Network Working Group D. Harrington
Internet-Draft Huawei Technologies (USA)
Intended status: Standards Track J. Schoenwaelder
Expires: June 16, 2007 International University Bremen
December 13, 2006
Transport Subsystem for the Simple Network Management Protocol (SNMP)
draft-ietf-isms-tmsm-05
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Copyright (C) The IETF Trust (2006).
Abstract
This document describes a Transport Subsystem, extending the Simple
Network Management Protocol (SNMP) architecture defined in RFC 3411.
This document describes a subsystem to contain transport models,
comparable to other subsystems in the RFC3411 architecture. As work
is being done to expand the transport to include secure transport
such as SSH and TLS, using a subsystem will enable consistent design
and modularity of such transport models. This document identifies
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and discusses some key aspects that need to be considered for any
transport model for SNMP.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. The Internet-Standard Management Framework . . . . . . . . 3
1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements of a Transport Model . . . . . . . . . . . . . . 6
3.1. Message Security Requirements . . . . . . . . . . . . . . 6
3.1.1. Security Protocol Requirements . . . . . . . . . . . . 6
3.2. SNMP Requirements . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Architectural Modularity Requirements . . . . . . . . 7
3.2.2. Access Control Requirements . . . . . . . . . . . . . 11
3.2.3. Security Parameter Passing Requirements . . . . . . . 12
3.3. Session Requirements . . . . . . . . . . . . . . . . . . . 14
3.3.1. Session Establishment Requirements . . . . . . . . . . 14
3.3.2. Session Maintenance Requirements . . . . . . . . . . . 16
3.3.3. Message security versus session security . . . . . . . 16
4. Scenario Diagrams for the Transport Subsystem . . . . . . . . 17
4.1. Command Generator or Notification Originator . . . . . . . 17
4.2. Command Responder . . . . . . . . . . . . . . . . . . . . 18
5. Cached Information and References . . . . . . . . . . . . . . 19
5.1. securityStateReference . . . . . . . . . . . . . . . . . . 20
5.2. tmStateReference . . . . . . . . . . . . . . . . . . . . . 21
6. Abstract Service Interfaces . . . . . . . . . . . . . . . . . 21
6.1. Generating an Outgoing SNMP Message . . . . . . . . . . . 22
6.2. Processing for an Outgoing Message . . . . . . . . . . . . 23
6.3. Processing an Incoming SNMP Message . . . . . . . . . . . 23
6.3.1. Processing an Incoming Message . . . . . . . . . . . . 23
6.3.2. Prepare Data Elements from Incoming Messages . . . . . 23
6.3.3. Processing an Incoming Message . . . . . . . . . . . . 24
7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
10.1. Normative References . . . . . . . . . . . . . . . . . . . 26
10.2. Informative References . . . . . . . . . . . . . . . . . . 27
Appendix A. Parameter Table . . . . . . . . . . . . . . . . . . . 28
A.1. ParameterList.csv . . . . . . . . . . . . . . . . . . . . 28
Appendix B. Why tmStateReference? . . . . . . . . . . . . . . . . 29
B.1. Define an Abstract Service Interface . . . . . . . . . . . 29
B.2. Using an Encapsulating Header . . . . . . . . . . . . . . 30
B.3. Modifying Existing Fields in an SNMP Message . . . . . . . 30
B.4. Using a Cache . . . . . . . . . . . . . . . . . . . . . . 30
Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . . 31
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 31
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1. Introduction
This document describes a Transport Subsystem, extending the Simple
Network Management Protocol (SNMP) architecture defined in [RFC3411].
This document identifies and discusses some key aspects that need to
be considered for any transport model for SNMP.
1.1. The Internet-Standard Management Framework
For a detailed overview of the documents that describe the current
Internet-Standard Management Framework, please refer to section 7 of
RFC 3410 [RFC3410].
1.2. Conventions
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 RFC 2119 [RFC2119].
2. Motivation
There are multiple ways to secure one's home or business, in a
continuum of alternatives. Let's consider three general approaches.
In the first approach, an individual could buy a gun, learn to use
it, and sit on your front porch waiting for intruders. In the second
approach, one could hire an employee with a gun, schedule the
employee, position the employee to guard what you want protected,
hire a second guard to cover if the first gets sick, and so on. In
the third approach, you could hire a security company, tell them what
you want protected, and they could hire employees, train them, buy
the guns, position the guards, schedule the guards, send a
replacement when a guard cannot make it, etc., thus providing the
security you want, with no significant effort on your part other than
identifying requirements and verifying the quality of the service
being provided.
The User-based Security Model (USM) as defined in [RFC3414] largely
uses the first approach - it provides its own security. It utilizes
existing mechanisms (SHA=the gun), but provides all the coordination.
USM provides for the authentication of a principal, message
encryption, data integrity checking, timeliness checking, etc.
USM was designed to be independent of other existing security
infrastructures. USM therefore requires a separate principal and key
management infrastructure. Operators have reported that deploying
another principal and key management infrastructure in order to use
SNMPv3 is a deterrent to deploying SNMPv3. It is possible but
difficult to define external mechanisms that handle the distribution
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of keys for use by the USM approach.
A solution based on the second approach might use a USM-compliant
architecture, but combine the authentication mechanism with an
external mechanism, such as RADIUS [RFC2865], to provide the
authentication service. It might be possible to utilize an external
protocol to encrypt a message, to check timeliness, to check data
integrity, etc. It is difficult to cobble together a number of
subcontracted services and coordinate them however, because it is
difficult to build solid security bindings between the various
services, and potential for gaps in the security is significant.
A solution based on the third approach might utilize one or more
lower-layer security mechanisms to provide the message-oriented
security services required. These would include authentication of
the sender, encryption, timeliness checking, and data integrity
checking. There are a number of IETF standards available or in
development to address these problems through security layers at the
transport layer or application layer, among them TLS [RFC4366], SASL
[RFC4422], and SSH [RFC4251].
From an operational perspective, it is highly desirable to use
security mechanisms that can unify the administrative security
management for SNMPv3, command line interfaces (CLIs) and other
management interfaces. The use of security services provided by
lower layers is the approach commonly used for the CLI, and is also
the approach being proposed for NETCONF [I-D.ietf-netconf-ssh].
