File: rfc2578.txt

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Network Working Group                 Editors of this version:
Request for Comments: 2578                                 K. McCloghrie
STD: 58                                                    Cisco Systems
Obsoletes: 1902                                               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


         Structure of Management Information Version 2 (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 .................................................3
   1.1 A Note on Terminology ......................................4
   2 Definitions ..................................................4
   2.1 The MODULE-IDENTITY macro ..................................5
   2.2 Object Names and Syntaxes ..................................5
   2.3 The OBJECT-TYPE macro ......................................8
   2.5 The NOTIFICATION-TYPE macro ...............................10
   2.6 Administrative Identifiers ................................11
   3 Information Modules .........................................11
   3.1 Macro Invocation ..........................................12
   3.1.1 Textual Values and Strings ..............................13


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   3.2 IMPORTing Symbols .........................................14
   3.3 Exporting Symbols .........................................14
   3.4 ASN.1 Comments ............................................14
   3.5 OBJECT IDENTIFIER values ..................................15
   3.6 OBJECT IDENTIFIER usage ...................................15
   3.7 Reserved Keywords .........................................16
   4 Naming Hierarchy ............................................16
   5 Mapping of the MODULE-IDENTITY macro ........................17
   5.1 Mapping of the LAST-UPDATED clause ........................17
   5.2 Mapping of the ORGANIZATION clause ........................17
   5.3 Mapping of the CONTACT-INFO clause ........................18
   5.4 Mapping of the DESCRIPTION clause .........................18
   5.5 Mapping of the REVISION clause ............................18
   5.5.1 Mapping of the DESCRIPTION sub-clause ...................18
   5.6 Mapping of the MODULE-IDENTITY value ......................18
   5.7 Usage Example .............................................18
   6 Mapping of the OBJECT-IDENTITY macro ........................19
   6.1 Mapping of the STATUS clause ..............................19
   6.2 Mapping of the DESCRIPTION clause .........................20
   6.3 Mapping of the REFERENCE clause ...........................20
   6.4 Mapping of the OBJECT-IDENTITY value ......................20
   6.5 Usage Example .............................................20
   7 Mapping of the OBJECT-TYPE macro ............................20
   7.1 Mapping of the SYNTAX clause ..............................21
   7.1.1 Integer32 and INTEGER ...................................21
   7.1.2 OCTET STRING ............................................21
   7.1.3 OBJECT IDENTIFIER .......................................22
   7.1.4 The BITS construct ......................................22
   7.1.5 IpAddress ...............................................22
   7.1.6 Counter32 ...............................................23
   7.1.7 Gauge32 .................................................23
   7.1.8 TimeTicks ...............................................24
   7.1.9 Opaque ..................................................24
   7.1.10 Counter64 ..............................................24
   7.1.11 Unsigned32 .............................................25
   7.1.12 Conceptual Tables ......................................25
   7.1.12.1 Creation and Deletion of Conceptual Rows .............26
   7.2 Mapping of the UNITS clause ...............................26
   7.3 Mapping of the MAX-ACCESS clause ..........................26
   7.4 Mapping of the STATUS clause ..............................27
   7.5 Mapping of the DESCRIPTION clause .........................27
   7.6 Mapping of the REFERENCE clause ...........................27
   7.7 Mapping of the INDEX clause ...............................27
   7.8 Mapping of the AUGMENTS clause ............................29
   7.8.1 Relation between INDEX and AUGMENTS clauses .............30
   7.9 Mapping of the DEFVAL clause ..............................30
   7.10 Mapping of the OBJECT-TYPE value .........................31
   7.11 Usage Example ............................................32


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   8 Mapping of the NOTIFICATION-TYPE macro ......................34
   8.1 Mapping of the OBJECTS clause .............................34
   8.2 Mapping of the STATUS clause ..............................34
   8.3 Mapping of the DESCRIPTION clause .........................35
   8.4 Mapping of the REFERENCE clause ...........................35
   8.5 Mapping of the NOTIFICATION-TYPE value ....................35
   8.6 Usage Example .............................................35
   9 Refined Syntax ..............................................36
   10 Extending an Information Module ............................37
   10.1 Object Assignments .......................................37
   10.2 Object Definitions .......................................38
   10.3 Notification Definitions .................................39
   11 Appendix A: Detailed Sub-typing Rules ......................40
   11.1 Syntax Rules .............................................40
   11.2 Examples .................................................41
   12 Security Considerations ....................................41
   13 Editors' Addresses .........................................41
   14 References .................................................42
   15 Full Copyright Statement ...................................43

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].  It is the
   purpose of this document, the Structure of Management Information
   (SMI), to define that adapted subset, and to assign a set of
   associated administrative values.

   The SMI is divided into three parts:  module definitions, object
   definitions, and, notification definitions.

(1)  Module definitions are used when describing information modules.
     An ASN.1 macro, MODULE-IDENTITY, is used to concisely convey the
     semantics of an information module.

(2)  Object definitions are used when describing managed objects.  An
     ASN.1 macro, OBJECT-TYPE, is used to concisely convey the syntax
     and semantics of a managed object.

(3)  Notification definitions are used when describing unsolicited
     transmissions of management information.  An ASN.1 macro,
     NOTIFICATION-TYPE, is used to concisely convey the syntax and
     semantics of a notification.




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RFC 2578                         SMIv2                        April 1999


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-SMI DEFINITIONS ::= BEGIN


-- the path to the root

org            OBJECT IDENTIFIER ::= { iso 3 }  --  "iso" = 1
dod            OBJECT IDENTIFIER ::= { org 6 }
internet       OBJECT IDENTIFIER ::= { dod 1 }

directory      OBJECT IDENTIFIER ::= { internet 1 }

mgmt           OBJECT IDENTIFIER ::= { internet 2 }
mib-2          OBJECT IDENTIFIER ::= { mgmt 1 }
transmission   OBJECT IDENTIFIER ::= { mib-2 10 }

experimental   OBJECT IDENTIFIER ::= { internet 3 }

private        OBJECT IDENTIFIER ::= { internet 4 }
enterprises    OBJECT IDENTIFIER ::= { private 1 }

security       OBJECT IDENTIFIER ::= { internet 5 }

snmpV2         OBJECT IDENTIFIER ::= { internet 6 }

-- transport domains
snmpDomains    OBJECT IDENTIFIER ::= { snmpV2 1 }

-- transport proxies
snmpProxys     OBJECT IDENTIFIER ::= { snmpV2 2 }

-- module identities
snmpModules    OBJECT IDENTIFIER ::= { snmpV2 3 }

-- Extended UTCTime, to allow dates with four-digit years
-- (Note that this definition of ExtUTCTime is not to be IMPORTed
--  by MIB modules.)
ExtUTCTime ::= OCTET STRING(SIZE(11 | 13))
    -- format is YYMMDDHHMMZ or YYYYMMDDHHMMZ


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RFC 2578                         SMIv2                        April 1999


    --   where: YY   - last two digits of year (only years
    --                 between 1900-1999)
    --          YYYY - last four digits of the year (any year)
    --          MM   - month (01 through 12)
    --          DD   - day of month (01 through 31)
    --          HH   - hours (00 through 23)
    --          MM   - minutes (00 through 59)
    --          Z    - denotes GMT (the ASCII character Z)
    --
    -- For example, "9502192015Z" and "199502192015Z" represent
    -- 8:15pm GMT on 19 February 1995. Years after 1999 must use
    -- the four digit year format. Years 1900-1999 may use the
    -- two or four digit format.

-- definitions for information modules

MODULE-IDENTITY MACRO ::=
BEGIN
    TYPE NOTATION ::=
                  "LAST-UPDATED" value(Update ExtUTCTime)
                  "ORGANIZATION" Text
                  "CONTACT-INFO" Text
                  "DESCRIPTION" Text
                  RevisionPart

    VALUE NOTATION ::=
                  value(VALUE OBJECT IDENTIFIER)

    RevisionPart ::=
                  Revisions
                | empty
    Revisions ::=
                  Revision
                | Revisions Revision
    Revision ::=
                  "REVISION" value(Update ExtUTCTime)
                  "DESCRIPTION" Text

    -- a character string as defined in section 3.1.1
    Text ::= value(IA5String)
END


OBJECT-IDENTITY MACRO ::=
BEGIN
    TYPE NOTATION ::=
                  "STATUS" Status
                  "DESCRIPTION" Text


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RFC 2578                         SMIv2                        April 1999


                  ReferPart

    VALUE NOTATION ::=
                  value(VALUE OBJECT IDENTIFIER)

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

    ReferPart ::=
                  "REFERENCE" Text
                | empty

    -- a character string as defined in section 3.1.1
    Text ::= value(IA5String)
END


-- names of objects
-- (Note that these definitions of ObjectName and NotificationName
--  are not to be IMPORTed by MIB modules.)

