stracts.txt'' listing contained in the Internet- Drafts Shadow
Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe),
ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim).
Abstract
This document describes an architecture for describing Internet
Management Frameworks. The architecture is designed to be modular
to allow the evolution of the protocol 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 network management data. These SNMP applications are
of various types, including Command Generator and Command Responder
applications, Notification Originator and Notification Receiver
applications, and Proxy Forwarding applications.
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0. Issues
0.1. Issues to be resolved
. OID or Integer for auth/priv protocol identifiers
second interim meeting reached consensus on OIDs
some mailing list members still say Integers preferred
. forward references need to be handled
. Is Glossary needed to describe primitive parameters, or is the
expanded template adequate for this purpose?
. state_reference releases - are these consistently defined?
check documents.
. discuss utf8. - probably open WG discussion in Munich per NMAD
discuss tomorrow; remains open issue.
. need mechanism to discover securityModels supported
. new SnmpEngineID format rules to be discussed yet.
. needs changes to meet STDGUIDE guidelines
. add a "Decision History" section (as an appendix?)
. we punted snmpEngineMaxMessageSize at 2nd interim because that
info travels in each SNMPv3 message. However, we may want to
re-introduce it so that SNMPv1/v2c managers can learn the value!!
0.1.1. Issues discussed at second Interim Meeting:
. A "readable" introduction supplement may be done after Munich.
. Applications are responsible for retries, but implementations may
differ.
. TCs should not be defined just to describe primitive parameters.
If they cannot be described adequately in text, they can be defined
in a Glossary. Avoid describing implementation details.
. Is SnmpAdminString appropriate for all strings, such as
securityIdentifier and context and group? These had different
sizes and semantics. size and semantics may be defined in
syntax and description of OBJECT
. AdminString has size (0..255); revisit for utf8 discussions
. securityModel #s - 00 for IETF standards; from v2* documents
. protocol IDs - integer or OID? voted 13-0 for OID.
. uniqueness of securityName
. mapping between principal and securityName is outside scope of WG.
. principals may have more than one securityName in an entity
. mappings may exist between many types of MDID and a single
securityName
. mappings may exist between different (model, Name) and the same
securityName by varying the model or the Name.
. the securityName and a MDID may be identical. This can be defined
by the Security Model.
(user,"public") may map to securityName "public"
. [securityName, securityModel] yields zero or one MDName, with
exceptions for backwards compatibility. The exception is defined
by the model, and the problems are the province of the model to
resolve.
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0.2. Change Log
[version 4.4]
. Fixed one error in the MIB (found with SMICng)
. Reformatted text for SnmpAdminString, no change in text.
. Changed text for SnmpEngineID.. this is still under discussion.
But this new text seems to be getting close to what we want.
. Added an issue w.r.t. snmpEngineMaxMessageSize
. adapt Primitive names and parameters to very latest (july 11) names
. removed blank lines before the .p page controls.
[version 4.3]
. some minor editing adjustments
[version 4.2]
. modify abstract so there is no requirement for one entity
to contain both a command generator and a notification receiver.
. modify Introduction list of entities which are meant to be
supported
. reorganized sections 1 through 4 for more consistency in contents.
. described section contents in Introduction:Target Audience
. move documentation descriptions to section 2
. rewrite section 4 to be more like a real elements of procedure.
. modified SnmpSecurityModel and SnmpEngineID definitions
. replaced MIB with Bert's replacement
. added Randy's TC for SnmpAdminString
. modified the example algorithm text for SnmpEngineID
. rewrote security considerations for brevity.
. modified "context" description
. moved "Threats" to Goals/Requirements
. eliminated snmpEngineMaxMessageSize object
. posted to snmpv3 (by DBH)
[version 4.1]
. Adopt "abstract" to new terminology
. Addressed all comments I (BW) made to DBH in an earlier email
. Changed Introduction section to new terminology
. changed wording for "implementation" to indicate it may contain
multiple models.
. Section 2. Started some wording on Goals and Design decisions
. Added the overview picture of a traditional agent and a
traditional manager. This is in section 2.
. Changed overview figure in section 3. to address the comments
by Dave Levi. It now lists the type of applications
. At various places ensure that text (easily) fits within 72
columns as required by RFC-editors Guidelines document.
. Section 2.3 (new section) has the documents set overview.
I verified the claims about standards. Not sure I worded the
SNMPv2 std correctly,. We'll hear it if we did it wrong.
. Section 2.4 (new section) gives overview of SNMP entities based
on modified Dave Levi figure. I (Bert) wonder however if it would
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not be better to move it to after section 3.1.13
. Section 3. Added more figures... please let us know if you find
then useful and/or helpful. We could also move these back to
section 2 if such makes more sense.
. Added a picture in section 3.2.
It also shows some of access control, so not sure it really fits
here, although it does map principal to model dependent security
ID to securityName
. Replace "<" with "is lower than" in section 3.4.3 which seems
better in a text document.
. Renamed section 4.1 to "SNMP engine processing" instead of
"The Message Processing Subsystem" because the transport
mappings, mpc multiplexor and such is done in ARCH document so
it is done "in general in the engine" and it passes a specific
message to a Message Processing Subsystem.
. "bulletized" some stuff in section 4.2 and 4.3.
Dave, this is just how I (Bert) like it better. Feel free to
undo it if you strongly disagree
. Section 4.3 changed "initiate a transaction" to "originate a
notification".
. Inserted title line for section 4.4 (I think it was missing)
I have named it "Information Model" in accordance with the change
I made (after Russ's comments) in the document figure to lump SMI,
TC and Conformance together.
. Inserted a title for section 4.5 named "Operational Model" to
get in sync with the the lumping together of ProtoOps and Transport
Mappings in document overview
. Renumber section 4.4.4 to 4,5,1 and added 4.5.2 to follow the
document overview figure. If we really want to follow it, then
maybe we should also reorder some of these sections. Like
Access Control seems specifically misplaced. So I decided to move
it before applications as section 4.3, so the 4.x above should
all be read as 4.x+1
. Removed size from SnmpEngineID TC... why did you limit it to
(0..2048). Did we not decide to leave it open?
. Should we not remove snmpEngineMaxMessageSize from the MIB.
That was agreed at 2nd interim. It travels in every message and so
seems to be useless. However, I think it could indeed still help
SNMPv1 or SNMPv2c managers.
. I kept your definitions of registration-points for auth and priv
protocols, but my recollection is that they would be completely
removed from ARCH and that it would all be done in SEC document.
. Modified Security Considerations. Was still talking about LPM.
. Appendix. I am still wondering if we need to use capitals for
things like "Security Model" "Subsystem" and such. This is only
an appendix... but we better be consistent, no? Anyway
I changed it so it is consistent (at least I tried).
. Appendix, renamed imf to snmpFramework
. Appendix, changed state_reference and state_release to
stateReference and stateRelease to be consistent with other names
for abstract data and primitives.
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. A.2 changed MessageEngine to SNMP engine
. Fixed ASI primitives to be in sync with SEC document.
I also thought that our ARCH document-outline wanted to at least
have the primitives listed within the main body of the text, no?
. Adapted send_pdu to sendPdu primitive as reconciled by Randy
In fact I made sure all primitives are in-line with current
agreement on names and parameters.
. Rename title of A.2.4 and A.2.5 so it fits on 1 line in contents
. I did not look at appendix B. That is your (DBH) specialty is it
not ? ;-).
. Quick simple spell check done with "spell" on AIX
[version 4.0]
. move section 7 - Model Requirements to an appendix
. move Section 3 - Design Goals to an appendix
. modified Section 5 - Naming
. remove "possibly multiple"
. moved Section 5 to Section 3
. change orangelets to applications
. modify description of applications
. change scopedPDU-MMS and PDU-MMS to maxSizeResponseScopedPDU
. change Scoped-PDU and ScopedPDU to scopedPDU (no dash, lower case S)
. change imfxxx to snmpFrameworkxxx
. change security-entity to principal
. change securityIdentity to securityName
. change MIID to securityName
. eliminate all reference to groupName or group
. LoS ordering noAuthNoPriv < authNoPriv < authPriv
. Los TC naming - noAuthNoPriv(1), authNoPriv(2), authPriv(3)
. remove TCs not used in MIBs - securityIdentity TC etc
. changed Message Processing and Control to Message Processing
. changed future tense to present tense
. eliminate messageEngine
. added/updated primitives
. addressed issues raised on the mailing list
[version 3.1]
. change securityIdentity to MIID
. write text to explain the differences between security-identities,
model-dependent identifiers, and model-independent identifiers.
