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RFC 2570
Network Working Group J. Case
Request for Comments: 2570 SNMP Research, Inc.
Category: Informational R. Mundy
TIS Labs at Network Associates, Inc.
D. Partain
Ericsson
B. Stewart
Cisco Systems
April 1999
Introduction to Version 3 of the
Internet-standard Network Management Framework
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
The purpose of this document is to provide an overview of the third
version of the Internet-standard Management Framework, termed the
SNMP version 3 Framework (SNMPv3). This Framework is derived from
and builds upon both the original Internet-standard Management
Framework (SNMPv1) and the second Internet-standard Management
Framework (SNMPv2).
The architecture is designed to be modular to allow the evolution of
the Framework over time.
Table of Contents
1 Introduction .....................................................2
2 The Internet Standard Management Framework .......................3
2.1 Basic Structure and Components .................................3
2.2 Architecture of the Internet Standard Management Framework .....3
3 The SNMPv1 Management Framework ..................................4
3.1 The SNMPv1 Data Definition Language ............................5
3.2 Management Information .........................................6
3.3 Protocol Operations ............................................6
3.4 SNMPv1 Security and Administration .............................6
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4 The SNMPv2 Management Framework ..................................7
5 The SNMPv3 Working Group .........................................8
6 SNMPv3 Framework Module Specifications ..........................10
6.1 Data Definition Language ......................................10
6.2 MIB Modules ...................................................11
6.3 Protocol Operations and Transport Mappings ....................12
6.4 SNMPv3 Security and Administration ............................12
7 Document Summaries ..............................................13
7.1 Structure of Management Information ...........................13
7.1.1 Base SMI Specification ......................................13
7.1.2 Textual Conventions .........................................14
7.1.3 Conformance Statements ......................................15
7.2 Protocol Operations ...........................................15
7.3 Transport Mappings ............................................15
7.4 Protocol Instrumentation ......................................16
7.5 Architecture / Security and Administration ....................16
7.6 Message Processing and Dispatch (MPD) .........................16
7.7 SNMP Applications .............................................17
7.8 User-based Security Model (USM) ...............................17
7.9 View-based Access Control (VACM) ..............................18
7.10 SNMPv3 Coexistence and Transition ............................18
8 Security Considerations .........................................19
9 Editors' Addresses ..............................................19
10 References .....................................................20
11 Full Copyright Statement .......................................23
1 Introduction
This document is an introduction to the third version of the
Internet-standard Management Framework, termed the SNMP version 3
Management Framework (SNMPv3) and has multiple purposes.
First, it describes the relationship between the SNMP version 3
(SNMPv3) specifications and the specifications of the SNMP version 1
(SNMPv1) Management Framework, the SNMP version 2 (SNMPv2) Management
Framework, and the Community-based Administrative Framework for
SNMPv2.
Second, it provides a roadmap to the multiple documents which contain
the relevant specifications.
Third, this document provides a brief easy-to-read summary of the
contents of each of the relevant specification documents.
This document is intentionally tutorial in nature and, as such, may
occasionally be "guilty" of oversimplification. In the event of a
conflict or contradiction between this document and the more detailed
documents for which this document is a roadmap, the specifications in
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the more detailed documents shall prevail.
Further, the detailed documents attempt to maintain separation
between the various component modules in order to specify well-
defined interfaces between them. This roadmap document, however,
takes a different approach and attempts to provide an integrated view
of the various component modules in the interest of readability.
2 The Internet Standard Management Framework
The third version of the Internet Standard Management Framework (the
SNMPv3 Framework) is derived from and builds upon both the original
Internet-standard Management Framework (SNMPv1) and the second
Internet-standard Management Framework (SNMPv2).
All versions (SNMPv1, SNMPv2, and SNMPv3) of the Internet Standard
Management Framework share the same basic structure and components.
Furthermore, all versions of the specifications of the Internet
Standard Management Framework follow the same architecture.
2.1 Basic Structure and Components
An enterprise deploying the Internet Standard Management Framework
contains four basic components:
* several (typically many) managed nodes, each with an SNMP entity
which provides remote access to management instrumentation
(traditionally called an agent);
* at least one SNMP entity with management applications (typically
called a manager),
* a management protocol used to convey management information
between the SNMP entities, and
* management information.