ObjectName ::=
    OBJECT IDENTIFIER

NotificationName ::=
    OBJECT IDENTIFIER

-- syntax of objects

-- the "base types" defined here are:
--   3 built-in ASN.1 types: INTEGER, OCTET STRING, OBJECT IDENTIFIER
--   8 application-defined types: Integer32, IpAddress, Counter32,
--              Gauge32, Unsigned32, TimeTicks, Opaque, and Counter64

ObjectSyntax ::=
    CHOICE {
        simple
            SimpleSyntax,

          -- note that SEQUENCEs for conceptual tables and
          -- rows are not mentioned here...

        application-wide
            ApplicationSyntax
    }



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RFC 2578                         SMIv2                        April 1999


-- built-in ASN.1 types

SimpleSyntax ::=
    CHOICE {
        -- INTEGERs with a more restrictive range
        -- may also be used
        integer-value               -- includes Integer32
            INTEGER (-2147483648..2147483647),

        -- OCTET STRINGs with a more restrictive size
        -- may also be used
        string-value
            OCTET STRING (SIZE (0..65535)),

        objectID-value
            OBJECT IDENTIFIER
    }

-- indistinguishable from INTEGER, but never needs more than
-- 32-bits for a two's complement representation
Integer32 ::=
        INTEGER (-2147483648..2147483647)


-- application-wide types

ApplicationSyntax ::=
    CHOICE {
        ipAddress-value
            IpAddress,

        counter-value
            Counter32,

        timeticks-value
            TimeTicks,

        arbitrary-value
            Opaque,

        big-counter-value
            Counter64,

        unsigned-integer-value  -- includes Gauge32
            Unsigned32
    }

-- in network-byte order


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RFC 2578                         SMIv2                        April 1999


-- (this is a tagged type for historical reasons)
IpAddress ::=
    [APPLICATION 0]
        IMPLICIT OCTET STRING (SIZE (4))

-- this wraps
Counter32 ::=
    [APPLICATION 1]
        IMPLICIT INTEGER (0..4294967295)

-- this doesn't wrap
Gauge32 ::=
    [APPLICATION 2]
        IMPLICIT INTEGER (0..4294967295)

-- an unsigned 32-bit quantity
-- indistinguishable from Gauge32
Unsigned32 ::=
    [APPLICATION 2]
        IMPLICIT INTEGER (0..4294967295)

-- hundredths of seconds since an epoch
TimeTicks ::=
    [APPLICATION 3]
        IMPLICIT INTEGER (0..4294967295)

-- for backward-compatibility only
Opaque ::=
    [APPLICATION 4]
        IMPLICIT OCTET STRING

-- for counters that wrap in less than one hour with only 32 bits
Counter64 ::=
    [APPLICATION 6]
        IMPLICIT INTEGER (0..18446744073709551615)


-- definition for objects

OBJECT-TYPE MACRO ::=
BEGIN
    TYPE NOTATION ::=
                  "SYNTAX" Syntax
                  UnitsPart
                  "MAX-ACCESS" Access
                  "STATUS" Status
                  "DESCRIPTION" Text
                  ReferPart


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RFC 2578                         SMIv2                        April 1999


                  IndexPart
                  DefValPart

    VALUE NOTATION ::=
                  value(VALUE ObjectName)

    Syntax ::=   -- Must be one of the following:
                       -- a base type (or its refinement),
                       -- a textual convention (or its refinement), or
                       -- a BITS pseudo-type
                   type
                | "BITS" "{" NamedBits "}"

    NamedBits ::= NamedBit
                | NamedBits "," NamedBit

    NamedBit ::=  identifier "(" number ")" -- number is nonnegative

    UnitsPart ::=
                  "UNITS" Text
                | empty

    Access ::=
                  "not-accessible"
                | "accessible-for-notify"
                | "read-only"
                | "read-write"
                | "read-create"

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

    ReferPart ::=
                  "REFERENCE" Text
                | empty

    IndexPart ::=
                  "INDEX"    "{" IndexTypes "}"
                | "AUGMENTS" "{" Entry      "}"
                | empty
    IndexTypes ::=
                  IndexType
                | IndexTypes "," IndexType
    IndexType ::=
                  "IMPLIED" Index
                | Index


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RFC 2578                         SMIv2                        April 1999


    Index ::=
                    -- use the SYNTAX value of the
                    -- correspondent OBJECT-TYPE invocation
                  value(ObjectName)
    Entry ::=
                    -- use the INDEX value of the
                    -- correspondent OBJECT-TYPE invocation
                  value(ObjectName)

    DefValPart ::= "DEFVAL" "{" Defvalue "}"
                | empty

    Defvalue ::=  -- must be valid for the type specified in
                  -- SYNTAX clause of same OBJECT-TYPE macro
                  value(ObjectSyntax)
                | "{" BitsValue "}"

    BitsValue ::= BitNames
                | empty

    BitNames ::=  BitName
                | BitNames "," BitName

    BitName ::= identifier

    -- a character string as defined in section 3.1.1
    Text ::= value(IA5String)
END


-- definitions for notifications

NOTIFICATION-TYPE MACRO ::=
BEGIN
    TYPE NOTATION ::=
                  ObjectsPart
                  "STATUS" Status
                  "DESCRIPTION" Text
                  ReferPart

    VALUE NOTATION ::=
                  value(VALUE NotificationName)

    ObjectsPart ::=
                  "OBJECTS" "{" Objects "}"
                | empty
    Objects ::=
                  Object


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RFC 2578                         SMIv2                        April 1999


                | Objects "," Object
    Object ::=
                  value(ObjectName)

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

    ReferPart ::=
                  "REFERENCE" Text
                | empty

    -- a character string as defined in section 3.1.1
    Text ::= value(IA5String)
END

-- definitions of administrative identifiers

zeroDotZero    OBJECT-IDENTITY
    STATUS     current
    DESCRIPTION
            "A value used for null identifiers."
    ::= { 0 0 }

END

3.  Information Modules

   An "information module" is an ASN.1 module defining information
   relating to network management.

   The SMI describes how to use an adapted subset of ASN.1 (1988) to
   define an information module.  Further, additional restrictions are
   placed on "standard" information modules.  It is strongly recommended
   that "enterprise-specific" information modules also adhere to these
   restrictions.

   Typically, there are three kinds of information modules:

(1)  MIB modules, which contain definitions of inter-related managed
     objects, make use of the OBJECT-TYPE and NOTIFICATION-TYPE macros;

(2)  compliance statements for MIB modules, which make use of the
     MODULE-COMPLIANCE and OBJECT-GROUP macros [2]; and,

(3)  capability statements for agent implementations which make use of
     the AGENT-CAPABILITIES macros [2].


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RFC 2578                         SMIv2                        April 1999


   This classification scheme does not imply a rigid taxonomy.  For
   example, a "standard" information module will normally include
   definitions of managed objects and a compliance statement.
   Similarly, an "enterprise-specific" information module might include
   definitions of managed objects and a capability statement.  Of
   course, a "standard" information module may not contain capability
   statements.

   The constructs of ASN.1 allowed in SMIv2 information modules include:
   the IMPORTS clause, value definitions for OBJECT IDENTIFIERs, type
   definitions for SEQUENCEs (with restrictions), ASN.1 type assignments
   of the restricted ASN.1 types allowed in SMIv2, and instances of
   ASN.1 macros defined in this document and its companion documents [2,
   3].  Additional ASN.1 macros must not be defined in SMIv2 information
   modules.  SMIv1 macros must not be used in SMIv2 information modules.

   The names of all standard information modules must be unique (but
   different versions of the same information module should have the
   same name).  Developers of enterprise information modules are
   encouraged to choose names for their information modules that will
   have a low probability of colliding with standard or other enterprise
   information modules. An information module may not use the ASN.1
   construct of placing an object identifier value between the module
   name and the "DEFINITIONS" keyword.  For the purposes of this
   specification, an ASN.1 module name begins with an upper-case letter
   and continues with zero or more letters, digits, or hyphens, except
   that a hyphen can not be the last character, nor can there be two
   consecutive hyphens.

