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INTERNET-DRAFT D. Harrington
Cabletron Systems, Inc.
R. Presuhn
BMC Software, Inc.
B. Wijnen
IBM T. J. Watson Research
30 September 1997
An Architecture for Describing
SNMP Management Frameworks
<draft-ietf-snmpv3-next-gen-arch-05.txt>
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as ``work in progress.''
To learn the current status of any Internet-Draft, please check the
``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).
Abstract
This document describes an architecture for describing SNMP
Management Frameworks. The architecture is designed to be modular to
allow the evolution of the SNMP protocol standards over time. The
major portions of the architecture are an SNMP engine containing a
Message Processing Subsystem, a Security Subsystem and an Access
Control Subsystem, and possibly multiple SNMP applications which
provide specific functional processing of management data.
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1. Introduction
1.1. Overview
This document defines a vocabulary for describing SNMP Management
Frameworks, and an architecture for describing the major portions of
SNMP Management Frameworks.
This document does not provide a general introduction to SNMP. Other
documents and books can provide a much better introduction to SNMP.
Nor does this document provide a history of SNMP. That also can be
found in books and other documents.
Section 1 describes the purpose, goals, and design decisions of this
architecture.
Section 2 describes various types of documents which define SNMP
Frameworks, and how they fit into this architecture. It also provides
a minimal road map to the documents which have previously defined
SNMP frameworks.
Section 3 details the vocabulary of this architecture and its pieces.
This section is important for understanding the remaining sections,
and for understanding documents which are written to fit within this
architecture.
Section 4 describes the primitives used for the abstract service
interfaces between the various subsystems, models and applications
within this architecture.
Section 5 defines a collection of managed objects used to instrument
SNMP entities within this architecture.
Sections 6, 7, 8, and 9 are administrative in nature.
Appendix A contains guidelines for designers of Models which are
expected to fit within this architecture.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.2. SNMP
An SNMP management system contains:
- several (potentially many) nodes, each with an SNMP entity
containing command responder and notification originator
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applications, which have access to management instrumentation
(traditionally called agents);
- at least one SNMP entity containing command generator and/or
notification receiver applications (traditionally called a
manager) and,
- a management protocol, used to convey management information
between the SNMP entities.
SNMP entities executing command generator and notification receiver
applications monitor and control managed elements. Managed elements
are devices such as hosts, routers, terminal servers, etc., which are
monitored and controlled via access to their management information.
It is the purpose of this document to define an architecture which
can evolve to realize effective management in a variety of
configurations and environments. The architecture has been designed
to meet the needs of implementations of:
- minimal SNMP entities with command responder and/or
notification originator applications (traditionally called SNMP
agents),
- SNMP entities with proxy forwarder applications (traditionally
called SNMP proxy 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) 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*.
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- Address the need for secure SET support, which is considered
the most important deficiency in SNMPv1 and SNMPv2c.
- Make it possible to move portions of the architecture forward
in the standards track, even if consensus has not been reached
on all pieces.
- Define an architecture that allows for longevity of the SNMP
Frameworks that have been and will be defined.
- Keep SNMP as simple as possible.
- Make it relatively inexpensive to deploy a minimal conforming
implementation.
- Make it possible to upgrade portions of SNMP as new approaches
become available, without disrupting an entire SNMP framework.
- Make it possible to support features required in large
networks, but make the expense of supporting a feature directly
related to the support of the feature.
1.4. Security Requirements of this Architecture
Several of the classical threats to network protocols are applicable
to the management problem and therefore would be applicable to any
Security Model used in an SNMP Management Framework. Other threats
are not applicable to the management problem. This section discusses
principal threats, secondary threats, and threats which are of lesser
importance.
The principal threats against which any Security Model used within
this architecture SHOULD provide protection are:
Modification of Information
The modification threat is the danger that some unauthorized 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
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The SNMP protocol is typically based upon a connectionless
transport service which may operate over any subnetwork service.
The re-ordering, delay or replay of messages can and does occur
through the natural operation of many such subnetwork services.
The message stream modification threat is the danger that messages
may be maliciously re-ordered, delayed or replayed to an extent
which is greater than can occur through the natural operation of a
subnetwork service, in order to effect unauthorized management
operations.
Disclosure
The disclosure threat is the danger of eavesdropping on the
exchanges between SNMP engines. Protecting against this threat
may be required as a matter of local policy.
There are at least two threats against which a Security Model within
this architecture need not protect.
Denial of Service
A Security Model need not attempt to address the broad range of
attacks by which service on behalf of authorized users is denied.
Indeed, such denial-of-service attacks are in many cases
indistinguishable from the type of network failures with which any
viable management protocol must cope as a matter of course.
Traffic Analysis
A Security Model need not attempt to address traffic analysis
attacks. Many traffic patterns are predictable - entities may be
managed on a regular basis by a relatively small number of
management stations - and therefore there is no significant
advantage afforded by protecting against traffic analysis.
1.5. Design Decisions
Various design decisions were made in support of the goals of the
architecture and the security requirements:
- Architecture
An architecture should be defined which identifies the
conceptual boundaries between the documents. Subsystems should
be defined which describe the abstract services provided by
specific portions of an SNMP framework. Abstract service
interfaces, as described by service primitives, define the
abstract boundaries between documents, and the abstract
services that are provided by the conceptual subsystems of an
SNMP framework.
- Self-contained Documents
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Elements of procedure plus the MIB objects which are needed for
processing for a specific portion of an SNMP framework should
be defined in the same document, and as much as possible,
should not be referenced in other documents. This allows pieces
to be designed and documented as independent and self-contained
parts, which is consistent with the general SNMP MIB module
approach. As portions of SNMP change over time, the documents
describing other portions of SNMP are not directly impacted.
This modularity allows, for example, Security Models,
authentication and privacy mechanisms, and message formats to
be upgraded and supplemented as the need arises. The self-
contained documents can move along the standards track on
different time-lines.
- Threats
The Security Models in the Security Subsystem SHOULD protect
against the principal threats: modification of information,
masquerade, message stream modification and disclosure. They
do not need to protect against denial of service and traffic
analysis.
- Remote Configuration
The Security and Access Control Subsystems add a whole new set
of SNMP configuration parameters. The Security Subsystem also
requires frequent changes of secrets at the various SNMP
entities. To make this deployable in a large operational
environment, these SNMP parameters must be able to be remotely
configured.
- Controlled Complexity
It is recognized that producers of simple managed devices want
to keep the resources used by SNMP to a minimum. At the same
time, there is a need for more complex configurations which can
spend more resources for SNMP and thus provide more
functionality. The design tries to keep the competing
requirements of these two environments in balance and allows
the more complex environments to logically extend the simple
environment.
2. Documentation Overview
The following figure shows the set of documents that fit within the
SNMP Architecture.
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+------------------------- Document Set ----------------------------+
| |
| +------------+ +-----------------+ +----------------+ |
| | Document * | | Applicability * | | Coexistence * | |
| | Roadmap | | Statement | | & Transition | |
| +------------+ +-----------------+ +----------------+ |
| |
| +---------------------------------------------------------------+ |
| | Message Handling | |
| | +----------------+ +-----------------+ +-----------------+ | |
| | | Transport | | Message | | Security | | |
| | | Mappings | | Processing and | | | | |
| | | | | Dispatcher | | | | |
| | +----------------+ +-----------------+ +-----------------+ | |
| +---------------------------------------------------------------+ |
| |
| +---------------------------------------------------------------+ |
| | PDU Handling | |
| | +----------------+ +-----------------+ +-----------------+ | |
| | | Protocol | | Applications | | Access | | |
| | | Operations | | | | Control | | |
| | +----------------+ +-----------------+ +-----------------+ | |
| +---------------------------------------------------------------+ |
| |
| +---------------------------------------------------------------+ |
| | Information Model | |
| | +--------------+ +--------------+ +---------------+ | |
| | | Structure of | | Textual | | Conformance | | |
| | | Management | | Conventions | | Statements | | |
| | | Information | | | | | | |
| | +--------------+ +--------------+ +---------------+ | |
| +---------------------------------------------------------------+ |
| |
| +---------------------------------------------------------------+ |
| | MIBs | |
| | +-------------+ +-------------+ +----------+ +----------+ | |
| | | Standard v1 | | Standard v1 | | Historic | | Draft v2 | | |
| | | RFC1157 | | RFC1212 | | RFC14xx | | RFC19xx | | |
| | | format | | format | | format | | format | | |
| | +-------------+ +-------------+ +----------+ +----------+ | |
| +---------------------------------------------------------------+ |
| |
+-------------------------------------------------------------------+
Those marked with an asterisk (*) are expected to be written in the
future. Each of these documents may be replaced or supplemented.
