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. 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