A Beginner's Guide to the Internet/INTERNET.ISO/text/std/std0016.txt

Text File | 1995-04-05 | 80.4 KB | 2,303 lines

Network Working Group                                            M. Rose
Request for Comments:  1155            Performance Systems International
Obsoletes:  RFC 1065                                       K. McCloghrie
                                                      Hughes LAN Systems
                                                                May 1990



         Structure and Identification of Management Information
                       for TCP/IP-based Internets

                           Table of Contents

1. Status of this Memo .............................................  1
2. Introduction ....................................................  2
3. Structure and Identification of Management Information...........  4
3.1 Names ..........................................................  4
3.1.1 Directory ....................................................  5
3.1.2 Mgmt .........................................................  6
3.1.3 Experimental .................................................  6
3.1.4 Private ......................................................  7
3.2 Syntax .........................................................  7
3.2.1 Primitive Types ..............................................  7
3.2.1.1 Guidelines for Enumerated INTEGERs .........................  7
3.2.2 Constructor Types ............................................  8
3.2.3 Defined Types ................................................  8
3.2.3.1 NetworkAddress .............................................  8
3.2.3.2 IpAddress ..................................................  8
3.2.3.3 Counter ....................................................  8
3.2.3.4 Gauge ......................................................  9
3.2.3.5 TimeTicks ..................................................  9
3.2.3.6 Opaque .....................................................  9
3.3 Encodings ......................................................  9
4. Managed Objects ................................................. 10
4.1 Guidelines for Object Names .................................... 10
4.2 Object Types and Instances ..................................... 10
4.3 Macros for Managed Objects ..................................... 14
5. Extensions to the MIB ........................................... 16
6. Definitions ..................................................... 17
7. Acknowledgements ................................................ 20
8. References ...................................................... 21
9. Security Considerations.......................................... 21
10. Authors' Addresses.............................................. 22

1.  Status of this Memo

   This RFC is a re-release of RFC 1065, with a changed "Status of this
   Memo", plus a few minor typographical corrections.  The technical



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   content of the document is unchanged from RFC 1065.

   This memo provides the common definitions for the structure and
   identification of management information for TCP/IP-based internets.
   In particular, together with its companion memos which describe the
   management information base along with the network management
   protocol, these documents provide a simple, workable architecture and
   system for managing TCP/IP-based internets and in particular, the
   Internet.

   This memo specifies a Standard Protocol for the Internet community.
   Its status is "Recommended".  TCP/IP implementations in the Internet
   which are network manageable are expected to adopt and implement this
   specification.

   The Internet Activities Board recommends that all IP and TCP
   implementations be network manageable.  This implies implementation
   of the Internet MIB (RFC-1156) and at least one of the two
   recommended management protocols SNMP (RFC-1157) or CMOT (RFC-1095).
   It should be noted that, at this time, SNMP is a full Internet
   standard and CMOT is a draft standard.  See also the Host and Gateway
   Requirements RFCs for more specific information on the applicability
   of this standard.

   Please refer to the latest edition of the "IAB Official Protocol
   Standards" RFC for current information on the state and status of
   standard Internet protocols.

   Distribution of this memo is unlimited.

2.  Introduction

   This memo describes the common structures and identification scheme
   for the definition of management information used in managing
   TCP/IP-based internets.  Included are descriptions of an object
   information model for network management along with a set of generic
   types used to describe management information.  Formal descriptions
   of the structure are given using Abstract Syntax Notation One (ASN.1)
   [1].

   This memo is largely concerned with organizational concerns and
   administrative policy:  it neither specifies the objects which are
   managed, nor the protocols used to manage those objects.  These
   concerns are addressed by two companion memos:  one describing the
   Management Information Base (MIB) [2], and the other describing the
   Simple Network Management Protocol (SNMP) [3].

   This memo is based in part on the work of the Internet Engineering



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   Task Force, particularly the working note titled "Structure and
   Identification of Management Information for the Internet" [4].  This
   memo uses a skeletal structure derived from that note, but differs in
   one very significant way:  that note focuses entirely on the use of
   OSI-style network management.  As such, it is not suitable for use
   with SNMP.

   This memo attempts to achieve two goals:  simplicity and
   extensibility.  Both are motivated by a common concern:  although the
   management of TCP/IP-based internets has been a topic of study for
   some time, the authors do not feel that the depth and breadth of such
   understanding is complete.  More bluntly, we feel that previous
   experiences, while giving the community insight, are hardly
   conclusive.  By fostering a simple SMI, the minimal number of
   constraints are imposed on future potential approaches; further, by
   fostering an extensible SMI, the maximal number of potential
   approaches are available for experimentation.

   It is believed that this memo and its two companions comply with the
   guidelines set forth in RFC 1052, "IAB Recommendations for the
   Development of Internet Network Management Standards" [5] and RFC
   1109, "Report of the Second Ad Hoc Network Management Review Group"
   [6].  In particular, we feel that this memo, along with the memo
   describing the management information base, provide a solid basis for
   network management of the Internet.


























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3.  Structure and Identification of Management Information

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  Objects in the MIB are
   defined using Abstract Syntax Notation One (ASN.1) [1].

   Each type of object (termed an object type) has a name, a syntax, and
   an encoding.  The name is represented uniquely as an OBJECT
   IDENTIFIER.  An OBJECT IDENTIFIER is an administratively assigned
   name.  The administrative policies used for assigning names are
   discussed later in this memo.

   The syntax for an object type defines the abstract data structure
   corresponding to that object type.  For example, the structure of a
   given object type might be an INTEGER or OCTET STRING.  Although in
   general, we should permit any ASN.1 construct to be available for use
   in defining the syntax of an object type, this memo purposely
   restricts the ASN.1 constructs which may be used.  These restrictions
   are made solely for the sake of simplicity.

   The encoding of an object type is simply how instances of that object
   type are represented using the object's type syntax.  Implicitly tied
   to the notion of an object's syntax and encoding is how the object is
   represented when being transmitted on the network.  This memo
   specifies the use of the basic encoding rules of ASN.1 [7].

   It is beyond the scope of this memo to define either the MIB used for
   network management or the network management protocol.  As mentioned
   earlier, these tasks are left to companion memos.  This memo attempts
   to minimize the restrictions placed upon its companions so as to
   maximize generality.  However, in some cases, restrictions have been
   made (e.g., the syntax which may be used when defining object types
   in the MIB) in order to encourage a particular style of management.
   Future editions of this memo may remove these restrictions.

3.1.  Names

   Names are used to identify managed objects.  This memo specifies
   names which are hierarchical in nature.  The OBJECT IDENTIFIER
   concept is used to model this notion.  An OBJECT IDENTIFIER can be
   used for purposes other than naming managed object types; for
   example, each international standard has an OBJECT IDENTIFIER
   assigned to it for the purposes of identification.  In short, OBJECT
   IDENTIFIERs are a means for identifying some object, regardless of
   the semantics associated with the object (e.g., a network object, a
   standards document, etc.)

