Network Working Group J. Case
Request for Comments: 3410 SNMP Research, Inc.
Obsoletes: 2570 R. Mundy
Category: Informational Network Associates Laboratories
D. Partain
Ericsson
B. Stewart
Retired
December 2002
Introduction and Applicability Statements for
Internet Standard 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 (2002). 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.
The document explains why using SNMPv3 instead of SNMPv1 or SNMPv2 is
strongly recommended. The document also recommends that RFCs 1157,
1441, 1901, 1909 and 1910 be retired by moving them to Historic
status. This document obsoletes RFC 2570.
Table of Contents
1 Introduction ................................................. 2
2 The Internet Standard Management Framework ................... 3
2.1 Basic Structure and Components ............................. 4
2.2 Architecture of the Internet Standard Management Framework . 4
3 The SNMPv1 Management Framework .............................. 5
3.1 The SNMPv1 Data Definition Language ........................ 6
3.2 Management Information ..................................... 6
3.3 Protocol Operations ........................................ 7
3.4 SNMPv1 Security and Administration ......................... 7
4 The SNMPv2 Management Framework .............................. 8
5 The SNMPv3 Working Group ..................................... 8
6 SNMPv3 Framework Module Specifications ....................... 10
6.1 Data Definition Language ................................... 11
6.2 MIB Modules ................................................ 12
6.3 Protocol Operations and Transport Mappings ................. 13
6.4 SNMPv3 Security and Administration ......................... 13
7 Document Summaries ........................................... 14
7.1 Structure of Management Information ........................ 14
7.1.1 Base SMI Specification ................................... 15
7.1.2 Textual Conventions ...................................... 15
7.1.3 Conformance Statements ................................... 16
7.2 Protocol Operations ........................................ 16
7.3 Transport Mappings ......................................... 16
7.4 Protocol Instrumentation ................................... 17
7.5 Architecture / Security and Administration ................. 17
7.6 Message Processing and Dispatch (MPD) ...................... 17
7.7 SNMP Applications .......................................... 18
7.8 User-based Security Model (USM) ............................ 18
7.9 View-based Access Control (VACM) ........................... 19
7.10 SNMPv3 Coexistence and Transition ......................... 19
8 Standardization Status ....................................... 20
8.1 SMIv1 Status ............................................... 20
8.2 SNMPv1 and SNMPv2 Standardization Status ................... 21
8.3 Working Group Recommendation ............................... 22
9 Security Considerations ...................................... 22
10 References .................................................. 22
11 Editor's Addresses .......................................... 26
12 Full Copyright Statement .................................... 27
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
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.
This document is a work product of the SNMPv3 Working Group of the
Internet Engineering Task Force (IETF).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119 [1].
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 SNMP 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:
* 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 [2]. 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.
3. The SNMPv1 Management Framework
The original Internet-Standard Network Management Framework (SNMPv1)
is defined in the following documents:
* STD 16, RFC 1155 [3] 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 [4] 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 [5] 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 companions to
these three:
* STD 17, RFC 1213 [6] which contains definitions for the base set
of management information
* RFC 1215 [7] 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, i.e., RFCs 1155, 1212, and 1215,
describe the SNMPv1 data definition language and are often
collectively referred to as "SMIv1". 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.
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
[8], and was subsequently used to define MIB-II as specified in RFC
1213 [6].
Later, after the publication of MIB-II, a different approach to the
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 [5], 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 [5] 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.
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 described in [8-13] and
coexistence and transition issues relating to SNMPv1 and SNMPv2 are
discussed in [15].
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;
* 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, and
* "The Party-based SNMPv2" (sometimes called "SNMPv2p") 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) as described in RFC 1901
[16],
* "SNMPv2u" as described in RFCs 1909 and 1910, and
* "SNMPv2*."
SNMPv2c had the most support within the IETF but had no security and
administration whereas both SNMPv2u and SNMPv2* had security but
lacked a consensus of support within 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.
