net-snmp

Network Working Group Editors of this version: Request for Comments: 2578 K. McCloghrie STD: 58 Cisco Systems Obsoletes: 1902 D. Perkins Category: Standards Track SNMPinfo J. Schoenwaelder TU Braunschweig Authors of previous version: J. Case SNMP Research K. McCloghrie Cisco Systems M. Rose First Virtual Holdings S. Waldbusser International Network Services April 1999 Structure of Management Information Version 2 (SMIv2) 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. Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved. Table of Contents 1 Introduction .................................................3 1.1 A Note on Terminology ......................................4 2 Definitions ..................................................4 2.1 The MODULE-IDENTITY macro ..................................5 2.2 Object Names and Syntaxes ..................................5 2.3 The OBJECT-TYPE macro ......................................8 2.5 The NOTIFICATION-TYPE macro ...............................10 2.6 Administrative Identifiers ................................11 3 Information Modules .........................................11 3.1 Macro Invocation ..........................................12 3.1.1 Textual Values and Strings ..............................13 McCloghrie, et al. Standards Track [Page 1] RFC 2578 SMIv2 April 1999 3.2 IMPORTing Symbols .........................................14 3.3 Exporting Symbols .........................................14 3.4 ASN.1 Comments ............................................14 3.5 OBJECT IDENTIFIER values ..................................15 3.6 OBJECT IDENTIFIER usage ...................................15 3.7 Reserved Keywords .........................................16 4 Naming Hierarchy ............................................16 5 Mapping of the MODULE-IDENTITY macro ........................17 5.1 Mapping of the LAST-UPDATED clause ........................17 5.2 Mapping of the ORGANIZATION clause ........................17 5.3 Mapping of the CONTACT-INFO clause ........................18 5.4 Mapping of the DESCRIPTION clause .........................18 5.5 Mapping of the REVISION clause ............................18 5.5.1 Mapping of the DESCRIPTION sub-clause ...................18 5.6 Mapping of the MODULE-IDENTITY value ......................18 5.7 Usage Example .............................................18 6 Mapping of the OBJECT-IDENTITY macro ........................19 6.1 Mapping of the STATUS clause ..............................19 6.2 Mapping of the DESCRIPTION clause .........................20 6.3 Mapping of the REFERENCE clause ...........................20 6.4 Mapping of the OBJECT-IDENTITY value ......................20 6.5 Usage Example .............................................20 7 Mapping of the OBJECT-TYPE macro ............................20 7.1 Mapping of the SYNTAX clause ..............................21 7.1.1 Integer32 and INTEGER ...................................21 7.1.2 OCTET STRING ............................................21 7.1.3 OBJECT IDENTIFIER .......................................22 7.1.4 The BITS construct ......................................22 7.1.5 IpAddress ...............................................22 7.1.6 Counter32 ...............................................23 7.1.7 Gauge32 .................................................23 7.1.8 TimeTicks ...............................................24 7.1.9 Opaque ..................................................24 7.1.10 Counter64 ..............................................24 7.1.11 Unsigned32 .............................................25 7.1.12 Conceptual Tables ......................................25 7.1.12.1 Creation and Deletion of Conceptual Rows .............26 7.2 Mapping of the UNITS clause ...............................26 7.3 Mapping of the MAX-ACCESS clause ..........................26 7.4 Mapping of the STATUS clause ..............................27 7.5 Mapping of the DESCRIPTION clause .........................27 7.6 Mapping of the REFERENCE clause ...........................27 7.7 Mapping of the INDEX clause ...............................27 7.8 Mapping of the AUGMENTS clause ............................29 7.8.1 Relation between INDEX and AUGMENTS clauses .............30 7.9 Mapping of the DEFVAL clause ..............................30 7.10 Mapping of the OBJECT-TYPE value .........................31 7.11 Usage Example ............................................32 McCloghrie, et al. Standards Track [Page 2] RFC 2578 SMIv2 April 1999 8 Mapping of the NOTIFICATION-TYPE macro ......................34 8.1 Mapping of the OBJECTS clause .............................34 8.2 Mapping of the STATUS clause ..............................34 