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RFC2571 - An Architecture for Describing SNMP Management Frameworks

王朝other·作者佚名  2008-05-31
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Network Working Group D. Harrington

Request for Comments: 2571 Cabletron Systems, Inc.

Obsoletes: 2271 R. Presuhn

Category: Standards Track BMC Software, Inc.

B. Wijnen

IBM T. J. Watson Research

April 1999

An Architecture for Describing

SNMP Management Frameworks

Status of this Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (1999). All Rights Reserved.

Abstract

This document describes an architecture for describing SNMP

Management Frameworks. The architecture is designed to be modular to

allow the evolution of the SNMP protocol standards over time. The

major portions of the architecture are an SNMP engine containing a

Message Processing Subsystem, a Security Subsystem and an Access

Control Subsystem, and possibly multiple SNMP applications which

provide specific functional processing of management data.

Table of Contents

1. IntrodUCtion ................................................ 4

1.1. Overview .................................................. 4

1.2. SNMP ...................................................... 4

1.3. Goals of this Architecture ................................ 5

1.4. Security Requirements of this Architecture ................ 6

1.5. Design Decisions .......................................... 7

2. Documentation Overview ...................................... 9

2.1. Document Roadmap .......................................... 10

2.2. Applicability Statement ................................... 10

2.3. Coexistence and Transition ................................ 10

2.4. Transport Mappings ........................................ 11

2.5. Message Processing ........................................ 11

2.6. Security .................................................. 11

2.7. Access Control ............................................ 12

2.8. Protocol Operations ....................................... 12

2.9. Applications .............................................. 13

2.10. Structure of Management Information ...................... 14

2.11. Textual Conventions ...................................... 14

2.12. Conformance Statements ................................... 14

2.13. Management Information Base Modules ...................... 14

2.13.1. SNMP Instrumentation MIBs .............................. 14

2.14. SNMP Framework Documents ................................. 14

3. Elements of the Architecture ................................ 15

3.1. The Naming of Entities .................................... 16

3.1.1. SNMP engine ............................................. 17

3.1.1.1. snmpEngineID .......................................... 17

3.1.1.2. Dispatcher ............................................ 17

3.1.1.3. Message Processing Subsystem .......................... 18

3.1.1.3.1. Message Processing Model ............................ 18

3.1.1.4. Security Subsystem .................................... 18

3.1.1.4.1. Security Model ...................................... 19

3.1.1.4.2. Security Protocol ................................... 19

3.1.2. Access Control Subsystem ................................ 19

3.1.2.1. Access Control Model .................................. 20

3.1.3. Applications ............................................ 20

3.1.3.1. SNMP Manager .......................................... 20

3.1.3.2. SNMP Agent ............................................ 22

3.2. The Naming of Identities .................................. 23

3.2.1. Principal ............................................... 23

3.2.2. securityName ............................................ 23

3.2.3. Model-dependent security ID ............................. 24

3.3. The Naming of Management Information ...................... 25

3.3.1. An SNMP Context ......................................... 26

3.3.2. contextEngineID ......................................... 26

3.3.3. contextName ............................................. 27

3.3.4. scopedPDU ............................................... 27

3.4. Other Constructs .......................................... 27

3.4.1. maxSizeResponseScopedPDU ................................ 27

3.4.2. Local Configuration Datastore ........................... 27

3.4.3. securityLevel ........................................... 27

4. Abstract Service Interfaces ................................. 28

4.1. Dispatcher Primitives ..................................... 28

4.1.1. Generate Outgoing Request or Notification ............... 28

4.1.2. Process Incoming Request or Notification PDU ............ 29

4.1.3. Generate Outgoing Response .............................. 29

4.1.4. Process Incoming Response PDU ........................... 29

4.1.5. Registering Responsibility for Handling SNMP PDUs ....... 30

4.2. Message Processing Subsystem Primitives ................... 30

4.2.1. Prepare Outgoing SNMP Request or Notification Message ... 31

4.2.2. Prepare an Outgoing SNMP Response Message ............... 31

4.2.3. Prepare Data Elements from an Incoming SNMP Message ..... 32

4.3. Access Control Subsystem Primitives ....................... 32

4.4. Security Subsystem Primitives ............................. 33

4.4.1. Generate a Request or Notification Message .............. 33

4.4.2. Process Incoming Message ................................ 33

4.4.3. Generate a Response Message ............................. 34

4.5. Common Primitives ......................................... 34

4.5.1. Release State Reference Information ..................... 35

4.6. Scenario Diagrams ......................................... 36

4.6.1. Command Generator or Notification Originator ............ 36

4.6.2. Scenario Diagram for a Command Responder Application .... 37

5. Managed Object Definitions for SNMP Management Frameworks ... 38

6. IANA Considerations ......................................... 48

6.1. Security Models ........................................... 48

6.2. Message Processing Models ................................. 48

6.3. SnmpEngineID Formats ...................................... 49

7. Intellectual Property ....................................... 49

8. Acknowledgements ............................................ 49

9. Security Considerations ..................................... 51

10. References ................................................. 52

11. Editor's Addresses ......................................... 54

A. Guidelines for Model Designers .............................. 55

A.1. Security Model Design Requirements ........................ 55

A.1.1. Threats ................................................. 55

A.1.2. Security Processing ..................................... 56

A.1.3. Validate the security-stamp in a received message ....... 56

A.1.4. Security MIBs ........................................... 57

A.1.5. Cached Security Data .................................... 57

A.2. Message Processing Model Design Requirements .............. 57

A.2.1. Receiving an SNMP Message from the Network .............. 58

A.2.2. Sending an SNMP Message to the Network .................. 58

A.3. Application Design Requirements ........................... 59

A.3.1. Applications that Initiate Messages ..................... 59

A.3.2. Applications that Receive Responses ..................... 59

A.3.3. Applications that Receive Asynchronous Messages ......... 60

A.3.4. Applications that Send Responses ........................ 60

A.4. Access Control Model Design Requirements .................. 60

B. Full Copyright Statement .................................... 62

1. Introduction

1.1. Overview

This document defines a vocabulary for describing SNMP Management

Frameworks, and an architecture for describing the major portions of

SNMP Management Frameworks.

This document does not provide a general introduction to SNMP. Other

documents and books can provide a much better introduction to SNMP.

Nor does this document provide a history of SNMP. That also can be

found in books and other documents.

Section 1 describes the purpose, goals, and design decisions of this

architecture.

Section 2 describes various types of documents which define (elements

of) SNMP Frameworks, and how they fit into this architecture. It also

provides a minimal road map to the documents which have previously

defined SNMP frameworks.

Section 3 details the vocabulary of this architecture and its pieces.