. write text to explain distinction within the LCD of the security
data, the access control data, and the orangelet data.
. identify issues
. publish as <draft-ietf-snmpv3-next-gen-arch-02.txt>
[version 3.0]
. add section on threats for message security
. add section on threats for access control
. change application to orangelet
. remove references to F-Ts
. change securityIdentity to security-identity
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. change securityCookie to securityIdentity
. the format of securityIdentity is defined by the model
. add securityModel to passed parameters as needed
. eliminate group from passed parameters
. remove unused IMPORTS
. add glossary section with initial set of words to define
. differentiate the messageEngine from the contextEngine
. eliminate the term SNMPng
. rewrote 1.1. A Note on Terminology
. eliminated assumptions about SNMP processing always being
message related
. rewrote 4.x to reflect new thinking
. rewrote 5.x to reflect new thinking
. rewrote 6.x (the MIB) to reflect new thinking
. added MIB objects at this level (previously only TCs)
. rewrote 7.x
. sent to v3edit list
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1. Introduction
1.1. Target Audience
This document will have as its audience persons with varying levels
of technical understanding of SNMP.
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.
This document does define a vocabulary for describing Internet
Management Frameworks, and an architecture for describing the
major portions of Internet Management Frameworks.
Section 1 describes the purpose, goals, and design decisions of
the architecture.
Section 2 describes various types of documents which define Internet
Frameworks, and how they fit into this architecture. It also provides
a minimal roadmap to the documents which have defined previous
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 elements of procedure followed by an SNMP
engine in coordinating the processing of messages by the subsystems
of the engine and by applications.
Section 5 defines a collection of managed objects used to instrument
SNMP engines within this architecture.
Sections 6, 7, 8, and 9 are administrative in nature.
Appendix A contains guidelines for developers of Models which are
expected to fit within this architecture.
Appendix B contains a discussion of software design principles which
guided the development of this architecture. Many books provide a
more in-depth discussion of these topics.
1.2. Management Systems
A 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;
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- at least one SNMP entity containing command generator and/or
notification receiver applications; 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.
Operations of the protocol are carried out under an administrative
framework which defines minimum requirements for standard services,
such as sending and receiving messages, countering security threats
to messages, controlling access to managed objects, and processing
various types of requests.
It is the purpose of this document to define an architecture which
can evolve to realize effective network 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 agent),
- 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 enterprise 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*.
- 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.
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- Keep SNMP as simple as possible.
- Make it relatively inexpensive to deploy a minimal conformant
implementation
- Make it possible to upgrade portions of a framework as new
approaches become available, without disrupting the entire
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 network management problem and therefore would be applicable
to any Security Model used in an Internet Management Framework. Other
threats are not applicable to the network 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 SNMP
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.
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.
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There are at least two threats against which a Security Model used by
a framework within this architecture need not protect.
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 network 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 designs decision were made in support of these goals:
- Architecture
An architecture should be defined which identifies the
conceptual boundaries between the documents of a framework.
Subsystems should be defined which describe the abstract
services provided by specific portions of the 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 a framework.
- Self-contained Documents
Elements of procedure plus the MIB objects which are needed for
processing for a specific portion of a framework should be
defined in the same document, and as much as possible, should
not be referenced in other documents. This allows various
pieces of SNMP Frameworks 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 the
framework 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.
- 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
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environment, these SNMP parameters must be able to be remotely
configured.
- Controlled Complexity
It is recognized that 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.
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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 | |
| +------------+ +-----------------+ +----------------+ |
| |
| +-------------------+ +-----------------------------------------+ |
| | Operational Model | | Security and Administration | |
| | | | | |
| | +-------------+ | | +------------+ +----------+ +---------+ | |
| | | | | | | | | | | | | |
| | | Protocol | | | | Message | | Security | | Access | | |
| | | Operations | | | | Processing | | | | Control | | |
| | +-------------+ | | +------------+ +----------+ +---------+ | |
| | +-------------+ | | | |
| | | | | | +--------------+ +----------+ | |
| | | Transport | | | | | | | | |
| | | Mappings | | | | Applications | ......... | | | |
| | +-------------+ | | +--------------+ +----------+ | |
| | | | | |
| +-------------------+ +-----------------------------------------+ |
| |
| +----------------------------------------------------------------+ |
| | Information Model | |
| | | |
| | +--------------+ +--------------+ +---------------+ | |
| | | Structure of | | Textual | | Conformance | | |
| | | Management | | Conventions | | Statements | | |
| | | Information | | | | | | |
| | +--------------+ +--------------+ +---------------+ | |
| +----------------------------------------------------------------+ |
| |
| +----------------------------------------------------------------+ |
| | MIBs | |
| | | |
| | +-------------+ +-------------+ +----------+ +----------+ | |
| | | Standard v1 | | Standard v1 | | Historic | | Draft v2 | | |
| | | RFC1157 | | RFC1212 | | RFC14xx | | RFC19xx | | |
| | | format | | format | | format | | format | | |
| | +-------------+ +-------------+ +----------+ +----------+ | |
| +----------------------------------------------------------------+ |
| |
+--------------------------------------------------------------------+
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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 Security and Administration area.
2.1. Document Roadmap
One or more documents may be written that will describe how sets
of documents taken together form a specific SNMP framework.
The configuration of document sets might change over time, so the
"roadmap" should be maintained in a document separate from the
standards documents themselves.
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 network
management. Some models will be designed to address specific
problems of network management, such as message security.
One or more documents may be written which 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.
It would be very difficult to document all the possible interactions
between a model and all other previously existing models while in the
process of developing a new model.
Coexistence documents are therefore expected to 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.
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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. A specific implementation of an SNMP engine
defines which transports it supports.
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 engine will include one or more Message Processing Models, and thus
may support sending and receiving multiple SNMP versions of
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 will describe 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 passwords.
An SNMP engine may support multiple Security Models concurrently.
2.7. Access Control
During processing, it may be required to control access to certain
instrumentation for certain operations. An Access Control Model
determines whether access to an object should be allowed. The
mechanism by which access control is checked is defined by the
Access Control Model.
An Access Control Model document defines the mechanisms used to
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determine whether access to a managed object should be allowed,
and may define a MIB module used during processing, and to allow
the remote configuration of access control policies.
2.8. 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 network 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.
2.9. 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 syntax for defining objects, modules, and other
elements of managed information.
2.10. 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 defined in
separate documents, or within a MIB module.
2.11. 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 Conformance Statements to define
the notation used for these purposes.
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2.12. Protocol Operations
SNMP messages encapsulate an SNMP Protocol Data Unit (PDU). It is the
purpose of a Protocol Operations document to define the operations
of the protocol with respect to the processing of the PDUs.
An application document defines which Protocol Operations documents
are supported by the application.
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 an updated design of portions of SNMPv1,
as described in RFCs 1902-1908. SNMPv2 has an incomplete message
definition.
Community-based SNMP version 2 (SNMPv2c) is an experimental Framework
which supplements the incomplete message format of SNMPv2 with
portions of the message format of SNMPv1, as described in RFC1901.
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SNMP version 3 (SNMPv3) Framework is a particular configuration of
implemented subsystems, consistent with the architecture described
in this document.
Other SNMP Frameworks, i.e. other configurations of implemented
subsystems, are expected to also be consistent with this architecture.
This document does not describe any framework, but describes an
architecture into which multiple frameworks may be fitted.
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3. Naming
This architecture deals with 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
The following picture shows detail about an SNMP entity and how
components within it are named.