8.3 Mapping of the DESCRIPTION clause .........................35 8.4 Mapping of the REFERENCE clause ...........................35 8.5 Mapping of the NOTIFICATION-TYPE value ....................35 8.6 Usage Example .............................................35 9 Refined Syntax ..............................................36 10 Extending an Information Module ............................37 10.1 Object Assignments .......................................37 10.2 Object Definitions .......................................38 10.3 Notification Definitions .................................39 11 Appendix A: Detailed Sub-typing Rules ......................40 11.1 Syntax Rules .............................................40 11.2 Examples .................................................41 12 Security Considerations ....................................41 13 Editors' Addresses .........................................41 14 References .................................................42 15 Full Copyright Statement ...................................43 1. Introduction Management information is viewed as a collection of managed objects, residing in a virtual information store, termed the Management Information Base (MIB). Collections of related objects are defined in MIB modules. These modules are written using an adapted subset of OSI's Abstract Syntax Notation One, ASN.1 (1988) [1]. It is the purpose of this document, the Structure of Management Information (SMI), to define that adapted subset, and to assign a set of associated administrative values. The SMI is divided 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. McCloghrie, et al. Standards Track [Page 3] RFC 2578 SMIv2 April 1999 1.1. A Note on Terminology For the purpose of exposition, the original Structure of Management Information, as described in RFCs 1155 (STD 16), 1212 (STD 16), and RFC 1215, is termed the SMI version 1 (SMIv1). The current version of the Structure of Management Information is termed SMI version 2 (SMIv2). 2. Definitions SNMPv2-SMI DEFINITIONS ::= BEGIN -- the path to the root org OBJECT IDENTIFIER ::= { iso 3 } -- "iso" = 1 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 } -- Extended UTCTime, to allow dates with four-digit years -- (Note that this definition of ExtUTCTime is not to be IMPORTed -- by MIB modules.) ExtUTCTime ::= OCTET STRING(SIZE(11 | 13)) -- format is YYMMDDHHMMZ or YYYYMMDDHHMMZ McCloghrie, et al. Standards Track [Page 4] RFC 2578 SMIv2 April 1999 -- where: YY - last two digits of year (only years -- between 1900-1999) -- YYYY - last four digits of the year (any year) -- MM - month (01 through 12) -- DD - day of month (01 through 31) -- HH - hours (00 through 23) -- MM - minutes (00 through 59) -- Z - denotes GMT (the ASCII character Z) -- -- For example, "9502192015Z" and "199502192015Z" represent -- 8:15pm GMT on 19 February 1995. Years after 1999 must use -- the four digit year format. Years 1900-1999 may use the -- two or four digit format. -- definitions for information modules MODULE-IDENTITY MACRO ::= BEGIN TYPE NOTATION ::= "LAST-UPDATED" value(Update ExtUTCTime) "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 ExtUTCTime) "DESCRIPTION" Text -- a character string as defined in section 3.1.1 Text ::= value(IA5String) END OBJECT-IDENTITY MACRO ::= BEGIN TYPE NOTATION ::= "STATUS" Status "DESCRIPTION" Text McCloghrie, et al. Standards Track [Page 5] RFC 2578 SMIv2 April 1999 ReferPart VALUE NOTATION ::= value(VALUE OBJECT IDENTIFIER) Status ::= "current" | "deprecated" | "obsolete" ReferPart ::= "REFERENCE" Text | empty -- a character string as defined in section 3.1.1 Text ::= value(IA5String) END -- names of objects -- (Note that these definitions of ObjectName and NotificationName -- are not to be IMPORTed by MIB modules.) ObjectName ::= OBJECT IDENTIFIER NotificationName ::= OBJECT IDENTIFIER -- syntax of objects -- the "base types" defined here are: -- 3 built-in ASN.1 types: INTEGER, OCTET STRING, OBJECT IDENTIFIER -- 8 application-defined types: Integer32, IpAddress, Counter32, -- Gauge32, Unsigned32, TimeTicks, Opaque, and Counter64 ObjectSyntax ::= CHOICE { simple SimpleSyntax, -- note that SEQUENCEs for conceptual tables and -- rows are not mentioned here... application-wide ApplicationSyntax } McCloghrie, et al. Standards Track [Page 6] RFC 2578 SMIv2 April 1999 -- 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 ::= 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 McCloghrie, et al. Standards Track [Page 7] RFC 2578 SMIv2 April 1999 -- (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 McCloghrie, et al. Standards Track [Page 8] RFC 2578 SMIv2 April 1999 IndexPart DefValPart VALUE NOTATION ::= value(VALUE ObjectName) Syntax ::= -- Must be one of the