INTERNET DRAFT Advertising Generic Information in IS-IS Feb 2007 Network Working Group L. Ginsberg Internet Draft S. Previdi Expiration Date: Aug 2007 M. Shand Cisco Systems Feb 2007 Advertising Generic Information in IS-IS draft-ginsberg-isis-genapp-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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Abstract This draft describes the manner in which generic application information (i.e. information not directly related to the operation of the IS-IS protocol) SHOULD be advertised in IS-IS LSPs and defines guidelines which SHOULD be used when flooding such information. Ginsberg Expires Aug 2007 [Page 1] INTERNET DRAFT Advertising Generic Information in IS-IS Feb 2007 Table of Contents 1. Conventions used in this document..........................2 2. Overview...................................................2 3. Encoding Format for GENINFO................................3 3.1 GENINFO TLV .............................................3 3.2 Use of subTLVs in GENINFO TLV............................5 4. GENINFO Flooding Procedures................................6 4.1 Leaking Procedures ......................................6 4.2 Minimizing Update Confusion..............................7 4.3 Interpreting Attribute Information ......................7 5. Security Considerations....................................8 6. IANA Considerations........................................8 7. References.................................................8 7.1 Normative References.....................................8 7.2 Informative References...................................9 8. Acknowledgments............................................9 9. Authors' Addresses.........................................9 10. Full Copyright Statement..................................9 1. Conventions used in this document 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 [BCP14]. 2. Overview [IS-IS] defines the format of TLVs which may be sent in IS-IS PDUs. The first octet of a TLV encodes the "type" or "codepoint" which provides a scope for the information and information format which follows. The protocol is therefore limited to 256 different codepoints which may be assigned. This number has proved generous as regards the information required for correct operation of the IS-IS protocol. However, the increasing use of IS-IS LSPs for advertisement of generic information (GENINFO) not directly related to the operation of the IS-IS protocol places additional demands on the TLV encoding space which has the potential to consume a significant number of TLV codepoints. This document therefore defines an encoding format for GENINFO which minimizes the consumption of TLV codepoints and also maximizes the flexibility of the formats which can be used to represent GENINFO. This document also discusses optimal behavior associated with the advertisement and flooding of LSPs containing GENINFO in order to avoid the advertisement of stale information and minimize the Ginsberg Expires Aug 2007 [Page 2] INTERNET DRAFT Advertising Generic Information in IS-IS Feb 2007 presence of duplicate or conflicting information when advertisements are updated. The manner in which the information contained in GENINFO TLVs is exchanged between an instance of the IS-IS protocol and the application which generates/consumes the GENINFO is outside the scope of this specification. The use of the IS-IS flooding mechanism as a means of reliably and efficiently propagating information is understandably attractive. However, it is prudent to remember that the primary purpose of this mechanism is to flood information necessary for the correct operation of the IS-IS protocol. Use of this mechanism to propagate information not required for operation of the IS-IS protocol decreases the efficiency of the protocol and therefore may negatively impact routing. One of the most egregious oversights is a failure to appropriately dampen changes in the information to be advertised, which can lead to flooding storms and possibly destabilize routing. Documents which specify the use of the mechanisms defined here MUST define the expected rate of change of the information to be advertised. 3. Encoding Format for GENINFO The encoding format defined below has the following goals regarding the advertisement of GENINFO in IS-IS LSPs: o Minimize the number of codepoints required o Minimize the depth of subTLV levels required In order to support these goals, a new IANA registry is required. This registry is required to manage the assignment of IS-IS GENINFO Application Identifiers. These numbers are unsigned 16 bit numbers ranging in value from 1 to 65535. The registry is also required to manage the assignment of application specific subTLV codepoints. These numbers are unsigned 8 bit numbers ranging in value from 0 to 255. The assignment of the subTLV codepoints is scoped by the Application Identifier. 