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 [RFC1907] counter is incremented, and
 the message is discarded without further processing. If the
 version is not supported, then the snmpInBadVersions [RFC1907]
 counter is incremented, and the message is discarded without
 further processing.
 3) The origin transportDomain and origin transportAddress are
 determined.
 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 to use
 OUT securityName -- on behalf of this principal
 OUT securityLevel -- Level of Security requested
 OUT contextEngineID -- data from/at this entity
 OUT contextName -- data from/in this context
 OUT pduVersion -- the version of the PDU
 OUT PDU -- SNMP Protocol Data Unit
 OUT pduType -- SNMP PDU type
 OUT sendPduHandle -- handle for 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.
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 transportDomain -- destination transportDomain
 OUT transportAddress -- 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.
 d) The incoming message is discarded without further processing.
 Message Processing for this message is complete.
 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 PDU 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.
 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 means for
 requesting simultaneous registration for multiple values of
 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.
 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 means for requesting
 unregistration for simultaneous multiple contextEngineID values,
 e.g., all contextEngineID values, and may also provide 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 "9711200000Z" -- 20 November 1997
 ORGANIZATION "SNMPv3 Working Group"
 CONTACT-INFO "WG-email: snmpv3@tis.com
 Subscribe: majordomo@tis.com
 In message body: subscribe snmpv3
 Chair: Russ Mundy
 Trusted Information Systems
 postal: 3060 Washington Road
 Glenwood, MD 21738
 USA
 email: mundy@tis.com
 phone: +1 301-854-6889
 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 Dave Harrington
 Cabletron Systems, Inc.
 postal: Post Office Box 5005
 MailStop: Durham
 35 Industrial Way
 Rochester, NH 03867-5005
 USA
 email: dbh@ctron.com
 phone: +1 603-337-7357
 Co-editor: Randy Presuhn
 BMC Software, Inc.
 postal: 1190 Saratoga Ave, Suite 190
 San Jose, CA 95120
 USA
 email: rpresuhn@bmc.com
 phone: +1 408-556-0720
 Co-editor: Bert Wijnen
 IBM T. J. Watson Research
 postal: Schagen 33
 3461 GL Linschoten
 Netherlands
 email: wijnen@vnet.ibm.com
 phone: +31 348-432-794
 "
 DESCRIPTION "The MIB for Message Processing and Dispatching"
 ::= { snmpModules 11 }
 -- 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 }
 -- Conformance information ******************************************
 snmpMPDMIBCompliances OBJECT IDENTIFIER ::= {snmpMPDMIBConformance 1}
 snmpMPDMIBGroups OBJECT IDENTIFIER ::= {snmpMPDMIBConformance 2}
 -- 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
 msgVersion INTEGER { snmpv3 (3) },
 -- administrative parameters
 msgGlobalData HeaderData,
 -- security model-specific parameters
 -- format defined by Security Model
 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 (0..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 RFC1905
 }
 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 [RFC2271] as the high-order
 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 is 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 may need to identify the
 message even if decrypting 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.
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.
 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 how big the Response
 to a Request message can be.
6.4. msgFlags
 The msgFlags field of the message contains several bit fields which
 control processing of the message.
 When the reportableFlag is one, a Report PDU must be returned to the
 sender under those conditions which can cause the generation of
 Report PDUs. When the reportableFlag is zero, then a Report PDU must
 not be sent. The reportableFlag must always be zero when the message
 contains 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 request-type PDU
 (such as a Get PDU) and an acknowledged notification-type PDU (such
 as an Inform PDU).
 If the reportableFlag is set to one for a message containing 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 engine-to-engine communications and are processed
 directly by the SNMPv3 Message Processing Model, and are generally
 not passed to applications for processing, unlike all other PDU
 types.
 Note that 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 ecryption key. If the PDU can be decoded, the PDU type
 forms the basis for decisions on sending Report PDUs.
 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 [RFC2271] 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
 identification. In general, this authentication will allow the
 receiver to determine with reasonable certainty that the message
 was:
 - sent on behalf of the principal associated with the
 securityName,
 - was not redirected,
 - was not modified in transit, and
 - 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., 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
 authFlag one, privFlag zero -> securityLevel is authNoPriv
 authFlag one, privFlag one -> securityLevel is authPriv
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 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.
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 [RFC1905].
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 reportableFlag is set in the
 received message.
 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 must also be released at that same time.
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 GetRequest-PDU, GetNextRequest-PDU, GetBulkRequest-
 PDU, SetRequest-PDU, InformRequest-PDU, or SNMPv2-Trap-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
 )
 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.