following: -- a base type (or its refinement), -- a textual convention (or its refinement), or -- a BITS pseudo-type type | "BITS" "{" NamedBits "}" NamedBits ::= NamedBit | NamedBits "," NamedBit NamedBit ::= identifier "(" number ")" -- number is nonnegative 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 McCloghrie, et al. Standards Track [Page 9] RFC 2578 SMIv2 April 1999 Index ::= -- use the SYNTAX value of the -- correspondent OBJECT-TYPE invocation value(ObjectName) Entry ::= -- use the INDEX value of the -- correspondent OBJECT-TYPE invocation value(ObjectName) DefValPart ::= "DEFVAL" "{" Defvalue "}" | empty Defvalue ::= -- must be valid for the type specified in -- SYNTAX clause of same OBJECT-TYPE macro value(ObjectSyntax) | "{" BitsValue "}" BitsValue ::= BitNames | empty BitNames ::= BitName | BitNames "," BitName BitName ::= identifier -- a character string as defined in section 3.1.1 Text ::= value(IA5String) 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 McCloghrie, et al. Standards Track [Page 10] RFC 2578 SMIv2 April 1999 | Objects "," Object Object ::= value(ObjectName) Status ::= "current" | "deprecated" | "obsolete" ReferPart ::= "REFERENCE" Text | empty -- a character string as defined in section 3.1.1 Text ::= value(IA5String) END -- definitions of administrative identifiers zeroDotZero OBJECT-IDENTITY STATUS current DESCRIPTION "A value used for null identifiers." ::= { 0 0 } END 3. Information Modules An "information module" is an ASN.1 module defining information relating to network management. The SMI describes how to use an adapted subset of ASN.1 (1988) to define an information module. Further, additional restrictions are placed on "standard" information modules. It is strongly recommended that "enterprise-specific" information modules also adhere to these restrictions. Typically, there are three kinds of information modules: (1) MIB modules, which contain definitions of inter-related managed objects, 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]. McCloghrie, et al. Standards Track [Page 11] RFC 2578 SMIv2 April 1999 This classification scheme does not imply a rigid taxonomy. For example, a "standard" information module will normally include definitions of managed objects and a compliance statement. Similarly, an "enterprise-specific" information module might include definitions of managed objects and a capability statement. Of course, a "standard" information module may not contain capability statements. The constructs of ASN.1 allowed in SMIv2 information modules include: 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 SMIv2, and instances of ASN.1 macros defined in this document and its companion documents [2, 3]. Additional ASN.1 macros must not be defined in SMIv2 information modules. SMIv1 macros must not be used in SMIv2 information modules. The names of all standard information modules must be unique (but different versions of the same information module should have the same name). Developers of enterprise information modules are encouraged to choose names for their information modules that will have a low probability of colliding with standard or other enterprise information modules. An information module may not use the ASN.1 construct of placing an object identifier value between the module name and the "DEFINITIONS" keyword. For the purposes of this specification, an ASN.1 module name begins with an upper-case letter and continues with zero or more letters, digits, or hyphens, except that a hyphen can not be the last character, nor can there be two consecutive hyphens. All information modules start with exactly one invocation of the MODULE-IDENTITY macro, which provides contact information as well as revision history to distinguish between versions of the same information module. This invocation must appear immediately after any IMPORTs statements. 3.1. Macro Invocation Within an information module, each macro invocation appears as: <descriptor> <macro> <clauses> ::= <value> where <descriptor> corresponds to an ASN.1 identifier, <macro> names the macro being invoked, and <clauses> and <value> depend on the definition of the macro. (Note that this definition of a descriptor applies to all macros defined in this memo and in [2].) McCloghrie, et al. Standards Track [Page 12] RFC 2578 SMIv2 April 1999 For the purposes of this specification, an ASN.1 identifier consists of one or more letters or digits, and its initial character must be a lower-case letter. Note that hyphens are not allowed by this specification (except for use by information modules converted from SMIv1 which did allow hyphens). For all descriptors appearing in an information module, the 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 for humans to use when discussing the information module and also facilitates simple table mappings for user-interfaces. The set of descriptors defined in all "standard" information modules shall be unique. Finally, by convention, if the descriptor refers to an object with a SYNTAX clause value of either Counter32 or Counter64, then the descriptor used for the object should denote plurality. 