path: root/doc/rfc/rfc1443.txt

          Network Working Group                                  J. Case
          Request for Comments: 1443                 SNMP Research, Inc.
                                                           K. McCloghrie
                                                      Hughes LAN Systems
                                                                 M. Rose
                                            Dover Beach Consulting, Inc.
                                                           S. Waldbusser
                                              Carnegie Mellon University
                                                              April 1993


                               Textual Conventions
                               for version 2 of the
                   Simple Network Management Protocol (SNMPv2)


          Status of this Memo

          This RFC specifes an IAB standards track protocol for the
          Internet community, and requests discussion and suggestions
          for improvements.  Please refer to the current edition of the
          "IAB Official Protocol Standards" for the standardization
          state and status of this protocol.  Distribution of this memo
          is unlimited.


          Table of Contents


          1 Introduction ..........................................    2
          1.1 A Note on Terminology ...............................    3
          2 Definitions ...........................................    4
          3 Mapping of the TEXTUAL-CONVENTION macro ...............   22
          3.1 Mapping of the DISPLAY-HINT clause ..................   22
          3.2 Mapping of the STATUS clause ........................   24
          3.3 Mapping of the DESCRIPTION clause ...................   24
          3.4 Mapping of the REFERENCE clause .....................   24
          3.5 Mapping of the SYNTAX clause ........................   24
          4 Acknowledgements ......................................   26
          5 References ............................................   30
          6 Security Considerations ...............................   31
          7 Authors' Addresses ....................................   31












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          1.  Introduction

          A network management system contains: several (potentially
          many) nodes, each with a processing entity, termed an agent,
          which has access to management instrumentation; at least one
          management station; and, a management protocol, used to convey
          management information between the agents and management
          stations.  Operations of the protocol are carried out under an
          administrative framework which defines both authentication and
          authorization policies.

          Network management stations execute management applications
          which monitor and control network elements.  Network elements
          are devices such as hosts, routers, terminal servers, etc.,
          which are monitored and controlled through access to their
          management information.

          Management information is viewed as a collection of managed
          objects, residing in a virtual information store, termed the
          Management Information Base (MIB).  Collections of related
          objects are defined in MIB modules.  These modules are written
          using a subset of OSI's Abstract Syntax Notation One (ASN.1)
          [1], termed the Structure of Management Information (SMI) [2].

          When designing a MIB module, it is often useful to new define
          types similar to those defined in the SMI.  In comparison to a
          type defined in the SMI, each of these new types has a
          different name, a similar syntax, but a more precise
          semantics.  These newly defined types are termed textual
          conventions, and are used for the convenience of humans
          reading the MIB module.  It is the purpose of this document to
          define the initial set of textual conventions available to all
          MIB modules.

          Objects defined using a textual convention are always encoded
          by means of the rules that define their primitive type.
          However, textual conventions often have special semantics
          associated with them.  As such, an ASN.1 macro, TEXTUAL-
          CONVENTION, is used to concisely convey the syntax and
          semantics of a textual convention.

          For all textual conventions defined in an information module,
          the name shall be unique and mnemonic, and shall not exceed 64
          characters in length.  All names used for the textual
          conventions defined in all "standard" information modules





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          shall be unique.


          1.1.  A Note on Terminology

          For the purpose of exposition, the original Internet-standard
          Network Management Framework, as described in RFCs 1155, 1157,
          and 1212, is termed the SNMP version 1 framework (SNMPv1).
          The current framework is termed the SNMP version 2 framework
          (SNMPv2).








































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          2.  Definitions

          SNMPv2-TC DEFINITIONS ::= BEGIN

          IMPORTS
              ObjectSyntax, Integer32, TimeTicks
                  FROM SNMPv2-SMI;


          -- definition of textual conventions

          TEXTUAL-CONVENTION MACRO ::=
          BEGIN
              TYPE NOTATION ::=
                            DisplayPart
                            "STATUS" Status
                            "DESCRIPTION" Text
                            ReferPart
                            "SYNTAX" type(Syntax)