The management protocol is used to convey management information
between SNMP entities such as managers and agents.
This basic structure is common to all versions of the Internet
Standard Management Framework; i.e., SNMPv1, SNMPv2, and SNMPv3.
2.2 Architecture of the Internet Standard Management Framework
The specifications of the Internet Standard Management Framework are
based on a modular architecture. This framework is more than just a
protocol for moving data. It consists of:
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* a data definition language,
* definitions of management information (the Management
Information Base, or MIB),
* a protocol definition, and
* security and administration.
Over time, as the Framework has evolved from SNMPv1, through SNMPv2,
to SNMPv3, the definitions of each of these architectural components
have become richer and more clearly defined, but the fundamental
architecture has remained consistent.
One prime motivator for this modularity was to enable the ongoing
evolution of the Framework as is documented in RFC 1052 [14]. When
originally envisioned, this capability was to be used to ease the
transition from SNMP-based management of internets to management
based on OSI protocols. To this end, the framework was architected
with a protocol-independent data definition language and Management
Information Base along with a MIB-independent protocol. This
separation was designed to allow the SNMP-based protocol to be
replaced without requiring the management information to be redefined
or reinstrumented. History has shown that the selection of this
architecture was the right decision for the wrong reason -- it turned
out that this architecture has eased the transition from SNMPv1 to
SNMPv2 and from SNMPv2 to SNMPv3 rather than easing the transition
away from management based on the Simple Network Management Protocol.
The SNMPv3 Framework builds and extends these architectural
principles by:
* building on these four basic architectural components, in some
cases incorporating them from the SNMPv2 Framework by reference,
and
* by using these same layering principles in the definition of new
capabilities in the security and administration portion of the
architecture.
Those who are familiar with the architecture of the SNMPv1 Management
Framework and the SNMPv2 Management Framework will find many familiar
concepts in the architecture of the SNMPv3 Management Framework.
However, in some cases, the terminology may be somewhat different.
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3 The SNMPv1 Management Framework
The original Internet-standard Network Management Framework (SNMPv1)
is defined in the following documents:
* STD 16, RFC 1155 [1] which defines the Structure of Management
Information (SMI), the mechanisms used for describing and naming
objects for the purpose of management.
* STD 16, RFC 1212 [2] which defines a more concise description
mechanism for describing and naming management information objects,
but which is wholly consistent with the SMI.
* STD 15, RFC 1157 [3] which defines the Simple Network Management
Protocol (SNMP), the protocol used for network access to managed
objects and event notification. Note this document also defines an
initial set of event notifications.
Additionally, two documents are generally considered to be companions
to these three:
* STD 17, RFC 1213 [13] which contains definitions for the base
set of management information
* RFC 1215 [25] defines a concise description mechanism for
defining event notifications, which are called traps in the SNMPv1
protocol. It also specifies the generic traps from RFC 1157 in the
concise notation.
These documents describe the four parts of the first version of the
SNMP Framework.
3.1 The SNMPv1 Data Definition Language
The first two and the last document describe the SNMPv1 data
definition language. Note that due to the initial requirement that
the SMI be protocol-independent, the first two SMI documents do not
provide a means for defining event notifications (traps). Instead,
the SNMP protocol document defines a few standardized event
notifications (generic traps) and provides a means for additional
event notifications to be defined. The last document specifies a
straight-forward approach towards defining event notifications used
with the SNMPv1 protocol. At the time that it was written, use of
traps in the Internet-standard network management framework was
controversial. As such, RFC 1215 was put forward with the status of
"Informational", which was never updated because it was believed that
the second version of the SNMP Framework would replace the first
version. Note that the SNMPv1 data definition language is sometimes
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referred to as SMIv1.
3.2 Management Information
The data definition language described in the first two documents was
first used to define the now-historic MIB-I as specified in RFC 1066
[12], and was subsequently used to define MIB-II as specified in RFC
1213 [13].