This document describes a Transport Subsystem extension to the
RFC3411 architecture.
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+-------------------------------------------------------------------+
| SNMP entity |
| |
| +-------------------------------------------------------------+ |
| | SNMP engine (identified by snmpEngineID) | |
| | | |
| | +------------+ | |
| | | Transport | | |
| | | Subsystem | | |
| | +------------+ | |
| | | |
| | +------------+ +------------+ +-----------+ +-----------+ | |
| | | Dispatcher | | Message | | Security | | Access | | |
| | | | | Processing | | Subsystem | | Control | | |
| | | | | Subsystem | | | | Subsystem | | |
| | +------------+ +------------+ +-----------+ +-----------+ | |
| +-------------------------------------------------------------+ |
| |
| +-------------------------------------------------------------+ |
| | Application(s) | |
| | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | Command | | Notification | | Proxy | | |
| | | Generator | | Receiver | | Forwarder | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | Command | | Notification | | Other | | |
| | | Responder | | Originator | | | | |
| | +-------------+ +--------------+ +--------------+ | |
| +-------------------------------------------------------------+ |
| |
+-------------------------------------------------------------------+
This extension allows security to be provided by an external protocol
connected to the SNMP engine through an SNMP transport-model
[RFC3417]. Such a transport model would then enable the use of
existing security mechanisms such as (TLS) [RFC4366] or SSH [RFC4251]
within the RFC3411 architecture.
There are a number of Internet security protocols and mechanisms that
are in wide spread use. Many of them try to provide a generic
infrastructure to be used by many different application layer
protocols. The motivation behind the transport subsystem is to
leverage these protocols where it seems useful.
There are a number of challenges to be addressed to map the security
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provided by a secure transport into the SNMP architecture so that
SNMP continues to work without any surprises. These challenges are
discussed in detail in this document. For some key issues, design
choices are discussed that may be made to provide a workable solution
that meets operational requirements and fits into the SNMP
architecture defined in [RFC3411].
3. Requirements of a Transport Model
3.1. Message Security Requirements
Transport security protocols SHOULD ideally provide the protection
against the following message-oriented threats [RFC3411]:
1. modification of information
2. masquerade
3. message stream modification
4. disclosure
According to [RFC3411], it is not required to protect against denial
of service or traffic analysis.
3.1.1. Security Protocol Requirements
There are a number of standard protocols that could be proposed as
possible solutions within the transport subsystem. Some factors
should be considered when selecting a protocol.
Using a protocol in a manner for which it was not designed has
numerous problems. The advertised security characteristics of a
protocol may depend on its being used as designed; when used in other
ways, it may not deliver the expected security characteristics. It
is recommended that any proposed model include a discussion of the
applicability of the transport model.
A transport model should require no modifications to the underlying
protocol. Modifying the protocol may change its security
characteristics in ways that would impact other existing usages. If
a change is necessary, the change should be an extension that has no
impact on the existing usages. It is recommended that any transport
model include a discussion of potential impact on other usages of the
protocol.
It has been a long-standing requirement that SNMP be able to work
when the network is unstable, to enable network troubleshooting and
repair. The UDP approach has been considered to meet that need well,
with an assumption that getting small messages through, even if out
of order, is better than getting no messages through. There has been
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a long debate about whether UDP actually offers better support than
TCP when the underlying IP or lower layers are unstable. There has
been recent discussion of whether operators actually use SNMP to
troubleshoot and repair unstable networks.
There has been discussion of ways SNMP could be extended to better
support management/monitoring needs when a network is running just
fine. Use of a TCP transport, for example, could enable larger
message sizes and more efficient table retrievals.
Transport models MUST be able to coexist with other transport models,
and may be designed to utilize either TCP or UDP or SCTP.
3.2. SNMP Requirements
3.2.1. Architectural Modularity Requirements
SNMP version 3 (SNMPv3) is based on a modular architecture (described
in [RFC3411] section 3) to allow the evolution of the SNMP protocol
standards over time, and to minimize side effects between subsystems
when changes are made.
The RFC3411 architecture includes a security subsystem for enabling
different methods of providing security services, a messaging
subsystem permitting different message versions to be handled by a
single engine, an application subsystem to support different types of
application processors, and an access control subsystem for allowing
multiple approaches to access control. The RFC3411 architecture does
not include a subsystem for transport models, despite the fact there
are multiple transport mappings already defined for SNMP. This
document addresses the need for a transport subsystem compatible with
the RFC3411 architecture.
In SNMPv2, there were many problems of side effects between
subsystems caused by the manipulation of MIB objects, especially
those related to authentication and authorization, because many of
the parameters were stored in shared MIB objects, and different
models and protocols could assign different values to the objects.
Contributors assumed slightly different shades of meaning depending
on the models and protocols being used. As the shared MIB module
design was modified to accommodate a specific model, other models
which used the same MIB objects would be broken.
Abstract Service Interfaces (ASIs) were developed to pass model-
independent parameters. The models were required to translate from
their model-dependent formats into a model-independent format,
defined using model-independent semantics, which would not impact
other models.
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Parameters have been provided in the ASIs to pass model-independent
information about the authentication that has been provided. These
parameters include a model-independent identifier of the security
"principal", the security model used to perform the authentication,
and which SNMP-specific security features were applied to the message
(authentication and/or privacy).
Parameters have been provided in the ASIs to pass model-independent
transport address information. These parameters utilize the
transportDomain and transportAddress
The design of a transport subsystem must abide the goals of the
RFC3411 architecture defined in [RFC3411]. To that end, this
transport subsystem proposal uses a modular design that will permit
transport models to be advanced through the standards process
independently of other transport models, and independent of other
modular SNMP components as much as possible.
IETF standards typically require one mandatory to implement solution,
with the capability of adding new mechanisms in the future. Part of
the motivstion of developing transport models is to develop support
for secure transport protocols, such as a transport model that
utilizes the Secure Shell protocol. Any transport model should
define one minimum-compliance security mechanism, preferably one
which is already widely used to secure the transport layer protocol.