   An OBJECT IDENTIFIER is a sequence of integers which traverse a



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   global tree.  The tree consists of a root connected to a number of
   labeled nodes via edges.  Each node may, in turn, have children of
   its own which are labeled.  In this case, we may term the node a
   subtree.  This process may continue to an arbitrary level of depth.
   Central to the notion of the OBJECT IDENTIFIER is the understanding
   that administrative control of the meanings assigned to the nodes may
   be delegated as one traverses the tree.  A label is a pairing of a
   brief textual description and an integer.

   The root node itself is unlabeled, but has at least three children
   directly under it:  one node is administered by the International
   Organization for Standardization, with label iso(1); another is
   administrated by the International Telegraph and Telephone
   Consultative Committee, with label ccitt(0); and the third is jointly
   administered by the ISO and the CCITT, joint-iso-ccitt(2).

   Under the iso(1) node, the ISO has designated one subtree for use by
   other (inter)national organizations, org(3).  Of the children nodes
   present, two have been assigned to the U.S. National Institutes of
   Standards and Technology.  One of these subtrees has been transferred
   by the NIST to the U.S. Department of Defense, dod(6).

   As of this writing, the DoD has not indicated how it will manage its
   subtree of OBJECT IDENTIFIERs.  This memo assumes that DoD will
   allocate a node to the Internet community, to be administered by the
   Internet Activities Board (IAB) as follows:

      internet    OBJECT IDENTIFIER ::= { iso org(3) dod(6) 1 }

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

      1.3.6.1.

   This memo, as a standard approved by the IAB, now specifies the
   policy under which this subtree of OBJECT IDENTIFIERs is
   administered.  Initially, four nodes are present:

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

3.1.1.  Directory

   The directory(1) subtree is reserved for use with a future memo that
   discusses how the OSI Directory may be used in the Internet.




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3.1.2.  Mgmt

   The mgmt(2) subtree is used to identify objects which are defined in
   IAB-approved documents.  Administration of the mgmt(2) subtree is
   delegated by the IAB to the Internet Assigned Numbers Authority for
   the Internet.  As RFCs which define new versions of the Internet-
   standard Management Information Base are approved, they are assigned
   an OBJECT IDENTIFIER by the Internet Assigned Numbers Authority for
   identifying the objects defined by that memo.

   For example, the RFC which defines the initial Internet standard MIB
   would be assigned management document number 1.  This RFC would use
   the OBJECT IDENTIFIER

      { mgmt 1 }

   or

      1.3.6.1.2.1

   in defining the Internet-standard MIB.

   The generation of new versions of the Internet-standard MIB is a
   rigorous process.  Section 5 of this memo describes the rules used
   when a new version is defined.

3.1.3.  Experimental

   The experimental(3) subtree is used to identify objects used in
   Internet experiments.  Administration of the experimental(3) subtree
   is delegated by the IAB to the Internet Assigned Numbers Authority of
   the Internet.

   For example, an experimenter might received number 17, and would have
   available the OBJECT IDENTIFIER

      { experimental 17 }

   or

      1.3.6.1.3.17

   for use.

   As a part of the assignment process, the Internet Assigned Numbers
   Authority may make requirements as to how that subtree is used.





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3.1.4.  Private

   The private(4) subtree is used to identify objects defined
   unilaterally.  Administration of the private(4) subtree is delegated
   by the IAB to the Internet Assigned Numbers Authority for the
   Internet.  Initially, this subtree has at least one child:

      enterprises   OBJECT IDENTIFIER ::= { private 1 }

   The enterprises(1) subtree is used, among other things, to permit
   parties providing networking subsystems to register models of their
   products.

   Upon receiving a subtree, the enterprise may, for example, define new
   MIB objects in this subtree.  In addition, it is strongly recommended
   that the enterprise will also register its networking subsystems
   under this subtree, in order to provide an unambiguous identification
   mechanism for use in management protocols.  For example, if the
   "Flintstones, Inc."  enterprise produced networking subsystems, then
   they could request a node under the enterprises subtree from the
   Internet Assigned Numbers Authority.  Such a node might be numbered:

      1.3.6.1.4.1.42

   The "Flintstones, Inc." enterprise might then register their "Fred
   Router" under the name of:

      1.3.6.1.4.1.42.1.1

3.2.  Syntax

   Syntax is used to define the structure corresponding to object types.
   ASN.1 constructs are used to define this structure, although the full
   generality of ASN.1 is not permitted.

   The ASN.1 type ObjectSyntax defines the different syntaxes which may
   be used in defining an object type.

3.2.1.  Primitive Types

   Only the ASN.1 primitive types INTEGER, OCTET STRING, OBJECT
   IDENTIFIER, and NULL are permitted.  These are sometimes referred to
   as non-aggregate types.

3.2.1.1.  Guidelines for Enumerated INTEGERs

   If an enumerated INTEGER is listed as an object type, then a named-
   number having the value 0 shall not be present in the list of



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   enumerations.  Use of this value is prohibited.

3.2.2.  Constructor Types

   The ASN.1 constructor type SEQUENCE is permitted, providing that it
   is used to generate either lists or tables.

   For lists, the syntax takes the form:

      SEQUENCE { <type1>, ..., <typeN> }

   where each <type> resolves to one of the ASN.1 primitive types listed
   above.  Further, these ASN.1 types are always present (the DEFAULT
   and OPTIONAL clauses do not appear in the SEQUENCE definition).

   For tables, the syntax takes the form:

      SEQUENCE OF <entry>

   where <entry> resolves to a list constructor.

   Lists and tables are sometimes referred to as aggregate types.

3.2.3.  Defined Types

   In addition, new application-wide types may be defined, so long as
   they resolve into an IMPLICITly defined ASN.1 primitive type, list,
   table, or some other application-wide type.  Initially, few
   application-wide types are defined.  Future memos will no doubt
   define others once a consensus is reached.

3.2.3.1.  NetworkAddress

   This CHOICE represents an address from one of possibly several
   protocol families.  Currently, only one protocol family, the Internet
   family, is present in this CHOICE.

3.2.3.2.  IpAddress

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

   When this ASN.1 type is encoded using the ASN.1 basic encoding rules,
   only the primitive encoding form shall be used.

3.2.3.3.  Counter

   This application-wide type represents a non-negative integer which



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   monotonically increases until it reaches a maximum value, when it
   wraps around and starts increasing again from zero.  This memo
   specifies a maximum value of 2^32-1 (4294967295 decimal) for
   counters.

3.2.3.4.  Gauge

   This application-wide type represents a non-negative integer, which
   may increase or decrease, but which latches at a maximum value.  This
   memo specifies a maximum value of 2^32-1 (4294967295 decimal) for
   gauges.

3.2.3.5.  TimeTicks

   This application-wide type represents a non-negative integer which
   counts the time in hundredths of a second since some epoch.  When
   object types are defined in the MIB which use this ASN.1 type, the
   description of the object type identifies the reference epoch.

