path: root/doc/rfc/rfc1442.txt

          Network Working Group                                  J. Case
          Request for Comments: 1442                 SNMP Research, Inc.
                                                           K. McCloghrie
                                                      Hughes LAN Systems
                                                                 M. Rose
                                            Dover Beach Consulting, Inc.
                                                           S. Waldbusser
                                              Carnegie Mellon University
                                                              April 1993


                       Structure of Management Information
                               for version 2 of the
                   Simple Network Management Protocol (SNMPv2)


          Status of this Memo

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


          Table of Contents


          1 Introduction ..........................................    2
          1.1 A Note on Terminology ...............................    3
          2 Definitions ...........................................    4
          3.1 The MODULE-IDENTITY macro ...........................    5
          3.2 Object Names and Syntaxes ...........................    7
          3.3 The OBJECT-TYPE macro ...............................   10
          3.5 The NOTIFICATION-TYPE macro .........................   12
          3 Information Modules ...................................   13
          3.1 Macro Invocation ....................................   13
          3.1.1 Textual Clauses ...................................   14
          3.2 IMPORTing Symbols ...................................   14
          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 ..................   17
          5.4 Mapping of the DESCRIPTION clause ...................   17
          5.5 Mapping of the REVISION clause ......................   17
          5.6 Mapping of the DESCRIPTION clause ...................   18
          5.7 Mapping of the MODULE-IDENTITY value ................   18
          5.8 Usage Example .......................................   19



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          6 Mapping of the OBJECT-IDENTITY macro ..................   20
          6.1 Mapping of the STATUS clause ........................   20
          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 .......................................   21
          7 Mapping of the OBJECT-TYPE macro ......................   22
          7.1 Mapping of the SYNTAX clause ........................   22
          7.1.1 Integer32 and INTEGER .............................   22
          7.1.2 OCTET STRING ......................................   23
          7.1.3 OBJECT IDENTIFIER .................................   23
          7.1.4 BIT STRING ........................................   23
          7.1.5 IpAddress .........................................   23
          7.1.6 Counter32 .........................................   24
          7.1.7 Gauge32 ...........................................   24
          7.1.8 TimeTicks .........................................   24
          7.1.9 Opaque ............................................   25
          7.1.10 NsapAddress ......................................   25
          7.1.11 Counter64 ........................................   26
          7.1.12 UInteger32 .......................................   26
          7.2 Mapping of the UNITS clause .........................   26
          7.3 Mapping of the MAX-ACCESS clause ....................   27
          7.4 Mapping of the STATUS clause ........................   27
          7.5 Mapping of the DESCRIPTION clause ...................   27
          7.6 Mapping of the REFERENCE clause .....................   28
          7.7 Mapping of the INDEX clause .........................   28
          7.7.1 Creation and Deletion of Conceptual Rows ..........   30
          7.8 Mapping of the AUGMENTS clause ......................   31
          7.8.1 Relation between INDEX and AUGMENTS clauses .......   31
          7.9 Mapping of the DEFVAL clause ........................   32
          7.10 Mapping of the OBJECT-TYPE value ...................   33
          7.11 Usage Example ......................................   35
          8 Mapping of the NOTIFICATION-TYPE macro ................   37
          8.1 Mapping of the OBJECTS clause .......................   37
          8.2 Mapping of the STATUS clause ........................   37
          8.3 Mapping of the DESCRIPTION clause ...................   37
          8.4 Mapping of the REFERENCE clause .....................   37
          8.5 Mapping of the NOTIFICATION-TYPE value ..............   38
          8.6 Usage Example .......................................   39
          9 Refined Syntax ........................................   40
          10 Extending an Information Module ......................   41
          10.1 Object Assignments .................................   41
          10.2 Object Definitions .................................   41
          10.3 Notification Definitions ...........................   42



