INTERNET DRAFT Simplified Extension of LSP Space Mar 2006 Network Working Group L. Ginsberg Internet Draft S. Previdi Expiration Date: Aug 2006 M. Shand Cisco Systems March 2006 Simplified Extension of LSP Space for IS-IS draft-ginsberg-isis-extlsp-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 a simplified method for extending the LSP space beyond the 256 Link State PDU (LSP) limit defined in ISO 10589. This method is intended as a preferred replacement for the method defined in RFC 3786. Table of Contents Ginsberg Expires Sep 2006 [Page 1] INTERNET DRAFT Simplified Extension of LSP Space Mar 2006 1. Conventions used in this document..............................2 2. Overview.......................................................2 3. Definitions of Commonly Used Terms.............................3 4. Utilizing Additional System IDs................................3 4.1 Additional Information in Extended LSPs......................4 4.2 Extended LSP Restrictions....................................4 4.2.1 TLVs Which MUST NOT Appear................................4 4.2.2 Overload, Attached, and Partition Repair Bits.............5 4.3 Originating LSP Restrictions.................................5 4.4 IS Alias ID TLV (IS-Alias)...................................5 5. Comparison with the RFC 3786 Solution..........................6 6. Deployment Considerations......................................7 6.1 Advertising New TLVs in Extended LSPs........................7 6.2 Reachability and TLV Staleness...............................7 6.3 Moving TE Information to Extended LSPs.......................7 7. Security Considerations........................................8 8. IANA Considerations............................................8 9. Normative References...........................................8 10. Acknowledgments...............................................9 11. Authors' Addresses............................................9 12. 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 [BCP4]. 2. Overview [IS-IS] defines the set of LSP fragments which may be originated by a system at each level. This set is limited to 256 fragments. [IS- IS] also defines a maximum value for an LSP fragment (originatingLxLSPBufferSize) as 1492 bytes. The carrying capacity of an LSP set is sufficient to advertise the neighbor and leaf node reachability advertisements of an area/domain in anticipated deployment scenarios. However, the definition of additional information to be included in LSPs (e.g. traffic engineering information, router capabilities, etc.) has the potential to exceed the carrying capacity of an LSP set. This issue first drew interest when traffic engineering extensions were introduced. This interest resulted in the solution defined in RFC 3786. However, that solution suffers from restrictions required Ginsberg Expires Sep 2006 [Page 2] INTERNET DRAFT Simplified Extension of LSP Space Mar 2006 to maintain interoperability with systems which do not support the extensions. This document defines extensions which allow a system to exceed the 256 fragment limit and do so in a way which has no interoperability issues with systems which do not support the extension. It is seen as a simpler and therefore preferred solution to the problem. 3. Definitions of Commonly Used Terms This section provides definitions for terms that are used throughout the text. The terminology is consistent with that used in RFC 3786. Originating System: A router physically running the IS-IS protocol. As this document describes a method which allows a single IS-IS instance to originate LSPs using multiple instance identifiers, the Originating System represents the single "physical" IS-IS instance. Normal system-id: The system-id of an Originating System as defined by [IS-IS]. Additional system-id: A system-id other than the "Normal system-id" that is assigned by the network administrator to an Originating System in order to allow the generation of extended LSP fragments. The Additional system-id, like the Normal system-id, must be unique throughout the routing area (Level-1) or domain (Level-2). Original LSP: An LSP using the Normal system-id in its LSP ID. Extended LSP: An LSP using an Additional system-id in its LSP ID. LSP set: Logical LSP. This term is used only to resolve the ambiguity between a logical LSP and an LSP fragment, both of which are sometimes termed "LSP". Extended LSP set: A group of LSP fragments using an Additional system-id, and originated by the Originating System. Extension-capable IS: An IS implementing the mechanisms described in this document. 