As per Relevance of the word identifier, we have this rfc below:
Network Working Group SNMPv2 Working
Request for Comments: 1902 J.
Obsoletes: 1442 SNMP Research, Inc
Category: Standards Track K.
Cisco Systems, Inc
M.
Dover Beach Consulting, Inc
S.
International Network
January 1996
Structure of Management
for Version 2 of
Simple Network Management Protocol (SNMPv2)
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
1.
A management system contains: several (potentially many) nodes,
with a processing entity, termed an agent, which has access
management instrumentation; at least one management station; and,
management protocol, used to convey management information
the agents and management stations. Operations of the protocol
carried out under an administrative framework which
authentication, authorization, access control, and privacy policies
Management stations execute management applications which monitor
control managed elements. Managed elements are devices such
hosts, routers, terminal servers, etc., which are monitored
controlled via access to their management information
Management information is viewed as a collection of managed objects
residing in a virtual information store, termed the
Information Base (MIB). Collections of related objects are
in MIB modules. These modules are written using an adapted subset
OSI's Abstract Syntax Notation One (ASN.1) [1]. It is the purpose
this document, the Structure of Management Information (SMI),
define that adapted subset, and to assign a set of
administrative values
SNMPv2 Working Group Standards Track [Page 1]
RFC 1902 SMI for SNMPv2 January 1996
The SMI is divided into three parts: module definitions,
definitions, and, notification definitions
(1) Module definitions are used when describing information modules
An ASN.1 macro, MODULE-IDENTITY, is used to concisely convey
semantics of an information module
(2) Object definitions are used when describing managed objects.
ASN.1 macro, OBJECT-TYPE, is used to concisely convey the
and semantics of a managed object
(3) Notification definitions are used when describing
transmissions of management information. An ASN.1 macro
NOTIFICATION-TYPE, is used to concisely convey the syntax
semantics of a notification
1.1. A Note on
For the purpose of exposition, the original Internet-standard
Management Framework, as described in RFCs 1155 (STD 16), 1157 (
15), and 1212 (STD 16), is termed the SNMP version 1
(SNMPv1). The current framework is termed the SNMP version 2
framework (SNMPv2).
2.
SNMPv2-SMI DEFINITIONS ::=
-- the path to the
org OBJECT IDENTIFIER ::= { iso 3 }
dod OBJECT IDENTIFIER ::= { org 6 }
internet OBJECT IDENTIFIER ::= { dod 1 }
directory OBJECT IDENTIFIER ::= { internet 1 }
mgmt OBJECT IDENTIFIER ::= { internet 2 }
mib-2 OBJECT IDENTIFIER ::= { mgmt 1 }
transmission OBJECT IDENTIFIER ::= { mib-2 10 }
experimental OBJECT IDENTIFIER ::= { internet 3 }
private OBJECT IDENTIFIER ::= { internet 4 }
enterprises OBJECT IDENTIFIER ::= { private 1 }
security OBJECT IDENTIFIER ::= { internet 5 }
SNMPv2 Working Group Standards Track [Page 2]
RFC 1902 SMI for SNMPv2 January 1996
snmpV2 OBJECT IDENTIFIER ::= { internet 6 }
-- transport
snmpDomains OBJECT IDENTIFIER ::= { snmpV2 1 }
-- transport
snmpProxys OBJECT IDENTIFIER ::= { snmpV2 2 }
-- module
snmpModules OBJECT IDENTIFIER ::= { snmpV2 3 }
-- definitions for information
MODULE-IDENTITY MACRO ::=
TYPE NOTATION ::=
"LAST-UPDATED" value(Update UTCTime
"ORGANIZATION"
"CONTACT-INFO"
"DESCRIPTION"
VALUE NOTATION ::=
value(VALUE OBJECT IDENTIFIER
RevisionPart ::=
|
Revisions ::=
| Revisions
Revision ::=
"REVISION" value(Update UTCTime
"DESCRIPTION"
-- uses the NVT ASCII character
Text ::= """" string """"
OBJECT-IDENTITY MACRO ::=
TYPE NOTATION ::=
"STATUS"
"DESCRIPTION"
SNMPv2 Working Group Standards Track [Page 3]
RFC 1902 SMI for SNMPv2 January 1996
VALUE NOTATION ::=
value(VALUE OBJECT IDENTIFIER
Status ::=
"current
| "deprecated
| "obsolete
ReferPart ::=
"REFERENCE"
|
Text ::= """" string """"
-- names of
ObjectName ::=
OBJECT
NotificationName ::=
OBJECT
-- syntax of
ObjectSyntax ::=
CHOICE {
SimpleSyntax
-- note that SEQUENCEs for conceptual tables
-- rows are not mentioned here...
