rfc3413.txt

开发snmp的开发包有两个开放的SNMP开发库

   - The messageProcessingModel indicates which Message Processing Model
     the application wishes to use.

   - The securityModel is the security model that the application wishes
     to use.



Levi, et. al.               Standards Track                     [Page 6]

RFC 3413                   SNMP Applications               December 2002


   - The securityName is the security model independent name for the
     principal on whose behalf the application wishes the message to be
     generated.

   - The securityLevel is the security level that the application wishes
     to use.

   - The contextEngineID specifies the location of the management
     information it is requesting.  Note that unless the request is
     being sent to a proxy, this value will usually be equal to the
     snmpEngineID value of the engine to which the request is being
     sent.

   - The contextName specifies the local context name for the management
     information it is requesting.

   - The pduVersion indicates the version of the PDU to be sent.

   - The PDU is a value constructed by the command generator containing
     the management operation that the command generator wishes to
     perform.

   - The expectResponse argument indicates that a response is expected.

   The result of the sendPdu interface indicates whether the PDU was
   successfully sent.  If it was successfully sent, the returned value
   will be a sendPduHandle.  The command generator should store the
   sendPduHandle so that it can correlate a response to the original
   request.

   The Dispatcher is responsible for delivering the response to a
   particular request to the correct command generator application.  The
   abstract service interface used is:

      processResponsePdu(              -- process Response PDU
        IN   messageProcessingModel    -- typically, SNMP version
        IN   securityModel             -- Security Model in use
        IN   securityName              -- on behalf of this principal
        IN   securityLevel             -- Level of Security
        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   statusInformation         -- success or errorIndication
        IN   sendPduHandle             -- handle from sendPdu
             )





Levi, et. al.               Standards Track                     [Page 7]

RFC 3413                   SNMP Applications               December 2002


   Where:

   - The messageProcessingModel is the value from the received response.

   - The securityModel is the value from the received response.

   - The securityName is the value from the received response.

   - The securityLevel is the value from the received response.

   - The contextEngineID is the value from the received response.

   - The contextName is the value from the received response.

   - The pduVersion indicates the version of the PDU in the received
     response.

   - The PDU is the value from the received response.

   - The statusInformation indicates success or failure in receiving the
     response.

   - The sendPduHandle is the value returned by the sendPdu call which
     generated the original request to which this is a response.

   The procedure when a command generator receives a message is as
   follows:

   (1) If the received values of messageProcessingModel, securityModel,
       securityName, contextEngineID, contextName, and pduVersion are
       not all equal to the values used in the original request, the
       response is discarded.

   (2) The operation type, request-id, error-status, error-index, and
       variable-bindings are extracted from the PDU and saved.  If the
       request-id is not equal to the value used in the original
       request, the response is discarded.

   (3) At this point, it is up to the application to take an appropriate
       action.  The specific action is implementation dependent.  If the
       statusInformation indicates that the request failed, an
       appropriate action might be to attempt to transmit the request
       again, or to notify the person operating the application that a
       failure occurred.







Levi, et. al.               Standards Track                     [Page 8]

RFC 3413                   SNMP Applications               December 2002


3.2. Command Responder Applications

   Before a command responder application can process messages, it must
   first associate itself with an SNMP engine.  The abstract service
   interface used for this purpose is:

      statusInformation =       -- success or errorIndication
       registerContextEngineID(
       IN   contextEngineID     -- take responsibility for this one
       IN   pduType             -- the pduType(s) to be registered
            )

   Where:

   - The statusInformation indicates success or failure of the
     registration attempt.

   - The contextEngineID is equal to the snmpEngineID of the SNMP engine
     with which the command responder is registering.

   - The pduType indicates a Read-Class and/or Write-Class PDU.

   Note that if another command responder application is already
   registered with an SNMP engine, any further attempts to register with
   the same contextEngineID and pduType will be denied.  This implies
   that separate command responder applications could register
   separately for the various pdu types.  However, in practice this is
   undesirable, and only a single command responder application should
   be registered with an SNMP engine at any given time.

   A command responder application can disassociate with an SNMP engine
   using the following abstract service interface:

      unregisterContextEngineID(
        IN   contextEngineID     -- give up responsibility for this one
        IN   pduType             -- the pduType(s) to be unregistered
             )

   Where:

   - The contextEngineID is equal to the snmpEngineID of the SNMP engine
     with which the command responder is cancelling the registration.