This Architecture document specifically describes how new documents
fit into the set of documents in the area of Message and PDU
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handling.
2.1. Document Roadmap
One or more documents may be written to describe how sets of
documents taken together form specific Frameworks. The configuration
of document sets might change over time, so the "road map" should be
maintained in a document separate from the standards documents
themselves.
2.2. Applicability Statement
SNMP is used in networks that vary widely in size and complexity, by
organizations that vary widely in their requirements of management.
Some models will be designed to address specific problems of
management, such as message security.
One or more documents may be written to describe the environments to
which certain versions of SNMP or models within SNMP would be
appropriately applied, and those to which a given model might be
inappropriately applied.
2.3. Coexistence and Transition
The purpose of an evolutionary architecture is to permit new models
to replace or supplement existing models. The interactions between
models could result in incompatibilities, security "holes", and other
undesirable effects.
The purpose of Coexistence documents is to detail recognized
anomalies and to describe required and recommended behaviors for
resolving the interactions between models within the architecture.
Coexistence documents may be prepared separately from model
definition documents, to describe and resolve interaction anomalies
between a model definition and one or more other model definitions.
Additionally, recommendations for transitions between models may also
be described, either in a coexistence document or in a separate
document.
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.
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2.5. Message Processing
A Message Processing Model document defines a message format, which
is typically identified by a version field in an SNMP message header.
The document may also define a MIB module for use in message
processing and for instrumentation of version-specific interactions.
An SNMP engine includes one or more Message Processing Models, and
thus may support sending and receiving multiple versions of SNMP
messages.
2.6. Security
Some environments require secure protocol interactions. Security is
normally applied at two different stages:
- in the transmission/receipt of messages, and
- in the processing of the contents of messages.
For purposes of this document, "security" refers to message-level
security; "access control" refers to the security applied to protocol
operations.
Authentication, encryption, and timeliness checking are common
functions of message level security.
A security document describes a Security Model, the threats against
which the model protects, the goals of the Security Model, the
protocols which it uses to meet those goals, and it may define a MIB
module to describe the data used during processing, and to allow the
remote configuration of message-level security parameters, such as
passwords.
An SNMP engine may support multiple Security Models concurrently.
2.7. Access Control
During processing, it may be required to control access to managed
objects for operations.
An Access Control Model defines mechanisms to determine whether
access to a managed object should be allowed. An Access Control
Model may define a MIB module used during processing and to allow the
remote configuration of access control policies.
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2.8. 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.
2.9. Applications
An SNMP entity normally includes a number of applications.
Applications use the services of an SNMP engine to accomplish
specific tasks. They coordinate the processing of management
information operations, and may use SNMP messages to communicate with
other SNMP entities.
Applications documents describe the purpose of an application, the
services required of the associated SNMP engine, and the protocol
operations and informational model that the application uses to
perform management operations.
An application document defines which set of documents are used to
specifically define the structure of management information, textual
conventions, conformance requirements, and operations supported by
the application.
2.10. Structure of Management Information
Management information is viewed as a collection of managed objects,
residing in a virtual information store, termed the Management
Information Base (MIB). Collections of related objects are defined in
MIB modules.
It is the purpose of a Structure of Management Information document
to establish the syntax for defining objects, modules, and other
elements of managed information.
2.11. Textual Conventions
When designing a MIB module, it is often useful to define new types
similar to those defined in the SMI, but with more precise semantics,
or which have special semantics associated with them. These newly
defined types are termed textual conventions, and may defined in
separate documents, or within a MIB module.
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2.12. Conformance Statements
It may be useful to define the acceptable lower-bounds of
implementation, along with the actual level of implementation
achieved. It is the purpose of Conformance Statements to define the
notation used for these purposes.
2.13. Management Information Base Modules
MIB documents describe collections of managed objects which
instrument some aspect of a managed node.
2.13.1. SNMP Instrumentation MIBs
An SNMP MIB document may define a collection of managed objects which
instrument the SNMP protocol itself. In addition, MIB modules may be
defined within the documents which describe portions of the SNMP
architecture, such as the documents for Message processing Models,
Security Models, etc. for the purpose of instrumenting those Models,
and for the purpose of allowing remote configuration of the Model.
2.14. SNMP Framework Documents
This architecture is designed to allow an orderly evolution of
portions of SNMP Frameworks.
Throughout the rest of this document, the term "subsystem" refers to
an abstract and incomplete specification of a portion of a Framework,
that is further refined by a model specification.
A "model" describes a specific design of a subsystem, defining
additional constraints and rules for conformance to the model. A
model is sufficiently detailed to make it possible to implement the
specification.
An "implementation" is an instantiation of a subsystem, conforming to
one or more specific models.
SNMP version 1 (SNMPv1), is the original Internet-standard Network
Management Framework, as described in RFCs 1155, 1157, and 1212.
SNMP version 2 (SNMPv2), is the SNMPv2 Framework as derived from the
SNMPv1 Framework. It is described in RFCs 1902-1907. SNMPv2 has no
message definition.
The Community-based SNMP version 2 (SNMPv2c), is an experimental SNMP
Framework which supplements the SNMPv2 Framework, as described in
RFC1901. It adds the SNMPv2c message format, which is similar to the
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SNMPv1 message format.
SNMP version 3 (SNMPv3), is an extensible SNMP Framework which
supplements the SNMPv2 Framework, by supporting the following:
- a new SNMP message format,
- Security for Messages, and
- Access Control.
Other SNMP Frameworks, i.e., other configurations of implemented
subsystems, are expected to also be consistent with this
architecture.
3. Elements of the Architecture
This section describes the various elements of the architecture and
how they are named. There are three kinds of naming:
1) the naming of entities,
2) the naming of identities, and
3) the naming of management information.
This architecture also defines some names for other constructs that
are used in the documentation.
3.1. The Naming of Entities
The following figure shows detail about an SNMP entity and how
components within it are named.
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+-------------------------------------------------------------------+
| SNMP entity |
| |
| +-------------------------------------------------------------+ |
| | SNMP engine (identified by snmpEngineID) | |
| | | |
| | +------------+ +------------+ +-----------+ +-----------+ | |
| | | | | | | | | | | |
| | | Dispatcher | | Message | | Security | | Access | | |
| | | | | Processing | | Subsystem | | Control | | |
| | | | | Subsystem | | | | Subsystem | | |
| | | | | | | | | | | |
| | +------------+ +------------+ +-----------+ +-----------+ | |
| | | |
| +-------------------------------------------------------------+ |
| |
| +-------------------------------------------------------------+ |
| | Application(s) | |
| | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | Command | | Notification | | Proxy | | |
| | | Generator | | Receiver | | Forwarder | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | Command | | Notification | | Other | | |
| | | Responder | | Originator | | | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | |
| +-------------------------------------------------------------+ |
| |
+-------------------------------------------------------------------+
3.1.1. SNMP 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 provides services for sending and receiving messages,
authenticating and encrypting messages, and controlling access to
managed objects. There is a one-to-one association between an SNMP
engine and the SNMP entity which contains it.
The engine contains:
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1) a Dispatcher,
2) a Message Processing Subsystem,
3) a Security Subsystem, and
4) 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. Dispatcher
There is only one Dispatcher in an SNMP engine. It allows for
concurrent support of multiple versions of SNMP messages in the SNMP
engine. It does so by:
- sending and receiving SNMP messages to/from the network,
- determining the version of an SNMP message and interact with
the corresponding Message Processing Model,
- providing an abstract interface to SNMP applications for
delivery of a PDU to an application.
- providing an abstract interface for SNMP applications that
allows them to send a PDU to a remote SNMP entity.
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3.1.5. Message Processing Subsystem
The Message Processing Subsystem is responsible for preparing
messages for sending, and extracting data from received messages.
The Message Processing Subsystem potentially contains multiple
Message Processing Models as shown in the next figure.