+--------------------------------------------------------------------+
| |
| SNMP entity |
| |
| +--------------------------------------------------------------+ |
| | | |
| | SNMP engine (identified by snmpEngineID) | |
| | | |
| | +---------------+ +--------------+ +---------------+ | |
| | | | | | | | | |
| | | Message | | Security | | Access | | |
| | | Processing | | Subsystem | | Control | | |
| | | Subsystem | | | | Subsystem | | |
| | | | | | | | | |
| | +---------------+ +--------------+ +---------------+ | |
| | | |
| +--------------------------------------------------------------+ |
| |
| +--------------------------------------------------------------+ |
| | | |
| | Application(s) | |
| | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | Command | | Notification | | Proxy | | |
| | | Generator | | Receiver | | Forwarder | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | Command | | Notification | | Other | | |
| | | Responder | | Originator | | | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | |
| +--------------------------------------------------------------+ |
| |
+--------------------------------------------------------------------+
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3.1.1. SNMP entity
An SNMP entity is an implementation of this architecture. Each such
SNMP entity consists of an SNMP engine and one or more associated
applications.
3.1.2. SNMP engine
An SNMP engine has three subsystems:
1) a Message Processing Subsystem,
2) a Security Subsystem, and
3) an Access Control Subsystem.
3.1.3. 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.
3.1.4. Message Processing Subsystem
The Message Processing Subsystem is responsible for preparing and
sending messages, and receiving and distributing messages.
The Message Processing Subsystem potentially contains multiple
Message Processing Models as shown in the next picture. Those
marked with an asterisk (*) may be absent.
+------------------------------------------------------------------+
| |
| Message Processing Subsystem |
| |
| +------------+ +------------+ +------------+ +------------+ |
| | | | * | | * | | * | |
| | SNMPv3 | | SNMPv1 | | SNMPv2c | | Other | |
| | Message | | Message | | Message | | Message | |
| | Processing | | Processing | | Processing | | Processing | |
| | Model | | Model | | Model | | Model | |
| | | | | | | | | |
| +------------+ +------------+ +------------+ +------------+ |
| |
+------------------------------------------------------------------+
3.1.5. Message Processing Model
Each Message Processing Model defines the format of a particular
version of an SNMP message and coordinates the processing of each
version-specific message.
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3.1.6. 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 next picture. Those
marked with an asterisk (*) may be absent.
+------------------------------------------------------------------+
| |
| Security Subsystem |
| |
| +------------+ +-------------------+ +---------------------+ |
| | | | * | | * | |
| | User-Based | | Community-based | | Other | |
| | Security | | Security | | Security | |
| | Model | | Model | | Model | |
| | | | | | | |
| +------------+ +-------------------+ +---------------------+ |
| |
+------------------------------------------------------------------+
3.1.7. Security Model
A Security Model defines 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.
3.1.8. Security Protocol
A Security Protocol defines the mechanisms, procedures, and MIB
data used to provide a security service such as authentication
or privacy.
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3.1.9. Access Control Subsystem
The Access Control Subsystem provides authorization services by
means of one or more Access Control Models.
+------------------------------------------------------------------+
| |
| Access Control Subsystem |
| |
| +------------+ +-------------------+ +---------------------+ |
| | | | * | | * | |
| | View-Based | | Community | | Other | |
| | Access | | Access | | Access | |
| | Control | | Control | | Control | |
| | Model | | Model | | Model | |
| | | | | | | |
| +------------+ +-------------------+ +---------------------+ |
| |
+------------------------------------------------------------------+
3.1.10. Access Control Model
An Access Control Model defines a particular access decision function
in order to support decisions regarding authorization.
3.1.11. Applications
There are several types of applications, which include:
- command generator,
- command responder,
- notification originator,
- notification receiver, and
- proxy forwarder.
These applications make use of the services provided by the Security
and Administration Framework.
3.1.12. 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.
3.1.13. 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.
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3.2. The Naming of Identities
principal <---------------------------------+
|
+-------------------------------------|-----+
| SNMP engine | |
| | |
| +-----------------------+ | |
| | Security Model | | |
| | +-------------+ | | |
wire | | | Model | +------------+--+ |
<----------->| Dependent |<-->| | securityName| |
| | | Security ID | +---------------+ |
| | +-------------+ | |
| | | |
| +-----------------------+ |
| |
| |
+-------------------------------------------+
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,
user names, and parties.
The transformation of model dependent security IDs into securityNames
and vice versa is the responsibility of the relevant Security Model.
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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. Such a Command Responder 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) | |
| | | |
| | +---------------+ +--------------+ +---------------+ | |
| | | | | | | | | |
| | | Message | | Security | | Access | | |
| | | Processing | | Subsystem | | Control | | |
| | | Subsystem | | | | Subsystem | | |
| | | | | | | | | |
| | +---------------+ +--------------+ +---------------+ | |
| | | |
| +----------------------------------------------------------+ |
| |
| +----------------------------------------------------------+ |
| | Command Responder Application | |
| | (contextEngineID, example: abcd) | |
| | | |
| | example contextNames: | |
| | | |
| | "repeater1" "repeater2" "" (default) | |
| | ----------- ----------- ------------ | |
| | | | | | |
| +-----|-------------------|--------------------|-----------+ |
| | | | |
| +-----|-------------------|--------------------|-----------+ |
| | MIB | instrumentation | | | |
| |-----v------------+ +----v-------------+ +----v-----------| |
| | context | | context | | context | |
| | | | | | | |
| | +--------------+ | | +--------------+ | | +------------+ | |
| | | repeater MIB | | | | repeater MIB | | | | other MIB | | |
| | +--------------+ | | +--------------+ | | +------------+ | |
| | | | | | | |
| | | | | | +------------+ | |
| | | | | | | some MIB | | |
| | | | | | +------------+ | |
| | | | | | | |
+--------------------------------------------------------------+
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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
engine 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 [RFC1573], 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
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. So, an item of management information can have
multiple unique identifications, either because it exists in multiple
contexts, and/or because each such context has multiple unique
identifications.
The combination of a contextEngineID and a contextName unambiguously
identifies a context within an administrative domain.
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
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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 to
be included in a response message, making allowance for the 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. LoS
This architecture recognizes three levels of security (LoS):
- 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 lower than
authNoPriv and authNoPriv is lower than authPriv.
Every message has an associated LoS. All Subsystems (Message
Processing, Security, Access Control) and applications are required
to either supply a value of LoS or to abide by the supplied value of
LoS while processing the message and its contents.
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4. Architectural Elements of Procedure
The architecture described here contains three subsystems, each
capable of being defined as one or more different models which may
be replaced or supplemented as the growing needs of network management
require. The architecture also includes applications which utilize the
services provided by the subsystems.
An SNMP engine deals with SNMP messages, and is responsible for
sending and receiving messages, including having authentication
and encryption services applied to the messages, and determining
to which application the message contents should be delivered.
Applications deal with processing network management operations.
Depending on the network management service needed, an application
may use the Access Control Subsystem, and may use SNMP messages to
communicate with remote nodes. The network management service may
be requested via the payload of an SNMP message, or may be requested
via a local process.
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4.1. Operational Overview
The following pictures show two communicating SNMP entities using
the conceptual modularity described by the SNMP Architecture.
The pictures represent SNMP entities that have traditionally been
called SNMP manager and SNMP agent respectively. The boxes marked
with an asterisk (*) may be absent.