The Transport Subsystem permits multiple transport protocols to be
"plugged into" the RFC3411 architecture, supported by corresponding
transport models, including models that are security-aware.
The RFC3411 architecture,and the USM assume that a security model is
called by a message-processing model and will perform multiple
security functions within the security subsystem. A transport model
that supports a secure transport protocol may perform similar
security functions within the transport subsystem. A transport model
may perform the translation of transport security parameters to/from
security-model-independent parameters. To accommodate this, the ASIs
for the transport subsystem, the messaging subsystem, and the
security subsystem will be extended to pass security-model-
independent values, and a cache of transport-specific information.
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+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v (traditional SNMP agent)
+-------------------------------------------------------------------+
| +--------------------------------------------------+ |
| | Transport Subsystem | |
| | +-----+ +-----+ +-----+ +-----+ +-------+ | |
| | | UDP | | TCP | | SSH | | TLS | . . . | other | | |
| | +-----+ +-----+ +-----+ +-----+ +-------+ | |
| +--------------------------------------------------+ |
| ^ |
| | |
| Dispatcher v |
| +-------------------+ +---------------------+ +----------------+ |
| | Transport | | Message Processing | | Security | |
| | Dispatch | | Subsystem | | Subsystem | |
| | | | +------------+ | | +------------+ | |
| | | | +->| v1MP * |<--->| | USM * | | |
| | | | | +------------+ | | +------------+ | |
| | | | | +------------+ | | +------------+ | |
| | | | +->| v2cMP * |<--->| | Transport* | | |
| | Message | | | +------------+ | | | Security | | |
| | Dispatch <--------->| +------------+ | | | Model | | |
| | | | +->| v3MP * |<--->| +------------+ | |
| | | | | +------------+ | | +------------+ | |
| | PDU Dispatch | | | +------------+ | | | Other * | | |
| +-------------------+ | +->| otherMP * |<--->| | Model(s) | | |
| ^ | +------------+ | | +------------+ | |
| | +---------------------+ +----------------+ |
| 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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3.2.1.1. USM and the RFC3411 Architecture
The following diagrams illustrate the difference in the security
processing done by the USM model and the security processing
potentially done by a transport model.
The USM security model is encapsulated by the messaging model,
because the messaging model needs to perform the following steps (for
incoming messages)
1) decode the ASN.1 (messaging model)
2) determine the SNMP security model and parameters (messaging model)
3) decrypt the encrypted portions of the message (security model)
4) translate parameters to model-independent parameters (security
model)
5) determine which application should get the decrypted portions
(messaging model), and
6) pass on the decrypted portions with model-independent parameters.
The USM approach uses SNMP-specific message security and parameters.
3.2.1.2. Transport Subsystem and the RFC3411 Architecture
With the Transport Subsystem, the order of the steps may differ and
may be handled by different subsystems:
1) decrypt the encrypted portions of the message (transport layer)
2*) translate parameters to model-independent parameters (transport
model)
3) determine the SNMP security model and parameters (transport model)
4) decode the ASN.1 (messaging model)
5) determine which application should get the decrypted portions
(messaging model)
7) pass on the decrypted portions with model-independent security
parameters
If a message is secured using non-SNMP-specific message security and
parameters, then the transport model should provide the translation
from the authenticated identity (e.g., an SSH user name) to the
securityName in step 3.
3.2.1.3. Passing Information between Engines
A secure transport model will establish an encrypted tunnel between
the transport models of two SNMP engines. One transport model
instance encrypts all messages, and the other transport model
instance decrypts the messages.
After a transport layer tunnel is established, then SNMP messages can
conceptually be sent through the tunnel from one SNMP engine to
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another SNMP engine. Once the tunnel is established, multiple SNMP
messages may be able to be passed through the same tunnel.
3.2.2. Access Control Requirements
3.2.2.1. securityName Binding
For SNMP access control to function properly, security processing
must establish a securityModel identifier, a securityLevel, and a
securityName, which is the security model independent identifier for
a principal. The message processing subsystem relies on a security
model, such as USM, to play a role in security that goes beyond
protecting the message - it provides a mapping between the USM-
specific principal to a security-model independent securityName which
can be used for subsequent processing, such as for access control.
The securityName MUST be bound to the mechanism-specific
authenticated identity, and this mapping MUST be done for incoming
messages before the security model passes securityName to the message
processing model via the processIncoming() ASI. This translation
from a mechanism-specific authenticated identity to a securityName
MAY be done by the transport model, and the securityname is then
provided to the security model to be passed to the message processing
model.
If the type of authentication provided by the transport layer (e.g.
TLS) is considered adequate to secure and/or encrypt the message, but
inadequate to provide the desired granularity of access control (e.g.
user-based), then a second authentication (e.g., one provided via a
RADIUS server) MAY be used to provide the authentication identity
which is bound to the securityName. This approach would require a
good analysis of the potential for man-in-the-middle attacks or
masquerade possibilities.
3.2.2.2. Separation of Authentication and Authorization
A transport model that provides security services should take care to
not violate the separation of authentication and authorization in the
RFC3411 architecture. The isAccessAllowed() primitive is used for
passing security-model independent parameters between the subsystems
of the architecture.
Mapping of (securityModel, securityName) to an access control policy
should be handled within the access control subsystem, not the
transport or security subsystems, to be consistent with the
modularity of the RFC3411 architecture. This separation was a
deliberate decision of the SNMPv3 WG, to allow support for
authentication protocols which did not provide authorization
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capabilities, and to support authorization schemes, such as VACM,
that do not perform their own authentication.
An authorization model (in the access control subsystem) MAY require
authentication by certain securityModels and a minimum securityLevel
to allow access to the data.
Transport models that provide secure transport are an enhancement for
the SNMPv3 privacy and authentication, but they are not a significant
improvement for the authorization (access control) needs of SNMPv3.
Only the model-independent parameters for the isAccessAllowed()
primitive [RFC3411] are provided by the transport and security
subsystems.