* One or more Message Processing Models may be present.
+------------------------------------------------------------------+
| |
| Message Processing Subsystem |
| |
| +------------+ +------------+ +------------+ +------------+ |
| | * | | * | | * | | * | |
| | SNMPv3 | | SNMPv1 | | SNMPv2c | | Other | |
| | Message | | Message | | Message | | Message | |
| | Processing | | Processing | | Processing | | Processing | |
| | Model | | Model | | Model | | Model | |
| | | | | | | | | |
| +------------+ +------------+ +------------+ +------------+ |
| |
+------------------------------------------------------------------+
3.1.6. Message Processing Model
Each Message Processing Model defines the format of a particular
version of an SNMP message and coordinates the preparation and
extraction of each such version-specific messages.
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3.1.7. Security Subsystem
The Security Subsystem provides security services such as the
authentication and privacy of messages and potentially contains
multiple Security Models as shown in the following figure
* One or more Security Models may be present.
+------------------------------------------------------------------+
| |
| Security Subsystem |
| |
| +----------------+ +-----------------+ +-------------------+ |
| | * | | * | | * | |
| | User-Based | | Other | | Other | |
| | Security | | Security | | Security | |
| | Model | | Model | | Model | |
| | | | | | | |
| +----------------+ +-----------------+ +-------------------+ |
| |
+------------------------------------------------------------------+
3.1.8. 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.
3.1.9. 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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3.1.10. Access Control Subsystem
The Access Control Subsystem provides authorization services by means
of one or more Access Control Models.
+------------------------------------------------------------------+
| |
| Access Control Subsystem |
| |
| +---------------+ +-----------------+ +------------------+ |
| | * | | * | | * | |
| | View-Based | | Other | | Other | |
| | Access | | Access | | Access | |
| | Control | | Control | | Control | |
| | Model | | Model | | Model | |
| | | | | | | |
| +---------------+ +-----------------+ +------------------+ |
| |
+------------------------------------------------------------------+
3.1.11. Access Control Model
An Access Control Model defines a particular access decision function
in order to support decisions regarding access rights.
3.1.12. Applications
There are several types of applications, including:
- command generators, which monitor and manipulate management
data,
- command responders, which provide access to management data,
- notification originators, which initiate asynchronous messages,
- notification receivers, which process asynchronous messages,
and
- proxy forwarders, which forward messages between entities.
These applications make use of the services provided by the SNMP
engine.
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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.
* One or more models may be present.
(traditional SNMP manager)
+-------------------------------------------------------------------+
| +--------------+ +--------------+ +--------------+ SNMP entity |
| | NOTIFICATION | | NOTIFICATION | | COMMAND | |
| | ORIGINATOR | | RECEIVER | | GENERATOR | |
| | applications | | applications | | applications | |
| +--------------+ +--------------+ +--------------+ |
| ^ ^ ^ |
| | | | |
| v v v |
| +-------+--------+-----------------+ |
| ^ |
| | +---------------------+ +----------------+ |
| | | Message Processing | | Security | |
| Dispatcher v | Subsystem | | Subsystem | |
| +-------------------+ | +------------+ | | | |
| | PDU Dispatcher | | +->| v1MP * |<--->| +------------+ | |
| | | | | +------------+ | | | Other | | |
| | | | | +------------+ | | | Security | | |
| | | | +->| v2cMP * |<--->| | Model | | |
| | Message | | | +------------+ | | +------------+ | |
| | Dispatcher <--------->+ | | | |
| | | | | +------------+ | | +------------+ | |
| | | | +->| v3MP * |<--->| | User-based | | |
| | Transport | | | +------------+ | | | Security | | |
| | Mapping | | | +------------+ | | | Model | | |
| | (e.g RFC1906) | | +->| otherMP * |<--->| +------------+ | |
| +-------------------+ | +------------+ | | | |
| ^ +---------------------+ +----------------+ |
| | |
| v |
+-------------------------------------------------------------------+
+-----+ +-----+ +-------+
| UDP | | IPX | . . . | other |
+-----+ +-----+ +-------+
^ ^ ^
| | |
v v v
+------------------------------+
| Network |
+------------------------------+
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3.1.14. SNMP Agent
An SNMP entity containing one or more command responder and/or
notification originator applications (along with their associated
SNMP engine) has traditionally been called an SNMP agent.
+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v
+-----+ +-----+ +-------+
| UDP | | IPX | . . . | other |
+-----+ +-----+ +-------+ (traditional SNMP agent)
+-------------------------------------------------------------------+
| ^ |
| | +---------------------+ +----------------+ |
| | | Message Processing | | Security | |
| Dispatcher v | Subsystem | | Subsystem | |
| +-------------------+ | +------------+ | | | |
| | Transport | | +->| v1MP * |<--->| +------------+ | |
| | Mapping | | | +------------+ | | | Other | | |
| | (e.g. RFC1906) | | | +------------+ | | | Security | | |
| | | | +->| v2cMP * |<--->| | Model | | |
| | Message | | | +------------+ | | +------------+ | |
| | Dispatcher <--------->| +------------+ | | +------------+ | |
| | | | +->| v3MP * |<--->| | User-based | | |
| | | | | +------------+ | | | Security | | |
| | PDU Dispatcher | | | +------------+ | | | Model | | |
| +-------------------+ | +->| otherMP * |<--->| +------------+ | |
| ^ | +------------+ | | | |
| | +---------------------+ +----------------+ |
| v |
| +-------+-------------------------+---------------+ |
| ^ ^ ^ |
| | | | |
| v v v |
| +-------------+ +---------+ +--------------+ +-------------+ |
| | COMMAND | | ACCESS | | NOTIFICATION | | PROXY * | |
| | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | |
| | application | | | | applications | | application | |
| +-------------+ +---------+ +--------------+ +-------------+ |
| ^ ^ |
| | | |
| v v |
| +----------------------------------------------+ |
| | MIB instrumentation | SNMP entity |
+-------------------------------------------------------------------+
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3.2. The Naming of Identities
principal
^
|
|
+----------------------------|-------------+
| SNMP engine v |
| +--------------+ |
| | | |
| +-----------------| securityName |---+ |
| | Security Model | | | |
| | +--------------+ | |
| | ^ | |
| | | | |
| | v | |
| | +------------------------------+ | |
| | | | | |
| | | Model | | |
| | | Dependent | | |
| | | Security ID | | |
| | | | | |
| | +------------------------------+ | |
| | ^ | |
| | | | |
| +-------------------------|----------+ |
| | |
| | |
+----------------------------|-------------+
|
v
wire
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.
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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) | |
| | | |
| | +-------------+ +------------+ +-----------+ +-----------+ | |
| | | | | | | | | | | |
| | | Dispatcher | | Message | | Security | | Access | | |
| | | | | Processing | | Subsystem | | Control | | |
| | | | | Subsystem | | | | Subsystem | | |
| | | | | | | | | | | |
| | +-------------+ +------------+ +-----------+ +-----------+ | |
| | | |
| +------------------------------------------------------------+ |
| |
| +------------------------------------------------------------+ |
| | Command Responder Application | |
| | (contextEngineID, example: abcd) | |
| | | |
| | example contextNames: | |
| | | |
| | "bridge1" "bridge2" "" (default) | |
| | --------- --------- ------------ | |
| | | | | | |
| +------|------------------|-------------------|--------------+ |
| | | | |
| +------|------------------|-------------------|--------------+ |
| | MIB | instrumentation | | | |
| | +---v------------+ +---v------------+ +----v-----------+ | |
| | | context | | context | | context | | |
| | | | | | | | | |
| | | +------------+ | | +------------+ | | +------------+ | | |
| | | | bridge MIB | | | | bridge MIB | | | | 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
the management information at device-X, the contextName (device-X),
the managed object type (ifDescr), and the instance ("1").
Each context has (at least) one unique identification within the
management domain. The same item of management information can exist
in multiple contexts. An item of management information may have
multiple unique identifications. This occurs when an item of
management information exists in multiple contexts, and this also
occurs when a context has multiple unique identifications.
The combination of a contextEngineID and a contextName unambiguously
identifies a context within an administrative domain; note that there
may be multiple unique combinations of contextEngineID and
contextName that unambiguously identify the same context.