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
documents in the fourth set 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 include STD 58,
RFC 2578, "Structure of Management Information Version 2 (SMIv2)"
[17], and related specifications. These documents are updates of
RFCs 1902 - 1904 [9-11] which have evolved independently from the
other parts of the framework and were republished with minor
editorial changes as STD 58, RFCs 2578 - 2580 [17-19] when promoted
from Draft Standard to full Standard.
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.
STD 58, RFC 2579, "Textual Conventions for SMIv2" [18], 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" [19], 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.
The term "SMIv2" is somewhat ambiguous because users of the term
intend it to have at least two different meanings. Sometimes the
term is used to refer the entire data definition language of STD 58,
defined collectively in RFCs 2578 - 2580 whereas at other times it is
used to refer to only the portion of the data definition language
defined in RFC 2578. This ambiguity is unfortunate but is rarely a
significant problem in practice.
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 to 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-track MIB modules,
as defined in the periodically updated "Internet Official Protocol
Standards" list [20]. As of this writing, there are more than 100
standards-track MIB modules with a total number of defined objects
exceeding 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:
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. It can be conveyed by an SNMPv2 or an SNMPv3 engine, but
cannot be conveyed by an engine which exclusively supports SNMPv1.
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 which have subsequently been updated.
The specification for protocol operations is found in STD 62, RFC
3416, "Version 2 of the Protocol Operations for the Simple Network
Management Protocol (SNMP)" [21].
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 STD 62, RFC 3417,
"Transport Mappings for the Simple Network Management Protocol
(SNMP)" [22].
6.4. SNMPv3 Security and Administration
The document series pertaining to SNMPv3 Security and Administration
defined by the SNMPv3 Working Group consists of seven documents at
this time:
RFC 3410, "Introduction and Applicability Statements for the
Internet-Standard Management Framework", which is this document.
STD 62, RFC 3411, "An Architecture for Describing Simple Network
Management Protocol (SNMP) Management Frameworks" [23], describes
the overall architecture with special emphasis on the architecture
for security and administration.
STD 62, RFC 3412, "Message Processing and Dispatching for the
Simple Network Management Protocol (SNMP)" [24], describes the
possibility of multiple message processing models and the
dispatcher portion that can be a part of an SNMP protocol engine.
STD 62, RFC 3413, "Simple Network Management Protocol (SNMP)
Applications" [25], describes the five initial types of
applications that can be associated with an SNMPv3 engine and
their elements of procedure.
STD 62, RFC 3414, "User-Based Security Model (USM) for Version 3
of the Simple Network Management Protocol (SNMPv3)" [26],
describes the threats against which protection is provided, as
well as the mechanisms, protocols, and supporting data used to
provide SNMP message-level security with the user-based security
model.
STD 62, RFC 3415, "View-based Access Control Model (VCAM) for the
Simple Network Management Protocol (SNMP)" [27], describes how
view-based access control can be applied within command responder
and notification originator applications.
RFC 2576, "SNMPv3 Coexistence and Transition" [28], describes
coexistence between the SNMPv3 Management Framework, the SNMPv2
Management Framework, and the original SNMPv1 Management
Framework, and is in the process of being updated by a Work in
Progress.
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 data
definition language, which evolved from an adapted subset of OSI's
Abstract Syntax Notation One (ASN.1) [29] language. STD 58, RFCs
2578, 2579, 2580, collectively define the data definition 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.
As noted earlier, the term "SMIv2" is somewhat ambiguous because
users of the term intend it to have at least two different meanings.
Sometimes the term is used to refer to the entire data definition
language of STD 58, defined collectively in RFCs 2578 - 2580 whereas
at other times it is used to refer to only the portion of the data
definition language defined in RFC 2578. This ambiguity is
unfortunate but is rarely a significant problem in practice.
