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rfc:rfc2579

Network Working Group Editors of this version: Request for Comments: 2579 K. McCloghrie STD: 58 Cisco Systems Obsoletes: 1903 D. Perkins Category: Standards Track SNMPinfo

                                                      J. Schoenwaelder
                                                       TU Braunschweig
                                    Authors of previous version:
                                                               J. Case
                                                         SNMP Research
                                                         K. McCloghrie
                                                         Cisco Systems
                                                               M. Rose
                                                First Virtual Holdings
                                                         S. Waldbusser
                                        International Network Services
                                                            April 1999
                   Textual Conventions for SMIv2

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1999).  All Rights Reserved.

Table of Contents

 1 Introduction ..................................................2
 1.1 A Note on Terminology .......................................2
 2 Definitions ...................................................2
 3 Mapping of the TEXTUAL-CONVENTION macro ......................20
 3.1 Mapping of the DISPLAY-HINT clause .........................21
 3.2 Mapping of the STATUS clause ...............................22
 3.3 Mapping of the DESCRIPTION clause ..........................23
 3.4 Mapping of the REFERENCE clause ............................23
 3.5 Mapping of the SYNTAX clause ...............................23
 4 Sub-typing of Textual Conventions ............................23
 5 Revising a Textual Convention Definition .....................23

McCloghrie, et al. Standards Track [Page 1]

RFC 2579 Textual Conventions for SMIv2 April 1999

 6 Security Considerations ......................................24
 7 Editors' Addresses ...........................................25
 8 References ...................................................25
 9 Full Copyright Statement .....................................26

1. Introduction

 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 an adapted subset of
 OSI's Abstract Syntax Notation One, ASN.1 (1988) [1], termed the
 Structure of Management Information (SMI) [2].
 When designing a MIB module, it is often useful to define new 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.

1.1. A Note on Terminology

 For the purpose of exposition, the original Structure of Management
 Information, as described in RFCs 1155 (STD 16), 1212 (STD 16), and
 RFC 1215, is termed the SMI version 1 (SMIv1).  The current version
 of the Structure of Management Information is termed SMI version 2
 (SMIv2).

2. Definitions

SNMPv2-TC DEFINITIONS ::= BEGIN

IMPORTS

  TimeTicks         FROM SNMPv2-SMI;

– definition of textual conventions

TEXTUAL-CONVENTION MACRO ::=

McCloghrie, et al. Standards Track [Page 2]

RFC 2579 Textual Conventions for SMIv2 April 1999

BEGIN

  TYPE NOTATION ::=
                DisplayPart
                "STATUS" Status
                "DESCRIPTION" Text
                ReferPart
                "SYNTAX" Syntax
  VALUE NOTATION ::=
                 value(VALUE Syntax)      -- adapted ASN.1
  DisplayPart ::=
                "DISPLAY-HINT" Text
              | empty
  Status ::=
                "current"
              | "deprecated"
              | "obsolete"
  ReferPart ::=
                "REFERENCE" Text
              | empty
  1. - a character string as defined in [2]

Text ::= value(IA5String)

  Syntax ::=   -- Must be one of the following:
                     -- a base type (or its refinement), or
                     -- a BITS pseudo-type
                type
              | "BITS" "{" NamedBits "}"
  NamedBits ::= NamedBit
              | NamedBits "," NamedBit
  NamedBit ::=  identifier "(" number ")" -- number is nonnegative

END

DisplayString ::= TEXTUAL-CONVENTION

  DISPLAY-HINT "255a"
  STATUS       current
  DESCRIPTION
          "Represents textual information taken from the NVT ASCII

McCloghrie, et al. Standards Track [Page 3]

RFC 2579 Textual Conventions for SMIv2 April 1999

          character set, as defined in pages 4, 10-11 of RFC 854.
          To summarize RFC 854, the NVT ASCII repertoire specifies:
  1. the use of character codes 0-127 (decimal)
  1. the graphics characters (32-126) are interpreted as

US ASCII

  1. NUL, LF, CR, BEL, BS, HT, VT and FF have the special

meanings specified in RFC 854

  1. the other 25 codes have no standard interpretation
  1. the sequence 'CR LF' means newline
  1. the sequence 'CR NUL' means carriage-return
  1. an 'LF' not preceded by a 'CR' means moving to the

same column on the next line.

