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Network Working Group J. Case
Request for Comments: 1157 SNMP Research
Obsoletes: RFC 1098 M. Fedor
Performance Systems International
M. Schoffstall
Performance Systems International
J. Davin
MIT Laboratory for Computer Science
May 1990
A Simple Network Management Protocol (SNMP)
Table of Contents
1. Status of this Memo ................................... 2
2. Introduction .......................................... 2
3. The SNMP Architecture ................................. 5
3.1 Goals of the Architecture ............................ 5
3.2 Elements of the Architecture ......................... 5
3.2.1 Scope of Management Information .................... 6
3.2.2 Representation of Management Information ........... 6
3.2.3 Operations Supported on Management Information ..... 7
3.2.4 Form and Meaning of Protocol Exchanges ............. 8
3.2.5 Definition of Administrative Relationships ......... 8
3.2.6 Form and Meaning of References to Managed Objects .. 12
3.2.6.1 Resolution of Ambiguous MIB References ........... 12
3.2.6.2 Resolution of References across MIB Versions...... 12
3.2.6.3 Identification of Object Instances ............... 12
3.2.6.3.1 ifTable Object Type Names ...................... 13
3.2.6.3.2 atTable Object Type Names ...................... 13
3.2.6.3.3 ipAddrTable Object Type Names .................. 14
3.2.6.3.4 ipRoutingTable Object Type Names ............... 14
3.2.6.3.5 tcpConnTable Object Type Names ................. 14
3.2.6.3.6 egpNeighTable Object Type Names ................ 15
4. Protocol Specification ................................ 16
4.1 Elements of Procedure ................................ 17
4.1.1 Common Constructs .................................. 19
4.1.2 The GetRequest-PDU ................................. 20
4.1.3 The GetNextRequest-PDU ............................. 21
4.1.3.1 Example of Table Traversal ....................... 23
4.1.4 The GetResponse-PDU ................................ 24
4.1.5 The SetRequest-PDU ................................. 25
4.1.6 The Trap-PDU ....................................... 27
4.1.6.1 The coldStart Trap ............................... 28
4.1.6.2 The warmStart Trap ............................... 28
4.1.6.3 The linkDown Trap ................................ 28
4.1.6.4 The linkUp Trap .................................. 28
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RFC 1157 SNMP May 1990
4.1.6.5 The authenticationFailure Trap ................... 28
4.1.6.6 The egpNeighborLoss Trap ......................... 28
4.1.6.7 The enterpriseSpecific Trap ...................... 29
5. Definitions ........................................... 30
6. Acknowledgements ...................................... 33
7. References ............................................ 34
8. Security Considerations................................ 35
9. Authors' Addresses..................................... 35
1. Status of this Memo
This RFC is a re-release of RFC 1098, with a changed "Status of this
Memo" section plus a few minor typographical corrections. This memo
defines a simple protocol by which management information for a
network element may be inspected or altered by logically remote
users. In particular, together with its companion memos which
describe the structure of management information along with the
management information base, these documents provide a simple,
workable architecture and system for managing TCP/IP-based internets
and in particular the Internet.
The Internet Activities Board recommends that all IP and TCP
implementations be network manageable. This implies implementation
of the Internet MIB (RFC-1156) and at least one of the two
recommended management protocols SNMP (RFC-1157) or CMOT (RFC-1095).
It should be noted that, at this time, SNMP is a full Internet
standard and CMOT is a draft standard. See also the Host and Gateway
Requirements RFCs for more specific information on the applicability
of this standard.
Please refer to the latest edition of the "IAB Official Protocol
Standards" RFC for current information on the state and status of
standard Internet protocols.
Distribution of this memo is unlimited.
2. Introduction
As reported in RFC 1052, IAB Recommendations for the Development of
Internet Network Management Standards [1], a two-prong strategy for
network management of TCP/IP-based internets was undertaken. In the
short-term, the Simple Network Management Protocol (SNMP) was to be
used to manage nodes in the Internet community. In the long-term,
the use of the OSI network management framework was to be examined.
Two documents were produced to define the management information: RFC
1065, which defined the Structure of Management Information (SMI)
[2], and RFC 1066, which defined the Management Information Base
(MIB) [3]. Both of these documents were designed so as to be
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RFC 1157 SNMP May 1990
compatible with both the SNMP and the OSI network management
framework.
This strategy was quite successful in the short-term: Internet-based
network management technology was fielded, by both the research and
commercial communities, within a few months. As a result of this,
portions of the Internet community became network manageable in a
timely fashion.
As reported in RFC 1109, Report of the Second Ad Hoc Network
Management Review Group [4], the requirements of the SNMP and the OSI
network management frameworks were more different than anticipated.
As such, the requirement for compatibility between the SMI/MIB and
both frameworks was suspended. This action permitted the operational
network management framework, the SNMP, to respond to new operational
needs in the Internet community by producing documents defining new
MIB items.