7.1.1. Base SMI Specification
STD 58, RFC 2578 specifies the base data types for the data
definition 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 data definition
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 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 [18], to define the
construct, TEXTUAL-CONVENTION, of the data definition language used
to define such new types and to specify an initial set of textual
conventions available to all MIB modules.
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 [19], to define the constructs of the data
definition 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 STD 62, RFC 3416, "Version 2 of the Protocol
Operations for the Simple Network Management Protocol (SNMP)" [21],
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 STD 62, RFC 3417, "Transport Mappings for the Simple
Network Management Protocol (SNMP)" [22], to define how SNMP messages
map 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.
7.4. Protocol Instrumentation
It is the purpose of STD 62, RFC 3418, "Management Information Base
(MIB) for the Simple Network Management Protocol (SNMP)" [30], to
define managed objects which describe the behavior of portions of an
SNMP entity.
7.5. Architecture / Security and Administration
It is the purpose of STD 62, RFC 3411, "An Architecture for
Describing Simple Network Management Protocol (SNMP) Management
Frameworks" [23], to define an architecture for specifying 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)
STD 62, RFC 3412, "Message Processing and Dispatching for the Simple
Network Management Protocol (SNMP)" [24], 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.
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. For
example, such a tri-lingual system which provides simultaneous
support for SNMPv1, SNMPv2c, and SNMPv3 supports three message
processing models.
7.7. SNMP Applications
It is the purpose of STD 62, RFC 3413, "Simple Network Management
Protocol (SNMP) Applications" [25] 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)
STD 62, RFC 3414, the "User-based Security Model (USM) for version 3
of the Simple Network Management Protocol (SNMPv3)" [26] 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 [31] and the Secure Hash Algorithm [32] as keyed
hashing algorithms [33] 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) [34] 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.
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
symmetric and asymmetric mechanisms and protocols (asymmetric
mechanisms are commonly called public key cryptography) but, as of
this writing, there are no SNMPv3 security models on the IETF
standards track that use public key cryptography.
Work is underway to specify how AES is to be used within the User-
based Security Model (USM). This will be a separate document.
7.9. View-based Access Control (VACM)
The purpose of STD 62, RFC 3415, the "View-based Access Control Model
(VACM) for the Simple Network Management Protocol (SNMP)" [27], 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 RFC 2576, "Coexistence between Version 1, Version 2,
and Version 3 of the Internet-Standard Network Management Framework"
[28], 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
* 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) [27]
8. Standardization Status
Readers should consult the latest version of the "Internet Official
Protocol Standards" list [20] to determine the standardization status
of any document.
However, the SNMPv3 Working Group explicitly requested that text be
included in this document to amplify on the status of SMIv1, SNMPv1,
and SNMPv2c.
8.1. SMIv1 Status
SMIv1, as described in STD 16, RFCs 1155 and 1212, was promoted to
full Standard status in 1990 and has remained a Standard even after
SMIv2 reached full Standard (see RFC 2026 [35] for more information
about the Internet Standards Process). In many cases, a Standard is
declared "Historic" when its replacement reaches full Standard. For
example, MIB-1 [8] was declared "Historic" when MIB-2 [6] reached
full Standard. Similarly, when SMIv2 reached full Standard, it might
have been reasonable at that time to retire SMIv1 and declare it to
be "Historic" but as the result of a conscious decision, STD 16, RFCs
1155 and 1212 continue to have the standardization status of full
"Standard" but are not recommended. These documents were not
declared "Historic" and remain on the standards track because they
provide normative references for other documents on the standards
track and cannot be declared "Historic" without rendering the
documents which rely on them to also become "Historic".
Consequently, STD 16 retains its standardization status but is not
recommended because it has been superseded by the newer SMIv2
specifications which are identified somewhat later in this document.
On a pragmatic level, since about 1993 it has been wise for users of
the data definition language to use SMIv2 for all new work because
the realities of the marketplace have occasionally required the
support of data definitions in both the SMIv1 and SMIv2 formats.
