    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

        -- 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:

                  - the use of character codes 0-127 (decimal)

                  - the graphics characters (32-126) are interpreted as
                    US ASCII

                  - NUL, LF, CR, BEL, BS, HT, VT and FF have the special
                    meanings specified in RFC 854

                  - the other 25 codes have no standard interpretation

                  - the sequence 'CR LF' means newline

                  - the sequence 'CR NUL' means carriage-return

                  - an 'LF' not preceded by a 'CR' means moving to the
                    same column on the next line.

                  - 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:

                     - `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); 'notInService' has
                     no implication regarding the internal consistency of
                     the row, availability of resources, or consistency with
                     the current state of the managed device;

                     - `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);

                     - `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;

                     - `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,

                     - `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.

    McCloghrie, et al.          Standards Track                    [Page 10]

    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

    McCloghrie, et al.          Standards Track                    [Page 11]

    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:

                     - 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.

    McCloghrie, et al.          Standards Track                    [Page 12]

    RFC 2579             Textual Conventions for SMIv2            April 1999

                     - 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.

    McCloghrie, et al.          Standards Track                    [Page 13]

    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]

    RFC 2579             Textual Conventions for SMIv2            April 1999

                     - 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.

                     - 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 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.

    McCloghrie, et al.          Standards Track                    [Page 16]

    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),

                         -- 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)
                     }

    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:
                - the value of year is in network-byte order
                - 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]