application-
}
-- built-in ASN.1
SimpleSyntax ::=
CHOICE {
-- INTEGERs with a more restrictive
-- may also be
integer-value -- includes Integer32
INTEGER (-2147483648..2147483647),
SNMPv2 Working Group Standards Track [Page 4]
RFC 1902 SMI for SNMPv2 January 1996
-- OCTET STRINGs with a more restrictive
-- may also be
string-
OCTET STRING (SIZE (0..65535)),
objectID-
OBJECT
}
-- indistinguishable from INTEGER, but never needs more
-- 32-bits for a two's complement
Integer32 ::=
[UNIVERSAL 2]
IMPLICIT INTEGER (-2147483648..2147483647)
-- application-wide
ApplicationSyntax ::=
CHOICE {
ipAddress-
IpAddress
counter-
Counter32,
timeticks-
TimeTicks
arbitrary-
Opaque
big-counter-
Counter64,
unsigned-integer-value -- includes Gauge32
Unsigned32
}
-- in network-byte
-- (this is a tagged type for historical reasons
IpAddress ::=
[APPLICATION 0]
IMPLICIT OCTET STRING (SIZE (4))
-- this
Counter32 ::=
SNMPv2 Working Group Standards Track [Page 5]
RFC 1902 SMI for SNMPv2 January 1996
[APPLICATION 1]
IMPLICIT INTEGER (0..4294967295)
-- this doesn't
Gauge32 ::=
[APPLICATION 2]
IMPLICIT INTEGER (0..4294967295)
-- an unsigned 32-bit
-- indistinguishable from Gauge32
Unsigned32 ::=
[APPLICATION 2]
IMPLICIT INTEGER (0..4294967295)
-- hundredths of seconds since an
TimeTicks ::=
[APPLICATION 3]
IMPLICIT INTEGER (0..4294967295)
-- for backward-compatibility
Opaque ::=
[APPLICATION 4]
IMPLICIT OCTET
-- for counters that wrap in less than one hour with only 32
Counter64 ::=
[APPLICATION 6]
IMPLICIT INTEGER (0..18446744073709551615)
-- definition for
OBJECT-TYPE MACRO ::=
TYPE NOTATION ::=
"SYNTAX"
"MAX-ACCESS"
"STATUS"
"DESCRIPTION"
VALUE NOTATION ::=
value(VALUE ObjectName
Syntax ::=
SNMPv2 Working Group Standards Track [Page 6]
RFC 1902 SMI for SNMPv2 January 1996
type(ObjectSyntax
| "BITS" "{" Kibbles "}"
Kibbles ::=
| Kibbles ","
Kibble ::=
identifier "(" nonNegativeNumber ")"
UnitsPart ::=
"UNITS"
|
Access ::=
"not-accessible
| "accessible-for-notify
| "read-only
| "read-write
| "read-create
Status ::=
"current
| "deprecated
| "obsolete
ReferPart ::=
"REFERENCE"
|
IndexPart ::=
"INDEX" "{" IndexTypes "}"
| "AUGMENTS" "{" Entry "}"
|
IndexTypes ::=
| IndexTypes ","
IndexType ::=
"IMPLIED"
|
Index ::=
-- use the SYNTAX value of
-- correspondent OBJECT-TYPE
value(Indexobject ObjectName
Entry ::=
-- use the INDEX value of
-- correspondent OBJECT-TYPE
value(Entryobject ObjectName
DefValPart ::=
SNMPv2 Working Group Standards Track [Page 7]
RFC 1902 SMI for SNMPv2 January 1996
"DEFVAL" "{" value(Defval Syntax) "}"
|
-- uses the NVT ASCII character
Text ::= """" string """"
-- definitions for
NOTIFICATION-TYPE MACRO ::=
TYPE NOTATION ::=
"STATUS"
"DESCRIPTION"
VALUE NOTATION ::=
value(VALUE NotificationName
ObjectsPart ::=
"OBJECTS" "{" Objects "}"
|
Objects ::=
| Objects ","
Object ::=
value(Name ObjectName
Status ::=
"current
| "deprecated
| "obsolete
ReferPart ::=
"REFERENCE"
|
-- uses the NVT ASCII character
Text ::= """" string """"
-- definitions of administrative
zeroDotZero OBJECT-
STATUS
SNMPv2 Working Group Standards Track [Page 8]
RFC 1902 SMI for SNMPv2 January 1996
"A value used for null identifiers."
::= { 0 0 }
3. Information
An "information module" is an ASN.1 module defining
relating to network management
The SMI describes how to use a subset of ASN.1 to define
information module. Further, additional restrictions are placed
"standard" information modules. It is strongly recommended
"enterprise-specific" information modules also adhere to
restrictions
Typically, there are three kinds of information modules
(1) MIB modules, which contain definitions of inter-related
objects, make use of the OBJECT-TYPE and NOTIFICATION-TYPE macros
(2) compliance statements for MIB modules, which make use of
MODULE-COMPLIANCE and OBJECT-GROUP macros [2]; and
(3) capability statements for agent implementations which make use
the AGENT-CAPABILITIES macros [2].
This classification scheme does not imply a rigid taxonomy.
example, a "standard" information module will normally
definitions of managed objects and a compliance statement
Similarly, an "enterprise-specific" information module might
definitions of managed objects and a capability statement.
course, a "standard" information module may not contain
statements
The constructs of ASN.1 allowed in SNMPv2 information
include: the IMPORTS clause, value definitions for
IDENTIFIERs, type definitions for SEQUENCEs (with restrictions),
ASN.1 type assignments of the restricted ASN.1 types allowed
SNMPv2, and instances of ASN.1 macros defined in this document and
other documents [2, 3] of the SNMPv2 framework. Additional ASN.1
macros may not be defined in SNMPv2 information modules
The names of all standard information modules must be unique (
different versions of the same information module should have
same name). Developers of enterprise information modules
encouraged to choose names for their information modules that
have a low probability of colliding with standard or other
SNMPv2 Working Group Standards Track [Page 9]
RFC 1902 SMI for SNMPv2 January 1996
information modules. An information module may not use the ASN.1
construct of placing an object identifier value between the
name and the "DEFINITIONS" keyword
All information modules start with exactly one invocation of
MODULE-IDENTITY macro, which provides contact information as well
revision history to distinguish between versions of the
information module. This invocation must appear immediately
any IMPORTs statements
3.1. Macro
Within an information module, each macro invocation appears as
<descriptor> ::=
where <descriptor> corresponds to an ASN.1 identifier,
the macro being invoked, and and depend on
definition of the macro. (Note that this definition of a
applies to all macros defined in this memo and in [2].)
For the purposes of this specification, an ASN.1 identifier
of one or more letters or digits, and its initial character must be
lower-case letter. (Note that hyphens are not allowed by
specification, even though hyphen is allowed by [1].
restriction enables arithmetic expressions in languages which use
minus sign to reference these descriptors without ambiguity.)