While there are tools widely available at low cost or no cost to
translate SMIv2 definitions to SMIv1 definitions, it is impractical
to build automatic tools that automatically translate SMIv1
definitions to SMIv2 definitions. Consequently, if one works in
primarily SMIv2, the cost of providing data definitions in both SMIv1
and SMIv2 formats is trivial. In contrast, if one works primarily in
SMIv1 format, providing data definitions in both SMIv1 and SMIv2 is
significantly more expensive. The market requirements today for
providing data definitions in SMIv1 format are greatly diminished
when compared to those of 1993, and SMIv2 continues to be the
strongly preferred format even though SMIv1 has not been declared
"Historic". Indeed, the IETF currently requires that new MIB modules
be written using SMIv2.
8.2. SNMPv1 and SNMPv2 Standardization Status
Protocol operations via SNMPv1 and SNMPv2c message wrappers support
only trivial authentication based on plain-text community strings
and, as a result, are fundamentally insecure. When the SNMPv3
specifications for security and administration, which include strong
security, reached full Standard status, the full Standard SNMPv1,
formerly STD 15 [5], and the experimental SNMPv2c specifications
described in RFC 1901 [16] were declared Historic due to their
weaknesses with respect to security and to send a clear message that
the third version of the Internet Standard Management Framework is
the framework of choice. The Party-based SNMPv2 (SNMPv2p), SNMPv2u,
and SNMPv2* were either declared Historic circa 1995 or were never on
the standards track.
On a pragmatic level, it is expected that a number of vendors will
continue to produce and users will continue to deploy and use multi-
lingual implementations that support SNMPv1 and/or SNMPv2c as well as
SNMPv3. It should be noted that the IETF standards process does not
control actions of vendors or users who may choose to promote or
deploy historic protocols, such as SNMPv1 and SNMPv2c, in spite of
known short-comings. However, it is not expected that vendors will
produce nor that users will deploy multi-lingual implementations that
support the Party-based SNMPv2p (SNMPv2p), SNMPv2u, or SNMPv2*.
Indeed, as described above, one of the SNMPv3 specifications for
security and administration, RFC 2576, Coexistence between Version 1,
Version 2, and Version 3 of the Internet-Standard Management
Framework [28], addresses these issues.
Of course, it is important that users deploying multi-lingual systems
with insecure protocols exercise sufficient due diligence to insure
that configurations limit access via SNMPv1 and SNMPv2c
appropriately, in keeping with the organization's security policy,
just as they should carefully limit access granted via SNMPv3 with a
security level of no authentication and no privacy which is roughly
equivalent from a security point of view. For example, it is
probably unwise to allow SNMPv1 or SNMPv2c a greater level of access
than is provided to unauthenticated SNMPv3 users, e.g., it does not
make sense to guard the front door with armed guards, trained attack
dogs, moats and drawbridges while providing unfettered access through
an open back door.
The SNMPv1 framework, SNMPv2 framework, and SNMPv2c had limited
capabilities for administering the SNMPv1 and SNMPv2c protocols. For
example, there are no objects defined to view and configure
communities or destinations for notifications (traps and informs).
The result has been vendor defined mechanisms for administration that
range from proprietary format configuration files that cannot be
viewed or configured via SNMP to enterprise specific object
definitions. The SNMPv3 framework provides a rich standards-based
approach to administration which, by design, can be used for the
SNMPv1 and SNMPv2c protocols. Thus, to foster interoperability of
administration of SNMPv1 and SNMPv2c protocols in multi-lingual
systems, the mechanisms and objects specified in [25], [27], and [28]
should be used to supplement or replace the equivalent proprietary
mechanisms.
8.3. Working Group Recommendation
Based on the explanations above, the SNMPv3 Working Group recommends
that RFCs 1157, 1441, 1901, 1909 and 1910 be reclassified as
Historical documents.
9. 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.
10. References
10.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March, 1997.