Later, after the publication of MIB-II, a different approach to
management information definition was taken from the earlier approach
of having a single committee staffed by generalists work on a single
document to define the Internet-standard MIB. Rather, many mini-MIB
documents were produced in a parallel and distributed fashion by
groups chartered to produce a specification for a focused portion of
the Internet-standard MIB and staffed by personnel with expertise in
those particular areas ranging from various aspects of network
management, to system management, and application management.
3.3 Protocol Operations
The third document, STD 15, describes the SNMPv1 protocol operations
performed by protocol data units (PDUs) on lists of variable bindings
and describes the format of SNMPv1 messages. The operators defined by
SNMPv1 are: get, get-next, get-response, set-request, and trap.
Typical layering of SNMP on a connectionless transport service is
also defined.
3.4 SNMPv1 Security and Administration
STD 15 also describes an approach to security and administration.
Many of these concepts are carried forward and some, particularly
security, are extended by the SNMPv3 Framework.
The SNMPv1 Framework describes the encapsulation of SNMPv1 PDUs in
SNMP messages between SNMP entities and distinguishes between
application entities and protocol entities. In SNMPv3, these are
renamed applications and engines, respectively.
The SNMPv1 Framework also introduces the concept of an authentication
service supporting one or more authentication schemes. In addition
to authentication, SNMPv3 defines the additional security capability
referred to as privacy. (Note: some literature from the security
community would describe SNMPv3 security capabilities as providing
data integrity, source authenticity, and confidentiality.) The
modular nature of the SNMPv3 Framework permits both changes and
additions to the security capabilities.
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Finally, the SNMPv1 Framework introduces access control based on a
concept called an SNMP MIB view. The SNMPv3 Framework specifies a
fundamentally similar concept called view-based access control. With
this capability, SNMPv3 provides the means for controlling access to
information on managed devices.
However, while the SNMPv1 Framework anticipated the definition of
multiple authentication schemes, it did not define any such schemes
other than a trivial authentication scheme based on community
strings. This was a known fundamental weakness in the SNMPv1
Framework but it was thought at that time that the definition of
commercial grade security might be contentious in its design and
difficult to get approved because "security" means many different
things to different people. To that end, and because some users do
not require strong authentication, the SNMPv1 architected an
authentication service as a separate block to be defined "later" and
the SNMPv3 Framework provides an architecture for use within that
block as well as a definition for its subsystems.
4 The SNMPv2 Management Framework
The SNMPv2 Management Framework is fully described in [4-9] and
coexistence and transition issues relating to SNMPv1 and SNMPv2 are
discussed in [10].
SNMPv2 provides several advantages over SNMPv1, including:
* expanded data types (e.g., 64 bit counter)
* improved efficiency and performance (get-bulk operator)
* confirmed event notification (inform operator)
* richer error handling (errors and exceptions)
* improved sets, especially row creation and deletion
* fine tuning of the data definition language
However, the SNMPv2 Framework, as described in these documents, is
incomplete in that it does not meet the original design goals of the
SNMPv2 project. The unmet goals included provision of security and
administration delivering so-called "commercial grade" security with
* authentication: origin identification, message integrity,
and some aspects of replay protection;
* privacy: confidentiality;
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* authorization and access control; and
* suitable remote configuration and administration capabilities
for these features.
The SNMPv3 Management Framework, as described in this document and
the companion documents, addresses these significant deficiencies.
5 The SNMPv3 Working Group
This document, and its companion documents, were produced by the
SNMPv3 Working Group of the Internet Engineering Task Force (IETF).
The SNMPv3 Working Group was chartered to prepare recommendations for
the next generation of SNMP. The goal of the Working Group was to
produce the necessary set of documents that provide a single standard
for the next generation of core SNMP functions. The single, most
critical need in the next generation is a definition of security and
administration that makes SNMP-based management transactions secure
in a way which is useful for users who wish to use SNMPv3 to manage
networks, the systems that make up those networks, and the
applications which reside on those systems, including manager-to-
agent, agent-to-manager, and manager-to-manager transactions.
In the several years prior to the chartering of the Working Group,
there were a number of activities aimed at incorporating security and
other improvements to SNMP. These efforts included:
* "SNMP Security" circa 1991-1992 [RFC 1351 - RFC 1353],
* "SMP" circa 1992-1993,
* "The Party-based SNMPv2" circa 1993-1995 [RFC 1441 - RFC 1452].