For all descriptors appearing in an information module,
descriptor shall be unique and mnemonic, and shall not exceed 64
characters in length. (However, descriptors longer than 32
characters are not recommended.) This promotes a common language
humans to use when discussing the information module and
facilitates simple table mappings for user-interfaces
The set of descriptors defined in all "standard" information
shall be unique
Finally, by convention, if the descriptor refers to an object with
SYNTAX clause value of either Counter32 or Counter64, then
descriptor used for the object should denote plurality
3.1.1. Textual
Some clauses in a macro invocation may take a textual value (e.g.,
the DESCRIPTION clause). Note that, in order to conform to the ASN.1
syntax, the entire value of these clauses must be enclosed in
quotation marks, and therefore cannot itself contain double
SNMPv2 Working Group Standards Track [Page 10]
RFC 1902 SMI for SNMPv2 January 1996
marks, although the value may be multi-line
3.2. IMPORTing
To reference an external object, the IMPORTS statement must be
to identify both the descriptor and the module in which
descriptor is defined, where the module is identified by its ASN.1
module name
Note that when symbols from "enterprise-specific" information
are referenced (e.g., a descriptor), there is the possibility
collision. As such, if different objects with the same
are IMPORTed, then this ambiguity is resolved by prefixing
descriptor with the name of the information module and a dot ("."),
i.e.,
"module.descriptor
(All descriptors must be unique within any information module.)
Of course, this notation can be used even when there is no
when IMPORTing symbols
Finally, the IMPORTS statement may not be used to import an ASN.1
named type which corresponds to either the SEQUENCE or SEQUENCE
type
3.3. Exporting
The ASN.1 EXPORTS statement is not allowed in SNMPv2
modules. All items defined in an information module
automatically exported
3.4. ASN.1
Comments in ASN.1 commence with a pair of adjacent hyphens and
with the next pair of adjacent hyphens or at the end of the line
whichever occurs first
3.5. OBJECT IDENTIFIER
An OBJECT IDENTIFIER value is an ordered list of non-
numbers. For the SNMPv2 framework, each number in the list
referred to as a sub-identifier, there are at most 128 sub
identifiers in a value, and each sub-identifier has a maximum
of 2^32-1 (4294967295 decimal). All OBJECT IDENTIFIER values have
least two sub-identifiers, where the value of the first sub
identifier is one of the following well-known names
SNMPv2 Working Group Standards Track [Page 11]
RFC 1902 SMI for SNMPv2 January 1996
Value
0
1
2 joint-iso-
4. Naming
The root of the subtree administered by the Internet Assigned
Authority (IANA) for the Internet is
internet OBJECT IDENTIFIER ::= { iso 3 6 1 }
That is, the Internet subtree of OBJECT IDENTIFIERs starts with
prefix
1.3.6.1.
Several branches underneath this subtree are used for
management
mgmt OBJECT IDENTIFIER ::= { internet 2 }
experimental OBJECT IDENTIFIER ::= { internet 3 }
private OBJECT IDENTIFIER ::= { internet 4 }
enterprises OBJECT IDENTIFIER ::= { private 1 }
However, the SMI does not prohibit the definition of objects in
portions of the object tree
The mgmt(2) subtree is used to identify "standard" objects
The experimental(3) subtree is used to identify objects
designed by working groups of the IETF. If an information
produced by a working group becomes a "standard" information module
then at the very beginning of its entry onto the Internet
track, the objects are moved under the mgmt(2) subtree
The private(4) subtree is used to identify objects
unilaterally. The enterprises(1) subtree beneath private is used
among other things, to permit providers of networking subsystems
register models of their products
5. Mapping of the MODULE-IDENTITY
The MODULE-IDENTITY macro is used to provide contact and
history for each information module. It must appear exactly once
every information module. It should be noted that the expansion
the MODULE-IDENTITY macro is something which conceptually
during implementation and not during run-time
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RFC 1902 SMI for SNMPv2 January 1996
Note that reference in an IMPORTS clause or in clauses of SNMPv
macros to an information module is NOT through the use of
'descriptor' of a MODULE-IDENTITY macro; rather, an
module is referenced through specifying its module name
5.1. Mapping of the LAST-UPDATED
The LAST-UPDATED clause, which must be present, contains the date
time that this information module was last edited. The date and
are represented in UTC Time format (see Appendix B).
5.2. Mapping of the ORGANIZATION
The ORGANIZATION clause, which must be present, contains a
description of the organization under whose auspices this
module was developed
5.3. Mapping of the CONTACT-INFO
The CONTACT-INFO clause, which must be present, contains the name
postal address, telephone number, and electronic mail address of
person to whom technical queries concerning this information
should be sent
5.4. Mapping of the DESCRIPTION
The DESCRIPTION clause, which must be present, contains a high-
textual description of the contents of this information module
5.5. Mapping of the REVISION
The REVISION clause, which need not be present, is repeatedly used
describe the revisions (including the initial version) made to
information module, in reverse chronological order (i.e., most
first). Each instance of this clause contains the date and time
the revision. The date and time are represented in UTC Time
(see Appendix B).
5.5.1. Mapping of the DESCRIPTION sub-
The DESCRIPTION clause, which must be present for each
clause, contains a high-level textual description of the
identified in that REVISION clause
5.6. Mapping of the MODULE-IDENTITY
The value of an invocation of the MODULE-IDENTITY macro is an
IDENTIFIER. As such, this value may be authoritatively used
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RFC 1902 SMI for SNMPv2 January 1996
specifying an OBJECT IDENTIFIER value to refer to the
module containing the invocation
5.7. Usage
Consider how a skeletal MIB module might be constructed: e.g.,
FIZBIN-MIB DEFINITIONS ::=
MODULE-IDENTITY, OBJECT-TYPE,
FROM SNMPv2-SMI
fizbin MODULE-
LAST-UPDATED "9505241811Z
ORGANIZATION "IETF SNMPv2 Working Group
CONTACT-
" Marshall T.
Postal: Dover Beach Consulting, Inc
420 Whisman
Mountain View, CA 94043-2186
Tel: +1 415 968 1052
Fax: +1 415 968 2510
E-mail: mrose@dbc.mtview.ca.us
"The MIB module for entities implementing the
protocol."
REVISION "9505241811Z
"The latest version of this MIB module."
REVISION "9210070433Z
"The initial version of this MIB module."
-- contact IANA for actual
::= { experimental xx }
SNMPv2 Working Group Standards Track [Page 14]
RFC 1902 SMI for SNMPv2 January 1996
6. Mapping of the OBJECT-IDENTITY
The OBJECT-IDENTITY macro is used to define information about
OBJECT IDENTIFIER assignment. All administrative OBJECT
assignments which define a type identification value (
AutonomousType, a textual convention defined in [3]) should
defined via the OBJECT-IDENTITY macro. It should be noted that
expansion of the OBJECT-IDENTITY macro is something
conceptually happens during implementation and not during run-time
6.1. Mapping of the STATUS
The STATUS clause, which must be present, indicates whether
definition is current or historic
The values "current", and "obsolete" are self-explanatory.
