Network Working Group J. Schoenwaelder
Internet-Draft International University Bremen
Expires: June 15, 2007 December 12, 2006
Simple Network Management Protocol (SNMP) EngineID Discovery
draft-schoenw-snmp-discover-00.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on June 15, 2007.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
To retrieve management information using the third version of the
Simple Network Management Protocol (SNMP), it is necessary to know
the identifier of the remote SNMP protocol engine. This document
introduces a discovery mechanism which can be used to learn the
engine identifier of a remote SNMP protocol engine. The proposed
mechanism is independent of the features provided by SNMP security
models and may be used also by other protocol interfaces to discover
the engine identifier.
Schoenwaelder Expires June 15, 2007 [Page 1]
Internet-Draft SNMP EngineID Discovery December 2006
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Local EngineID . . . . . . . . . . . . . . . . . . . . . . 4
3.2. EngineID Discovery . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 8
Schoenwaelder Expires June 15, 2007 [Page 2]
Internet-Draft SNMP EngineID Discovery December 2006
1. Introduction
To retrieve management information using the third version of the
Simple Network Management Protocol (SNMPv3) [RFC3410], it is
necessary to know the identifier of the remote SNMP protocol engine.
While an appropriate engine identifier can in principle be configured
by an operator, it is often desirable to discover the engine
identifier automatically.
This document introduces a discovery mechanism which can be used to
learn the engine identifier of a remote SNMP protocol engine. The
proposed mechanism is independent of the features provided by SNMP
security models and may be used also by other protocol interfaces to
discover the engine identifier. The mechanism has been designed that
it nicely co-exists with discovery mechanisms which may exist in
security models, such as the authoritative engine identifier
discovery of the User-based Security Model (USM) of SNMP [RFC3414].
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. Background
Within an administrative domain, an SNMP engine is uniquely
identified by an snmpEngineID value [RFC3411]. An SNMP entity, which
consists of an SNMP engine and several SNMP applications, may provide
access to multiple contexts.
An SNMP context is a collection of management information accessible
by an SNMP entity. An item of management information may exist in
more than one context and an SNMP entity potentially has access to
many contexts [RFC3411]. A context is identified by the snmpEngineID
value of the entity hosting the management information (called a
contextEngineID) and a context name which identifies the specific
context (called a contextName).
To identify an individual item of management information within an
administrative domain, a four tuple is used consisting of
1. a contextEngineID,
2. a contextName,
3. an object type, and
4. its instance identification.
The last two elements are typically encoded in an object identifier
(OID) value. The contextName is a string while the contextEngineID
Schoenwaelder Expires June 15, 2007 [Page 3]
Internet-Draft SNMP EngineID Discovery December 2006
is a binary value constructed according to the rules defined as part
of the SnmpEngineID textual convention of the SNMP-FRAMEWORK-MIB
[RFC3411].
The SNMP protocol operations and the protocol data units (PDUs)
operate on OIDs and thus deal with object types and instances
[RFC3416]. The SNMP architecture [RFC3411] introduces the concept of
a scopedPDU as a data structure containing a contextEngineID, a
contextName, and a PDU. The SNMP version 3 (SNMPv3) message format
uses ScopedPDUs to exchange management information [RFC3412].
Within the SNMP framework, contextEngineIDs serve as end-to-end
identifiers. This becomes important in situations where SNMP proxies
are deployed to translate between protocol versions or to cross
middleboxes such as network address translators. In addition,
snmpEngineIDs separate the identification of an SNMP engine from the
transport endpoints used to communicate with an SNMP engine. This
property allows to correlate management information easily even in
situations where multiple different transports were used to retrieve
the information or where transport endpoints can changed dynamically.
To retrieve data from an SNMPv3 agent, it is necessary to know the
appropriate contextEngineID. The User-based Security Model (USM) of
SNMPv3 provides a mechanism to discover the snmpEngineID of the
remote SNMP engine since this is needed for security processing
reasons. This discovered snmpEngineID can subsequently be used as a
contextEngineID in a ScopedPDU to access management information local
to the remote SNMP engine. Other security models, such as the
Transport Security Model (TMS) [RFC.TSM], lack such a procedure and
may use the discovery mechanism defined in this memo.
3. Procedure
The proposed discovery mechanism consists of two parts, namely the
definition of a special well-known snmpEngineID value which always
refers to a local context, and the definition of a procedure to
require the snmpEngineID scalar of the SNMP-FRAMEWORK-MIB using the
special well-known local snmpEngineID value.
3.1. Local EngineID
To facilitate discovery, it is assumed that SNMP agents register
their snmpEngineID scalar using a special well known contextEngineID.
This is consistent with the SNMPv3 specifications which explicitly
allow to register management information in multiple contexts.
The SnmpEngineID textual convention defines that an snmpEngineID
Schoenwaelder Expires June 15, 2007 [Page 4]
Internet-Draft SNMP EngineID Discovery December 2006
value MUST be between 5 and 12 octets long. This specification
proposes to use the variable length format 3) and to allocate the
format value 6 using the enterprise ID 0 for a well-known
SnmpEngineID value which always refers to the "local" engine. In
concrete terms, the SnmpEngineID value '8000000006'H is allocated to
refer to the local engineID.
Agent implementations MAY choose to register additional objects under
the local engineID. However, management applications SHOULD NOT rely
on this.
3.2. EngineID Discovery
Discovery of the snmpEngineID is simply done by sending an SNMP get
request to retrieve the snmpEngineID scalar using the local engineID
defined above as a contextEngineID. Implementations SHOULD only
perform this discovery step when it is needed. In particular, if
security models are used which already discover the remote engineID
(such as USM), then no further discovery is necessary. The same is
true in situations where the application already supplies a suitable
engineID value (e.g., in proxy situations).
The pseudo code below illustrates how the engineID discovery fits
into the control flow of an SNMP engine hosting a command generator
application.
do_discovery()
{
if (usm) {
do_usm_security_engineid_discovery();
if (contextEngineID == nil) {
contextEngineID = securityEngineID;
}
}
if (contextEngineID == nil) {
contextEngineID = '8000000006'H;
contextEngineID = get(snmpEngineID.0)
}
}
4. Security Considerations
TBD
Schoenwaelder Expires June 15, 2007 [Page 5]
Internet-Draft SNMP EngineID Discovery December 2006
5. Acknowledgments
Dave Perkins suggested to introduce a "local" contextEngineID during
the ISMS interim meeting in Boston, 2006. The email discussion in
Fall 2006 with Joe Fernandez helped to clarify many details.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, March 1997.
[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.
[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.
[RFC3416] Presuhn, R., "Version 2 of the Protocol Operations for the
Simple Network Management Protocol (SNMP)", STD 62,
RFC 3416, December 2002.
6.2. Informative References
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
[RFC.TSM] Harrington, D., "Transport Security Model for SNMP",
draft-ietf-isms-transport-security-model-00.txt (work in
progress), October 2006.
Schoenwaelder Expires June 15, 2007 [Page 6]
Internet-Draft SNMP EngineID Discovery December 2006
Author's Address
Juergen Schoenwaelder
International University Bremen
Campus Ring 1
28725 Bremen
Germany
Phone: +49 421 200-3587
Email: j.schoenwaelder@iu-bremen.de
Schoenwaelder Expires June 15, 2007 [Page 7]
Internet-Draft SNMP EngineID Discovery December 2006
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Schoenwaelder Expires June 15, 2007 [Page 8]