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Versions: (RFC 2570) 00 01 02 RFC 3410

INTERNET-DRAFT                                           Jeffrey D. Case
                                                     SNMP Research, Inc.
                                                              Russ Mundy
                                    TIS Labs at Network Associates, Inc.
                                                           David Partain
                                                                Ericsson
                                                             Bob Stewart
                                                           Cisco Systems

                    Introduction to Version 3 of the
             Internet-standard Network Management Framework

                          1999/03/24 08:30:58
                     draft-ietf-snmpv3-rfc2570bis-00.txt
                      1.14 -- 1999/03/24 08:30:58

Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups.  Note that other groups
may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet- Drafts as reference material
or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

                                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.




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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.























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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.


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.


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.




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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.



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



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    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.


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 referred to as SMIv1.


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



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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.


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.


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.

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



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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.



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;

  * 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.





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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

  * "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



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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.









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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.



The specifications of the data definition language includes RFC 1902,
"The Structure of Management Information for Version 2 of the Simple
Network Management Protocol (SNMPv2)" [4], and related specifications.
The Structure of Management Information (SMI) defines fundamental data
types, an object model, and the rules for writing and revising MIB
modules.  Related specifications include RFC 1903 and RFC 1904.  The
updated data definition language is sometimes referred to as SMIv2.

RFC 1903, "Textual Conventions for Version 2 of the Simple Network
Management Protocol (SNMPv2)" [5], defines an initial set of shorthand
abbreviations which are available for use within all MIB modules for the
convenience of human readers and writers.




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RFC 1904, "Conformance Statements for Version 2 of the Simple Network
Management Protocol (SNMPv2)" [6], 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.


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
0001, 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:  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.


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



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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].



The SNMPv3 document series defined by the SNMPv3 Working Group consists
of seven documents at this time:

      RFC xxxx (draft-ietf-snmpv3-intro-04.txt), "Introduction to
      Version 3 of the Internet-standard Network Management Framework",
      which is this document.

      RFC xxx1 (draft-ietf-snmpv3-arch-05.txt), "An Architecture for
      Describing SNMP Management Frameworks" [15], describes the overall
      architecture with special emphasis on the architecture for
      security and administration.

      RFC xxx2 (draft-ietf-snmpv3-mpc-05.txt), "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 xxx3 (draft-ietf-snmpv3-appl-v2-03.txt), "SNMP Applications"
      [17], describes the five types of applications that can be
      associated with an SNMPv3 engine and their elements of procedure.

      RFC xxx4 (draft-ietf-snmpv3-usm-v2-05.txt), "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.

      RFC xxx5 (draft-ietf-snmpv3-vacm-04.txt), "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.




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      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.












































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The following sections provide brief summaries of each document with
slightly more detail than is provided in the overviews above.


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.  RFC 1902, RFC 1903, and RFC 1904 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.


RFC 1902 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.  RFC 1902 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.




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  * 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.


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 RFC 1903, Textual Conventions for SNMPv2 [5], 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.


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 RFC 1904, Conformance Statements for SNMPv2 [6], 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



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an event notification group.


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.


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.


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.


It is the purpose of RFC xxx1 (draft-ietf-snmpv3-arch-05.txt), "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.



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The document contains a small MIB module which is implemented by all
authoritative SNMPv3 protocol engines.


RFC xxx2 (draft-ietf-snmpv3-mpc-05.txt), "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.


It is the purpose of RFC xxx3 (draft-ietf-snmpv3-appl-v2-03.txt), "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.


RFC xxx4 (draft-ietf-snmpv3-usm-v2-05.txt), 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,




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  * 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.

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.


The purpose of RFC xxx5 (draft-ietf-snmpv3-vacm-04.txt), 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.



The purpose of "Coexistence between Version 1, Version 2, and Version 3
of the Internet-standard Network Management Framework" is to describe



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                           - 19 -


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 behaviour 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) [19]































                       April 11, 1999





                           - 20 -


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.


   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@tis.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








                       April 11, 1999





                           - 21 -


   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."




[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., Davin, J., "Simple Network
     Management Protocol", STD 15, RFC 1157, SNMP Research, Performance
     Systems International, MIT Laboratory for Computer Science, 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.




                       April 11, 1999





                           - 22 -


[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).

[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, 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",
     <draft-ietf-snmpv3-arch-05.txt>, January 1999.




                       April 11, 1999





                           - 23 -


[16] Case, J., Harrington, D., Presuhn, R., and B. Wijnen, "Message
     Processing and Dispatching for the Simple Network Management
     Protocol (SNMP)", <draft-ietf-snmpv3-mpc-05.txt>,
     January, 1999.

[17] Levi, D., Meyer, P., and B. Stewart, "SNMP Applications",
     <draft-ietf-snmpv3-appl-v2-03.txt>, January 1999.

[18] Blumenthal, U. and B. Wijnen, "The User-Based Security
     Model for Version 3 of the Simple Network Management Protocol
     (SNMPv3)", <draft-ietf-snmpv3-usm-v2-05.txt>, January 1999.

[19] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
     Access Control Model for the Simple Network Management Protocol
     (SNMP)", <draft-ietf-snmpv3-vacm-04.txt>, January 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).

[25] M.T. Rose, "A Convention for Defining Traps for use with the
     SNMP", RFC 1215, March 1991.











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Table of Contents




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