(traditional SNMP manager)
+--------------------------------------------------------------------+
| SNMP entity |
| |
| +--------------+ +--------------+ +--------------+ |
| | NOTIFICATION | | NOTIFICATION | | COMMAND | |
| | ORIGINATOR | | RECEIVER | | GENERATOR | |
| | applications | | applications | | applications | |
| +--------------+ +--------------+ +--------------+ |
| ^ ^ ^ |
| | | | |
| v v v |
| +----------------------------------------------------------------+ |
| | Message Processing Application Multiplexor | |
| +----------------------------------------------------------------+ |
| ^ ^ ^ ^ |
| +-----------+ | | | | |
| | | v v v v |
| | Security | +------+ +---------+ +--------+ +-----------+ |
| | Subsystem |<-->| v3MP | | v2cMP * | | v1MP * |...| otherMP * | |
| | | +------+ +---------+ +--------+ +-----------+ |
| +-----------+ ^ ^ ^ ^ |
| | | | | |
| v v v v |
| +----------------------------------------------------------------+ |
| | Message Processing Model selection (incoming only) | |
| +----------------------------------------------------------------+ |
| ^ |
| | |
| v |
| +----------------------------------------------------------------+ |
| | TRANSPORT MAPPING (for example RFC1906) | |
| +----------------------------------------------------------------+ |
+--------------------------------------------------------------------+
+-----+ +-----+ +-------+
| UDP | | IPX | . . . | other |
+-----+ +-----+ +-------+
^ ^ ^
| | |
v v v
+------------------------------+
| Network |
+------------------------------+
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+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v
+-----+ +-----+ +-------+
| UDP | | IPX | . . . | other |
+-----+ +-----+ +-------+ (traditional SNMP agent)
+--------------------------------------------------------------------+
| +----------------------------------------------------------------+ |
| | TRANSPORT MAPPING (for example RFC1906) | |
| +----------------------------------------------------------------+ |
| ^ |
| | |
| v |
| +----------------------------------------------------------------+ |
| | Message Processing Model selection (incoming only) | |
| +----------------------------------------------------------------+ |
| ^ ^ ^ ^ |
| +-----------+ | | | | |
| | | v v v v |
| | Security | +------+ +---------+ +--------+ +-----------+ |
| | Subsystem |<-->| v3MP | | v2cMP * | | v1MP * |...| otherMP * | |
| | | +------+ +---------+ +--------+ +-----------+ |
| +-----------+ ^ ^ ^ ^ |
| | | | | |
| v v v v |
| +----------------------------------------------------------------+ |
| | Message Processing Abstract Service Interface | |
| +----------------------------------------------------------------+ |
| ^ ^ ^ |
| | | | |
| v v v |
| +-------------+ +---------+ +--------------+ +-------------+ |
| | COMMAND | | ACCESS | | NOTIFICATION | | PROXY * | |
| | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | |
| | application | | | | applications | | application | |
| +-------------+ +---------+ +--------------+ +-------------+ |
| ^ ^ |
| | | |
| v v |
| +----------------------------------------------+ |
| | MIB instrumentation | SNMP entity |
+--------------------------------------------------------------------+
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4.2. Sending and Receiving SNMP Messages
4.2.1. Send a Message to the Network
Applications may request that messages be generated and sent. The
application has the responsibility of providing the information
necessary to generate the message, as detailed below, and of
providing the transport address to which the message should be sent.
The engine passes a request for a message to be generated to the
specified Message Processing Model which, utilizing the services of
the selected Security Model, generates the message and prepares it
for sending.
The SNMP engine sends the message to the specified transport address.
It then advises the sending Message Processing Model about the success
or failure of the sending of the message.
4.2.2. Receive a Message from the Network
It is the responsibility of the SNMP engine to listen for incoming
messages at the appropriate local addresses. Some local addresses
for listening are recommended by SNMP Transport Mapping documents,
such as [RFC1906].
Upon receipt of an SNMP message, the SNMP engine increments the
snmpInPkts counter [RFC1907].
SNMP messages received from the network use a format defined by a
version-specific Message Processing Model, typically identified
by a version field in the message header.
The engine determines the SNMP version of an incoming message by
inspecting the serialized values for a recognizable pattern.
The mechanism by which it makes the determination of version is
implementation-specific, and dependent on the Message Processing
Models supported by the engine.
If the engine has no Message Processing Model for the determined
version, then the snmpInBadVersions counter [RFC1907] is incremented,
and the message is discarded without further processing.
The SNMP engine caches the msgID, which is subsequently used for
coordinating all processing regarding this received message, and
caches the origin network address so a possible response can be
sent to the origin address.
Based on the SNMP version of the message, the engine passes the
message to the appropriate version-specific Message Processing Model.
The Message Processing Model extracts the information in the message,
utilizing services of the appropriate Security Model to authenticate
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and decrypt the message as needed.
4.3. Send a Request or Notification Message for an Application
The Application Multiplexor receives a request for the generation
of an SNMP message from an application via the sendPdu primitive:
sendPdu(
transportDomain -- transport domain to be used
transportAddress -- destination network address
messageProcessingModel -- typically, SNMP version
securityModel -- Security Model to use
securityName -- on behalf of this principal
LoS -- Level of Security requested
contextEngineID -- data from/at this entity
contextName -- data from/in this context
PDU -- SNMP Protocol Data Unit
expectResponse) -- TRUE or FALSE
The SNMP engine checks the "expectResponse" parameter to determine if
it is a message which is expected to receive a response, and if so,
caches the msgID of the generated message and which application
made the request.
The engine sends the message according to the procedure detailed
in section 4.2.1. Send a Message to the Network.
4.4. Receive a Request or Notification Message from the Network
The engine receives the message according to the procedure detailed
in section 4.2.2. Receive a Message from the Network.
The Application Demultiplexor looks into the scopedPDU to determine
the contextEngineID and the PDU type, then determines which
application has registered (see section 4.7) to support that PDU type
for that contextEngineID.
The Application Demultiplexor passes the request or notification
to the registered application using the processPdu primitive:
processPdu(
contextEngineID -- data from/at this SNMP engine
contextName -- data from/in this context
PDU -- SNMP Protocol Data Unit
maxSizeResponseScopedPDU -- maximum size of the Response PDU
securityModel -- Security Model in use
securityName -- on behalf of this principal
LoS -- Level of Security
stateReference) -- reference to state information
-- needed when sending a response
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4.5. Generate a Response Message for an Application
The Application Multiplexor receives a request for the generation
of an SNMP response message from an application via the
returnResponsePdu primitive:
returnResponsePdu(
contextEngineID -- data from/at this SNMP engine
contextName -- data from/in this context
securityModel -- Security Model in use
securityName -- on behalf of this principal
LoS -- Level of Security
stateReference -- reference to state information
-- as presented with the request
PDU -- SNMP Protocol Data Unit
maxSizeResponseScopedPDU -- maximum size of the Response PDU
statusInformation -- success or errorIndication
) -- error counter OID/value if error
The engine sends the message according to the procedure detailed
in section 4.2.1. Send a Message to the Network.
4.6. Receive a Response Message
The engine receives the message according to the procedure detailed
in section 4.2.2. Receive a Message from the Network.
The Application Demultiplexor looks into the scopedPDU to determine
the contextEngineID and the PDU type.
If the PDU type is a Response PDU, the Demultiplexor matches the
msgID of the incoming response to the cached msgIDs of messages
sent by this SNMP engine.
If a matching cached msgID is found, the cached msgID and the cached
origin network address are released, and the response is passed to the
associated application using the processResponsePdu primitive:
processResponsePdu(
contextEngineID -- data from/at this SNMP engine
contextName -- data from/in this context
PDU -- SNMP Protocol Data Unit
LoS -- Level of Security
statusInformation -- success or errorIndication
)
4.7. Registering to Receive Asynchronous Messages
When an SNMP engine receives a message that is not the response to a
request from this SNMP engine, it must determine to which application
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the message should be given.
An Application that wishes to receive asynchronous messages registers
itself with the engine using the registration primitive. The
application registers to handle all incoming messages containing
a particular PDU type regarding a specific contextEngineID.
statusInformation = -- success or errorIndication
registerContextEngineID(
contextEngineID -- take responsibility for this one
pduType -- the pduType(s) to be registered
)
Only one registration per PDU type per contextEngineID is permitted
at the same time. Duplicate registrations are ignored. An
errorIndication will be returned to the application if it attempts
to duplicate an existing registration.
An Application that wishes to stop receiving asynchronous messages
should unregister itself with the SNMP engine.
unregisterContextEngineID(
contextEngineID -- give up responsibility for this one
pduType -- the pduType(s) to be unregistered
)
SNMP does not provide a mechanism for identifying an application,
so the mechanism used to identify which application is registering
is implementation-specific.