"deprecated" value indicates that the definition is obsolete,
that an implementor may wish to support it to foster
with older implementations
6.2. Mapping of the DESCRIPTION
The DESCRIPTION clause, which must be present, contains a
description of the object assignment
6.3. Mapping of the REFERENCE
The REFERENCE clause, which need not be present, contains a
cross-reference to an object assignment defined in some
information module
6.4. Mapping of the OBJECT-IDENTITY
The value of an invocation of the OBJECT-IDENTITY macro is an
IDENTIFIER
6.5. Usage
Consider how an OBJECT IDENTIFIER assignment might be made: e.g.,
fizbin69 OBJECT-
STATUS
"The authoritative identity of the Fizbin 69 chipset."
::= { fizbinChipSets 1 }
SNMPv2 Working Group Standards Track [Page 15]
RFC 1902 SMI for SNMPv2 January 1996
7. Mapping of the OBJECT-TYPE
The OBJECT-TYPE macro is used to define a type of managed object.
should be noted that the expansion of the OBJECT-TYPE macro
something which conceptually happens during implementation and
during run-time
For leaf objects which are not columnar objects (i.e., not
within a conceptual table), instances of the object are identified
appending a sub-identifier of zero to the name of that object
Otherwise, the INDEX clause of the conceptual row object superior
a columnar object defines instance identification information
7.1. Mapping of the SYNTAX
The SYNTAX clause, which must be present, defines the abstract
structure corresponding to that object. The data structure must
one of the following: a base type, the BITS construct, or a
convention. (SEQUENCE OF and SEQUENCE are also possible
conceptual tables, see section 7.1.12). The base types are
defined in the ObjectSyntax CHOICE. A textual convention is
newly-defined type defined as a sub-type of a base type [3].
A extended subset of the full capabilities of ASN.1 sub-typing
allowed, as appropriate to the underingly ASN.1 type. Any
restriction on size, range, enumerations or repertoire specified
this clause represents the maximal level of support which
"protocol sense". Restrictions on sub-typing are specified in
in Section 9 and Appendix C of this memo
The semantics of ObjectSyntax are now described
7.1.1. Integer32 and
The Integer32 type represents integer-valued information
-2^31 and 2^31-1 inclusive (-2147483648 to 2147483647 decimal).
type is indistinguishable from the INTEGER type. Both the
and Integer32 types may be sub-typed to be more constrained than
Integer32 type
The INTEGER type may also be used to represent integer-
information as named-number enumerations. In this case, only
named-numbers so enumerated may be present as a value. Note
although it is recommended that enumerated values start at 1 and
numbered contiguously, any valid value for Integer32 is allowed
an enumerated value and, further, enumerated values needn't
contiguously assigned
SNMPv2 Working Group Standards Track [Page 16]
RFC 1902 SMI for SNMPv2 January 1996
Finally, a label for a named-number enumeration must consist of
or more letters or digits (no hyphens), up to a maximum of 64
characters, and the initial character must be a lower-case letter
(However, labels longer than 32 characters are not recommended.)
7.1.2. OCTET
The OCTET STRING type represents arbitrary binary or textual data
Although there is no SMI-specified size limitation for this type,
designers should realize that there may be implementation
interoperability limitations for sizes in excess of 255 octets
7.1.3. OBJECT
The OBJECT IDENTIFIER type represents administratively
names. Any instance of this type may have at most 128 sub
identifiers. Further, each sub-identifier must not exceed the
2^32-1 (4294967295 decimal).
7.1.4. The BITS
The BITS construct represents an enumeration of named bits.
collection is assigned non-negative, contiguous values, starting
zero. Only those named-bits so enumerated may be present in a value
(Thus, enumerations must be assigned to consecutive bits; however
see Section 9 for refinements of an object with this syntax.)
Although there is no SMI-specified limitation on the number
enumerations (and therefore on the length of a value), MIB
should realize that there may be implementation and
limitations for sizes in excess of 128 bits
Finally, a label for a named-number enumeration must consist of
or more letters or digits (no hyphens), up to a maximum of 64
characters, and the initial character must be a lower-case letter
(However, labels longer than 32 characters are not recommended.)
7.1.5.
The IpAddress type represents a 32-bit internet address. It
represented as an OCTET STRING of length 4, in network byte-order
Note that the IpAddress type is a tagged type for historical reasons
Network addresses should be represented using an invocation of
TEXTUAL-CONVENTION macro [3].
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RFC 1902 SMI for SNMPv2 January 1996
7.1.6. Counter32
The Counter32 type represents a non-negative integer
monotonically increases until it reaches a maximum value of 2^32-1
(4294967295 decimal), when it wraps around and starts
again from zero
Counters have no defined "initial" value, and thus, a single value
a Counter has (in general) no information content.
in the monotonically increasing value normally occur at re
initialization of the management system, and at other times
specified in the description of an object-type using this ASN.1 type
If such other times can occur, for example, the creation of an
instance at times other than re-initialization, then a
object should be defined with a SYNTAX clause value of TimeStamp (
textual convention defined in [3]) indicating the time of the
discontinuity
The value of the MAX-ACCESS clause for objects with a SYNTAX
value of Counter32 is either "read-only" or "accessible-for-notify".
A DEFVAL clause is not allowed for objects with a SYNTAX clause
of Counter32.
7.1.7. Gauge32
The Gauge32 type represents a non-negative integer, which
increase or decrease, but shall never exceed a maximum value.
maximum value can not be greater than 2^32-1 (4294967295 decimal).
The value of a Gauge has its maximum value whenever the
being modeled is greater or equal to that maximum value; if
information being modeled subsequently decreases below the
value, the Gauge also decreases
7.1.8.