 * SNMPv3 does not use the values of expectResponse or
 pduVersion.
 2) The Message Dispatcher may request that an SNMPv3 message
 containing a Response-PDU or Report-PDU be prepared for sending.
 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 of Response PDU
 IN stateReference -- reference to state
 -- information presented with
 -- the request
 IN statusInformation -- success or errorIndication
 -- error counter OID and value
 -- when errorIndication
 OUT transportDomain -- destination transport domain
 OUT transportAddress -- 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
 - msgID,
 - contextEngineID,
 - contextName,
 - securityModel,
 - securityName,
 - securityLevel,
 - securityStateReference,
 - reportableFlag,
 - transportDomain, and
 - transportAddress.
 The SNMPv3 Message Processing Model does not allow cached data
 to be overridden, except by error indications as detailed in
 (3) below.
 3) If statusInformation contains values for an OID/value combination
 (potentially also containing a securityLevel value,
 contextEngineID value, or contextName value), then
 a) If reportableFlag is zero, then the original message is
 discarded, and no further processing is done. A result of
 FAILURE is returned. SNMPv3 Message Processing is complete.
 b) If a PDU is provided, it is the PDU from the original request.
 If possible, extract the request-id.
 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.
 4) If 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:
 - If securityLevel specifies noAuthNoPriv, then authFlag and
 privFlag are both set to zero.
 - If securityLevel specifies authNoPriv, then authFlag is set
 to one and privFlag is set to zero.
 - If securityLevel specifies authPriv, then authFlag is set to
 one and privFlag is set to one.
 - If the PDU is a Response-PDU, Report-PDU or SNMPv2-Trap-PDU,
 then the reportableFlag is set to zero.
 - If the PDU is a GetRequest-PDU, GetNextRequest-PDU,
 GetBulkRequest-PDU, SetRequest-PDU, or InformRequest-PDU
 then the reportableFlag is set to one.
 - All other msgFlags bits are set to zero.
 e) msgSecurityModel is set to the value of securityModel
 8) If the PDU is a Response-PDU or Report-PDU, 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 a GetRequest-PDU, GetNextRequest-PDU,
 GetBulkRequest-PDU, SetRequest-PDU, InformRequest-PDU, or or
 SNMPv2-Trap-PDU, then
 a) If the PDU is an SNMPv2-Trap-PDU, 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
 securityEngineID is set to the value of the target entity's
 snmpEngineID.
 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
 IN securityName -- as provided by caller
 IN securityLevel -- as provided by caller
 IN snmpEngineID -- as determined in step 9 a)
 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) Information about the outgoing message is cached, and a
 stateReference is created (implementation-specific).
 Information to be cached includes the values of:
 - sendPduHandle
 - msgID
 - snmpEngineID
 - securityModel
 - securityName
 - securityLevel
 - contextEngineID
 - contextName
 d) A SUCCESS result is returned. SNMPv3 Message Processing is
 complete.
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 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
 2) If the received message is not the serialization (according to
 the conventions of [RFC1906]) of an SNMPv3Message value, then the
 snmpInASNParseErrs counter [RFC1907] 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, a Report PDU is generated, the message is
 discarded without further processing, and a FAILURE result is
 returned. SNMPv3 Message Processing is complete.
 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, a Report PDU is
 generated, the message is discarded without further processing,
 and a FAILURE result is returned. SNMPv3 Message Processing is
 complete.
 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 expectResponse -- TRUE or FALSE
 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 of Response PDU
 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 a Report PDU is generated.
 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
 OUT transportDomain -- destination's transport
 -- domain
 OUT transportAddress -- destination's transport
 -- address
 OUT outgoingMessage -- the message to send
 OUT outgoingMessageLength -- the length of the message
 )
 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 [RFC1907] 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.
 8) The pduVersion is set to an SNMPv2-PDU.
 9) The pduType is determined, in an implementation-dependent manner,
 to be:
 - a GetRequest-PDU,
 - a GetNextRequest-PDU,
 - a GetBulkRequest-PDU,
 - a SetRequest-PDU,
 - an InformRequest-PDU,
 - an SNMPv2-Trap-PDU,
 - a Response-PDU, or
 - a Report-PDU.