A transport model must not specify how the securityModel and
securityName could be dynamically mapped to an access control
mechanism, such as a VACM-style groupName. The mapping of
(securityModel, securityName) to a groupName is a VACM-specific
mechanism for naming an access control policy, and for tying the
named policy to the addressing capabilities of the data modeling
language (e.g. SMIv2 [RFC2578]), the operations supported, and other
factors. Providing a binding outside the Access Control subsystem
might create dependencies that could make it harder to develop
alternate models of access control, such as one built on UNIX groups
or Windows domains. The preferred approach is to pass the model-
independent security parameters via the isAccessAllowed() ASI, and
perform the mapping from the model-independent security parameters to
an authorization-model-dependent access policy within the access
control model.
To provide support for protocols which simultaneously send
information for authentication and authorization, such as RADIUS
[RFC2865], model-specific authorization information MAY be cached or
otherwise made available to the access control subsystem, e.g., via a
MIB table similar to the vacmSecurityToGroupTable, so the access
control subsystem can create an appropriate binding between the
model-independent securityModel and securityName and a model-specific
access control policy. This may be highly undesirable, however, if
it creates a dependency between a transport model or a security model
and an access control model, just as it is undesirable for a
transport model to create a dependency between an SNMP message
version and the security provided by a transport model.
3.2.3. Security Parameter Passing Requirements
RFC3411 section 4 describes primitives to describe the abstract data
flows between the various subsystems, models and applications within
the architecture. Abstract Service Interfaces describe the flow of
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data between subsystems within an engine. The ASIs generally pass
model-independent information.
Within an engine using a transport model, outgoing SNMP messages are
passed unencrypted from the message dispatcher to the transport
model, and incoming messages are passed unencrypted from the
transport model to the message dispatcher.
The security parameters include a model-independent identifier of the
security "principal", the security model used to perform the
authentication, and which SNMP-specific security services were
(should be) applied to the message (authentication and/or privacy).
In the RFC3411 architecture, which reflects the USM security model
design, the messaging model must unpack SNMP-specific security
parameters from an incoming message before calling a specific
security model to authenticate and decrypt an incoming message,
perform integrity checking, and translate model-specific security
parameters into model-independent parameters.
When using a secure transport model, security parameters MAY be
provided through means other than carrying them in the SNMP message.
The parameters MAY be provided by SNMP applications for outgoing
messages, and the parameters for incoming messages MAY be extracted
from the transport layer by the transport model before the message is
passed to the message processing subsystem.
For outgoing messages, even when a secure transport model will
provide the security services, it is necessary to have an security
model because it is the security model that actually creates the
message from its component parts. Whether there are any security
services provided by the security model for an outgoing message is
model-dependent.
For incoming messages, even when a secure transport model provides
security services, a security model is necessary because there might
be some security functionality that can only be provided after the
message version is known. The message version is determined by the
Message Processing model and passed to the security model via the
processIncoming() ASI.
The RFC3411 architecture has no ASI parameters for passing security
information between a transport mapping (a transport model) and the
dispatcher, and between the dispatcher and the message processing
model.
This document describes a cache mechanism, into which the transport
model puts information about the transport and security parameters
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applied to a transport connection or an incoming message, and a
security model MAY extract that information from the cache. A
tmStateReference is passed as an extra parameter in the ASIs of the
transport subsystem and the messaging and security subsystems, to
identify the relevant cache.
This approach of passing a model-independent reference is consistent
with the securityStateReference cache already being passed around in
the RFC3411 ASIs.
3.3. Session Requirements
Some secure transports may have a notion of sessions, while other
secure transports might provide channels or other session-like thing.
Throughout this document, the term session is used in a broad sense
to cover sessions, channels, and session-like things. Session refers
to an association between two SNMP engines that permits the
transmission of one or more SNMP messages within the lifetime of the
session. How the session is actually established, opened, closed, or
maintained is specific to a particular transport model.
Sessions are not part of the SNMP architecture described in
[RFC3411], but are considered desirable because the cost of
authentication can be amortized over potentially many transactions.
It is important to note that the architecture described in [RFC3411]
does not include a session selector in the Abstract Service
Interfaces, and neither is that done for the transport subsystem, so
an SNMP application cannot select the session except by passing a
unique combination of transport type, transport address,
securityName, securityModel, and securityLevel.
All transport models should discuss the impact of sessions on SNMP
usage, including how to establish/open a transport session (i.e., how
it maps to the concepts of session-like things of the underlying
protocol), how to behave when a session cannot be established, how to
close a session properly, how to behave when a session is closed
improperly, the session security properties, session establishment
overhead, and session maintenance overhead.
To reduce redundancy, this document will discuss aspects that are
expected to be common to all transport model sessions.
3.3.1. Session Establishment Requirements
SNMP applications must provide the transport type, transport address,
securityName, securityModel, and securityLevel to be used for a
session.
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SNMP Applications typically have no knowledge of whether the session
that will be used to carry commands was initially established as a
notification session, or a request-response session, and SHOULD NOT
make any assumptions based on knowing the direction of the session.
If an administrator or transport model designer wants to
differentiate a session established for different purposes, such as a
notification session versus a request-response session, the
application can use different securityNames or transport addresses
(e.g., port 161 vs. port 162) for different purposes.
An SNMP engine containing an application that initiates
communication, e.g., a Command Generator or Notification Originator,
MUST be able to attempt to establish a session for delivery if a
session does not yet exist. If a session cannot be established then
the message is discarded.
Sessions are usually established by the transport model when no
appropriate session is found for an outgoing message, but sessions
may be established in advance to support features such as
notifications. How sessions are established in advance is beyond the
scope of this document.
Sessions are initiated by notification originators when there is no
currently established connection that can be used to send the
notification. For a client-server security protocol, this may
require provisioning authentication credentials on the agent, either
statically or dynamically, so the client/agent can successfully
authenticate to a notification receiver.
A transport model must be able to determine whether a session does or
does not exist, and must be able to determine which session has the
appropriate security characteristics (transport type, transport
address, securityName, securityModel, and securityLevel) for an
outgoing message.
A transport model implementation MAY reuse an already established
session with the appropriate transport type, transport address,
securityName, securityModel, and securityLevel characteristics for
delivery of a message originated by a different type of application
than originally caused the session to be created. For example, an
implementation that has an existing session originally established to
receive a request may use that session to send an outgoing
notification, and may use a session that was originally established
to send a notification to send a request. Responses are expected to
be returned using the same session that carried the corresponding
request message. Reuse of sessions is not required for conformance.