This section is important for understanding the remaining sections,

and for understanding documents which are written to fit within this

architecture.

Section 4 describes the primitives used for the abstract service

interfaces between the various subsystems, models and applications

within this architecture.

Section 5 defines a collection of managed objects used to instrument

SNMP entities within this architecture.

Sections 6, 7, 8, 9, 10 and 11 are administrative in nature.

Appendix A contains guidelines for designers of Models which are

eXPected to fit within this architecture.

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 [RFC2119].

1.2. SNMP

An SNMP management system contains:

- several (potentially many) nodes, each with an SNMP entity

containing command responder and notification originator

applications, which have access to management instrumentation

(traditionally called agents);

- at least one SNMP entity containing command generator and/or

notification receiver applications (traditionally called a

manager) and,

- a management protocol, used to convey management information

between the SNMP entities.

SNMP entities executing command generator and notification receiver

applications monitor and control managed elements. Managed elements

are devices such as hosts, routers, terminal servers, etc., which are

monitored and controlled via access to their management information.

It is the purpose of this document to define an architecture which

can evolve to realize effective management in a variety of

configurations and environments. The architecture has been designed

to meet the needs of implementations of:

- minimal SNMP entities with command responder and/or

notification originator applications (traditionally called SNMP

agents),

- SNMP entities with proxy forwarder applications (traditionally

called SNMP proxy agents),

- command line driven SNMP entities with command generator and/or

notification receiver applications (traditionally called SNMP

command line managers),

- SNMP entities with command generator and/or notification

receiver, plus command responder and/or notification originator

applications (traditionally called SNMP mid-level managers or

dual-role entities),

- SNMP entities with command generator and/or notification

receiver and possibly other types of applications for managing

a potentially very large number of managed nodes (traditionally

called (network) management stations).

1.3. Goals of this Architecture

This architecture was driven by the following goals:

- Use existing materials as much as possible. It is heavily based

on previous work, informally known as SNMPv2u and SNMPv2*,

based in turn on SNMPv2p.

- Address the need for secure SET support, which is considered

the most important deficiency in SNMPv1 and SNMPv2c.

- Make it possible to move portions of the architecture forward

in the standards track, even if consensus has not been reached

on all pieces.

- Define an architecture that allows for longevity of the SNMP

Frameworks that have been and will be defined.

- Keep SNMP as simple as possible.

- Make it relatively inexpensive to deploy a minimal conforming

implementation.

- Make it possible to upgrade portions of SNMP as new approaches

become available, without disrupting an entire SNMP framework.

- Make it possible to support features required in large

networks, but make the expense of supporting a feature directly

related to the support of the feature.

1.4. Security Requirements of this Architecture

Several of the classical threats to network protocols are applicable

to the management problem and therefore would be applicable to any

Security Model used in an SNMP Management Framework. Other threats

are not applicable to the management problem. This section discusses

principal threats, secondary threats, and threats which are of lesser

importance.

The principal threats against which any Security Model used within

this architecture SHOULD provide protection are:

Modification of Information

The modification threat is the danger that some unauthorized

entity may alter in-transit SNMP messages generated on behalf

of an authorized principal in such a way as to effect

unauthorized management operations, including falsifying the

value of an object.

Masquerade

The masquerade threat is the danger that management operations

not authorized for some principal may be attempted by assuming

the identity of another principal that has the appropriate

authorizations.

Secondary threats against which any Security Model used within this

architecture SHOULD provide protection are:

Message Stream Modification

The SNMP protocol is typically based upon a connectionless

transport service which may operate over any subnetwork

service. The re-ordering, delay or replay of messages can and

does occur through the natural operation of many such

subnetwork services. The message stream modification threat is

the danger that messages may be maliciously re-ordered, delayed

or replayed to an extent which is greater than can occur

through the natural operation of a subnetwork service, in order

to effect unauthorized management operations.

Disclosure

The disclosure threat is the danger of eavesdropping on the

exchanges between SNMP engines. Protecting against this threat

may be required as a matter of local policy.

There are at least two threats against which a Security Model within

this architecture need not protect, since they are deemed to be of

lesser importance in this context:

Denial of Service

A Security Model need not attempt to address the broad range of

attacks by which service on behalf of authorized users is

denied. Indeed, such denial-of-service attacks are in many

cases indistinguishable from the type of network failures with

which any viable management protocol must cope as a matter of

course.

Traffic Analysis

A Security Model need not attempt to address traffic analysis

attacks. Many traffic patterns are predictable - entities may

be managed on a regular basis by a relatively small number of

management stations - and therefore there is no significant

advantage afforded by protecting against traffic analysis.

1.5. Design Decisions

Various design decisions were made in support of the goals of the

architecture and the security requirements:

- Architecture

An architecture should be defined which identifies the

conceptual boundaries between the documents. Subsystems should

be defined which describe the abstract services provided by

specific portions of an SNMP framework. Abstract service

interfaces, as described by service primitives, define the

abstract boundaries between documents, and the abstract

services that are provided by the conceptual subsystems of an

SNMP framework.

- Self-contained Documents

Elements of procedure plus the MIB objects which are needed for

processing for a specific portion of an SNMP framework should

be defined in the same document, and as much as possible,

should not be referenced in other documents. This allows pieces

to be designed and documented as independent and self-contained

parts, which is consistent with the general SNMP MIB module

approach. As portions of SNMP change over time, the documents

describing other portions of SNMP are not directly impacted.

This modularity allows, for example, Security Models,

authentication and privacy mechanisms, and message formats to

be upgraded and supplemented as the need arises. The self-

contained documents can move along the standards track on

different time-lines.

This modularity of specification is not meant to be interpreted as

imposing any specific requirements on implementation.

- Threats

The Security Models in the Security Subsystem SHOULD protect

against the principal and secondary threats: modification of

information, masquerade, message stream modification and

disclosure. They do not need to protect against denial of

service and traffic analysis.

- Remote Configuration

The Security and Access Control Subsystems add a whole new set

of SNMP configuration parameters. The Security Subsystem also

requires frequent changes of secrets at the various SNMP

entities. To make this deployable in a large operational

environment, these SNMP parameters must be remotely

configurable.

- Controlled Complexity

It is recognized that producers of simple managed devices want

to keep the resources used by SNMP to a minimum. At the same

time, there is a need for more complex configurations which can

spend more resources for SNMP and thus provide more

functionality. The design tries to keep the competing

requirements of these two environments in balance and allows

the more complex environments to logically extend the simple

environment.

2. Documentation Overview

The following figure shows the set of documents that fit within the

SNMP Architecture.