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          11 Appendix: de-OSIfying a MIB module ...................   43
          11.1 Managed Object Mapping .............................   43
          11.1.1 Mapping to the SYNTAX clause .....................   44
          11.1.2 Mapping to the UNITS clause ......................   45
          11.1.3 Mapping to the MAX-ACCESS clause .................   45
          11.1.4 Mapping to the STATUS clause .....................   45
          11.1.5 Mapping to the DESCRIPTION clause ................   45
          11.1.6 Mapping to the REFERENCE clause ..................   45
          11.1.7 Mapping to the INDEX clause ......................   45
          11.1.8 Mapping to the DEFVAL clause .....................   45
          11.2 Action Mapping .....................................   46
          11.2.1 Mapping to the SYNTAX clause .....................   46
          11.2.2 Mapping to the MAX-ACCESS clause .................   46
          11.2.3 Mapping to the STATUS clause .....................   46
          11.2.4 Mapping to the DESCRIPTION clause ................   46
          11.2.5 Mapping to the REFERENCE clause ..................   46
          11.3 Event Mapping ......................................   46
          11.3.1 Mapping to the STATUS clause .....................   47
          11.3.2 Mapping to the DESCRIPTION clause ................   47
          11.3.3 Mapping to the REFERENCE clause ..................   47
          12 Acknowledgements .....................................   48
          13 References ...........................................   52
          14 Security Considerations ..............................   54
          15 Authors' Addresses ...................................   54

























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          1.  Introduction

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

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

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

          The SMI is divided into three parts: module definitions,
          object definitions, and, trap 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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          1.1.  A Note on Terminology

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











































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          2.  Definitions

          SNMPv2-SMI DEFINITIONS ::= BEGIN


          -- the path to the root

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

          directory      OBJECT IDENTIFIER ::= { internet 1 }

          mgmt           OBJECT IDENTIFIER ::= { internet 2 }

          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 }




















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          -- definitions for information modules

          MODULE-IDENTITY MACRO ::=
          BEGIN
              TYPE NOTATION ::=
                            "LAST-UPDATED" value(Update UTCTime)
                            "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 UTCTime)
                            "DESCRIPTION" Text

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























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

              VALUE NOTATION ::=
                            value(VALUE OBJECT IDENTIFIER)

              Status ::=
                            "current"
                          | "obsolete"

              ReferPart ::=
                          "REFERENCE" Text
                        | empty

              Text ::= """" string """"
          END






























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          -- names of objects

          ObjectName ::=
              OBJECT IDENTIFIER


          -- syntax of objects

          ObjectSyntax ::=
              CHOICE {
                  simple
                      SimpleSyntax,

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

                  application-wide
                      ApplicationSyntax
              }


          -- built-in ASN.1 types

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

                  string-value
                      OCTET STRING,

                  objectID-value
                      OBJECT IDENTIFIER,

                  -- only the enumerated form is allowed
                  bit-value
                      BIT STRING
              }










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          -- indistinguishable from INTEGER, but never needs more than
          -- 32-bits for a two's complement representation
          Integer32 ::=
              [UNIVERSAL 2]
                  IMPLICIT INTEGER (-2147483648..2147483647)


          -- application-wide types

          ApplicationSyntax ::=
              CHOICE {
                  ipAddress-value
                      IpAddress,

                  counter-value
                      Counter32,

                  gauge-value
                      Gauge32,

                  timeticks-value
                      TimeTicks,

                  arbitrary-value
                      Opaque,

                  nsapAddress-value
                      NsapAddress,

                  big-counter-value
                      Counter64,

                  unsigned-integer-value
                      UInteger32
              }

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









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

          -- this doesn't wrap
          Gauge32 ::=
              [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 OSI NSAP addresses
          -- (this is a tagged type for historical reasons)
          NsapAddress ::=
              [APPLICATION 5]
                  IMPLICIT OCTET STRING (SIZE (1 | 4..21))

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

          -- an unsigned 32-bit quantity
          UInteger32 ::=
              [APPLICATION 7]
                  IMPLICIT INTEGER (0..4294967295)















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          -- definition for objects

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

              VALUE NOTATION ::=
                            value(VALUE ObjectName)

              UnitsPart ::=
                            "UNITS" Text
                          | empty

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

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

              ReferPart ::=
                            "REFERENCE" Text
                          | empty

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







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              IndexType ::=
                            "IMPLIED" Index
                          | Index
              Index ::=
                              -- use the SYNTAX value of the
                              -- correspondent OBJECT-TYPE invocation
                            value(Indexobject ObjectName)
              Entry ::=
                              -- use the INDEX value of the
                              -- correspondent OBJECT-TYPE invocation
                            value(Entryobject ObjectName)

              DefValPart ::=
                            "DEFVAL" "{" value(Defval Syntax) "}"
                          | empty

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































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          -- definitions for notifications

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

              VALUE NOTATION ::=
                            value(VALUE OBJECT IDENTIFIER)

              ObjectsPart ::=
                            "OBJECTS" "{" Objects "}"
                          | empty
              Objects ::=
                            Object
                          | Objects "," Object
              Object ::=
                            value(Name ObjectName)

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

              ReferPart ::=
                          "REFERENCE" Text
                        | empty

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


          END













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          3.  Information Modules

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

          The SMI describes how to use a subset of ASN.1 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].