3.1.1. Textual Values and Strings Some clauses in a macro invocation may take a character string as a textual value (e.g., the DESCRIPTION clause). Other clauses take binary or hexadecimal strings (in any position where a non-negative number is allowed). A character string is preceded and followed by the quote character ("), and consists of an arbitrary number (possibly zero) of: - any 7-bit displayable ASCII characters except quote ("), - tab characters, - spaces, and - line terminator characters (\n or \r\n). The value of a character string is interpreted as ASCII. A binary string consists of a number (possibly zero) of zeros and ones preceded by a single (') and followed by either the pair ('B) or ('b), where the number is a multiple of eight. A hexadecimal string consists of an even number (possibly zero) of hexadecimal digits, preceded by a single (') and followed by either the pair ('H) or ('h). Digits specified via letters can be in upper or lower case. Note that ASN.1 comments can not be enclosed inside any of these types of strings. McCloghrie, et al. Standards Track [Page 13] RFC 2578 SMIv2 April 1999 3.2. IMPORTing Symbols To reference an external object, the IMPORTS statement must be used to identify both the descriptor and the module in which the descriptor is defined, where the module is identified by its ASN.1 module name. Note that when symbols from "enterprise-specific" information modules are referenced (e.g., a descriptor), there is the possibility of collision. As such, if different objects with the same descriptor are IMPORTed, then this ambiguity is resolved by prefixing the 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 to refer to objects even when there is no collision when IMPORTing symbols. Finally, if any of the ASN.1 named types and macros defined in this document, specifically: Counter32, Counter64, Gauge32, Integer32, IpAddress, MODULE- IDENTITY, NOTIFICATION-TYPE, Opaque, OBJECT-TYPE, OBJECT- IDENTITY, TimeTicks, Unsigned32, or any of those defined in [2] or [3], are used in an information module, then they must be imported using the IMPORTS statement. However, the following must not be included in an IMPORTS statement: - named types defined by ASN.1 itself, specifically: INTEGER, OCTET STRING, OBJECT IDENTIFIER, SEQUENCE, SEQUENCE OF type, - the BITS construct. 3.3. Exporting Symbols The ASN.1 EXPORTS statement is not allowed in SMIv2 information modules. All items defined in an information module are automatically exported. 3.4. ASN.1 Comments ASN.1 comments can be included in an information module. However, it is recommended that all substantive descriptions be placed within an appropriate DESCRIPTION clause. McCloghrie, et al. Standards Track [Page 14] RFC 2578 SMIv2 April 1999 ASN.1 comments commence with a pair of adjacent hyphens and end with the next pair of adjacent hyphens or at the end of the line, whichever occurs first. Comments ended by a pair of hyphens have the effect of a single space character. 3.5. OBJECT IDENTIFIER values An OBJECT IDENTIFIER value is an ordered list of non-negative numbers. For the SMIv2, each number in the list is referred to as 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). All OBJECT IDENTIFIER values have at least two sub-identifiers, where the value of the first sub-identifier is one of the following well- known names: Value Name 0 ccitt 1 iso 2 joint-iso-ccitt (Note that this SMI does not recognize "new" well-known names, e.g., as defined when the CCITT became the ITU.) 3.6. OBJECT IDENTIFIER usage OBJECT IDENTIFIERs are used in information modules in two ways: (1) registration: the definition of a particular item is registered as a particular OBJECT IDENTIFIER value, and associated with a particular descriptor. After such a registration, the semantics thereby associated with the value are not allowed to change, the OBJECT IDENTIFIER can not be used for any other registration, and the descriptor can not be changed nor associated with any other registration. The following macros result in a registration: OBJECT-TYPE, MODULE-IDENTITY, NOTIFICATION-TYPE, OBJECT-GROUP, OBJECT-IDENTITY, NOTIFICATION-GROUP, MODULE-COMPLIANCE, AGENT-CAPABILITIES. (2) assignment: a descriptor can be assigned to a particular OBJECT IDENTIFIER value. For this usage, the semantics associated with the OBJECT IDENTIFIER value is not allowed to change, and a descriptor assigned to