The TimeTicks type represents a non-negative integer which
the time, modulo 2^32 (4294967296 decimal), in hundredths of a
between two epochs. When objects are defined which use this ASN.1
type, the description of the object identifies both of the
epochs
For example, [3] defines the TimeStamp textual convention which
based on the TimeTicks type. With a TimeStamp, the first
epoch is defined as the time when sysUpTime [5] was zero, and
second reference epoch is defined as the current value of sysUpTime
The TimeTicks type may not be sub-typed
SNMPv2 Working Group Standards Track [Page 18]
RFC 1902 SMI for SNMPv2 January 1996
7.1.9.
The Opaque type is provided solely for backward-compatibility,
shall not be used for newly-defined object types
The Opaque type supports the capability to pass arbitrary ASN.1
syntax. A value is encoded using the ASN.1 Basic Encoding Rules [4]
into a string of octets. This, in turn, is encoded as an
STRING, in effect "double-wrapping" the original ASN.1 value
Note that a conforming implementation need only be able to accept
recognize opaquely-encoded data. It need not be able to unwrap
data and then interpret its contents
A requirement on "standard" MIB modules is that no object may have
SYNTAX clause value of Opaque
7.1.10. Counter64
The Counter64 type represents a non-negative integer
monotonically increases until it reaches a maximum value of 2^64-1
(18446744073709551615 decimal), when it wraps around and
increasing again from zero
Counters have no defined "initial" value, and thus, a single value
a Counter has (in general) no information content.
in the monotonically increasing value normally occur at re
initialization of the management system, and at other times
specified in the description of an object-type using this ASN.1 type
If such other times can occur, for example, the creation of an
instance at times other than re-initialization, then a
object should be defined with a SYNTAX clause value of TimeStamp (
textual convention defined in [3]) indicating the time of the
discontinuity
The value of the MAX-ACCESS clause for objects with a SYNTAX
value of Counter64 is either "read-only" or "accessible-for-notify".
A requirement on "standard" MIB modules is that the Counter64
may be used only if the information being modeled would wrap in
than one hour if the Counter32 type was used instead
A DEFVAL clause is not allowed for objects with a SYNTAX clause
of Counter64.
SNMPv2 Working Group Standards Track [Page 19]
RFC 1902 SMI for SNMPv2 January 1996
7.1.11. Unsigned32
The Unsigned32 type represents integer-valued information between 0
and 2^32-1 inclusive (0 to 4294967295 decimal).
7.1.12. Conceptual
Management operations apply exclusively to scalar objects. However
it is sometimes convenient for developers of management
to impose an imaginary, tabular structure on an ordered collection
objects within the MIB. Each such conceptual table contains zero
more rows, and each row may contain one or more scalar objects
termed columnar objects. This conceptualization is formalized
using the OBJECT-TYPE macro to define both an object
corresponds to a table and an object which corresponds to a row
that table. A conceptual table has SYNTAX of the form
SEQUENCE OF
where refers to the SEQUENCE type of its
conceptual row. A conceptual row has SYNTAX of the form
where is a SEQUENCE type defined as follows
::= SEQUENCE { , ... , }
where there is one for each subordinate object, and
is of the form
<descriptor>
where <descriptor> is the descriptor naming a subordinate object,
has the value of that subordinate object's SYNTAX clause
normally omitting the sub-typing information. Further, these ASN.1
types are always present (the DEFAULT and OPTIONAL clauses
disallowed in the SEQUENCE definition). The MAX-ACCESS clause
conceptual tables and rows is "not-accessible".
7.1.12.1. Creation and Deletion of Conceptual
For newly-defined conceptual rows which allow the creation of
object instances and/or the deletion of existing object instances
there should be one columnar object with a SYNTAX clause value
RowStatus (a textual convention defined in [3]) and a MAX-
clause value of read-create. By convention, this is termed
status column for the conceptual row
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7.2. Mapping of the UNITS
This UNITS clause, which need not be present, contains a
definition of the units associated with that object
7.3. Mapping of the MAX-ACCESS
The MAX-ACCESS clause, which must be present, defines whether
makes "protocol sense" to read, write and/or create an instance
the object, or to include its value in a notification. This is
maximal level of access for the object. (This maximal level
access is independent of any administrative authorization policy.)
The value "read-write" indicates that read and write access
"protocol sense", but create does not. The value "read-create
indicates that read, write and create access make "protocol sense".
The value "not-accessible" indicates an auxiliary object (see
7.7). The value "accessible-for-notify" indicates an object which
accessible only via a notification (e.g., snmpTrapOID [5]).
These values are ordered, from least to greatest: "not-accessible",
"accessible-for-notify", "read-only", "read-write", "read-create".
If any columnar object in a conceptual row has "read-create" as
maximal level of access, then no other columnar object of the
conceptual row may have a maximal access of "read-write". (Note
"read-create" is a superset of "read-write".)
7.4. Mapping of the STATUS
The STATUS clause, which must be present, indicates whether
definition is current or historic
The values "current", and "obsolete" are self-explanatory.
"deprecated" value indicates that the definition is obsolete,
that an implementor may wish to support that object to
interoperability with older implementations
7.5. Mapping of the DESCRIPTION
The DESCRIPTION clause, which must be present, contains a
definition of that object which provides all semantic
necessary for implementation, and should embody any information
would otherwise be communicated in any ASN.1 commentary
associated with the object
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7.6. Mapping of the REFERENCE
The REFERENCE clause, which need not be present, contains a
cross-reference to an object defined in some other
module. This is useful when de-osifying a MIB module produced
some other organization
7.7. Mapping of the INDEX
The INDEX clause, which must be present if that object corresponds
a conceptual row (unless an AUGMENTS clause is present instead),
must be absent otherwise, defines instance identification
for the columnar objects subordinate to that object
The instance identification information in an INDEX clause
specify object(s) such that value(s) of those object(s)
unambiguously distinguish a conceptual row. The syntax of
objects indicate how to form the instance-identifier
(1) integer-valued: a single sub-identifier taking the integer
(this works only for non-negative integers);
(2) string-valued, fixed-length strings (or variable-length preceded
the IMPLIED keyword): `n' sub-identifiers, where `n' is the
of the string (each octet of the string is encoded in a
sub-identifier);
(3) string-valued, variable-length strings (not preceded by the
keyword): `n+1' sub-identifiers, where `n' is the length of
string (the first sub-identifier is `n' itself, following this
each octet of the string is encoded in a separate sub-identifier);
(4) object identifier-valued (when preceded by the IMPLIED keyword):
`n' sub-identifiers, where `n' is the number of sub-identifiers
the value (each sub-identifier of the value is copied into
separate sub-identifier);
(5) object identifier-valued (when not preceded by the
keyword): `n+1' sub-identifiers, where `n' is the number of sub
identifiers in the value (the first sub-identifier is `n' itself
following this, each sub-identifier in the value is copied);
(6) IpAddress-valued: 4 sub-identifiers, in the familiar a.b.c.