+------------------------- Document Set ----------------------------+

+----------+ +-----------------+ +----------------+

Document Applicability * Coexistence

Roadmap Statement & Transition

+----------+ +-----------------+ +----------------+

+---------------------------------------------------------------+

Message Handling

+----------------+ +-----------------+ +-----------------+

Transport Message Security

Mappings Processing and

Dispatcher

+----------------+ +-----------------+ +-----------------+

+---------------------------------------------------------------+

+---------------------------------------------------------------+

PDU Handling

+----------------+ +-----------------+ +-----------------+

Protocol Applications Access

Operations Control

+----------------+ +-----------------+ +-----------------+

+---------------------------------------------------------------+

+---------------------------------------------------------------+

Information Model

+--------------+ +--------------+ +---------------+

Structure of Textual Conformance

Management Conventions Statements

Information

+--------------+ +--------------+ +---------------+

+---------------------------------------------------------------+

+---------------------------------------------------------------+

MIB Modules written in various formats, e.g.:

+-------------+ +-------------+ +----------+ +----------+

Standard v1 Standard v1 Historic Draft v2

RFC1157 RFC1212 RFC14xx RFC19xx

format format format format

+-------------+ +-------------+ +----------+ +----------+

+---------------------------------------------------------------+

+-------------------------------------------------------------------+

Those marked with an asterisk (*) are expected to be written in the

future. Each of these documents may be replaced or supplemented.

This Architecture document specifically describes how new documents

fit into the set of documents in the area of Message and PDU

handling.

2.1. Document Roadmap

One or more documents may be written to describe how sets of

documents taken together form specific Frameworks. The configuration

of document sets might change over time, so the "road map" should be

maintained in a document separate from the standards documents

themselves.

An example of such a roadmap is "Introduction to Version 3 of the

Internet-standard Network Management Framework" [RFC2570].

2.2. Applicability Statement

SNMP is used in networks that vary widely in size and complexity, by

organizations that vary widely in their requirements of management.

Some models will be designed to address specific problems of

management, such as message security.

One or more documents may be written to describe the environments to

which certain versions of SNMP or models within SNMP would be

appropriately applied, and those to which a given model might be

inappropriately applied.

2.3. Coexistence and Transition

The purpose of an evolutionary architecture is to permit new models

to replace or supplement existing models. The interactions between

models could result in incompatibilities, security "holes", and other

undesirable effects.

The purpose of Coexistence documents is to detail recognized

anomalies and to describe required and recommended behaviors for

resolving the interactions between models within the architecture.

Coexistence documents may be prepared separately from model

definition documents, to describe and resolve interaction anomalies

between a model definition and one or more other model definitions.

Additionally, recommendations for transitions between models may also

be described, either in a coexistence document or in a separate

document.

One such coexistance document is [SNMP-COEX], "Coexistence between

Version 1, Version 2, and Version 3 of the Internet-standard Network

Management Framework".

2.4. Transport Mappings

SNMP messages are sent over various transports. It is the purpose of

Transport Mapping documents to define how the mapping between SNMP

and the transport is done.

2.5. Message Processing

A Message Processing Model document defines a message format, which

is typically identified by a version field in an SNMP message header.

The document may also define a MIB module for use in message

processing and for instrumentation of version-specific interactions.

An SNMP engine includes one or more Message Processing Models, and

thus may support sending and receiving multiple versions of SNMP

messages.

2.6. Security

Some environments require secure protocol interactions. Security is

normally applied at two different stages:

- in the transmission/receipt of messages, and

- in the processing of the contents of messages.

For purposes of this document, "security" refers to message-level

security; "access control" refers to the security applied to protocol

operations.

Authentication, encryption, and timeliness checking are common

functions of message level security.

A security document describes a Security Model, the threats against

which the model protects, the goals of the Security Model, the

protocols which it uses to meet those goals, and it may define a MIB

module to describe the data used during processing, and to allow the

remote configuration of message-level security parameters, such as

keys.

An SNMP engine may support multiple Security Models concurrently.

2.7. Access Control

During processing, it may be required to control access to managed

objects for operations.

An Access Control Model defines mechanisms to determine whether

access to a managed object should be allowed. An Access Control

Model may define a MIB module used during processing and to allow the

remote configuration of access control policies.

2.8. Protocol Operations

SNMP messages encapsulate an SNMP Protocol Data Unit (PDU). SNMP

PDUs define the operations performed by the receiving SNMP engine.

It is the purpose of a Protocol Operations document to define the

operations of the protocol with respect to the processing of the

PDUs. Every PDU belongs to one or more of the PDU classes defined

below:

1) Read Class:

The Read Class contains protocol operations that retrieve

management information. For example, RFC1905 defines the

following protocol operations for the Read Class: GetRequest-

PDU, GetNextRequest-PDU, and GetBulkRequest-PDU.

2) Write Class:

The Write Class contains protocol operations which attempt to

modify management information. For example, RFC1905 defines

the following protocol operation for the Write Class:

SetRequest-PDU.

3) Response Class:

The Response Class contains protocol operations which are sent

in response to a previous request. For example, RFC1905

defines the following for the Response Class: Response-PDU,

Report-PDU.

4) Notification Class:

The Notification Class contains protocol operations which send

a notification to a notification receiver application. For

example, RFC1905 defines the following operations for the

Notification Class: Trapv2-PDU, InformRequest-PDU.

5) Internal Class:

The Internal Class contains protocol operations which are

exchanged internally between SNMP engines. For example, RFC

1905 defines the following operations for the Internal Class:

Report-PDU.

The preceding five classifications are based on the functional

properties of a PDU. It is also useful to classify PDUs based on

whether a response is expected:

6) Confirmed Class:

The Confirmed Class contains all protocol operations which

cause the receiving SNMP engine to send back a response. For

example, RFC1905 defines the following operations for the

Confirmed Class: GetRequest-PDU, GetNextRequest-PDU,

GetBulkRequest-PDU, SetRequest-PDU, and InformRequest-PDU.

7) Unconfirmed Class:

The Unconfirmed Class contains all protocol operations which

are not acknowledged. For example, RFC1905 defines the

following operations for the Unconfirmed Class: Report-PDU,

Trapv2-PDU, and GetResponse-PDU.

An application document defines which Protocol Operations are

supported by the application.

2.9. Applications

An SNMP entity normally includes a number of applications.

Applications use the services of an SNMP engine to accomplish

specific tasks. They coordinate the processing of management

information operations, and may use SNMP messages to communicate with

other SNMP entities.

Applications documents describe the purpose of an application, the

services required of the associated SNMP engine, and the protocol

operations and informational model that the application uses to

perform management operations.

An application document defines which set of documents are used to

specifically define the structure of management information, textual

conventions, conformance requirements, and operations supported by

the application.

2.10. 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.

