SNMPv2: Introduction to version 2 of the Internet-standard Network Management Framework
Overview of version 2 of the Internet-standard framework for managing networks, and where each part is defined.
Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Introduction to version 2 of the Internet-standard Network Management Framework", RFC 1441, DOI 10.17487/RFC1441, April 1993, <https://www.rfc-editor.org/info/rfc1441>.
@misc{rfc1441,
series = {Request for Comments},
number = 1441,
howpublished = {RFC 1441},
publisher = {RFC Editor},
doi = {10.17487/RFC1441},
url = {https://www.rfc-editor.org/info/rfc1441},
author = {J. Case and K. McCloghrie and M. Rose and S. Waldbusser},
title = {{Introduction to version 2 of the Internet-standard Network Management Framework}},
pagetotal = 13,
year = 1993,
month = apr,
} RFC text
Network Working Group J. Case
Request for Comments: 1441 SNMP Research, Inc.
K. McCloghrie
Hughes LAN Systems
M. Rose
Dover Beach Consulting, Inc.
S. Waldbusser
Carnegie Mellon University
April 1993
Introduction to version 2 of the
Internet-standard Network Management Framework
Status of this Memo
This RFC specifes an IAB standards track protocol for the
Internet community, and requests discussion and suggestions
for improvements. Please refer to the current edition of the
"IAB Official Protocol Standards" for the standardization
state and status of this protocol. Distribution of this memo
is unlimited.
Table of Contents
1 Introduction .......................................... 2
2 Components of the SNMPv2 Framework .................... 3
2.1 Structure of Management Information ................. 3
2.2 Textual Conventions ................................. 4
2.3 Protocol Operations ................................. 4
2.4 Transport Mappings .................................. 4
2.5 Protocol Instrumentation ............................ 5
2.6 Administrative Framework ............................ 5
2.7 Conformance Statements .............................. 5
3 Acknowledgements ...................................... 7
4 References ............................................ 11
5 Security Considerations ............................... 13
6 Authors' Addresses .................................... 13
1. Introduction
The purpose of this document is to provide an overview of
version 2 of the Internet-standard Network Management
Framework, termed the SNMP version 2 framework (SNMPv2). This
framework is derived from the original Internet-standard
Network Management Framework (SNMPv1), which consists of these
three documents:
RFC 1155 [1] which defines the Structure of Management
Information (SMI), the mechanisms used for describing and
naming objects for the purpose of management.
RFC 1212 [2] which defines a more concise description
mechanism, which is wholly consistent with the SMI.
RFC 1157 [3] which defines the Simple Network Management
Protocol (SNMP), the protocol used for network access to
managed objects.
For information on coexistence between SNMPv1 and SNMPv2,
consult [4].
2. Components of the SNMPv2 Framework
A network management system contains: several (potentially
many) nodes, each with a processing entity, termed an agent,
which has access to management instrumentation; at least one
management station; and, a management protocol, used to convey
management information between the agents and management
stations. Operations of the protocol are carried out under an
administrative framework which defines both authentication and
authorization policies.
Network management stations execute management applications
which monitor and control network elements. Network elements
are devices such as hosts, routers, terminal servers, etc.,
which are monitored and controlled through access to their
management information.
2.1. Structure of Management Information
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 a subset of OSI's Abstract Syntax Notation One (ASN.1)
[5]. It is the purpose of the Structure of Management
Information for SNMPv2 document [6] to define that subset.
The SMI is divided into three parts: module definitions,
object definitions, and, trap 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.
2.2. Textual Conventions
When designing a MIB module, it is often useful to new define
types similar to those defined in the SMI. In comparison to a
type defined in the SMI, each of these new types has a
different name, a similar syntax, but a more precise
semantics. These newly defined types are termed textual
conventions, and are used for the convenience of humans
reading the MIB module. It is the purpose of the Textual
Conventions for SNMPv2 document [7] to define the initial set
of textual conventions available to all MIB modules.
Objects defined using a textual convention are always encoded
by means of the rules that define their primitive type.