   All information modules start with exactly one invocation of the
   MODULE-IDENTITY macro, which provides contact information as well as
   revision history to distinguish between versions of the same
   information module.  This invocation must appear immediately after
   any IMPORTs statements.

3.1.  Macro Invocation

   Within an information module, each macro invocation appears as:

        <descriptor> <macro> <clauses> ::= <value>

   where <descriptor> corresponds to an ASN.1 identifier, <macro> names
   the macro being invoked, and <clauses> and <value> depend on the
   definition of the macro.  (Note that this definition of a descriptor
   applies to all macros defined in this memo and in [2].)





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RFC 2578                         SMIv2                        April 1999


   For the purposes of this specification, an ASN.1 identifier consists
   of one or more letters or digits, and its initial character must be a
   lower-case letter.  Note that hyphens are not allowed by this
   specification (except for use by information modules converted from
   SMIv1 which did allow hyphens).

   For all descriptors appearing in an information module, the
   descriptor shall be unique and mnemonic, and shall not exceed 64
   characters in length.  (However, descriptors longer than 32
   characters are not recommended.)  This promotes a common language for
   humans to use when discussing the information module and also
   facilitates simple table mappings for user-interfaces.

   The set of descriptors defined in all "standard" information modules
   shall be unique.

   Finally, by convention, if the descriptor refers to an object with a
   SYNTAX clause value of either Counter32 or Counter64, then the
   descriptor used for the object should denote plurality.

3.1.1.  Textual Values and Strings

   Some clauses in a macro invocation may take a character string as a
   textual value (e.g., the DESCRIPTION clause).  Other clauses take
   binary or hexadecimal strings (in any position where a non-negative
   number is allowed).

   A character string is preceded and followed by the quote character
   ("), and consists of an arbitrary number (possibly zero) of:

      - any 7-bit displayable ASCII characters except quote ("),
      - tab characters,
      - spaces, and
      - line terminator characters (\n or \r\n).

   The value of a character string is interpreted as ASCII.

   A binary string consists of a number (possibly zero) of zeros and
   ones preceded by a single (') and followed by either the pair ('B) or
   ('b), where the number is a multiple of eight.

   A hexadecimal string consists of an even number (possibly zero) of
   hexadecimal digits, preceded by a single (') and followed by either
   the pair ('H) or ('h).  Digits specified via letters can be in upper
   or lower case.

   Note that ASN.1 comments can not be enclosed inside any of these
   types of strings.


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RFC 2578                         SMIv2                        April 1999


3.2.  IMPORTing Symbols

   To reference an external object, the IMPORTS statement must be used
   to identify both the descriptor and the module in which the
   descriptor is defined, where the module is identified by its ASN.1
   module name.

   Note that when symbols from "enterprise-specific" information modules
   are referenced  (e.g., a descriptor), there is the possibility of
   collision.  As such, if different objects with the same descriptor
   are IMPORTed, then this ambiguity is resolved by prefixing the
   descriptor with the name of the information module and a dot ("."),
   i.e.,

        "module.descriptor"

   (All descriptors must be unique within any information module.)

   Of course, this notation can be used to refer to objects even when
   there is no collision when IMPORTing symbols.

   Finally, if any of the ASN.1 named types and macros defined in this
   document, specifically:

        Counter32, Counter64, Gauge32, Integer32, IpAddress, MODULE-
        IDENTITY, NOTIFICATION-TYPE, Opaque, OBJECT-TYPE, OBJECT-
        IDENTITY, TimeTicks, Unsigned32,

   or any of those defined in [2] or [3], are used in an information
   module, then they must be imported using the IMPORTS statement.
   However, the following must not be included in an IMPORTS statement:

      - named types defined by ASN.1 itself, specifically: INTEGER,
        OCTET STRING, OBJECT IDENTIFIER, SEQUENCE, SEQUENCE OF type,
      - the BITS construct.

3.3.  Exporting Symbols

   The ASN.1 EXPORTS statement is not allowed in SMIv2 information
   modules.  All items defined in an information module are
   automatically exported.

3.4.  ASN.1 Comments

   ASN.1 comments can be included in an information module.  However, it
   is recommended that all substantive descriptions be placed within an
   appropriate DESCRIPTION clause.



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RFC 2578                         SMIv2                        April 1999


   ASN.1 comments commence with a pair of adjacent hyphens and end with
   the next pair of adjacent hyphens or at the end of the line,
   whichever occurs first.  Comments ended by a pair of hyphens have the
   effect of a single space character.

3.5.  OBJECT IDENTIFIER values

   An OBJECT IDENTIFIER value is an ordered list of non-negative
   numbers.  For the SMIv2, each number in the list is referred to as a
   sub-identifier, there are at most 128 sub-identifiers in a value, and
   each sub-identifier has a maximum value of 2^32-1 (4294967295
   decimal).

   All OBJECT IDENTIFIER values have at least two sub-identifiers, where
   the value of the first sub-identifier is one of the following well-
   known names:

        Value   Name
          0     ccitt
          1     iso
          2     joint-iso-ccitt

   (Note that this SMI does not recognize "new" well-known names, e.g.,
   as defined when the CCITT became the ITU.)

3.6.  OBJECT IDENTIFIER usage

   OBJECT IDENTIFIERs are used in information modules in two ways:

(1)  registration: the definition of a particular item is registered as
     a particular OBJECT IDENTIFIER value, and associated with a
     particular descriptor.  After such a registration, the semantics
     thereby associated with the value are not allowed to change, the
     OBJECT IDENTIFIER can not be used for any other registration, and
     the descriptor can not be changed nor associated with any other
     registration.  The following macros result in a registration:

          OBJECT-TYPE, MODULE-IDENTITY, NOTIFICATION-TYPE, OBJECT-GROUP,
          OBJECT-IDENTITY, NOTIFICATION-GROUP, MODULE-COMPLIANCE,
          AGENT-CAPABILITIES.

(2)  assignment: a descriptor can be assigned to a particular OBJECT
     IDENTIFIER value.  For this usage, the semantics associated with
     the OBJECT IDENTIFIER value is not allowed to change, and a
     descriptor assigned to a particular OBJECT IDENTIFIER value cannot
     subsequently be assigned to another.  However, multiple descriptors
     can be assigned to the same OBJECT IDENTIFIER value.  Such
     assignments are specified in the following manner:


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          mib         OBJECT IDENTIFIER ::= { mgmt 1 }  -- from RFC1156
          mib-2       OBJECT IDENTIFIER ::= { mgmt 1 }  -- from RFC1213
          fredRouter  OBJECT IDENTIFIER ::= { flintStones 1 1 }
          barneySwitch OBJECT IDENTIFIER ::= { flintStones bedrock(2) 1 }

     Note while the above examples are legal, the following is not:

          dinoHost OBJECT IDENTIFIER ::= { flintStones bedrock 2 }

   A descriptor is allowed to be associated with both a registration and
   an assignment, providing both are associated with the same OBJECT
   IDENTIFIER value and semantics.

3.7.  Reserved Keywords

   The following are reserved keywords which must not be used as
   descriptors or module names:

        ABSENT ACCESS AGENT-CAPABILITIES ANY APPLICATION AUGMENTS BEGIN
        BIT BITS BOOLEAN BY CHOICE COMPONENT COMPONENTS CONTACT-INFO
        CREATION-REQUIRES Counter32 Counter64 DEFAULT DEFINED
        DEFINITIONS DEFVAL DESCRIPTION DISPLAY-HINT END ENUMERATED
        ENTERPRISE EXPLICIT EXPORTS EXTERNAL FALSE FROM GROUP Gauge32
        IDENTIFIER IMPLICIT IMPLIED IMPORTS INCLUDES INDEX INTEGER
        Integer32 IpAddress LAST-UPDATED MANDATORY-GROUPS MAX MAX-ACCESS
        MIN MIN-ACCESS MINUS-INFINITY MODULE MODULE-COMPLIANCE MODULE-
        IDENTITY NOTIFICATION-GROUP NOTIFICATION-TYPE NOTIFICATIONS NULL
        OBJECT OBJECT-GROUP OBJECT-IDENTITY OBJECT-TYPE OBJECTS OCTET OF
        OPTIONAL ORGANIZATION Opaque PLUS-INFINITY PRESENT PRIVATE
        PRODUCT-RELEASE REAL REFERENCE REVISION SEQUENCE SET SIZE STATUS
        STRING SUPPORTS SYNTAX TAGS TEXTUAL-CONVENTION TRAP-TYPE TRUE
        TimeTicks UNITS UNIVERSAL Unsigned32 VARIABLES VARIATION WITH
        WRITE-SYNTAX

4.  Naming Hierarchy

   The root of the subtree administered by the Internet Assigned Numbers
   Authority (IANA) for the Internet is:

        internet       OBJECT IDENTIFIER ::= { iso 3 6 1 }

   That is, the Internet subtree of OBJECT IDENTIFIERs starts with the
   prefix:

        1.3.6.1.