  1. the sequence 'CR x' for any x other than LF or NUL is

illegal. (Note that this also means that a string may

              end with either 'CR LF' or 'CR NUL', but not with CR.)
          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))

McCloghrie, et al. Standards Track [Page 4]

RFC 2579 Textual Conventions for SMIv2 April 1999

TruthValue ::= TEXTUAL-CONVENTION

  STATUS       current
  DESCRIPTION
          "Represents a boolean value."
  SYNTAX       INTEGER { true(1), false(2) }

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.
          When the network management portion of the system is re-
          initialized, the value of every object instance having this
          syntax must either be incremented from its value prior to
          the re-initialization, or (if the value prior to the re-
          initialization is unknown) be set to a pseudo-randomly
          generated value."
  SYNTAX       INTEGER (0..2147483647)

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       obsolete

McCloghrie, et al. Standards Track [Page 5]

RFC 2579 Textual Conventions for SMIv2 April 1999

  DESCRIPTION
          "A pointer to either a specific instance of a MIB object or
          a conceptual row of a MIB table in the managed device.  In
          the latter case, by convention, it is the name of the
          particular instance of the first accessible columnar object
          in the conceptual row.
          The two uses of this textual convention are replaced by
          VariablePointer and RowPointer, respectively."
  SYNTAX       OBJECT IDENTIFIER

VariablePointer ::= TEXTUAL-CONVENTION

  STATUS       current
  DESCRIPTION
          "A pointer to a specific object instance.  For example,
          sysContact.0 or ifInOctets.3."
  SYNTAX       OBJECT IDENTIFIER

RowPointer ::= TEXTUAL-CONVENTION

  STATUS       current
  DESCRIPTION
          "Represents a pointer to a conceptual row.  The value is the
          name of the instance of the first accessible columnar object
          in the conceptual row.
          For example, ifIndex.3 would point to the 3rd row in the
          ifTable (note that if ifIndex were not-accessible, then
          ifDescr.3 would be used instead)."
  SYNTAX       OBJECT IDENTIFIER

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].)

McCloghrie, et al. Standards Track [Page 6]

RFC 2579 Textual Conventions for SMIv2 April 1999

          The status column has six defined values:
  1. `active', which indicates that the conceptual row is

available for use by the managed device;

  1. `notInService', which indicates that the conceptual

row exists in the agent, but is unavailable for use by

               the managed device (see NOTE below); 'notInService' has
               no implication regarding the internal consistency of
               the row, availability of resources, or consistency with
               the current state of the managed device;
  1. `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 (i.e., one or more required columns in
               the conceptual row have not been instanciated);
  1. `createAndGo', which is supplied by a management

station wishing to create a new instance of a

               conceptual row and to have its status automatically set
               to active, making it available for use by the managed
               device;
  1. `createAndWait', which is supplied by a management

station wishing to create a new instance of a

               conceptual row (but not make it available for use by
               the managed device); and,
  1. `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 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 attempt to make it
          so (the status column has value `notInService'); or, it is
          not available for use by the managed device, and an attempt
          to make it so would fail because the agent has insufficient
          information (the state column has value `notReady').

McCloghrie, et al. Standards Track [Page 7]

RFC 2579 Textual Conventions for SMIv2 April 1999

                                   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
               not be `active' in order for the value of some other
               column of the same conceptual row to be modified.  If
               such a specification is made, affected columns may be
               changed by an SNMP set PDU if the RowStatus would not
               be equal to `active' either immediately before or after
               processing the PDU.  In other words, if the PDU also
               contained a varbind that would change the RowStatus
               value, the column in question may be changed if the
               RowStatus was not equal to `active' as the PDU was
               received, or if the varbind sets the status to a value
               other than 'active'.
          Also note that whenever any elements of a row exist, the
          RowStatus column must also exist.

McCloghrie, et al. Standards Track [Page 8]

RFC 2579 Textual Conventions for SMIv2 April 1999

          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|see 8     ->D|          ->D

————–+————–+———–+————-+————- set status |inconsistent- |inconsist- |noError |noError →C column to | Value| entValue| | notInService | | | |

            |              |     or    |             |      or
            |              |           |             |
            |              |see 3   ->C|          ->C|see 6

————–+————–+———–+————-+————- set status |noError |noError |noError |noError →A column to | | | | or destroy | →A| →A| →A|see 7 ————–+————–+———–+————-+————- set any other |see 4 |noError |noError |see 5 column to some| | | | value | | see 1| →C| →D ————–+————–+———–+————-+————-

          (1) goto B or C, depending on information available to the
          agent.
          (2) if other variable bindings included in the same PDU,

McCloghrie, et al. Standards Track [Page 9]