              VALUE NOTATION ::=
                            value(VALUE Syntax)

              DisplayPart ::=
                            "DISPLAY-HINT" Text
                          | empty

              Status ::=
                            "current"
                          | "deprecated"
                          | "obsolete"

              ReferPart ::=
                            "REFERENCE" Text
                          | empty

              -- uses the NVT ASCII character set
              Text ::= """" string """"
          END











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          DisplayString ::= TEXTUAL-CONVENTION
              DISPLAY-HINT "255a"
              STATUS       current
              DESCRIPTION
                      "Represents textual information taken from the NVT
                      ASCII character set, as defined in pages 4, 10-11
                      of RFC 854.  Any object defined using this syntax
                      may not exceed 255 characters in length."
              SYNTAX       OCTET STRING (SIZE (0..255))


          PhysAddress ::= TEXTUAL-CONVENTION
              DISPLAY-HINT "1x:"
              STATUS       current
              DESCRIPTION
                      "Represents media- or physical-level addresses."
              SYNTAX       OCTET STRING


          MacAddress ::= TEXTUAL-CONVENTION
              DISPLAY-HINT "1x:"
              STATUS       current
              DESCRIPTION
                      "Represents an 802 MAC address represented in the
                      'canonical' order defined by IEEE 802.1a, i.e., as
                      if it were transmitted least significant bit
                      first, even though 802.5 (in contrast to other
                      802.x protocols) requires MAC addresses to be
                      transmitted most significant bit first."
              SYNTAX       OCTET STRING (SIZE (6))


          TruthValue ::= TEXTUAL-CONVENTION
              STATUS       current
              DESCRIPTION
                      "Represents a boolean value."
              SYNTAX       INTEGER { true(1), false(2) }













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          TestAndIncr ::= TEXTUAL-CONVENTION
              STATUS       current
              DESCRIPTION
                      "Represents integer-valued information used for
                      atomic operations.  When the management protocol
                      is used to specify that an object instance having
                      this syntax is to be modified, the new value
                      supplied via the management protocol must
                      precisely match the value presently held by the
                      instance.  If not, the management protocol set
                      operation fails with an error of
                      'inconsistentValue'.  Otherwise, if the current
                      value is the maximum value of 2^31-1 (2147483647
                      decimal), then the value held by the instance is
                      wrapped to zero; otherwise, the value held by the
                      instance is incremented by one.  (Note that
                      regardless of whether the management protocol set
                      operation succeeds, the variable-binding in the
                      request and response PDUs are identical.)

                      The value of the ACCESS clause for objects having
                      this syntax is either 'read-write' or 'read-
                      create'.  When an instance of a columnar object
                      having this syntax is created, any value may be
                      supplied via the management protocol."
              SYNTAX       INTEGER (0..2147483647)
























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          AutonomousType ::= TEXTUAL-CONVENTION
              STATUS       current
              DESCRIPTION
                      "Represents an independently extensible type
                      identification value.  It may, for example,
                      indicate a particular sub-tree with further MIB
                      definitions, or define a particular type of
                      protocol or hardware."
              SYNTAX       OBJECT IDENTIFIER


          InstancePointer ::= TEXTUAL-CONVENTION
              STATUS       current
              DESCRIPTION
                      "A pointer to a specific instance of a conceptual
                      row of a MIB table in the managed device.  By
                      convention, it is the name of the particular
                      instance of the first columnar object in the
                      conceptual row."
              SYNTAX       OBJECT IDENTIFIER






























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          RowStatus ::= TEXTUAL-CONVENTION
              STATUS       current
              DESCRIPTION
                      "The RowStatus textual convention is used to
                      manage the creation and deletion of conceptual
                      rows, and is used as the value of the SYNTAX
                      clause for the status column of a conceptual row
                      (as described in Section 7.7.1 of [2].)