It is the purpose of a Structure of Management Information document

to establish the notation for defining objects, modules, and other

elements of managed information.

2.11. Textual Conventions

When designing a MIB module, it is often useful to define new types

similar to those defined in the SMI, but with more precise semantics,

or which have special semantics associated with them. These newly

defined types are termed textual conventions, and may be defined in

separate documents, or within a MIB module.

2.12. Conformance Statements

It may be useful to define the acceptable lower-bounds of

implementation, along with the actual level of implementation

achieved. It is the purpose of the Conformance Statements document to

define the notation used for these purposes.

2.13. Management Information Base Modules

MIB documents describe collections of managed objects which

instrument some ASPect of a managed node.

2.13.1. SNMP Instrumentation MIBs

An SNMP MIB document may define a collection of managed objects which

instrument the SNMP protocol itself. In addition, MIB modules may be

defined within the documents which describe portions of the SNMP

architecture, such as the documents for Message processing Models,

Security Models, etc. for the purpose of instrumenting those Models,

and for the purpose of allowing remote configuration of the Model.

2.14. SNMP Framework Documents

This architecture is designed to allow an orderly evolution of

portions of SNMP Frameworks.

Throughout the rest of this document, the term "subsystem" refers to

an abstract and incomplete specification of a portion of a Framework,

that is further refined by a model specification.

A "model" describes a specific design of a subsystem, defining

additional constraints and rules for conformance to the model. A

model is sufficiently detailed to make it possible to implement the

specification.

An "implementation" is an instantiation of a subsystem, conforming to

one or more specific models.

SNMP version 1 (SNMPv1), is the original Internet-standard Network

Management Framework, as described in RFCs 1155, 1157, and 1212.

SNMP version 2 (SNMPv2), is the SNMPv2 Framework as derived from the

SNMPv1 Framework. It is described in STD 58, RFCs 2578, 2579, 2580,

and RFCs 1905-1907. SNMPv2 has no message definition.

The Community-based SNMP version 2 (SNMPv2c), is an experimental SNMP

Framework which supplements the SNMPv2 Framework, as described in RFC

1901. It adds the SNMPv2c message format, which is similar to the

SNMPv1 message format.

SNMP version 3 (SNMPv3), is an extensible SNMP Framework which

supplements the SNMPv2 Framework, by supporting the following:

- a new SNMP message format,

- Security for Messages,

- Access Control, and

- Remote configuration of SNMP parameters.

Other SNMP Frameworks, i.e., other configurations of implemented

subsystems, are expected to also be consistent with this

architecture.

3. Elements of the Architecture

This section describes the various elements of the architecture and

how they are named. There are three kinds of naming:

1) the naming of entities,

2) the naming of identities, and

3) the naming of management information.

This architecture also defines some names for other constructs that

are used in the documentation.

3.1. The Naming of Entities

An SNMP entity is an implementation of this architecture. Each such

SNMP entity consists of an SNMP engine and one or more associated

applications.

The following figure shows details about an SNMP entity and the

components within it.

+-------------------------------------------------------------------+

SNMP entity

+-------------------------------------------------------------+

SNMP engine (identified by snmpEngineID)

+------------+ +------------+ +-----------+ +-----------+

Dispatcher Message Security Access

Processing Subsystem Control

Subsystem Subsystem

+------------+ +------------+ +-----------+ +-----------+

+-------------------------------------------------------------+

+-------------------------------------------------------------+

Application(s)

+-------------+ +--------------+ +--------------+

Command Notification Proxy

Generator Receiver Forwarder

+-------------+ +--------------+ +--------------+

+-------------+ +--------------+ +--------------+

Command Notification Other

Responder Originator

+-------------+ +--------------+ +--------------+

+-------------------------------------------------------------+

+-------------------------------------------------------------------+

3.1.1. SNMP engine

An SNMP engine provides services for sending and receiving messages,

authenticating and encrypting messages, and controlling access to

managed objects. There is a one-to-one association between an SNMP

engine and the SNMP entity which contains it.

The engine contains:

1) a Dispatcher,

2) a Message Processing Subsystem,

3) a Security Subsystem, and

4) an Access Control Subsystem.

3.1.1.1. snmpEngineID

Within an administrative domain, an snmpEngineID is the unique and

unambiguous identifier of an SNMP engine. Since there is a one-to-one

association between SNMP engines and SNMP entities, it also uniquely

and unambiguously identifies the SNMP entity within that

administrative domain. Note that it is possible for SNMP entities in

different administrative domains to have the same value for

snmpEngineID. Federation of administrative domains may necessitate

assignment of new values.

3.1.1.2. Dispatcher

There is only one Dispatcher in an SNMP engine. It allows for

concurrent support of multiple versions of SNMP messages in the SNMP

engine. It does so by:

- sending and receiving SNMP messages to/from the network,

- determining the version of an SNMP message and interacting with

the corresponding Message Processing Model,

- providing an abstract interface to SNMP applications for

delivery of a PDU to an application.

- providing an abstract interface for SNMP applications that

allows them to send a PDU to a remote SNMP entity.

3.1.1.3. Message Processing Subsystem

The Message Processing Subsystem is responsible for preparing

messages for sending, and extracting data from received messages.

The Message Processing Subsystem potentially contains multiple

Message Processing Models as shown in the next figure.

* One or more Message Processing Models may be present.

+------------------------------------------------------------------+

Message Processing Subsystem

+------------+ +------------+ +------------+ +------------+

* * * *

SNMPv3 SNMPv1 SNMPv2c Other

Message Message Message Message

Processing Processing Processing Processing

Model Model Model Model

+------------+ +------------+ +------------+ +------------+

+------------------------------------------------------------------+

3.1.1.3.1. Message Processing Model

Each Message Processing Model defines the format of a particular

version of an SNMP message and coordinates the preparation and

extraction of each such version-specific message format.

3.1.1.4. Security Subsystem

The Security Subsystem provides security services such as the

authentication and privacy of messages and potentially contains

multiple Security Models as shown in the following figure

* One or more Security Models may be present.

+------------------------------------------------------------------+

Security Subsystem

+----------------+ +-----------------+ +-------------------+

* * *

User-Based Other Other

Security Security Security

Model Model Model

+----------------+ +-----------------+ +-------------------+

+------------------------------------------------------------------+

3.1.1.4.1. Security Model

A Security Model specifies the threats against which it protects, the

goals of its services, and the security protocols used to provide

security services such as authentication and privacy.

3.1.1.4.2. Security Protocol

A Security Protocol specifies the mechanisms, procedures, and MIB

objects used to provide a security service such as authentication or

privacy.

3.1.2. Access Control Subsystem

The Access Control Subsystem provides authorization services by means

of one or more (*) Access Control Models.