a particular OBJECT IDENTIFIER value cannot subsequently be assigned to another. However, multiple descriptors can be assigned to the same OBJECT IDENTIFIER value. Such assignments are specified in the following manner: McCloghrie, et al. Standards Track [Page 15] RFC 2578 SMIv2 April 1999 mib OBJECT IDENTIFIER ::= { mgmt 1 } -- from RFC1156 mib-2 OBJECT IDENTIFIER ::= { mgmt 1 } -- from RFC1213 fredRouter OBJECT IDENTIFIER ::= { flintStones 1 1 } barneySwitch OBJECT IDENTIFIER ::= { flintStones bedrock(2) 1 } Note while the above examples are legal, the following is not: dinoHost OBJECT IDENTIFIER ::= { flintStones bedrock 2 } A descriptor is allowed to be associated with both a registration and an assignment, providing both are associated with the same OBJECT IDENTIFIER value and semantics. 3.7. Reserved Keywords The following are reserved keywords which must not be used as descriptors or module names: ABSENT ACCESS AGENT-CAPABILITIES ANY APPLICATION AUGMENTS BEGIN BIT BITS BOOLEAN BY CHOICE COMPONENT COMPONENTS CONTACT-INFO CREATION-REQUIRES Counter32 Counter64 DEFAULT DEFINED DEFINITIONS DEFVAL DESCRIPTION DISPLAY-HINT END ENUMERATED ENTERPRISE EXPLICIT EXPORTS EXTERNAL FALSE FROM GROUP Gauge32 IDENTIFIER IMPLICIT IMPLIED IMPORTS INCLUDES INDEX INTEGER Integer32 IpAddress LAST-UPDATED MANDATORY-GROUPS MAX MAX-ACCESS MIN MIN-ACCESS MINUS-INFINITY MODULE MODULE-COMPLIANCE MODULE- IDENTITY NOTIFICATION-GROUP NOTIFICATION-TYPE NOTIFICATIONS NULL OBJECT OBJECT-GROUP OBJECT-IDENTITY OBJECT-TYPE OBJECTS OCTET OF OPTIONAL ORGANIZATION Opaque PLUS-INFINITY PRESENT PRIVATE PRODUCT-RELEASE REAL REFERENCE REVISION SEQUENCE SET SIZE STATUS STRING SUPPORTS SYNTAX TAGS TEXTUAL-CONVENTION TRAP-TYPE TRUE TimeTicks UNITS UNIVERSAL Unsigned32 VARIABLES VARIATION WITH WRITE-SYNTAX 4. 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 } That is, the Internet subtree of OBJECT IDENTIFIERs starts with the prefix: 1.3.6.1. Several branches underneath this subtree are used for network management: McCloghrie, et al. Standards Track [Page 16] RFC 2578 SMIv2 April 1999 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 other portions of the object tree. The mgmt(2) subtree is used to identify "standard" objects. The experimental(3) subtree is used to identify objects being designed by working groups of the IETF. If an information module produced by a working group becomes a "standard" information module, then at the very beginning of its entry onto the Internet standards track, the objects are moved under the mgmt(2) subtree. The private(4) subtree is used to identify objects defined unilaterally. The enterprises(1) subtree beneath private is used, among other things, to permit providers of networking subsystems to register models of their products. 5. Mapping of the MODULE-IDENTITY macro The MODULE-IDENTITY macro is used to provide contact 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 is something which conceptually happens during implementation and not during run-time. Note that reference in an IMPORTS clause or in clauses of SMIv2 macros to an information module is NOT through the use of the 'descriptor' of a MODULE-IDENTITY macro; rather, an information module is referenced through specifying its module name. 5.1. Mapping of the LAST-UPDATED clause The LAST-UPDATED clause, which must be present, contains the date and time that this information module was last edited. 5.2. Mapping of the ORGANIZATION clause The ORGANIZATION clause, which must be present, contains a textual description of the organization under whose auspices this information module was developed. McCloghrie, et al. Standards Track [Page 17] RFC 2578 SMIv2 April 1999 5.3. Mapping of the CONTACT-INFO clause The CONTACT-INFO clause, which must be present, contains the name, postal address, telephone number, and electronic mail address of the person to whom technical queries concerning this information module should be sent. 5.4. Mapping of the DESCRIPTION clause The DESCRIPTION clause, which must be present, contains a high-level textual description of the contents of this information module. 5.5. Mapping of the REVISION clause The REVISION clause, which need not be present, is repeatedly used to describe the revisions (including the initial version) made to this information module, in reverse chronological order (i.e., most recent first). Each instance of this clause contains the date and time of the revision. 