                      The status column has six defined values:

                           - 'active', which indicates that the
                           conceptual row is available for use by the
                           managed device;

                           - 'notInService', which indicates that the
                           conceptual row exists in the agent, but is
                           unavailable for use by the managed device
                           (see NOTE below);

                           - 'notReady', which indicates that the
                           conceptual row exists in the agent, but is
                           missing information necessary in order to be
                           available for use by the managed device;

                           - 'createAndGo', which is supplied by a
                           management station wishing to create a new
                           instance of a conceptual row and to have it
                           available for use by the managed device;

                           - 'createAndWait', which is supplied by a
                           management station wishing to create a new
                           instance of a conceptual row but not to have
                           it available for use by the managed device;
                           and,

                           - 'destroy', which is supplied by a
                           management station wishing to delete all of
                           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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                      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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                      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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                      (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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                      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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                      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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                      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
                           by the retrieval were it to exist. However,
                           the agent does not have sufficient
                           information to provide a value, and until a
                           value is provided, the conceptual row may not
                           be made available for use by the managed
                           device.  For those columns to which the agent
                           provides read-create access, the
                           'noSuchInstance' exception tells the
                           management station that it must issue
                           additional management protocol set
                           operations, in order to provide a value
                           associated with this column.

                           - 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





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                           an instance of this column.

                      If the value associated with the status column is
                      'notReady', then the management station must first
                      deal with all 'noSuchInstance' columns, if any.
                      Having done so, the value of the status column
                      becomes 'notInService', and we proceed to
                      interaction 4.

                      Interaction 4: Making the Conceptual Row Available

                      Once the management station is satisfied with the
                      values associated with the columns of the
                      conceptual row, it issues a management protocol
                      set operation to set the status column to
                      'active'.  If the agent has sufficient information
                      to make the conceptual row available for use by
                      the managed device, the management protocol set
                      operation succeeds (a 'noError' response is
                      returned).  Otherwise, the management protocol set
                      operation fails with an error of
                      'inconsistentValue'.

                                          NOTE WELL

                           A conceptual row having a status column with
                           value 'notInService' or 'notReady' is
                           unavailable to the managed device.  As such,
                           it is possible for the managed device to
                           create its own instances during the time
                           between the management protocol set operation
                           which sets the status column to
                           'createAndWait' and the management protocol
                           set operation which sets the status column to
                           'active'.  In this case, when the management
                           protocol set operation is issued to set the
                           status column to 'active', the values held in
                           the agent supersede those used by the managed
                           device.

                      If the management station is prevented from
                      setting the status column to 'active' (e.g., due
                      to management station or network failure) the
                      conceptual row will be left in the 'notInService'
                      or 'notReady' state, consuming resources





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                      indefinitely.  The agent must detect conceptual
                      rows that have been in either state for an
                      abnormally long period of time and remove them.
                      This period of time should be long enough to allow
                      for human response time (including 'think time')
                      between the creation of the conceptual row and the
                      setting of the status to 'active'.  It is
                      suggested that this period be approximately 5
                      minutes in length.


                                  Conceptual Row Suspension

                      When a conceptual row is 'active', the management
                      station may issue a management protocol set
                      operation which sets the instance of the status
                      column to 'notInService'.  If the agent is
                      unwilling to do so, the set operation fails with
                      an error of 'wrongValue'.  Otherwise, the
                      conceptual row is taken out of service, and a
                      'noError' response is returned.  It is the
                      responsibility of the the DESCRIPTION clause of
                      the status column to indicate under what
                      circumstances the status column should be taken
                      out of service (e.g., in order for the value of
                      some other column of the same conceptual row to be
                      modified).


                                   Conceptual Row Deletion

                      For deletion of conceptual rows, a management
                      protocol set operation is issued which sets the
                      instance of the status column to 'destroy'.  This
                      request may be made regardless of the current
                      value of the status column (e.g., it is possible
                      to delete conceptual rows which are either
                      'notReady', 'notInService' or 'active'.) If the
                      operation succeeds, then all instances associated
                      with the conceptual row are immediately removed."