Each of these efforts incorporated commercial grade, industrial
strength security including authentication, privacy, authorization,
view-based access control, and administration, including remote
configuration.
These efforts fed the development of the SNMPv2 Management Framework
as described in RFCs 1902 - 1908. However, the Framework described
in those RFCs had no standards-based security and administrative
framework of its own; rather, it was associated with multiple
security and administrative frameworks, including:
* "The Community-based SNMPv2" (SNMPv2c) [RFC 1901],
* "SNMPv2u" [RFCs 1909 - 1910] and
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* "SNMPv2*".
SNMPv2c had the endorsement of the IETF but no security and
administration whereas both SNMPv2u and SNMPv2* had security but
lacked the endorsement of the IETF.
The SNMPv3 Working Group was chartered to produce a single set of
specifications for the next generation of SNMP, based upon a
convergence of the concepts and technical elements of SNMPv2u and
SNMPv2*, as was suggested by an advisory team which was formed to
provide a single recommended approach for SNMP evolution.
In so doing, the Working Group charter defined the following
objectives:
* accommodate the wide range of operational environments with
differing management demands;
* facilitate the need to transition from previous, multiple
protocols to SNMPv3;
* facilitate the ease of setup and maintenance activities.
In the initial work of the SNMPv3 Working Group, the group focused on
security and administration, including
* authentication and privacy,
* authorization and view-based access control, and
* standards-based remote configuration of the above.
The SNMPv3 Working Group did not "reinvent the wheel," but reused the
SNMPv2 Draft Standard documents, i.e., RFCs 1902 through 1908 for
those portions of the design that were outside the focused scope.
Rather, the primary contributors to the SNMPv3 Working Group, and the
Working Group in general, devoted their considerable efforts to
addressing the missing link -- security and administration -- and in
the process made invaluable contributions to the state-of-the-art of
management.
They produced a design based on a modular architecture with
evolutionary capabilities with emphasis on layering. As a result,
SNMPv3 can be thought of as SNMPv2 with additional security and
administration capabilities.
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In doing so, the Working Group achieved the goal of producing a
single specification which has not only the endorsement of the IETF
but also has security and administration.
6 SNMPv3 Framework Module Specifications
The specification of the SNMPv3 Management Framework is partitioned
in a modular fashion among several documents. It is the intention of
the SNMPv3 Working Group that, with proper care, any or all of the
individual documents can be revised, upgraded, or replaced as
requirements change, new understandings are obtained, and new
technologies become available.
Whenever feasible, the initial document set which defines the SNMPv3
Management Framework leverages prior investments defining and
implementing the SNMPv2 Management Framework by incorporating by
reference each of the specifications of the SNMPv2 Management
Framework.
The SNMPv3 Framework augments those specifications with
specifications for security and administration for SNMPv3.
The documents which specify the SNMPv3 Management Framework follow
the same architecture as those of the prior versions and can be
organized for expository purposes into four main categories as
follows:
* the data definition language,
* Management Information Base (MIB) modules,
* protocol operations, and
* security and administration.
The first three sets of documents are incorporated from SNMPv2. The
fourth set of documents are new to SNMPv3, but, as described
previously, build on significant prior related works.
6.1 Data Definition Language
The specifications of the data definition language includes STD 58,
RFC 2578, "Structure of Management Information Version 2 (SMIv2)"
[26], and related specifications. These documents are updates of
RFCs 1902 - 1904 [4-6] which have evolved independently from the
other parts of the framework and were republished as STD 58, RFCs
2578 - 2580 [26-28] when promoted from Draft Standard.
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The Structure of Management Information (SMIv2) defines fundamental
data types, an object model, and the rules for writing and revising
MIB modules. Related specifications include STD 58, RFCs 2579, 2580.
The updated data definition language is sometimes referred to as
SMIv2.
STD 58, RFC 2579, "Textual Conventions for SMIv2" [27], defines an
initial set of shorthand abbreviations which are available for use
within all MIB modules for the convenience of human readers and
writers.