3.2.3.6.  Opaque

   This application-wide type supports the capability to pass arbitrary
   ASN.1 syntax.  A value is encoded using the ASN.1 basic rules 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.

   Further note that by use of the ASN.1 EXTERNAL type, encodings other
   than ASN.1 may be used in opaquely-encoded data.

3.3.  Encodings

   Once an instance of an object type has been identified, its value may
   be transmitted by applying the basic encoding rules of ASN.1 to the
   syntax for the object type.













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4.  Managed Objects

   Although it is not the purpose of this memo to define objects in the
   MIB, this memo specifies a format to be used by other memos which
   define these objects.

   An object type definition consists of five fields:

   OBJECT:
   -------
      A textual name, termed the OBJECT DESCRIPTOR, for the object type,
      along with its corresponding OBJECT IDENTIFIER.

   Syntax:
      The abstract syntax for the object type.  This must resolve to an
      instance of the ASN.1 type ObjectSyntax (defined below).

   Definition:
      A textual description of the semantics of the object type.
      Implementations should ensure that their instance of the object
      fulfills this definition since this MIB is intended for use in
      multi-vendor environments.  As such it is vital that objects have
      consistent meaning across all machines.

   Access:
      One of read-only, read-write, write-only, or not-accessible.

   Status:
      One of mandatory, optional, or obsolete.

   Future memos may also specify other fields for the objects which they
   define.

4.1.  Guidelines for Object Names

   No object type in the Internet-Standard MIB shall use a sub-
   identifier of 0 in its name.  This value is reserved for use with
   future extensions.

   Each OBJECT DESCRIPTOR corresponding to an object type in the
   internet-standard MIB shall be a unique, but mnemonic, printable
   string.  This promotes a common language for humans to use when
   discussing the MIB and also facilitates simple table mappings for
   user interfaces.

4.2.  Object Types and Instances

   An object type is a definition of a kind of managed object; it is



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   declarative in nature.  In contrast, an object instance is an
   instantiation of an object type which has been bound to a value.  For
   example, the notion of an entry in a routing table might be defined
   in the MIB.  Such a notion corresponds to an object type; individual
   entries in a particular routing table which exist at some time are
   object instances of that object type.

   A collection of object types is defined in the MIB.  Each such
   subject type is uniquely named by its OBJECT IDENTIFIER and also has
   a textual name, which is its OBJECT DESCRIPTOR.  The means whereby
   object instances are referenced is not defined in the MIB.  Reference
   to object instances is achieved by a protocol-specific mechanism:  it
   is the responsibility of each management protocol adhering to the SMI
   to define this mechanism.

   An object type may be defined in the MIB such that an instance of
   that object type represents an aggregation of information also
   represented by instances of some number of "subordinate" object
   types.  For example, suppose the following object types are defined
   in the MIB:


   OBJECT:
   -------
      atIndex { atEntry 1 }

   Syntax:
      INTEGER

   Definition:
      The interface number for the physical address.

   Access:
      read-write.

   Status:
      mandatory.


   OBJECT:
   -------
      atPhysAddress { atEntry 2 }

   Syntax:
      OCTET STRING

   Definition:
      The media-dependent physical address.



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   Access:
      read-write.

   Status:
      mandatory.


   OBJECT:
   -------
      atNetAddress { atEntry 3 }

   Syntax:
      NetworkAddress

   Definition:
      The network address corresponding to the media-dependent physical
      address.

   Access:
      read-write.

   Status:
      mandatory.

   Then, a fourth object type might also be defined in the MIB:


   OBJECT:
   -------
      atEntry { atTable 1 }

   Syntax:

      AtEntry ::= SEQUENCE {
            atIndex
            INTEGER,
            atPhysAddress
            OCTET STRING,
            atNetAddress
            NetworkAddress
            }

   Definition:
      An entry in the address translation table.

   Access:
      read-write.




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   Status:
      mandatory.

   Each instance of this object type comprises information represented
   by instances of the former three object types.  An object type
   defined in this way is called a list.

   Similarly, tables can be formed by aggregations of a list type.  For
   example, a fifth object type might also be defined in the MIB:


   OBJECT:
   ------
      atTable { at 1 }

   Syntax:
      SEQUENCE OF AtEntry

   Definition:
      The address translation table.

   Access:
      read-write.

   Status:
      mandatory.

   such that each instance of the atTable object comprises information
   represented by the set of atEntry object types that collectively
   constitute a given atTable object instance, that is, a given address
   translation table.

   Consider how one might refer to a simple object within a table.
   Continuing with the previous example, one might name the object type

      { atPhysAddress }

   and specify, using a protocol-specific mechanism, the object instance

      { atNetAddress } = { internet "10.0.0.52" }

   This pairing of object type and object instance would refer to all
   instances of atPhysAddress which are part of any entry in some
   address translation table for which the associated atNetAddress value
   is { internet "10.0.0.52" }.

   To continue with this example, consider how one might refer to an
   aggregate object (list) within a table.  Naming the object type



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      { atEntry }

   and specifying, using a protocol-specific mechanism, the object
   instance

      { atNetAddress } = { internet "10.0.0.52" }

   refers to all instances of entries in the table for which the
   associated atNetAddress value is { internet "10.0.0.52" }.

   Each management protocol must provide a mechanism for accessing
   simple (non-aggregate) object types.  Each management protocol
   specifies whether or not it supports access to aggregate object
   types.  Further, the protocol must specify which instances are
   "returned" when an object type/instance pairing refers to more than
   one instance of a type.

   To afford support for a variety of management protocols, all
   information by which instances of a given object type may be usefully
   distinguished, one from another, is represented by instances of
   object types defined in the MIB.

4.3.  Macros for Managed Objects

   In order to facilitate the use of tools for processing the definition
   of the MIB, the OBJECT-TYPE macro may be used.  This macro permits
   the key aspects of an object type to be represented in a formal way.

      OBJECT-TYPE MACRO ::=
      BEGIN
          TYPE NOTATION ::= "SYNTAX" type (TYPE ObjectSyntax)
                            "ACCESS" Access
                            "STATUS" Status
          VALUE NOTATION ::= value (VALUE ObjectName)

          Access ::= "read-only"
                          | "read-write"
                          | "write-only"
                          | "not-accessible"
          Status ::= "mandatory"
                          | "optional"
                          | "obsolete"
          END

   Given the object types defined earlier, we might imagine the
   following definitions being present in the MIB:

                  atIndex OBJECT-TYPE



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                          SYNTAX  INTEGER
                          ACCESS  read-write
                          STATUS  mandatory
                          ::= { atEntry 1 }

                  atPhysAddress OBJECT-TYPE
                          SYNTAX  OCTET STRING
                          ACCESS  read-write
                          STATUS  mandatory
                          ::= { atEntry 2 }

                  atNetAddress OBJECT-TYPE
                          SYNTAX  NetworkAddress
                          ACCESS  read-write
                          STATUS  mandatory
                          ::= { atEntry 3 }

                  atEntry OBJECT-TYPE
                          SYNTAX  AtEntry
                          ACCESS  read-write
                          STATUS  mandatory
                          ::= { atTable 1 }

                  atTable OBJECT-TYPE
                          SYNTAX  SEQUENCE OF AtEntry
                          ACCESS  read-write
                          STATUS  mandatory
                          ::= { at 1 }

                  AtEntry ::= SEQUENCE {
                      atIndex
                          INTEGER,
                      atPhysAddress
                          OCTET STRING,
                      atNetAddress
                          NetworkAddress
                  }

   The first five definitions describe object types, relating, for
   example, the OBJECT DESCRIPTOR atIndex to the OBJECT IDENTIFIER {
   atEntry 1 }.  In addition, the syntax of this object is defined
   (INTEGER) along with the access permitted (read-write) and status
   (mandatory).  The sixth definition describes an ASN.1 type called
   AtEntry.