However, textual conventions often have special semantics
associated with them. As such, an ASN.1 macro, TEXTUAL-
CONVENTION, is used to concisely convey the syntax and
semantics of a textual convention.
2.3. Protocol Operations
The management protocol provides for the exchange of messages
which convey management information between the agents and the
management stations. The form of these messages is a message
"wrapper" which encapsulates a Protocol Data Unit (PDU). The
form and meaning of the "wrapper" is determined by an
administrative framework which defines both authentication and
authorization policies.
It is the purpose of the Protocol Operations for SNMPv2
document [8] to define the operations of the protocol with
respect to the sending and receiving of the PDUs.
2.4. Transport Mappings
The management protocol, version 2 of the Simple Network
Management Protocol, may be used over a variety of protocol
suites. It is the purpose of the Transport Mappings for
SNMPv2 document [9] to define how the SNMPv2 maps onto an
initial set of transport domains. Other mappings may be
defined in the future.
Although several mappings are defined, the mapping onto UDP is
the preferred mapping. As such, to provide for the greatest
level of interoperability, systems which choose to deploy
other mappings should also provide for proxy service to the
UDP mapping.
2.5. Protocol Instrumentation
It is the purpose of the Management Information Base for
SNMPv2 document [10] to define managed objects which describe
the behavior of a SNMPv2 entity. The Manager-to-Manager MIB
document [11] defines an initial set of managed objects which
describe the behavior of a SNMPv2 entity which acts in a
manager role. It is expected that extensions to this MIB will
be defined in the future.
2.6. Administrative Framework
It is the purpose of the Administrative Model for SNMPv2
document [12] to define the behavior of a SNMPv2 party - a
conceptual, virtual execution context whose operation is
restricted (for security or other purposes) to an
administratively defined subset of all possible operations of
a particular SNMPv2 entity.
Associated with each SNMPv2 party is a single authentication
protocol and a single privacy protocol. It is the purpose of
the Security Protocols for SNMPv2 document [13] to define
those protocols.
The Party MIB for SNMPv2 document [14] defines managed objects
which correspond to the properties associated with a SNMPv2
party.
2.7. Conformance Statements
It may be useful to define the acceptable lower-bounds of
implementation, along with the actual level of implementation
achieved. It is the purpose of the Conformance Statements for
SNMPv2 document [15] to define the notation used for these
purposes. There are two kinds of notations:
(1) Compliance statements are used when describing
requirements for agents with respect to object
definitions. An ASN.1 macro, MODULE-COMPLIANCE, is used
to concisely convey such requirements.
(2) Capability statements are used when describing
capabilities of agents with respect to object
definitions. An ASN.1 macro, AGENT-CAPABILITIES, is used
to concisely convey such capabilities.
Finally, collections of related objects are grouped together
to form a unit of conformance. An ASN.1 macro, OBJECT-GROUP,
is used to concisely convey the syntax and semantics of a
group.
3. Acknowledgements
The SNMPv2 framework is based on the outstanding technical
direction pioneered by the original authors of the SGMP: James
R. (Chuck) Davin, of the MIT Laboratory for Computer Science,
Mark S. Fedor, of Performance Systems International, Inc.,
Martin L. Schoffstall, also of PSI, and Jeffrey D. Case.
Since the invention of the SGMP in 1987, many individuals have
devoted much energy toward creating the unprecedented success
of the Internet-standard Network Management Framework. As
such, the list of people worthy of acknowledgement is too
great to enumerate here.
However, in retrospect, it seems clear that the concepts in
the original architecture, as envisioned by Chuck Davin, have
provided the basis for the success of the current framework.
We hope that the SNMPv2 framework will be able to successfully
build on this work.
Finally, the comments of the SNMP version 2 working group are
gratefully acknowledged:
Beth Adams, Network Management Forum
Steve Alexander, INTERACTIVE Systems Corporation
David Arneson, Cabletron Systems
Toshiya Asaba
Fred Baker, ACC
Jim Barnes, Xylogics, Inc.
Brian Bataille
Andy Bierman, SynOptics Communications, Inc.