If a session can be reused for a different type of message, but a
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receiver is not prepared to accept different message types over the
same session, then the message MAY be dropped by the receiver. This
may strongly affect the usefulness of session reuse, and transport
models should define a standard behavior for this circumstance.
3.3.2. Session Maintenance Requirements
A transport model can tear down sessions as needed. It may be
necessary for some implementations to tear down sessions as the
result of resource constraints, for example.
The decision to tear down a session is implementation-dependent.
While it is possible for an implementation to automatically tear down
each session once an operation has completed, this is not recommended
for anticipated performance reasons. How an implementation
determines that an operation has completed, including all potential
error paths, is implementation-dependent.
The elements of procedure may discuss when cached information can be
discarded, and the timing of cache cleanup may have security
implications, but cache memory management is an implementation issue.
If a transport model defines MIB module objects to maintain session
state information, then the transport model MUST describe what
happens to the objects when a related session is torn down, since
this will impact interoperability of the MIB module.
3.3.3. Message security versus session security
A transport model session is associated with state information that
is maintained for its lifetime. This state information allows for
the application of various security services to multiple messages.
Cryptographic keys established at the beginning of the session SHOULD
be used to provide authentication, integrity checking, and encryption
services for data that is communicated during the session. The
cryptographic protocols used to establish keys for a transport model
session SHOULD ensure that fresh new session keys are generated for
each session. If each session uses new session keys, then messages
cannot be replayed from one session to another. In addition sequence
information MAY be maintained in the session which can be used to
prevent the replay and reordering of messages within a session.
A transport model session will typically have a single transport
type, transport address, securityModel, securityName and
securityLevel associated with it. If an exchange between
communicating engines requires a different securityLevel or is on
behalf of a different securityName, or uses a different
securityModel, then another session would be needed. An immediate
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consequence of this is that implementations should be able to
maintain some reasonable number of concurrent sessions.
For transport models, securityName is typically specified during
session setup, and associated with the session identifier.
SNMPv3 was designed to support multiple levels of security,
selectable on a per-message basis by an SNMP application, because
there is not much value in using encryption for a Commander Generator
to poll for non-sensitive performance data on thousands of interfaces
every ten minutes; the encryption may add significant overhead to
processing of the messages.
Some transport models MAY support only specific authentication and
encryption services, such as requiring all messages to be carried
using both authentication and encryption, regardless of the security
level requested by an SNMP application. A transport model MAY
upgrade the requested security level, i.e. noAuth/noPriv and auth/
noPriv MAY be sent over an authenticated and encrypted session.
4. Scenario Diagrams for the Transport Subsystem
RFC3411 section 4.6 provides scenario diagrams to illustrate how an
outgoing message is created, and how an incoming message is
processed. Both diagrams are incomplete, however. In section 4.6.1,
the diagram doesn't show the ASI for sending an SNMP request to the
network or receiving an SNMP response message from the network. In
section 4.6.2, the diagram doesn't illustrate the interfaces required
to receive an SNMP message from the network, or to send an SNMP
message to the network.
4.1. Command Generator or Notification Originator
This diagram from RFC3411 4.6.1 shows how a Command Generator or
Notification Originator application [RFC3413] requests that a PDU be
sent, and how the response is returned (asynchronously) to that
application.
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Command Dispatcher Message Security
Generator | Processing Model
| | Model |
| sendPdu | | |
|------------------->| | |
| | prepareOutgoingMessage | |
: |----------------------->| |
: | | generateRequestMsg |
: | |-------------------->|
: | | |
: | |<--------------------|
: | | |
: |<-----------------------| |
: | | |
: |------------------+ | |
: | Send SNMP | | |
: | Request Message | | |
: | to Network | | |
: | v | |
: : : : :
: : : : :
: : : : :
: | | | |
: | Receive SNMP | | |
: | Response Message | | |
: | from Network | | |
: |<-----------------+ | |
: | | |
: | prepareDataElements | |
: |----------------------->| |
: | | processIncomingMsg |
: | |-------------------->|
: | | |
: | |<--------------------|
: | | |
: |<-----------------------| |
| processResponsePdu | | |
|<-------------------| | |
| | | |
4.2. Command Responder
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 an SNMP message is received, and how the
Response is (asynchronously) send back to the network.
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Command Dispatcher Message Security
Responder | Processing Model
| | Model |
| | | |
| registerContextEngineID | | |
|------------------------>| | |
|<------------------------| | | |
| | Receive SNMP | | |
: | Message | | |
: | from Network | | |
: |<-------------+ | |
: | | |
: |prepareDataElements | |
: |------------------->| |
: | | processIncomingMsg |
: | |------------------->|
: | | |
: | |<-------------------|
: | | |
: |<-------------------| |
| processPdu | | |
|<------------------------| | |
| | | |
: : : :
: : : :
| returnResponsePdu | | |
|------------------------>| | |
: | prepareResponseMsg | |
: |------------------->| |
: | |generateResponseMsg |
: | |------------------->|
: | | |
: | |<-------------------|
: | | |
: |<-------------------| |
: | | |
: |--------------+ | |
: | Send SNMP | | |
: | Message | | |
: | to Network | | |
: | v | |
5. Cached Information and References
The RFC3411 architecture uses caches to store dynamic model-specific
information, and uses references in the ASIs to indicate in a model-
independent manner which cached information must flow between
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subsystems.
There are two levels of state that may need to be maintained: the
security state in a request-response pair, and potentially long-term
state relating to transport and security.
This state is maintained in caches. To simplify the elements of
procedure, the release of state information is not always explicitly
specified. As a general rule, if state information is available when
a message being processed gets discarded, the state related to that
message should also be discarded, and if state information is
available when a relationship between engines is severed, such as the
closing of a transport session, the state information for that
relationship might also be discarded.