   Several branches underneath this subtree are used for network
   management:


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        mgmt           OBJECT IDENTIFIER ::= { internet 2 }
        experimental   OBJECT IDENTIFIER ::= { internet 3 }
        private        OBJECT IDENTIFIER ::= { internet 4 }
        enterprises    OBJECT IDENTIFIER ::= { private 1 }

   However, the SMI does not prohibit the definition of objects in other
   portions of the object tree.

   The mgmt(2) subtree is used to identify "standard" objects.

   The experimental(3) subtree is used to identify objects being
   designed by working groups of the IETF.  If an information module
   produced by a working group becomes a "standard" information module,
   then at the very beginning of its entry onto the Internet standards
   track, the objects are moved under the mgmt(2) subtree.

   The private(4) subtree is used to identify objects defined
   unilaterally.  The enterprises(1) subtree beneath private is used,
   among other things, to permit providers of networking subsystems to
   register models of their products.

5.  Mapping of the MODULE-IDENTITY macro

   The MODULE-IDENTITY macro is used to provide contact and revision
   history for each information module.  It must appear exactly once in
   every information module.  It should be noted that the expansion of
   the MODULE-IDENTITY macro is something which conceptually happens
   during implementation and not during run-time.

   Note that reference in an IMPORTS clause or in clauses of SMIv2
   macros to an information module is NOT through the use of the
   'descriptor' of a MODULE-IDENTITY macro; rather, an information
   module is referenced through specifying its module name.

5.1.  Mapping of the LAST-UPDATED clause

   The LAST-UPDATED clause, which must be present, contains the date and
   time that this information module was last edited.

5.2.  Mapping of the ORGANIZATION clause

   The ORGANIZATION clause, which must be present, contains a textual
   description of the organization under whose auspices this information
   module was developed.






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5.3.  Mapping of the CONTACT-INFO clause

   The CONTACT-INFO clause, which must be present, contains the name,
   postal address, telephone number, and electronic mail address of the
   person to whom technical queries concerning this information module
   should be sent.

5.4.  Mapping of the DESCRIPTION clause

   The DESCRIPTION clause, which must be present, contains a high-level
   textual description of the contents of this information module.

5.5.  Mapping of the REVISION clause

   The REVISION clause, which need not be present, is repeatedly used to
   describe the revisions (including the initial version) made to this
   information module, in reverse chronological order (i.e., most recent
   first).  Each instance of this clause contains the date and time of
   the revision.

5.5.1.  Mapping of the DESCRIPTION sub-clause

   The DESCRIPTION sub-clause, which must be present for each REVISION
   clause, contains a high-level textual description of the revision
   identified in that REVISION clause.

5.6.  Mapping of the MODULE-IDENTITY value

   The value of an invocation of the MODULE-IDENTITY macro is an OBJECT
   IDENTIFIER.  As such, this value may be authoritatively used when
   specifying an OBJECT IDENTIFIER value to refer to the information
   module containing the invocation.

   Note that it is a common practice to use the value of the MODULE-
   IDENTITY macro as a subtree under which other OBJECT IDENTIFIER
   values assigned within the module are defined.  However, it is legal
   (and occasionally necessary) for the other OBJECT IDENTIFIER values
   assigned within the module to be unrelated to the OBJECT IDENTIFIER
   value of the MODULE-IDENTITY macro.

5.7.  Usage Example

   Consider how a skeletal MIB module might be constructed:  e.g.,

   FIZBIN-MIB DEFINITIONS ::= BEGIN

   IMPORTS
       MODULE-IDENTITY, OBJECT-TYPE, experimental


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           FROM SNMPv2-SMI;


   fizbin MODULE-IDENTITY
       LAST-UPDATED "199505241811Z"
       ORGANIZATION "IETF SNMPv2 Working Group"
       CONTACT-INFO
               "        Marshall T. Rose

                Postal: Dover Beach Consulting, Inc.
                        420 Whisman Court
                        Mountain View, CA  94043-2186
                        US

                   Tel: +1 415 968 1052
                   Fax: +1 415 968 2510

                E-mail: mrose@dbc.mtview.ca.us"

       DESCRIPTION
               "The MIB module for entities implementing the xxxx
               protocol."
       REVISION      "9505241811Z"
       DESCRIPTION
               "The latest version of this MIB module."
       REVISION      "9210070433Z"
       DESCRIPTION
               "The initial version of this MIB module, published in
               RFC yyyy."
   -- contact IANA for actual number
       ::= { experimental xx }

   END

6.  Mapping of the OBJECT-IDENTITY macro

   The OBJECT-IDENTITY macro is used to define information about an
   OBJECT IDENTIFIER assignment.  All administrative OBJECT IDENTIFIER
   assignments which define a type identification value (see
   AutonomousType, a textual convention defined in [3]) should be
   defined via the OBJECT-IDENTITY macro.  It should be noted that the
   expansion of the OBJECT-IDENTITY macro is something which
   conceptually happens during implementation and not during run-time.

6.1.  Mapping of the STATUS clause

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


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   The value "current" means that the definition is current and valid.
   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.

6.2.  Mapping of the DESCRIPTION clause

   The DESCRIPTION clause, which must be present, contains a textual
   description of the object assignment.

6.3.  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.

6.4.  Mapping of the OBJECT-IDENTITY value

   The value of an invocation of the OBJECT-IDENTITY macro is an OBJECT
   IDENTIFIER.

6.5.  Usage Example

   Consider how an OBJECT IDENTIFIER assignment might be made:  e.g.,

   fizbin69 OBJECT-IDENTITY
       STATUS  current
       DESCRIPTION
               "The authoritative identity of the Fizbin 69 chipset."
      ::= { fizbinChipSets 1 }

7.  Mapping of the OBJECT-TYPE macro

   The OBJECT-TYPE macro is used to define a type of managed object.  It
   should be noted that the expansion of the OBJECT-TYPE macro is
   something which conceptually happens during implementation and not
   during run-time.

   For leaf objects which are not columnar objects (i.e., not contained
   within a conceptual table), instances of the object are identified by
   appending a sub-identifier of zero to the name of that object.
   Otherwise, the INDEX clause of the conceptual row object superior to
   a columnar object defines instance identification information.




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7.1.  Mapping of the SYNTAX clause

   The SYNTAX clause, which must be present, defines the abstract data
   structure corresponding to that object.  The data structure must be
   one of the following: a base type, the BITS construct, or a textual
   convention.  (SEQUENCE OF and SEQUENCE are also possible for
   conceptual tables, see section 7.1.12).  The base types are those
   defined in the ObjectSyntax CHOICE.  A textual convention is a
   newly-defined type defined as a sub-type of a base type [3].

   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 this memo.

   The semantics of ObjectSyntax are now described.

7.1.1.  Integer32 and INTEGER

   The Integer32 type represents integer-valued information between
   -2^31 and 2^31-1 inclusive (-2147483648 to 2147483647 decimal).  This
   type is indistinguishable from the INTEGER type.  Both the INTEGER
   and Integer32 types may be sub-typed to be more constrained than the
   Integer32 type.

   The INTEGER type (but not the Integer32 type) may also be used to
   represent integer-valued information as named-number enumerations.
   In this case, only those named-numbers so enumerated may be present
   as a value.  Note that although it is recommended that enumerated
   values start at 1 and be numbered contiguously, any valid value for
   Integer32 is allowed for an enumerated value and, further, enumerated
   values needn't be contiguously assigned.

   Finally, a label for a named-number enumeration must consist of one
   or more letters or digits, up to a maximum of 64 characters, and the
   initial character must be a lower-case letter.  (However, labels
   longer than 32 characters are not recommended.)  Note that hyphens
   are not allowed by this specification (except for use by information
   modules converted from SMIv1 which did allow hyphens).