Uri Blumenthal, IBM Corporation
Fred Bohle, Interlink
Jack Brown
Theodore Brunner, Bellcore
Stephen F. Bush, GE Information Services
Jeffrey D. Case, University of Tennessee, Knoxville
John Chang, IBM Corporation
Szusin Chen, Sun Microsystems
Robert Ching
Chris Chiotasso, Ungermann-Bass
Bobby A. Clay, NASA/Boeing
John Cooke, Chipcom
Tracy Cox, Bellcore
Juan Cruz, Datability, Inc.
David Cullerot, Cabletron Systems
Cathy Cunningham, Microcom
James R. (Chuck) Davin, Bellcore
Michael Davis, Clearpoint
Mike Davison, FiberCom
Cynthia DellaTorre, MITRE
Taso N. Devetzis, Bellcore
Manual Diaz, DAVID Systems, Inc.
Jon Dreyer, Sun Microsystems
David Engel, Optical Data Systems
Mike Erlinger, Lexcel
Roger Fajman, NIH
Daniel Fauvarque, Sun Microsystems
Karen Frisa, CMU
Shari Galitzer, MITRE
Shawn Gallagher, Digital Equipment Corporation
Richard Graveman, Bellcore
Maria Greene, Xyplex, Inc.
Michel Guittet, Apple
Robert Gutierrez, NASA
Bill Hagerty, Cabletron Systems
Gary W. Haney, Martin Marietta Energy Systems
Patrick Hanil, Nokia Telecommunications
Matt Hecht, SNMP Research, Inc.
Edward A. Heiner, Jr., Synernetics Inc.
Susan E. Hicks, Martin Marietta Energy Systems
Geral Holzhauer, Apple
John Hopprich, DAVID Systems, Inc.
Jeff Hughes, Hewlett-Packard
Robin Iddon, Axon Networks, Inc.
David Itusak
Kevin M. Jackson, Concord Communications, Inc.
Ole J. Jacobsen, Interop Company
Ronald Jacoby, Silicon Graphics, Inc.
Satish Joshi, SynOptics Communications, Inc.
Frank Kastenholz, FTP Software
Mark Kepke, Hewlett-Packard
Ken Key, SNMP Research, Inc.
Zbiginew Kielczewski, Eicon
Jongyeoi Kim
Andrew Knutsen, The Santa Cruz Operation
Michael L. Kornegay, VisiSoft
Deirdre C. Kostik, Bellcore
Cheryl Krupczak, Georgia Tech
Mark S. Lewis, Telebit
David Lin
David Lindemulder, AT&T/NCR
Ben Lisowski, Sprint
David Liu, Bell-Northern Research
John Lunny, The Wollongong Group
Robert C. Lushbaugh Martin, Marietta Energy Systems
Michael Luufer, BBN
Carl Madison, Star-Tek, Inc.
Keith McCloghrie, Hughes LAN Systems
Evan McGinnis, 3Com Corporation
Bill McKenzie, IBM Corporation
Donna McMaster, SynOptics Communications, Inc.
John Medicke, IBM Corporation
Doug Miller, Telebit
Dave Minnich, FiberCom
Mohammad Mirhakkak, MITRE
Rohit Mital, Protools
George Mouradian, AT&T Bell Labs
Patrick Mullaney, Cabletron Systems
Dan Myers, 3Com Corporation
Rina Nathaniel, Rad Network Devices Ltd.
Hien V. Nguyen, Sprint
Mo Nikain
Tom Nisbet
William B. Norton, MERIT
Steve Onishi, Wellfleet Communications, Inc.
David T. Perkins, SynOptics Communications, Inc.
Carl Powell, BBN
Ilan Raab, SynOptics Communications, Inc.
Richard Ramons, AT&T
Venkat D. Rangan, Metric Network Systems, Inc.
Louise Reingold, Sprint
Sam Roberts, Farallon Computing, Inc.
Kary Robertson, Concord Communications, Inc.
Dan Romascanu, Lannet Data Communications Ltd.
Marshall T. Rose, Dover Beach Consulting, Inc.