3.3.2. contextEngineID
Within an administrative domain, a contextEngineID uniquely
identifies an SNMP entity that may realize an instance of a context
with a particular contextName.
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3.3.3. contextName
A contextName is used to name a context. Each contextName MUST be
unique within an SNMP entity.
3.3.4. scopedPDU
A scopedPDU is a block of data containing a contextEngineID, a
contextName, and a PDU.
The PDU is an SNMP Protocol Data Unit containing information named in
the context which is unambiguously identified within an
administrative domain by the combination of the contextEngineID and
the contextName. See, for example, RFC1905 for more information about
SNMP PDUs.
3.4. Other Constructs
3.4.1. maxSizeResponseScopedPDU
The maxSizeResponseScopedPDU is the maximum size of a scopedPDU to be
included in a response message. Note that the size of a scopedPDU
does not include the size of the SNMP message header.
3.4.2. Local Configuration Datastore
The subsystems, models, and applications within an SNMP entity may
need to retain their own sets of configuration information.
Portions of the configuration information may be accessible as
managed objects.
The collection of these sets of information is referred to as an
entity's Local Configuration Datastore (LCD).
3.4.3. securityLevel
This architecture recognizes three levels of security:
- without authentication and without privacy (noAuthNoPriv)
- with authentication but without privacy (authNoPriv)
- with authentication and with privacy (authPriv)
These three values are ordered such that noAuthNoPriv is less than
authNoPriv and authNoPriv is less than authPriv.
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Every message has an associated securityLevel. All Subsystems
(Message Processing, Security, Access Control) and applications are
required to either supply a value of securityLevel or to abide by the
supplied value of securityLevel while processing the message and its
contents.
4. Abstract Service Interfaces.
Abstract service interfaces have been defined to describe the
conceptual interfaces between the various subsystems within an SNMP
entity.
These abstract service interfaces are defined by a set of primitives
that define the services provided and the abstract data elements that
are to be passed when the services are invoked. This section lists
the primitives that have been defined for the various subsystems.
4.1. Common Primitives
These primitive(s) are provided by multiple Subsystems.
4.1.1. Release State Reference Information
All Subsystems which pass stateReference information also provide a
primitive to release the memory that holds the referenced state
information:
stateRelease(
IN stateReference -- handle of reference to be released
)
4.2. Dispatcher Primitives
The Dispatcher typically provides services to the SNMP applications
via its PDU Dispatcher. This section describes the primitives
provided by the PDU Dispatcher.
4.2.1. Generate Outgoing Request or Notification
The PDU Dispatcher provides the following primitive for an
application to send an SNMP Request or Notification to another SNMP
entity:
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statusInformation = -- sendPduHandle if success
-- errorIndication if failure
sendPdu(
IN transportDomain -- transport domain to be used
IN transportAddress -- transport address to be used
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model to use
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN contextEngineID -- data from/at this entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN expectResponse -- TRUE or FALSE
)
4.2.2. Process Incoming Request or Notification PDU
The PDU Dispatcher provides the following primitive to pass an
incoming SNMP PDU to an application:
processPdu( -- process Request/Notification PDU
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model in use
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security
IN contextEngineID -- data from/at this SNMP entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN maxSizeResponseScopedPDU -- maximum size of the Response PDU
IN stateReference -- reference to state information
) -- needed when sending a response
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4.2.3. Generate Outgoing Response
The PDU Dispatcher provides the following primitive for an
application to return an SNMP Response PDU to the PDU Dispatcher:
returnResponsePdu(
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model in use
IN securityName -- on behalf of this principal
IN securityLevel -- same as on incoming request
IN contextEngineID -- data from/at this SNMP entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN maxSizeResponseScopedPDU -- maximum size of the Response PDU
IN stateReference -- reference to state information
-- as presented with the request
IN statusInformation -- success or errorIndication
) -- error counter OID/value if error
4.2.4. Process Incoming Response PDU
The PDU Dispatcher provides the following primitive to pass an
incoming SNMP Response PDU to an application:
processResponsePdu( -- process Response PDU
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model in use
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security
IN contextEngineID -- data from/at this SNMP entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN statusInformation -- success or errorIndication
IN sendPduHandle -- handle from sendPdu
)
4.2.5. Registering Responsibility for Handling SNMP PDUs.
Applications can register/unregister responsibility for a specific
contextEngineID, for specific pduTypes, with the PDU Dispatcher
according to these primitives:
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statusInformation = -- success or errorIndication
registerContextEngineID(
IN contextEngineID -- take responsibility for this one
IN pduType -- the pduType(s) to be registered
)
unregisterContextEngineID(
IN contextEngineID -- give up responsibility for this one
IN pduType -- the pduType(s) to be unregistered
)
Note that realizations of the registerContextEngineID and
unregisterContextEngineID abstract service interfaces may provide
implementation-specific ways for applications to register/deregister
responsiblity for all possible values of the contextEngineID or
pduType parameters.
4.3. Message Processing Subsystem Primitives
The Dispatcher interacts with a Message Processing Model to process a
specific version of an SNMP Message. This section describes the
primitives provided by the Message Processing Subsystem.
4.3.1. Prepare Outgoing SNMP Request or Notification Message
The Message Processing Subsystem provides this service primitive for
preparing an outgoing SNMP Request or Notification Message:
statusInformation = -- success or errorIndication
prepareOutgoingMessage(
IN transportDomain -- transport domain to be used
IN transportAddress -- transport address to be used
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model to use
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN contextEngineID -- data from/at this entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN expectResponse -- TRUE or FALSE
IN sendPduHandle -- the handle for matching
-- incoming responses
OUT destTransportDomain -- destination transport domain
OUT destTransportAddress -- destination transport address
OUT outgoingMessage -- the message to send
OUT outgoingMessageLength -- its length
)
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4.3.2. Prepare an Outgoing SNMP Response Message
The Message Processing Subsystem provides this service primitive for
preparing an outgoing SNMP Response Message:
result = -- SUCCESS or FAILURE
prepareResponseMessage(
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- same as on incoming request
IN securityName -- same as on incoming request
IN securityLevel -- same as on incoming request
IN contextEngineID -- data from/at this SNMP entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN maxSizeResponseScopedPDU -- maximum size of the Response PDU
IN stateReference -- reference to state information
-- as presented with the request
IN statusInformation -- success or errorIndication
-- error counter OID/value if error
OUT destTransportDomain -- destination transport domain
OUT destTransportAddress -- destination transport address
OUT outgoingMessage -- the message to send
OUT outgoingMessageLength -- its length
)
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4.3.3. Prepare Data Elements from an Incoming SNMP Message
The Message Processing Subsystem provides this service primitive for
preparing the abstract data elements from an incoming SNMP message:
result = -- SUCCESS or errorIndication
prepareDataElements(
IN transportDomain -- origin transport domain
IN transportAddress -- origin transport address
IN wholeMsg -- as received from the network
IN wholeMsgLength -- as received from the network
OUT messageProcessingModel -- typically, SNMP version
OUT securityModel -- Security Model to use
OUT securityName -- on behalf of this principal
OUT securityLevel -- Level of Security requested
OUT contextEngineID -- data from/at this entity
OUT contextName -- data from/in this context
OUT pduVersion -- the version of the PDU
OUT PDU -- SNMP Protocol Data Unit
OUT pduType -- SNMP PDU type
OUT sendPduHandle -- handle for matched request
OUT maxSizeResponseScopedPDU -- maximum size of the Response PDU
OUT statusInformation -- success or errorIndication
-- error counter OID/value if error
OUT stateReference -- reference to state information
-- to be used for possible Response
)
4.4. Access Control Subsystem Primitives
Applications are the typical clients of the service(s) of the Access
Control Subsystem.
The following primitive is provided by the Access Control Subsystem
to check if access is allowed:
statusInformation = -- success or errorIndication
isAccessAllowed(
IN securityModel -- Security Model in use
IN securityName -- principal who wants to access
IN securityLevel -- Level of Security
IN viewType -- read, write, or notify view
IN contextName -- context containing variableName
IN variableName -- OID for the managed object
)
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4.5. Security Subsystem Primitives
The Message Processing Subsystem is the typical client of the
services of the Security Subsystem.