   - The pduType indicates a Read-Class and/or Write-Class PDU.







Levi, et. al.               Standards Track                     [Page 9]

RFC 3413                   SNMP Applications               December 2002


   Once the command responder has registered with the SNMP engine, it
   waits to receive SNMP messages.  The abstract service interface used
   for receiving messages is:

   processPdu(                     -- process Request/Notification PDU
     IN   messageProcessingModel   -- typically, SNMP version
     IN   securityModel            -- Security Model in use
     IN   securityName             -- on behalf of this principal
     IN   securityLevel            -- Level of Security
     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 the Response PDU
     IN   stateReference           -- reference to state information
          )                        -- needed when sending a response

   Where:

   - The messageProcessingModel indicates which Message Processing Model
     received and processed the message.

   - The securityModel is the value from the received message.

   - The securityName is the value from the received message.

   - The securityLevel is the value from the received message.

   - The contextEngineID is the value from the received message.

   - The contextName is the value from the received message.

   - The pduVersion indicates the version of the PDU in the received
     message.

   - The PDU is the value from the received message.

   - The maxSizeResponseScopedPDU is the maximum allowable size of a
     ScopedPDU containing a Response PDU (based on the maximum message
     size that the originator of the message can accept).

   - The stateReference is a value which references cached information
     about each received request message.  This value must be returned
     to the Dispatcher in order to generate a response.







Levi, et. al.               Standards Track                    [Page 10]

RFC 3413                   SNMP Applications               December 2002


   The procedure when a message is received is as follows:

   (1) The operation type is determined from the ASN.1 tag value
       associated with the PDU parameter.  The operation type should
       always be one of the types previously registered by the
       application.

   (2) The request-id is extracted from the PDU and saved.

   (3) Any PDU type specific parameters are extracted from the PDU and
       saved (for example, if the PDU type is an SNMPv2 GetBulk PDU, the
       non-repeaters and max-repetitions values are extracted).

   (4) The variable-bindings are extracted from the PDU and saved.

   (5) The management operation represented by the PDU type is performed
       with respect to the relevant MIB view within the context named by
       the contextName (for an SNMPv2 PDU type, the operation is
       performed according to the procedures set forth in [RFC1905]).
       The relevant MIB view is determined by the securityLevel,
       securityModel, contextName, securityName, and the class of the
       PDU type.  To determine whether a particular object instance is
       within the relevant MIB view, the following abstract service
       interface is called:

          statusInformation =      -- success or errorIndication
            isAccessAllowed(
            IN   securityModel     -- Security Model in use
            IN   securityName      -- principal who wants to access
            IN   securityLevel     -- Level of Security
            IN   viewType          -- read, write, or notify view
            IN   contextName       -- context containing variableName
            IN   variableName      -- OID for the managed object
                 )

       Where:

       - The securityModel is the value from the received message.

       - The securityName is the value from the received message.

       - The securityLevel is the value from the received message.

       - The viewType indicates whether the PDU type is a Read-Class or
         Write-Class operation.

       - The contextName is the value from the received message.




Levi, et. al.               Standards Track                    [Page 11]

RFC 3413                   SNMP Applications               December 2002


       - The variableName is the object instance of the variable for
         which access rights are to be checked.

       Normally, the result of the management operation will be a new
       PDU value, and processing will continue in step (6) below.
       However, at any time during the processing of the management
       operation:

       - If the isAccessAllowed ASI returns a noSuchView, noAccessEntry,
         or noGroupName error, processing of the management operation is
         halted, a PDU value is constructed using the values from the
         originally received PDU, but replacing the error-status with an
         authorizationError code, and error-index value of 0, and
         control is passed to step (6) below.

       - If the isAccessAllowed ASI returns an otherError, processing of
         the management operation is halted, a different PDU value is
         constructed using the values from the originally received PDU,
         but replacing the error-status with a genError code and the
         error-index with the index of the failed variable binding, and
         control is passed to step (6) below.

       - If the isAccessAllowed ASI returns a noSuchContext error,
         processing of the management operation is halted, no result PDU
         is generated, the snmpUnknownContexts counter is incremented,
         and control is passed to step (6) below for generation of a
         report message.

       - If the context named by the contextName parameter is
         unavailable, processing of the management operation is halted,
         no result PDU is generated, the snmpUnavailableContexts counter
         is incremented, and control is passed to step (6) below for
         generation of a report message.