3.1 GENINFO TLV The GENINFO TLV supports the advertisement of application specific information which is not directly related to the operation of the IS-IS protocol. Ginsberg Expires Aug 2007 [Page 3] INTERNET DRAFT Advertising Generic Information in IS-IS Feb 2007 Type 251 Length # of octets in the value field (3 to 255) Value No. of octets +-----------------------+ | Flags | 1 +-----------------------+ | Application ID | 2 +-----------------------+ | Application | | IP Address Info | 0 to 20 +-----------------------+ | Additional Application| 0 to (252 - | Specific Information | len of IP Address info) +-----------------------+ Flags 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Rsvd |V|I|D|S| +-+-+-+-+-+-+-+-+ The following bit flags are defined. S bit (0x01): If the S bit is set(1), the GENINFO TLV MUST be flooded across the entire routing domain. If the S bit is not set(0), the TLV MUST NOT be leaked between levels. This bit MUST NOT be altered during the TLV leaking. D bit (0x02): When the GENINFO TLV is leaked from level-2 to level-1, the D bit MUST be set. Otherwise this bit MUST be clear. GENINFO TLVs with the D bit set MUST NOT be leaked from level-1 to level-2. This is to prevent TLV looping. I bit (0x04): When the I bit is set the 4 octet IPv4 address associated with the application immediately follows the Application ID. V bit (0x08): When the V bit is set, the 16 octet IPv6 address associated with the application immediately follows either the Application ID (if I bit is clear) or the IPv4 address (if I bit is set). Ginsberg Expires Aug 2007 [Page 4] INTERNET DRAFT Advertising Generic Information in IS-IS Feb 2007 Application ID An identifier assigned to this application via the GENINFO-REG. Application IPv4 Address Info The IPv4 address associated with the application. This is not necessarily an address of a router running the IS-IS protocol. Application IPv6 Address Info The IPv6 address associated with the application. This is not necessarily an address of a router running the IS-IS protocol. Additional Application Specific Information Each application may define additional information to be encoded in a GENINFO TLV following the fixed information. Definition of such information is beyond the scope of this document. The Application ID in combination with the Application IPv4/IPv6 Address Information uniquely identifies the GENINFO Application Context (GENINFO-CTX). 3.2 Use of subTLVs in GENINFO TLV [RFC3784] introduced the definition and use of subTLVs. One of the advantages of using subTLVs rather than fixed encoding of information inside a TLV is to allow for the addition of new information in a backwards compatible manner i.e. just as with TLVs, implementations are required to ignore subTLVs which they do not understand. GENINFO TLVs MAY include subTLVs in the application specific information as deemed necessary and appropriate for each application. The scope of the codepoints used in such subTLVs is defined by the GENINFO TLV codepoint AND the Application ID i.e. the subTLV codepoints are private to the application. Such subTLVs are referred to as APPSUBTLVs and MUST be assigned via the GENINFO-REG IANA registry. Additional levels of APPSUBTLVs may be required when there is variable information which is scoped by a specific APPSUBTLV. These "nested" subTLVs MUST be encoded in the same manner as subTLVs i.e. with a one-octet Type field, a one-octet Length field, and zero or Ginsberg Expires Aug 2007 [Page 5] INTERNET DRAFT Advertising Generic Information in IS-IS Feb 2007 more octets of Value. These types MUST also be assigned via the GENINFO-REG IANA registry. The use of additional levels of subTLVs is discouraged due to the inherent inefficiency in encoding introduced because the parent subTLV must encode the nested subTLV length. While this inefficiency is small (one additional octet), it may be sufficient to extend the total information about a single application object beyond the carrying capacity of a single GENINFO TLV. Given that each Application ID can utilize the full range of subTLV codepoints (0 to 255) without conflict with any other application, the need to be frugal in the use of APPSUBTLV codepoints is greatly reduced. 4. GENINFO Flooding Procedures This section describes procedures which apply to the propagation of LSPs which contain GENINFO TLVs. These procedures have been previously discussed in [IS-IS-CAP]. This section is intended to serve as a reference specification for future documents which define the use of GENINFO TLV(s) for a specific application - eliminating the need to repeat the definition of these procedures in the application specific documents. Each GENINFO TLV contains information regarding exactly one application instance as identified by the GENINFO-CTX. When it is necessary to advertise sets of information with the same GENINFO-CTX which have different flooding scopes, a router MUST originate a minimum of one GENINFO TLV for each required flooding scope. GENINFO TLVs which contain information having area/level scope will have the S bit clear. These TLVs MUST NOT be leaked into another level. GENINFO TLVs which contain information which has domain scope will have the S bit set. These TLVs MUST be leaked into other IS-IS levels. When a TLV is leaked from level-2 to level-1, the D bit MUST be set in the level-1 LSP advertisement. 