STD 58, RFC 2580, "Conformance Statements for SMIv2" [28], defines
the format for compliance statements which are used for describing
requirements for agent implementations and capability statements
which can be used to document the characteristics of particular
implementations.
6.2 MIB Modules
MIB modules usually contain object definitions, may contain
definitions of event notifications, and sometimes include compliance
statements specified in terms of appropriate object and event
notification groups. As such, MIB modules define the management
information maintained by the instrumentation in managed nodes, made
remotely accessible by management agents, conveyed by the management
protocol, and manipulated by management applications.
MIB modules are defined according the rules defined in the documents
which specify the data definition language, principally the SMI as
supplemented by the related specifications.
There is a large and growing number of standards-based MIB modules,
as defined in the periodically updated list of standard protocols
[STD 1, RFC 2400]. As of this writing, there are nearly 100
standards-based MIB modules with a total number of defined objects
approaching 10,000. In addition, there is an even larger and growing
number of enterprise-specific MIB modules defined unilaterally by
various vendors, research groups, consortia, and the like resulting
in an unknown and virtually uncountable number of defined objects.
In general, management information defined in any MIB module,
regardless of the version of the data definition language used, can
be used with any version of the protocol. For example, MIB modules
defined in terms of the SNMPv1 SMI (SMIv1) are compatible with the
SNMPv3 Management Framework and can be conveyed by the protocols
specified therein. Furthermore, MIB modules defined in terms of the
SNMPv2 SMI (SMIv2) are compatible with SNMPv1 protocol operations and
can be conveyed by it. However, there is one noteworthy exception:
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the Counter64 datatype which can be defined in a MIB module defined
in SMIv2 format but which cannot be conveyed by an SNMPv1 protocol
engine.
6.3 Protocol Operations and Transport Mappings
The specifications for the protocol operations and transport mappings
of the SNMPv3 Framework are incorporated by reference to the two
SNMPv2 Framework documents.
The specification for protocol operations is found in RFC 1905,
"Protocol Operations for Version 2 of the Simple Network Management
Protocol (SNMPv2)" [7]. The SNMPv3 Framework is designed to allow
various portions of the architecture to evolve independently. For
example, it might be possible for a new specification of protocol
operations to be defined within the Framework to allow for additional
protocol operations.
The specification of transport mappings is found in RFC 1906,
"Transport Mappings for Version 2 of the Simple Network Management
Protocol (SNMPv2)" [8].
6.4 SNMPv3 Security and Administration
The SNMPv3 document series defined by the SNMPv3 Working Group
consists of seven documents at this time:
RFC 2570, "Introduction to Version 3 of the Internet-standard
Network Management Framework", which is this document.
RFC 2571, "An Architecture for Describing SNMP Management
Frameworks" [15], describes the overall architecture with special
emphasis on the architecture for security and administration.
RFC 2572, "Message Processing and Dispatching for the Simple
Network Management Protocol (SNMP)" [16], describes the possibly
multiple message processing models and the dispatcher portion that
can be a part of an SNMP protocol engine.
RFC 2573, "SNMP Applications" [17], describes the five types of
applications that can be associated with an SNMPv3 engine and
their elements of procedure.
RFC 2574, "The User-Based Security Model for Version 3 of the
Simple Network Management Protocol (SNMPv3)" [18], describes the
threats, mechanisms, protocols, and supporting data used to
provide SNMP message-level security.
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RFC 2575, "View-based Access Control Model for the Simple Network
Management Protocol (SNMP)" [19], describes how view-based access
control can be applied within command responder and notification
originator applications.
The Work in Progress, "Coexistence between Version 1, Version 2,
and Version 3 of the Internet-standard Network Management
Framework" [20], describes coexistence between the SNMPv3
Management Framework, the SNMPv2 Management Framework, and the
original SNMPv1 Management Framework.
7 Document Summaries
The following sections provide brief summaries of each document with
slightly more detail than is provided in the overviews above.
7.1 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 in the SNMP MIB module
language, which contains elements of OSI's Abstract Syntax Notation
One (ASN.1) [11] language. STD 58, RFCs 2578, 2579, 2580, together
define the MIB module language, specify the base data types for
objects, specify a core set of short-hand specifications for data
types called textual conventions, and specify a few administrative
assignments of object identifier (OID) 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 convey concisely the
semantics of an information module.