+------------------------------------------------------------------+

Access Control Subsystem

+---------------+ +-----------------+ +------------------+

* * *

View-Based Other Other

Access Access Access

Control Control Control

Model Model Model

+---------------+ +-----------------+ +------------------+

+------------------------------------------------------------------+

3.1.2.1. Access Control Model

An Access Control Model defines a particular access decision function

in order to support decisions regarding access rights.

3.1.3. Applications

There are several types of applications, including:

- command generators, which monitor and manipulate management

data,

- command responders, which provide access to management data,

- notification originators, which initiate asynchronous messages,

- notification receivers, which process asynchronous messages,

and

- proxy forwarders, which forward messages between entities.

These applications make use of the services provided by the SNMP

engine.

3.1.3.1. SNMP Manager

An SNMP entity containing one or more command generator and/or

notification receiver applications (along with their associated SNMP

engine) has traditionally been called an SNMP manager.

* One or more models may be present.

(traditional SNMP manager)

+-------------------------------------------------------------------+

+--------------+ +--------------+ +--------------+ SNMP entity

NOTIFICATION NOTIFICATION COMMAND

ORIGINATOR RECEIVER GENERATOR

applications applications applications

+--------------+ +--------------+ +--------------+

^ ^ ^

v v v

+-------+--------+-----------------+

^

+---------------------+ +----------------+

Message Processing Security

Dispatcher v Subsystem Subsystem

+-------------------+ +------------+

PDU Dispatcher +-> v1MP * <---> +------------+

+------------+ Other

+------------+ Security

+-> v2cMP * <---> Model

Message +------------+ +------------+

Dispatcher <--------->+

+------------+ +------------+

+-> v3MP * <---> User-based

Transport +------------+ Security

Mapping +------------+ Model

(e.g RFC1906) +-> otherMP * <---> +------------+

+-------------------+ +------------+

^ +---------------------+ +----------------+

v

+-------------------------------------------------------------------+

+-----+ +-----+ +-------+

UDP IPX . . . other

+-----+ +-----+ +-------+

^ ^ ^

v v v

+------------------------------+

Network

+------------------------------+

3.1.3.2. SNMP Agent

An SNMP entity containing one or more command responder and/or

notification originator applications (along with their associated

SNMP engine) has traditionally been called an SNMP agent.

+------------------------------+

Network

+------------------------------+

^ ^ ^

v v v

+-----+ +-----+ +-------+

UDP IPX . . . other

+-----+ +-----+ +-------+ (traditional SNMP agent)

+-------------------------------------------------------------------+

^

+---------------------+ +----------------+

Message Processing Security

Dispatcher v Subsystem Subsystem

+-------------------+ +------------+

Transport +-> v1MP * <---> +------------+

Mapping +------------+ Other

(e.g. RFC1906) +------------+ Security

+-> v2cMP * <---> Model

Message +------------+ +------------+

Dispatcher <---------> +------------+ +------------+

+-> v3MP * <---> User-based

+------------+ Security

PDU Dispatcher +------------+ Model

+-------------------+ +-> otherMP * <---> +------------+

^ +------------+

+---------------------+ +----------------+

v

+-------+-------------------------+---------------+

^ ^ ^

v v v

+-------------+ +---------+ +--------------+ +-------------+

COMMAND ACCESS NOTIFICATION PROXY *

RESPONDER <-> CONTROL <-> ORIGINATOR FORWARDER

application applications application

+-------------+ +---------+ +--------------+ +-------------+

^ ^

v v

+----------------------------------------------+

MIB instrumentation SNMP entity

+-------------------------------------------------------------------+

3.2. The Naming of Identities

principal

^

+-----------------------------------------+

SNMP engine v

+--------------+

+----------------- securityName ---+

Security Model

+--------------+

^

v

+------------------------------+

Model

Dependent

Security ID

+------------------------------+

^

+-----------------------------------+

+-----------------------------------------+

v

network

3.2.1. Principal

A principal is the "who" on whose behalf services are provided or

processing takes place.

A principal can be, among other things, an individual acting in a

particular role; a set of individuals, with each acting in a

particular role; an application or a set of applications; and

combinations thereof.

3.2.2. securityName

A securityName is a human readable string representing a principal.

It has a model-independent format, and can be used outside a

particular Security Model.

3.2.3. Model-dependent security ID

A model-dependent security ID is the model-specific representation of

a securityName within a particular Security Model.

Model-dependent security IDs may or may not be human readable, and

have a model-dependent syntax. Examples include community names, and

user names.

The transformation of model-dependent security IDs into securityNames

and vice versa is the responsibility of the relevant Security Model.

3.3. The Naming of Management Information

Management information resides at an SNMP entity where a Command

Responder Application has local access to potentially multiple

contexts. This application uses a contextEngineID equal to the

snmpEngineID of its associated SNMP engine.

+-----------------------------------------------------------------+

SNMP entity (identified by snmpEngineID, example: abcd)

+------------------------------------------------------------+

SNMP engine (identified by snmpEngineID)

+-------------+ +------------+ +-----------+ +-----------+

Dispatcher Message Security Access

Processing Subsystem Control

Subsystem Subsystem

+-------------+ +------------+ +-----------+ +-----------+

+------------------------------------------------------------+

+------------------------------------------------------------+

Command Responder Application

(contextEngineID, example: abcd)

example contextNames:

"bridge1" "bridge2" "" (default)

--------- --------- ------------

+---------------------------------------------------------+

+---------------------------------------------------------+

MIB instrumentation

+---v------------+ +---v------------+ +----v-----------+

context context context

+------------+ +------------+ +------------+

bridge MIB bridge MIB some MIB

+------------+ +------------+ +------------+

+------------+

other MIB

+------------+

+-----------------------------------------------------------------+

3.3.1. An SNMP Context

An SNMP context, or just "context" for short, is a collection of

management information accessible by an SNMP entity. An item of

management information may exist in more than one context. An SNMP

entity potentially has access to many contexts.

Typically, there are many instances of each managed object type

within a management domain. For simplicity, the method for

identifying instances specified by the MIB module does not allow each

instance to be distinguished amongst the set of all instances within

a management domain; rather, it allows each instance to be identified

only within some scope or "context", where there are multiple such

contexts within the management domain. Often, a context is a

physical device, or perhaps, a logical device, although a context can

also encompass multiple devices, or a subset of a single device, or

even a subset of multiple devices, but a context is always defined as

a subset of a single SNMP entity. Thus, in order to identify an

individual item of management information within the management

domain, its contextName and contextEngineID must be identified in

addition to its object type and its instance.

