RFC 1902
Structure of Management Information for Version 2 of the Simple Network Management Protocol (SNMPv2)
RFC 1902: Structure of Management Information for Version 2 of SNMPv2 🎀
okay bestie, this is the one where the SNMPv2 Working Group wrote the rulebook for how management data gets described. 💅 It's a Standards Track document, so it's an actual Internet standard and not just a casual suggestion. It's dated January 1996, and it obsoletes RFC 1442. Its authors are J. Case (SNMP Research, Inc.), K. McCloghrie (Cisco Systems, Inc.), M. Rose (Dover Beach Consulting, Inc.), and S. Waldbusser (International Network Services). The title block doesn't list anything it updates, so that's it for the lineup. ✨
Status of this Memo 📜
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
1. Introduction ✨
okay so a management system is basically a little squad 🫶 with a few parts. You've got several (potentially many) nodes, and each one has a processing entity called an agent that can get at management instrumentation. You also need at least one management station, plus a management protocol to carry management information between the agents and the stations. The protocol runs under an administrative framework that defines authentication, authorization, access control, and privacy policies. Main character energy, honestly. 🦋
Management stations run management applications that monitor and control managed elements. Managed elements are things like hosts, routers, terminal servers, and so on, and they get monitored and controlled through access to their management information. 🌈
Management information is seen as a collection of managed objects that live in a virtual information store called the Management Information Base (MIB). Collections of related objects get defined in MIB modules. These modules are written in an adapted subset of OSI's Abstract Syntax Notation One (ASN.1) [1]. The whole point of this document, the Structure of Management Information (SMI), is to define that adapted subset and assign a set of associated administrative values. 💖
The SMI is split into three parts: module definitions, object definitions, and notification definitions. 🍓
(1) Module definitions are used when describing information modules. An ASN.1 macro, MODULE-IDENTITY, is used to concisely convey the semantics of an information module.
(2) Object definitions are used when describing managed objects. An ASN.1 macro, OBJECT-TYPE, is used to concisely convey the syntax and semantics of a managed object.
(3) Notification definitions are used when describing unsolicited transmissions of management information. An ASN.1 macro, NOTIFICATION-TYPE, is used to concisely convey the syntax and semantics of a notification.
1.1. A Note on Terminology 💅
okay quick vocab check 🧚 for the exposition, the original Internet-standard Network Management Framework, as described in RFCs 1155 (STD 16), 1157 (STD 15), and 1212 (STD 16), gets called the SNMP version 1 framework (SNMPv1). The current framework is called the SNMP version 2 framework (SNMPv2). Now you know which one everyone's talking about. 😭
2. Definitions 🦋
Here's the full SMI module, copied exactly as written, because the details are everything. 🙈
SNMPv2-SMI DEFINITIONS ::= BEGIN
-- the path to the root
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 OBJECT IDENTIFIER ::= { internet 6 }
-- transport domains
snmpDomains OBJECT IDENTIFIER ::= { snmpV2 1 }
-- transport proxies
snmpProxys OBJECT IDENTIFIER ::= { snmpV2 2 }
-- module identities
snmpModules OBJECT IDENTIFIER ::= { snmpV2 3 }
-- definitions for information modules
MODULE-IDENTITY MACRO ::=
BEGIN
TYPE NOTATION ::=
"LAST-UPDATED" value(Update UTCTime)
"ORGANIZATION" Text
"CONTACT-INFO" Text
"DESCRIPTION" Text
RevisionPart
VALUE NOTATION ::=
value(VALUE OBJECT IDENTIFIER)
RevisionPart ::=
Revisions
| empty
Revisions ::=
Revision
| Revisions Revision
Revision ::=
"REVISION" value(Update UTCTime)
"DESCRIPTION" Text
-- uses the NVT ASCII character set
Text ::= """" string """"
END
OBJECT-IDENTITY MACRO ::=
BEGIN
TYPE NOTATION ::=
"STATUS" Status
"DESCRIPTION" Text
ReferPart
VALUE NOTATION ::=
value(VALUE OBJECT IDENTIFIER)
Status ::=
"current"
| "deprecated"
| "obsolete"
ReferPart ::=
"REFERENCE" Text
| empty
Text ::= """" string """"
END
-- names of objects
ObjectName ::=
OBJECT IDENTIFIER
NotificationName ::=
OBJECT IDENTIFIER
-- syntax of objects
ObjectSyntax ::=
CHOICE {
simple
SimpleSyntax,
-- note that SEQUENCEs for conceptual tables and
-- rows are not mentioned here...
application-wide
ApplicationSyntax
}
-- built-in ASN.1 types
SimpleSyntax ::=
CHOICE {
-- INTEGERs with a more restrictive range
-- may also be used
integer-value -- includes Integer32
INTEGER (-2147483648..2147483647),
-- OCTET STRINGs with a more restrictive size
-- may also be used
string-value
OCTET STRING (SIZE (0..65535)),
objectID-value
OBJECT IDENTIFIER
}
-- indistinguishable from INTEGER, but never needs more than
-- 32-bits for a two's complement representation
Integer32 ::=
[UNIVERSAL 2]
IMPLICIT INTEGER (-2147483648..2147483647)
-- application-wide types
ApplicationSyntax ::=
CHOICE {
ipAddress-value
IpAddress,
counter-value
Counter32,
timeticks-value
TimeTicks,
arbitrary-value
Opaque,
big-counter-value
Counter64,
unsigned-integer-value -- includes Gauge32
Unsigned32
}
-- in network-byte order
-- (this is a tagged type for historical reasons)
IpAddress ::=
[APPLICATION 0]
IMPLICIT OCTET STRING (SIZE (4))
-- this wraps
Counter32 ::=
[APPLICATION 1]
IMPLICIT INTEGER (0..4294967295)
-- this doesn't wrap
Gauge32 ::=
[APPLICATION 2]
IMPLICIT INTEGER (0..4294967295)
-- an unsigned 32-bit quantity
-- indistinguishable from Gauge32
Unsigned32 ::=
[APPLICATION 2]
IMPLICIT INTEGER (0..4294967295)
-- hundredths of seconds since an epoch
TimeTicks ::=
[APPLICATION 3]
IMPLICIT INTEGER (0..4294967295)
-- for backward-compatibility only
Opaque ::=
[APPLICATION 4]
IMPLICIT OCTET STRING
-- for counters that wrap in less than one hour with only 32 bits
Counter64 ::=
[APPLICATION 6]
IMPLICIT INTEGER (0..18446744073709551615)
-- definition for objects
OBJECT-TYPE MACRO ::=
BEGIN
TYPE NOTATION ::=
"SYNTAX" Syntax
UnitsPart
"MAX-ACCESS" Access
"STATUS" Status
"DESCRIPTION" Text
ReferPart
IndexPart
DefValPart
VALUE NOTATION ::=
value(VALUE ObjectName)
Syntax ::=
type(ObjectSyntax)
| "BITS" "{" Kibbles "}"
Kibbles ::=
Kibble
| Kibbles "," Kibble
Kibble ::=
identifier "(" nonNegativeNumber ")"
UnitsPart ::=
"UNITS" Text
| empty
Access ::=
"not-accessible"
| "accessible-for-notify"
| "read-only"
| "read-write"
| "read-create"
Status ::=
"current"
| "deprecated"
| "obsolete"
ReferPart ::=
"REFERENCE" Text
| empty
IndexPart ::=
"INDEX" "{" IndexTypes "}"
| "AUGMENTS" "{" Entry "}"
| empty
IndexTypes ::=
IndexType
| IndexTypes "," IndexType
IndexType ::=
"IMPLIED" Index
| Index
Index ::=
-- use the SYNTAX value of the
-- correspondent OBJECT-TYPE invocation
value(Indexobject ObjectName)
Entry ::=
-- use the INDEX value of the
-- correspondent OBJECT-TYPE invocation
value(Entryobject ObjectName)
DefValPart ::=
"DEFVAL" "{" value(Defval Syntax) "}"
| empty
-- uses the NVT ASCII character set
Text ::= """" string """"
END
-- definitions for notifications
NOTIFICATION-TYPE MACRO ::=
BEGIN
TYPE NOTATION ::=
ObjectsPart
"STATUS" Status
"DESCRIPTION" Text
ReferPart
VALUE NOTATION ::=
value(VALUE NotificationName)
ObjectsPart ::=
"OBJECTS" "{" Objects "}"
| empty
Objects ::=
Object
| Objects "," Object
Object ::=
value(Name ObjectName)
Status ::=
"current"
| "deprecated"
| "obsolete"
ReferPart ::=
"REFERENCE" Text
| empty
-- uses the NVT ASCII character set
Text ::= """" string """"
END
-- definitions of administrative identifiers
zeroDotZero OBJECT-IDENTITY
STATUS current
DESCRIPTION
"A value used for null identifiers."