(2) Object definitions are used when describing managed objects. An
ASN.1 macro, OBJECT-TYPE, is used to convey concisely 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 convey concisely the syntax and
semantics of a notification.
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7.1.1 Base SMI Specification
STD 58, RFC 2578 specifies the base data types for the MIB module
language, which include: Integer32, enumerated integers, Unsigned32,
Gauge32, Counter32, Counter64, TimeTicks, INTEGER, OCTET STRING,
OBJECT IDENTIFIER, IpAddress, Opaque, and BITS. It also assigns
values to several object identifiers. STD 58, RFC 2578 further
defines the following constructs of the MIB module language:
* IMPORTS to allow the specification of items that are used
in a MIB module, but defined in another MIB module.
* MODULE-IDENTITY to specify for a MIB module a description
and administrative information such as contact and revision
history.
* OBJECT-IDENTITY and OID value assignments to specify a
an OID value.
* OBJECT-TYPE to specify the data type, status, and the semantics
of managed objects.
* SEQUENCE type assignment to list the columnar objects in
a table.
* NOTIFICATION-TYPE construct to specify an event notification.
7.1.2 Textual Conventions
When designing a MIB module, it is often useful to specify in a
short-hand way the semantics for a set of objects with similar
behavior. This is done by defining a new data type using a base data
type specified in the SMI. Each new type has a different name, and
specifies a base type with more restrictive semantics. These newly
defined types are termed textual conventions, and are used for the
convenience of humans reading a MIB module and potentially by
"intelligent" management applications. It is the purpose of STD 58,
RFC 2579, Textual Conventions for SMIv2 [27], to define the
construct, TEXTUAL-CONVENTION, of the MIB module language used to
define such new types and to specify an initial set of textual
conventions available to all MIB modules.
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7.1.3 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 STD 58, RFC 2580, Conformance
Statements for SMIv2 [28], to define the constructs of the MIB module
language used for these purposes. There are two kinds of constructs:
(1) Compliance statements are used when describing requirements for
agents with respect to object and event notification
definitions. The MODULE-COMPLIANCE construct is used to convey
concisely such requirements.
(2) Capability statements are used when describing capabilities of
agents with respect to object and event notification
definitions. The AGENT-CAPABILITIES construct is used to convey
concisely such capabilities.
Finally, collections of related objects and collections of related
event notifications are grouped together to form a unit of
conformance. The OBJECT-GROUP construct is used to convey concisely
the objects in and the semantics of an object group. The
NOTIFICATION-GROUP construct is used to convey concisely the event
notifications in and the semantics of an event notification group.
7.2 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).
It is the purpose of RFC 1905, Protocol Operations for SNMPv2 [7], to
define the operations of the protocol with respect to the sending and
receiving of the PDUs.
7.3 Transport Mappings
SNMP Messages may be used over a variety of protocol suites. It is
the purpose of RFC 1906, Transport Mappings for SNMPv2 [8], to define
how SNMP messages 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.
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7.4 Protocol Instrumentation
It is the purpose of RFC 1907, the Management Information Base for
SNMPv2 document [9] to define managed objects which describe the
behavior of an SNMPv2 entity.
7.5 Architecture / Security and Administration
It is the purpose of RFC 2571, "An Architecture for Describing SNMP
Management Frameworks" [15], to define an architecture for specifying
SNMP Management Frameworks. While addressing general architectural
issues, it focuses on aspects related to security and administration.
It defines a number of terms used throughout the SNMPv3 Management
Framework and, in so doing, clarifies and extends the naming of
* engines and applications,
* entities (service providers such as the engines in agents
and managers),
* identities (service users), and
* management information, including support for multiple
logical contexts.
The document contains a small MIB module which is implemented by all
authoritative SNMPv3 protocol engines.