For example, the managed object type ifDescr [RFC2233], is defined as

the description of a network interface. To identify the description

of device-X's first network interface, four pieces of information are

needed: the snmpEngineID of the SNMP entity which provides access to

the management information at device-X, the contextName (device-X),

the managed object type (ifDescr), and the instance ("1").

Each context has (at least) one unique identification within the

management domain. The same item of management information can exist

in multiple contexts. An item of management information may have

multiple unique identifications. This occurs when an item of

management information exists in multiple contexts, and this also

occurs when a context has multiple unique identifications.

The combination of a contextEngineID and a contextName unambiguously

identifies a context within an administrative domain; note that there

may be multiple unique combinations of contextEngineID and

contextName that unambiguously identify the same context.

3.3.2. contextEngineID

Within an administrative domain, a contextEngineID uniquely

identifies an SNMP entity that may realize an instance of a context

with a particular contextName.

3.3.3. contextName

A contextName is used to name a context. Each contextName MUST be

unique within an SNMP entity.

3.3.4. scopedPDU

A scopedPDU is a block of data containing a contextEngineID, a

contextName, and a PDU.

The PDU is an SNMP Protocol Data Unit containing information named in

the context which is unambiguously identified within an

administrative domain by the combination of the contextEngineID and

the contextName. See, for example, RFC1905 for more information about

SNMP PDUs.

3.4. Other Constructs

3.4.1. maxSizeResponseScopedPDU

The maxSizeResponseScopedPDU is the maximum size of a scopedPDU that

a PDU's sender would be willing to accept. Note that the size of a

scopedPDU does not include the size of the SNMP message header.

3.4.2. Local Configuration Datastore

The subsystems, models, and applications within an SNMP entity may

need to retain their own sets of configuration information.

Portions of the configuration information may be accessible as

managed objects.

The collection of these sets of information is referred to as an

entity's Local Configuration Datastore (LCD).

3.4.3. securityLevel

This architecture recognizes three levels of security:

- without authentication and without privacy (noAuthNoPriv)

- with authentication but without privacy (authNoPriv)

- with authentication and with privacy (authPriv)

These three values are ordered such that noAuthNoPriv is less than

authNoPriv and authNoPriv is less than authPriv.

Every message has an associated securityLevel. All Subsystems

(Message Processing, Security, Access Control) and applications are

REQUIRED to either supply a value of securityLevel or to abide by the

supplied value of securityLevel while processing the message and its

contents.

4. Abstract Service Interfaces

Abstract service interfaces have been defined to describe the

conceptual interfaces between the various subsystems within an SNMP

entity. The abstract service interfaces are intended to help clarify

the externally observable behavior of SNMP entities, and are not

intended to constrain the structure or organization of

implementations in any way. Most specifically, they should not be

interpreted as APIs or as requirements statements for APIs.

These abstract service interfaces are defined by a set of primitives

that define the services provided and the abstract data elements that

are to be passed when the services are invoked. This section lists

the primitives that have been defined for the various subsystems.

4.1. Dispatcher Primitives

The Dispatcher typically provides services to the SNMP applications

via its PDU Dispatcher. This section describes the primitives

provided by the PDU Dispatcher.

4.1.1. Generate Outgoing Request or Notification

The PDU Dispatcher provides the following primitive for an

application to send an SNMP Request or Notification to another SNMP

entity:

statusInformation = -- sendPduHandle if success

-- errorIndication if failure

sendPdu(

IN transportDomain -- transport domain to be used

IN transportAddress -- transport address to be used

IN messageProcessingModel -- typically, SNMP version

IN securityModel -- Security Model to use

IN securityName -- on behalf of this principal

IN securityLevel -- Level of Security requested

IN contextEngineID -- data from/at this entity

IN contextName -- data from/in this context

IN pduVersion -- the version of the PDU

IN PDU -- SNMP Protocol Data Unit

IN expectResponse -- TRUE or FALSE

)

4.1.2. Process Incoming Request or Notification PDU

The PDU Dispatcher provides the following primitive to pass an

incoming SNMP PDU to an application:

processPdu( -- process Request/Notification PDU

IN messageProcessingModel -- typically, SNMP version

IN securityModel -- Security Model in use

IN securityName -- on behalf of this principal

IN securityLevel -- Level of Security

IN contextEngineID -- data from/at this SNMP entity

IN contextName -- data from/in this context

IN pduVersion -- the version of the PDU

IN PDU -- SNMP Protocol Data Unit

IN maxSizeResponseScopedPDU -- maximum size of the Response PDU

IN stateReference -- reference to state information

) -- needed when sending a response

4.1.3. Generate Outgoing Response

The PDU Dispatcher provides the following primitive for an

application to return an SNMP Response PDU to the PDU Dispatcher:

result = -- SUCCESS or FAILURE

returnResponsePdu(

IN messageProcessingModel -- typically, SNMP version

IN securityModel -- Security Model in use

IN securityName -- on behalf of this principal

IN securityLevel -- same as on incoming request

IN contextEngineID -- data from/at this SNMP entity

IN contextName -- data from/in this context

IN pduVersion -- the version of the PDU

IN PDU -- SNMP Protocol Data Unit

IN maxSizeResponseScopedPDU -- maximum size sender can accept

IN stateReference -- reference to state information

-- as presented with the request

IN statusInformation -- success or errorIndication

) -- error counter OID/value if error

4.1.4. Process Incoming Response PDU

The PDU Dispatcher provides the following primitive to pass an

incoming SNMP Response PDU to an application:

processResponsePdu( -- process Response PDU

IN messageProcessingModel -- typically, SNMP version

IN securityModel -- Security Model in use

IN securityName -- on behalf of this principal

IN securityLevel -- Level of Security

IN contextEngineID -- data from/at this SNMP entity

IN contextName -- data from/in this context

IN pduVersion -- the version of the PDU

IN PDU -- SNMP Protocol Data Unit

IN statusInformation -- success or errorIndication

IN sendPduHandle -- handle from sendPdu

)

4.1.5. Registering Responsibility for Handling SNMP PDUs

Applications can register/unregister responsibility for a specific

contextEngineID, for specific pduTypes, with the PDU Dispatcher

according to the following primitives. The list of particular

pduTypes that an application can register for is determined by the

Message Processing Model(s) supported by the SNMP entity that

contains the PDU Dispatcher.

statusInformation = -- success or errorIndication

registerContextEngineID(

IN contextEngineID -- take responsibility for this one

IN pduType -- the pduType(s) to be registered

)

unregisterContextEngineID(

IN contextEngineID -- give up responsibility for this one

IN pduType -- the pduType(s) to be unregistered

)

Note that realizations of the registerContextEngineID and

unregisterContextEngineID abstract service interfaces may provide

implementation-specific ways for applications to register/deregister

responsibility for all possible values of the contextEngineID or

pduType parameters.