4. Utilizing Additional System IDs This extension allows an Originating System to be assigned additional system-ids which may be used to generate additional LSP sets. The additional system-ids are subject to the same restrictions as normal system-ids i.e. when used at Level-1 the additional system-id MUST be unique within the Level-1 area. When used at Level-2 the additional system-id MUST be unique within the domain. Ginsberg Expires Sep 2006 [Page 3] INTERNET DRAFT Simplified Extension of LSP Space Mar 2006 Extended LSPs are treated by the IS-IS Update Process in the same manner as normal LSPs i.e. the same rules as to generation, flooding, purging, etc. apply. In particular, if the Extended LSP with LSP Number zero and remaining lifetime > 0 is not present for a particular additional system-id then none of the extended LSPs in that LSP set shall be processed. 4.1 Additional Information in Extended LSPs Fragment 0 of an Extended LSP Set MUST include the new IS alias ID TLV defined in Section 4.4. This allows the Extended LSP set to be associated with the Originating System which generated the LSP(s). 4.2 Extended LSP Restrictions The following restrictions on the information which may appear in an Extended LSP are defined in order to avoid interoperability issues with systems which do not support the extensions defined in this document, 4.2.1 TLVs Which MUST NOT Appear Information which is directly utilized in the SPF calculation MUST NOT appear in an Extended LSP. This includes the following TLVs currently defined in the IANA IS-IS TLV Codepoints Registry: TLV Name (#) ----------- Area Addresses (1) ES Neighbors (3) Part. DIS (4) Prefix Neighbors (5) The extended IS reachability TLV (22) IP Int. Reach (128) IP Ext. Address (130) The extended IP reachability TLV (135) MT-ISN (222) M-Topologies (229) MT IP. Reach (235) IPv6 IP. Reach (236) MT IPv6 IP. Reach (237) If any of the TLVs listed above appear in an Extended LSP, an Extension Capable IS MUST ignore those TLVs on receipt and SHOULD report an error. Other TLVs in that extended LSP set MUST be processed normally. Ginsberg Expires Sep 2006 [Page 4] INTERNET DRAFT Simplified Extension of LSP Space Mar 2006 4.2.2 Overload, Attached, and Partition Repair Bits As Extended LSPs do not contain neighbor or area information the use of the Overload, Attached, and Partition Repair Bits have no significance. All of these bits MUST be set to 0 in all Extended LSP fragments by the originating system and MUST be ignored on receipt. 4.3 Originating LSP Restrictions An originating LSP MUST NOT advertise a neighbor relationship to any of its additional system-ids. 4.4 IS Alias ID TLV (IS-Alias) The proposed IS-Alias TLV allows extension-capable ISs to recognize the Originating System of an Extended LSP set. It identifies the Normal system-id of the Originating System. Type 24 Length # of octets in the value field (7 to 255) Value No. of octets +-----------------------+ | Normal System-id | 6 +-----------------------+ | Sub-TLV length | 1 +-----------------------+ | Sub-TLVs (optional) | 0 to 248 +-----------------------+ Normal system-id The Normal system-id of the Originating System Sub-TLVs length Total length of all sub-TLVs. Sub-TLVs A series of tuples with the following format: Ginsberg Expires Sep 2006 [Page 5] INTERNET DRAFT Simplified Extension of LSP Space Mar 2006 No. of Octets +-------------------+ | Sub-type | 1 +-------------------+ | Length | 1 +-------------------+ | | 0-246 : Value : : : | | +-------------------+ Sub-type Type of the sub-TLV Length Total length of the value field Value Type-specific TLV payload. No subTLVs are defined in this document. Should future extensions define subTLVs, the subTLVs MUST be formatted as described in RFC 3784. 5. Comparison with the RFC 3786 Solution This document utilizes the same basic mechanism (additional system- ids) as RFC 3786 to allow an originating system to generate more than 256 LSP fragments. It differs from RFC 3786 in that it restricts the content of Extended LSPs to information which is NOT utilized in the SPF calculation. Extended LSPs in this new definition are utilized solely to accommodate the additional information which various extensions have defined as new TLV content in LSPs. This distinction allows original LSPs to be used in the traditional manner and supports implementation optimizations which ignore extended LSP content when performing an SPF calculation. Legacy IS-IS implementations which do not support the extensions defined in this document see the extended LSPs as information Ginsberg Expires Sep 2006 [Page 6] INTERNET DRAFT Simplified Extension of LSP Space Mar 2006 associated with an unreachable system. Their SPF calculation is therefore consistent with that performed by extension capable ISs. There is therefore no need for the two different operating modes defined in RFC 3786. There is also no need for the special handling of the original LSP set and the extended LSP set(s) as a single Logical LSP during the SPF as specified in Section 5 of RFC 3786. 