Shawn A. Routhier, Epilogue Technology Corporation
Chris Rozman
Asaf Rubissa, Fibronics
Jon Saperia, Digital Equipment Corporation
Michael Sapich
Mike Scanlon, Interlan
Sam Schaen, MITRE
John Seligson, Ultra Network Technologies
Paul A. Serice, Corporation for Open Systems
Chris Shaw, Banyan Systems
Timon Sloane
Robert Snyder, Cisco Systems
Joo Young Song
Roy Spitier, Sprint
Einar Stefferud, Network Management Associates
John Stephens, Cayman Systems, Inc.
Robert L. Stewart, Xyplex, Inc. (chair)
Kaj Tesink, Bellcore
Dean Throop, Data General
Ahmet Tuncay, France Telecom-CNET
Maurice Turcotte, Racal Datacom
Warren Vik, INTERACTIVE Systems Corporation
Yannis Viniotis
Steven L. Waldbusser, Carnegie Mellon Universitty
Timothy M. Walden, ACC
Alice Wang, Sun Microsystems
James Watt, Newbridge
Luanne Waul, Timeplex
Donald E. Westlake III, Digital Equipment Corporation
Gerry White
Bert Wijnen, IBM Corporation
Peter Wilson, 3Com Corporation
Steven Wong, Digital Equipment Corporation
Randy Worzella, IBM Corporation
Daniel Woycke, MITRE
Honda Wu
Jeff Yarnell, Protools
Chris Young, Cabletron
Kiho Yum, 3Com Corporation
4. References
[1] Rose, M., and McCloghrie, K., "Structure and
Identification of Management Information for TCP/IP-based
internets", STD 16, RFC 1155, May 1990.
[2] Rose, M., and McCloghrie, K., "Concise MIB Definitions",
STD 16, RFC 1212, March 1991.
[3] Case, J., Fedor, M., Schoffstall, M., Davin, J., "Simple
Network Management Protocol", STD 15, RFC 1157, SNMP
Research, Performance Systems International, MIT
Laboratory for Computer Science, May 1990.
[4] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Coexistence between version 1 and version 2 of the
Internet-standard Network Management Framework", RFC
1452, SNMP Research, Inc., Hughes LAN Systems, Dover
Beach Consulting, Inc., Carnegie Mellon University, April
1993.
[5] Information processing systems - Open Systems
Interconnection - Specification of Abstract Syntax
Notation One (ASN.1), International Organization for
Standardization. International Standard 8824, (December,
1987).
[6] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Structure of Management Information for version 2 of the
Simple Network Management Protocol (SNMPv2)", RFC 1442,
SNMP Research, Inc., Hughes LAN Systems, Dover Beach
Consulting, Inc., Carnegie Mellon University, April 1993.
[7] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Textual Conventions for version 2 of the the Simple
Network Management Protocol (SNMPv2)", RFC 1443, SNMP
Research, Inc., Hughes LAN Systems, Dover Beach
Consulting, Inc., Carnegie Mellon University, April 1993.
[8] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Protocol Operations for version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1448, SNMP Research,
Inc., Hughes LAN Systems, Dover Beach Consulting, Inc.,
Carnegie Mellon University, April 1993.
[9] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Transport Mappings for version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1449, SNMP Research,
Inc., Hughes LAN Systems, Dover Beach Consulting, Inc.,
Carnegie Mellon University, April 1993.
[10] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Management Information Base for version 2 of the Simple
Network Management Protocol (SNMPv2)", RFC 1450, SNMP
Research, Inc., Hughes LAN Systems, Dover Beach
Consulting, Inc., Carnegie Mellon University, April 1993.
[11] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Manager-to-Manager Management Information Base", RFC
1451, SNMP Research, Inc., Hughes LAN Systems, Dover
Beach Consulting, Inc., Carnegie Mellon University, April
1993.
[12] Galvin, J., and McCloghrie, K., "Administrative Model for
version 2 of the Simple Network Management Protocol
(SNMPv2)", RFC 1445, Trusted Information Systems, Hughes
LAN Systems, April 1993.