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              SYNTAX       INTEGER {
                               -- the following two values are states:
                               -- these values may be read or written
                               active(1),
                               notInService(2),

                               -- the following value is a state:
                               -- this value may be read, but not written
                               notReady(3),

                               -- the following three values are
                               -- actions: these values may be written,
                               --   but are never read
                               createAndGo(4),
                               createAndWait(5),
                               destroy(6)
                           }

































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          RFC 1443        Textual Conventions for SNMPv2      April 1993


          TimeStamp ::= TEXTUAL-CONVENTION
              STATUS       current
              DESCRIPTION
                      "The value of MIB-II's sysUpTime object at which a
                      specific occurrence happened.  The specific
                      occurrence must be defined in the description of
                      any object defined using this type."
              SYNTAX       TimeTicks


          TimeInterval ::= TEXTUAL-CONVENTION
              STATUS       current
              DESCRIPTION
                      "A period of time, measured in units of 0.01
                      seconds."
              SYNTAX       INTEGER (0..2147483647)


































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          DateAndTime ::= TEXTUAL-CONVENTION
              DISPLAY-HINT "2d-1d-1d,1d:1d:1d.1d,1a1d:1d"
              STATUS       current
              DESCRIPTION
                      "A date-time specification.

                      field  octets  contents                  range
                      -----  ------  --------                  -----
                        1      1-2   year                      0..65536
                        2       3    month                     1..12
                        3       4    day                       1..31
                        4       5    hour                      0..23
                        5       6    minutes                   0..59
                        6       7    seconds                   0..60
                                     (use 60 for leap-second)
                        7       8    deci-seconds              0..9
                        8       9    direction from UTC        '+' / '-'
                        9      10    hours from UTC            0..11
                       10      11    minutes from UTC          0..59

                      For example, Tuesday May 26, 1992 at 1:30:15 PM
                      EDT would be displayed as:

                                  1992-5-26,13:30:15.0,-4:0

                      Note that if only local time is known, then
                      timezone information (fields 8-10) is not
                      present."
              SYNTAX       OCTET STRING (SIZE (8 | 11))


          END


















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          RFC 1443        Textual Conventions for SNMPv2      April 1993


          3.  Mapping of the TEXTUAL-CONVENTION macro

          The TEXTUAL-CONVENTION macro is used to convey the syntax and
          semantics associated with a textual convention.  It should be
          noted that the expansion of the TEXTUAL-CONVENTION macro is
          something which conceptually happens during implementation and
          not during run-time.

          For all descriptors appearing in an information module, the
          descriptor shall be unique and mnemonic, and shall not exceed
          64 characters in length.  Further, the hyphen is not allowed
          as a character in the name of any textual convention.


          3.1.  Mapping of the DISPLAY-HINT clause

          The DISPLAY-HINT clause, which need not be present, gives a
          hint as to how the value of an instance of an object with the
          syntax defined using this textual convention might be
          displayed.  The DISPLAY-HINT clause may only be present when
          the syntax has an underlying primitive type of INTEGER or
          OCTET STRING.

          When the syntax has an underlying primitive type of INTEGER,
          the hint consists of a single character suggesting a display
          format, either: 'x' for hexadecimal, 'd' for decimal, or 'o'
          for octal, or 'b' for binary.

          When the syntax has an underlying primitive type of OCTET
          STRING, the hint consists of one or more octet-format
          specifications.  Each specification consists of five parts,
          with each part using and removing zero or more of the next
          octets from the value and producing the next zero or more
          characters to be displayed.  The octets within the value are
          processed in order of significance, most significant first.

          The five parts of a octet-format specification are:

          (1)  the (optional) repeat indicator; if present, this part is
               a '*', and indicates that the current octet of the value
               is to be used as the repeat count.  The repeat count is
               an unsigned integer (which may be zero) which specifies
               how many times the remainder of this octet-format
               specification should be successively applied.  If the
               repeat indicator is not present, the repeat count is one.