6. Deployment Considerations There are a number of deployment considerations which limit the usefulness of extended LSPs unless all systems are extension-capable ISs. 6.1 Advertising New TLVs in Extended LSPs As extended LSPs will be utilized to advertise TLVs associated with other protocol extensions (definition of which is outside the scope of this document), it is obvious that the utilization of the information in extended LSPs by legacy IS-IS implementations will be limited. The implication of this is that as implementations are revised to support the protocol extensions which define new TLVs that MAY be advertised in extended LSPs, the implementation SHOULD also be revised to support the extensions defined in this document so that they are capable of processing the new TLVs whether they appear in normal or extended LSPs. 6.2 Reachability and TLV Staleness In cases where non-SPF information is advertised in LSPs, it is necessary to determine whether the system which originated the advertisement is reachable in order to guarantee that a receiving router does not use or leak stale information. In the case of TLV information found in extended LSPs, the reachability test MUST be to the originating system, not to the additional system ID associated with the extended LSP. Systems which do NOT support the extensions defined in this document will always see the extended LSPs as coming from an unreachable system. They will therefore NOT use information in extended LSPs in cases where reachability is a requirement. 6.3 Moving TE Information to Extended LSPs One of the major sources of non-SPF related additional information in LSPs is the Traffic Engineering (TE) information carried in the extended IS reachability TLV (22) as defined in RFC 3784 and RFC 4205. The restrictions defined in this document prohibit the presence of TLV 22 in Extended LSPs. In the event that there is a need to advertise TE information in Extended LSPs, it would be necessary to define a new TLV to carry the TE information. Ginsberg Expires Sep 2006 [Page 7] INTERNET DRAFT Simplified Extension of LSP Space Mar 2006 Utilization of a new TLV for TE information would provide additional benefits which include: . Elimination of the need for redundant IS neighbor TLVs to be processed as part of the SPF. . Easier support for a set of TE information associated with a single link which exceeds the 255 byte TLV limit by allowing the interpretation of multiple TLVs to be considered additive rather than mutually exclusive. Such an extension would require all routers on which the TE information is processed to support the new TLV as well as the extensions defined in this document. Definition of a new TLV to advertise TE information is outside the scope of this document. 7. Security Considerations This document raises no new security issues for IS-IS. 8. IANA Considerations This document defines the following new ISIS TLV that needs to be reflected in the ISIS TLV code-point registry: Type Description IIH LSP SNP ---- ----------------------------------- --- --- --- 24 IS Alias ID n y n 9. 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. [RFC 3784] Smit, H. and T. Li, "Intermediate System to Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)", RFC 3784, June 2004. [RFC 3786] Hermelin, A., Previdi, S. and Shand, M., "Extending the Number of Intermediate to Intermediate (IS-IS) Link State PDU (LSP) Fragments Beyond the 256 Limit," RFC 3786, May 2004. [RFC 4205] Kompella, K. and Rehkter, Y., "Intermediate System to Intermediate System (IS-IS) Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4205, October 2005. Ginsberg Expires Sep 2006 [Page 8] INTERNET DRAFT Simplified Extension of LSP Space Mar 2006 [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 10. Acknowledgments 11. 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 12. Full Copyright Statement Copyright (C) The Internet Society (2006). All Rights Reserved. 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. 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 Ginsberg Expires Sep 2006 [Page 9] INTERNET DRAFT Simplified Extension of LSP Space Mar 2006 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. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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