[13] Galvin, J., and McCloghrie, K., "Security Protocols for
version 2 of the Simple Network Management Protocol
(SNMPv2)", RFC 1446, Trusted Information Systems, Hughes
LAN Systems, April 1993.
[14] McCloghrie, K., and Galvin, J., "Party MIB for version 2
of the Simple Network Management Protocol (SNMPv2)", RFC
1447, Hughes LAN Systems, Trusted Information Systems,
April 1993.
[15] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Conformance Statements for version 2 of the the Simple
Network Management Protocol (SNMPv2)", RFC 1444, SNMP
Research, Inc., Hughes LAN Systems, Dover Beach
Consulting, Inc., Carnegie Mellon University, April 1993.
5. Security Considerations
Security issues are not discussed in this memo.
6. Authors' Addresses
Jeffrey D. Case
SNMP Research, Inc.
3001 Kimberlin Heights Rd.
Knoxville, TN 37920-9716
US
Phone: +1 615 573 1434
Email: case@snmp.com
Keith McCloghrie
Hughes LAN Systems
1225 Charleston Road
Mountain View, CA 94043
US
Phone: +1 415 966 7934
Email: kzm@hls.com
Marshall T. Rose
Dover Beach Consulting, Inc.
420 Whisman Court
Mountain View, CA 94043-2186
US
Phone: +1 415 968 1052
Email: mrose@dbc.mtview.ca.us
Steven Waldbusser
Carnegie Mellon University
4910 Forbes Ave
Pittsburgh, PA 15213
US
Phone: +1 412 268 6628
Email: waldbusser@cmu.edu
ISO Plain Language
On this page
§1An Overview, Not a Specification
RFC 1441 defines no protocol. It is an introduction to version 2 of the Internet-standard Network Management Framework, called SNMPv2, and it points to the document that defines each part of that framework.
SNMPv2 is derived from the original Internet-standard Network Management Framework, SNMPv1, which consists of three documents. RFC 1155 defines the Structure of Management Information (SMI), the mechanisms used for describing and naming objects for the purpose of management. RFC 1212 defines a more concise description mechanism, which is wholly consistent with the SMI. RFC 1157 defines the Simple Network Management Protocol (SNMP) itself, the protocol used for network access to managed objects.
Version 2 keeps that division of labour and adds more parts. This memo names ten of them, together with the document that defines each: the SMI, textual conventions, conformance statements, the administrative model, the security protocols, the Party MIB, the protocol operations, the transport mappings, the Management Information Base for SNMPv2, and the Manager-to-Manager MIB. The memo also records that the framework builds on the technical direction set by the original authors of the SGMP, which was invented in 1987.
This memo is a guide to a set of documents, not a protocol itself. It lists the parts of the second version of SNMP and names the document that defines each part.
- SNMPv2 framework Each part has its own defining document
- Structure of Management Information (RFC 1442)
- Textual Conventions (RFC 1443)
- Conformance Statements (RFC 1444)
- Administrative Model (RFC 1445)
- Security Protocols (RFC 1446)
- Party MIB (RFC 1447)
- Protocol Operations (RFC 1448)
- Transport Mappings (RFC 1449)
- Management Information Base (RFC 1450)
- Manager-to-Manager MIB (RFC 1451)
§2The Parts of a Network Management System
A network management system contains several, possibly many, nodes. Each node has a processing entity called an agent, which has access to management instrumentation. There is at least one management station, and there is a management protocol used to convey management information between the agents and the management stations. Operations of the protocol are carried out under an administrative framework, which defines both authentication and authorization policies.
Management stations execute management applications, which monitor and control network elements. Network elements are devices such as hosts, routers and terminal servers, and they are monitored and controlled through access to their management information.
Every managed device runs a small program that answers questions about it. A management station sends those questions over the network and collects the answers. An administrative framework decides who may ask what.