4.5.1. Generate a Request or Notification Message
The Security Subsystem provides the following primitive to generate a
Request or Notification message:
statusInformation =
generateRequestMsg(
IN messageProcessingModel -- typically, SNMP version
IN globalData -- message header, admin data
IN maxMessageSize -- of the sending SNMP entity
IN securityModel -- for the outgoing message
IN securityEngineID -- authoritative SNMP entity
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN scopedPDU -- message (plaintext) payload
OUT securityParameters -- filled in by Security Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of the generated message
)
4.5.2. Process Incoming Message
The Security Subsystem provides the following primitive to process an
incoming message:
statusInformation = -- errorIndication or success
-- error counter OID/value if error
processIncomingMsg(
IN messageProcessingModel -- typically, SNMP version
IN maxMessageSize -- of the sending SNMP entity
IN securityParameters -- for the received message
IN securityModel -- for the received message
IN securityLevel -- Level of Security
IN wholeMsg -- as received on the wire
IN wholeMsgLength -- length as received on the wire
OUT securityEngineID -- identification of the principal
OUT securityName -- identification of the principal
OUT scopedPDU, -- message (plaintext) payload
OUT maxSizeResponseScopedPDU -- maximum size of the Response PDU
OUT securityStateReference -- reference to security state
) -- information, needed for response
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4.5.3. Generate a Response Message
The Security Subsystem provides the following primitive to generate a
Response message:
statusInformation =
generateResponseMsg(
IN messageProcessingModel -- typically, SNMP version
IN globalData -- message header, admin data
IN maxMessageSize -- of the sending SNMP entity
IN securityModel -- for the outgoing message
IN securityEngineID -- authoritative SNMP entity
IN securityName -- on behalf of this principal
IN securityLevel -- for the outgoing message
IN scopedPDU -- message (plaintext) payload
IN securityStateReference -- reference to security state
-- information from original request
OUT securityParameters -- filled in by Security Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of the generated message
)
4.6. Common Primitives
These primitive(s) are provided by multiple Subsystems.
4.6.1. Release State Reference Information
All Subsystems which pass stateReference information also provide a
primitive to release the memory that holds the referenced state
information:
stateRelease(
IN stateReference -- handle of reference to be released
)
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4.7. Scenario Diagrams
4.7.1. Command Generator or Notification Originator
This diagram shows how a Command Generator or Notification Originator
application requests that a PDU be sent, and how the response is
returned (asynchronously) to that application.
Command Dispatcher Message Security
Generator | Processing Model
| | Model |
| sendPdu | | |
|------------------->| | |
| | prepareOutgoingMessage | |
: |----------------------->| |
: | | generateRequestMsg |
: | |-------------------->|
: | | |
: | |<--------------------|
: | | |
: |<-----------------------| |
: | | |
: |------------------+ | |
: | Send SNMP | | |
: | Request Message | | |
: | to Network | | |
: | v | |
: : : : :
: : : : :
: : : : :
: | | | |
: | Receive SNMP | | |
: | Response Message | | |
: | from Network | | |
: |<-----------------+ | |
: | | |
: | prepareDataElements | |
: |----------------------->| |
: | | processIncomingMsg |
: | |-------------------->|
: | | |
: | |<--------------------|
: | | |
: |<-----------------------| |
| processResponsePdu | | |
|<-------------------| | |
| | | |
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4.7.2. Scenario Diagram for a Command Responder Application
This diagram shows how a Command Responder or Notification Receiver
application registers for handling a pduType, how a PDU is dispatched
to the application after a SNMP message is received, and how the
Response is (asynchronously) send back to the network.
Command Dispatcher Message Security
Responder | Processing Model
| | Model |
| | | |
| registerContextEngineID | | |
|------------------------>| | |
|<------------------------| | | |
| | Receive SNMP | | |
: | Message | | |
: | from Network | | |
: |<-------------+ | |
: | | |
: |prepareDataElements | |
: |------------------->| |
: | | processIncomingMsg |
: | |------------------->|
: | | |
: | |<-------------------|
: | | |
: |<-------------------| |
| processPdu | | |
|<------------------------| | |
| | | |
: : : :
: : : :
| returnResponsePdu | | |
|------------------------>| | |
: | prepareResponseMsg | |
: |------------------->| |
: | |generateResponseMsg |
: | |------------------->|
: | | |
: | |<-------------------|
: | | |
: |<-------------------| |
: | | |
: |--------------+ | |
: | Send SNMP | | |
: | Message | | |
: | to Network | | |
: | v | |
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5. Managed Object Definitions for SNMP Management Frameworks
SNMP-FRAMEWORK-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
OBJECT-IDENTITY,
snmpModules FROM SNMPv2-SMI
TEXTUAL-CONVENTION FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF;
snmpFrameworkMIB MODULE-IDENTITY
LAST-UPDATED "9709300000Z" -- 30 September 1997
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
Mail Stop: Durham
35 Industrial Way
Rochester, NH 03867-5005
USA
email: dbh@cabletron.com
phone: +1 603-337-7357
Co-editor Randy Presuhn
BMC Software, Inc.
postal: 1190 Saratoga Avenue
Suite 130
San Jose, CA 95129
USA
email: rpresuhn@bmc.com
phone: +1 408-556-0720
Co-editor: Bert Wijnen
IBM T.J. Watson Research
postal: Schagen 33
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3461 GL Linschoten
Netherlands
email: wijnen@vnet.ibm.com
phone: +31 348-432-794
"
DESCRIPTION "The SNMP Management Architecture MIB"
::= { snmpModules 7 } -- DBH: check if this number is indeed OK
-- Textual Conventions used in the SNMP Management Architecture ***
SnmpEngineID ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "An SNMP engine's administratively-unique identifier.
The value for this object may not be all zeros or
all 'ff'H or the empty (zero length) string.
The initial value for this object may be configured
via an operator console entry or via an algorithmic
function. In the latter case, the following
example algorithm is recommended.
In cases where there are multiple engines on the
same system, the use of this algorithm is NOT
appropriate, as it would result in all of those
engines ending up with the same ID value.
1) The very first bit is used to indicate how the
rest of the data is composed.
0 - as defined by enterprise using former methods
that existed before SNMPv3. See item 2 below.
1 - as defined by this architecture, see item 3
below.
Note that this allows existing uses of the
engineID (also known as AgentID [RFC1910]) to
co-exist with any new uses.
2) The snmpEngineID has a length of 12 octets.
The first four octets are set to the binary
equivalent of the agent's SNMP management
private enterprise number as assigned by the
Internet Assigned Numbers Authority (IANA).
For example, if Acme Networks has been assigned
{ enterprises 696 }, the first four octets would
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be assigned '000002b8'H.
The remaining eight octets are determined via
one or more enterprise-specific methods. Such
methods must be designed so as to maximize the
possibility that the value of this object will
be unique in the agent's administrative domain.
For example, it may be the IP address of the SNMP
entity, or the MAC address of one of the
interfaces, with each address suitably padded
with random octets. If multiple methods are
defined, then it is recommended that the first
octet indicate the method being used and the
remaining octets be a function of the method.
3) The length of the octet strings varies.
The first four octets are set to the binary
equivalent of the agent's SNMP management
private enterprise number as assigned by the
Internet Assigned Numbers Authority (IANA).
For example, if Acme Networks has been assigned
{ enterprises 696 }, the first four octets would
be assigned '000002b8'H.
The very first bit is set to 1. For example, the
above value for Acme Networks now changes to be
'800002b8'H.
The fifth octet indicates how the rest (6th and
following octets) are formatted. The values for
the fifth octet are:
0 - reserved, unused.
1 - IPv4 address (4 octets)
lowest non-special IP address
2 - IPv6 address (16 octets)
lowest non-special IP address
3 - MAC address (6 octets)
lowest IEEE MAC address, canonical
order
4 - Text, administratively assigned
Maximum remaining length 27
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5 - Octets, administratively assigned
Maximum remaining length 27
6-127 - reserved, unused
127-255 - as defined by the enterprise
Maximum remaining length 27
"
SYNTAX OCTET STRING (SIZE(1..32))
SnmpSecurityModel ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "An identifier that uniquely identifies a
securityModel of the Security Subsystem within the
SNMP Management Architecture.
The values for securityModel are allocated as
follows:
- The zero value is reserved.
- Values between 1 and 255, inclusive, are reserved
for standards-track Security Models and are
managed by the Internet Assigned Numbers Authority
(IANA).
