<- STD Index (1..100)
STD 16
(also RFC 1155, RFC 1212)
Obsoletes RFC 1065
[Note that this file is a concatenation of more than one RFC.]
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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-- 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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-- 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
Rose & McCloghrie [Page 20]
RFC 1155 SMI May 1990
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.
Rose & McCloghrie [Page 21]
RFC 1155 SMI May 1990
Authors' Addresses
Marshall T. Rose
PSI, Inc.
PSI California Office
P.O. Box 391776
Mountain View, CA 94039
Phone: (415) 961-3380
EMail: mrose@PSI.COM
Keith McCloghrie
The Wollongong Group
1129 San Antonio Road
Palo Alto, CA 04303
Phone: (415) 962-7160
EMail: sytek!kzm@HPLABS.HP.COM
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: +1 408 562 6222
EMail: mrose@psi.com
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: (415) 966-7934
EMail: kzm@hls.com
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