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          RFC 1443        Textual Conventions for SNMPv2      April 1993


          (2)  the octet length: one or more decimal digits specifying
               the number of octets of the value to be used and
               formatted by this octet-specification.  Note that the
               octet length can be zero.  If less than this number of
               octets remain in the value, then the lesser number of
               octets are used.

          (3)  the display format, either: 'x' for hexadecimal, 'd' for
               decimal, 'o' for octal, or 'a' for ascii.  If the octet
               length part is greater than one, and the display format
               part refers to a numeric format, then network-byte
               ordering (big-endian encoding) is used interpreting the
               octets in the value.

          (4)  the (optional) display separator character; if present,
               this part is a single character which is produced for
               display after each application of this octet-
               specification; however, this character is not produced
               for display if it would be immediately followed by the
               display of the repeat terminator character for this
               octet-specification.  This character can be any character
               other than a decimal digit and a '*'.

          (5)  the (optional) repeat terminator character, which can be
               present only if the display separator character is
               present and this octet-specification begins with a repeat
               indicator; if present, this part is a single character
               which is produced after all the zero or more repeated
               applications (as given by the repeat count) of this
               octet-specification.  This character can be any character
               other than a decimal digit and a '*'.

          Output of a display separator character or a repeat terminator
          character is suppressed if it would occur as the last
          character of the display.

          If the octets of the value are exhausted before all the
          octet-format specification have been used, then the excess
          specifications are ignored.  If additional octets remain in
          the value after interpreting all the octet-format
          specifications, then the last octet-format specification is
          re-interpreted to process the additional octets, until no
          octets remain in the value.







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          RFC 1443        Textual Conventions for SNMPv2      April 1993


          3.2.  Mapping of the STATUS clause

          The STATUS clause, which must be present, indicates whether
          this definition is current or historic.

          The values "current", and "obsolete" are self-explanatory.
          The "deprecated" value indicates that the textual convention
          is obsolete, but that an implementor may wish to support that
          object to foster interoperability with older implementations.


          3.3.  Mapping of the DESCRIPTION clause

          The DESCRIPTION clause, which must be present, contains a
          textual definition of the textual convention, which provides
          all semantic definitions necessary for implementation, and
          should embody any information which would otherwise be
          communicated in any ASN.1 commentary annotations associated
          with the object.

          Note that, in order to conform to the ASN.1 syntax, the entire
          value of this clause must be enclosed in double quotation
          marks, and therefore cannot itself contain double quotation
          marks, although the value may be multi-line.


          3.4.  Mapping of the REFERENCE clause

          The REFERENCE clause, which need not be present, contains a
          textual cross-reference to a related item defined in some
          other published work.


          3.5.  Mapping of the SYNTAX clause

          The SYNTAX clause, which must be present, defines abstract
          data structure corresponding to the textual convention.  The
          data structure must be one of the alternatives defined in the
          ObjectSyntax CHOICE [2].

          Full ASN.1 sub-typing is allowed, as appropriate to the
          underingly ASN.1 type, primarily as an aid to implementors in
          understanding the meaning of the textual convention.  Of
          course, sub-typing is not allowed for textual conventions
          derived from either the Counter32 or Counter64 types, but is





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          RFC 1443        Textual Conventions for SNMPv2      April 1993


          allowed for textual conventions derived from the Gauge32 type.

















































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          RFC 1443        Textual Conventions for SNMPv2      April 1993


          4.  Acknowledgements

          PhysAddress (and textual conventions) originated in RFC 1213.

          MacAddress originated in RFCs 1230 and 1231.

          TruthValue originated in RFC 1253.

          AutonomousType and InstancePointer originated in RFC 1316.

          RowStatus originated in RFC 1271.

          A special thanks to Bancroft Scott of Open Systems Solutions,
          Inc., for helping in the definition of the TEXTUAL-CONVENTIONS
          macro.