notation
Note that the IMPLIED keyword can only be present for an
having a variable-length syntax (e.g., variable-length strings
object identifier-valued objects), Further, the IMPLIED keyword
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only be associated with the last object in the INDEX clause
Finally, the IMPLIED keyword may not be used on a variable-
string object if that string might have a value of zero-length
Instances identified by use of integer-valued objects should
numbered starting from one (i.e., not from zero). The use of zero
a value for an integer-valued index object should be avoided,
in special cases
Objects which are both specified in the INDEX clause of a
row and also columnar objects of the same conceptual row are
auxiliary objects. The MAX-ACCESS clause for auxiliary objects
"not-accessible", except in the following circumstances
(1) within a MIB module originally written to conform to the SNMPv
framework, and later converted to conform to the SNMPv2 framework
(2) a conceptual row must contain at least one columnar object which
not an auxiliary object. In the event that all of a
row's columnar objects are also specified in its INDEX clause,
one of them must be accessible, i.e., have a MAX-ACCESS clause
"read-only". (Note that this situation does not arise for
conceptual row allowing create access, since such a row will have
status column which will not be an auxiliary object.)
Note that objects specified in a conceptual row's INDEX clause
not be columnar objects of that conceptual row. In this situation
the DESCRIPTION clause of the conceptual row must include a
explanation of how the objects which are included in the INDEX
but not columnar objects of that conceptual row, are used in
identifying instances of the conceptual row's columnar objects
7.8. Mapping of the AUGMENTS
The AUGMENTS clause, which must not be present unless the
corresponds to a conceptual row, is an alternative to the
clause. Every object corresponding to a conceptual row has either
INDEX clause or an AUGMENTS clause
If an object corresponding to a conceptual row has an INDEX clause
that row is termed a base conceptual row; alternatively, if
object has an AUGMENTS clause, the row is said to be a conceptual
augmentation, where the AUGMENTS clause names the
corresponding to the base conceptual row which is augmented by
conceptual row augmentation. (Thus, a conceptual row
cannot itself be augmented.) Instances of subordinate
objects of a conceptual row augmentation are identified according
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the INDEX clause of the base conceptual row corresponding to
object named in the AUGMENTS clause. Further, instances
subordinate columnar objects of a conceptual row augmentation
according to the same semantics as instances of subordinate
objects of the base conceptual row being augmented. As such,
that creation of a base conceptual row implies the
creation of any conceptual row augmentations
For example, a MIB designer might wish to define additional
in an "enterprise-specific" MIB which logically extend a
row in a "standard" MIB. The "standard" MIB definition of
conceptual row would include the INDEX clause and the "enterprise
specific" MIB would contain the definition of a conceptual row
the AUGMENTS clause. On the other hand, it would be incorrect to
the AUGMENTS clause for the relationship between RFC 1573's
and the many media-specific MIBs which extend it for specific
(e.g., the dot3Table in RFC 1650), since not all interfaces are
the same media
Note that a base conceptual row may be augmented by
conceptual row augmentations
7.8.1. Relation between INDEX and AUGMENTS
When defining instance identification information for a
table
(1) If there is a one-to-one correspondence between the conceptual
of this table and an existing table, then the AUGMENTS
should be used
(2) Otherwise, if there is a sparse relationship between the
rows of this table and an existing table, then an INDEX
should be used which is identical to that in the existing table
For example, the relationship between RFC 1573's ifTable and
media-specific MIB which extends the ifTable for a specific
(e.g., the dot3Table in RFC 1650), is a sparse relationship
(3) Otherwise, if no existing objects have the required syntax
semantics, then auxiliary objects should be defined within
conceptual row for the new table, and those objects should be
within the INDEX clause for the conceptual row
7.9. Mapping of the DEFVAL
The DEFVAL clause, which need not be present, defines an
default value which may be used at the discretion of a SNMPv2
acting in an agent role when an object instance is created
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During conceptual row creation, if an instance of a columnar
is not present as one of the operands in the correspondent
protocol set operation, then the value of the DEFVAL clause,
present, indicates an acceptable default value that a SNMPv2
acting in an agent role might use
The value of the DEFVAL clause must, of course, correspond to
SYNTAX clause for the object. If the value is an OBJECT IDENTIFIER
then it must be expressed as a single ASN.1 identifier, and not as
collection of sub-identifiers
Note that if an operand to the management protocol set operation
an instance of a read-only object, then the error `notWritable' [6]
will be returned. As such, the DEFVAL clause can be used to
an acceptable default value that a SNMPv2 entity acting in an
role might use
By way of example, consider the following possible DEFVAL clauses
ObjectSyntax DEFVAL
---------------- ------------
Integer32 DEFVAL { 1 }
-- same for Gauge32, TimeTicks, Unsigned32
INTEGER DEFVAL { valid } -- enumerated
OCTET STRING DEFVAL { 'ffffffffffff'H }
OBJECT IDENTIFIER DEFVAL { sysDescr }
BITS DEFVAL { { primary, secondary } }
-- enumerated values that are
IpAddress DEFVAL { 'c0210415'H } -- 192.33.4.21
Object types with SYNTAX of Counter32 and Counter64 may not
DEFVAL clauses, since they do not have defined initial values
However, it is recommended that they be initialized to zero
7.10. Mapping of the OBJECT-TYPE
The value of an invocation of the OBJECT-TYPE macro is the name
the object, which is an OBJECT IDENTIFIER, an
assigned name
When an OBJECT IDENTIFIER is assigned to an object
(1) If the object corresponds to a conceptual table, then only a
assignment, that for a conceptual row, is present
beneath that object. The administratively assigned name for
conceptual row object is derived by appending a sub-identifier
"1" to the administratively assigned name for the conceptual table
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(2) If the object corresponds to a conceptual row, then at least
assignment, one for each column in the conceptual row, is
beneath that object. The administratively assigned name for
column is derived by appending a unique, positive sub-identifier
the administratively assigned name for the conceptual row
(3) Otherwise, no other OBJECT IDENTIFIERs which are subordinate to
object may be assigned
Note that the final sub-identifier of any administratively
name for an object shall be positive. A zero-valued final sub
identifier is reserved for future use
Further note that although conceptual tables and rows are
administratively assigned names, these conceptual objects may not
manipulated in aggregate form by the management protocol
7.11. Usage
Consider how one might define a conceptual table and
subordinates. (This example uses the RowStatus textual
defined in [3].)