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5.  Extensions to the MIB

   Every Internet-standard MIB document obsoletes all previous such
   documents.  The portion of a name, termed the tail, following the
   OBJECT IDENTIFIER

      { mgmt version-number }

   used to name objects shall remain unchanged between versions.  New
   versions may:

      (1) declare old object types obsolete (if necessary), but not
      delete their names;

      (2) augment the definition of an object type corresponding to a
      list by appending non-aggregate object types to the object types
      in the list; or,

      (3) define entirely new object types.

   New versions may not:

      (1) change the semantics of any previously defined object without
      changing the name of that object.

   These rules are important because they admit easier support for
   multiple versions of the Internet-standard MIB.  In particular, the
   semantics associated with the tail of a name remain constant
   throughout different versions of the MIB.  Because multiple versions
   of the MIB may thus coincide in "tail-space," implementations
   supporting multiple versions of the MIB can be vastly simplified.

   However, as a consequence, a management agent might return an
   instance corresponding to a superset of the expected object type.
   Following the principle of robustness, in this exceptional case, a
   manager should ignore any additional information beyond the
   definition of the expected object type.  However, the robustness
   principle requires that one exercise care with respect to control
   actions:  if an instance does not have the same syntax as its
   expected object type, then those control actions must fail.  In both
   the monitoring and control cases, the name of an object returned by
   an operation must be identical to the name requested by an operation.









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6.  Definitions

           RFC1155-SMI DEFINITIONS ::= BEGIN

           EXPORTS -- EVERYTHING
                   internet, directory, mgmt,
                   experimental, private, enterprises,
                   OBJECT-TYPE, ObjectName, ObjectSyntax, SimpleSyntax,
                   ApplicationSyntax, NetworkAddress, IpAddress,
                   Counter, Gauge, TimeTicks, Opaque;

            -- the path to the root

            internet      OBJECT IDENTIFIER ::= { iso org(3) dod(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 }


            -- definition of object types

            OBJECT-TYPE MACRO ::=
            BEGIN
                TYPE NOTATION ::= "SYNTAX" type (TYPE ObjectSyntax)
                                  "ACCESS" Access
                                  "STATUS" Status
                VALUE NOTATION ::= value (VALUE ObjectName)

                Access ::= "read-only"
                                | "read-write"
                                | "write-only"
                                | "not-accessible"
                Status ::= "mandatory"
                                | "optional"
                                | "obsolete"
            END

               -- names of objects in the MIB

               ObjectName ::=
                   OBJECT IDENTIFIER




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RFC 1155                          SMI                           May 1990


               -- syntax of objects in the MIB

               ObjectSyntax ::=
                   CHOICE {
                       simple
                           SimpleSyntax,

               -- note that simple SEQUENCEs are not directly
               -- mentioned here to keep things simple (i.e.,
               -- prevent mis-use).  However, application-wide
               -- types which are IMPLICITly encoded simple
               -- SEQUENCEs may appear in the following CHOICE

                       application-wide
                           ApplicationSyntax
                   }

                  SimpleSyntax ::=
                      CHOICE {
                          number
                              INTEGER,

                          string
                              OCTET STRING,

                          object
                              OBJECT IDENTIFIER,

                          empty
                              NULL
                      }

                  ApplicationSyntax ::=
                      CHOICE {
                          address
                              NetworkAddress,

                          counter
                              Counter,

                          gauge
                              Gauge,

                          ticks
                              TimeTicks,

                          arbitrary
                              Opaque



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RFC 1155                          SMI                           May 1990


                  -- other application-wide types, as they are
                  -- defined, will be added here
                      }


                  -- application-wide types

                  NetworkAddress ::=
                      CHOICE {
                          internet
                              IpAddress
                      }

                  IpAddress ::=
                      [APPLICATION 0]          -- in network-byte order
                          IMPLICIT OCTET STRING (SIZE (4))

                  Counter ::=
                      [APPLICATION 1]
                          IMPLICIT INTEGER (0..4294967295)

                  Gauge ::=
                      [APPLICATION 2]
                          IMPLICIT INTEGER (0..4294967295)

                  TimeTicks ::=
                      [APPLICATION 3]
                          IMPLICIT INTEGER (0..4294967295)

                  Opaque ::=
                      [APPLICATION 4]          -- arbitrary ASN.1 value,
                          IMPLICIT OCTET STRING   --   "double-wrapped"

                  END

















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7.  Acknowledgements

   This memo was influenced by three sets of contributors to earlier
   drafts:

   First, Lee Labarre of the MITRE Corporation, who as author of the
   NETMAN SMI [4], presented the basic roadmap for the SMI.

   Second, several individuals who provided valuable comments on this
   memo prior to its initial distribution:

         James R. Davin, Proteon
         Mark S. Fedor, NYSERNet
         Craig Partridge, BBN Laboratories
         Martin Lee Schoffstall, Rensselaer Polytechnic Institute
         Wengyik Yeong, NYSERNet


   Third, the IETF MIB working group:

         Karl Auerbach, Epilogue Technology
         K. Ramesh Babu, Excelan
         Lawrence Besaw, Hewlett-Packard
         Jeffrey D. Case, University of Tennessee at Knoxville
         James R. Davin, Proteon
         Mark S. Fedor, NYSERNet
         Robb Foster, BBN
         Phill Gross, The MITRE Corporation
         Bent Torp Jensen, Convergent Technology
         Lee Labarre, The MITRE Corporation
         Dan Lynch, Advanced Computing Environments
         Keith McCloghrie, The Wollongong Group
         Dave Mackie, 3Com/Bridge
         Craig Partridge, BBN (chair)
         Jim Robertson, 3Com/Bridge
         Marshall T. Rose, The Wollongong Group
         Greg Satz, cisco
         Martin Lee Schoffstall, Rensselaer Polytechnic Institute
         Lou Steinberg, IBM
         Dean Throop, Data General
         Unni Warrier, Unisys










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8.  References

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

   [2] McCloghrie K., and M. Rose, "Management Information Base for
       Network Management of TCP/IP-based Internets", RFC 1156,
       Performance Systems International and Hughes LAN Systems, May
       1990.