4.1 Leaking Procedures When leaking GENINFO TLVs downward from Level-2 into Level-1, if the originator of the TLV is a Level-1 router in another area, it is possible that multiple copies of the same TLV may be received from multiple L2 routers in the originating area. A router performing downward leaking MUST check for such duplication by comparing the contents of the TLVs. The set of LSPs generated by a router for a given level MUST NOT contain two or more copies of the same GENTLV. In order to prevent the use of stale GENINFO information, a system MUST NOT use a GENINFO TLV present in an LSP of a system which is not currently reachable via Level-x paths, where "x" is the level (1 or 2) associated with the LSP in which the GENINFO TLV appears. Note that leaking a GENINFO TLV is one of the uses which is prohibited Ginsberg Expires Aug 2007 [Page 6] INTERNET DRAFT Advertising Generic Information in IS-IS Feb 2007 under these conditions. The following example illustrates what might occur in the absence of this restriction. Example: If Level-1 router A generates a GENINFO TLV and floods it to two L1/L2 routers S and T, they will flood it into the Level-2 sub-domain. Now suppose the Level-1 area partitions, such that A and S are in one partition and T is in another. IP routing will still continue to work, but if A now issues a revised version of the GENINFO TLV, or decides to stop advertising it, S will follow suit, but T will continue to advertise the old version until the LSP times out. Routers in other areas have to choose whether to trust T's copy of A's GENINFO TLV or S's copy of A's information and they have no reliable way to choose. By making sure that T stops leaking A's information, this removes the possibility that other routers will use stale information from A. 4.2 Minimizing Update Confusion If an update to a TLV is advertised in an LSP with a different number than the LSP associated with the old advertisement, the possibility exists that other systems can temporarily have either 0 copies of a particular advertisement or 2 copies of a particular advertisement, depending on the order in which new copies of the LSP which had the old advertisement and the LSP which has the new advertisement arrive at other systems. Whenever possible, an implementation SHOULD advertise the update to a GENINFO TLV in the LSP with the same number as the advertisement which it replaces. Where this is not possible, the two affected LSPs SHOULD be flooded as an atomic action. Systems which receive an update to an existing GENINFO TLV can minimize the potential disruption associated with the update by employing a holddown time prior to processing the update so as to allow for the receipt of multiple LSPs associated with the same update prior to beginning processing. 4.3 Interpreting Attribute Information Where a receiving system has two copies of a GENINFO TLV with the same GENINFO-CTX, attribute information in the two TLVs which does not conflict MUST be considered additive. When information in the two GENINFO TLVs conflicts i.e there are different settings for a given attribute, the procedure used to choose which copy shall be used is undefined. Ginsberg Expires Aug 2007 [Page 7] INTERNET DRAFT Advertising Generic Information in IS-IS Feb 2007 5. Security Considerations This document raises no new security issues for IS-IS. 6. IANA Considerations This document defines a new ISIS TLV that needs to be reflected in the ISIS TLV code-point registry: Type Description IIH LSP SNP ---- ----------------------------------- --- --- --- 251 Generic Information n y n This document also defines a new registry which needs to be created. The new registry is required to manage two types of assigned numbers: 1)Application Identifiers which may be used in the Generic Information TLV. These identifiers are unsigned 16 bit numbers ranging in value from 1 to 65535. 2)Application specific subTLV codepoints which may be used in a GENINFO TLV when a specific Application Identifier is used. These numbers are unsigned 8 bit numbers ranging in value from 0 to 255. 7. References 7.1 Normative References [IS-IS] ISO, "Intermediate system to Intermediate system routeing information exchange protocol for use in conjunction with the Protocol for providing the Connectionless-mode Network Service (ISO 8473)," ISO/IEC 10589:2002, Second Edition. [RFC3784] Smit, H. and T. Li, "Intermediate System to Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)", RFC 3784, June 2004. [BCP9] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [BCP14] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 [BCP26] Narten, T. and Alvestrand, H., "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26 , RFC 2434, October 1998 Ginsberg Expires Aug 2007 [Page 8] INTERNET DRAFT Advertising Generic Information in IS-IS Feb 2007 [BCP79] Bradner, S. Ed., "Intellectual Property Rights in IETF Technology ", BCP 79 , RFC 3979, March 2005 7.2 Informative References [IS-IS-CAP] Vasseur, JP., Shen N., and Aggarwal, R., "IS-IS extensions for advertising router information", draft-ietf-isis- caps-06.txt, January 2006 8. Acknowledgments The authors would like to thank JP Vasseur and David Ward for providing the need to produce this document. 9. Authors' Addresses Les Ginsberg Cisco Systems 510 McCarthy Blvd. Milpitas, Ca. 95035 USA Email: ginsberg@cisco.com Stefano Previdi CISCO Systems, Inc. Via Del Serafico 200 00142 - Roma ITALY Email: sprevidi@cisco.com Mike Shand Cisco Systems 250 Longwater Avenue, Reading, Berkshire, RG2 6GB UK Email: mshand@cisco.com 10. Full Copyright Statement Copyright (C) The IETF Trust (2007). 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. 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