This document differentiates the tmStateReference from the
securityStateReference. This document does not specify an
implementation strategy, only an abstract discussion of the data that
must flow between subsystems. An implementation MAY use one cache
and one reference to serve both functions, but an implementer must be
aware of the cache-release issues to prevent the cache from being
released before a security or transport model has had an opportunity
to extract the information it needs.
5.1. securityStateReference
From RFC3411: "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 RFC3411 section 4.5.1."
The information saved should include the model-independent parameters
(transportDomain, transportAddress, securityName, securityModel, and
securityLevel), related security parameters, and other information
needed to imatch the response with the request. The Message
Processing Model has the responsibility for explicitly releasing the
securityStateReference when such data is no longer needed. The
securityStateReference cached data may be implicitly released via the
generation of a response, or explicitly released by using the
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stateRelease primitive, as described in RFC 3411 section 4.5.1."
If the transport model connection is closed between the time a
Request is received and a Response message is being prepared, then
the Response message MAY be discarded.
5.2. tmStateReference
For each message or transport session, information about the message
security is stored in a cache, which may inlcude model- and
mechanism-specific parameters. The tmStateReference is passed
between subsystems to provide a handle for the cache. A transport
model may store transport-specific parameters in the cache for
subsequent usage. Since the contents of a cache are meaningful only
within an implementation, and not on-the-wire, the format of the
cache is implementation-specific.
The state referenced by tmStateReference may be saved in a Local
Configuration Datastore (LCD) to make it available across multiple
messages, as compared to securityStateReference which is designed to
be saved only for the life of a request-response pair of messages.
It is expected that an LCD will allow lookup based on the combination
of transportDomain, transportAddress, securityName, securityModel,
and securityLevel, and that the cache contain these values to
reference entries in the LCD.
6. Abstract Service Interfaces
Abstract service interfaces have been defined by RFC 3411 to describe
the conceptual data flows between the various subsystems within an
SNMP entity.
To simplify the elements of procedure, the release of state
information is not always explicitly specified. As a general rule,
if state information is available when a message gets discarded, the
message-state information should also be released, and if state
information is available when a session is closed, the session state
information should also be released.
An error indication may return an OID and value for an incremented
counter and a value for securityLevel, and values for contextEngineID
and contextName for the counter, and the securityStateReference if
the information is available at the point where the error is
detected.
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6.1. Generating an Outgoing SNMP Message
This section describes the procedure followed by an RFC3411-
compatible system whenever it generates a message containing a
management operation (such as a request, a response, a notification,
or a report) on behalf of a user.
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
OUT tmStateReference -- (NEW) reference to transport state
)
Note that tmStateReference has been added to this ASI.
The IN parameters of the prepareOutgoingMessage() ASI are used to
pass information from the dispatcher (from the application subsystem)
to the message processing subsystem.
The abstract service primitive from a Message Processing Model to a
Security Model to generate the components of a Request message is
generateRequestMsg().
The abstract service primitive from a Message Processing Model to a
Security Model to generate the components of a Response message is
generateResponseMsg().
Upon completion of processing, the Security Model returns
statusInformation. If the process was successful, the completed
message is returned. If the process was not successful, then an
errorIndication is returned.
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The OUT parameters of the prepareOutgoingMessage() ASI are used to
pass information from the message processing model to the dispatcher
and on to the transport model:
6.2. Processing for an Outgoing Message
The sendMessage ASI is used to pass a message from the Dispatcher to
the appropriate transport model for sending.
statusInformation =
sendMessage(
IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length
IN tmStateReference -- reference to transport state
)
6.3. Processing an Incoming SNMP Message
6.3.1. Processing an Incoming Message
If one does not exist, the Transport Model will need to create an
entry in a Local Configuration Datastore referenced by
tmStateReference. This information will include transportDomain,
transportAddress, the securityModel, the securityLevel, and the
securityName, plus any model or mechanism-specific details. How this
information is determined is model-specific.
The recvMessage ASI is used to pass a message from the transport
subsystem to the Dispatcher.
statusInformation =
recvMessage(
IN transportDomain -- origin transport domain
IN transportAddress -- origin transport address
IN incomingMessage -- the message received
IN incomingMessageLength -- its length
IN tmStateReference -- reference to transport state
)
6.3.2. Prepare Data Elements from Incoming Messages
The abstract service primitive from the Dispatcher to a Message
Processing Model for a received message is:
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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
IN tmStateReference -- (NEW) from the transport model
OUT messageProcessingModel -- typically, SNMP version
OUT securityModel -- Security Model to use
OUT securityName -- on behalf of this principal
OUT securityLevel -- Level of Security requested
OUT contextEngineID -- data from/at this entity
OUT contextName -- data from/in this context
OUT pduVersion -- the version of the PDU
OUT PDU -- SNMP Protocol Data Unit
OUT pduType -- SNMP PDU type
OUT sendPduHandle -- handle for matched request
OUT maxSizeResponseScopedPDU -- maximum size sender can accept
OUT statusInformation -- success or errorIndication
-- error counter OID/value if error
OUT stateReference -- reference to state information
-- to be used for possible Response
)
Note that tmStateReference has been added to this ASI.
6.3.3. Processing an Incoming Message
This section describes the procedure followed by the Security Model
whenever it receives an incoming message containing a management
operation on behalf of a user from a Message Processing model.
The Message Processing Model extracts some information from the
wholeMsg. The abstract service primitive from a Message Processing
Model to the Security Subsystem for a received message is:
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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
IN tmStateReference -- (NEW) from the transport model
OUT securityEngineID -- authoritative SNMP entity
OUT securityName -- identification of the principal
OUT scopedPDU, -- message (plaintext) payload
OUT maxSizeResponseScopedPDU -- maximum size sender can handle
OUT securityStateReference -- reference to security state
) -- information, needed for response
1) The securityEngineID is set to a value in a model-specific manner.
If the securityEngineID is not utilized by the specific model, then
it should be set to the local snmpEngineID, to satisfy the SNMPv3
message processing model in RFC 3412 section 7.2 13a).
2) Extract the value of securityName from the Local Configuration
Datastore entry referenced by tmStateReference.
3) The scopedPDU component is extracted from the wholeMsg.
4) The maxSizeResponseScopedPDU is calculated. This is the maximum
size allowed for a scopedPDU for a possible Response message.