   [3] Case, J., M. Fedor, M. Schoffstall, and J. Davin, The Simple
       Network Management Protocol", RFC 1157, University of Tennessee
       at Knoxville, Performance Systems International, Performance
       Systems International, and the MIT Laboratory for Computer
       Science, May 1990.

   [4] LaBarre, L., "Structure and Identification of Management
       Information for the Internet", Internet Engineering Task Force
       working note, Network Information Center, SRI International,
       Menlo Park, California, April 1988.

   [5] Cerf, V., "IAB Recommendations for the Development of Internet
       Network Management Standards", RFC 1052, IAB, April 1988.

   [6] Cerf, V., "Report of the Second Ad Hoc Network Management Review
       Group", RFC 1109, IAB, August 1989.

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

Security Considerations

   Security issues are not discussed in this memo.














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Authors' Addresses

   Marshall T. Rose
   PSI, Inc.
   PSI California Office
   P.O. Box 391776
   Mountain View, CA 94039

   Phone: [phone]

   EMail: [e-mail]


   Keith McCloghrie
   The Wollongong Group
   1129 San Antonio Road
   Palo Alto, CA 04303

   Phone: [phone]

   EMail: sytek![e-mail]






























Rose & McCloghrie                                              [Page 22]

=======================================================================






Network Working Group                                           M. Rose
Request for Comments: 1212            Performance Systems International
                                                          K. McCloghrie
                                                     Hughes LAN Systems
                                                                Editors
                                                             March 1991


                        Concise MIB Definitions
Status of this Memo

   This memo defines a format for producing MIB modules.  This RFC
   specifies an IAB standards track document 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. Abstract..............................................    2
   2. Historical Perspective ...............................    2
   3. Columnar Objects .....................................    3
   3.1 Row Deletion ........................................    4
   3.2 Row Addition ........................................    4
   4. Defining Objects .....................................    5
   4.1 Mapping of the OBJECT-TYPE macro ....................    7
   4.1.1 Mapping of the SYNTAX clause ......................    7
   4.1.2 Mapping of the ACCESS clause ......................    8
   4.1.3 Mapping of the STATUS clause ......................    8
   4.1.4 Mapping of the DESCRIPTION clause .................    8
   4.1.5 Mapping of the REFERENCE clause ...................    8
   4.1.6 Mapping of the INDEX clause .......................    8
   4.1.7 Mapping of the DEFVAL clause ......................   10
   4.1.8 Mapping of the OBJECT-TYPE value ..................   11
   4.2 Usage Example .......................................   11
   5. Appendix: DE-osifying MIBs ...........................   13
   5.1 Managed Object Mapping ..............................   14
   5.1.1 Mapping to the SYNTAX clause ......................   15
   5.1.2 Mapping to the ACCESS clause ......................   15
   5.1.3 Mapping to the STATUS clause ......................   15
   5.1.4 Mapping to the DESCRIPTION clause .................   15
   5.1.5 Mapping to the REFERENCE clause ...................   16
   5.1.6 Mapping to the INDEX clause .......................   16
   5.1.7 Mapping to the DEFVAL clause ......................   16
   5.2 Action Mapping ......................................   16
   5.2.1 Mapping to the SYNTAX clause ......................   16
   5.2.2 Mapping to the ACCESS clause ......................   16



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   5.2.3 Mapping to the STATUS clause ......................   16
   5.2.4 Mapping to the DESCRIPTION clause .................   16
   5.2.5 Mapping to the REFERENCE clause ...................   16
   6. Acknowledgements .....................................   17
   7. References ...........................................   18
   8. Security Considerations...............................   19
   9. Authors' Addresses....................................   19

1.  Abstract

   This memo describes a straight-forward approach toward producing
   concise, yet descriptive, MIB modules.  It is intended that all
   future MIB modules be written in this format.

2.  Historical Perspective

   As reported in RFC 1052, IAB Recommendations for the Development of
   Internet Network Management Standards [1], a two-prong strategy for
   network management of TCP/IP-based internets was undertaken.  In the
   short-term, the Simple Network Management Protocol (SNMP), defined in
   RFC 1067, was to be used to manage nodes in the Internet community.
   In the long-term, the use of the OSI network management framework was
   to be examined.  Two documents were produced to define the management
   information: RFC 1065, which defined the Structure of Management
   Information (SMI), and RFC 1066, which defined the Management
   Information Base (MIB).  Both of these documents were designed so as
   to be compatible with both the SNMP and the OSI network management
   framework.

   This strategy was quite successful in the short-term: Internet-based
   network management technology was fielded, by both the research and
   commercial communities, within a few months.  As a result of this,
   portions of the Internet community became network manageable in a
   timely fashion.

   As reported in RFC 1109, Report of the Second Ad Hoc Network
   Management Review Group [2], the requirements of the SNMP and the OSI
   network management frameworks were more different than anticipated.
   As such, the requirement for compatibility between the SMI/MIB and
   both frameworks was suspended.  This action permitted the operational
   network management framework, based on the SNMP, to respond to new
   operational needs in the Internet community by producing MIB-II.

   In May of 1990, the core documents were elevated to "Standard
   Protocols" with "Recommended" status.  As such, the Internet-standard
   network management framework consists of: Structure and
   Identification of Management Information for TCP/IP-based internets,
   RFC 1155 [3], which describes how managed objects contained in the



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   MIB are defined; Management Information Base for Network Management
   of TCP/IP-based internets, which describes the managed objects
   contained in the MIB, RFC 1156 [4]; and, the Simple Network
   Management Protocol, RFC 1157 [5], which defines the protocol used to
   manage these objects.  Consistent with the IAB directive to produce
   simple, workable systems in the short-term, the list of managed
   objects defined in the Internet-standard MIB was derived by taking
   only those elements which are considered essential.  However, the SMI
   defined three extensibility mechanisms: one, the addition of new
   standard objects through the definitions of new versions of the MIB;
   two, the addition of widely-available but non-standard objects
   through the experimental subtree; and three, the addition of private
   objects through the enterprises subtree.  Such additional objects can
   not only be used for vendor-specific elements, but also for
   experimentation as required to further the knowledge of which other
   objects are essential.

   As more objects are defined using the second method, experience has
   shown that the resulting MIB descriptions contain redundant
   information.  In order to provide for MIB descriptions which are more
   concise, and yet as informative, an enhancement is suggested.  This
   enhancement allows the author of a MIB to remove the redundant
   information, while retaining the important descriptive text.

   Before presenting the approach, a brief presentation of columnar
   object handling by the SNMP is necessary.  This explains and further
   motivates the value of the enhancement.

3.  Columnar Objects

   The SNMP supports operations on MIB objects whose syntax is
   ObjectSyntax as defined in the SMI.  Informally stated, SNMP
   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.  Historically, this conceptualization has
   been 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.  (The ACCESS clause for such objects is
   "not-accessible", of course.) However, it must be emphasized that, at
   the protocol level, relationships among columnar objects in the same
   row is a matter of convention, not of protocol.