RFC 2579 Textual Conventions for SMIv2 April 1999

          provide values for all columns which are missing but
          required, and all columns have acceptable values, then
          return noError and goto D.
          (3) if other variable bindings included in the same PDU,
          provide legal values for all columns which are missing but
          required, then return noError and goto C.
          (4) at the discretion of the agent, the return value may be
          either:
               inconsistentName:  because the agent does not choose to
               create such an instance when the corresponding
               RowStatus instance does not exist, or
               inconsistentValue:  if the supplied value is
               inconsistent with the state of some other MIB object's
               value, or
               noError: because the agent chooses to create the
               instance.
          If noError is returned, then the instance of the status
          column must also be created, and the new state is B or C,
          depending on the information available to the agent.  If
          inconsistentName or inconsistentValue is returned, the row
          remains in state A.
          (5) depending on the MIB definition for the column/table,
          either noError or inconsistentValue may be returned.
          (6) the return value can indicate one of the following
          errors:
               wrongValue: because the agent does not support
               notInService (e.g., an agent which does not support
               createAndWait), or
               inconsistentValue: because the agent is unable to take
               the row out of service at this time, perhaps because it
               is in use and cannot be de-activated.
          (7) the return value can indicate the following error:
               inconsistentValue: because the agent is unable to
               remove the row at this time, perhaps because it is in
               use and cannot be de-activated.

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RFC 2579 Textual Conventions for SMIv2 April 1999

          (8) the transition to D can fail, e.g., if the values of the
          conceptual row are inconsistent, then the error code would
          be inconsistentValue.
          NOTE: Other processing of (this and other varbinds 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 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

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RFC 2579 Textual Conventions for SMIv2 April 1999

          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.
          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:
  1. a value is returned, indicating that some other

management station has already created this conceptual

               row.  We return to interaction 1.
  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.

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RFC 2579 Textual Conventions for SMIv2 April 1999

  1. 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 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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RFC 2579 Textual Conventions for SMIv2 April 1999

                                   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 (attempt 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.
          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:

McCloghrie, et al. Standards Track [Page 14]

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  1. 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 (and for which the agent allows their values to
               be changed after their creation), 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.
  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. 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.
  1. 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.
          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.

McCloghrie, et al. Standards Track [Page 15]

RFC 2579 Textual Conventions for SMIv2 April 1999

          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
          indefinitely.  The agent must detect conceptual rows that
          have been in either state for an abnormally long period of
          time and remove them.  It is the responsibility of the
          DESCRIPTION clause of the status column to indicate what an
          abnormally long period of time would be.  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'.
          In the absence of such information in the DESCRIPTION
          clause, it is suggested that this period be approximately 5
          minutes in length.  This removal action applies not only to
          newly-created rows, but also to previously active rows which
          are set to, and left in, the notInService state for a
          prolonged period exceeding that which is considered normal
          for such a conceptual row.

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RFC 2579 Textual Conventions for SMIv2 April 1999

                           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' or `inconsistentValue'.  Otherwise,
          the conceptual row is taken out of service, and a `noError'
          response is returned.  It is the responsibility of 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."
  SYNTAX       INTEGER {
                   -- the following two values are states:
                   -- these values may be read or written
                   active(1),
                   notInService(2),
  1. - the following value is a state:
  2. - this value may be read, but not written

notReady(3),

  1. - the following three values are
  2. - actions: these values may be written,
  3. - but are never read

createAndGo(4),

                   createAndWait(5),
                   destroy(6)
               }

TimeStamp ::= TEXTUAL-CONVENTION

  STATUS       current
  DESCRIPTION
          "The value of the sysUpTime object at which a specific
          occurrence happened.  The specific occurrence must be

McCloghrie, et al. Standards Track [Page 17]

RFC 2579 Textual Conventions for SMIv2 April 1999

          defined in the description of any object defined using this
          type.
          If sysUpTime is reset to zero as a result of a re-
          initialization of the network management (sub)system, then
          the values of all TimeStamp objects are also reset.
          However, after approximately 497 days without a re-
          initialization, the sysUpTime object will reach 2^^32-1 and
          then increment around to zero; in this case, existing values
          of TimeStamp objects do not change.  This can lead to
          ambiguities in the value of TimeStamp objects."
  SYNTAX       TimeTicks

TimeInterval ::= TEXTUAL-CONVENTION

  STATUS       current
  DESCRIPTION
          "A period of time, measured in units of 0.01 seconds."
  SYNTAX       INTEGER (0..2147483647)

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..13
           10      11    minutes from UTC          0..59
  • Notes:
  1. the value of year is in network-byte order
  2. daylight saving time in New Zealand is +13
          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

McCloghrie, et al. Standards Track [Page 18]