4.2. Message Processing Subsystem Primitives

The Dispatcher interacts with a Message Processing Model to process a

specific version of an SNMP Message. This section describes the

primitives provided by the Message Processing Subsystem.

4.2.1. Prepare Outgoing SNMP Request or Notification Message

The Message Processing Subsystem provides this service primitive for

preparing an outgoing SNMP Request or Notification Message:

statusInformation = -- success or errorIndication

prepareOutgoingMessage(

IN transportDomain -- transport domain to be used

IN transportAddress -- transport address to be used

IN messageProcessingModel -- typically, SNMP version

IN securityModel -- Security Model to use

IN securityName -- on behalf of this principal

IN securityLevel -- Level of Security requested

IN contextEngineID -- data from/at this entity

IN contextName -- data from/in this context

IN pduVersion -- the version of the PDU

IN PDU -- SNMP Protocol Data Unit

IN expectResponse -- TRUE or FALSE

IN sendPduHandle -- the handle for matching

-- incoming responses

OUT destTransportDomain -- destination transport domain

OUT destTransportAddress -- destination transport address

OUT outgoingMessage -- the message to send

OUT outgoingMessageLength -- its length

)

4.2.2. Prepare an Outgoing SNMP Response Message

The Message Processing Subsystem provides this service primitive for

preparing an outgoing SNMP Response Message:

result = -- SUCCESS or FAILURE

prepareResponseMessage(

IN messageProcessingModel -- typically, SNMP version

IN securityModel -- same as on incoming request

IN securityName -- same as on incoming request

IN securityLevel -- same as on incoming request

IN contextEngineID -- data from/at this SNMP entity

IN contextName -- data from/in this context

IN pduVersion -- the version of the PDU

IN PDU -- SNMP Protocol Data Unit

IN maxSizeResponseScopedPDU -- maximum size able to accept

IN stateReference -- reference to state information

-- as presented with the request

IN statusInformation -- success or errorIndication

-- error counter OID/value if error

OUT destTransportDomain -- destination transport domain

OUT destTransportAddress -- destination transport address

OUT outgoingMessage -- the message to send

OUT outgoingMessageLength -- its length

)

4.2.3. Prepare Data Elements from an Incoming SNMP Message

The Message Processing Subsystem provides this service primitive for

preparing the abstract data elements from an incoming SNMP message:

result = -- SUCCESS or errorIndication

prepareDataElements(

IN transportDomain -- origin transport domain

IN transportAddress -- origin transport address

IN wholeMsg -- as received from the network

IN wholeMsgLength -- as received from the network

OUT messageProcessingModel -- typically, SNMP version

OUT securityModel -- Security Model to use

OUT securityName -- on behalf of this principal

OUT securityLevel -- Level of Security requested

OUT contextEngineID -- data from/at this entity

OUT contextName -- data from/in this context

OUT pduVersion -- the version of the PDU

OUT PDU -- SNMP Protocol Data Unit

OUT pduType -- SNMP PDU type

OUT sendPduHandle -- handle for matched request

OUT maxSizeResponseScopedPDU -- maximum size sender can accept

OUT statusInformation -- success or errorIndication

-- error counter OID/value if error

OUT stateReference -- reference to state information

-- to be used for possible Response

)

4.3. Access Control Subsystem Primitives

Applications are the typical clients of the service(s) of the Access

Control Subsystem.

The following primitive is provided by the Access Control Subsystem

to check if access is allowed:

statusInformation = -- success or errorIndication

isAccessAllowed(

IN securityModel -- Security Model in use

IN securityName -- principal who wants to access

IN securityLevel -- Level of Security

IN viewType -- read, write, or notify view

IN contextName -- context containing variableName

IN variableName -- OID for the managed object

)

4.4. Security Subsystem Primitives

The Message Processing Subsystem is the typical client of the

services of the Security Subsystem.

4.4.1. Generate a Request or Notification Message

The Security Subsystem provides the following primitive to generate a

Request or Notification message:

statusInformation =

generateRequestMsg(

IN messageProcessingModel -- typically, SNMP version

IN globalData -- message header, admin data

IN maxMessageSize -- of the sending SNMP entity

IN securityModel -- for the outgoing message

IN securityEngineID -- authoritative SNMP entity

IN securityName -- on behalf of this principal

IN securityLevel -- Level of Security requested

IN scopedPDU -- message (plaintext) payload

OUT securityParameters -- filled in by Security Module

OUT wholeMsg -- complete generated message

OUT wholeMsgLength -- length of the generated message

)

4.4.2. Process Incoming Message

The Security Subsystem provides the following primitive to process an

incoming message:

statusInformation = -- errorIndication or success

-- error counter OID/value if error

processIncomingMsg(

IN messageProcessingModel -- typically, SNMP version

IN maxMessageSize -- of the sending SNMP entity

IN securityParameters -- for the received message

IN securityModel -- for the received message

IN securityLevel -- Level of Security

IN wholeMsg -- as received on the wire

IN wholeMsgLength -- length as received on the wire

OUT securityEngineID -- identification of the principal

OUT securityName -- identification of the principal

OUT scopedPDU, -- message (plaintext) payload

OUT maxSizeResponseScopedPDU -- maximum size sender can handle

OUT securityStateReference -- reference to security state

) -- information, needed for response

4.4.3. Generate a Response Message

The Security Subsystem provides the following primitive to generate a

Response message:

statusInformation =

generateResponseMsg(

IN messageProcessingModel -- typically, SNMP version

IN globalData -- message header, admin data

IN maxMessageSize -- of the sending SNMP entity

IN securityModel -- for the outgoing message

IN securityEngineID -- authoritative SNMP entity

IN securityName -- on behalf of this principal

IN securityLevel -- for the outgoing message

IN scopedPDU -- message (plaintext) payload

IN securityStateReference -- reference to security state

-- information from original request

OUT securityParameters -- filled in by Security Module

OUT wholeMsg -- complete generated message

OUT wholeMsgLength -- length of the generated message

)

4.5. Common Primitives

These primitive(s) are provided by multiple Subsystems.

4.5.1. Release State Reference Information

All Subsystems which pass stateReference information also provide a

primitive to release the memory that holds the referenced state

information:

stateRelease(

IN stateReference -- handle of reference to be released

)

4.6. Scenario Diagrams

4.6.1. Command Generator or Notification Originator

This diagram shows how a Command Generator or Notification Originator

application requests that a PDU be sent, and how the response is

returned (asynchronously) to that application.