7.1.2.  OCTET STRING

   The OCTET STRING type represents arbitrary binary or textual data.
   Although the SMI-specified size limitation for this type is 65535
   octets, MIB designers should realize that there may be implementation
   and interoperability limitations for sizes in excess of 255 octets.


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7.1.3.  OBJECT IDENTIFIER

   The OBJECT IDENTIFIER type represents administratively assigned
   names.  Any instance of this type may have at most 128 sub-
   identifiers.  Further, each sub-identifier must not exceed the value
   2^32-1 (4294967295 decimal).

7.1.4.  The BITS construct

   The BITS construct represents an enumeration of named bits.  This
   collection is assigned non-negative, contiguous (but see below)
   values, starting at zero.  Only those named-bits so enumerated may be
   present in a value.  (Thus, enumerations must be assigned to
   consecutive bits; however, see Section 9 for refinements of an object
   with this syntax.)

   As part of updating an information module, for an object defined
   using the BITS construct, new enumerations can be added or existing
   enumerations can have new labels assigned to them.  After an
   enumeration is added, it might not be possible to distinguish between
   an implementation of the updated object for which the new enumeration
   is not asserted, and an implementation of the object prior to the
   addition.  Depending on the circumstances, such an ambiguity could
   either be desirable or could be undesirable.  The means to avoid such
   an ambiguity is dependent on the encoding of values on the wire;
   however, one possibility is to define new enumerations starting at
   the next multiple of eight bits.  (Of course, this can also result in
   the enumerations no longer being contiguous.)

   Although there is no SMI-specified limitation on the number of
   enumerations (and therefore on the length of a value), except as may
   be imposed by the limit on the length of an OCTET STRING, MIB
   designers should realize that there may be implementation and
   interoperability limitations for sizes in excess of 128 bits.

   Finally, a label for a named-number enumeration must consist of one
   or more letters or digits, up to a maximum of 64 characters, and the
   initial character must be a lower-case letter.  (However, labels
   longer than 32 characters are not recommended.)  Note that hyphens
   are not allowed by this specification.

7.1.5.  IpAddress

   The IpAddress type represents a 32-bit internet address.  It is
   represented as an OCTET STRING of length 4, in network byte-order.





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   Note that the IpAddress type is a tagged type for historical reasons.
   Network addresses should be represented using an invocation of the
   TEXTUAL-CONVENTION macro [3].

7.1.6.  Counter32

   The Counter32 type represents a non-negative integer which
   monotonically increases until it reaches a maximum value of 2^32-1
   (4294967295 decimal), when it wraps around and starts increasing
   again from zero.

   Counters have no defined "initial" value, and thus, a single value of
   a Counter has (in general) no information content.  Discontinuities
   in the monotonically increasing value normally occur at re-
   initialization of the management system, and at other times as
   specified in the description of an object-type using this ASN.1 type.
   If such other times can occur, for example, the creation of an object
   instance at times other than re-initialization, then a corresponding
   object should be defined, with an appropriate SYNTAX clause, to
   indicate the last discontinuity.  Examples of appropriate SYNTAX
   clause include:  TimeStamp (a textual convention defined in [3]),
   DateAndTime (another textual convention from [3]) or TimeTicks.

   The value of the MAX-ACCESS clause for objects with a SYNTAX clause
   value of Counter32 is either "read-only" or "accessible-for-notify".

   A DEFVAL clause is not allowed for objects with a SYNTAX clause value
   of Counter32.

7.1.7.  Gauge32

   The Gauge32 type represents a non-negative integer, which may
   increase or decrease, but shall never exceed a maximum value, nor
   fall below a minimum value.  The maximum value can not be greater
   than 2^32-1 (4294967295 decimal), and the minimum value can not be
   smaller than 0.  The value of a Gauge32 has its maximum value
   whenever the information being modeled is greater than or equal to
   its maximum value, and has its minimum value whenever the information
   being modeled is smaller than or equal to its minimum value.  If the
   information being modeled subsequently decreases below (increases
   above) the maximum (minimum) value, the Gauge32 also decreases
   (increases).  (Note that despite of the use of the term "latched" in
   the original definition of this type, it does not become "stuck" at
   its maximum or minimum value.)






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7.1.8.  TimeTicks

   The TimeTicks type represents a non-negative integer which represents
   the time, modulo 2^32 (4294967296 decimal), in hundredths of a second
   between two epochs.  When objects are defined which use this ASN.1
   type, the description of the object identifies both of the reference
   epochs.

   For example, [3] defines the TimeStamp textual convention which is
   based on the TimeTicks type.  With a TimeStamp, the first reference
   epoch is defined as the time when sysUpTime [5] was zero, and the
   second reference epoch is defined as the current value of sysUpTime.

   The TimeTicks type may not be sub-typed.

7.1.9.  Opaque

   The Opaque type is provided solely for backward-compatibility, and
   shall not be used for newly-defined object types.

   The Opaque type supports the capability to pass arbitrary ASN.1
   syntax.  A value is encoded using the ASN.1 Basic Encoding Rules [4]
   into a string of octets.  This, in turn, is encoded as an OCTET
   STRING, in effect "double-wrapping" the original ASN.1 value.

   Note that a conforming implementation need only be able to accept and
   recognize opaquely-encoded data.  It need not be able to unwrap the
   data and then interpret its contents.

   A requirement on "standard" MIB modules is that no object may have a
   SYNTAX clause value of Opaque.

7.1.10.  Counter64

   The Counter64 type represents a non-negative integer which
   monotonically increases until it reaches a maximum value of 2^64-1
   (18446744073709551615 decimal), when it wraps around and starts
   increasing again from zero.

   Counters have no defined "initial" value, and thus, a single value of
   a Counter has (in general) no information content.  Discontinuities
   in the monotonically increasing value normally occur at re-
   initialization of the management system, and at other times as
   specified in the description of an object-type using this ASN.1 type.
   If such other times can occur, for example, the creation of an object
   instance at times other than re-initialization, then a corresponding
   object should be defined, with an appropriate SYNTAX clause, to
   indicate the last discontinuity.  Examples of appropriate SYNTAX


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   clause are:  TimeStamp (a textual convention defined in [3]),
   DateAndTime (another textual convention from [3]) or TimeTicks.

   The value of the MAX-ACCESS clause for objects with a SYNTAX clause
   value of Counter64 is either "read-only" or "accessible-for-notify".

   A requirement on "standard" MIB modules is that the Counter64 type
   may be used only if the information being modeled would wrap in less
   than one hour if the Counter32 type was used instead.

   A DEFVAL clause is not allowed for objects with a SYNTAX clause value
   of Counter64.

7.1.11.  Unsigned32

   The Unsigned32 type represents integer-valued information between 0
   and 2^32-1 inclusive (0 to 4294967295 decimal).

7.1.12.  Conceptual Tables

   Management operations apply exclusively to scalar objects.  However,
   it is sometimes convenient for developers of management applications
   to impose an imaginary, tabular structure on an ordered collection of
   objects within the MIB.  Each such conceptual table contains zero or
   more rows, and each row may contain one or more scalar objects,
   termed columnar objects.  This conceptualization is formalized by
   using the OBJECT-TYPE macro to define both an object which
   corresponds to a table and an object which corresponds to a row in
   that table.  A conceptual table has SYNTAX of the form:

        SEQUENCE OF <EntryType>

   where <EntryType> refers to the SEQUENCE type of its subordinate
   conceptual row.  A conceptual row has SYNTAX of the form:

        <EntryType>

   where <EntryType> is a SEQUENCE type defined as follows:

        <EntryType> ::= SEQUENCE { <type1>, ... , <typeN> }

   where there is one <type> for each subordinate object, and each
   <type> is of the form:

        <descriptor> <syntax>

   where <descriptor> is the descriptor naming a subordinate object, and
   <syntax> has the value of that subordinate object's SYNTAX clause,


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   except that both sub-typing information and the named values for
   enumerated integers or the named bits for the BITS construct, are
   omitted from <syntax>.

   Further, a <type> is always present for every subordinate object.
   (The ASN.1 DEFAULT and OPTIONAL clauses are disallowed in the
   SEQUENCE definition.)  The MAX-ACCESS clause for conceptual tables
   and rows is "not-accessible".