RFC 2579 Textual Conventions for SMIv2 April 1999

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

StorageType ::= TEXTUAL-CONVENTION

  STATUS       current
  DESCRIPTION
          "Describes the memory realization of a conceptual row.  A
          row which is volatile(2) is lost upon reboot.  A row which
          is either nonVolatile(3), permanent(4) or readOnly(5), is
          backed up by stable storage.  A row which is permanent(4)
          can be changed but not deleted.  A row which is readOnly(5)
          cannot be changed nor deleted.
          If the value of an object with this syntax is either
          permanent(4) or readOnly(5), it cannot be written.
          Conversely, if the value is either other(1), volatile(2) or
          nonVolatile(3), it cannot be modified to be permanent(4) or
          readOnly(5).  (All illegal modifications result in a
          'wrongValue' error.)
          Every usage of this textual convention is required to
          specify the columnar objects which a permanent(4) row must
          at a minimum allow to be writable."
  SYNTAX       INTEGER {
                   other(1),       -- eh?
                   volatile(2),    -- e.g., in RAM
                   nonVolatile(3), -- e.g., in NVRAM
                   permanent(4),   -- e.g., partially in ROM
                   readOnly(5)     -- e.g., completely in ROM
               }

McCloghrie, et al. Standards Track [Page 19]

RFC 2579 Textual Conventions for SMIv2 April 1999

TDomain ::= TEXTUAL-CONVENTION

  STATUS       current
  DESCRIPTION
        "Denotes a kind of transport service.
        Some possible values, such as snmpUDPDomain, are defined in
        the SNMPv2-TM MIB module.  Other possible values are defined
        in other MIB modules."
  REFERENCE    "The SNMPv2-TM MIB module is defined in RFC 1906."
  SYNTAX       OBJECT IDENTIFIER

TAddress ::= TEXTUAL-CONVENTION

  STATUS       current
  DESCRIPTION
        "Denotes a transport service address.
        A TAddress value is always interpreted within the context of a
        TDomain value.  Thus, each definition of a TDomain value must
        be accompanied by a definition of a textual convention for use
        with that TDomain.  Some possible textual conventions, such as
        SnmpUDPAddress for snmpUDPDomain, are defined in the SNMPv2-TM
        MIB module.  Other possible textual conventions are defined in
        other MIB modules."
  REFERENCE    "The SNMPv2-TM MIB module is defined in RFC 1906."
  SYNTAX       OCTET STRING (SIZE (1..255))

END

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.
 The name of a textual convention must consist of one or more letters
 or digits, with the initial character being an upper case letter.
 The name must not conflict with any of the reserved words listed in
 section 3.7 of [2], should not consist of all upper case letters, and
 shall not exceed 64 characters in length.  (However, names longer
 than 32 characters are not recommended.)  The hyphen is not allowed
 in the name of a textual convention (except for use in information
 modules converted from SMIv1 which allowed hyphens in ASN.1 type
 assignments).  Further, all names used for the textual conventions
 defined in all "standard" information modules shall be unique.

McCloghrie, et al. Standards Track [Page 20]

RFC 2579 Textual Conventions for SMIv2 April 1999

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 must not be present if the Textual Convention is defined with
 a syntax of:  OBJECT IDENTIFIER, IpAddress, Counter32, Counter64, or
 any enumerated syntax (BITS or INTEGER).  The determination of
 whether it makes sense for other syntax types is dependent on the
 specific definition of the Textual Convention.
 When the syntax has an underlying primitive type of INTEGER, the hint
 consists of an integer-format specification, containing two parts.
 The first part is a single character suggesting a display format,
 either: `x' for hexadecimal, or `d' for decimal, or `o' for octal, or
 `b' for binary.  For all types, when rendering the value, leading
 zeros are omitted, and for negative values, a minus sign is rendered
 immediately before the digits.  The second part is always omitted for
 `x', `o' and `b', and need not be present for `d'.  If present, the
 second part starts with a hyphen and is followed by a decimal number,
 which defines the implied decimal point when rendering the value.
 For example:
      Hundredths ::= TEXTUAL-CONVENTION
          DISPLAY-HINT "d-2"
          ...
          SYNTAX     INTEGER (0..10000)
 suggests that a Hundredths value of 1234 be rendered as "12.34"
 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.

McCloghrie, et al. Standards Track [Page 21]

RFC 2579 Textual Conventions for SMIv2 April 1999

(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, `a' for ascii, or `t' for UTF-8.  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.  The octets
   processed by the `t' display format do not necessarily form an
   integral number of UTF-8 characters.  Trailing octets which do not
   form a valid UTF-8 encoded character are discarded.