- Values greater than 255 are allocated to
enterprise-specific Security Models. An
enterprise-specific securityModel value is defined
to be:
enterpriseID * 256 + security model within
enterprise
For example, the fourth Security Model defined by
the enterprise whose enterpriseID is 1 would be
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
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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 'any'
1 reserved for SNMPv1
2 reserved for SNMPv2c
3 User-Based Security Model (USM)
"
SYNTAX INTEGER(0..2147483647)
SnmpMessageProcessingModel ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "An identifier that uniquely identifies a Message
Processing Model of the Message Processing
Subsystem within a SNMP Management Architecture.
The values for messageProcessingModel are
allocated as follows:
- Values between 0 and 255, inclusive, are
reserved for standards-track Message Processing
Models and are managed by the Internet Assigned
Numbers Authority (IANA).
- Values greater than 255 are allocated to
enterprise-specific Message Processing Models.
An enterprise messageProcessingModel value is
defined to be:
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enterpriseID * 256 +
messageProcessingModel within enterprise
For example, the fourth Message Processing Model
defined by the enterprise whose enterpriseID
is 1 would be 260.
The eight bits allow a maximum of 256 standards
based Message Processing Models. Similarly, they
allow a maximum 256 Message Processing Models
per enterprise.
It is believed that the assignment of new
messageProcessingModel values will be rare
in practice because the larger the number of
simultaneously utilized Message Processing Models,
the larger the chance that interoperability
will suffer. 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 256
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
messageProcessingModels. This limits the ability
to define new proprietary implementations of
Message Processing 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
messageProcessingModel defined for use with SNMP.
They are as follows:
0 reserved for SNMPv1
1 reserved for SNMPv2c
2 reserved for SNMPv2u and SNMPv2*
3 reserved for SNMPv3
"
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SYNTAX INTEGER(0..2147483647)
SnmpSecurityLevel ::= 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:
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 less than authNoPriv and
authNoPriv is less 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 transformation format
described in [RFC2044].
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.
When it is necessary to represent a newline,
the control code sequence CR LF should be used.
The use of leading or trailing white space should
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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 encoding is identical to the
US-ASCII encoding.
Note that when this TC is used for an object that
is used or envisioned to be used as an index, then
a SIZE restriction must be specified so that the
number sub-identifiers for any object instance
do not exceed the limit of 128, as defined by
[RFC1905].
"
SYNTAX OCTET STRING (SIZE (0..255))
-- Administrative assignments ***************************************
snmpFrameworkAdmin
OBJECT IDENTIFIER ::= { snmpFrameworkMIB 1 }
snmpFrameworkMIBObjects
OBJECT IDENTIFIER ::= { snmpFrameworkMIB 2 }
snmpFrameworkMIBConformance
OBJECT IDENTIFIER ::= { snmpFrameworkMIB 3 }
-- 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 INTEGER (1..2147483647)
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of times that the SNMP engine has
(re-)initialized itself since its initial
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configuration.
"
::= { snmpEngine 2 }
snmpEngineTime OBJECT-TYPE
SYNTAX INTEGER (0..2147483647)
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of seconds since the SNMP engine last
incremented the snmpEngineBoots object.
"
::= { snmpEngine 3 }
snmpEngineMaxMessageSize OBJECT-TYPE
SYNTAX INTEGER (484..2147483647)
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The maximum length in octets of an SNMP message
which this SNMP engine can send or receive and
process, determined as the minimum of the maximum
message size values supported among all of the
transports available to and supported by the engine.
"
::= { snmpEngine 4 }
-- Registration Points for Authentication and Privacy Protocols **
snmpAuthProtocols OBJECT-IDENTITY
STATUS current
DESCRIPTION "Registration point for standards-track
authentication protocols used in SNMP Management
Frameworks.
"
::= { snmpFrameworkAdmin 1 }
snmpPrivProtocols OBJECT-IDENTITY
STATUS current
DESCRIPTION "Registration point for standards-track privacy
protocols used in SNMP Management Frameworks.
"
::= { snmpFrameworkAdmin 2 }
-- Conformance information ******************************************
snmpFrameworkMIBCompliances
OBJECT IDENTIFIER ::= {snmpFrameworkMIBConformance 1}
snmpFrameworkMIBGroups
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OBJECT IDENTIFIER ::= {snmpFrameworkMIBConformance 2}
-- compliance statements
snmpFrameworkMIBCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION "The compliance statement for SNMP engines which
implement the SNMP Management Framework MIB.
"
MODULE -- this module
MANDATORY-GROUPS { snmpEngineGroup }
::= { snmpFrameworkMIBCompliances 1 }
-- units of conformance
snmpEngineGroup OBJECT-GROUP
OBJECTS {
snmpEngineID,
snmpEngineBoots,
snmpEngineTime,
snmpEngineMaxMessageSize
}
STATUS current
DESCRIPTION "A collection of objects for identifying and
determining the configuration and current timeliness
values of an SNMP engine.
"
::= { snmpFrameworkMIBGroups 1 }
END
6. Security Considerations
This document describes how an implementation can include a Security
Model to protect management messages and an Access Control Model to
control 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) used.
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 an implementation to
ensure that:
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1) an implementation 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.
7. 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
Mail Stop: Durham
35 Industrial Way
Rochester, NH 03867-5005
USA
email: dbh@cabletron.com
phone: +1 603-337-7357
Co-editor Randy Presuhn
BMC Software, Inc.
postal: 1190 Saratoga Avenue
Suite 130
San Jose, CA 95129
USA
email: rpresuhn@bmc.com
phone: +1 408-556-0720
8. Acknowledgements
This document is the result of the efforts of the SNMPv3 Working
Group. Some special thanks are in order to the following SNMPv3 WG
members:
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Dave Battle (SNMP Research, Inc.)
Uri Blumenthal (IBM T.J. Watson Research Center)
Jeff Case (SNMP Research, Inc.)
John Curran (BBN)
T. Max Devlin (Hi-TECH Connections)
John Flick (Hewlett Packard)
David Harrington (Cabletron Systems Inc.)
N.C. Hien (IBM T.J. Watson Research Center)
Dave Levi (SNMP Research, Inc.)
Louis A Mamakos (UUNET Technologies Inc.)
Paul Meyer (Secure Computing Corporation)
Keith McCloghrie (Cisco Systems)
Russ Mundy (Trusted Information Systems, Inc.)
Bob Natale (ACE*COMM Corporation)
Mike O'Dell (UUNET Technologies Inc.)
Dave Perkins (DeskTalk)
Peter Polkinghorne (Brunel University)
Randy Presuhn (BMC Software, Inc.)
David Reid (SNMP Research, Inc.)
Shawn Routhier (Epilogue)
Juergen Schoenwaelder (TU Braunschweig)
Bob Stewart (Cisco Systems)
Bert Wijnen (IBM T.J. Watson Research Center)
The document is based on recommendations of the IETF Security and
Administrative Framework Evolution for SNMP Advisory Team. Members
of that Advisory Team were:
David Harrington (Cabletron Systems Inc.)
Jeff Johnson (Cisco Systems)
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 Center)
As recommended by the Advisory Team and the SNMPv3 Working Group
Charter, the design incorporates as much as practical from previous
RFCs and drafts. As a result, special thanks are due to the authors
of previous designs known as SNMPv2u and SNMPv2*:
Jeff Case (SNMP Research, Inc.)
David Harrington (Cabletron Systems Inc.)
David Levi (SNMP Research, Inc.)
Keith McCloghrie (Cisco Systems)
Brian O'Keefe (Hewlett Packard)
Marshall T. Rose (Dover Beach Consulting)
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Jon Saperia (BGS Systems Inc.)
Steve Waldbusser (International Network Services)
Glenn W. Waters (Bell-Northern Research Ltd.)
9. 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 1902, 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.
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[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 SNMP-standard Network Management 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.
[RFC2044] Yergeau, F., "UTF-8, a transformation format of Unicode and
ISO 10646", RFC 2044, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[SNMP-MPD] The SNMPv3 Working Group, Case, J., Harrington, D.,
Wijnen, B., "Message Processing and Dispatching for the Simple
Network Management Protocol (SNMP)", draft-ietf-snmpv3-mpc-03.txt,
August 1997.