          This classification scheme does not imply a rigid taxonomy.
          For example, a "standard" information module might 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.

          All information modules start with exactly one invocation of
          the MODULE-IDENTITY macro, which provides contact and revision
          history.  This invocation must appear immediately after any
          IMPORTs or EXPORTs 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>





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          names the macro being invoked, and <clauses> and <value>
          depend on the definition of the macro.

          An ASN.1 identifier consists of one or more letters, digits,
          or hyphens.  The initial character must be a lower-case
          letter, and the final character may not be a hyphen.  Further,
          a hyphen may not be immediatedly followed by another hyphen.

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

          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 Clauses

          Some clauses in a macro invocation may take a textual value
          (e.g., the DESCRIPTION clause).  Note that, in order to
          conform to the ASN.1 syntax, the entire value of these clauses
          must be enclosed in double quotation marks, and therefore
          cannot itself contain double quotation marks, although the
          value may be multi-line.


          3.2.  IMPORTing Symbols

          To reference an external object, the IMPORTS statement must be
          used to identify both the descriptor and the module defining
          the descriptor.

          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





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          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 even when there is no
          collision when IMPORTing symbols.

          Finally, the IMPORTS statement may not be used to import an
          ASN.1 named type which corresponds to either the SEQUENCE or
          SEQUENCE OF type.




































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          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:

               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.














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          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.


          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.


          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 made to this information
          module, in reverse chronological order.  Each instance of this
          clause contains the date and time of the revision.






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          5.6.  Mapping of the DESCRIPTION clause

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


          5.7.  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 referring to the information module containing the
          invocation.





































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          5.8.  Usage Example

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

          FIZBIN-MIB DEFINITIONS ::= BEGIN

          IMPORTS
              MODULE-IDENTITY, OBJECT-TYPE, experimental
                  FROM SNMPv2-SMI;


          fizbin MODULE-IDENTITY
              LAST-UPDATED "9210070433Z"
              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      "9210070433Z"
              DESCRIPTION
                      "Initial version of this MIB module."
          -- contact IANA for actual number
              ::= { experimental xx }


          END













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          6.  Mapping of the OBJECT-IDENTITY macro

          The OBJECT-IDENTITY macro is used to define information about
          an OBJECT IDENTIFIER assignment.  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.

          The values "current", and "obsolete" are self-explanatory.


          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 an object assignment defined in
          some other information module.


          6.4.  Mapping of the OBJECT-IDENTITY value

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
















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          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 }







































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          7.  Mapping of the OBJECT-TYPE macro

          The OBJECT-TYPE macro is used to define a 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.


          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 alternatives defined in the
          ObjectSyntax CHOICE.

          Full ASN.1 sub-typing is allowed, as appropriate to the
          underingly ASN.1 type, primarily as an aid to implementors in
          understanding the meaning of the object.  Any such restriction
          on size, range, enumerations or repertoire specified in this
          clause represents the maximal level of support which makes
          "protocol sense".  Of course, sub-typing is not allowed for
          the Counter32 or Counter64 types, but is allowed for the
          Gauge32 type.

          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.

          The INTEGER type may also be used to represent integer-valued
          information, if it contains named-number enumerations, or if
          it is sub-typed to be more constrained than the Integer32
          type.  In the former 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.







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          Finally, the hyphen character is not allowed as a part of the
          label name for any named-number enumeration.


          7.1.2.  OCTET STRING

          The OCTET STRING type represents arbitrary binary or textual
          data.  Although there is no SMI-specified size limitation for
          this type, MIB designers should realize that there may be
          implementation and interoperability limitations for sizes in
          excess of 255 octets.


          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.  BIT STRING

          The BIT STRING type represents an enumeration of named bits.
          This collection is assigned non-negative, contiguous values,
          starting at zero.  Only those named-bits so enumerated may be
          present in a value.

          A requirement on "standard" MIB modules is that the hyphen
          character is not allowed as a part of the label name for any
          named-bit enumeration.


          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.

          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].








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          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 a SYNTAX clause value of TimeStamp (a textual
          convention defined in [3]) indicating the time of the last
          discontinuity.

          The value of the MAX-ACCESS clause for objects with a SYNTAX
          clause value of Counter32 is always "read-only".