7.6 Message Processing and Dispatch (MPD)
RFC 2572, "Message Processing and Dispatching for the Simple Network
Management Protocol (SNMP)" [16], describes the Message Processing
and Dispatching for SNMP messages within the SNMP architecture. It
defines the procedures for dispatching potentially multiple versions
of SNMP messages to the proper SNMP Message Processing Models, and
for dispatching PDUs to SNMP applications. This document also
describes one Message Processing Model - the SNMPv3 Message
Processing Model.
It is expected that an SNMPv3 protocol engine MUST support at least
one Message Processing Model. An SNMPv3 protocol engine MAY support
more than one, for example in a multi-lingual system which provides
simultaneous support of SNMPv3 and SNMPv1 and/or SNMPv2c.
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7.7 SNMP Applications
It is the purpose of RFC 2573, "SNMP Applications" to describe the
five types of applications which can be associated with an SNMP
engine. They are: Command Generators, Command Responders,
Notification Originators, Notification Receivers, and Proxy
Forwarders.
The document also defines MIB modules for specifying targets of
management operations (including notifications), for notification
filtering, and for proxy forwarding.
7.8 User-based Security Model (USM)
RFC 2574, the "User-based Security Model (USM) for version 3 of the
Simple Network Management Protocol (SNMPv3)" describes the User-based
Security Model for SNMPv3. It defines the Elements of Procedure for
providing SNMP message-level security.
The document describes the two primary and two secondary threats
which are defended against by the User-based Security Model. They
are: modification of information, masquerade, message stream
modification, and disclosure.
The USM utilizes MD5 [21] and the Secure Hash Algorithm [22] as keyed
hashing algorithms [23] for digest computation to provide data
integrity
* to directly protect against data modification attacks,
* to indirectly provide data origin authentication, and
* to defend against masquerade attacks.
The USM uses loosely synchronized monotonically increasing time
indicators to defend against certain message stream modification
attacks. Automatic clock synchronization mechanisms based on the
protocol are specified without dependence on third-party time sources
and concomitant security considerations.
The USM uses the Data Encryption Standard (DES) [24] in the cipher
block chaining mode (CBC) if disclosure protection is desired.
Support for DES in the USM is optional, primarily because export and
usage restrictions in many countries make it difficult to export and
use products which include cryptographic technology.
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The document also includes a MIB suitable for remotely monitoring and
managing the configuration parameters for the USM, including key
distribution and key management.
An entity may provide simultaneous support for multiple security
models as well as multiple authentication and privacy protocols. All
of the protocols used by the USM are based on pre-placed keys, i.e.,
private key mechanisms. The SNMPv3 architecture permits the use of
asymmetric mechanisms and protocols (commonly called "public key
cryptography") but as of this writing, no such SNMPv3 security models
utilizing public key cryptography have been published.
7.9 View-based Access Control (VACM)
The purpose of RFC 2575, the "View-based Access Control Model (VACM)
for the Simple Network Management Protocol (SNMP)" is to describe the
View-based Access Control Model for use in the SNMP architecture.
The VACM can simultaneously be associated in a single engine
implementation with multiple Message Processing Models and multiple
Security Models.
It is architecturally possible to have multiple, different, Access
Control Models active and present simultaneously in a single engine
implementation, but this is expected to be *_very_* rare in practice
and *_far_* less common than simultaneous support for multiple
Message Processing Models and/or multiple Security Models.
7.10 SNMPv3 Coexistence and Transition
The purpose of "Coexistence between Version 1, Version 2, and Version
3 of the Internet-standard Network Management Framework" is to
describe coexistence between the SNMPv3 Management Framework, the
SNMPv2 Management Framework, and the original SNMPv1 Management
Framework. In particular, this document describes four aspects of
coexistence:
* Conversion of MIB documents from SMIv1 to SMIv2 format
* Mapping of notification parameters
* Approaches to coexistence between entities which support
the various versions of SNMP in a multi-lingual network, in
particular the processing of protocol operations in
multi-lingual implementations, as well as behavior of
proxy implementations
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* The SNMPv1 Message Processing Model and Community-Based
Security Model, which provides mechanisms for adapting
SNMPv1 and SNMPv2c into the View-Based Access Control Model
(VACM) [19]
8 Security Considerations
As this document is primarily a roadmap document, it introduces no
new security considerations. The reader is referred to the relevant
sections of each of the referenced documents for information about
security considerations.