§2.1The Structure of Management Information
Management information is a collection of managed objects residing in a virtual information store called the Management Information Base (MIB). Collections of related objects are defined in MIB modules, and these modules are written using a subset of OSI's Abstract Syntax Notation One (ASN.1). The SMI is divided into three parts. Module definitions describe information modules, and the ASN.1 macro MODULE-IDENTITY conveys the semantics of such a module. Object definitions describe managed objects, and OBJECT-TYPE conveys the syntax and semantics of a managed object. The third part, trap definitions, also called notification definitions, describe unsolicited transmissions of management information, and NOTIFICATION-TYPE conveys the syntax and semantics of a notification.
When a MIB module needs a type that the SMI does not define, the module can define a textual convention: a new type with a different name, a syntax similar to a type defined in the SMI, and a more precise semantics. Objects defined using a textual convention are always encoded by the rules that define their primitive type, although a convention often has special semantics attached to it. The macro TEXTUAL-CONVENTION conveys the syntax and semantics of the convention, and the Textual Conventions document defines the initial set of textual conventions available to all MIB modules.
All the facts a device reports are organised into named objects and written down in a standard notation called ASN.1. A module can also give a common type a more precise name, so a reader knows exactly what it means.
- MODULE-IDENTITYConveys the semantics of an information module.
- OBJECT-TYPEConveys the syntax and semantics of a managed object.
- NOTIFICATION-TYPEConveys the syntax and semantics of a notification.
- TEXTUAL-CONVENTIONConveys the syntax and semantics of a new named type.
- MODULE-COMPLIANCEConveys the requirements an agent must meet.
- AGENT-CAPABILITIESConveys the capabilities an agent may offer.
- OBJECT-GROUPGroups related objects into one unit of conformance.
§2.3Protocol Operations and Transport Mappings
The management protocol provides for the exchange of messages that convey management information between the agents and the management stations. The form of each message is a wrapper that encapsulates a Protocol Data Unit (PDU). The form and the meaning of that wrapper are determined by an administrative framework, which defines both authentication and authorization policies. The Protocol Operations document defines the operations of the protocol with respect to the sending and receiving of the PDUs.
SNMPv2 may be used over a variety of protocol suites. The Transport Mappings document defines how SNMPv2 maps onto an initial set of transport domains, and other mappings may be defined in the future. Although several mappings are defined, the mapping onto UDP is the preferred one. To provide the greatest level of interoperability, systems that deploy other mappings should also provide for proxy service to the UDP mapping.
A management request travels inside a wrapper that says who is sending it and what they may do. The wrapper holds the request itself. UDP is the preferred way to carry these messages over the network.
- Management applicationsPrograms that monitor and control network elements
- SNMPExchanges management information between stations and agents
- UDPThe preferred transport mapping
§2.6The Administrative Framework
An SNMPv2 party is a conceptual, virtual execution context whose operation is restricted, for security or other purposes, to an administratively defined subset of all possible operations of a particular SNMPv2 entity. Associated with each party is a single authentication protocol and a single privacy protocol.
The administrative model document defines the behaviour of an SNMPv2 party. The security protocols document defines the authentication and privacy protocols used by parties. The Party MIB defines managed objects which correspond to the properties associated with an SNMPv2 party.
Each manager acts as a party, and each party has its own rules about what it may look at and change. A request outside those rules is refused.
§2.7Conformance Statements and Instrumentation
It may be useful to define the acceptable lower bounds of an implementation, along with the actual level of implementation achieved. The Conformance Statements document defines the notation used for this, in two kinds. Compliance statements describe requirements for agents with respect to object definitions, and the ASN.1 macro MODULE-COMPLIANCE conveys such requirements. Capability statements describe the capabilities of agents with respect to object definitions, and the macro AGENT-CAPABILITIES conveys them. Collections of related objects are grouped together to form a unit of conformance, and the macro OBJECT-GROUP conveys the syntax and semantics of such a group.
Two MIB documents describe behaviour. The Management Information Base for SNMPv2 defines managed objects which describe the behaviour of an SNMPv2 entity, and the Manager-to-Manager MIB defines an initial set of managed objects which describe the behaviour of an SNMPv2 entity acting in a manager role. The memo expects extensions to that MIB to be defined in the future.
Vendors agree on what a device must support and what it may support. That way two devices from different makers can be managed by the same program.