          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.
          The maximum value can not be greater than 2^32-1 (4294967295
          decimal).  The value of a Gauge has its maximum value whenever
          the information being modeled is greater or equal to that
          maximum value; if the information being modeled subsequently
          decreases below the maximum value, the Gauge also decreases.


          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.






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          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 when MIB-II's sysUpTime
          [7] was zero, and the second reference epoch is defined as the
          current value of sysUpTime.


          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.  NsapAddress

          The NsapAddress type represents an OSI address as a variable-
          length OCTET STRING.  The first octet of the string contains a
          binary value in the range of 0..20, and indicates the length
          in octets of the NSAP.  Following the first octet, is the
          NSAP, expressed in concrete binary notation, starting with the
          most significant octet.  A zero-length NSAP is used as a
          "special" address meaning "the default NSAP" (analogous to the
          IP address of 0.0.0.0).  Such an NSAP is encoded as a single
          octet, containing the value 0.  All other NSAPs are encoded in
          at least 4 octets.

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








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          7.1.11.  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 a SYNTAX clause value of TimeStamp (a textual
          convention defined in [3]) indicating the time of the last
          discontinuity.

          The value of the MAX-ACCESS clause for objects with a SYNTAX
          clause value of Counter64 is always "read-only".

          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.


          7.1.12.  UInteger32

          The UInteger32 type represents integer-valued information
          between 0 and 2^32-1 inclusive (0 to 4294967295 decimal).


          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.









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          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.  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 either
          an auxiliary object (see Section 7.7) or an object which is
          accessible only via a notificationn (e.g., snmpTrapOID [5]).

          These values are ordered, from least to greatest: "not-
          accessible", "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".)


          7.4.  Mapping of the STATUS clause

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

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







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          7.6.  Mapping of the REFERENCE clause

          The REFERENCE clause, which need not be present, contains a
          textual cross-reference to an object defined in some other
          information module.  This is useful when de-osifying a MIB
          module produced by some other organization.


          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.

          Management operations apply exclusively to scalar objects.
          However, it is convenient for developers of management
          applications to impose imaginary, tabular structures on the
          ordered collection of objects that constitute 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





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          object, and <syntax> has the value of that subordinate
          object's SYNTAX clause, optionally omitting the sub-typing
          information.  Further, these ASN.1 types are always present
          (the DEFAULT and OPTIONAL clauses are disallowed in the
          SEQUENCE definition).  The MAX-ACCESS clause for conceptual
          tables and rows is "not-accessible".

          For leaf objects which are not columnar objects, 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.

          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 syntax
          of those objects indicate how to form the instance-identifier:

          (1)  integer-valued: a single sub-identifier taking the
               integer value (this works only for non-negative
               integers);

          (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: `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);

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

          (6)  NsapAddress-valued: `n' sub-identifiers, where `n' is the
               length of the value (each octet of the value is encoded
               in a separate sub-identifier);






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          Note that the IMPLIED keyword can only be present for objects
          having a variable-length syntax (e.g., variable-length strings
          or object identifier-valued objects).  Further, the IMPLIED
          keyword may appear at most once within the INDEX clause, and
          if so, is associated with the right-most object having a
          variable-length syntax.  Finally, the IMPLIED keyword may not
          be used on a variable-length string object if that string
          might have a value of zero-length.

          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 newly-defined auxiliary objects is "not-
          accessible".  However, a conceptual row must contain at least
          one columnar object which is not an auxiliary object (i.e.,
          the value of the MAX-ACCESS clause for such an object is
          either "read-only" or "read-create").

          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.


          7.7.1.  Creation and Deletion of Conceptual Rows

          For newly-defined conceptual rows which allow the creation of
          new object instances and 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.









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          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
          extension.  Instances of subordinate columnar objects of a
          conceptual row extension 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 extension
          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.

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


          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.







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          (2)  Otherwise, if there is a sparse relationship between the
               conceptuals rows of this table and an existing table,
               then an INDEX clause should be used which is identical to
               that in the existing table.

          (3)  Otherwise, 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 a SNMPv2 entity acting in an agent role when an object
          instance is created.

          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 a SNMPv2 entity acting in an
          agent role might use.

          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
          a SNMPv2 entity acting in an agent role might use.