5.5.1. Mapping of the DESCRIPTION sub-clause The DESCRIPTION sub-clause, which must be present for each REVISION clause, 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. As such, this value may be authoritatively used when specifying an OBJECT IDENTIFIER value to refer to the information module containing the invocation. Note that it is a common practice to use the value of the MODULE- IDENTITY macro as a subtree under which other OBJECT IDENTIFIER values assigned within the module are defined. However, it is legal (and occasionally necessary) for the other OBJECT IDENTIFIER values assigned within the module to be unrelated to the OBJECT IDENTIFIER value of the MODULE-IDENTITY macro. 5.7. Usage Example Consider how a skeletal MIB module might be constructed: e.g., FIZBIN-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, experimental McCloghrie, et al. Standards Track [Page 18] RFC 2578 SMIv2 April 1999 FROM SNMPv2-SMI; fizbin MODULE-IDENTITY LAST-UPDATED "199505241811Z" 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, published in RFC yyyy." -- contact IANA for actual number ::= { experimental xx } END 6. Mapping of the OBJECT-IDENTITY macro The OBJECT-IDENTITY macro is used to define information about an OBJECT IDENTIFIER assignment. All administrative OBJECT IDENTIFIER assignments which 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 is something which conceptually happens during implementation and not during run-time. 6.1. Mapping of the STATUS clause The STATUS clause, which must be present, indicates whether this definition is current or historic. McCloghrie, et al. Standards Track [Page 19] RFC 2578 SMIv2 April 1999 The value "current" means that the definition is current and valid. The value "obsolete" means the definition is obsolete and should not be implemented and/or can be removed if previously implemented. While the value "deprecated" also indicates an obsolete definition, it permits new/continued implementation in order to foster interoperability with older/existing implementations. 6.2. Mapping of the DESCRIPTION clause The DESCRIPTION clause, which must be present, contains a textual description of the object assignment. 6.3. Mapping of the REFERENCE clause The REFERENCE clause, which need not be present, contains a textual cross-reference to some other document, either another information module which defines a related assignment, or some other document which provides additional information relevant to this definition. 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 Consider 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 The OBJECT-TYPE macro is used to define a type of managed object. It should be noted that the expansion of the OBJECT-TYPE macro is something which conceptually happens during implementation and not during run-time. For leaf objects which are not columnar objects (i.e., not contained within a conceptual table), instances of the object are identified 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 instance identification information. McCloghrie, et al. Standards Track [Page 20] RFC 2578 SMIv2 April 1999 7.1. Mapping of the SYNTAX clause The SYNTAX clause, which must be present, defines the abstract data structure corresponding to 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 those defined in the ObjectSyntax CHOICE. A textual convention is a newly-defined type defined as a sub-type of a base type [3]. An extended subset of the full capabilities of ASN.1 (1988) sub- typing is allowed, as appropriate to the underlying ASN.1 type. Any such restriction on size, range or enumerations specified in this clause represents the maximal level of support which makes "protocol sense". Restrictions on sub-typing are specified in detail in Section 9 and Appendix A of this memo. The semantics of ObjectSyntax are now described. 7.1.1. Integer32 and INTEGER The Integer32 type represents integer-valued information 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 (but not the Integer32 type) may also be used to represent integer-valued information as named-number enumerations. In this case, only those named-numbers so enumerated may be present as a value. Note that although 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, further, enumerated values needn't be contiguously assigned. Finally, a label for a named-number enumeration must consist of one or more letters or digits, 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.) Note that hyphens are not allowed by this specification (except for use by information modules converted from SMIv1 which did allow hyphens). 