::= { 0 0 }
END3. Information Modules 🌸
okay so an "information module" is an ASN.1 module that defines information about network management. ✨
The SMI tells you how to use a subset of ASN.1 to define an information module. On top of that, "standard" information modules get extra restrictions. It is strongly recommended that "enterprise-specific" information modules also follow these restrictions. 💜
Typically there are three kinds of information modules: 🌈
(1) MIB modules, which contain definitions of inter-related managed objects, and make use of the OBJECT-TYPE and NOTIFICATION-TYPE macros;
(2) compliance statements for MIB modules, which make use of the MODULE-COMPLIANCE and OBJECT-GROUP macros [2]; and,
- (3) capability statements for agent implementations which make use of the AGENT-CAPABILITIES macros [2].
okay so this classification is NOT a strict box system, bestie 💅 A "standard" information module will normally include managed object definitions AND a compliance statement, and an "enterprise-specific" one might include managed object definitions AND a capability statement. The only hard no is that a "standard" information module may not contain capability statements 🙅♀️
The ASN.1 constructs you're allowed to use in SNMPv2 information modules are: the IMPORTS clause, value definitions for OBJECT IDENTIFIERs, type definitions for SEQUENCEs (with restrictions), ASN.1 type assignments of the restricted ASN.1 types allowed in SNMPv2, and instances of ASN.1 macros defined in this document and in other documents [2, 3] of the SNMPv2 framework. Additional ASN.1 macros may not be defined in SNMPv2 information modules. No inventing your own macros, periodt ✨
The names of all standard information modules MUST be unique, but different versions of the same information module SHOULD have the same name 🌸 Enterprise devs are encouraged to pick names that are unlikely to collide with standard or other enterprise information modules, so nobody's module gets mixed up with someone else's 🫶 Also, an information module may not use the ASN.1 construct of placing an object identifier value between the module name and the "DEFINITIONS" keyword 🙈
All information modules start with exactly one invocation of the MODULE-IDENTITY macro. This is the bit that gives contact info and revision history so people can tell versions of the same module apart 📖 This invocation MUST appear immediately after any IMPORTs statements, no exceptions bestie 👑
3.1. Macro Invocation 🦋
Within an information module, each macro invocation looks like this:
<descriptor> <macro> <clauses> ::= <value>where <descriptor> is an ASN.1 identifier, <macro> names the macro being invoked, and <clauses> and <value> depend on how that macro is defined. (Heads up: this definition of a descriptor applies to all macros defined in this memo and in [2], so it's a whole family thing 💕)
For the purposes of this spec, an ASN.1 identifier is made of one or more letters or digits, and its initial character MUST be a lower-case letter. Hyphens are NOT allowed by this spec, even though hyphen is allowed by [1]. Why? Because this restriction lets arithmetic expressions in languages that use the minus sign reference these descriptors without any ambiguity 🧠 Galaxy brain move ✨
For all descriptors in an information module, the descriptor SHALL be unique and mnemonic, and SHALL NOT exceed 64 characters in length. Descriptors longer than 32 characters are NOT RECOMMENDED, though 🙃 The whole point is a common language humans can use when talking about the module, and it makes simple table mappings for user interfaces way easier 💖
The set of descriptors defined in all "standard" information modules SHALL be unique 🔥
Finally, by convention: if the descriptor refers to an object whose SYNTAX clause value is either Counter32 or Counter64, then the descriptor used for that object SHOULD denote plurality 🍓
3.1.1. Textual Clauses 🎀
Some clauses in a macro invocation take a textual value (the DESCRIPTION clause is the classic example). To keep the ASN.1 syntax happy, the entire value of these clauses MUST be enclosed in double quotation marks. That means the value cannot itself contain double quotation marks, although it MAY be multi-line 🌈
3.2. IMPORTing Symbols 📦
To reference an external object, you MUST use the IMPORTS statement to identify both the descriptor and the module it's defined in. The module gets identified by its ASN.1 module name 💜
Heads up on enterprise-specific modules: referencing symbols from them (like a descriptor) can cause collisions 😬 So if different objects with the same descriptor get IMPORTed, the ambiguity is resolved by prefixing the descriptor with the information module name and a dot, like this:
"module.descriptor"(All descriptors MUST be unique within any information module, btw 🙌)
Of course you can use this notation even when there's no collision when IMPORTing symbols. Extra clarity never hurt anyone 💅
Finally, the IMPORTS statement may not be used to import an ASN.1 named type that corresponds to either the SEQUENCE or SEQUENCE OF type 🚫
3.3. Exporting Symbols 🦢
The ASN.1 EXPORTS statement is not allowed in SNMPv2 information modules. Everything defined in an information module is automatically exported, so you don't have to do anything extra ✨
3.4. ASN.1 Comments 💬
Comments in ASN.1 start with a pair of adjacent hyphens and end at the next pair of adjacent hyphens or at the end of the line, whichever comes first 🌸
3.5. OBJECT IDENTIFIER values 🔢
An OBJECT IDENTIFIER value is an ordered list of non-negative numbers. For the SNMPv2 framework, each number in the list is called a sub-identifier. There are at most 128 sub-identifiers in a value, and each sub-identifier has a maximum value of 2^32-1 (4294967295 decimal) 😭 Every OBJECT IDENTIFIER value has at least two sub-identifiers, and the first one MUST be one of these well-known names:
Value Name
0 ccitt
1 iso
2 joint-iso-ccitt4. Naming Hierarchy 🌳
The root of the subtree administered by the Internet Assigned Numbers Authority (IANA) for the Internet is:
internet OBJECT IDENTIFIER ::= { iso 3 6 1 }So the Internet subtree of OBJECT IDENTIFIERs starts with the prefix:
1.3.6.1.A few branches underneath this subtree are used for network management:
mgmt OBJECT IDENTIFIER ::= { internet 2 }
experimental OBJECT IDENTIFIER ::= { internet 3 }
private OBJECT IDENTIFIER ::= { internet 4 }
enterprises OBJECT IDENTIFIER ::= { private 1 }The SMI doesn't prohibit defining objects in other parts of the object tree, though 👀
The mgmt(2) subtree is used to identify "standard" objects 🏆