7.1.12.1.  Creation and Deletion of Conceptual Rows

   For newly-defined conceptual rows which allow the creation of new
   object instances and/or the deletion of existing object instances,
   there should be one columnar object with a SYNTAX clause value of
   RowStatus (a textual convention defined in [3]) and a MAX-ACCESS
   clause value of read-create.  By convention, this is termed the
   status column for the conceptual row.

7.2.  Mapping of the UNITS clause

   This UNITS clause, which need not be present, contains a textual
   definition of the units associated with that object.

7.3.  Mapping of the MAX-ACCESS clause

   The MAX-ACCESS clause, which must be present, defines whether it
   makes "protocol sense" to read, write and/or create an instance of
   the object, or to include its value in a notification.  This is the
   maximal level of access for the object.  (This maximal level of
   access is independent of any administrative authorization policy.)

   The value "read-write" indicates that read and write access make
   "protocol sense", but create does not.  The value "read-create"
   indicates that read, write and create access make "protocol sense".
   The value "not-accessible" indicates an auxiliary object (see Section
   7.7).  The value "accessible-for-notify" indicates an object which is
   accessible only via a notification (e.g., snmpTrapOID [5]).

   These values are ordered, from least to greatest:  "not-accessible",
   "accessible-for-notify", "read-only", "read-write", "read-create".

   If any columnar object in a conceptual row has "read-create" as its
   maximal level of access, then no other columnar object of the same
   conceptual row may have a maximal access of "read-write".  (Note that
   "read-create" is a superset of "read-write".)





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7.4.  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.
   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.

7.5.  Mapping of the DESCRIPTION clause

   The DESCRIPTION clause, which must be present, contains a textual
   definition of that object 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.

7.6.  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.

7.7.  Mapping of the INDEX clause

   The INDEX clause, which must be present if that object corresponds to
   a conceptual row (unless an AUGMENTS clause is present instead), and
   must be absent otherwise, defines instance identification information
   for the columnar objects subordinate to that object.

   The instance identification information in an INDEX clause must
   specify object(s) such that value(s) of those object(s) will
   unambiguously distinguish a conceptual row.  The objects can be
   columnar objects from the same and/or another conceptual table, but
   must not be scalar objects.  Multiple occurrences of the same object
   in a single INDEX clause is strongly discouraged.

   The syntax of the objects in the INDEX clause indicate how to form
   the instance-identifier:

(1)  integer-valued (i.e., having INTEGER as its underlying primitive
     type):  a single sub-identifier taking the integer value (this
     works only for non-negative integers);



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(2)  string-valued, fixed-length strings (or variable-length preceded by
     the IMPLIED keyword):  `n' sub-identifiers, where `n' is the length
     of the string (each octet of the string is encoded in a separate
     sub-identifier);

(3)  string-valued, variable-length strings (not preceded by the IMPLIED
     keyword):  `n+1' sub-identifiers, where `n' is the length of the
     string (the first sub-identifier is `n' itself, following this,
     each octet of the string is encoded in a separate sub-identifier);

(4)  object identifier-valued (when preceded by the IMPLIED keyword):
     `n' sub-identifiers, where `n' is the number of sub-identifiers in
     the value (each sub-identifier of the value is copied into a
     separate sub-identifier);

(5)  object identifier-valued (when not preceded by the IMPLIED
     keyword):  `n+1' sub-identifiers, where `n' is the number of sub-
     identifiers in the value (the first sub-identifier is `n' itself,
     following this, each sub-identifier in the value is copied);

(6)  IpAddress-valued:  4 sub-identifiers, in the familiar a.b.c.d
     notation.

   Note that the IMPLIED keyword can only be present for an object
   having a variable-length syntax (e.g., variable-length strings or
   object identifier-valued objects), Further, the IMPLIED keyword can
   only be associated with the last object in the INDEX clause.
   Finally, the IMPLIED keyword may not be used on a variable-length
   string object if that string might have a value of zero-length.

   Since a single value of a Counter has (in general) no information
   content (see section 7.1.6 and 7.1.10), objects defined using the
   syntax, Counter32 or Counter64, must not be specified in an INDEX

   clause. If an object defined using the BITS construct is used in an
   INDEX clause, it is considered a variable-length string.

   Instances identified by use of integer-valued objects should be
   numbered starting from one (i.e., not from zero).  The use of zero as
   a value for an integer-valued index object should be avoided, except
   in special cases.

   Objects which are both specified in the INDEX clause of a conceptual
   row and also columnar objects of the same conceptual row are termed
   auxiliary objects.  The MAX-ACCESS clause for auxiliary objects is
   "not-accessible", except in the following circumstances:




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(1)  within a MIB module originally written to conform to SMIv1, and
     later converted to conform to SMIv2; or

(2)  a conceptual row must contain at least one columnar object which is
     not an auxiliary object.  In the event that all of a conceptual
     row's columnar objects are also specified in its INDEX clause, then
     one of them must be accessible, i.e., have a MAX-ACCESS clause of
     "read-only". (Note that this situation does not arise for a
     conceptual row allowing create access, since such a row will have a
     status column which will not be an auxiliary object.)

   Note that objects specified in a conceptual row's INDEX clause need
   not be columnar objects of that conceptual row.  In this situation,
   the DESCRIPTION clause of the conceptual row must include a textual
   explanation of how the objects which are included in the INDEX clause
   but not columnar objects of that conceptual row, are used in uniquely
   identifying instances of the conceptual row's columnar objects.

7.8.  Mapping of the AUGMENTS clause

   The AUGMENTS clause, which must not be present unless the object
   corresponds to a conceptual row, is an alternative to the INDEX
   clause.  Every object corresponding to a conceptual row has either an
   INDEX clause or an AUGMENTS clause.

   If an object corresponding to a conceptual row has an INDEX clause,
   that row is termed a base conceptual row; alternatively, if the
   object has an AUGMENTS clause, the row is said to be a conceptual row
   augmentation, where the AUGMENTS clause names the object
   corresponding to the base conceptual row which is augmented by this
   conceptual row augmentation.  (Thus, a conceptual row augmentation
   cannot itself be augmented.)  Instances of subordinate columnar
   objects of a conceptual row augmentation are identified according to
   the INDEX clause of the base conceptual row corresponding to the
   object named in the AUGMENTS clause.  Further, instances of
   subordinate columnar objects of a conceptual row augmentation exist
   according to the same semantics as instances of subordinate columnar
   objects of the base conceptual row being augmented.  As such, note
   that creation of a base conceptual row implies the correspondent
   creation of any conceptual row augmentations.

   For example, a MIB designer might wish to define additional columns
   in an "enterprise-specific" MIB which logically extend a conceptual
   row in a "standard" MIB.  The "standard" MIB definition of the
   conceptual row would include the INDEX clause and the "enterprise-
   specific" MIB would contain the definition of a conceptual row using
   the AUGMENTS clause.  On the other hand, it would be incorrect to use
   the AUGMENTS clause for the relationship between RFC 2233's ifTable


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   and the many media-specific MIBs which extend it for specific media
   (e.g., the dot3Table in RFC 2358), since not all interfaces are of
   the same media.

   Note that a base conceptual row may be augmented by multiple
   conceptual row augmentations.

7.8.1.  Relation between INDEX and AUGMENTS clauses

   When defining instance identification information for a conceptual
   table:

(1)  If there is a one-to-one correspondence between the conceptual rows
     of this table and an existing table, then the AUGMENTS clause
     should be used.

(2)  Otherwise, if there is a sparse relationship between the conceptual
     rows of this table and an existing table, then an INDEX clause
     should be used which is identical to that in the existing table.
     For example, the relationship between RFC 2233's ifTable and a
     media-specific MIB which extends the ifTable for a specific media
     (e.g., the dot3Table in RFC 2358), is a sparse relationship.

(3)  Otherwise, if no existing objects have the required syntax and
     semantics, then auxiliary objects should be defined within the
     conceptual row for the new table, and those objects should be used
     within the INDEX clause for the conceptual row.

7.9.  Mapping of the DEFVAL clause

   The DEFVAL clause, which need not be present, defines an acceptable
   default value which may be used at the discretion of an agent when an
   object instance is created.  That is, the value is a "hint" to
   implementors.

   During conceptual row creation, if an instance of a columnar object
   is not present as one of the operands in the correspondent management
   protocol set operation, then the value of the DEFVAL clause, if
   present, indicates an acceptable default value that an agent might
   use (especially for a read-only object).