evalSlot OBJECT-
SYNTAX
MAX-ACCESS read-
STATUS
"The index number of the first unassigned entry in
evaluation table
A management station should create new entries in
evaluation table using this algorithm: first, issue
management protocol retrieval operation to determine
value of evalSlot; and, second, issue a management
set operation to create an instance of the evalStatus
setting its value to createAndGo(4) or createAndWait(5).
this latter operation succeeds, then the management
may continue modifying the instances corresponding to
newly created conceptual row, without fear of collision
other management stations."
::= { eval 1 }
evalTable OBJECT-
SYNTAX SEQUENCE OF
MAX-ACCESS not-
STATUS
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"The (conceptual) evaluation table."
::= { eval 2 }
evalEntry OBJECT-
SYNTAX
MAX-ACCESS not-
STATUS
"An entry (conceptual row) in the evaluation table."
INDEX { evalIndex }
::= { evalTable 1 }
EvalEntry ::=
SEQUENCE {
evalIndex Integer32,
evalString DisplayString
evalValue Integer32,
evalStatus
}
evalIndex OBJECT-
SYNTAX Integer32
MAX-ACCESS not-
STATUS
"The auxiliary variable used for identifying instances
the columnar objects in the evaluation table."
::= { evalEntry 1 }
evalString OBJECT-
SYNTAX
MAX-ACCESS read-
STATUS
"The string to evaluate."
::= { evalEntry 2 }
evalValue OBJECT-
SYNTAX Integer32
MAX-ACCESS read-
STATUS
"The value when evalString was last executed."
DEFVAL { 0 }
::= { evalEntry 3 }
evalStatus OBJECT-
SYNTAX
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MAX-ACCESS read-
STATUS
"The status column used for creating, modifying,
deleting instances of the columnar objects in the
table."
DEFVAL { active }
::= { evalEntry 4 }
8. Mapping of the NOTIFICATION-TYPE
The NOTIFICATION-TYPE macro is used to define the
contained within an unsolicited transmission of
information (i.e., within either a SNMPv2-Trap-PDU or InformRequest
PDU). It should be noted that the expansion of the NOTIFICATION-
macro is something which conceptually happens during
and not during run-time
8.1. Mapping of the OBJECTS
The OBJECTS clause, which need not be present, defines the
sequence of MIB object types which are contained within
instance of the notification. An object type specified in
clause may not have an MAX-ACCESS clause of "not-accessible".
8.2. Mapping of the STATUS
The STATUS clause, which must be present, indicates whether
definition is current or historic
The values "current", and "obsolete" are self-explanatory.
"deprecated" value indicates that the definition is obsolete,
that an implementor may wish to support the notification to
interoperability with older implementations
8.3. Mapping of the DESCRIPTION
The DESCRIPTION clause, which must be present, contains a
definition of the notification which provides all
definitions necessary for implementation, and should embody
information which would otherwise be communicated in any ASN.1
commentary annotations associated with the notification.
particular, the DESCRIPTION clause should document which instances
the objects mentioned in the OBJECTS clause should be
within notifications of this type
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8.4. Mapping of the REFERENCE
The REFERENCE clause, which need not be present, contains a
cross-reference to a notification defined in some other
module. This is useful when de-osifying a MIB module produced
some other organization
8.5. Mapping of the NOTIFICATION-TYPE
The value of an invocation of the NOTIFICATION-TYPE macro is the
of the notification, which is an OBJECT IDENTIFIER,
administratively assigned name. In order to achieve
with the procedures employed by proxy agents (see Section 3.1.2
[7]), the next to last sub-identifier in the name of any newly
defined notification must have the value zero
Sections 4.2.6 and 4.2.7 of [6] describe how the NOTIFICATION-
macro is used to generate a SNMPv2-Trap-PDU or InformRequest-PDU
respectively
8.6. Usage
Consider how a linkUp trap might be described
linkUp NOTIFICATION-
OBJECTS { ifIndex }
STATUS
"A linkUp trap signifies that the SNMPv2 entity, acting
an agent role, recognizes that one of the
links represented in its configuration has come up."