   Note that there are good reasons why the tabular structure is not a
   matter of protocol.  Consider the operation of the SNMP Get-Next-PDU
   acting on the last columnar object of an instance of a conceptual



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   row; it returns the next column of the first conceptual row or the
   first object instance occurring after the table.  In contrast, if the
   rows were a matter of protocol, then it would instead return an
   error.  By not returning an error, a single PDU exchange informs the
   manager that not only has the end of the conceptual row/table been
   reached, but also provides information on the next object instance,
   thereby increasing the information density of the PDU exchange.

3.1.  Row Deletion

   Nonetheless, it is highly useful to provide a means whereby a
   conceptual row may be removed from a table. In MIB-II, this was
   achieved by defining, for each conceptual row, an integer-valued
   columnar object.  If a management station sets the value of this
   object to some value, usually termed "invalid", then the effect is
   one of invalidating the corresponding row in the table.  However, it
   is an implementation-specific matter as to whether an agent removes
   an invalidated entry from the table.  Accordingly, management
   stations must be prepared to receive tabular information from agents
   that corresponds to entries not currently in use.  Proper
   interpretation of such entries requires examination of the columnar
   object indicating the in-use status.

3.2.  Row Addition

   It is also highly useful to have a clear understanding of how a
   conceptual row may be added to a table.  In the SNMP, at the protocol
   level, a management station issues an SNMP set operation containing
   an arbitrary set of variable bindings.  In the case that an agent
   detects that one or more of those variable bindings refers to an
   object instance not currently available in that agent, it may,
   according to the rules of the SNMP, behave according to any of the
   following paradigms:

          (1)  It may reject the SNMP set operation as referring to
               non-existent object instances by returning a response
               with the error-status field set to "noSuchName" and the
               error-index field set to refer to the first vacuous
               reference.

          (2)  It may accept the SNMP set operation as requesting the
               creation  of new object instances corresponding to each
               of the object instances named in the variable bindings.
               The value of each (potentially) newly created object
               instance is specified by the "value" component of the
               relevant variable binding.  In this case, if the request
               specifies a value for a newly (or previously) created
               object that it deems inappropriate by reason of value or



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               syntax, then it rejects the SNMP set operation by
               responding with the error-status field set to badValue
               and the error-index field set to refer to the first
               offending variable binding.

          (3)  It may accept the SNMP set operation and create new
               object instances as described in (2) above and, in
               addition, at its discretion, create supplemental object
               instances to complete a row in a conceptual table of
               which the new object instances specified in the request
               may be a part.

   It should be emphasized that all three of the above behaviors are
   fully conformant to the SNMP specification and are fully acceptable,
   subject to any restrictions which may be imposed by access control
   and/or the definitions of the MIB objects themselves.

4.  Defining Objects

   The Internet-standard SMI employs a two-level approach towards object
   definition.  A MIB definition consists of two parts: a textual part,
   in which objects are placed into groups, and a MIB module, in which
   objects are described solely in terms of the ASN.1 macro OBJECT-TYPE,
   which is defined by the SMI.

   An example of the former definition might be:

          OBJECT:
          -------
               sysLocation { system 6 }

          Syntax:
               DisplayString (SIZE (0..255))

          Definition:
               The physical location of this node (e.g., "telephone
               closet, 3rd floor").

          Access:
               read-only.

          Status:
               mandatory.

          An example of the latter definition might be:

               sysLocation OBJECT-TYPE
                   SYNTAX  DisplayString (SIZE (0..255))



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                   ACCESS  read-only
                   STATUS  mandatory
                   ::= { system 6 }

          In the interests of brevity and to reduce the chance of
          editing errors, it would seem useful to combine the two
          definitions.  This can be accomplished by defining an
          extension to the OBJECT-TYPE macro:

          IMPORTS
              ObjectName
                  FROM RFC1155-SMI
              DisplayString
                  FROM RFC1158-MIB;

          OBJECT-TYPE MACRO ::=
          BEGIN
              TYPE NOTATION ::=
                                          -- must conform to
                                          -- RFC1155's ObjectSyntax
                                "SYNTAX" type(ObjectSyntax)
                                "ACCESS" Access
                                "STATUS" Status
                                DescrPart
                                ReferPart
                                IndexPart
                                DefValPart
              VALUE NOTATION ::= value (VALUE ObjectName)

              Access ::= "read-only"
                              | "read-write"
                              | "write-only"
                              | "not-accessible"
              Status ::= "mandatory"
                              | "optional"
                              | "obsolete"
                              | "deprecated"

              DescrPart ::=
                         "DESCRIPTION" value (description DisplayString)
                              | empty

              ReferPart ::=
                         "REFERENCE" value (reference DisplayString)
                              | empty

              IndexPart ::=
                         "INDEX" "{" IndexTypes "}"



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                              | empty
              IndexTypes ::=
                         IndexType | IndexTypes "," IndexType
              IndexType ::=
                                  -- if indexobject, use the SYNTAX
                                  -- value of the correspondent
                                  -- OBJECT-TYPE invocation
                         value (indexobject ObjectName)
                                  -- otherwise use named SMI type
                                  -- must conform to IndexSyntax below
                              | type (indextype)

              DefValPart ::=
                         "DEFVAL" "{" value (defvalue ObjectSyntax) "}"
                              | empty

          END

          IndexSyntax ::=
              CHOICE {
                  number
                      INTEGER (0..MAX),
                  string
                      OCTET STRING,
                  object
                      OBJECT IDENTIFIER,
                  address
                      NetworkAddress,
                  ipAddress
                      IpAddress
              }


4.1.  Mapping of the OBJECT-TYPE macro

   It should be noted that the expansion of the OBJECT-TYPE macro is
   something which conceptually happens during implementation and not
   during run-time.

4.1.1.  Mapping of the SYNTAX clause

   The SYNTAX clause, which must be present, defines the abstract data
   structure corresponding to that object type.  The ASN.1 language [6]
   is used for this purpose.  However, the SMI purposely restricts the
   ASN.1 constructs which may be used.  These restrictions are made
   expressly for simplicity.





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4.1.2.  Mapping of the ACCESS clause

   The ACCESS clause, which must be present, defines the minimum level
   of support required for that object type.  As a local matter,
   implementations may support other access types (e.g., an
   implementation may elect to permitting writing a variable marked as
   read-only).  Further, protocol-specific "views" (e.g., those
   indirectly implied by an SNMP community) may make further
   restrictions on access to a variable.

4.1.3.  Mapping of the STATUS clause

   The STATUS clause, which must be present, defines the implementation
   support required for that object type.

4.1.4.  Mapping of the DESCRIPTION clause

   The DESCRIPTION clause, which need not be present, contains a textual
   definition of that object type 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.  Note that, in
   order to conform to the ASN.1 syntax, the entire value of this clause
   must be enclosed in double quotation marks, although the value may be
   multi-line.

   Further, note that if the MIB module does not contain a textual
   description of the object type elsewhere then the DESCRIPTION clause
   must be present.