   Note that with this definition of the DEFVAL clause, it is
   appropriate to use it for any columnar object of a read-create table.
   It is also permitted to use it for scalar objects dynamically created
   by an agent, or for columnar objects of a read-write table
   dynamically created by an agent.




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   The value of the DEFVAL clause must, of course, correspond to the
   SYNTAX clause for the object.  If the value is an OBJECT IDENTIFIER,
   then it must be expressed as a single ASN.1 identifier, and not as a
   collection of sub-identifiers.

   Note that if an operand to the management protocol set operation is
   an instance of a read-only object, then the error `notWritable' [6]
   will be returned.  As such, the DEFVAL clause can be used to provide
   an acceptable default value that an agent might use.

   By way of example, consider the following possible DEFVAL clauses:

        ObjectSyntax       DEFVAL clause
        ----------------   ------------
        Integer32          DEFVAL { 1 }
                           -- same for Gauge32, TimeTicks, Unsigned32
        INTEGER            DEFVAL { valid } -- enumerated value
        OCTET STRING       DEFVAL { 'ffffffffffff'H }
        DisplayString      DEFVAL { "SNMP agent" }
        IpAddress          DEFVAL { 'c0210415'H } -- 192.33.4.21
        OBJECT IDENTIFIER  DEFVAL { sysDescr }
        BITS               DEFVAL { { primary, secondary } }
                           -- enumerated values that are set
        BITS               DEFVAL { { } }
                           -- no enumerated values are set

   A binary string used in a DEFVAL clause for an OCTET STRING must be
   either an integral multiple of eight or zero bits in length;
   similarly, a hexadecimal string must be an even number of hexadecimal
   digits.  The value of a character string used in a DEFVAL clause must
   not contain tab characters or line terminator characters.

   Object types with SYNTAX of Counter32 and Counter64 may not have
   DEFVAL clauses, since they do not have defined initial values.
   However, it is recommended that they be initialized to zero.

7.10.  Mapping of the OBJECT-TYPE value

   The value of an invocation of the OBJECT-TYPE macro is the name of
   the object, which is an OBJECT IDENTIFIER, an administratively
   assigned name.

   When an OBJECT IDENTIFIER is assigned to an object:

(1)  If the object corresponds to a conceptual table, then only a single
     assignment, that for a conceptual row, is present immediately
     beneath that object.  The administratively assigned name for the
     conceptual row object is derived by appending a sub-identifier of


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     "1" to the administratively assigned name for the conceptual table.

(2)  If the object corresponds to a conceptual row, then at least one
     assignment, one for each column in the conceptual row, is present
     beneath that object.  The administratively assigned name for each
     column is derived by appending a unique, positive sub-identifier to
     the administratively assigned name for the conceptual row.

(3)  Otherwise, no other OBJECT IDENTIFIERs which are subordinate to the
     object may be assigned.

   Note that the final sub-identifier of any administratively assigned
   name for an object shall be positive.  A zero-valued  final sub-
   identifier is reserved for future use.

7.11.  Usage Example

   Consider how one might define a conceptual table and its
   subordinates.  (This example uses the RowStatus textual convention
   defined in [3].)

   evalSlot OBJECT-TYPE
       SYNTAX      Integer32 (0..2147483647)
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The index number of the first unassigned entry in the
               evaluation table, or the value of zero indicating that
               all entries are assigned.

               A management station should create new entries in the
               evaluation table using this algorithm:  first, issue a
               management protocol retrieval operation to determine the
               value of evalSlot; and, second, issue a management
               protocol set operation to create an instance of the
               evalStatus object setting its value to createAndGo(4) or
               createAndWait(5).  If this latter operation succeeds,
               then the management station may continue modifying the
               instances corresponding to the newly created conceptual
               row, without fear of collision with other management
               stations."
      ::= { eval 1 }

   evalTable OBJECT-TYPE
       SYNTAX      SEQUENCE OF EvalEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION


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               "The (conceptual) evaluation table."
      ::= { eval 2 }

   evalEntry OBJECT-TYPE
       SYNTAX      EvalEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
               "An entry (conceptual row) in the evaluation table."
      INDEX   { evalIndex }
      ::= { evalTable 1 }

   EvalEntry ::=
       SEQUENCE {
           evalIndex       Integer32,
           evalString      DisplayString,
           evalValue       Integer32,
           evalStatus      RowStatus
       }

   evalIndex OBJECT-TYPE
       SYNTAX      Integer32 (1..2147483647)
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
               "The auxiliary variable used for identifying instances of
               the columnar objects in the evaluation table."
           ::= { evalEntry 1 }

   evalString OBJECT-TYPE
       SYNTAX      DisplayString
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
               "The string to evaluate."
           ::= { evalEntry 2 }

   evalValue OBJECT-TYPE
       SYNTAX      Integer32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The value when evalString was last evaluated, or zero if
                no such value is available."
       DEFVAL  { 0 }
           ::= { evalEntry 3 }

   evalStatus OBJECT-TYPE


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       SYNTAX      RowStatus
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
               "The status column used for creating, modifying, and
               deleting instances of the columnar objects in the
               evaluation table."
    DEFVAL  { active }
        ::= { evalEntry 4 }

8.  Mapping of the NOTIFICATION-TYPE macro

   The NOTIFICATION-TYPE macro is used to define the information
   contained within an unsolicited transmission of management
   information (i.e., within either a SNMPv2-Trap-PDU or InformRequest-
   PDU).  It should be noted that the expansion of the NOTIFICATION-TYPE
   macro is something which conceptually happens during implementation
   and not during run-time.

8.1.  Mapping of the OBJECTS clause

   The OBJECTS clause, which need not be present, defines an ordered
   sequence of MIB object types.  One and only one object instance for
   each occurrence of each object type must be present, and in the
   specified order, in every instance of the notification.  If the same
   object type occurs multiple times in a notification's ordered
   sequence, then an object instance is present for each of them.  An
   object type specified in this clause must not have an MAX-ACCESS
   clause of "not-accessible".  The notification's DESCRIPTION clause
   must specify the information/meaning conveyed by each occurrence of
   each object type in the sequence.  The DESCRIPTION clause must also
   specify which object instance is present for each object type in the
   notification.

   Note that an agent is allowed, at its own discretion, to append as
   many additional objects as it considers useful to the end of the
   notification (i.e., after the objects defined by the OBJECTS clause).

8.2.  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.
   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


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   interoperability with older/existing implementations.

8.3.  Mapping of the DESCRIPTION clause

   The DESCRIPTION clause, which must be present, contains a textual
   definition of the notification 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 notification.  In
   particular, the DESCRIPTION clause should document which instances of
   the objects mentioned in the OBJECTS clause should be contained
   within notifications of this type.

8.4.  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.

8.5.  Mapping of the NOTIFICATION-TYPE value

   The value of an invocation of the NOTIFICATION-TYPE macro is the name
   of the notification, which is an OBJECT IDENTIFIER, an
   administratively assigned name.  In order to achieve compatibility
   with SNMPv1 traps, both when converting SMIv1 information modules
   to/from this SMI, and in the procedures employed by multi-lingual
   systems and proxy forwarding applications, the next to last sub-
   identifier in the name of any newly-defined notification must have
   the value zero.

   Sections 4.2.6 and 4.2.7 of [6] describe how the NOTIFICATION-TYPE
   macro is used to generate a SNMPv2-Trap-PDU or InformRequest-PDU,
   respectively.

8.6.  Usage Example

   Consider how a configuration change notification might be described:

   entityMIBTraps      OBJECT IDENTIFIER ::= { entityMIB 2 }
   entityMIBTrapPrefix OBJECT IDENTIFIER ::= { entityMIBTraps 0 }

   entConfigChange NOTIFICATION-TYPE
       STATUS             current
       DESCRIPTION
               "An entConfigChange trap is sent when the value of
               entLastChangeTime changes. It can be utilized by an NMS to
               trigger logical/physical entity table maintenance polls.


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               An agent must not generate more than one entConfigChange
               'trap-event' in a five second period, where a 'trap-event'
               is the transmission of a single trap PDU to a list of
               trap destinations.  If additional configuration changes
               occur within the five second 'throttling' period, then
               these trap-events should be suppressed by the agent. An
               NMS should periodically check the value of
               entLastChangeTime to detect any missed entConfigChange
               trap-events, e.g. due to throttling or transmission loss."
      ::= { entityMIBTrapPrefix 1 }

   According to this invocation, the notification authoritatively
   identified as

        { entityMIBTrapPrefix 1 }

   is used to report a particular type of configuration change.