The experimental(3) subtree is used to identify objects being designed by IETF working groups 🧪 If an information module produced by a working group becomes a "standard" information module, then right at the very beginning of its entry onto the Internet standards track, its objects get moved under the mgmt(2) subtree. Glow-up arc unlocked 🦋
The private(4) subtree is used to identify objects defined unilaterally 🕶️ The enterprises(1) subtree under private is used, among other things, to let networking subsystem providers register models of their products 🏢
5. Mapping of the MODULE-IDENTITY macro 🪪
The MODULE-IDENTITY macro gives contact info and revision history for each information module. It MUST appear exactly once in every information module. It SHOULD be noted that the expansion of the MODULE-IDENTITY macro conceptually happens during implementation and NOT at run-time ⏰
Note that when you reference an information module in an IMPORTS clause or in clauses of SNMPv2 macros, you do NOT use the 'descriptor' of a MODULE-IDENTITY macro. Instead, you reference the information module by specifying its module name 📛
5.1. Mapping of the LAST-UPDATED clause 🗓️
The LAST-UPDATED clause MUST be present. It contains the date and time this information module was last edited, represented in UTC Time format (see Appendix B) ⏳
5.2. Mapping of the ORGANIZATION clause 🏛️
The ORGANIZATION clause MUST be present. It contains a textual description of the organization under whose auspices this information module was developed 🤝
5.3. Mapping of the CONTACT-INFO clause ☎️
The CONTACT-INFO clause MUST be present. It contains the name, postal address, telephone number, and electronic mail address of the person to whom technical queries about this information module should be sent 📮
5.4. Mapping of the DESCRIPTION clause 📝
The DESCRIPTION clause MUST be present. It contains a high-level textual description of the contents of this information module 🍭
5.5. Mapping of the REVISION clause 🔁
The REVISION clause need not be present. It's used repeatedly to describe the revisions (including the initial version) made to this information module, in reverse chronological order (most recent first) 🕰️ Each instance of this clause contains the date and time of the revision, represented in UTC Time format (see Appendix B) 📅
5.5.1. Mapping of the DESCRIPTION sub-clause 🖊️
The DESCRIPTION clause MUST be present for each REVISION clause. It contains a high-level textual description of the revision identified in that REVISION clause 💌
5.6. Mapping of the MODULE-IDENTITY value 🆔
The value of an invocation of the MODULE-IDENTITY macro is an OBJECT IDENTIFIER. Because of that, this value MAY be authoritatively used when specifying an OBJECT IDENTIFIER value to refer to the information module containing the invocation 🎯
5.7. Usage Example 🧁
Let's look at how a skeletal MIB module might be constructed, e.g.,
FIZBIN-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE, experimental
FROM SNMPv2-SMI;
fizbin MODULE-IDENTITY
LAST-UPDATED "9505241811Z"
ORGANIZATION "IETF SNMPv2 Working Group"
CONTACT-INFO
" Marshall T. Rose
Postal: Dover Beach Consulting, Inc.
420 Whisman Court
Mountain View, CA 94043-2186
US
Tel: +1 415 968 1052
Fax: +1 415 968 2510
E-mail: mrose@dbc.mtview.ca.us"
DESCRIPTION
"The MIB module for entities implementing the xxxx
protocol."
REVISION "9505241811Z"
DESCRIPTION
"The latest version of this MIB module."
REVISION "9210070433Z"
DESCRIPTION
"The initial version of this MIB module."
-- contact IANA for actual number
::= { experimental xx }
END6. Mapping of the OBJECT-IDENTITY macro 🪄
The OBJECT-IDENTITY macro defines information about an OBJECT IDENTIFIER assignment. All administrative OBJECT IDENTIFIER assignments that define a type identification value (see AutonomousType, a textual convention defined in [3]) SHOULD be defined via the OBJECT-IDENTITY macro ✨ It SHOULD be noted that the expansion of the OBJECT-IDENTITY macro conceptually happens during implementation and NOT at run-time 🕐
6.1. Mapping of the STATUS clause 🚦
The STATUS clause MUST be present. It indicates whether this definition is current or historic 📜
The values "current" and "obsolete" are self-explanatory 💁♀️ The "deprecated" value indicates that the definition is obsolete, but that an implementor MAY wish to support it to foster interoperability with older implementations 🤝💖
6.2. Mapping of the DESCRIPTION clause 📝
The DESCRIPTION clause MUST be present. It contains a textual description of the object assignment 🌷
6.3. Mapping of the REFERENCE clause 🔗
The REFERENCE clause need not be present. It contains a textual cross-reference to an object assignment defined in some other information module 📚
6.4. Mapping of the OBJECT-IDENTITY value 🧩
The value of an invocation of the OBJECT-IDENTITY macro is an OBJECT IDENTIFIER 💎
6.5. Usage Example 🌟
Let's look at how an OBJECT IDENTIFIER assignment might be made, e.g.,
fizbin69 OBJECT-IDENTITY
STATUS current
DESCRIPTION
"The authoritative identity of the Fizbin 69 chipset."
::= { fizbinChipSets 1 }7. Mapping of the OBJECT-TYPE macro ✨
Okay so the OBJECT-TYPE macro is how we define a type of managed object 🎀. Bestie, the expansion of this macro happens conceptually during implementation, and it's NOT something that happens at run-time 🙈.
For leaf objects that aren't columnar objects (i.e., not contained within a conceptual table), you find an instance by appending a sub-identifier of zero to the name of that object. Otherwise, the INDEX clause of the conceptual row object superior to a columnar object defines the instance identification info 💅.
7.1. Mapping of the SYNTAX clause 🧚
The SYNTAX clause is the one that MUST be present 💖. It defines the abstract data structure that matches that object. The data structure MUST be one of the following: a base type, the BITS construct, or a textual convention. (SEQUENCE OF and SEQUENCE are also possible for conceptual tables, see section 7.1.12.) The base types are the ones defined in the ObjectSyntax CHOICE, and a textual convention is a newly-defined type that's a sub-type of a base type [3] 🦋.
An extended subset of the full ASN.1 sub-typing capabilities is allowed, depending on the underlying ASN.1 type. Any restriction on size, range, enumerations or repertoire that's specified in this clause is the maximal level of support that "makes protocol sense" 💜. Restrictions on sub-typing are specified in detail in Section 9 and Appendix C of this memo, so go check those out 👑.
The semantics of ObjectSyntax are described next 🌸.
7.1.1. Integer32 and INTEGER
The Integer32 type represents integer-valued info between -2^31 and 2^31-1 inclusive (-2147483648 to 2147483647 decimal). This type is indistinguishable from the INTEGER type. Both the INTEGER and Integer32 types may be sub-typed to be more constrained than the Integer32 type 🍓.