5) The security data is cached as cachedSecurityData, so that a
possible response to this message can and will use the same security
parameters. Then securityStateReference is set for subsequent
reference to this cached data.
6) The statusInformation is set to success and a return is made to
the calling module passing back the OUT parameters as specified in
the processIncomingMsg primitive.
7. Security Considerations
This document describes an architectural approach that would permit
SNMP to utilize transport layer security services. Each proposed
transport model should discuss the security considerations of the
transport model.
It is considered desirable by some industry segments that SNMP
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transport models should utilize transport layer security that
addresses perfect forward secrecy at least for encryption keys.
Perfect forward secrecy guarantees that compromise of long term
secret keys does not result in disclosure of past session keys. The
editors recommend that each proposed transport model include a
discussion in its security considerations of whether perfect forward
security is appropriate for the transport model.
Since the cache and LCD will contain security-related parameters,
they should be kept in protected storage.
8. IANA Considerations
This document requires no action by IANA.
9. Acknowledgments
The Integrated Security for SNMP WG would like to thank the following
people for their contributions to the process:
The authors of submitted security model proposals: Chris Elliot, Wes
Hardaker, Dave Harrington, Keith McCloghrie, Kaushik Narayan, Dave
Perkins, Joseph Salowey, and Juergen Schoenwaelder.
The members of the Protocol Evaluation Team: Uri Blumenthal,
Lakshminath Dondeti, Randy Presuhn, and Eric Rescorla.
WG members who committed to and performed detailed reviews: Jeffrey
Hutzelman
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14,
RFC 2119, March 1997.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management
Information Version 2 (SMIv2)", STD 58,
RFC 2578, April 1999.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen,
"An Architecture for Describing Simple
Network Management Protocol (SNMP) Management
Frameworks", STD 62, RFC 3411, December 2002.
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[RFC3412] Case, J., Harrington, D., Presuhn, R., and B.
Wijnen, "Message Processing and Dispatching
for the Simple Network Management Protocol
(SNMP)", STD 62, RFC 3412, December 2002.
[RFC3414] Blumenthal, U. and B. Wijnen, "User-based
Security Model (USM) for version 3 of the
Simple Network Management Protocol (SNMPv3)",
STD 62, RFC 3414, December 2002.
[RFC3417] Presuhn, R., "Transport Mappings for the
Simple Network Management Protocol (SNMP)",
STD 62, RFC 3417, December 2002.
10.2. Informative References
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W.
Simpson, "Remote Authentication Dial In User
Service (RADIUS)", RFC 2865, June 2000.
[RFC3410] Case, J., Mundy, R., Partain, D., and B.
Stewart, "Introduction and Applicability
Statements for Internet-Standard Management
Framework", RFC 3410, December 2002.
[RFC3413] Levi, D., Meyer, P., and B. Stewart, "Simple
Network Management Protocol (SNMP)
Applications", STD 62, RFC 3413,
December 2002.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D.,
Mikkelsen, J., and T. Wright, "Transport
Layer Security (TLS) Extensions", RFC 4366,
April 2006.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple
Authentication and Security Layer (SASL)",
RFC 4422, June 2006.
[RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell
(SSH) Protocol Architecture", RFC 4251,
January 2006.
[I-D.ietf-netconf-ssh] Wasserman, M. and T. Goddard, "Using the
NETCONF Configuration Protocol over Secure
Shell (SSH)", draft-ietf-netconf-ssh-06 (work
in progress), March 2006.
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Appendix A. Parameter Table
Following is a CSV formatted matrix useful for tracking data flows
into and out of the dispatcher, transport, message, and security
subsystems. Import this into your favorite spreadsheet or other CSV
compatible application. You will need to remove lines feeds from the
second, third, and fourth lines, which needed to be wrapped to fit
into RFC limits.
A.1. ParameterList.csv
,Dispatcher,,,,Messaging,,,Security,,,Transport,
,sendPDU,returnResponse,processPDU,processResponse,
prepareOutgoingMessage,prepareResponseMessage,prepareDataElements,
generateRequest,processIncoming,generateResponse,
sendMessage,recvMessage
transportDomain,In,,,,In,,In,,,,,In
transportAddress,In,,,,In,,In,,,,,In
destTransportDomain,,,,,Out,Out,,,,,In,
destTransportAddress,,,,,Out,Out,,,,,In,
messageProcessingModel,In,In,In,In,In,In,Out,In,In,In,,
securityModel,In,In,In,In,In,In,Out,In,In,In,,
securityName,In,In,In,In,In,In,Out,In,Out,In,,
securityLevel,In,In,In,In,In,In,Out,In,In,In,,
contextEngineID,In,In,In,In,In,In,Out,,,,,
contextName,In,In,In,In,In,In,Out,,,,,
expectResponse,In,,,,In,,,,,,,
PDU,In,In,In,In,In,In,Out,,,,,
pduVersion,In,In,In,In,In,In,Out,,,,,
statusInfo,Out,In,,In,,In,Out,Out,Out,Out,,
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errorIndication,Out,Out,,,,,Out,,,,,
sendPduHandle,Out,,,In,In,,Out,,,,,
maxSizeResponsePDU,,In,In,,,In,Out,,Out,,,
stateReference,,In,In,,,In,Out,,,,,
wholeMessage,,,,,Out,Out,In,Out,In,Out,In,In
messageLength,,,,,Out,Out,In,Out,In,Out,In,In
maxMessageSize,,,,,,,,In,In,In,,
globalData,,,,,,,,In,,In,,
securityEngineID,,,,,,,,In,Out,In,,
scopedPDU,,,,,,,,In,Out,In,,
securityParameters,,,,,,,,Out,In,Out,,
securityStateReference,,,,,,,,,Out,In,,
pduType,,,,,,,Out,,,,,
tmStateReference,,,,,Out,Out,In,,In,,In,In
Appendix B. Why tmStateReference?
This appendix considers why a cache-based approach was selected for
passing parameters. This section may be removed from subsequent
revisions of the document.
There are four approaches that could be used for passing information
between the Transport Model and an Security Model.