7.1.2. OCTET STRING The OCTET STRING type represents arbitrary binary or textual data. Although the SMI-specified size limitation for this type is 65535 octets, MIB designers should realize that there may be implementation and interoperability limitations for sizes in excess of 255 octets. McCloghrie, et al. Standards Track [Page 21] RFC 2578 SMIv2 April 1999 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 (but see below) values, starting at 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.) As part of updating an information module, for an object defined using the BITS construct, new enumerations can be added or existing enumerations can have new labels assigned to them. After an enumeration is added, it might not be possible to distinguish between an implementation of the updated object for which the new enumeration is not asserted, and an implementation of the object prior to the addition. Depending on the circumstances, such an ambiguity could either be desirable or could be undesirable. The means to avoid such an ambiguity is dependent on the encoding of values on the wire; however, one possibility is to define new enumerations starting at the next multiple of eight bits. (Of course, this can also result in the enumerations no longer being contiguous.) Although there is no SMI-specified limitation on the number of enumerations (and therefore on the length of a value), except as may be imposed by the limit on the length of an OCTET STRING, 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, 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.) Note that hyphens are not allowed by this specification. 7.1.5. IpAddress The IpAddress type represents a 32-bit internet address. It is represented as an OCTET STRING of length 4, in network byte-order. McCloghrie, et al. Standards Track [Page 22] RFC 2578 SMIv2 April 1999 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 which monotonically increases until it reaches a maximum value of 2^32-1 (4294967295 decimal), when it wraps around and starts increasing again from zero. Counters have no defined "initial" value, and thus, a single value of a Counter has (in general) no information content. Discontinuities in the monotonically increasing value normally occur at re- initialization of the management system, and at other times as 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 object instance at times other than re-initialization, then a corresponding object should be defined, with an appropriate SYNTAX clause, to indicate the last discontinuity. Examples of appropriate SYNTAX clause include: TimeStamp (a textual convention defined in [3]), DateAndTime (another textual convention from [3]) or TimeTicks. The value of 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, which may increase or decrease, but shall never exceed a maximum value, nor fall below a minimum value. The maximum value can not be greater than 2^32-1 (4294967295 decimal), and the minimum value can not be smaller than 0. The value of a Gauge32 has its maximum value whenever the information being modeled is greater than or equal to its maximum value, and has its minimum value whenever the information being modeled is smaller than or equal to its minimum value. If the information being modeled subsequently decreases below (increases above) the maximum (minimum) value, the Gauge32 also decreases (increases). (Note that despite of the use of the term "latched" in the original definition of this type, it does not become "stuck" at its maximum or minimum value.) McCloghrie, et al. Standards Track [Page 23] RFC 2578 SMIv2 April 1999 7.1.8. TimeTicks The TimeTicks type represents a non-negative integer which represents the time, modulo 2^32 (4294967296 decimal), in hundredths of a second between two epochs. When objects are defined which 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 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 OCTET STRING, in effect "double-wrapping" the original ASN.1 value. Note that a conforming implementation need only be able to accept and recognize opaquely-encoded data. It need not be able to unwrap the data and then interpret its contents. 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 which monotonically increases until it reaches a maximum value of 2^64-1 (18446744073709551615 decimal), when it wraps around and starts increasing again from zero. Counters have no defined "initial" value, and thus, a single value of a Counter has (in general) no information content. Discontinuities in the monotonically increasing value normally occur at re- initialization of the management system, and at other times as 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 object instance at times other than re-initialization, then a corresponding object should be defined, with an appropriate SYNTAX clause, to indicate the last discontinuity. Examples of appropriate SYNTAX McCloghrie, et al. Standards Track [Page 24] RFC 2578 SMIv2 April 1999 clause are: TimeStamp (a textual convention defined in [3]), DateAndTime (another textual convention from [3]) or TimeTicks. The value of the MAX-ACCESS clause for objects with a SYNTAX clause value of Counter64 is either "read-only" or "accessible-for-notify". A requirement on "stan