(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.

3.2. Mapping of the STATUS clause

 The STATUS clause, which must be present, indicates whether this
 definition is current or historic.
 The value "current" means that the definition is current and valid.

McCloghrie, et al. Standards Track [Page 22]

RFC 2579 Textual Conventions for SMIv2 April 1999

 The value "obsolete" means the definition is obsolete and should not
 be implemented and/or can be removed if previously implemented.
 While the value "deprecated" also indicates an obsolete definition,
 it permits new/continued implementation in order to foster
 interoperability with older/existing 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.

3.4. Mapping of the REFERENCE clause

 The REFERENCE clause, which need not be present, contains a textual
 cross-reference to some other document, either another information
 module which defines a related assignment, or some other document
 which provides additional information relevant to this definition.

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 or the BITS construct (see section 7.1 in [2]).  Note that
 this means that the SYNTAX clause of a Textual Convention can not
 refer to a previously defined Textual Convention.
 An extended subset of the full capabilities of ASN.1 (1988) sub-
 typing is allowed, as appropriate to the underlying ASN.1 type.  Any
 such restriction on size, range or enumerations specified in this
 clause represents the maximal level of support which makes "protocol
 sense".  Restrictions on sub-typing are specified in detail in
 Section 9 and Appendix A of [2].

4. Sub-typing of Textual Conventions

 The SYNTAX clause of a TEXTUAL CONVENTION macro may be sub-typed in
 the same way as the SYNTAX clause of an OBJECT-TYPE macro (see
 section 11 of [2]).

5. Revising a Textual Convention Definition

 It may be desirable to revise the definition of a textual convention
 after experience is gained with it.  However, changes are not allowed
 if they have any potential to cause interoperability problems "over

McCloghrie, et al. Standards Track [Page 23]

RFC 2579 Textual Conventions for SMIv2 April 1999

 the wire" between an implementation using an original specification
 and an implementation using an updated specification(s).  Such
 changes can only be accommodated by defining a new textual convention
 (i.e., a new name).
 The following revisions are allowed:

(1) A SYNTAX clause containing an enumerated INTEGER may have new

   enumerations added or existing labels changed.  Similarly, named
   bits may be added or existing labels changed for the BITS
   construct.

(2) A STATUS clause value of "current" may be revised as "deprecated"

   or "obsolete".  Similarly, a STATUS clause value of "deprecated"
   may be revised as "obsolete".  When making such a change, the
   DESCRIPTION clause should be updated to explain the rationale.

(3) A REFERENCE clause may be added or updated.

(4) A DISPLAY-HINTS clause may be added or updated.

(5) Clarifications and additional information may be included in the

   DESCRIPTION clause.

(6) Any editorial change.

 Note that with the introduction of the TEXTUAL-CONVENTION macro,
 there is no longer any need to define types in the following manner:
      DisplayString ::= OCTET STRING (SIZE (0..255))
 When revising an information module containing a definition such as
 this, that definition should be replaced by a TEXTUAL-CONVENTION
 macro.

6. Security Considerations

 This document defines the means to define new data types for the
 language used to write and read descriptions of management
 information.  These data types have no security impact on the
 Internet.

McCloghrie, et al. Standards Track [Page 24]

RFC 2579 Textual Conventions for SMIv2 April 1999

7. Editors' Addresses

 Keith McCloghrie
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, CA  95134-1706
 USA
 Phone: +1 408 526 5260
 EMail: kzm@cisco.com
 David Perkins
 SNMPinfo
 3763 Benton Street
 Santa Clara, CA 95051
 USA
 Phone: +1 408 221-8702
 EMail: dperkins@snmpinfo.com
 Juergen Schoenwaelder
 TU Braunschweig
 Bueltenweg 74/75
 38106 Braunschweig
 Germany
 Phone: +49 531 391-3283
 EMail: schoenw@ibr.cs.tu-bs.de

8. 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] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M.

   and S. Waldbusser, "Structure of Management Information Version 2
   (SMIv2)", STD 58, RFC 2578, April 1999.

[3] The SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M. and

   Waldbusser, S., "Transport Mappings for Version 2 of the" Simple
   Network Management Protocol (SNMPv2)", RFC 1906, January 1996.

McCloghrie, et al. Standards Track [Page 25]

RFC 2579 Textual Conventions for SMIv2 April 1999

9. Full Copyright Statement

 Copyright (C) The Internet Society (1999).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."

McCloghrie, et al. Standards Track [Page 26]

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