The INTEGER type can also represent integer-valued info as named-number enumerations. In that case, only the named-numbers that are enumerated may be present as a value. Also, even though it is RECOMMENDED that enumerated values start at 1 and be numbered contiguously, any valid value for Integer32 is allowed for an enumerated value, and enumerated values needn't be contiguously assigned 🤓.
Finally, a label for a named-number enumeration MUST consist of one 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 STRING
The OCTET STRING type represents arbitrary binary or textual data 🦋. There's no SMI-specified size limit for this type, but MIB designers SHOULD realize that there may be implementation and interoperability limitations for sizes in excess of 255 octets 😭.
7.1.3. OBJECT IDENTIFIER
The OBJECT IDENTIFIER type represents administratively assigned names 📛. Any instance of this type may have at most 128 sub-identifiers. Further, each sub-identifier MUST NOT exceed the value 2^32-1 (4294967295 decimal) 💅.
7.1.4. The BITS construct
The BITS construct represents an enumeration of named bits 🌈. This collection is assigned non-negative, contiguous values, starting at zero. Only the named-bits that are enumerated may be present in a value. (So enumerations MUST be assigned to consecutive bits. However, see Section 9 for refinements of an object with this syntax 🫶.)
There's no SMI-specified limitation on the number of enumerations (and so on the length of a value), but MIB designers SHOULD realize that there may be implementation and interoperability limitations for sizes in excess of 128 bits ✨.
Finally, a label for a named-number enumeration MUST consist of one 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. IpAddress
The IpAddress type represents a 32-bit internet address 🌸. It's represented as an OCTET STRING of length 4, in network byte-order 🔥.
Note that the IpAddress type is a tagged type for historical reasons 🙈. Network addresses SHOULD be represented using an invocation of the TEXTUAL-CONVENTION macro [3] 💅.
7.1.6. Counter32
The Counter32 type represents a non-negative integer that monotonically increases until it reaches a maximum value of 2^32-1 (4294967295 decimal). Then it wraps around and starts increasing again from zero 🔄.
Counters have no defined "initial" value, so a single value of a Counter has (in general) no information content 🤷♀️. Discontinuities in the monotonically increasing value normally happen at re-initialization of the management system, and at other times as specified in the description of an object-type that uses this ASN.1 type. If such other times can occur (for example, creating an object instance at times other than re-initialization), then a corresponding object SHOULD be defined with a SYNTAX clause value of TimeStamp (a textual convention defined in [3]) that indicates the time of the last discontinuity 💜.
The MAX-ACCESS clause for objects with a SYNTAX clause value of Counter32 is either "read-only" or "accessible-for-notify" 👑. A DEFVAL clause is not allowed for objects with a SYNTAX clause value of Counter32 🚫.
7.1.7. Gauge32
The Gauge32 type represents a non-negative integer that may increase or decrease, but SHALL never exceed a maximum value 📈. The maximum value can not be greater than 2^32-1 (4294967295 decimal). The value of a Gauge has its maximum value whenever the info being modeled is greater than or equal to that maximum value. If the info being modeled later decreases below the maximum value, the Gauge also decreases 🎢.
7.1.8. TimeTicks
The TimeTicks type represents a non-negative integer that represents the time, modulo 2^32 (4294967296 decimal), in hundredths of a second between two epochs ⏰. When objects are defined that use this ASN.1 type, the description of the object identifies both of the reference epochs 🧠.
For example, [3] defines the TimeStamp textual convention, which is based on the TimeTicks type. With a TimeStamp, the first reference epoch is defined as the time when sysUpTime [5] was zero, and the second reference epoch is defined as the current value of sysUpTime 🕰️.
The TimeTicks type may not be sub-typed 🙅♀️.
7.1.9. Opaque
The Opaque type is provided solely for backward-compatibility, and it SHALL NOT be used for newly-defined object types 🚫. It's the type that lets you pass arbitrary ASN.1 syntax. A value is encoded using the ASN.1 Basic Encoding Rules [4] into a string of octets. That then gets encoded as an OCTET STRING, which is in effect "double-wrapping" the original ASN.1 value 🎁.
Note that a conforming implementation only needs to be able to accept and recognize opaquely-encoded data. It doesn't need to be able to unwrap the data and then interpret its contents 🫠.
A requirement on "standard" MIB modules is that no object may have a SYNTAX clause value of Opaque ✋.
7.1.10. Counter64
The Counter64 type represents a non-negative integer that monotonically increases until it reaches a maximum value of 2^64-1 (18446744073709551615 decimal). Then it wraps around and starts increasing again from zero 🌊.
Counters have no defined "initial" value, so a single value of a Counter has (in general) no information content. Discontinuities in the monotonically increasing value normally happen at re-initialization of the management system, and at other times as specified in the description of an object-type that uses this ASN.1 type. If such other times can occur (for example, creating an object instance at times other than re-initialization), then a corresponding object SHOULD be defined with a SYNTAX clause value of TimeStamp (a textual convention defined in [3]) that indicates the time of the last discontinuity 🍭.
The MAX-ACCESS clause for objects with a SYNTAX clause value of Counter64 is either "read-only" or "accessible-for-notify" 💫.
A requirement on "standard" MIB modules is that the Counter64 type MAY be used only if the information being modeled would wrap in less than one hour if the Counter32 type was used instead ⏳.
A DEFVAL clause is not allowed for objects with a SYNTAX clause value of Counter64 🚫.
7.1.11. Unsigned32
The Unsigned32 type represents integer-valued information between 0 and 2^32-1 inclusive (0 to 4294967295 decimal) 🩷.
7.1.12. Conceptual Tables
Management operations apply exclusively to scalar objects 🎯. But it's sometimes convenient for developers of management apps to impose an imaginary, tabular structure on an ordered collection of objects within the MIB 📊. Each conceptual table contains zero or more rows, and each row may contain one or more scalar objects, called columnar objects. This idea is formalized by using the OBJECT-TYPE macro to define both an object that corresponds to a table and an object that corresponds to a row in that table 🧩. A conceptual table has SYNTAX of the form:
SEQUENCE OF <EntryType>where <EntryType> refers to the SEQUENCE type of its subordinate conceptual row. A conceptual row has SYNTAX of the form:
<EntryType>where <EntryType> is a SEQUENCE type defined as follows:
<EntryType> ::= SEQUENCE { <type1>, ... , <typeN> }where there is one <type> for each subordinate object, and each <type> is of the form:
<descriptor> <syntax>where <descriptor> is the descriptor naming a subordinate object, and <syntax> has the value of that subordinate object's SYNTAX clause, normally with the sub-typing info left out. Also, these ASN.1 types are always present (the DEFAULT and OPTIONAL clauses are disallowed in the SEQUENCE definition) 🙅. The MAX-ACCESS clause for conceptual tables and rows is "not-accessible" 🔒.
7.1.12.1. Creation and Deletion of Conceptual Rows
For newly-defined conceptual rows that allow the creation of new object instances and/or the deletion of existing object instances, there SHOULD be one columnar object with a SYNTAX clause value of RowStatus (a textual convention defined in [3]) and a MAX-ACCESS clause value of read-create. By convention, this is termed the status column for the conceptual row 🚦.
7.2. Mapping of the UNITS clause 📏
This UNITS clause, which need not be present, contains a textual definition of the units associated with that object 💕.