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5. Definition of Managed Objects for Internet Management Frameworks
SNMP-FRAMEWORK-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
OBJECT-IDENTITY,
snmpModules, Unsigned32, Integer32 FROM SNMPv2-SMI
TEXTUAL-CONVENTION FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF;
snmpFrameworkMIB MODULE-IDENTITY
LAST-UPDATED "9707110000Z" -- 11 July 1997, midnight
ORGANIZATION "SNMPv3 Working Group"
CONTACT-INFO "WG-email: snmpv3@tis.com
Subscribe: majordomo@tis.com
In message body: subscribe snmpv3
Chair: Russ Mundy
Trusted Information Systems
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
MailStop: Durham
35 Industrial Way
Rochester NH 03867-5005
USA
email: dbh@cabletron.com
phone: +1-603-337-7357
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 Internet Management Architecture MIB"
::= { snmpModules 7 } -- DBH: check if this number is indeed OK
-- Textual Conventions used in the Internet Management Architecture ***
SnmpEngineID ::= TEXTUAL-CONVENTION
STATUS current
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DESCRIPTION "An SNMP engine's administratively-unique identifier.
The value for this object may not be all zeros or
all 'ff'H. It may also not be the empty 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 for a twelve-octet identifier
is recommended:
1) The first four octets are set to the binary
equivalent of the entity's SNMP network 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.
2) 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 entity'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 that indicates the method being used and
the remaining octets are a function of the method.
"
SYNTAX OCTET STRING
SnmpSecurityModel ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "An identifier that uniquely identifies a securityModel
of the Security Subsystem within the Internet
Management Architecture.
The values for securityModel are allocated as follows:
- Negative and zero values are 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
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For example, the fourth Security Model defined by
the enterprise whose enterpriseID is 1 would be 260.
The eight bits allow a maximum of 255 (256-1 reserved)
standards based Security Models. Similarly, they
allow a maximum of 255 Security Models per enterprise.
It is believed that the assignment of new
securityModel values will be rare in practice
because the larger the number of simultaneously
utilized Security Models, the larger the chance that
interoperability will suffer. Consequently, it is
believed that such a range will be sufficient.
In the unlikely event that the standards committee
finds this number to be insufficient over time, an
enterprise number can be allocated to obtain an
additional 255 possible values.
Note that the most significant bit must be zero;
hence, there are 23 bits allocated for various
organizations to design and define non-standard
securityModels. This limits the ability to define
new proprietary implementations of Security Models
to the first 8,388,608 enterprises.
It is worthwhile to note that, in its encoded form,
the securityModel value will normally require only a
single byte since, in practice, the leftmost bits will
be zero for most messages and sign extension is
suppressed by the encoding rules.
As of this writing, there are several values of
securityModel defined for use with SNMP or reserved
for use with supporting MIB objects. They are as
follows:
0 reserved for 'none'
1 reserved for SNMPv1
2 reserved for SNMPv2c
3 User-Base Security Model (USM)
255 reserved for 'any'
"
SYNTAX INTEGER(0..2147483647)
SnmpLoS ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "A Level of Security at which SNMP messages can be
sent or with which operations are being processed;
in particular, one of:
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noAuthNoPriv - without authentication and
without privacy,
authNoPriv - with authentication but
without privacy,
authPriv - with authentication and
with privacy.
These three values are ordered such that noAuthNoPriv
is lower than authNoPriv and authNoPriv is lower than
authPriv.
"
SYNTAX INTEGER { noAuthNoPriv(1),
authNoPriv(2),
authPriv(3)
}
SnmpAdminString ::= TEXTUAL-CONVENTION
DISPLAY-HINT "255a"
STATUS current
DESCRIPTION "An octet string containing administrative information,
preferably in human-readable form.
To facilitate internationalization, this information
is represented using the ISO/IEC IS 10646-1 character
set, encoded as an octet string using the UTF-8
character encoding scheme described in RFC 2044.
Since additional code points are added by amendments
to the 10646 standard from time to time,
implementations must be prepared to encounter any code
point from 0x00000000 to 0x7fffffff.
The use of control codes should be avoided.
For code points not directly supported by user
interface hardware or software, an alternative means
of entry and display, such as hexadecimal, may be
provided.
For information encoded in 7-bit US-ASCII, the UTF-8
representation is identical to the US-ASCII encoding.
"
SYNTAX OCTET STRING (SIZE (0..255))
-- Administrative assignments ****************************************
snmpFrameworkAdmin OBJECT IDENTIFIER ::= { snmpFrameworkMIB 1 }
snmpFrameworkMIBObjects OBJECT IDENTIFIER ::= { snmpFrameworkMIB 2 }
snmpFrameworkMIBConformance OBJECT IDENTIFIER ::= { snmpFrameworkMIB 3 }
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-- the snmpEngine Group **********************************************
snmpEngine OBJECT IDENTIFIER ::= { snmpFrameworkMIBObjects 1 }
snmpEngineID OBJECT-TYPE
SYNTAX SnmpEngineID
MAX-ACCESS read-only
STATUS current
DESCRIPTION "An SNMP engine's administratively-unique identifier.
"
::= { snmpEngine 1 }
snmpEngineBoots OBJECT-TYPE
SYNTAX Unsigned32 -- (1..4294967295)
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of times that the SNMP engine has
(re-)initialized itself since its initial
configuration.
"
::= { snmpEngine 2 }
snmpEngineTime OBJECT-TYPE
SYNTAX Integer32 (0..2147483647)
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of seconds since the SNMP engine last
incremented the snmpEngineBoots object.
"
::= { snmpEngine 3 }
-- Registration Points for IMF Authentication and Privacy Protocols **
snmpAuthProtocols OBJECT-IDENTITY
STATUS current
DESCRIPTION "Registration point for standards-track authentication
protocols used in the Internet Management Framework.
"
::= { snmpFrameworkAdmin 1 }
snmpPrivProtocols OBJECT-IDENTITY
STATUS current
DESCRIPTION "Registration point for standards-track privacy
protocols used in the Internet Management Framework.
"
::= { snmpFrameworkAdmin 2 }
-- Conformance information *******************************************
snmpFrameworkMIBCompliances
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OBJECT IDENTIFIER ::= { snmpFrameworkMIBConformance 1 }
snmpFrameworkMIBGroups
OBJECT IDENTIFIER ::= { snmpFrameworkMIBConformance 2 }
-- compliance statements
snmpFrameworkMIBCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION "The compliance statement for SNMP engines which
implement the Internet Management Framework MIB.
"
MODULE -- this module
MANDATORY-GROUPS { snmpEngineGroup }
::= { snmpFrameworkMIBCompliances 1 }
-- units of conformance
snmpEngineGroup OBJECT-GROUP
OBJECTS {
snmpEngineID,
snmpEngineBoots,
snmpEngineTime
}
STATUS current
DESCRIPTION "A collection of objects for identifying and
determining the configuration and current timeliness
values of an SNMP engine.
"
::= { snmpFrameworkMIBGroups 1 }
END
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6. Security Considerations
This document describes how a framework can use a Security Model and
an Access Control Model to achieve a level of security for network
management messages and controlled access to management information.
The level of security provided is determined by the specific Security
Model implementation(s) and the specific Access Control Model
implementation(s) incorporated into this framework.
Applications have access to data which is not secured. Applications
should take reasonable steps to protect the data from disclosure.
It is the responsibility of the purchaser of a management framework
implementation to ensure that:
1) an implementation of this framework complies with the rules
defined by this architecture,
2) the Security and Access Control Models utilized satisfy the
security and access control needs of the organization,
3) the implementations of the Models and Applications comply with
the model and application specifications,
4) and the implementation protects configuration secrets from
inadvertent disclosure.
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7. Glossary
8. References
[RFC1155] Rose, M., and K. McCloghrie, "Structure and Identification
of Management Information for TCP/IP-based internets", STD 16,
RFC 1155, May 1990.
[RFC1157] Case, J., M. Fedor, M. Schoffstall, and J. Davin,
"The Simple Network Management Protocol", STD 15, RFC 1157,
University of Tennessee at Knoxville, Performance Systems s
International, Performance International, and the MIT Laboratory
for Computer Science, May 1990.
[RFC1212] Rose, M., and K. McCloghrie, "Concise MIB Definitions",
STD 16, RFC 1212, March 1991.
[RFC1901] The SNMPv2 Working Group, Case, J., McCloghrie, K.,
Rose, M., and S., Waldbusser, "Introduction to
Community-based SNMPv2", RFC 1901, January 1996.
[RFC1902] The 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 1905, January 1996.
[RFC1903] The 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.
[RFC1904] The 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.
[RFC1905] The 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.