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












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         ObjectSyntax        DEFVAL clause
         -----------------   ------------
         Integer32           1
                             -- same for Gauge32, TimeTicks, UInteger32
         INTEGER             valid -- enumerated value
         OCTET STRING        'ffffffffffff'H
         OBJECT IDENTIFIER   sysDescr
         BIT STRING          { primary, secondary } -- enumerated values
               IpAddress           'c0210415'H -- 192.33.4.21

          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 "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.





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          Further note that although conceptual tables and rows are
          given administratively assigned names, these conceptual
          objects may not be manipulated in aggregate form by the
          management protocol.














































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          7.11.  Usage Example

          Consider how one might define a conceptual table and its
          subordinates.

          evalSlot OBJECT-TYPE
              SYNTAX      INTEGER
              MAX-ACCESS  read-only
              STATUS      current
              DESCRIPTION
                      "The index number of the first unassigned entry in
                      the evaluation table.

                      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 underCreation(1).  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
                      "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 }






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

          evalIndex OBJECT-TYPE
              SYNTAX      Integer32
              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 executed."
              DEFVAL  { 0 }
                  ::= { evalEntry 3 }

          evalStatus OBJECT-TYPE
              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 }





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          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 the
          ordered sequence of MIB objects which are contained within
          every instance of the notification.


          8.2.  Mapping of the STATUS clause

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

          The values "current", and "obsolete" are self-explanatory.
          The "deprecated" value indicates that the notification is
          obsolete, but that an implementor may wish to support that
          object to foster interoperability with older 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
          object.  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 a notification defined in some
          other information module.  This is useful when de-osifying a





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          MIB module produced by some other organization.


          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.

          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.






































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          8.6.  Usage Example

          Consider how a linkUp trap might be described:

          linkUp NOTIFICATION-TYPE
              OBJECTS { ifIndex }
              STATUS  current
              DESCRIPTION
                      "A linkUp trap signifies that the SNMPv2 entity,
                      acting in an agent role, recognizes that one of
                      the communication links represented in its
                      configuration has come up."
              ::= { snmpTraps 4 }

          According to this invocation, the trap authoritatively
          identified as

               { snmpTraps 4 }

          is used to report a link coming up.

          Note that a SNMPv2 entity acting in an agent role can be
          configured to send this trap to zero or more SNMPv2 entities
          acting in a manager role, depending on the contents of the
          aclTable and viewTable [8] tables.  For example, by judicious
          use of the viewTable, a SNMPv2 entity acting in an agent role
          might be configured to send all linkUp traps to one particular
          SNMPv2 entity, and linkUp traps for only certain interfaces to
          other SNMPv2 entities.





















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          9.  Refined Syntax

          Some macros allow an object's syntax to be refined (e.g., the
          SYNTAX clause in the MODULE-COMPLIANCE macro [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 on
      object syntax         range   enumeration     size    repertoire
      -----------------     -----   -----------     ----    ----------
                INTEGER      (1)        (2)           -         -
           OCTET STRING       -          -           (3)       (4)
      OBJECT IDENTIFIER       -          -            -         -
             BIT STRING       -         (2)           -         -
              IpAddress       -          -            -         -
              Counter32       -          -            -         -
                Gauge32      (1)         -            -         -
              TimeTicks       -          -            -         -
            NsapAddress       -          -            -         -
              Counter64       -          -            -         -

          where:

          (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;

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

          (4)  the repertoire of characters in the value may be reduced
               by further sub-typing.

          Otherwise no refinements are possible.

          Note that when refining an object with a SYNTAX clause value
          of Integer32 or UInteger32, the refined SYNTAX is expressed as
          an INTEGER and the restrictions of the table above are used.





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          10.  Extending an Information Module

          As experience is gained with a published information module,
          it may be desirable to revise that information module.

          To begin, the invocation of the MODULE-IDENTITY macro should
          be updated to include information about the revision.
          Usually, this consists of updating the LAST-UPDATED clause and
          adding a pair of REVISION and DESCRIPTION clauses.  However,
          other existing clauses in the invocation may be updated.

          Note that the module's label (e.g., "FIZBIN-MIB" from the
          example in Section 5.8), is not changed when the information
          module is revised.


          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.

          (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".

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

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

          (5)  A UNITS clause may be added.

          (6)  A conceptual row may be augmented by adding new columnar
               objects at the end of the row.






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          (7)  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 those specifically allowed above), then the
          OBJECT IDENTIFIER value associated with that object must also
          be changed.

          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.

          Finally, note that if an object has the value of its STATUS
          clause changed, then the value of its DESCRIPTION clause
          should be updated accordingly.


          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.

          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.