          Finally, the comments of the SNMP version 2 working group are
          gratefully acknowledged:

               Beth Adams, Network Management Forum
               Steve Alexander, INTERACTIVE Systems Corporation
               David Arneson, Cabletron Systems
               Toshiya Asaba
               Fred Baker, ACC
               Jim Barnes, Xylogics, Inc.
               Brian Bataille
               Andy Bierman, SynOptics Communications, Inc.
               Uri Blumenthal, IBM Corporation
               Fred Bohle, Interlink
               Jack Brown
               Theodore Brunner, Bellcore
               Stephen F. Bush, GE Information Services
               Jeffrey D. Case, University of Tennessee, Knoxville
               John Chang, IBM Corporation
               Szusin Chen, Sun Microsystems
               Robert Ching
               Chris Chiotasso, Ungermann-Bass
               Bobby A. Clay, NASA/Boeing
               John Cooke, Chipcom
               Tracy Cox, Bellcore
               Juan Cruz, Datability, Inc.
               David Cullerot, Cabletron Systems
               Cathy Cunningham, Microcom
               James R. (Chuck) Davin, Bellcore
               Michael Davis, Clearpoint





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          RFC 1443        Textual Conventions for SNMPv2      April 1993


               Mike Davison, FiberCom
               Cynthia DellaTorre, MITRE
               Taso N. Devetzis, Bellcore
               Manual Diaz, DAVID Systems, Inc.
               Jon Dreyer, Sun Microsystems
               David Engel, Optical Data Systems
               Mike Erlinger, Lexcel
               Roger Fajman, NIH
               Daniel Fauvarque, Sun Microsystems
               Karen Frisa, CMU
               Shari Galitzer, MITRE
               Shawn Gallagher, Digital Equipment Corporation
               Richard Graveman, Bellcore
               Maria Greene, Xyplex, Inc.
               Michel Guittet, Apple
               Robert Gutierrez, NASA
               Bill Hagerty, Cabletron Systems
               Gary W. Haney, Martin Marietta Energy Systems
               Patrick Hanil, Nokia Telecommunications
               Matt Hecht, SNMP Research, Inc.
               Edward A. Heiner, Jr., Synernetics Inc.
               Susan E. Hicks, Martin Marietta Energy Systems
               Geral Holzhauer, Apple
               John Hopprich, DAVID Systems, Inc.
               Jeff Hughes, Hewlett-Packard
               Robin Iddon, Axon Networks, Inc.
               David Itusak
               Kevin M. Jackson, Concord Communications, Inc.
               Ole J. Jacobsen, Interop Company
               Ronald Jacoby, Silicon Graphics, Inc.
               Satish Joshi, SynOptics Communications, Inc.
               Frank Kastenholz, FTP Software
               Mark Kepke, Hewlett-Packard
               Ken Key, SNMP Research, Inc.
               Zbiginew Kielczewski, Eicon
               Jongyeoi Kim
               Andrew Knutsen, The Santa Cruz Operation
               Michael L. Kornegay, VisiSoft
               Deirdre C. Kostik, Bellcore
               Cheryl Krupczak, Georgia Tech
               Mark S. Lewis, Telebit
               David Lin
               David Lindemulder, AT&T/NCR
               Ben Lisowski, Sprint
               David Liu, Bell-Northern Research





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          RFC 1443        Textual Conventions for SNMPv2      April 1993