The IAB has designated the SNMP, SMI, and the initial Internet MIB to
be full "Standard Protocols" with "Recommended" status. By this
action, the IAB recommends that all IP and TCP implementations be
network manageable and that the implementations that are network
manageable are expected to adopt and implement the SMI, MIB, and
SNMP.
As such, the current network management framework for TCP/IP- based
internets consists of: Structure and Identification of Management
Information for TCP/IP-based Internets, which describes how managed
objects contained in the MIB are defined as set forth in RFC 1155
[5]; Management Information Base for Network Management of TCP/IP-
based Internets, which describes the managed objects contained in the
MIB as set forth in RFC 1156 [6]; and, the Simple Network Management
Protocol, which defines the protocol used to manage these objects, as
set forth in this memo.
As reported in RFC 1052, IAB Recommendations for the Development of
Internet Network Management Standards [1], the Internet Activities
Board has directed the Internet Engineering Task Force (IETF) to
create two new working groups in the area of network management. One
group was charged with the further specification and definition of
elements to be included in the Management Information Base (MIB).
The other was charged with defining the modifications to the Simple
Network Management Protocol (SNMP) to accommodate the short-term
needs of the network vendor and operations communities, and to align
with the output of the MIB working group.
The MIB working group produced two memos, one which defines a
Structure for Management Information (SMI) [2] for use by the managed
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RFC 1157 SNMP May 1990
objects contained in the MIB. A second memo [3] defines the list of
managed objects.
The output of the SNMP Extensions working group is this memo, which
incorporates changes to the initial SNMP definition [7] required to
attain alignment with the output of the MIB working group. The
changes should be minimal in order to be consistent with the IAB's
directive that the working groups be "extremely sensitive to the need
to keep the SNMP simple." Although considerable care and debate has
gone into the changes to the SNMP which are reflected in this memo,
the resulting protocol is not backwardly-compatible with its
predecessor, the Simple Gateway Monitoring Protocol (SGMP) [8].
Although the syntax of the protocol has been altered, the original
philosophy, design decisions, and architecture remain intact. In
order to avoid confusion, new UDP ports have been allocated for use
by the protocol described in this memo.
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3. The SNMP Architecture
Implicit in the SNMP architectural model is a collection of network
management stations and network elements. Network management
stations execute management applications which monitor and control
network elements. Network elements are devices such as hosts,
gateways, terminal servers, and the like, which have management
agents responsible for performing the network management functions
requested by the network management stations. The Simple Network
Management Protocol (SNMP) is used to communicate management
information between the network management stations and the agents in
the network elements.
3.1. Goals of the Architecture
The SNMP explicitly minimizes the number and complexity of management
functions realized by the management agent itself. This goal is
attractive in at least four respects:
(1) The development cost for management agent software
necessary to support the protocol is accordingly reduced.
(2) The degree of management function that is remotely
supported is accordingly increased, thereby admitting
fullest use of internet resources in the management task.
(3) The degree of management function that is remotely
supported is accordingly increased, thereby imposing the
fewest possible restrictions on the form and
sophistication of management tools.
(4) Simplified sets of management functions are easily
understood and used by developers of network management
tools.
A second goal of the protocol is that the functional paradigm for
monitoring and control be sufficiently extensible to accommodate
additional, possibly unanticipated aspects of network operation and
management.
A third goal is that the architecture be, as much as possible,
independent of the architecture and mechanisms of particular hosts or
particular gateways.
3.2. Elements of the Architecture
The SNMP architecture articulates a solution to the network
management problem in terms of:
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(1) the scope of the management information communicated by
the protocol,
(2) the representation of the management information
communicated by the protocol,
(3) operations on management information supported by the
protocol,
(4) the form and meaning of exchanges among management
entities,
(5) the definition of administrative relationships among
management entities, and
(6) the form and meaning of references to management
information.
3.2.1. Scope of Management Information
The scope of the management information communicated by operation of
the SNMP is exactly that represented by instances of all non-
aggregate object types either defined in Internet-standard MIB or
defined elsewhere according to the conventions set forth in
Internet-standard SMI [5].
Support for aggregate object types in the MIB is neither required for
conformance with the SMI nor realized by the SNMP.
3.2.2. Representation of Management Information
Management information communicated by operation of the SNMP is
represented according to the subset of the ASN.1 language [9] that is
specified for the definition of non-aggregate types in the SMI.
The SGMP adopted the convention of using a well-defined subset of the
ASN.1 language [9]. The SNMP continues and extends this tradition by
utilizing a moderately more complex subset of ASN.1 for describing
managed objects and for describing the protocol data units used for
managing those objects. In addition, the desire to ease eventual
transition to OSI-based network management protocols led to the
definition in the ASN.1 language of an Internet-standard Structure of
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