9.  Refined Syntax

   Some macros have clauses which allows syntax to be refined,
   specifically: the SYNTAX clause of the OBJECT-TYPE macro, and the
   SYNTAX/WRITE-SYNTAX clauses of the MODULE-COMPLIANCE and AGENT-
   CAPABILITIES macros [2].  However, not all refinements of syntax are
   appropriate.  In particular, the object's primitive or application
   type must not be changed.

   Further, the following restrictions apply:

                          Restrictions to Refinement of
     object syntax         range   enumeration     size
     -----------------     -----   -----------     ----
               INTEGER      (1)        (2)           -
             Integer32      (1)         -            -
            Unsigned32      (1)         -            -
          OCTET STRING       -          -           (3)
     OBJECT IDENTIFIER       -          -            -
                  BITS       -         (2)           -
             IpAddress       -          -            -
             Counter32       -          -            -
             Counter64       -          -            -
               Gauge32      (1)         -            -
             TimeTicks       -          -            -

  where:




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(1)  the range of permitted values may be refined by raising the lower-
     bounds, by reducing the upper-bounds, and/or by reducing the
     alternative value/range choices;

(2)  the enumeration of named-values may be refined by removing one or
     more named-values (note that for BITS, a refinement may cause the
     enumerations to no longer be contiguous); or,

(3)  the size in octets of the value may be refined by raising the
     lower-bounds, by reducing the upper-bounds, and/or by reducing the
     alternative size choices.

   No other types of refinements can be specified in the SYNTAX clause.
   However, the DESCRIPTION clause is available to specify additional
   restrictions which can not be expressed in the SYNTAX clause.
   Further details on (and examples of) sub-typing are provided in
   Appendix A.

10.  Extending an Information Module

   As experience is gained with an information module, it may be
   desirable to revise that information module.  However, changes are
   not allowed if they have any potential to cause interoperability
   problems "over the wire" between an implementation using an original
   specification and an implementation using an updated
   specification(s).

   For any change, the invocation of the MODULE-IDENTITY macro must be
   updated to include information about the revision: specifically,
   updating the LAST-UPDATED clause, adding a pair of REVISION and
   DESCRIPTION clauses (see section 5.5), and making any necessary
   changes to existing clauses, including the ORGANIZATION and CONTACT-
   INFO clauses.

   Note that any definition contained in an information module is
   available to be IMPORT-ed by any other information module, and is
   referenced in an IMPORTS clause via the module name.  Thus, a module
   name should not be changed.  Specifically, the module name (e.g.,
   "FIZBIN-MIB" in the example of Section 5.7) should not be changed
   when revising an information module (except to correct typographical
   errors), and definitions should not be moved from one information
   module to another.

   Also note that obsolete definitions must not be removed from MIB
   modules since their descriptors may still be referenced by other
   information modules, and the OBJECT IDENTIFIERs used to name them
   must never be re-assigned.



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10.1.  Object Assignments

   If any non-editorial change is made to any clause of a object
   assignment, then the OBJECT IDENTIFIER value associated with that
   object assignment must also be changed, along with its associated
   descriptor.

10.2.  Object Definitions

   An object definition may be revised in any of the following ways:

(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)  The value of a SYNTAX clause may be replaced by a textual
     convention, providing the textual convention is defined to use the
     same primitive ASN.1 type, has the same set of values, and has
     identical semantics.

(3)  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.

(4)  A DEFVAL clause may be added or updated.

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

(6)  A UNITS clause may be added.

(7)  A conceptual row may be augmented by adding new columnar objects at
     the end of the row, and making the corresponding update to the
     SEQUENCE definition.

(8)  Clarifications and additional information may be included in the
     DESCRIPTION clause.

(9)  Entirely new objects may be defined, named with previously
     unassigned OBJECT IDENTIFIER values.

   Otherwise, if the semantics of any previously defined object are
   changed (i.e., if a non-editorial change is made to any clause other
   than those specifically allowed above), then the OBJECT IDENTIFIER
   value associated with that object must also be changed.




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   Note that changing the descriptor associated with an existing object
   is considered a semantic change, as these strings may be used in an
   IMPORTS statement.

10.3.  Notification Definitions

   A notification definition may be revised in any of the following
   ways:

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

(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 DESCRIPTION clause may be clarified.

   Otherwise, if the semantics of any previously defined notification
   are changed (i.e., if a non-editorial change is made to any clause
   other those specifically allowed above), then the OBJECT IDENTIFIER
   value associated with that notification must also be changed.

   Note that changing the descriptor associated with an existing
   notification is considered a semantic change, as these strings may be
   used in an IMPORTS statement.
























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11.  Appendix A: Detailed Sub-typing Rules


11.1.  Syntax Rules

   The syntax rules for sub-typing are given below.  Note that while
   this syntax is based on ASN.1, it includes some extensions beyond
   what is allowed in ASN.1, and a number of ASN.1 constructs are not
   allowed by this syntax.

        <integerSubType>
            ::= <empty>
              | "(" <range> ["|" <range>]... ")"

        <octetStringSubType>
            ::= <empty>
              | "(" "SIZE" "(" <range> ["|" <range>]... ")" ")"

        <range>
            ::= <value>
              | <value> ".." <value>

        <value>
            ::= "-" <number>
              | <number>
              | <hexString>
              | <binString>

        where:
            <empty>     is the empty string
            <number>    is a non-negative integer
            <hexString> is a hexadecimal string (e.g., '0F0F'H)
            <binString> is a binary string (e.g, '1010'B)

            <range> is further restricted as follows:
                - any <value> used in a SIZE clause must be non-negative.
                - when a pair of values is specified, the first value
                  must be less than the second value.
                - when multiple ranges are specified, the ranges may
                  not overlap but may touch. For example, (1..4 | 4..9)
                  is invalid, and (1..4 | 5..9) is valid.
                - the ranges must be a subset of the maximum range of the
                  base type.







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11.2.  Examples

   Some examples of legal sub-typing:

            Integer32 (-20..100)
            Integer32 (0..100 | 300..500)
            Integer32 (300..500 | 0..100)
            Integer32 (0 | 2 | 4 | 6 | 8 | 10)
            OCTET STRING (SIZE(0..100))
            OCTET STRING (SIZE(0..100 | 300..500))
            OCTET STRING (SIZE(0 | 2 | 4 | 6 | 8 | 10))
            SYNTAX   TimeInterval (0..100)
            SYNTAX   DisplayString (SIZE(0..32))

   (Note the last two examples above are not valid in a TEXTUAL
   CONVENTION, see [3].)

   Some examples of illegal sub-typing:

        Integer32 (150..100)         -- first greater than second
        Integer32 (0..100 | 50..500) -- ranges overlap
        Integer32 (0 | 2 | 0 )       -- value duplicated
        Integer32 (MIN..-1 | 1..MAX) -- MIN and MAX not allowed
        Integer32 (SIZE (0..34))     -- must not use SIZE
        OCTET STRING (0..100)        -- must use SIZE
        OCTET STRING (SIZE(-10..100)) -- negative SIZE

12.  Security Considerations

   This document defines a language with which to write and read
   descriptions of management information.  The language itself has no
   security impact on the Internet.



13.  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






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   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


14.  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, "Conformance Statements for SMIv2", STD 58,
     RFC 2580, April 1999.

[3]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M.
     and S. Waldbusser, "Textual Conventions for SMIv2", STD 58,
     RFC 2579, April 1999.

[4]  Information processing systems - Open Systems Interconnection -
     Specification of Basic Encoding Rules for Abstract Syntax Notation
     One (ASN.1), International Organization for Standardization.
     International Standard 8825, (December, 1987).

[5]  The SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M. and
     S. Waldbusser, "Management Information Base for Version 2 of the
     Simple Network Management Protocol (SNMPv2)", RFC 1907, January
     1996.

[6]  The SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M. and
     S. Waldbusser, "Protocol Operations for Version 2 of the Simple
     Network Management Protocol (SNMPv2)", RFC 1905, January 1996.





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15.  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
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McCloghrie, et al.          Standards Track                    [Page 43]