rfc1443.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

                           the instances associated with an existing
                           conceptual row.

                      Whereas five of the six values (all except
                      'notReady') may be specified in a management
                      protocol set operation, only three values will be
                      returned in response to a management protocol





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          RFC 1443        Textual Conventions for SNMPv2      April 1993


                      retrieval operation: 'notReady', 'notInService' or
                      'active'.  That is, when queried, an existing
                      conceptual row has only three states: it is either
                      available for use by the managed device (the
                      status column has value 'active'); it is not
                      available for use by the managed device, though
                      the agent has sufficient information to make it so
                      (the status column has value 'notInService'); or,
                      it is not available for use by the managed device,
                      because the agent lacks sufficient information
                      (the status column has value 'notReady').

                                          NOTE WELL

                           This textual convention may be used for a MIB
                           table, irrespective of whether the values of
                           that table's conceptual rows are able to be
                           modified while it is active, or whether its
                           conceptual rows must be taken out of service
                           in order to be modified.  That is, it is the
                           responsibility of the DESCRIPTION clause of
                           the status column to specify whether the
                           status column must be 'notInService' in order
                           for the value of some other column of the
                           same conceptual row to be modified.

























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          RFC 1443        Textual Conventions for SNMPv2      April 1993


                      To summarize the effect of having a conceptual row
                      with a status column having a SYNTAX clause value
                      of RowStatus, consider the following state
                      diagram:


                                            STATE
                 +--------------+-----------+-------------+-------------
                 |      A       |     B     |      C      |      D
                 |              |status col.|status column|
                 |status column |    is     |      is     |status column
       ACTION    |does not exist|  notReady | notInService|  is active
   --------------+--------------+-----------+-------------+-------------
   set status    |noError    ->D|inconsist- |inconsistent-|inconsistent-
   column to     |       or     |   entValue|        Value|        Value
   createAndGo   |inconsistent- |           |             |
                 |         Value|           |             |
   --------------+--------------+-----------+-------------+-------------
   set status    |noError  see 1|inconsist- |inconsistent-|inconsistent-
   column to     |       or     |   entValue|        Value|        Value
   createAndWait |wrongValue    |           |             |
   --------------+--------------+-----------+-------------+-------------
   set status    |inconsistent- |inconsist- |noError      |noError
   column to     |         Value|   entValue|             |
   active        |              |           |             |
                 |              |     or    |             |
                 |              |           |             |
                 |              |see 2   ->D|          ->D|          ->D
   --------------+--------------+-----------+-------------+-------------
   set status    |inconsistent- |inconsist- |noError      |noError   ->C
   column to     |         Value|   entValue|             |
   notInService  |              |           |             |
                 |              |     or    |             |      or
                 |              |           |             |
                 |              |see 3   ->C|          ->C|wrongValue
   --------------+--------------+-----------+-------------+-------------
   set status    |noError       |noError    |noError      |noError
   column to     |              |           |             |
   destroy       |           ->A|        ->A|          ->A|          ->A
   --------------+--------------+-----------+-------------+-------------
   set any other |see 4         |noError    |noError      |noError
   column to some|              |           |             |
   value         |           ->A|      see 1|          ->C|          ->D
   --------------+--------------+-----------+-------------+-------------






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          RFC 1443        Textual Conventions for SNMPv2      April 1993


                      (1) goto B or C, depending on information
                      available to the agent.

                      (2) if other variable bindings included in the
                      same PDU, provide values for all columns which are
                      missing but required, then return noError and goto
                      D.

                      (3) if other variable bindings included in the
                      same PDU, provide values for all columns which are
                      missing but required, then return noError and goto
                      C.

                      (4) at the discretion of the agent, either noError
                      or inconsistentValue may be returned.

                      NOTE: Other processing of the set request may
                      result in a response other than noError being
                      returned, e.g., wrongValue, noCreation, etc.


                                   Conceptual Row Creation

                      There are four potential interactions when
                      creating a conceptual row: selecting an instance-
                      identifier which is not in use; creating the
                      conceptual row; initializing any objects for which
                      the agent does not supply a default; and, making
                      the conceptual row available for use by the
                      managed device.

                      Interaction 1: Selecting an Instance-Identifier

                      The algorithm used to select an instance-
                      identifier varies for each conceptual row.  In
                      some cases, the instance-identifier is
                      semantically significant, e.g., the destination
                      address of a route, and a management station
                      selects the instance-identifier according to the
                      semantics.

                      In other cases, the instance-identifier is used
                      solely to distinguish conceptual rows, and a
                      management station without specific knowledge of
                      the conceptual row might examine the instances





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          RFC 1443        Textual Conventions for SNMPv2      April 1993


                      present in order to determine an unused instance-
                      identifier.  (This approach may be used, but it is
                      often highly sub-optimal; however, it is also a
                      questionable practice for a naive management
                      station to attempt conceptual row creation.)

                      Alternately, the MIB module which defines the
                      conceptual row might provide one or more objects
                      which provide assistance in determining an unused
                      instance-identifier.  For example, if the
                      conceptual row is indexed by an integer-value,
                      then an object having an integer-valued SYNTAX
                      clause might be defined for such a purpose,
                      allowing a management station to issue a
                      management protocol retrieval operation.  In order
                      to avoid unnecessary collisions between competing
                      management stations, 'adjacent' retrievals of this
                      object should be different.

                      Finally, the management station could select a
                      pseudo-random number to use as the index.  In the
                      event that this index was already in use and an
                      inconsistentValue was returned in response to the
                      management protocol set operation, the management
                      station should simply select a new pseudo-random
                      number and retry the operation.