          Finally, note that if an object has the value of its STATUS
          clause changed, then the value of its DESCRIPTION clause
          should be updated accordingly.












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          11.  Appendix: de-OSIfying a MIB module

          There has been an increasing amount of work recently on taking
          MIBs defined by other organizations (e.g., the IEEE) and de-
          osifying them for use with the Internet-standard network
          management framework.  The steps to achieve this are
          straight-forward, though tedious.  Of course, it is helpful to
          already be experienced in writing MIB modules for use with the
          Internet-standard network management framework.

          The first step is to construct a skeletal MIB module, as shown
          earlier in Section 5.8.  The next step is to categorize the
          objects into groups.  Optional objects are not permitted.
          Thus, when a MIB module is created, optional objects must be
          placed in a additional groups, which, if implemented, all
          objects in the group must be implemented.  For the first pass,
          it is wisest to simply ignore any optional objects in the
          original MIB: experience shows it is better to define a core
          MIB module first, containing only essential objects; later, if
          experience demands, other objects can be added.


          11.1.  Managed Object Mapping

          Next for each managed object class, determine whether there
          can exist multiple instances of that managed object class.  If
          not, then for each of its attributes, use the OBJECT-TYPE
          macro to make an equivalent definition.

          Otherwise, if multiple instances of the managed object class
          can exist, then define a conceptual table having conceptual
          rows each containing a columnar object for each of the managed
          object class's attributes.  If the managed object class is
          contained within the containment tree of another managed
          object class, then the assignment of an object is normally
          required for each of the "distinguished attributes" of the
          containing managed object class.  If they do not already exist
          within the MIB module, then they can be added via the
          definition of additional columnar objects in the conceptual
          row corresponding to the contained managed object class.

          In defining a conceptual row, it is useful to consider the
          optimization of network management operations which will act
          upon its columnar objects.  In particular, it is wisest to
          avoid defining more columnar objects within a conceptual row,





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          than can fit in a single PDU.  As a rule of thumb, a
          conceptual row should contain no more than approximately 20
          objects.  Similarly, or as a way to abide by the "20 object
          guideline", columnar objects should be grouped into tables
          according to the expected grouping of network management
          operations upon them.  As such, the content of conceptual rows
          should reflect typical access scenarios, e.g., they should be
          organized along functional lines such as one row for
          statistics and another row for parameters, or along usage
          lines such as commonly-needed objects versus rarely-needed
          objects.

          On the other hand, the definition of conceptual rows where the
          number of columnar objects used as indexes outnumbers the
          number used to hold information, should also be avoided.  In
          particular, the splitting of a managed object class's
          attributes into many conceptual tables should not be used as a
          way to obtain the same degree of flexibility/complexity as is
          often found in MIBs with a myriad of optionals.


          11.1.1.  Mapping to the SYNTAX clause

          When mapping to the SYNTAX clause of the OBJECT-type macro:

          (1)  An object with BOOLEAN syntax becomes a TruthValue [3].

          (2)  An object with INTEGER syntax becomes an Integer32.

          (3)  An object with ENUMERATED syntax becomes an INTEGER with
               enumerations, taking any of the values given which can be
               represented with an Integer32.

          (4)  An object with BIT STRING syntax but no enumerations
               becomes an OCTET STRING.

          (5)  An object with a character string syntax becomes either
               an OCTET STRING, or a DisplayString [3], depending on the
               repertoire of the character string.

          (6)  A non-tabular object with a complex syntax, such as REAL
               or EXTERNAL, must be decomposed, usually into an OCTET
               STRING (if sensible).  As a rule, any object with a
               complicated syntax should be avoided.






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          (7)  Tabular objects must be decomposed into rows of columnar
               objects.


          11.1.2.  Mapping to the UNITS clause

          If the description of this managed object defines a unit-
          basis, then mapping to this clause is straight-forward.


          11.1.3.  Mapping to the MAX-ACCESS clause

          This is straight-forward.


          11.1.4.  Mapping to the STATUS clause

          This is straight-forward.


          11.1.5.  Mapping to the DESCRIPTION clause

          This is straight-forward: simply copy the text, making sure
          that any embedded double quotation marks are sanitized (i.e.,
          replaced with single-quotes or removed).


          11.1.6.  Mapping to the REFERENCE clause

          This is straight-forward: simply include a textual reference
          to the object being mapped, the document which defines the
          object, and perhaps a page number in the document.