4.1.5.  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 MIB module.  This
   is useful when de-osifying a MIB produced by some other organization.

4.1.6.  Mapping of the INDEX clause

   The INDEX clause, which may be present only if that object type
   corresponds to a conceptual row, defines instance identification
   information for that object type.  (Historically, each MIB definition
   contained a section entitled "Identification of OBJECT instances for
   use with the SNMP".  By using the INDEX clause, this section need no
   longer occur as this clause concisely captures the precise semantics
   needed for instance identification.)

   If the INDEX clause is not present, and the object type corresponds
   to a non-columnar object, then instances of the object are identified



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   by appending a sub-identifier of zero to the name of that object.
   Further, note that if the MIB module does not contain a textual
   description of how instance identification information is derived for
   columnar objects, then the INDEX clause must be present.

   To define the instance identification information, determine which
   object value(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: `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: `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)  NetworkAddress-valued: `n+1' sub-identifiers, where `n'
               depends on the kind of address being encoded (the first
               sub-identifier indicates the kind of address, value 1
               indicates an IpAddress); or,

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

   Note that if an "indextype" value is present (e.g., INTEGER rather
   than ifIndex), then a DESCRIPTION clause must be present; the text
   contained therein indicates the semantics of the "indextype" value.












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   By way of example, in the context of MIB-II [7], the following INDEX
   clauses might be present:

                 objects under         INDEX clause
               -----------------       ------------
               ifEntry                 { ifIndex }
               atEntry                 { atNetIfIndex,
                                         atNetAddress }
               ipAddrEntry             { ipAdEntAddr }
               ipRouteEntry            { ipRouteDest }
               ipNetToMediaEntry       { ipNetToMediaIfIndex,
                                         ipNetToMediaNetAddress }
               tcpConnEntry            { tcpConnLocalAddress,
                                         tcpConnLocalPort,
                                         tcpConnRemoteAddress,
                                         tcpConnRemotePort }
               udpEntry                { udpLocalAddress,
                                         udpLocalPort }
               egpNeighEntry           { egpNeighAddr }


4.1.7.  Mapping of the DEFVAL clause

   The DEFVAL clause, which need not be present, defines an acceptable
   default value which may be used when an object instance is created at
   the discretion of the agent acting in conformance with the third
   paradigm described in Section 4.2 above.

   During conceptual row creation, if an instance of a columnar object
   is not present as one of the operands in the correspondent SNMP set
   operation, then the value of the DEFVAL clause, if present, indicates
   an acceptable default value that the agent might use.

   The value of the DEFVAL clause must, of course, correspond to the
   SYNTAX clause for the object.  Note that if an operand to the SNMP
   set operation is an instance of a read-only object, then the error
   noSuchName will be returned.  As such, the DEFVAL clause can be used
   to provide an acceptable default value that the agent might use.

   It is possible that no acceptable default value may exist for any of
   the columnar objects in a conceptual row for which the creation of
   new object instances is allowed.  In this case, the objects specified
   in the INDEX clause must have a corresponding ACCESS clause value of
   read-write.







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

       ObjectSyntax            DEFVAL clause
       -----------------       ------------
       INTEGER                 1 -- same for Counter, Gauge, TimeTicks
       OCTET STRING            'ffffffffffff'h
       DisplayString           "any NVT ASCII string"
       OBJECT IDENTIFIER       sysDescr
       OBJECT IDENTIFIER       { system 2 }
       NULL                    NULL
       NetworkAddress          { internet 'c0210415'h }
       IpAddress               'c0210415'h -- 192.33.4.21


4.1.8.  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.

4.2.  Usage Example

   Consider how the ipNetToMediaTable from MIB-II might be fully
   described:

          -- the IP Address Translation tables

          -- The Address Translation tables contain IpAddress to
          -- "physical" address equivalences.  Some interfaces do not
          -- use translation tables for determining address equivalences
          -- (e.g., DDN-X.25 has an algorithmic method); if all
          -- interfaces are of this type, then the Address Translation
          -- table is empty, i.e., has zero entries.

          ipNetToMediaTable OBJECT-TYPE
              SYNTAX  SEQUENCE OF IpNetToMediaEntry
              ACCESS  not-accessible
              STATUS  mandatory
              DESCRIPTION
                      "The IP Address Translation table used for mapping
                      from IP addresses to physical addresses."
              ::= { ip 22 }

          ipNetToMediaEntry OBJECT-TYPE
              SYNTAX  IpNetToMediaEntry
              ACCESS  not-accessible
              STATUS  mandatory
              DESCRIPTION
                      "Each entry contains one IpAddress to 'physical'



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                      address equivalence."
              INDEX   { ipNetToMediaIfIndex,
                        ipNetToMediaNetAddress }
              ::= { ipNetToMediaTable 1 }

          IpNetToMediaEntry ::=
              SEQUENCE {
                  ipNetToMediaIfIndex
                      INTEGER,
                  ipNetToMediaPhysAddress
                      OCTET STRING,
                  ipNetToMediaNetAddress
                      IpAddress,
                  ipNetoToMediaType
                      INTEGER
              }

          ipNetToMediaIfIndex OBJECT-TYPE
              SYNTAX  INTEGER
              ACCESS  read-write
              STATUS  mandatory
              DESCRIPTION
                      "The interface on which this entry's equivalence
                      is effective.  The interface identified by a
                      particular value of this index is the same
                      interface as identified by the same value of
                      ifIndex."
              ::= { ipNetToMediaEntry 1 }

          ipNetToMediaPhysAddress OBJECT-TYPE
              SYNTAX  OCTET STRING
              ACCESS  read-write
              STATUS  mandatory
              DESCRIPTION
                      "The media-dependent 'physical' address."
              ::= { ipNetToMediaEntry 2 }

          ipNetToMediaNetAddress OBJECT-TYPE
              SYNTAX  IpAddress
              ACCESS  read-write
              STATUS  mandatory
              DESCRIPTION
                      "The IpAddress corresponding to the media-
                      dependent 'physical' address."
              ::= { ipNetToMediaEntry 3 }

          ipNetToMediaType OBJECT-TYPE
              SYNTAX  INTEGER {



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                          other(1),   -- none of the following
                          invalid(2), -- an invalidated mapping
                          dynamic(3),
                          static(4)
                      }
              ACCESS  read-write
              STATUS  mandatory
              DESCRIPTION
                      "The type of mapping.