Command Dispatcher Message Security

Generator Processing Model

Model

sendPdu

------------------->

prepareOutgoingMessage

: ----------------------->

: generateRequestMsg

: -------------------->

:

: <--------------------

:

: <-----------------------

:

: ------------------+

: Send SNMP

: Request Message

: to Network

: v

: : : : :

: : : : :

: : : : :

:

: Receive SNMP

: Response Message

: from Network

: <-----------------+

:

: prepareDataElements

: ----------------------->

: processIncomingMsg

: -------------------->

:

: <--------------------

:

: <-----------------------

processResponsePdu

<-------------------

4.6.2. Scenario Diagram for a Command Responder Application

This diagram shows how a Command Responder or Notification Receiver

application registers for handling a pduType, how a PDU is dispatched

to the application after a SNMP message is received, and how the

Response is (asynchronously) send back to the network.

Command Dispatcher Message Security

Responder Processing Model

Model

registerContextEngineID

------------------------>

<------------------------

Receive SNMP

: Message

: from Network

: <-------------+

:

: prepareDataElements

: ------------------->

: processIncomingMsg

: ------------------->

:

: <-------------------

:

: <-------------------

processPdu

<------------------------

: : : :

: : : :

returnResponsePdu

------------------------>

: prepareResponseMsg

: ------------------->

: generateResponseMsg

: ------------------->

:

: <-------------------

:

: <-------------------

:

: --------------+

: Send SNMP

: Message

: to Network

: v

5. Managed Object Definitions for SNMP Management Frameworks

SNMP-FRAMEWORK-MIB DEFINITIONS ::= BEGIN

IMPORTS

MODULE-IDENTITY, OBJECT-TYPE,

OBJECT-IDENTITY,

snmpModules FROM SNMPv2-SMI

TEXTUAL-CONVENTION FROM SNMPv2-TC

MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF;

snmpFrameworkMIB MODULE-IDENTITY

LAST-UPDATED "9901190000Z" -- 19 January 1999

ORGANIZATION "SNMPv3 Working Group"

CONTACT-INFO "WG-EMail: snmpv3@tis.com

Subscribe: majordomo@tis.com

In message body: subscribe snmpv3

Chair: Russ Mundy

TIS Labs at Network Associates

postal: 3060 Washington Rd

Glenwood MD 21738

USA

EMail: mundy@tis.com

phone: +1 301-854-6889

Co-editor Dave Harrington

Cabletron Systems, Inc.

postal: Post Office Box 5005

Mail Stop: Durham

35 Industrial Way

Rochester, NH 03867-5005

USA

EMail: dbh@ctron.com

phone: +1 603-337-7357

Co-editor Randy Presuhn

BMC Software, Inc.

postal: 965 Stewart Drive

Sunnyvale, CA 94086

USA

EMail: randy_presuhn@bmc.com

phone: +1 408-616-3100

Co-editor: Bert Wijnen

IBM T.J. Watson Research

postal: Schagen 33

3461 GL Linschoten

Netherlands

EMail: wijnen@vnet.ibm.com

phone: +31 348-432-794

"

DESCRIPTION "The SNMP Management Architecture MIB"

-- Revision History

REVISION "9901190000Z" -- 19 January 1999

DESCRIPTION "Updated editors' addresses, fixed typos.

Published as RFC2571.

"

REVISION "9711200000Z" -- 20 November 1997

DESCRIPTION "The initial version, published in RFC2271.

"

::= { snmpModules 10 }

-- Textual Conventions used in the SNMP Management Architecture ***

SnmpEngineID ::= TEXTUAL-CONVENTION

STATUS current

DESCRIPTION "An SNMP engine's administratively-unique identifier.

Objects of this type are for identification, not for

addressing, even though it is possible that an

address may have been used in the generation of

a specific value.

The value for this object may not be all zeros or

all 'ff'H or the empty (zero length) string.

The initial value for this object may be configured

via an operator console entry or via an algorithmic

function. In the latter case, the following

example algorithm is recommended.

In cases where there are multiple engines on the

same system, the use of this algorithm is NOT

appropriate, as it would result in all of those

engines ending up with the same ID value.

1) The very first bit is used to indicate how the

rest of the data is composed.

0 - as defined by enterprise using former methods

that existed before SNMPv3. See item 2 below.

1 - as defined by this architecture, see item 3

below.

Note that this allows existing uses of the

engineID (also known as AgentID [RFC1910]) to

co-exist with any new uses.

2) The snmpEngineID has a length of 12 octets.

The first four octets are set to the binary

equivalent of the agent's SNMP management

private enterprise number as assigned by the

Internet Assigned Numbers Authority (IANA).

For example, if Acme Networks has been assigned

{ enterprises 696 }, the first four octets would

be assigned '000002b8'H.

The remaining eight octets are determined via

one or more enterprise-specific methods. Such

methods must be designed so as to maximize the

possibility that the value of this object will

be unique in the agent's administrative domain.

For example, it may be the IP address of the SNMP

entity, or the MAC address of one of the

interfaces, with each address suitably padded

with random octets. If multiple methods are

defined, then it is recommended that the first

octet indicate the method being used and the

remaining octets be a function of the method.

3) The length of the octet strings varies.

The first four octets are set to the binary

equivalent of the agent's SNMP management

private enterprise number as assigned by the

Internet Assigned Numbers Authority (IANA).

For example, if Acme Networks has been assigned

{ enterprises 696 }, the first four octets would

be assigned '000002b8'H.

The very first bit is set to 1. For example, the

above value for Acme Networks now changes to be

'800002b8'H.

The fifth octet indicates how the rest (6th and

following octets) are formatted. The values for

the fifth octet are:

0 - reserved, unused.

1 - IPv4 address (4 octets)

lowest non-special IP address

2 - IPv6 address (16 octets)

lowest non-special IP address

3 - MAC address (6 octets)

lowest IEEE MAC address, canonical

order

4 - Text, administratively assigned

Maximum remaining length 27

5 - Octets, administratively assigned

Maximum remaining length 27

6-127 - reserved, unused

127-255 - as defined by the enterprise

Maximum remaining length 27

"

SYNTAX OCTET STRING (SIZE(5..32))

SnmpSecurityModel ::= TEXTUAL-CONVENTION

STATUS current

DESCRIPTION "An identifier that uniquely identifies a

securityModel of the Security Subsystem within the

SNMP Management Architecture.

The values for securityModel are allocated as

follows:

- The zero value is reserved.

- Values between 1 and 255, inclusive, are reserved

for standards-track Security Models and are

managed by the Internet Assigned Numbers Authority

(IANA).

- Values greater than 255 are allocated to

enterprise-specific Security Models. An

enterprise-specific securityModel value is defined

to be:

enterpriseID * 256 + security model within

enterprise

For example, the fourth Security Model defined by

the enterprise whose enterpriseID is 1 would be

 
 
 
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