7.3. Mapping of the MAX-ACCESS clause 🎀
okay so the MAX-ACCESS clause, which MUST be present, is all about whether it makes "protocol sense" to read, write and/or create an instance of the object, or to include its value in a notification 🦋 this is the maximal level of access for the object. (This maximal level of access is independent of any administrative authorization policy.) 💅
The value read-write means read and write access make "protocol sense", but create does not. The value read-create means read, write and create access all make "protocol sense" ✨ The value not-accessible is for an auxiliary object (see Section 7.7). The value accessible-for-notify is for an object that's only reachable through 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 📊
Here's the tea 🫖 if any columnar object in a conceptual row has read-create as its maximal level of access, then no other columnar object of the same conceptual row MAY have a maximal access of read-write. (Note that read-create is a superset of read-write.) main character energy, literally 👑
7.4. Mapping of the STATUS clause 🌸
The STATUS clause, which MUST be present, tells you whether a definition is current or historic 🕰️
"current" and "obsolete" are self-explanatory, bestie 🙈 the "deprecated" value means the definition is obsolete, but an implementor MAY wish to support that object to foster interoperability with older implementations 🫶
7.5. Mapping of the DESCRIPTION clause 📝
The DESCRIPTION clause, which MUST be present, is the textual definition of the object. It gives all the semantic definitions needed for implementation, and it SHOULD embody any information that would otherwise be communicated in ASN.1 commentary annotations attached to the object 💜
7.6. Mapping of the REFERENCE clause 🔗
The REFERENCE clause, which need not be present, is a textual cross-reference to an object defined in some other information module. This is super useful when de-osifying a MIB module produced by some other organization 🧚
7.7. Mapping of the INDEX clause 🗂️
The INDEX clause, which MUST be present if that object corresponds to a conceptual row (unless an AUGMENTS clause is present instead), and MUST be absent otherwise, gives instance identification information for the columnar objects subordinate to that object 🎀
The instance identification information in an INDEX clause MUST specify object(s) such that the value(s) of those object(s) will unambiguously distinguish a conceptual row. The syntax of those objects shows how to form the instance-identifier 🔍
- integer-valued: a single sub-identifier taking the integer value (this works only for non-negative integers);
- string-valued, fixed-length strings (or variable-length preceded by the IMPLIED keyword):
nsub-identifiers, wherenis the length of the string (each octet of the string is encoded in a separate sub-identifier); - string-valued, variable-length strings (not preceded by the IMPLIED keyword):
n+1sub-identifiers, wherenis the length of the string (the first sub-identifier isnitself, and following this, each octet of the string is encoded in a separate sub-identifier); - object identifier-valued (when preceded by the IMPLIED keyword):
nsub-identifiers, wherenis the number of sub-identifiers in the value (each sub-identifier of the value is copied into a separate sub-identifier); - object identifier-valued (when not preceded by the IMPLIED keyword):
n+1sub-identifiers, wherenis the number of sub-identifiers in the value (the first sub-identifier isnitself, and following this, each sub-identifier in the value is copied); - IpAddress-valued: 4 sub-identifiers, in the familiar a.b.c.d notation.
Note that the IMPLIED keyword can only be present for an object with a variable-length syntax (e.g., variable-length strings or object identifier-valued objects). Further, the IMPLIED keyword can only be associated with the last object in the INDEX clause. Finally, the IMPLIED keyword may not be used on a variable-length string object if that string might have a value of zero-length. ⚠️
Instances identified by integer-valued objects SHOULD be numbered starting from one (i.e., not from zero). Using zero as a value for an integer-valued index object SHOULD be avoided, except in special cases 🙃
Objects that are both specified in the INDEX clause of a conceptual row and also columnar objects of the same conceptual row are called auxiliary objects. The MAX-ACCESS clause for auxiliary objects is "not-accessible", except in the following circumstances:
- within a MIB module originally written to conform to the SNMPv1 framework, and later converted to conform to the SNMPv2 framework; or
- a conceptual row MUST contain at least one columnar object which is not an auxiliary object. If all of a conceptual row's columnar objects are also specified in its INDEX clause, then one of them MUST be accessible, i.e., have a MAX-ACCESS clause of "read-only". (Note that this situation does not arise for a conceptual row allowing create access, since such a row will have a status column which will not be an auxiliary object.)
Note that objects specified in a conceptual row's INDEX clause need not be columnar objects of that conceptual row. In this situation, the DESCRIPTION clause of the conceptual row MUST include a textual explanation of how the objects which are included in the INDEX clause but are not columnar objects of that conceptual row are used to uniquely identify instances of the conceptual row's columnar objects 🧩
7.8. Mapping of the AUGMENTS clause ➕
The AUGMENTS clause, which MUST NOT be present unless the object corresponds to a conceptual row, is an alternative to the INDEX clause. Every object corresponding to a conceptual row has either an INDEX clause or an AUGMENTS clause 💖
If an object corresponding to a conceptual row has an INDEX clause, that row is called a base conceptual row. If the object has an AUGMENTS clause instead, the row is said to be a conceptual row augmentation, and the AUGMENTS clause names the object corresponding to the base conceptual row that this augmentation extends. (Thus, a conceptual row augmentation cannot itself be augmented.) Instances of subordinate columnar objects of a conceptual row augmentation are identified according to the INDEX clause of the base conceptual row corresponding to the object named in the AUGMENTS clause. Also, instances of subordinate columnar objects of a conceptual row augmentation exist under the same semantics as instances of subordinate columnar objects of the base conceptual row being augmented. So note that creating a base conceptual row implies the corresponding creation of any conceptual row augmentations 🌈
For example, a MIB designer might want to define additional columns in an "enterprise-specific" MIB that logically extend a conceptual row in a "standard" MIB. The "standard" MIB definition of the conceptual row would include the INDEX clause, and the "enterprise-specific" MIB would contain the definition of a conceptual row using the AUGMENTS clause. On the other hand, it would be incorrect to use the AUGMENTS clause for the relationship between RFC 1573's ifTable and the many media-specific MIBs that extend it for specific media (e.g., the dot3Table in RFC 1650), since not all interfaces are of the same media 🙅♀️
Note that a base conceptual row MAY be augmented by multiple conceptual row augmentations.
7.8.1. Relation between INDEX and AUGMENTS clauses 🧠
When defining instance identification information for a conceptual table:
- If there is a one-to-one correspondence between the conceptual rows of this table and an existing table, then the AUGMENTS clause SHOULD be used.
