rfc2741.txt

开发snmp的开发包有两个开放的SNMP开发库

            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 session ID that it will pass back
            in the corresponding agentx-Response-PDU.  From that point
            on, that same session ID 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 session ID, 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
            [13], nor is it the same as the SNMP Message's msgID (as
            described in section 6.2 of RFC 2572 [11]), nor can it be,
            since a master agent might receive SNMP requests with the
            same request-ids or msgIDs 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.

      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 SNMPv2c, 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. In
   SNMPv3 this notion of "context" is formalized (see section 3.3.1 in
   RFC 2571 [1].

   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.  (This does not mean there is a zero-
   length Octet String, it means there is no Octet String present.)  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.

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:

      o.timeout

            The length of time, in seconds, that a master agent should
            allow to elapse after dispatching a message on a session
            before it regards the subagent as not responding.  This is
            the default value for the session, and may be overridden by

            values associated with specific registered MIB regions.  The
            default value of 0 indicates that there is no session-wide
            default value.

      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:

           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                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

    (r.upper_bound)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             optional upper-bound sub-identifier               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   An agentx-Register-PDU contains the following fields:

      r.context

            An optional non-default context.

      r.timeout

            The length of time, in seconds, that a master agent should