               John Lunny, The Wollongong Group
               Robert C. Lushbaugh Martin, Marietta Energy Systems
               Michael Luufer, BBN
               Carl Madison, Star-Tek, Inc.
               Keith McCloghrie, Hughes LAN Systems
               Evan McGinnis, 3Com Corporation
               Bill McKenzie, IBM Corporation
               Donna McMaster, SynOptics Communications, Inc.
               John Medicke, IBM Corporation
               Doug Miller, Telebit
               Dave Minnich, FiberCom
               Mohammad Mirhakkak, MITRE
               Rohit Mital, Protools
               George Mouradian, AT&T Bell Labs
               Patrick Mullaney, Cabletron Systems
               Dan Myers, 3Com Corporation
               Rina Nathaniel, Rad Network Devices Ltd.
               Hien V. Nguyen, Sprint
               Mo Nikain
               Tom Nisbet
               William B. Norton, MERIT
               Steve Onishi, Wellfleet Communications, Inc.
               David T. Perkins, SynOptics Communications, Inc.
               Carl Powell, BBN
               Ilan Raab, SynOptics Communications, Inc.
               Richard Ramons, AT&T
               Venkat D. Rangan, Metric Network Systems, Inc.
               Louise Reingold, Sprint
               Sam Roberts, Farallon Computing, Inc.
               Kary Robertson, Concord Communications, Inc.
               Dan Romascanu, Lannet Data Communications Ltd.
               Marshall T. Rose, Dover Beach Consulting, Inc.
               Shawn A. Routhier, Epilogue Technology Corporation
               Chris Rozman
               Asaf Rubissa, Fibronics
               Jon Saperia, Digital Equipment Corporation
               Michael Sapich
               Mike Scanlon, Interlan
               Sam Schaen, MITRE
               John Seligson, Ultra Network Technologies
               Paul A. Serice, Corporation for Open Systems
               Chris Shaw, Banyan Systems
               Timon Sloane
               Robert Snyder, Cisco Systems
               Joo Young Song





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          RFC 1443        Textual Conventions for SNMPv2      April 1993


               Roy Spitier, Sprint
               Einar Stefferud, Network Management Associates
               John Stephens, Cayman Systems, Inc.
               Robert L. Stewart, Xyplex, Inc. (chair)
               Kaj Tesink, Bellcore
               Dean Throop, Data General
               Ahmet Tuncay, France Telecom-CNET
               Maurice Turcotte, Racal Datacom
               Warren Vik, INTERACTIVE Systems Corporation
               Yannis Viniotis
               Steven L. Waldbusser, Carnegie Mellon Universitty
               Timothy M. Walden, ACC
               Alice Wang, Sun Microsystems
               James Watt, Newbridge
               Luanne Waul, Timeplex
               Donald E. Westlake III, Digital Equipment Corporation
               Gerry White
               Bert Wijnen, IBM Corporation
               Peter Wilson, 3Com Corporation
               Steven Wong, Digital Equipment Corporation
               Randy Worzella, IBM Corporation
               Daniel Woycke, MITRE
               Honda Wu
               Jeff Yarnell, Protools
               Chris Young, Cabletron
               Kiho Yum, 3Com Corporation
























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          RFC 1443        Textual Conventions for SNMPv2      April 1993


          5.  References

          [1]  Information processing systems - Open Systems
               Interconnection - Specification of Abstract Syntax
               Notation One (ASN.1), International Organization for
               Standardization.  International Standard 8824, (December,
               1987).

          [2]  Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Structure of Management Information for version 2 of the
               Simple Network Management Protocol (SNMPv2)", RFC 1442,
               SNMP Research, Inc., Hughes LAN Systems, Dover Beach
               Consulting, Inc., Carnegie Mellon University, April 1993.





































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          RFC 1443        Textual Conventions for SNMPv2      April 1993


          6.  Security Considerations

          Security issues are not discussed in this memo.


          7.  Authors' Addresses

               Jeffrey D. Case
               SNMP Research, Inc.
               3001 Kimberlin Heights Rd.
               Knoxville, TN  37920-9716
               US

               Phone: +1 615 573 1434
               Email: case@snmp.com


               Keith McCloghrie
               Hughes LAN Systems
               1225 Charleston Road
               Mountain View, CA  94043
               US

               Phone: +1 415 966 7934
               Email: kzm@hls.com


               Marshall T. Rose
               Dover Beach Consulting, Inc.
               420 Whisman Court
               Mountain View, CA  94043-2186
               US

               Phone: +1 415 968 1052
               Email: mrose@dbc.mtview.ca.us

               Steven Waldbusser
               Carnegie Mellon University
               4910 Forbes Ave
               Pittsburgh, PA  15213
               US

               Phone: +1 412 268 6628
               Email: waldbusser@cmu.edu






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