1. one could define an ASI to supplement the existing ASIs, or
2. one could add a header to encapsulate the SNMP message,
3. one could utilize fields already defined in the existing SNMPv3
message, or
4. one could pass the information in an implementation-specific
cache or via a MIB module.
B.1. Define an Abstract Service Interface
Abstract Service Interfaces (ASIs) [RFC3411] are defined by a set of
primitives that specify the services provided and the abstract data
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elements that are to be passed when the services are invoked.
Defining additional ASIs to pass the security and transport
information from the transport subsystem to security subsystem has
the advantage of being consistent with existing RFC3411/3412
practice, and helps to ensure that any transport model proposals pass
the necessary data, and do not cause side effects by creating model-
specific dependencies between itself and other models or other
subsystems other than those that are clearly defined by an ASI.
B.2. Using an Encapsulating Header
A header could encapsulate the SNMP message to pass necessary
information from the Transport Model to the dispatcher and then to a
messaging security model. The message header would be included in
the wholeMessage ASI parameter, and would be removed by a
corresponding messaging model. This would imply the (one and only)
messaging dispatcher would need to be modified to determine which
SNMP message version was involved, and a new message processing model
would need to be developed that knew how to extract the header from
the message and pass it to the Security Model.
B.3. Modifying Existing Fields in an SNMP Message
[RFC3412] describes the SNMPv3 message, which contains fields to pass
security related parameters. The transport subsystem could use these
fields in an SNMPv3 message, or comparable fields in other message
formats to pass information between transport models in different
SNMP engines, and to pass information between a transport model and a
corresponding messaging security model.
If the fields in an incoming SNMPv3 message are changed by the
Transport Model before passing it to the Security Model, then the
Transport Model will need to decode the ASN.1 message, modify the
fields, and re-encode the message in ASN.1 before passing the message
on to the message dispatcher or to the transport layer. This would
require an intimate knowledge of the message format and message
versions so the Transport Model knew which fields could be modified.
This would seriously violate the modularity of the architecture.
B.4. Using a Cache
This document describes a cache, into which the Transport Model puts
information about the security applied to an incoming message, and a
Security Model can extract that information from the cache. Given
that there may be multiple TM-security caches, a tmStateReference is
passed as an extra parameter in the ASIs between the transport
subsystem and the security subsystem, so the Security Model knows
which cache of information to consult.
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This approach does create dependencies between a specific Transport
Model and a corresponding specific Security Model. However, the
approach of passing a model-independent reference to a model-
dependent cache is consistent with the securityStateReference already
being passed around in the RFC3411 ASIs.
Appendix C. Open Issues
Appendix D. Change Log
NOTE to RFC editor: Please remove this change log before publishing
this document as an RFC.
Changes from revision -04- to -05-
removed all objects from the MIB module.
changed document status to "Standard" rather than the xml2rfc
default of informational.
changed mention of MD5 to SHA
moved addressing style to TDomain and TAddress
modified the diagrams as requested
removed the "layered stack" diagrams that compared USM and a
Transport Model processing
removed discussion of speculative features that might exist in
future transport models
removed openSession() and closeSession() ASIs, since those are
model-dependent
removed the MIB module
removed the MIB boilerplate into (this memo defines a SMIv2 MIB
...)
removed IANA considerations related to the now-gone MIB module
removed security considerations related to the MIB module
removed references needed for the MIB module
changed recvMessage ASI to use origin transport domain/address
updated Parameter CSV appendix
Changes from revision -03- to -04-
changed title from Transport Mapping Security Model Architectural
Extension to Transport Subsystem
modified the abstract and introduction
changed TMSM to TMS
changed MPSP to simply Security Model
changed SMSP to simply Security Model
changed TMSP to Transport Model
removed MPSP and TMSP and SMSP from Acronyms section
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modified diagrams
removed most references to dispatcher functionality
worked to remove dependencies between transport and security
models.
defined snmpTransportModel enumeration similar to
snmpSecurityModel, etc.
eliminated all reference to SNMPv3 msgXXXX fields
changed tmSessionReference back to tmStateReference
Changes from revision -02- to -03-
o removed session table from MIB module
o removed sessionID from ASIs
o reorganized to put ASI discussions in EOP section, as was done in
SSHSM
o changed user auth to client auth
o changed tmStateReference to tmSessionReference
o modified document to meet consensus positions published by JS
o
* authoritative is model-specific
* msgSecurityParameters usage is model-specific
* msgFlags vs. securityLevel is model/implementation-specific
* notifications must be able to cause creation of a session
* security considerations must be model-specific
* TDomain and TAddress are model-specific
* MPSP changed to SMSP (Security model security processing)
Changes from revision -01- to -02-
o wrote text for session establishment requirements section.
o wrote text for session maintenance requirements section.
o removed section on relation to SNMPv2-MIB
o updated MIB module to pass smilint
o Added Structure of the MIB module, and other expected MIB-related
sections.
o updated author address
o corrected spelling
o removed msgFlags appendix
o Removed section on implementation considerations.
o started modifying the security boilerplate to address TMS and MIB
security issues
o reorganized slightly to better separate requirements from proposed
solution. This probably needs additional work.
o removed section with sample protocols and sample
tmSessionReference.
o Added section for acronyms
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o moved section comparing parameter passing techniques to appendix.
o Removed section on notification requirements.
Changes from revision -00-
o changed SSH references from I-Ds to RFCs
o removed parameters from tmSessionReference for DTLS that revealed
lower layer info.
o Added TMS-MIB module
o Added Internet-Standard Management Framework boilerplate
o Added Structure of the MIB Module
o Added MIB security considerations boilerplate (to be completed)
o Added IANA Considerations
o Added ASI Parameter table
o Added discussion of Sessions
o Added Open issues and Change Log
o Rearranged sections
Authors' Addresses
David Harrington
Huawei Technologies (USA)
1700 Alma Dr. Suite 100
Plano, TX 75075
USA
Phone: +1 603 436 8634
EMail: dharrington@huawei.com
Juergen Schoenwaelder
International University Bremen
Campus Ring 1
28725 Bremen
Germany
Phone: +49 421 200-3587
EMail: j.schoenwaelder@iu-bremen.de
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