[RFC1906] The 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.
[RFC1907] The 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.
[RFC1908] The 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
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Framework", RFC 1908, January 1996.
[RFC1909] McCloghrie, K., Editor, "An Administrative Infrastructure
for SNMPv2", RFC1909, February 1996
[RFC1910] Waters, G., Editor, "User-based Security Model for SNMPv2",
RFC1910, February 1996
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9. Editor's Addresses
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
Co-editor Dave Harrington
Cabletron Systems, Inc
postal: Post Office Box 5005
MailStop: Durham
35 Industrial Way
Rochester NH 03867-5005
USA
email: dbh@cabletron.com
phone: +1-603-337-7357
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10. Acknowledgements
This document builds on the work of the SNMP Security and
Administrative Framework Evolution team, composed of
David Harrington (Cabletron Systems Inc.)
Jeff Johnson (Cisco)
David Levi (SNMP Research Inc.)
John Linn (Openvision)
Russ Mundy (Trusted Information Systems) chair
Shawn Routhier (Epilogue)
Glenn Waters (Nortel)
Bert Wijnen (IBM T.J. Watson Research)
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APPENDIX A
A. Guidelines for Model Designers
This appendix describes guidelines for designers of models which
are expected to fit into the architecture defined in this document.
The basic design elements come from SNMPv2u and SNMPv2*, as
described in RFCs 1909-1910, and from a set of internet drafts.
these are the two most popular de facto "administrative framework"
standards that include security and access control for SNMPv2.
SNMPv1 and SNMPv2c [RFC1901] are two administrative frameworks based
on communities to provide trivial authentication and access control.
SNMPv1 and SNMPv2c Frameworks can coexist with Frameworks designed
to fit into this architecture, and modified versions of SNMPv1 and
SNMPv2c Frameworks could be fit into this architecture, but this
document does not provide guidelines for that coexistence.
Within any subsystem model, there should be no reference to any
specific model of another subsystem, or to data defined by a specific
model of another subsystem.
Transfer of data between the subsystems is deliberately described
as a fixed set of abstract data elements and primitive functions
which can be overloaded to satisfy the needs of multiple model
definitions.
Documents which define models to be used within this architecture
SHOULD use the standard primitives between subsystems, possibly
defining specific mechanisms for converting the abstract data elements
into model-usable formats. This constraint exists to allow subsystem
and model documents to be written recognizing common borders of the
subsystem and model. Vendors are not constrained to recognize these
borders in their implementations.
The architecture defines certain standard services to be provided
between subsystems, and the architecture defines abstract service
interfaces to request the services.
Each model definition for a subsystem SHOULD support the standard
service interfaces, but whether, or how, or how well, it performs
the service is defined by the model definition.
A.1. Security Model Design Requirements
A.1.1. Threats
A document describing a Security Model MUST describe how the model
protects against the threats described under "Security Requirements
of this Architecture", section 1.4.
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A.1.2. Security Processing
Received messages MUST be validated by a Model of the Security
Subsystem. Validation includes authentication and privacy processing
if needed, but it is explicitly allowed to send messages which do
not require authentication or privacy.
A received message contains a specified Level of Security to be
used during processing. All messages requiring privacy MUST also
require authentication.
A Security Model specifies rules by which authentication and privacy
are to be done. A model may define mechanisms to provide additional
security features, but the model definition is constrained to using
(possibly a subset of) the abstract data elements defined in this
document for transferring data between subsystems.
Each Security Model may allow multiple security mechanisms to be used
concurrently within an implementation of the model. Each Security Model
defines how to determine which protocol to use, given the LoS and the
security parameters relevant to the message. Each Security Model, with
its associated protocol(s) defines how the sending/receiving entities
are identified, and how secrets are configured.
Authentication and Privacy protocols supported by Security Models are
uniquely identified using Object Identifiers. IETF standard protocol
for authentication or privacy should have an identifier defined within
the snmpAuthProtocols or the snmpPrivProtocols subtrees. Enterprise
specific protocol identifiers should be defined within the enterprise
subtree.
For privacy, the Security Model defines what portion of the message
is encrypted.
The persistent data used for security should be SNMP-manageable, but
the Security Model defines whether an instantiation of the MIB is a
conformance requirement.
Security Models are replaceable within the Security Subsystem.
Multiple Security Model implementations may exist concurrently within
an SNMP engine. The number of Security Models defined by the SNMP
community should remain small to promote interoperability.
A.1.3. validate the security-stamp in a received message
The Message Processing Model requests that the Security Model verify
that the message has not been altered, and authenticate the
identification of the principal for whom the message was generated.
If encrypted, decrypt the message.
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Additional requirements may be defined by the model, and additional
services provided by the model, but the model is constrained to use
the following primitives for transferring data between subsystems.
Implementations are not so constrained.
The Message Processing Model uses the following primitive:
processMsg(
messageProcessingModel -- typically, SNMP version
msgID -- of the received message
mms -- of the sending SNMP entity
msgFlags -- for the received message
securityParameters -- for the received message
securityModel -- for the received message
LoS -- Level of Security
wholeMsg -- as received on the wire
wholeMsgLength -- length as received on the wire
)
The Security Model uses the following primitive to respond:
returnProcessedMsg(
securityName -- identification of the principal
scopedPDU, -- message (plaintext) payload
maxSizeResponseScopedPDU -- maximum size of the Response PDU
securityStateReference -- reference to security state
-- information, needed for response
statusInformation -- errorIndication or success
) -- error counter OID/value if error
A.1.5. Security MIBs
Each Security Model defines the MIB modules required for security
processing, including any MIB modules required for the security
mechanism(s) supported. The MIB modules SHOULD be defined concurrently
with the procedures which use the MIB module. The MIB modules are
subject to normal security and access control rules.
The mapping between the model-dependent identifier and the securityName
MUST be able to be determined using SNMP, if the model-dependent
MIB is instantiated and access control policy allows access.
A.1.6. Security State Cache
For each message received, the Security Subsystem caches the state
information such that a Response message can be generated using the
same security state information, even if the Local Configuration
Datastore is altered between the time of the incoming request and
the outgoing response.
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Applications have the responsibility for explicitly releasing the
cached data. To enable this, an abstract stateReference data element
is passed from the Security Subsystem to the Message Processing
Subsystem, which passes it to the application.
The cached security data may be implicitly released via the
generation of a response, or explicitly released by using the
stateRelease primitive:
stateRelease(
stateReference -- handle of reference to be released
)
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A.2. SNMP engine and Message Processing Model Requirements
An SNMP engine contains a Message Processing Subsystem which may
contain multiple version-specific Message Processing Models.
Within any version-specific Message Processing Model, there may be
an explicit binding to a particular Security Model but there should
be no reference to any data defined by a specific Security Model.
There should be no reference to any specific application, or to any
data defined by a specific application; there should be no reference
to any specific Access Control Model, or to any data defined by a
specific Access Control Model.
The Message Processing Model MUST always (conceptually) pass the
complete PDU, i.e. it never forwards less than the complete list of
varBinds.
A.2.1. Receiving an SNMP Message from the Network
Upon receipt of a message from the network, the SNMP engine notes the
msgID, which is subsequently used for coordinating all processing
regarding this received message.
