rfc2257.txt

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         The NETWORK_BYTE_ORDER bit applies to all AgentX PDUs.

         The NON_DEFAULT_CONTEXT bit is used only in the AgentX PDUs
         described in section 6.1.1.




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RFC 2257                        AgentX                      January 1998


         The NEW_INDEX and ANY_INDEX bits are used only within the
         agentx-IndexAllocate-, and -IndexDeallocate-PDUs.

         The INSTANCE_REGISTRATION bit is used only within the agentx-
         Register-PDU.

      h.sessionID

         The session ID uniquely identifies a session over which AgentX
         PDUs are exchanged between a subagent and the master agent.
         The session ID has no significance and no defined value in the
         agentx-Open-PDU sent by a subagent to open a session with the
         master agent; in this case, the master agent will assign a
         unique sessionID that it will pass back in the corresponding
         agentx-Response-PDU.  From that point on, that same sessionID
         will appear in every AgentX PDU exchanged over that session
         between the master and the subagent.  A subagent may establish
         multiple AgentX sessions by sending multiple agentx-Open-PDUs
         to the master agent.

         In master agents that support multiple transport protocols, the
         sessionID should be globally unique rather than unique just to
         a particular transport.

      h.transactionID

         The transaction ID uniquely identifies, for a given session,
         the single SNMP management request (and single SNMP PDU) with
         which an AgentX PDU is associated.  If a single SNMP management
         request results in multiple AgentX PDUs being sent by the
         master agent with the same sessionID, each of these AgentX PDUs
         must contain the same transaction ID; conversely, AgentX PDUs
         sent during a particular session, that result from distinct
         SNMP management requests, must have distinct transaction IDs
         within the limits of the 32-bit field).

         Note that the transaction ID is not the same as the SNMP PDU's
         request-id (as described in section 4.1 of RFC 1905 [4]), nor
         can it be, since a master agent might receive SNMP requests
         with the same request-ids from different managers.

         The transaction ID has no significance and no defined value in
         AgentX administrative PDUs, i.e., AgentX PDUs that are not
         associated with an SNMP management request.







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RFC 2257                        AgentX                      January 1998


      h.packetID

         A packet ID generated by the sender for all AgentX PDUs except
         the agentx-Response-PDU. In an agentx-Response-PDU, the packet
         ID must be the same as that in the received AgentX PDU to which
         it is a response.  A master agent might use this field to
         associate subagent response PDUs with their corresponding
         request PDUs.  A subagent might use this field to correlate
         responses to multiple (batched) registrations.

      h.payload_length

         The size in octets of the PDU contents, excluding the 20-byte
         header.  As a result of the encoding schemes and PDU layouts,
         this value will always be either 0, or a multiple of 4.

6.1.1.  Context

   In the SNMPv1 or v2c frameworks, the community string may be used as
   an index into a local repository of configuration information that
   may include community profiles or more complex context information.
   Future versions of the SNMP will likely formalize this notion of
   "context".

   AgentX provides a mechanism for transmitting a context specification
   within relevant PDUs, but does not place any constraints on the
   content of that specification.

   An optional context field may be present in the agentx-Register-,
   UnRegister-, AddAgentCaps-, RemoveAgentCaps-, Get-, GetNext-,
   GetBulk-, IndexAllocate-, IndexDeallocate-, Notify-, TestSet-, and
   Ping- PDUs.

   If the NON_DEFAULT_CONTEXT bit in the AgentX header field h.flags is
   clear, then there is no context field in the PDU, and the operation
   refers to the default context.

   If the NON_DEFAULT_CONTEXT bit is set, then a context field
   immediately follows the AgentX header, and the operation refers to
   that specific context.  The context is represented as an Octet
   String.  There are no constraints on its length or contents.

   Thus, all of these AgentX PDUs (that is, those listed immediately
   above) refer to, or "indicate" a context, which is either the default
   context, or a non-default context explicitly named in the PDU.






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RFC 2257                        AgentX                      January 1998


6.2.  AgentX PDUs

6.2.1.  The agentx-Open-PDU

   An agentx-Open-PDU is generated by a subagent to request
   establishment of an AgentX session with the master agent.

   (AgentX header)

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | h.version (1) |  h.type (1)   |    h.flags    |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.sessionID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.transactionID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           h.packetID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.payload_length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  o.timeout    |                     <reserved>                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (o.id)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  n_subid      |  prefix       |       0       |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             subidentifier #1                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             subidentifier #n_subid                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (o.descr)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Octet String Length (L)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Octet L - 1  |  Octet L      |       Padding (as required)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   An agentx-Open-PDU contains the following fields:



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RFC 2257                        AgentX                      January 1998


      o.timeout

         The length of time, in seconds, that a master agent should
         allow to elapse after dispatching a message to a subagent
         before it regards the subagent as not responding.  This is a
         subagent-wide default value that may be overridden by values
         associated with specific registered MIB regions.  The default
         value of 0 indicates that no subagent-wide value is requested.

      o.id

         An Object Identifier that identifies the subagent.  Subagents
         that do not support such an notion may send a null Object
         Identifier.

      o.descr

         An Octet String containing a DisplayString describing the
         subagent.

6.2.2.  The agentx-Close-PDU

   An agentx-Close-PDU issued by either a subagent or the master agent
   terminates an AgentX session.

   (AgentX header)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | h.version (1) |  h.type (2)   |    h.flags    |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.sessionID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.transactionID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           h.packetID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.payload_length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  c.reason     |                     <reserved>                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   An agentx-Close-PDU contains the following field:








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RFC 2257                        AgentX                      January 1998


      c.reason

         An enumerated value that gives the reason that the master agent
         or subagent closed the AgentX session.  This field may take one
         of the following values:

            reasonOther(1)
               None of the following reasons

            reasonParseError(2)
               Too many AgentX parse errors from peer

            reasonProtocolError(3)
               Too many AgentX protocol errors from peer

            reasonTimeouts(4)
               Too many timeouts waiting for peer

            reasonShutdown(5)
               Sending entity is shutting down

            reasonByManager(6)
               Due to Set operation; this reason code can be used only
               by the master agent, in response to an SNMP management
               request.

6.2.3.  The agentx-Register-PDU

   An agentx-Register-PDU is generated by a subagent for each region of
   the MIB variable naming tree (within one or more contexts) that it
   wishes to support.

    (AgentX header)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | h.version (1) |  h.type (3)   |    h.flags    |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.sessionID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.transactionID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           h.packetID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.payload_length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







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RFC 2257                        AgentX                      January 1998


    (r.context) (OPTIONAL)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Padding (as required)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  r.timeout    |  r.priority   | r.range_subid |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (r.region)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  n_subid      |  prefix       |      0        |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #1                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...