          11.1.7.  Mapping to the INDEX clause

          If necessary, decide how instance-identifiers for columnar
          objects are to be formed and define this clause accordingly.


          11.1.8.  Mapping to the DEFVAL clause

          Decide if a meaningful default value can be assigned to the
          object being mapped, and if so, define the DEFVAL clause
          accordingly.





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          11.2.  Action Mapping

          Actions are modeled as read-write objects, in which writing a
          particular value results in a state change.  (Usually, as a
          part of this state change, some action might take place.)


          11.2.1.  Mapping to the SYNTAX clause

          Usually the Integer32 syntax is used with a distinguished
          value provided for each action that the object provides access
          to.  In addition, there is usually one other distinguished
          value, which is the one returned when the object is read.


          11.2.2.  Mapping to the MAX-ACCESS clause

          Always use read-write or read-create.


          11.2.3.  Mapping to the STATUS clause

          This is straight-forward.


          11.2.4.  Mapping to the DESCRIPTION clause

          This is straight-forward: simply copy the text, making sure
          that any embedded double quotation marks are sanitized (i.e.,
          replaced with single-quotes or removed).


          11.2.5.  Mapping to the REFERENCE clause

          This is straight-forward: simply include a textual reference
          to the action being mapped, the document which defines the
          action, and perhaps a page number in the document.


          11.3.  Event Mapping

          Events are modeled as SNMPv2 notifications using
          NOTIFICATION-TYPE macro.  However, recall that SNMPv2
          emphasizes trap-directed polling.  As such, few, and usually
          no, notifications, need be defined for any MIB module.





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          11.3.1.  Mapping to the STATUS clause

          This is straight-forward.


          11.3.2.  Mapping to the DESCRIPTION clause

          This is straight-forward: simply copy the text, making sure
          that any embedded double quotation marks are sanitized (i.e.,
          replaced with single-quotes or removed).


          11.3.3.  Mapping to the REFERENCE clause

          This is straight-forward: simply include a textual reference
          to the notification being mapped, the document which defines
          the notification, and perhaps a page number in the document.

































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          12.  Acknowledgements

          The section on object definitions (and MIB de-osification) is
          based, in part, on RFCs 1155 and 1212.  The IMPLIED keyword is
          based on a conversation with David T. Perkins in December,
          1991.

          The section on trap definitions is based, in part, on RFC
          1215.

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

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





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               Mike Erlinger, Lexcel
               Roger Fajman, NIH
               Daniel Fauvarque, Sun Microsystems
               Karen Frisa, CMU
               Shari Galitzer, MITRE
               Shawn Gallagher, Digital Equipment Corporation
               Richard Graveman, Bellcore
               Maria Greene, Xyplex, Inc.
               Michel Guittet, Apple
               Robert Gutierrez, NASA
               Bill Hagerty, Cabletron Systems
               Gary W. Haney, Martin Marietta Energy Systems
               Patrick Hanil, Nokia Telecommunications
               Matt Hecht, SNMP Research, Inc.
               Edward A. Heiner, Jr., Synernetics Inc.
               Susan E. Hicks, Martin Marietta Energy Systems
               Geral Holzhauer, Apple
               John Hopprich, DAVID Systems, Inc.
               Jeff Hughes, Hewlett-Packard
               Robin Iddon, Axon Networks, Inc.
               David Itusak
               Kevin M. Jackson, Concord Communications, Inc.
               Ole J. Jacobsen, Interop Company
               Ronald Jacoby, Silicon Graphics, Inc.
               Satish Joshi, SynOptics Communications, Inc.
               Frank Kastenholz, FTP Software
               Mark Kepke, Hewlett-Packard
               Ken Key, SNMP Research, Inc.
               Zbiginew Kielczewski, Eicon
               Jongyeoi Kim
               Andrew Knutsen, The Santa Cruz Operation
               Michael L. Kornegay, VisiSoft
               Deirdre C. Kostik, Bellcore
               Cheryl Krupczak, Georgia Tech
               Mark S. Lewis, Telebit
               David Lin
               David Lindemulder, AT&T/NCR
               Ben Lisowski, Sprint
               David Liu, Bell-Northern Research
               John Lunny, The Wollongong Group
               Robert C. Lushbaugh Martin, Marietta Energy Systems
               Michael Luufer, BBN
               Carl Madison, Star-Tek, Inc.
               Keith McCloghrie, Hughes LAN Systems
               Evan McGinnis, 3Com Corporation