- Otherwise, if there is a sparse relationship between the conceptual rows of this table and an existing table, then an INDEX clause SHOULD be used that is identical to the one in the existing table. For example, the relationship between RFC 1573's ifTable and a media-specific MIB that extends the ifTable for a specific media (e.g., the dot3Table in RFC 1650) is a sparse relationship 🌙
- Otherwise, if no existing objects have the required syntax and semantics, then auxiliary objects SHOULD be defined within the conceptual row for the new table, and those objects SHOULD be used within the INDEX clause for the conceptual row 🛠️
7.9. Mapping of the DEFVAL clause 🍓
The DEFVAL clause, which need not be present, defines an acceptable default value which MAY be used at the discretion of a SNMPv2 entity acting in an agent role when an object instance is created 🪄
During conceptual row creation, if an instance of a columnar object is not present as one of the operands in the corresponding management protocol set operation, then the value of the DEFVAL clause, if present, indicates an acceptable default value that a SNMPv2 entity acting in an agent role might use 💫
The value of the DEFVAL clause MUST, of course, correspond to the SYNTAX clause for the object. If the value is an OBJECT IDENTIFIER, then it MUST be expressed as a single ASN.1 identifier, and not as a collection of sub-identifiers 📏
Note that if an operand to the management protocol set operation is an instance of a read-only object, then the error `notWritable' [6] will be returned. As such, the DEFVAL clause can be used to provide an acceptable default value that a SNMPv2 entity acting in an agent role might use 🙏
By way of example, consider the following possible DEFVAL clauses:
ObjectSyntax DEFVAL clause
---------------- ------------
Integer32 DEFVAL { 1 }
-- same for Gauge32, TimeTicks, Unsigned32
INTEGER DEFVAL { valid } -- enumerated value
OCTET STRING DEFVAL { 'ffffffffffff'H }
OBJECT IDENTIFIER DEFVAL { sysDescr }
BITS DEFVAL { { primary, secondary } }
-- enumerated values that are set
IpAddress DEFVAL { 'c0210415'H } -- 192.33.4.21Object types with SYNTAX of Counter32 and Counter64 may not have DEFVAL clauses, since they do not have defined initial values. However, it is RECOMMENDED that they be initialized to zero. ⚠️
7.10. Mapping of the OBJECT-TYPE value 🏷️
The value of an invocation of the OBJECT-TYPE macro is the name of the object. That name is an OBJECT IDENTIFIER, an administratively assigned name 🪪
When an OBJECT IDENTIFIER is assigned to an object:
- If the object corresponds to a conceptual table, then only a single assignment, the one for a conceptual row, is present immediately beneath that object. The administratively assigned name for the conceptual row object is derived by appending a sub-identifier of "1" to the administratively assigned name for the conceptual table 🌷
- If the object corresponds to a conceptual row, then at least one assignment, one for each column in the conceptual row, is present beneath that object. The administratively assigned name for each column is derived by appending a unique, positive sub-identifier to the administratively assigned name for the conceptual row ✨
Okay so, the last sub-identifier of any administratively assigned name for an object shall be positive, bestie 💅. A zero-valued final sub-identifier is reserved for future use 🔒.
Also, even though conceptual tables and rows get administratively assigned names, the management protocol may not manipulate these conceptual objects in aggregate form 🙅♀️
7.11. Usage Example 🎀
Let's look at how you'd define a conceptual table and all its subordinates. (This example uses the RowStatus textual convention defined in [3].) 💖
evalSlot OBJECT-TYPE
SYNTAX INTEGER
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The index number of the first unassigned entry in the
evaluation table.
A management station should create new entries in the
evaluation table using this algorithm: first, issue a
management protocol retrieval operation to determine the
value of evalSlot; and, second, issue a management protocol
set operation to create an instance of the evalStatus object
setting its value to createAndGo(4) or createAndWait(5). If
this latter operation succeeds, then the management station
may continue modifying the instances corresponding to the
newly created conceptual row, without fear of collision with
other management stations."
::= { eval 1 }
evalTable OBJECT-TYPE
SYNTAX SEQUENCE OF EvalEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The (conceptual) evaluation table."
::= { eval 2 }
evalEntry OBJECT-TYPE
SYNTAX EvalEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry (conceptual row) in the evaluation table."
INDEX { evalIndex }
::= { evalTable 1 }
EvalEntry ::=
SEQUENCE {
evalIndex Integer32,
evalString DisplayString,
evalValue Integer32,
evalStatus RowStatus
}
evalIndex OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The auxiliary variable used for identifying instances of
the columnar objects in the evaluation table."
::= { evalEntry 1 }
evalString OBJECT-TYPE
SYNTAX DisplayString
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The string to evaluate."
::= { evalEntry 2 }
evalValue OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The value when evalString was last executed."
DEFVAL { 0 }
::= { evalEntry 3 }
evalStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status column used for creating, modifying, and
deleting instances of the columnar objects in the evaluation
table."
DEFVAL { active }
::= { evalEntry 4 }8. Mapping of the NOTIFICATION-TYPE macro 🔔
The NOTIFICATION-TYPE macro defines the information inside an unsolicited transmission of management information, meaning either a SNMPv2-Trap-PDU or an InformRequest-PDU. Heads up: expanding the NOTIFICATION-TYPE macro is something that conceptually happens during implementation, not at run-time ✨
8.1. Mapping of the OBJECTS clause 📋
The OBJECTS clause need not be present. When it is, it defines the ordered sequence of MIB object types contained within every instance of the notification. An object type listed here may not have a MAX-ACCESS clause of "not-accessible". 🙈
8.2. Mapping of the STATUS clause 🚦
The STATUS clause must be present, and it shows whether the definition is current or historic.
The values "current" and "obsolete" are self-explanatory 💁♀️ The "deprecated" value means the definition is obsolete, but an implementor may still want to support the notification to keep things interoperable with older implementations 🫶
8.3. Mapping of the DESCRIPTION clause 📝
The DESCRIPTION clause must be present. It holds a textual definition of the notification with all the semantic details needed for implementation, and it should carry any info that would otherwise go in ASN.1 commentary annotations attached to the notification. Especially, the DESCRIPTION clause should document which instances of the objects named in the OBJECTS clause should be contained within notifications of this type. 🧠
8.4. Mapping of the REFERENCE clause 🔗
The REFERENCE clause need not be present. It holds a textual cross-reference to a notification defined in some other information module. This comes in handy when de-osifying a MIB module that some other organization produced 🌈
8.5. Mapping of the NOTIFICATION-TYPE value 🏷️
The value of a NOTIFICATION-TYPE invocation is the name of the notification. That name is an OBJECT IDENTIFIER, an administratively assigned name. To stay compatible with the procedures proxy agents use (see Section 3.1.2 of [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] explain how the NOTIFICATION-TYPE macro is used to generate a SNMPv2-Trap-PDU or an InformRequest-PDU, respectively. ✨
8.6. Usage Example 🎀
Let's see how a linkUp trap might be described:
linkUp NOTIFICATION-TYPE
OBJECTS { ifIndex }
STATUS current
DESCRIPTION
"A linkUp trap signifies that the SNMPv2 entity, acting in
an agent role, recognizes that one of the communication
links represented in its configuration has come up."
::= { snmpTraps 4 }According to this invocation, the trap authoritatively identified as { snmpTraps 4 } is used to report a link coming up. That's giving link is up, we're so back 🚀
9. Refined Syntax 💅
Some macros have clauses that let you refine syntax. Specifically, that's the SYNTAX clause of the OBJECT-TYPE macro, and the SYNTAX/WRITE-SYNTAX clauses of the MODULE-COMPLIANCE and AGENT-CAPABILITIES macros [2]. Not every refinement is okay though 😭 In particular, the object's primitive or application type must not be changed.
Further, the following restrictions apply:
Restrictions to Refinement on
object syntax range enumeration size repertoire
----------------- ----- ----------- ---- ----------
INTEGER (1) (2) - -
Integer32 (1) - - -
Unsigned32 (1) - - -
OCTET STRING - - (3) (4)
OBJECT IDENTIFIER - - - -
BITS - (2) - -
IpAddress - - - -
Counter32 - - - -
Counter64 - - - -
Gauge32 (1) - - -
TimeTicks - - - -where:
- The range of permitted values may be refined by raising the lower-bounds, by reducing the upper-bounds, and/or by reducing the alternative value/range choices.