                      Setting this object to the value invalid(2) has
                      the effect of invalidating the corresponding entry
                      in the ipNetToMediaTable.  That is, it effectively
                      disassociates the interface identified with said
                      entry from the mapping identified with said entry.
                      It is an implementation-specific matter as to
                      whether the agent removes an invalidated entry
                      from the table.  Accordingly, management stations
                      must be prepared to receive tabular information
                      from agents that corresponds to entries not
                      currently in use.  Proper interpretation of such
                      entries requires examination of the relevant
                      ipNetToMediaType object."
                  ::= { ipNetToMediaEntry 4 }


5.  Appendix: DE-osifying MIBs

   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, e.g.,

               RFC1213-MIB DEFINITIONS ::= BEGIN

               IMPORTS
                       experimental, OBJECT-TYPE, Counter
                           FROM RFC1155-SMI;

                       -- contact IANA for actual number
               root    OBJECT IDENTIFIER ::= { experimental xx }

               END



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   The next step is to categorize the objects into groups.  For
   experimental MIBs, optional objects are permitted.  However, when a
   MIB module is placed in the Internet-standard space, these optional
   objects are either removed, or placed in a optional group, 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.

   It must be emphasized that groups are "units of conformance" within a
   MIB: everything in a group is "mandatory" and implementations do
   either whole groups or none.

5.1.  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 type 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, 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



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   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 MIB's with a myriad of
   optionals.

5.1.1.  Mapping to the SYNTAX clause

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

          (1)  An object with BOOLEAN syntax becomes an INTEGER taking
               either of values true(1) or false(2).

          (2)  An object with ENUMERATED syntax becomes an INTEGER,
               taking any of the values given.

          (3)  An object with BIT STRING syntax containing no more than
               32 bits becomes an INTEGER defined as a sum; otherwise if
               more than 32 bits are present, the object becomes an
               OCTET STRING, with the bits numbered from left-to-right,
               in which the least significant bits of the last octet may
               be "reserved for future use".

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

          (5)  An 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.

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

5.1.2.  Mapping to the ACCESS clause

   This is straight-forward.

5.1.3.  Mapping to the STATUS clause

   This is usually straight-forward; however, some osified-MIBs use the
   term "recommended".  In this case, a choice must be made between
   "mandatory" and "optional".

5.1.4.  Mapping to the DESCRIPTION clause

   This is straight-forward: simply copy the text, making sure that any



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   embedded double quotation marks are sanitized (i.e., replaced with
   single-quotes or removed).

5.1.5.  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.

5.1.6.  Mapping to the INDEX clause

   Decide how instance-identifiers for columnar objects are to be formed
   and define this clause accordingly.

5.1.7.  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.

5.2.  Action Mapping

   Actions are modeled as read-write objects, in which writing a
   particular value results in the action taking place.

5.2.1.  Mapping to the SYNTAX clause

   Usually an INTEGER 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.

5.2.2.  Mapping to the ACCESS clause

   Always use read-write.

5.2.3.  Mapping to the STATUS clause

   This is straight-forward.

5.2.4.  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).

5.2.5.  Mapping to the REFERENCE clause

   This is straight-forward: simply include a textual reference to the



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   action being mapped, the document which defines the action, and
   perhaps a page number in the document.

6.  Acknowledgements

   This document was produced by the SNMP Working Group:

               Anne Ambler, Spider
               Karl Auerbach, Sun
               Fred Baker, ACC
               Ken Brinkerhoff
               Ron Broersma, NOSC
               Jack Brown, US Army
               Theodore Brunner, Bellcore
               Jeffrey Buffum, HP
               John Burress, Wellfleet
               Jeffrey D. Case, University of Tennessee at Knoxville
               Chris Chiptasso, Spartacus
               Paul Ciarfella, DEC
               Bob Collet
               John Cook, Chipcom
               Tracy Cox, Bellcore
               James R. Davin, MIT-LCS
               Eric Decker, cisco
               Kurt Dobbins, Cabletron
               Nadya El-Afandi, Network Systems
               Gary Ellis, HP
               Fred Engle
               Mike Erlinger
               Mark S. Fedor, PSI
               Richard Fox, Synoptics
               Karen Frisa, CMU
               Chris Gunner, DEC
               Fred Harris, University of Tennessee at Knoxville
               Ken Hibbard, Xylogics
               Ole Jacobsen, Interop
               Ken Jones
               Satish Joshi, Synoptics
               Frank Kastenholz, Racal-Interlan
               Shimshon Kaufman, Spartacus
               Ken Key, University of Tennessee at Knoxville
               Jim Kinder, Fibercom
               Alex Koifman, BBN
               Christopher Kolb, PSI
               Cheryl Krupczak, NCR
               Paul Langille, DEC
               Peter Lin, Vitalink
               John Lunny, TWG



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               Carl Malamud
               Randy Mayhew, University of Tennessee at Knoxville
               Keith McCloghrie, Hughes LAN Systems
               Donna McMaster, David Systems
               Lynn Monsanto, Sun
               Dave Perkins, 3COM
               Jim Reinstedler, Ungerman Bass
               Anil Rijsinghani, DEC
               Kathy Rinehart, Arnold AFB
               Kary Robertson
               Marshall T. Rose, PSI (chair)
               L. Michael Sabo, NCSC
               Jon Saperia, DEC
               Greg Satz, cisco
               Martin Schoffstall, PSI
               John Seligson
               Steve Sherry, Xyplex
               Fei Shu, NEC
               Sam Sjogren, TGV
               Mark Sleeper, Sparta
               Lance Sprung
               Mike St.Johns
               Bob Stewart, Xyplex
               Emil Sturniold
               Kaj Tesink, Bellcore
               Dean Throop, Data General
               Bill Townsend, Xylogics
               Maurice Turcotte, Racal-Milgo
               Kannan Varadhou
               Sudhanshu Verma, HP
               Bill Versteeg, Network Research Corporation
               Warren Vik, Interactive Systems
               David Waitzman, BBN
               Steve Waldbusser, CMU
               Dan Wintringhan
               David Wood
               Wengyik Yeong, PSI
               Jeff Young, Cray Research

7.  References

   [1] Cerf, V., "IAB Recommendations for the Development of Internet
       Network Management Standards", RFC 1052, NRI, April 1988.

   [2] Cerf, V., "Report of the Second Ad Hoc Network Management Review
       Group", RFC 1109, NRI, August 1989.

   [3] Rose M., and K. McCloghrie, "Structure and Identification of



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       Management Information for TCP/IP-based internets", RFC 1155,
       Performance Systems International, Hughes LAN Systems, May 1990.

   [4] McCloghrie K., and M. Rose, "Management Information Base for
       Network Management of TCP/IP-based internets", RFC 1156, Hughes
       LAN Systems, Performance Systems International, May 1990.

   [5] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple
       Network Management Protocol", RFC 1157, SNMP Research,
       Performance Systems International, Performance Systems
       International, MIT Laboratory for Computer Science, May 1990.

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

   [7] Rose M., Editor, "Management Information Base for Network
       Management of TCP/IP-based internets: MIB-II", RFC 1213,
       Performance Systems International, March 1991.

8.  Security Considerations

   Security issues are not discussed in this memo.

9.  Authors' Addresses

   Marshall T. Rose
   Performance Systems International
   5201 Great America Parkway
   Suite 3106
   Santa Clara, CA  95054

   Phone: [phone]
   EMail: [e-mail]
   X.500:  rose, psi, us


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

   Phone: [phone]
   EMail: [e-mail]




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