 10) If the pduType is a Response-PDU or Report-PDU, 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 a Report-PDU, 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) Any cached information about the outstanding Request message
 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 a Response-PDU, then
 a) The cached data for the outstanding request, referred to by
 stateReference, is retrieved, including
 - snmpEngineID
 - securityModel
 - securityName
 - securityLevel
 - contextEngineID
 - contextName
 b) If the values extracted from the incoming message differ from
 the cached data, then the security state information is
 discarded, 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.
 c) Otherwise, any cached information about the outstanding
 Request message is discarded, and stateReference is set to
 <none>.
 d) A SUCCESS result is returned. SNMPv3 Message Processing is
 complete.
 13) If the pduType is a GetRequest-PDU, GetNextRequest-PDU,
 GetBulkRequest-PDU, SetRequest-PDU, or InformRequest-PDU, then
 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 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.
 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 an SNMPv2-Trap-PDU, 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.
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:
 Dave Battle (SNMP Research, Inc.)
 Uri Blumenthal (IBM T.J. Watson Research Center)
 Jeff Case (SNMP Research, Inc.)
 John Curran (BBN)
 T. Max Devlin (Hi-TECH Connections)
 John Flick (Hewlett Packard)
 David Harrington (Cabletron Systems Inc.)
 N.C. Hien (IBM T.J. Watson Research Center)
 Dave Levi (SNMP Research, Inc.)
 Louis A Mamakos (UUNET Technologies Inc.)
 Paul Meyer (Secure Computing Corporation)
 Keith McCloghrie (Cisco Systems)
 Russ Mundy (Trusted Information Systems, Inc.)
 Bob Natale (ACE*COMM Corporation)
 Mike O'Dell (UUNET Technologies Inc.)
 Dave Perkins (DeskTalk)
 Peter Polkinghorne (Brunel University)
 Randy Presuhn (BMC Software, Inc.)
 David Reid (SNMP Research, Inc.)
 Shawn Routhier (Epilogue)
 Juergen Schoenwaelder (TU Braunschweig)
 Bob Stewart (Cisco Systems)
 Bert Wijnen (IBM T.J. Watson Research Center)
 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 [RFC2271] 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.
 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.
11. References
 [RFC1901] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
 "Introduction to Community-based SNMPv2",
 RFC 1901, January 1996.
 [RFC1902] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
 "Structure of Management Information for
 Version 2 of the Simple Network Management Protocol (SNMPv2)",
 RFC 1902, January 1996.
 [RFC1905] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
 "Protocol Operations for Version 2 of the
 Simple Network Management Protocol (SNMPv2)", RFC 1905, January
 1996.
 [RFC1906] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
 "Transport Mappings for Version 2 of the
 Simple Network Management Protocol (SNMPv2)", RFC 1906, January
 1996.
 [RFC1907] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
 "Management Information Base for Version 2
 of the Simple Network Management Protocol (SNMPv2)", RFC 1907
 January 1996.
 [RFC1908] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
 "Coexistence between Version 1 and Version
 2 of the Internet-standard Network Management Framework", RFC
 1908, January 1996.
 [RFC 2028] Hovey, R., and S. Bradner, "The Organizations Involved in
 the IETF Standards Process", BCP 11, RFC 2028, October 1996.
 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
 Requirement Levels", RFC 2119, BCP 14, March 1997.
 [RFC2271] Harrington, D., Presuhn, R., and B. Wijnen, "An
 Architecture for describing SNMP Management Frameworks",
 RFC 2271, January 1998.
 [RFC2274] Blumenthal, U., and B. Wijnen, "The User-Based
 Security Model for Version 3 of the Simple Network
 Management Protocol (SNMPv3)", RFC 2274, January 1998.
 [RFC2275] Wijnen, B., Presuhn, R., and K. McCloghrie,
 "View-based Access Control Model for the Simple
 Network Management Protocol (SNMP)", RFC 2275, January 1998.
 [RFC2273] Levi, D., Meyer, P., and B. Stewart, "SNMPv3
 Applications", RFC 2273, January 1998.
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
 Dave Harrington
 Cabletron Systems, Inc
 Post Office Box 5005
 Mail Stop: Durham
 35 Industrial Way
 Rochester, NH 03867-5005
 USA
 Phone: +1 603-337-7357
 EMail: dbh@ctron.com
 Randy Presuhn
 BMC Software, Inc.
 1190 Saratoga Avenue
 Suite 130
 San Jose, CA 95129
 USA
 Phone: +1 408-556-0720
 EMail: rpresuhn@bmc.com
 Bert Wijnen
 IBM T. J. Watson Research
 Schagen 33
 3461 GL Linschoten
 Netherlands
 Phone: +31 348-432-794
 EMail: wijnen@vnet.ibm.com
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