- The enumeration of named-values may be refined by removing one or more named-values. (Heads up: for BITS, a refinement may cause the enumerations to no longer be contiguous 🙃)
- The size in characters of the value may be refined by raising the lower-bounds, by reducing the upper-bounds, and/or by reducing the alternative size choices; or,
- The repertoire of characters in the value may be reduced by further sub-typing.
Otherwise no refinements are possible. More details on sub-typing are in Appendix C. 🦋
10. Extending an Information Module 🌸
As experience builds up with a published information module, it may be desirable to revise that module. 🧚
To begin, the invocation of the MODULE-IDENTITY macro should be updated to include info about the revision. Usually that means updating the LAST-UPDATED clause and adding a pair of REVISION and DESCRIPTION clauses. However, other existing clauses in the invocation may be updated too.
Note that the module's label (e.g., "FIZBIN-MIB" from the example in Section 5.8) does not change when the information module is revised. Iconic stability 👑
10.1. Object Assignments 🏷️
If any non-editorial change is made to any clause of an object assignment, then the OBJECT IDENTIFIER value tied to that object assignment must also change, along with its associated descriptor. 😤
10.2. Object Definitions 🧩
An object definition may be revised in any of the following ways:
- A SYNTAX clause containing an enumerated INTEGER may have new enumerations added or existing labels changed.
- 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".
- A DEFVAL clause may be added or updated.
- A REFERENCE clause may be added or updated.
- A UNITS clause may be added.
- A conceptual row may be augmented by adding new columnar objects at the end of the row.
- Entirely new objects may be defined, named with previously unassigned OBJECT IDENTIFIER values.
Otherwise, if the semantics of any previously defined object change (meaning a non-editorial change is made to any clause other than those specifically allowed above), then the OBJECT IDENTIFIER value associated with that object must also change. 🚨
Note that changing the descriptor tied to an existing object counts as a semantic change, since these strings may be used in an IMPORTS statement. 💀
Finally, if an object has its STATUS clause value changed, then its DESCRIPTION clause should be updated to match. ✨
10.3. Notification Definitions 🔔
A notification definition may be revised in any of the following ways:
- A REFERENCE clause may be added or updated.
Otherwise, if the semantics of any previously defined notification change (meaning a non-editorial change is made to any clause other than those specifically allowed above), then the OBJECT IDENTIFIER value associated with that notification must also change. 🫠
Note that changing the descriptor tied to an existing notification counts as a semantic change, since these strings may be used in an IMPORTS statement. 🙌
Finally, if an object has its STATUS clause value changed, then its DESCRIPTION clause should be updated to match. 🌈
11. Appendix A: de-OSIfying a MIB module ✨
okay so this appendix is basically the recipe for taking MIBs that other orgs (like the IEEE) already wrote and making them work with the Internet-standard network management framework 🧁 there's been a lot of this lately, and the steps are super straightforward, just kinda tedious 😩 it helps a lot if you've already written MIB modules for this framework before, bestie 🫶
step one is building a skeletal MIB module, same as the one back in Section 5.8 💅 step two is sorting the objects into groups. optional objects are not permitted, so any optional object has to go into an additional group, and if you implement that group, every object in it must be implemented too 🙈 for your first pass, the wisest move is to just ignore the optional objects in the original MIB. experience shows it's better to define a core MIB module first with only the essential objects, and then add other stuff later if experience says you need it 🌸
11.1. Managed Object Mapping 🎀
next, for each managed object class, figure out whether multiple instances of that class can exist. if they can't, then for each of its attributes, use the OBJECT-TYPE macro to make an equivalent definition.
if multiple instances can exist, then define a conceptual table with conceptual rows, and each row gets a columnar object for each of the managed object class's attributes 🦋 and if the class sits inside the containment tree of another managed object class, you usually need an object assigned for each of the "distinguished attributes" of the containing class. if those don't already exist in the MIB module, you can add them as extra columnar objects in the conceptual row for the contained class ✨
when you're defining a conceptual row, think about how network management operations are going to act on its columnar objects 👀 the big thing is avoiding more columnar objects in one row than can fit in a single PDU. as a rule of thumb, a conceptual row should have no more than about 20 objects. the same idea goes for the "20 object guideline": group columnar objects into tables based on how network management operations are expected to hit them. so the contents of each row should match typical access patterns, like organizing by function (one row for statistics, another for parameters) or by usage (commonly-needed objects versus rarely-needed ones) 💜
but also, don't make conceptual rows where the number of columnar objects used as indexes outnumbers the ones holding actual information 🙅♀️ and don't split a managed object class's attributes across a bunch of conceptual tables just to get the same flexibility and complexity you'd see in MIBs with a myriad of optionals. that's a no, periodt 💀
11.1.1. Mapping to the SYNTAX clause 🍓
when you're mapping to the SYNTAX clause of the OBJECT-TYPE macro:
(1) an object with BOOLEAN syntax becomes a TruthValue [3].
(2) an object with INTEGER syntax becomes an Integer32.
(3) an object with ENUMERATED syntax becomes an INTEGER with enumerations, taking any of the given values that can be represented with an Integer32.
(4) an object with BIT STRING syntax that has enumerations becomes a BITS construct.
(5) an object with BIT STRING syntax but no enumerations becomes an OCTET STRING.
(6) an object with a character string syntax becomes either an OCTET STRING or a DisplayString [3], depending on the repertoire of the character string.
