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
initial management information base along with the initial network
management protocol, these documents provide a simple, workable
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architecture and system for managing TCP/IP-based internets and in
particular, the Internet.
This memo specifies a draft standard for the Internet community.
TCP/IP implementations in the Internet which are network manageable
are expected to adopt and implement this specification.
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
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 in
the short-term for which a non-OSI protocol, the SNMP, has been
designated as the standard.
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
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Development of Internet Network Management Standards" [5]. In
particular, we feel that this memo, along with the memo describing
the initial 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 [6].
It is beyond the scope of this memo to define either the initial MIB
used for network management or the network management protocol. As
mentioned earlier, these tasks are left to the 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.)
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An OBJECT IDENTIFIER is a sequence of integers which traverse a
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
Standards Organization, with label iso(1); another is administrated
by the International Telegraph and Telephone Consultative Committee,
with label ccitt(2); and the third is jointly administered by the ISO
and the CCITT, joint-iso-ccitt(3).
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 Bureau of
Standards. One of these subtrees has been transferred by the NBS 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 an RFC 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 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 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 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 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 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
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:
Definition:
An entry in the address translation table.
Access:
read-write.
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RFC 1065 SMI August 1988
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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RFC 1065 SMI August 1988
{ 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:
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.
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 1065 SMI August 1988
-- 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
This memo was influenced by three sets of contributors:
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 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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RFC 1065 SMI August 1988
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 1066, TWG,
August 1988.
[3] Case, J., M. Fedor, M. Schoffstall, and J. Davin, The Simple
Network Management Protocol", RFC 1067, University of Tennessee
at Knoxville, NYSERNet, Rensselaer Polytechnic, Proteon, August
1988.
[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] 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.