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               Bill McKenzie, IBM Corporation
               Donna McMaster, SynOptics Communications, Inc.
               John Medicke, IBM Corporation
               Doug Miller, Telebit
               Dave Minnich, FiberCom
               Mohammad Mirhakkak, MITRE
               Rohit Mital, Protools
               George Mouradian, AT&T Bell Labs
               Patrick Mullaney, Cabletron Systems
               Dan Myers, 3Com Corporation
               Rina Nathaniel, Rad Network Devices Ltd.
               Hien V. Nguyen, Sprint
               Mo Nikain
               Tom Nisbet
               William B. Norton, MERIT
               Steve Onishi, Wellfleet Communications, Inc.
               David T. Perkins, SynOptics Communications, Inc.
               Carl Powell, BBN
               Ilan Raab, SynOptics Communications, Inc.
               Richard Ramons, AT&T
               Venkat D. Rangan, Metric Network Systems, Inc.
               Louise Reingold, Sprint
               Sam Roberts, Farallon Computing, Inc.
               Kary Robertson, Concord Communications, Inc.
               Dan Romascanu, Lannet Data Communications Ltd.
               Marshall T. Rose, Dover Beach Consulting, Inc.
               Shawn A. Routhier, Epilogue Technology Corporation
               Chris Rozman
               Asaf Rubissa, Fibronics
               Jon Saperia, Digital Equipment Corporation
               Michael Sapich
               Mike Scanlon, Interlan
               Sam Schaen, MITRE
               John Seligson, Ultra Network Technologies
               Paul A. Serice, Corporation for Open Systems
               Chris Shaw, Banyan Systems
               Timon Sloane
               Robert Snyder, Cisco Systems
               Joo Young Song
               Roy Spitier, Sprint
               Einar Stefferud, Network Management Associates
               John Stephens, Cayman Systems, Inc.
               Robert L. Stewart, Xyplex, Inc. (chair)
               Kaj Tesink, Bellcore
               Dean Throop, Data General





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               Ahmet Tuncay, France Telecom-CNET
               Maurice Turcotte, Racal Datacom
               Warren Vik, INTERACTIVE Systems Corporation
               Yannis Viniotis
               Steven L. Waldbusser, Carnegie Mellon Universitty
               Timothy M. Walden, ACC
               Alice Wang, Sun Microsystems
               James Watt, Newbridge
               Luanne Waul, Timeplex
               Donald E. Westlake III, Digital Equipment Corporation
               Gerry White
               Bert Wijnen, IBM Corporation
               Peter Wilson, 3Com Corporation
               Steven Wong, Digital Equipment Corporation
               Randy Worzella, IBM Corporation
               Daniel Woycke, MITRE
               Honda Wu
               Jeff Yarnell, Protools
               Chris Young, Cabletron
               Kiho Yum, 3Com Corporation






























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          13.  References

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

          [2]  Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Conformance Statements for version 2 of the the Simple
               Network Management Protocol (SNMPv2)", RFC 1444, SNMP
               Research, Inc., Hughes LAN Systems, Dover Beach
               Consulting, Inc., Carnegie Mellon University, April 1993.

          [3]  Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Textual Conventions for version 2 of the the Simple
               Network Management Protocol (SNMPv2)", RFC 1443, SNMP
               Research, Inc., Hughes LAN Systems, Dover Beach
               Consulting, Inc., Carnegie Mellon University, April 1993.

          [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]  Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Management Information Base for version 2 of the Simple
               Network Management Protocol (SNMPv2)", RFC 1450, SNMP
               Research, Inc., Hughes LAN Systems, Dover Beach
               Consulting, Inc., Carnegie Mellon University, April 1993.

          [6]  Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Protocol Operations for version 2 of the Simple Network
               Management Protocol (SNMPv2)", RFC 1448, SNMP Research,
               Inc., Hughes LAN Systems, Dover Beach Consulting, Inc.,
               Carnegie Mellon University, April 1993.

          [7]  McCloghrie, K., and Rose, M., "Management Information
               Base for Network Management of TCP/IP-based internets:
               MIB-II", STD 17, RFC 1213, March 1991.

          [8]  McCloghrie, K., and Galvin, J., "Party MIB for version 2
               of the Simple Network Management Protocol (SNMPv2)", RFC
               1447, Hughes LAN Systems, Trusted Information Systems,





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               April 1993.

















































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          14.  Security Considerations

          Security issues are not discussed in this memo.


          15.  Authors' Addresses

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

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


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

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


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

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

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

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






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