9 Editors' Addresses
Jeffrey Case
SNMP Research, Inc.
3001 Kimberlin Heights Road
Knoxville, TN 37920-9716
USA
Phone: +1 423 573 1434
EMail: case@snmp.com
Russ Mundy
TIS Labs at Network Associates
3060 Washington Rd
Glenwood, MD 21738
USA
Phone: +1 301 854 6889
EMail: mundy@tislabs.com
David Partain
Ericsson Radio Systems
Research and Innovation
P.O. Box 1248
SE-581 12 Linkoping
Sweden
Phone: +46 13 28 41 44
EMail: David.Partain@ericsson.com
Bob Stewart
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134-1706
U.S.A.
Phone: +1 603 654 6923
EMail: bstewart@cisco.com
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10 References
[1] Rose, M. and K. McCloghrie, "Structure and Identification of
Management Information for TCP/IP-based internets", STD 16, RFC
1155, May 1990.
[2] Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16,
RFC 1212, March 1991.
[3] Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple
Network Management Protocol", STD 15, RFC 1157, May 1990.
[4] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S.
Waldbusser, "Structure of Management Information for Version 2
of the Simple Network Management Protocol (SNMPv2)", RFC 1902,
January 1996.
[5] 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.
[6] 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.
[7] 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.
[8] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M. and S.
Waldbusser, "Transport Mappings for Version 2 of the Simple
Network Management Protocol (SNMPv2)", RFC 1906, January 1996.
[9] 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.
[10] 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.
[11] Information processing systems - Open Systems Interconnection -
Specification of Abstract Syntax Notation One (ASN.1),
International Organization for Standardization. International
Standard 8824, (December, 1987).
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[12] McCloghrie, K. and M. Rose, "Management Information Base for
Network Management of TCP/IP-based Internets", RFC 1066, August
1988.
[13] McCloghrie, K. and M. Rose, "Management Information Base for
Network Management of TCP/IP-based internets: MIB-II, STD 17,
RFC 1213, March 1991.
[14] Cerf, V., "IAB Recommendations for the Development of Internet
Network Management Standards", RFC 1052, April 1988.
[15] Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for
Describing SNMP Management Frameworks", RFC 2571, April 1999.
[16] Case, J., Harrington, D., Presuhn, R. and B. Wijnen, "Message
Processing and Dispatching for the Simple Network Management
Protocol (SNMP)", RFC 2572, April 1999.
[17] Levi, D., Meyer, P. and B. Stewart, "SNMP Applications", RFC
2573, April 1999.
[18] Blumenthal, U. and B. Wijnen, "The User-Based Security Model for
Version 3 of the Simple Network Management Protocol (SNMPv3)",
RFC 2574, April 1999.
[19] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access
Control Model for the Simple Network Management Protocol
(SNMP)", RFC 2575, April 1999.
[20] Frye, R., Levi, D., Routhier, S., and B. Wijnen, "Coexistence
between Version 1, Version 2, and Version 3 of the Internet-
standard Network Management Framework", Work in Progress.
[21] Rivest, R., "Message Digest Algorithm MD5", RFC 1321, April
1992.
[22] Secure Hash Algorithm. NIST FIPS 180-1, (April, 1995)
http://csrc.nist.gov/fips/fip180-1.txt (ASCII)
http://csrc.nist.gov/fips/fip180-1.ps (Postscript)
[23] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997.
[24] Data Encryption Standard, National Institute of Standards and
Technology. Federal Information Processing Standard (FIPS)
Publication 46-1. Supersedes FIPS Publication 46, (January,
1977; reaffirmed January, 1988).
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[25] Rose, M., "A Convention for Defining Traps for use with the
SNMP", RFC 1215, March 1991.
[26] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M. and S. Waldbusser, "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[27] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M. and S. Waldbusser, "Textual Conventions for SMIv2", STD 58,
RFC 2579, April 1999.
[28] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M. and S. Waldbusser, "Conformance Statements for SMIv2", STD
58, RFC 2580, April 1999.
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11 Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
Acknowledgement
Funding for the RFC Editor function is currently provided by
the Internet Society.
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