                      A MIB designer should choose between the two
                      latter algorithms based on the size of the table
                      (and therefore the efficiency of each algorithm).
                      For tables in which a large number of entries are
                      expected, it is recommended that a MIB object be
                      defined that returns an acceptable index for
                      creation.  For tables with small numbers of
                      entries, it is recommended that the latter
                      pseudo-random index mechanism be used.

                      Interaction 2: Creating the Conceptual Row

                      Once an unused instance-identifier has been
                      selected, the management station determines if it
                      wishes to create and activate the conceptual row
                      in one transaction or in a negotiated set of
                      interactions.






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          RFC 1443        Textual Conventions for SNMPv2      April 1993


                      Interaction 2a: Creating and Activating the
                      Conceptual Row

                      The management station must first determine the
                      column requirements, i.e., it must determine those
                      columns for which it must or must not provide
                      values.  Depending on the complexity of the table
                      and the management station's knowledge of the
                      agent's capabilities, this determination can be
                      made locally by the management station.
                      Alternately, the management station issues a
                      management protocol get operation to examine all
                      columns in the conceptual row that it wishes to
                      create.  In response, for each column, there are
                      three possible outcomes:

                           - a value is returned, indicating that some
                           other management station has already created
                           this conceptual row.  We return to
                           interaction 1.

                           - the exception 'noSuchInstance' is returned,
                           indicating that the agent implements the
                           object-type associated with this column, and
                           that this column in at least one conceptual
                           row would be accessible in the MIB view used
                           by the retrieval were it to exist. For those
                           columns to which the agent provides read-
                           create access, the 'noSuchInstance' exception
                           tells the management station that it should
                           supply a value for this column when the
                           conceptual row is to be created.

                           - the exception 'noSuchObject' is returned,
                           indicating that the agent does not implement
                           the object-type associated with this column
                           or that there is no conceptual row for which
                           this column would be accessible in the MIB
                           view used by the retrieval.  As such, the
                           management station can not issue any
                           management protocol set operations to create
                           an instance of this column.

                      Once the column requirements have been determined,
                      a management protocol set operation is accordingly





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          RFC 1443        Textual Conventions for SNMPv2      April 1993


                      issued.  This operation also sets the new instance
                      of the status column to 'createAndGo'.

                      When the agent processes the set operation, it
                      verifies that it has sufficient information to
                      make the conceptual row available for use by the
                      managed device.  The information available to the
                      agent is provided by two sources: the management
                      protocol set operation which creates the
                      conceptual row, and, implementation-specific
                      defaults supplied by the agent (note that an agent
                      must provide implementation-specific defaults for
                      at least those objects which it implements as
                      read-only).  If there is sufficient information
                      available, then the conceptual row is created, a
                      'noError' response is returned, the status column
                      is set to 'active', and no further interactions
                      are necessary (i.e., interactions 3 and 4 are
                      skipped).  If there is insufficient information,
                      then the conceptual row is not created, and the
                      set operation fails with an error of
                      'inconsistentValue'.  On this error, the
                      management station can issue a management protocol
                      retrieval operation to determine if this was
                      because it failed to specify a value for a
                      required column, or, because the selected instance
                      of the status column already existed.  In the
                      latter case, we return to interaction 1.  In the
                      former case, the management station can re-issue
                      the set operation with the additional information,
                      or begin interaction 2 again using 'createAndWait'
                      in order to negotiate creation of the conceptual
                      row.

















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                                          NOTE WELL

                           Regardless of the method used to determine
                           the column requirements, it is possible that
                           the management station might deem a column
                           necessary when, in fact, the agent will not
                           allow that particular columnar instance to be
                           created or written.  In this case, the
                           management protocol set operation will fail
                           with an error such as 'noCreation' or
                           'notWritable'.  In this case, the management
                           station decides whether it needs to be able
                           to set a value for that particular columnar
                           instance.  If not, the management station
                           re-issues the management protocol set
                           operation, but without setting a value for
                           that particular columnar instance; otherwise,
                           the management station aborts the row
                           creation algorithm.

                      Interaction 2b: Negotiating the Creation of the
                      Conceptual Row

                      The management station issues a management
                      protocol set operation which sets the desired
                      instance of the status column to 'createAndWait'.
                      If the agent is unwilling to process a request of
                      this sort, the set operation fails with an error
                      of 'wrongValue'.  (As a consequence, such an agent
                      must be prepared to accept a single management
                      protocol set operation, i.e., interaction 2a
                      above, containing all of the columns indicated by
                      its column requirements.) Otherwise, the
                      conceptual row is created, a 'noError' response is
                      returned, and the status column is immediately set
                      to either 'notInService' or 'notReady', depending
                      on whether it has sufficient information to make
                      the conceptual row available for use by the
                      managed device.  If there is sufficient
                      information available, then the status column is
                      set to 'notInService'; otherwise, if there is
                      insufficient information, then the status column
                      is set to 'notReady'.  Regardless, we proceed to
                      interaction 3.






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                      Interaction 3: Initializing non-defaulted Objects

                      The management station must now determine the
                      column requirements.  It issues a management
                      protocol get operation to examine all columns in
                      the created conceptual row.  In the response, for
                      each column, there are three possible outcomes:

                           - a value is returned, indicating that the
                           agent implements the object-type associated
                           with this column and had sufficient
                           information to provide a value.  For those
                           columns to which the agent provides read-
                           create access, a value return tells the
                           management station that it may issue
                           additional management protocol set
                           operations, if it desires, in order to change
                           the value associated with this column.

                           - the exception 'noSuchInstance' is returned,
                           indicating that the agent implements the
                           object-type associated with this column, and
                           that this column in at least one conceptual
                           row would be accessible in the MIB view used