A Message Processing Model specifies how to determine the values of
the global data (mms, the securityModel, the LoS), and the security
parameters block. The Message Processing Model calls the Security
Model to provide security processing for the message using the
primitive:
processMsg(
messageProcessingModel -- typically, SNMP version
msgID -- of the received message
mms -- of the sending SNMP entity
msgFlags -- for the received message
securityParameters -- for the received message
securityModel -- for the received message
LoS -- Level of Security
wholeMsg -- as received on the wire
wholeMsgLength -- length as received on the wire
)
The Security Model uses the following primitive to respond:
returnProcessedMsg(
securityName -- identification of the principal
scopedPDU, -- message (plaintext) payload
maxSizeResponseScopedPDU -- maximum size of the Response PDU
securityStateReference -- reference to security state
-- information, needed for response
statusInformation -- errorIndication or success
) -- error counter OID/value if error
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A.2.2. Send SNMP messages to the network
The Message Processing Model passes a PDU, the
securityName, and all global data to be included in the message to
the Security model using the following primitives:
For requests and notifications:
generateRequestMsg(
messageProcessingModel -- typically, SNMP version
msgID -- for the outgoing message
mms -- of the sending SNMP entity
msgFlags -- for the outgoing message
securityParameters -- filled in by Security Module
securityModel -- for the outgoing message
securityName -- on behalf of this principal
LoS -- Level of Security requested
snmpEngineID -- authoritative SNMP engine
scopedPDU -- message (plaintext) payload
)
For response messages:
generateResponseMsg(
messageProcessingModel -- typically, SNMP version
msgID -- for the outgoing message
mms -- of the sending SNMP entity
msgFlags -- for the outgoing message
securityParameters -- filled in by Security Module
securityModel -- for the outgoing message
scopedPDU -- message (plaintext) payload
securityStateReference -- reference to security state
-- information, as received in
) -- processPdu primitive
The Security model constructs the message, and returns the completed
message to the Message Processing Model using the returnGeneratedMsg
primitive:
returnGeneratedMsg(
wholeMsg -- complete generated message
wholeMsgLength -- length of the generated message
statusInformation -- errorIndication or success
)
The SNMP engine sends the message to the desired address using the
appropriate transport.
A.2.3. Generate Request or Notification Message for an Application
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The SNMP engine receives a request for the generation of an SNMP
message from an application via the sendPdu primitive:
sendPdu(
transportDomain -- transport domain to be used
transportAddress -- destination network address
messageProcessingModel -- typically, SNMP version
securityModel -- Security Model to use
securityName -- on behalf of this principal
LoS -- Level of Security requested
contextEngineID -- data from/at this entity
contextName -- data from/in this context
PDU -- SNMP Protocol Data Unit
expectResponse -- TRUE or FALSE
)
The SNMP engine checks the "expectResponse" parameter to determine if
it is a message which is expected to receive a response, and if so,
caches the msgID of the generated message and the associated
application.
The Message Processing Model generates the message according to the
process described in A.2.2.
A.2.4. Pass Received Response Message to an Application
The Message Processing Model receives the SNMP message according to
the process described in A.2.1.
The Message Processing Model determines which application is awaiting
this response, using the msgID and the cached information from
step A.2.3
The Message Processing Model matches the msgID of an incoming response
to the cached msgIDs of messages sent by this SNMP engine, and
forwards the response to the associated application using the
processResponsePdu primitive:
processResponsePdu( -- process Response PDU
contextEngineID -- data from/at this SNMP entity
contextName -- data from/in this context
PDU -- SNMP Protocol Data Unit
LoS -- Level of Security
statusInformation -- success or errorIndication
)
A.2.5. Pass Received Request or Notification Message to Application
The Message Processing Model receives the SNMP message according to
the process described in A.2.1.
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The SNMP engine looks into the scopedPDU to determine the
contextEngineID, then determine which application has registered to
support that contextEngineID, and forwards the request or notification
to the registered application using the processPdu primitive:
processPdu( -- process Request/Notification PDU
contextEngineID -- data from/at this SNMP engine
contextName -- data from/in this context
PDU -- SNMP Protocol Data Unit
maxSizeResponseScopedPDU -- maximum size of the Response PDU
securityModel -- Security Model in use
securityName -- on behalf of this principal
LoS -- Level of Security
stateReference -- reference to state information
) -- needed when sending a response
A.2.6. Generate a Response Message for an Application
The SNMP engine receives a request for the generation of an SNMP
response message from an application via the returnResponsePdu
primitive:
returnResponsePdu(
contextEngineID -- data from/at this SNMP engine
contextName -- data from/in this context
PDU -- SNMP Protocol Data Unit
maxSizeResponseScopedPDU -- maximum size of the Response PDU
securityModel -- Security Model in use
securityName -- on behalf of this principal
LoS -- Level of Security
stateReference -- reference to state information
-- as presented with the request
statusInformation -- success or errorIndication
) -- error counter OID/value if error
The SNMP engine generates the message according to the process
described in A.2.2.
A.3. Application Design Requirements
Within an application, there may be an explicit binding to a specific
SNMP message version, i.e. a specific Message Processing Model, and to
a specific Access Control Model, but there should be no reference to
any data defined by a specific Message Processing Model or Access
Control Model.
Within an application, there should be no reference to any specific
Security Model, or any data defined by a specific Security Model.
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An application determines whether explicit or implicit access control
should be applied to the operation, and, if access control is needed,
which Access Control Model should be used.
An application has the responsibility to define any MIB modules used
to provide application-specific services.
Applications interact with the SNMP engine to initiate messages,
receive responses, receive asynchronous messages, and send responses.
A.3.1. Applications that Initiate Messages
Applications may request that the SNMP engine send messages containing
SNMP commands or notifications using the sendPdu primitive:
sendPdu(
transportDomain -- transport domain to be used
transportAddress -- destination network address
messageProcessingModel -- typically, SNMP version
securityModel -- Security Model to use
securityName -- on behalf of this principal
LoS -- Level of Security requested
contextEngineID -- data from/at this entity
contextName -- data from/in this context
PDU -- SNMP Protocol Data Unit
expectResponse -- TRUE or FALSE
)
If it is desired that a message be sent to multiple targets, it is the
responsibility of the application to provide the iteration.
The SNMP engine assumes necessary access control has been applied
to the PDU, and provides no access control services.
The SNMP engine looks at the "expectResponse" parameter, and for
operations which elicit a response, the msgID and the associated
application are cached.
A.3.2. Applications that Receive Responses
The SNMP engine matches the msgID of an incoming response to the
cached msgIDs of messages sent by this SNMP engine, and forwards the
response to the associated application using the processResponsePdu
primitive:
processResponsePdu( -- process Response PDU
contextEngineID -- data from/at this SNMP entity
contextName -- data from/in this context
PDU -- SNMP Protocol Data Unit
LoS -- Level of Security
statusInformation -- success or errorIndication
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)
The SNMP engine then releases its own state information about this
message.
A.3.3. Applications that Receive Asynchronous Messages
When an SNMP engine receives a message that is not the response to a
request from this SNMP engine, it must determine to which application
the message should be given.
An Application that wishes to receive asynchronous messages registers
itself with the engine using the registration primitive.
An Application that wishes to stop receiving asynchronous messages
should unregister itself with the SNMP engine.
statusInformation = -- success or errorIndication
registerContextEngineID(
contextEngineID -- take responsibility for this one
pduType -- the pduType(s) to be registered
)
unregisterContextEngineID(
contextEngineID -- give up responsibility for this one
pduType -- the pduType(s) to be unregistered
)
Only one registration per PDU type per contextEngineID is permitted
at the same time. Duplicate registrations are ignored. An
errorIndication will be returned to the application that attempts
to duplicate a registration.
All asynchronously received messages containing a registered
PDU type and contextEngineID are sent to the application which
registered to support that combination.
The engine forwards the PDU to the registered application, using the
processPdu primitive:
processPdu( -- process Request/Notification PDU
contextEngineID -- data from/at this SNMP engine
contextName -- data from/in this context
PDU -- SNMP Protocol Data Unit
maxSizeResponseScopedPDU -- maximum size of the Response PDU
securityModel -- Security Model in use
securityName -- on behalf of this principal
LoS -- Level of Security
stateReference -- reference to state information
) -- needed when sending a response
A.3.4. Applications that Send Responses
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Request operations require responses. These operations include Get
requests, Set requests, and Inform requests. An application sends a
response via the returnResponsePdu primitive:
returnResponsePdu(
contextEngineID -- data from/at this SNMP engine
contextName -- data from/in this context
PDU -- SNMP Protocol Data Unit
maxSizeResponseScopedPDU -- maximum size of the Response PDU
securityModel -- on behalf of this principal
securityName -- on behalf of this principal
LoS -- Level of Security
stateReference -- reference to state information
-- as presented with the request
statusInformation -- success or errorIndication
) -- error counter OID/value if error
The contextEngineID, contextName, securityModel, securityName, LoS, and
stateReference parameters are from the initial processPdu primitive.
The PDU and statusInformation are the results of processing.