10.2. Informative References
[2] Cerf, V., "IAB Recommendations for the Development of Internet
Network Management Standards", RFC 1052, April 1988.
[3] Rose, M. and K. McCloghrie, "Structure and Identification of
Management Information for TCP/IP-based internets", STD 16, RFC
1155, May 1990.
[4] Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16,
RFC 1212, March 1991.
[5] Case, J., Fedor, M., Schoffstall, M. and Davin, J., "Simple
Network Management Protocol", STD 15, RFC 1157, May 1990.
[6] McCloghrie, K. and M. Rose, "Management Information Base for
Network Management of TCP/IP-based internets: MIB-II", STD 17,
RFC 1213, March 1991.
[7] Rose, M., "A Convention for Defining Traps for use with the
SNMP", RFC 1215, March 1991.
[8] McCloghrie, K. and M. Rose, "Management Information Base for
Network Management of TCP/IP-based Internets", RFC 1156, March
1990.
[9] 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.
[10] 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.
[11] 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.
[12] 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.
[13] 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.
[14] 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.
[15] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Coexistence between Version 1 and Version 2 of the Internet-
Standard Network Management Framework", RFC 2576, January 1996.
[16] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Introduction to Community-based SNMPv2", RFC 1901, January
1996.
[17] 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.
[18] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M. and S. Waldbusser, "Textual Conventions for SMIv2", STD 58,
RFC 2579, April 1999.
[19] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M. and S. Waldbusser, "Conformance Statements for SMIv2", STD
58, RFC 2580, April 1999.
[20] "Official Internet Protocol Standards", http://www.rfc-
editor.org/rfcxx00.html also STD0001.
[21] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
Waldbusser, "Version 2 of the Protocol Operations for the Simple
Network Management Protocol (SNMP)", STD 62, RFC 3416, December
2002.
[22] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
Waldbusser, "Transport Mappings for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3417, December 2002.
[23] Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for
Describing Simple Network Management Protocol (SNMP) Management
Frameworks", STD 62, RFC 3411, December 2002.
[24] Case, J., Harrington, D., Presuhn, R. and B. Wijnen, "Message
Processing and Dispatching for the Simple Network Management
Protocol (SNMP)", STD 62, RFC 3412, December 2002.
[25] Levi, D., Meyer, P. and B. Stewart, "Simple Network Management
Protocol (SNMP) Applications", STD 62, RFC 3413, December 2002.
[26] Blumenthal, U. and B. Wijnen, "User-Based Security Model (USM)
for Version 3 of the Simple Network Management Protocol
(SNMPv3)", STD 62, RFC 3414, December 2002.
[27] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access
Control Model (VACM) for the Simple Network Management Protocol
(SNMP)", STD 62, RFC 3415, December 2002.
[28] 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", RFC 2576, March 2000.
[29] Information processing systems - Open Systems Interconnection -
Specification of Abstract Syntax Notation One (ASN.1),
International Organization for Standardization. International
Standard 8824, (December, 1987).
[30] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
Waldbusser, "Management Information Base (MIB) for the Simple
Network Management Protocol (SNMP)", STD 62, RFC 3418, December
2002.
[31] Rivest, R., "Message Digest Algorithm MD5", RFC 1321, April
1992.
[32] 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)
[33] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997.
[34] 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).
[35] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October, 1996.
11. Editors' Addresses
Jeffrey Case
SNMP Research, Inc.
3001 Kimberlin Heights Road
Knoxville, TN 37920-9716
USA
Phone: +1 865 573 1434
EMail: case@snmp.com
Russ Mundy
Network Associates Laboratories
15204 Omega Drive, Suite 300
Rockville, MD 20850-4601
USA
Phone: +1 301 947 7107
EMail: mundy@tislabs.com
David Partain
Ericsson
P.O. Box 1248
SE-581 12 Linkoping
Sweden
Phone: +46 13 28 41 44
EMail: David.Partain@ericsson.com
Bob Stewart
Retired
12. Full Copyright Statement
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
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