[SNMP-USM] The SNMPv3 Working Group, Blumenthal, U., Wijnen, B., "The
User-Based Security Model for Version 3 of the Simple Network
Management Protocol (SNMPv3)", draft-ietf-snmpv3-usm-01.txt,
August 1997.
[SNMP-ACM] The SNMPv3 Working Group, Wijnen, B., Presuhn, R.,
McCloghrie, K., "View-based Access Control Model for the Simple
Network Management Protocol (SNMP)", draft-ietf-snmpv3-acm-02.txt,
August 1997.
[SNMP-APPL] The SNMPv3 Working Group, Levi, D. B., Meyer, P.,
Stewart, B., "SNMPv3 Applications",
<draft-ietf-snmpv3-appl-01.txt>, August 1997
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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.
SNMPv1 and SNMPv2c are two SNMP frameworks which use communities to
provide trivial authentication and access control. SNMPv1 and SNMPv2c
Frameworks can coexist with Frameworks designed according to this
architecture, and modified versions of SNMPv1 and SNMPv2c Frameworks
could be designed to meet the requirements of 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 these 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 dependent on 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 securityLevel 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 protocols to be used
concurrently within an implementation of the model. Each Security
Model defines how to determine which protocol to use, given the
securityLevel 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 protocols
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
A Message Processing Model requests that a Security Model:
- verifies that the message has not been altered,
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- authenticates the identification of the principal for whom the
message was generated.
- decrypts the message if it was encrypted.
Additional requirements may be defined by the model, and additional
services may be provided by the model, but the model is constrained
to use the following primitives for transferring data between
subsystems. Implementations are not so constrained.
A Message Processing Model uses the processMsg primitive as described
in section 4.5.
A.1.4. Security MIBs
Each Security Model defines the MIB module(s) required for security
processing, including any MIB module(s) required for the security
protocol(s) supported. The MIB module(s) SHOULD be defined
concurrently with the procedures which use the MIB module(s). The
MIB module(s) are subject to normal access control rules.
The mapping between the model-dependent security ID and the
securityName MUST be able to be determined using SNMP, if the model-
dependent MIB is instantiated and if access control policy allows
access.
A.1.5. Cached Security Data
For each message received, the Security Model caches the state
information such that a Response message can be generated using the
same security information, even if the Local Configuration Datastore
is altered between the time of the incoming request and the outgoing
response.
A Message Processing Model has the responsibility for explicitly
releasing the cached data if such data is no longer needed. To enable
this, an abstract securityStateReference data element is passed from
the Security Model to the Message Processing Model.
The cached security data may be implicitly released via the
generation of a response, or explicitly released by using the
stateRelease primitive, as described in section 4.1.
A.2. Message Processing Model Design Requirements
An SNMP engine contains a Message Processing Subsystem which may
contain multiple Message Processing Models.
The Message Processing Model MUST always (conceptually) pass the
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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 Dispatcher in the
SNMP engine determines the version of the SNMP message and interacts
with the corresponding Message Processing Model to determine the
abstract data elements.
A Message Processing Model specifies the SNMP Message format it
supports and describes how to determine the values of the abstract
data elements (like msgID, msgMaxSize, msgFlags,
msgSecurityParameters, securityModel, securityLevel etc). A Message
Processing Model interacts with a Security Model to provide security
processing for the message using the processMsg primitive, as
described in section 4.5.
A.2.2. Sending an SNMP Message to the Network
The Dispatcher in the SNMP engine interacts with a Message Processing
Model to prepare an outgoing message. For that it uses the following
primitives:
- for requests and notifications: prepareOutgoingMessage, as
described in section 4.4
- for response messages: prepareResponseMessage, as described in
section 4.4
A Message Processing Model, when preparing an Outgoing SNMP Message,
interacts with a Security Model to secure the message. For that it
uses the following primitives:
- for requests and notifications: generateRequestMsg, as
described in section 4.5.
- for response messages: generateResponseMsg as described in
section 4.5.
Once the SNMP message is prepared by a Message Processing Model,
the Dispatcher sends the message to the desired address using the
appropriate transport.
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
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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.
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 module(s)
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
as described in section 4.2.
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 if a
response is expected, then the appropriate information is cached such
that a later response can be associated to this message, and can then
be returned to the application. A sendPduHandle is returned to the
application so it can later correspond the response with this message
as well.
A.3.2. Applications that Receive Responses
The SNMP engine matches the incoming response messages to outstanding
messages sent by this SNMP engine, and forwards the response to the
associated application using the processResponsePdu primitive, as
described in section 4.2.
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
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the message should be given.
An Application that wishes to receive asynchronous messages registers
itself with the engine using the primitive registerContextEngineID as
described in section 4.2.
An Application that wishes to stop receiving asynchronous messages
should unregister itself with the SNMP engine using the primitive
unregisterContextEngineID as described in section 4.2.
Only one registration per combination of PDU type and 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
combination of 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, as described in section 4.2.
A.3.4. Applications that Send Responses
Request operations require responses. An application sends a
response via the returnResponsePdu primitive, as described in section
4.2.
The contextEngineID, contextName, securityModel, securityName,
securityLevel, 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 Access Control Model must provide the primitive isAccessAllowed.
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B. Issues
The change log will be deleted for last call; the issues list will be
deleted when it is time to publish as an RFC.
B.1. Showstoppers
B.2. Open Issues
- we need a mechanism for a manager to be able to discover what
securityModels are supported by a particular implementation
B.3. Resolved Issues
. contextEngineID in reportPDU = snmpEngineID of report generator
. returnResponsePdu - are all parameters needed? overrides allowed?
all parameters kept for future flexibility
overrides not supported by SNMPv3
. use of IN/OUT indicators in primitives accepted
. NT/Unix-like access control - can be defined as future model
. user-friendly names? yes, but with limits
. SnmpAdminString as index? yes, but restrict sizes
. need both MMS and maxSizeResponseScopedPDU? yes.
. synchronous vs. asynchronous primitives? synchronous preferred
. should we change MIB naming? no, it is acceptable
. is it ok that USM is bound to SNMPv3? while undesirable, it is
acceptable. A cleaner model may be defined in the future.
. should securityModel "any" be supported? for ACM use, not SNMPv3
. what defines SNMPv3? a document will be published after Munich
. Is an application-level handle needed for request/response matching?
yes. create sendPduHandle
. Is wild card contextEngineID/pduType registration needed? No. This is
an internal interface, and wild carding can be supported by an
implementation, but is not required in the standard.
. Should indices be integers or SnmpAdminStrings? SnmpAdminStrings
is the consensus.
. Should protocols be identified as OIDs or Integers? OIDs
. terminology:
securityLevel rather than LoS
msgXXXX to identify message fields in SNMPv3
. OID or Integer for auth/priv protocol identifiers
Consensus: use OID
. Is Glossary needed to describe primitive parameters, or is the
expanded template adequate for this purpose?
Consensus: Terms are basically all defined in section 3.
. state_reference releases
Consensus: documents checked; we think it is OK now
. new SnmpEngineID format rules to be discussed yet.
Consensus: Limit size to be 1..32
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. needs changes to meet STDGUIDE guidelines
We think we're meeting them now
. 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!!
Consensus: Nobody picked up on this, so it seems not needed.
. Do we need a mechanism to discover securityModels supported
Can be decided after Munich
. add a "Decision History" section (as an appendix?)
Can be decided after Munich
B.3.1. 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 UTF-8 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.
B.4. Change Log
Current version
- Changed MIB objects from Integer32 to INTEGER to match USM
fields.
- changed "network management" to simply "management"
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- added caveat to EngineID selection algorithm
- Added language in register/deregister ASI to permit
implementation-specific wildcarding, as agreed in Munich.
- re-worded description of maxSizeResponseScopedPDU
- added RFC 2119 words and referece
- added reference for UTF-8
- removed "none" reserved value from SnmpSecurityModel textual
convention, changed "any" value from 255 to zero.
- modifications to SnmpAdminString agreed to in Munich meeting
- updated editor list
- converted to nroff, with some minor layout changes
[version 4.14]
. formatting
. pagination
[version 4.13]
. new acknowledgements
. updated references
. updated issues list
. ordered security, editors, acknowledgements, references sections
. checked line lengths
[version 4.12]
. cleanup
. added expectResponse to processIncomingMsg to address Levi-raised
concern
. acknowledgements
. MIB checked by SMICng
. post to snmpv3 mailing list
[version 4.11]
. Change Primitives between MP and SEC to try and address the issue
of architectural binding to message format.