(7) a non-tabular object with a complex syntax, like REAL or EXTERNAL, must be decomposed, usually into an OCTET STRING (if that makes sense). as a rule, any object with a complicated syntax should be avoided 😭
(8) tabular objects must be decomposed into rows of columnar objects 🧚
11.1.2. Mapping to the UNITS clause 📏
if the description of this managed object defines a unit-basis, then mapping to this clause is straightforward ✨
11.1.3. Mapping to the MAX-ACCESS clause 🔑
this is straightforward 💅
11.1.4. Mapping to the STATUS clause 🌈
this is straightforward 💖
11.1.5. Mapping to the DESCRIPTION clause 📝
this is straightforward: just copy the text, but make sure any embedded double quotation marks get sanitized (so swap them for single-quotes or remove them) 🫶
11.1.6. Mapping to the REFERENCE clause 🔖
this is straightforward too: include a textual reference to the object being mapped, the document that defines the object, and maybe a page number in that document 📖
11.1.7. Mapping to the INDEX clause 🗂️
if it's necessary, decide how instance-identifiers for columnar objects are going to be formed, and define this clause to match 🧩
11.1.8. Mapping to the DEFVAL clause 🎯
decide whether a meaningful default value can be assigned to the object you're mapping. if it can, define the DEFVAL clause accordingly 💜
11.2. Action Mapping ⚡
actions get modeled as read-write objects, where writing a particular value causes a state change. (usually, as part of that state change, some action happens too 🔥)
11.2.1. Mapping to the SYNTAX clause 🍭
usually you use the Integer32 syntax, with a distinguished value for each action the object gives access to. there's usually also one other distinguished value, which is the one returned when the object is read 🌸
11.2.2. Mapping to the MAX-ACCESS clause 🔐
always use read-write or read-create 🎀
11.2.3. Mapping to the STATUS clause 🌷
this is straightforward ✨
11.2.4. Mapping to the DESCRIPTION clause 📝
this is straightforward: copy the text, and sanitize any embedded double quotation marks (replace them with single-quotes or remove them) 💅
11.2.5. Mapping to the REFERENCE clause 🔖
this is straightforward: include a textual reference to the action being mapped, the document that defines the action, and maybe a page number 📚
11.3. Event Mapping 🔔
events get modeled as SNMPv2 notifications using the NOTIFICATION-TYPE macro. but remember, SNMPv2 leans heavily on trap-directed polling 🦋 so few notifications, and usually none, need to be defined for any MIB module 🌙
11.3.1. Mapping to the STATUS clause 🌼
this is straightforward ✨
11.3.2. Mapping to the DESCRIPTION clause 📝
this is straightforward: copy the text and sanitize any embedded double quotation marks (replace them with single-quotes or remove them) 🫶
11.3.3. Mapping to the REFERENCE clause 🔖
this is straightforward: include a textual reference to the notification being mapped, the document that defines the notification, and maybe a page number 💖
12. Appendix B: UTC Time Format 🕰️
several clauses in this document use the UTC Time format, which looks like this:
YYMMDDHHMMZ
where: YY - last two digits of year
MM - month (01 through 12)
DD - day of month (01 through 31)
HH - hours (00 through 23)
MM - minutes (00 through 59)
Z - the character "Z" denotes Greenwich Mean Time (GMT).for example, "9502192015Z" represents 8:15pm GMT on 19 February 1995 🌙✨
13. Appendix C: Detailed Sub-typing Rules 🧁
13.1. Syntax Rules 📐
here are the syntax rules for sub-typing. this syntax is based on ASN.1, but it has some extensions beyond what ASN.1 allows, and a bunch of ASN.1 constructs aren't allowed by this syntax at all 🤓
<integerSubType>
::= <empty>
| "(" <range> ["|" <range>]... ")"
<octetStringSubType>
::= <empty>
| "(" "SIZE" "(" <range> ["|" <range>]... ")" ")"
<range>
::= <value>
| <value> ".." <value>
<value>
::= "-" <number>
| <number>
| <hexString>
| <binString>
where:
<empty> is the empty string
<number> is a non-negative integer
<hexString> is a hexadecimal string (i.e. 'xxxx'H)
<binString> is a binary string (i.e. 'xxxx'B)
<range> is further restricted as follows:
- any <value> used in a SIZE clause must be non-negative.
- when a pair of values is specified, the first value
must be less than the second value.
- when multiple ranges are specified, the ranges may
not overlap but may touch. For example, (1..4 | 4..9)
is invalid, and (1..4 | 5..9) is valid.
- the ranges must be a subset of the maximum range of the
base type.13.2. Examples 🎀
here are some examples of legal sub-typing 💅
Integer32 (-20..100)
Integer32 (0..100 | 300..500)
Integer32 (300..500 | 0..100)
Integer32 (0 | 2 | 4 | 6 | 8 | 10)
OCTET STRING (SIZE(0..100))
OCTET STRING (SIZE(0..100 | 300..500))
OCTET STRING (SIZE(0 | 2 | 4 | 6 | 8 | 10))and here are some examples of illegal sub-typing, which is a big no 🙅♀️
Integer32 (150..100) -- first greater than second
Integer32 (0..100 | 50..500) -- ranges overlap
Integer32 (0 | 2 | 0 ) -- value duplicated
Integer32 (MIN..-1 | 1..MAX) -- MIN and MAX not allowed
Integer32 ((SIZE (0..34)) -- must not use SIZE
OCTET STRING (0..100) -- must use SIZE
OCTET STRING (SIZE(-10..100)) -- negative SIZE13.3. Rules for Textual Conventions 🦋
sub-typing of Textual Conventions (see [3]) is allowed, but it must be valid. specifically, each range you specify for the textual convention must be a subset of a range specified for the base type. for example:
Tc1 ::= INTEGER (1..10 | 11..20)
Tc2 ::= Tc1 (2..10 | 12..15) -- is valid
Tc3 ::= Tc1 (4..8) -- is valid
Tc4 ::= Tc1 (8..12) -- is invalid14. Security Considerations 🚨
security issues are not discussed in this memo. no cap, this is a big deal and the whole document is deliberately silent on it, so don't assume anything is covered here 😳
15. Editor's Address 💌
Keith McCloghrie
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134-1706
US
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EMail: kzm@cisco.com16. Acknowledgements 🎀
okay bestie, this part is all about the people who made this RFC happen 🫶 ✨ four major contributors did the heavy lifting, and they're listed right here 💅
Jeffrey D. Case (SNMP Research, case@snmp.com) 🌸 Keith McCloghrie (Cisco Systems, kzm@cisco.com) 🌸 Marshall T. Rose (Dover Beach Consulting, mrose@dbc.mtview.ca.us) 🌸 Steven Waldbusser (International Network Services, stevew@uni.ins.com) 🌸
ngl the list keeps going because the whole SNMPv2 Working Group got thanked too 💖 there's a special shoutout for a bunch of people who contributed a lot, so let's give them their flowers 🌷
Alexander I. Alten (Novell) 🦋 Dave Arneson (Cabletron) 🦋 Uri Blumenthal (IBM) 🦋 Doug Book (Chipcom) 🦋 Kim Curran (Bell-Northern Research) 🦋 Jim Galvin (Trusted Information Systems) 🦋 Maria Greene (Ascom Timeplex) 🦋 Iain Hanson (Digital) 🦋 Dave Harrington (Cabletron) 🦋 Nguyen Hien (IBM) 🦋 Jeff Johnson (Cisco Systems) 🦋 Michael Kornegay (Object Quest) 🦋 Deirdre Kostick (AT&T Bell Labs) 🦋 David Levi (SNMP Research) 🦋 Daniel Mahoney (Cabletron) 🦋 Bob Natale (ACE*COMM) 🦋 Brian O'Keefe (Hewlett Packard) 🦋 Andrew Pearson (SNMP Research) 🦋 Dave Perkins (Peer Networks) 🦋 Randy Presuhn (Peer Networks) 🦋 Aleksey Romanov (Quality Quorum) 🦋 Shawn Routhier (Epilogue) 🦋 Jon Saperia (BGS Systems) 🦋 Bob Stewart (Cisco Systems, bstewart@cisco.com), chair 👑 Kaj Tesink (Bellcore) 🦋 Glenn Waters (Bell-Northern Research) 🦋 Bert Wijnen (IBM) 🦋
17. References 📚
okay so the references are the other specs this one leans on, and you need them to make sense of everything 🧚 each one is listed with all its details 💅
[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] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Conformance Statements for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1904, January 1996.
[3] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Textual Conventions for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1903, January 1996.
[4] Information processing systems - Open Systems Interconnection - Specification of Basic Encoding Rules for Abstract Syntax Notation One (ASN.1), International Organization for Standardization. International Standard 8825, (December, 1987).
[5] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Management Information Base for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1907, January 1996.
[6] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Protocol Operations for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1905, January 1996.
[7] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Coexistence between Version 1 and Version 2 of the Internet-standard Network Management Framework", RFC 1908, January 1996.
📦 where this page comes from
- ietf: rfc1902 1996-01
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms