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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

McCloghrie, et al. Standards Track [Page 1]

RFC 2578 SMIv2 April 1999

 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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RFC 2578 SMIv2 April 1999

 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.

McCloghrie, et al. Standards Track [Page 3]

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))

  1. - format is YYMMDDHHMMZ or YYYYMMDDHHMMZ

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RFC 2578 SMIv2 April 1999

  1. - where: YY - last two digits of year (only years
  2. - between 1900-1999)
  3. - YYYY - last four digits of the year (any year)
  4. - MM - month (01 through 12)
  5. - DD - day of month (01 through 31)
  6. - HH - hours (00 through 23)
  7. - MM - minutes (00 through 59)
  8. - Z - denotes GMT (the ASCII character Z)
  9. -
  10. - For example, "9502192015Z" and "199502192015Z" represent
  11. - 8:15pm GMT on 19 February 1995. Years after 1999 must use
  12. - the four digit year format. Years 1900-1999 may use the
  13. - 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
  1. - 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
  1. - 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,
  1. - note that SEQUENCEs for conceptual tables and
  2. - 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),
  1. - OCTET STRINGs with a more restrictive size
  2. - 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
  1. - 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
  1. - 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].

McCloghrie, et al. Standards Track [Page 11]

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].)

McCloghrie, et al. Standards Track [Page 12]

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:
  1. any 7-bit displayable ASCII characters except quote ("),
  2. tab characters,
  3. spaces, and
  4. 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:
  1. named types defined by ASN.1 itself, specifically: INTEGER,

OCTET STRING, OBJECT IDENTIFIER, SEQUENCE, SEQUENCE OF type,

  1. 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.

McCloghrie, et al. Standards Track [Page 14]

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:

McCloghrie, et al. Standards Track [Page 15]

RFC 2578 SMIv2 April 1999

        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:

McCloghrie, et al. Standards Track [Page 16]

RFC 2578 SMIv2 April 1999

      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

McCloghrie, et al. Standards Track [Page 31]

RFC 2578 SMIv2 April 1999

   "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

McCloghrie, et al. Standards Track [Page 32]

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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

McCloghrie, et al. Standards Track [Page 34]

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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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RFC 2578 SMIv2 April 1999

             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:

McCloghrie, et al. Standards Track [Page 36]

RFC 2578 SMIv2 April 1999

(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.

McCloghrie, et al. Standards Track [Page 37]

RFC 2578 SMIv2 April 1999

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.

McCloghrie, et al. Standards Track [Page 38]

RFC 2578 SMIv2 April 1999

 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.

McCloghrie, et al. Standards Track [Page 39]

RFC 2578 SMIv2 April 1999

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.

McCloghrie, et al. Standards Track [Page 40]

RFC 2578 SMIv2 April 1999

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

McCloghrie, et al. Standards Track [Page 41]

RFC 2578 SMIv2 April 1999

 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.

McCloghrie, et al. Standards Track [Page 42]

RFC 2578 SMIv2 April 1999

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
 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 43]

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