. Added securityName and securityLevel to the returnResponsePdu
primitive so that architecturally it could be different for a
request and a response.
. Rename processMsg primitive to processIncomingMsg
[version 4.10]
. spell check
[version 4.9]
. editorial changes
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. fix SnmpEngineID TC
. add a note to SnmpAdminString
. rename title of section 1.1
. expand description of Dispatcher a bit
[version 4.8]
. Added parameter pduVersion on primitives:
sendPdu
processPdu
returnResponsePdu
processResponsePdu
prepareDataElements
prepareOutgoingMessage
prepareResponseMessage
. Added parameter messageProcessingModel on the primitive:
processPdu
processResponsePdu
returnResponsePdu
. Removed messageProcessingModel parameter from primitives:
registerContextEngineID
unregisterContextEngineID
. Renamed SNMP Version Multiplexer to Dispatcher
. Renamed Version Multiplexer to Message Multiplexer
. Renamed Application Multiplexer to PDU Dispatcher
. Rearranged some parameters in various Primitives so the sequence
of parameters is now more consistent.
[version 4.7]
. editorial cleanup
. changed asterisk text
. modified snmpv3 framework description to eliminate dependencies
. reorder 4.2.x to reflect transaction order
. changed SnmpEngineID size to 1..32
[version 4.6]
. Changes to use synchronous primitives where possible
. Changes to describe SNMP Version Multiplexer
. Remove (empty) glossary
. Redraw documentation figure
. Redraw Operational Overview Figure
. Remove old section 4 (Architectural Elements of Procedure)
These moved to the MP document into the SNMP Version Multiplexer
section.
. Move Overview of all primitives from Appendix to Section 4.
. Simplify Appendix A to just described Model Designer Guidelines
and refer back to section 4 for specific primitives
. Remove Appendix B (An Evolutionary Architecture - Design Goals)
. added design decision regarding security
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. Included latest Snmp SecurityModel TC (as it was actually posted
to the SNMPv3 mailing list).
[version 4.5]
. start with <draft-ietf-snmpv3-next-gen-arch-03.txt>
. change vendor to implementor
. change LoS to securityLevel
. remove mention of enterprise
. change Internet Management Framework to SNMP Management Framework
. modify usage of "frameworks" to improve internal consistency.
. change Message Processing Abstract Service Interface to
Application Multiplexor
. change description of SNMP engine
. moved "one-to-one association" for entity and engine to discussion
of engine.
. changed distributing to dispatching
. added asterisks to indicate v3* items are also not required.
. changed "community access control" to "other access control"
. added TC for SnmpMessageProcessingModel
. modified Security Considerations
. modified acknowledgements
[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.
. publish as <draft-ietf-snmpv3-next-gen-arch-03.txt>
[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.
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. 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
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
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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.
. 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
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. 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
. 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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Table of Contents
1. Introduction ................................................... 2
1.1. Overview ..................................................... 2
1.2. SNMP ......................................................... 2
1.3. Goals of this Architecture ................................... 3
1.4. Security Requirements of this Architecture ................... 4
1.5. Design Decisions ............................................. 5
2. Documentation Overview ......................................... 6
2.1. Document Roadmap ............................................. 8
2.2. Applicability Statement ...................................... 8
2.3. Coexistence and Transition ................................... 8
2.4. Transport Mappings ........................................... 8
2.5. Message Processing ........................................... 9
2.6. Security ..................................................... 9
2.7. Access Control ............................................... 9
2.8. Protocol Operations .......................................... 10
2.9. Applications ................................................. 10
2.10. Structure of Management Information ......................... 10
2.11. Textual Conventions ......................................... 10
2.12. Conformance Statements ...................................... 11
2.13. Management Information Base Modules ......................... 11
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2.13.1. SNMP Instrumentation MIBs ................................. 11
2.14. SNMP Framework Documents .................................... 11
3. Elements of the Architecture ................................... 12
3.1. The Naming of Entities ....................................... 12
3.1.1. SNMP entity ................................................ 13
3.1.2. SNMP engine ................................................ 13
3.1.3. snmpEngineID ............................................... 14
3.1.4. Dispatcher ................................................. 14
3.1.5. Message Processing Subsystem ............................... 15
3.1.6. Message Processing Model ................................... 15
3.1.7. Security Subsystem ......................................... 16
3.1.8. Security Model ............................................. 16
3.1.9. Security Protocol .......................................... 16
3.1.10. Access Control Subsystem .................................. 17
3.1.11. Access Control Model ...................................... 17
3.1.12. Applications .............................................. 17
3.1.13. SNMP Manager .............................................. 18
3.1.14. SNMP Agent ................................................ 19
3.2. The Naming of Identities ..................................... 20
3.2.1. Principal .................................................. 20
3.2.2. securityName ............................................... 20
3.2.3. Model-dependent security ID ................................ 21
3.3. The Naming of Management Information ......................... 22
3.3.1. An SNMP Context ............................................ 23
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3.3.2. contextEngineID ............................................ 23
3.3.3. contextName ................................................ 24
3.3.4. scopedPDU .................................................. 24
3.4. Other Constructs ............................................. 24
3.4.1. maxSizeResponseScopedPDU ................................... 24
3.4.2. Local Configuration Datastore .............................. 24
3.4.3. securityLevel .............................................. 24
4. Abstract Service Interfaces. .................................. 25
4.1. Common Primitives ............................................ 25
4.1.1. Release State Reference Information ........................ 25
4.2. Dispatcher Primitives ........................................ 25
4.2.1. Generate Outgoing Request or Notification .................. 25
4.2.2. Process Incoming Request or Notification PDU ............... 26
4.2.3. Generate Outgoing Response ................................. 27
4.2.4. Process Incoming Response PDU .............................. 27
4.2.5. Registering Responsibility for Handling SNMP PDUs. ........ 27
4.3. Message Processing Subsystem Primitives ...................... 28
4.3.1. Prepare Outgoing SNMP Request or Notification Message ...... 28
4.3.2. Prepare an Outgoing SNMP Response Message .................. 29
4.3.3. Prepare Data Elements from an Incoming SNMP Message ........ 30
4.4. Access Control Subsystem Primitives .......................... 30
4.5. Security Subsystem Primitives ................................ 31
4.5.1. Generate a Request or Notification Message ................. 31
4.5.2. Process Incoming Message ................................... 31
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4.5.3. Generate a Response Message ................................ 32
4.6. Common Primitives ............................................ 32
4.6.1. Release State Reference Information ........................ 32
4.7. Scenario Diagrams ............................................ 33
4.7.1. Command Generator or Notification Originator ............... 33
4.7.2. Scenario Diagram for a Command Responder Application ....... 34
5. Managed Object Definitions for SNMP Management Frameworks ...... 35
6. Security Considerations ........................................ 44
7. Editor's Addresses ............................................. 45
8. Acknowledgements ............................................... 45
9. References ..................................................... 47
A. Guidelines for Model Designers ................................. 49
A.1. Security Model Design Requirements ........................... 49
A.1.1. Threats .................................................... 49
A.1.2. Security Processing ........................................ 50
A.1.3. Validate the security-stamp in a received message .......... 50
A.1.4. Security MIBs .............................................. 51
A.1.5. Cached Security Data ....................................... 51
A.2. Message Processing Model Design Requirements ................. 51
A.2.1. Receiving an SNMP Message from the Network ................. 52
A.2.2. Sending an SNMP Message to the Network ..................... 52
A.3. Application Design Requirements .............................. 52
A.3.1. Applications that Initiate Messages ........................ 53
A.3.2. Applications that Receive Responses ........................ 53
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A.3.3. Applications that Receive Asynchronous Messages ............ 53
A.3.4. Applications that Send Responses ........................... 54
A.4. Access Control Model Design Requirements ..................... 54
B. Issues ......................................................... 55
B.1. Showstoppers ................................................. 55
B.2. Open Issues .................................................. 55
B.3. Resolved Issues .............................................. 55
B.3.1. Issues discussed at second Interim Meeting: ................ 56
B.4. Change Log ................................................... 56
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