A.4. Access Control Model Design Requirements
An Access Control Model determines whether the specified
securityName is allowed to perform the requested operation on
a specified managed object. The Access Control Model specifies the
rules by which access control is determined.
The persistent data used for access control should be manageable
using SNMP, but the Access Control model defines whether an
instantiation of the MIB is a conformance requirement.
The following primitive is used to invoke the access control service:
statusInformation = -- success or errorIndication
isAccessAllowed(
securityModel -- Security Model in use
securityName -- principal who wants to access
LoS -- Level of Security
viewType -- read, write, or notify view
contextName -- context containing variableName
variableName -- OID for the managed object
)
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APPENDIX B
B. An Evolutionary Architecture - Design Goals
The goals of the architectural design are to use encapsulation,
cohesion, hierarchical rules, and loose coupling to reduce complexity
of design and make the evolution of portions of the architecture
possible.
B.1. Encapsulation
Encapsulation describes the practice of hiding the details that are
used internal to a process. Some data is required for a given
procedure, but isn't needed by any other part of the process.
In networking, the concept of a layered stack reflects this approach.
The transport layer contains data specific to its processing; the data
is not visible to the other layers. In programming this is reflected
in language elements such as "file static" variables in C, and
"private" in C++, etc.
In this architecture, all data used for processing only within
a functional portion of the architecture should have its visibility
restricted to that portion if possible. The data should be accessed
only by that functionality defined with the data. No reference to the
data should be made from outside the functional portion of the
architecture, except through predefined public interfaces.
B.2. Cohesion
Similar functions can be grouped together and their differences
ignored, so they can be dealt with as a single entity. It is important
that the functions which are grouped together are actually similar.
Similarity of the data used to perform functions can be a good
indicator of the similarity of the functions.
For example, authentication and encryption are both security functions
which are applied to a message. Access control, while similar in some
ways, is dissimilar in that it is not applied to a message, it is
applied to a (proposed) request for a management operation.
The data required to perform authentication and encryption are
different than the data needed to perform access control, and the
two sets of services can be described independently.
Similar functions, especially those that use the same data elements,
should be defined together. The security functions which operate at
the message level should be defined in a document together with the
definitions for those data elements that are used only by those
security functions. For example, a MIB with authentication keys is
used only by authentication functions; they should be defined together.
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B.3. Hierarchical Rules
Functionality can be grouped into hierarchies where each element in the
hierarchy receives general characteristics from its direct superior,
and passes on those characteristics to each of its direct subordinates.
This architecture uses the hierarchical approach by defining
subsystems, which specify the general rules of a portion of the system,
models which define the specific rules to be followed by an
implementation of the portion of the system, and implementations which
encode those rules into reality for a portion of the system.
Within portions of the system, hierarchical relationships are used to
compartmentalize, or modularize, the implementation of specific
functionality. For example, within the security portion of the system,
authentication and privacy may be contained in separate modules, and
multiple authentication and privacy mechanisms may be supported by
allowing supplemental modules that provide protocol-specific
authentication and privacy services.
B.4. Coupling
Coupling describes the amount of interdependence between parts of
a system. Loose coupling indicates that two sub-systems are relatively
independent of each other; tight coupling indicates a high degree of
mutual dependence.
To make it possible to evolve the architecture by replacing only part
of the system, or by supplementing existing portions with alternate
mechanisms for similar functionality, without obsoleting the complete
system, it is necessary to limit the coupling of the parts.
Encapsulation and cohesion help to reduce coupling by limiting the
visibility of those parts that are only needed within portions of a
system. Another mechanism is to constrain the nature of interactions
between various parts of the system.
This can be done by defining fixed, generic, flexible interfaces
for transferring data between the parts of the system. The concept of
plug-and-play hardware components is based on that type of interface
between the hardware component and system into which it is "plugged."
This approach has been chosen so individual portions of the system
can be upgraded over time, while keeping the overall system intact.
To avoid specifying fixed interfaces, which would constrain a vendor's
choice of implementation strategies, a set of abstract data elements
is used for (conceptually) transferring data between subsystems in
documents which describe subsystem or model interactions. Documents
describing the interaction of subsystems or models should use only
the abstract data elements provided for transferring data but vendors
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are not constrained to using the described data elements for
transferring data between portions of their implementation.
Loose coupling works well with the IETF standards process. If we
separate message-handling from security and from local processing,
then the separate portions of the system can move through the standards
process with less dependence on the status of the other portions of the
standard. Security models may be able to be re-opened for discussion
due to patents, new research, export laws, etc., as is clearly expected
by the WG, without needing to reopen the documents which detail the
message format or the local processing of PDUs. Thus, the standards
track status of related, but independent, documents is not affected.
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Table of Contents
0. Issues 2
0.1. Issues to be resolved 2
0.1.1. Issues discussed at second Interim Meeting: 2
0.2. Change Log 3
1. Introduction 7
1.1. Target Audience 7
1.2. Management Systems 7
1.3. Goals of this Architecture 8
1.4. Security Requirements of this Architecture 9
1.5. Design Decisions 10
2. Documentation Overview 12
2.1. Document Roadmap 13
2.2. Applicability Statement 13
2.3. Coexistence and Transition 13
2.4. Transport Mappings 14
2.5. Message Processing 14
2.6. Security 14
2.7. Access Control 14
2.8. Applications 15
2.9. Structure of Management Information 15
2.10. Textual Conventions 15
2.11. Conformance Statements 15
2.12. Protocol Operations 16
2.13. Management Information Base Modules 16
2.13.1. SNMP Instrumentation MIBs 16
2.14. SNMP Framework Documents 16
3. Naming 18
3.1. The Naming of Entities 18
3.1.1. SNMP entity 19
3.1.2. SNMP engine 19
3.1.3. snmpEngineID 19
3.1.4. Message Processing Subsystem 19
3.1.5. Message Processing Model 19
3.1.6. Security Subsystem 20
3.1.7. Security Model 20
3.1.8. Security Protocol 20
3.1.9. Access Control Subsystem 21
3.1.10. Access Control Model 21
3.1.11. Applications 21
3.1.12. SNMP Agent 21
3.1.13. SNMP Manager 21
3.2. The Naming of Identities 22
3.2.1. Principal 22
3.2.2. securityName 22
3.2.3. Model dependent security ID 22
3.3. The Naming of Management Information 23
3.3.1. An SNMP Context 24
3.3.2. contextEngineID 24
3.3.3. contextName 24
3.3.4. scopedPDU 24
3.4. Other Constructs 25
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3.4.1. maxSizeResponseScopedPDU 25
3.4.2. Local Configuration Datastore 25
3.4.3. LoS 25
4. Architectural Elements of Procedure 26
4.1. Operational Overview 27
4.2. Sending and Receiving SNMP Messages 29
4.2.1. Send a Message to the Network 29
4.2.2. Receive a Message from the Network 29
4.3. Send a Request or Notification Message for an Application 30
4.4. Receive a Request or Notification Message from the Network 30
4.5. Generate a Response Message for an Application 31
4.6. Receive a Response Message 31
4.7. Registering to Receive Asynchronous Messages 31
5. Definition of Managed Objects for Internet Management Frameworks 33
6. Security Considerations 39
7. Glossary 40
8. References 40
9. Editor's Addresses 42
10. Acknowledgements 43
A. Guidelines for Model Designers 44
A.1. Security Model Design Requirements 44
A.1.1. Threats 44
A.1.2. Security Processing 45
A.1.3. validate the security-stamp in a received message 45
A.1.5. Security MIBs 46
A.1.6. Security State Cache 46
A.2. SNMP engine and Message Processing Model Requirements 48
A.2.1. Receiving an SNMP Message from the Network 48
A.2.2. Send SNMP messages to the network 49
A.2.3. Generate Request or Notification Message for an Application 49
A.2.4. Pass Received Response Message to an Application 50
A.2.5. Pass Received Request or Notification Message to Application 50
A.2.6. Generate a Response Message for an Application 51
A.3. Application Design Requirements 51
A.3.1. Applications that Initiate Messages 52
A.3.2. Applications that Receive Responses 52
A.3.3. Applications that Receive Asynchronous Messages 53
A.3.4. Applications that Send Responses 53
A.4. Access Control Model Design Requirements 54
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