::= { snmpTraps 4 }
According to this invocation, the trap authoritatively identified
{ snmpTraps 4 }
is used to report a link coming up
9. Refined
Some macros have clauses which allows syntax to be refined
specifically: the SYNTAX clause of the OBJECT-TYPE macro, and
SYNTAX/WRITE-SYNTAX clauses of the MODULE-COMPLIANCE and AGENT
CAPABILITIES macros [2]. However, not all refinements of syntax
appropriate. In particular, the object's primitive or
type must not be changed
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Further, the following restrictions apply
Restrictions to Refinement
object syntax range enumeration size
----------------- ----- ----------- ---- ----------
INTEGER (1) (2) - -
Integer32 (1) - - -
Unsigned32 (1) - - -
OCTET STRING - - (3) (4)
OBJECT IDENTIFIER - - - -
BITS - (2) - -
IpAddress - - - -
Counter32 - - - -
Counter64 - - - -
Gauge32 (1) - - -
TimeTicks - - - -
where
(1) the range of permitted values may be refined by raising the lower
bounds, by reducing the upper-bounds, and/or by reducing
alternative value/range choices
(2) the enumeration of named-values may be refined by removing one
more named-values (note that for BITS, a refinement may cause
enumerations to no longer be contiguous);
(3) the size in characters of the value may be refined by raising
lower-bounds, by reducing the upper-bounds, and/or by reducing
alternative size choices; or
(4) the repertoire of characters in the value may be reduced by
sub-typing
Otherwise no refinements are possible. Further details on sub-
are provided in Appendix C
10. Extending an Information
As experience is gained with a published information module, it
be desirable to revise that information module
To begin, the invocation of the MODULE-IDENTITY macro should
updated to include information about the revision. Usually,
consists of updating the LAST-UPDATED clause and adding a pair
REVISION and DESCRIPTION clauses. However, other existing clauses
the invocation may be updated
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Note that the module's label (e.g., "FIZBIN-MIB" from the example
Section 5.8), is not changed when the information module is revised
10.1. Object
If any non-editorial change is made to any clause of a
assignment, then the OBJECT IDENTIFIER value associated with
object assignment must also be changed, along with its
descriptor
10.2. Object
An object definition may be revised in any of the following ways
(1) A SYNTAX clause containing an enumerated INTEGER may have
enumerations added or existing labels changed
(2) A STATUS clause value of "current" may be revised as "deprecated
or "obsolete". Similarly, a STATUS clause value of "deprecated
may be revised as "obsolete".
(3) A DEFVAL clause may be added or updated
(4) A REFERENCE clause may be added or updated
(5) A UNITS clause may be added
(6) A conceptual row may be augmented by adding new columnar objects
the end of the row
(7) Entirely new objects may be defined, named with
unassigned OBJECT IDENTIFIER values
Otherwise, if the semantics of any previously defined object
changed (i.e., if a non-editorial change is made to any clause
those specifically allowed above), then the OBJECT IDENTIFIER
associated with that object must also be changed
Note that changing the descriptor associated with an existing
is considered a semantic change, as these strings may be used in
IMPORTS statement
Finally, note that if an object has the value of its STATUS
changed, then the value of its DESCRIPTION clause should be
accordingly
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10.3. Notification
A notification definition may be revised in any of the
ways
(1) A REFERENCE clause may be added or updated
Otherwise, if the semantics of any previously defined
are changed (i.e., if a non-editorial change is made to any
other those specifically allowed above), then the OBJECT
value associated with that notification must also be changed
Note that changing the descriptor associated with an
notification is considered a semantic change, as these strings may
used in an IMPORTS statement
Finally, note that if an object has the value of its STATUS
changed, then the value of its DESCRIPTION clause should be
accordingly
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11. Appendix A: de-OSIfying a MIB
There has been an increasing amount of work recently on taking
defined by other organizations (e.g., the IEEE) and de-osifying
for use with the Internet-standard network management framework.
steps to achieve this are straight-forward, though tedious.
course, it is helpful to already be experienced in writing
modules for use with the Internet-standard network
framework
The first step is to construct a skeletal MIB module, as
earlier in Section 5.8. The next step is to categorize the
into groups. Optional objects are not permitted. Thus, when a
module is created, optional objects must be placed in a
groups, which, if implemented, all objects in the group must
implemented. For the first pass, it is wisest to simply ignore
optional objects in the original MIB: experience shows it is
to define a core MIB module first, containing only essential objects
later, if experience demands, other objects can be added
11.1. Managed Object
Next for each managed object class, determine whether there can
multiple instances of that managed object class. If not, then
each of its attributes, use the OBJECT-TYPE macro to make
equivalent definition
Otherwise, if multiple instances of the managed object class
exist, then define a conceptual table having conceptual rows
containing a columnar object for each of the managed object class'
attributes. If the managed object class is contained within
containment tree of another managed object class, then the
of an object is normally required for each of the "
attributes" of the containing managed object class. If they do
already exist within the MIB module, then they can be added via
definition of additional columnar objects in the conceptual
corresponding to the contained managed object class
In defining a conceptual row, it is useful to consider
optimization of network management operations which will act upon
columnar objects. In particular, it is wisest to avoid defining
columnar objects within a conceptual row, than can fit in a
PDU. As a rule of thumb, a conceptual row should contain no
than approximately 20 objects. Similarly, or as a way to abide
the "20 object guideline", columnar objects should be grouped
tables according to the expected grouping of network
operations upon them. As such, the content of conceptual rows
reflect typical access scenarios, e.g., they should be
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along functional lines such as one row for statistics and another
for parameters, or along usage lines such as commonly-needed
versus rarely-needed objects
On the other hand, the definition of conceptual rows where the
of columnar objects used as indexes outnumbers the number used
hold information, should also be avoided. In particular,
splitting of a managed object class's attributes into many
tables should not be used as a way to obtain the same degree
flexibility/complexity as is often found in MIBs with a myriad
optionals
11.1.1. Mapping to the SYNTAX
When mapping to the SYNTAX clause of the OBJECT-TYPE macro
(1) An object with BOOLEAN syntax becomes a TruthValue [3].
(2) An object with INTEGER syntax becomes an Integer32.
(3) An object with ENUMERATED syntax becomes an INTEGER
enumerations, taking any of the values given which can
represented with an Integer32.
(4) An object with BIT STRING syntax having enumerations becomes a
construct
(5) An object with BIT STRING syntax but no enumerations becomes
OCTET STRING
(6) An object with a character string syntax becomes either an
STRING, or a DisplayString [3], depending on the repertoire of
character string
(7) A non-tabular object with a complex syntax, such as REAL
EXTERNAL, must be decomposed, usually into an OCTET STRING (
sensible). As a rule, any object with a complicated syntax
be avoided
(8) Tabular objects must be decomposed into rows of columnar objects
11.1.2. Mapping to the UNITS
If the description of this managed object defines a unit-basis,
mapping to this clause is straight-forward
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11.1.3. Mapping to the MAX-ACCESS
This is straight-forward
11.1.4. Mapping to the STATUS
This is straight-forward
11.1.5. Mapping to the DESCRIPTION
This is straight-forward: simply copy the text, making sure that
embedded double quotation marks are 