Extending the Number of Intermediate System to Intermediate System (IS-IS) Link State PDU (LSP) Fragments Beyond the 256 Limit
RFC 3786
Document | Type |
RFC - Informational
(May 2004; No errata)
Obsoleted by RFC 5311
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Authors | Amir Hermelin , Stefano Previdi , Mike Shand | ||
Last updated | 2013-03-02 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 3786 (Informational) | |
Action Holders |
(None)
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Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Alex Zinin | ||
Send notices to | <dward@cisco.com>, <chopps@procket.com> |
Network Working Group A. Hermelin Request for Comments: 3786 Montilio Inc. Category: Informational S. Previdi M. Shand Cisco Systems May 2004 Extending the Number of Intermediate System to Intermediate System (IS-IS) Link State PDU (LSP) Fragments Beyond the 256 Limit Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document describes a mechanism that allows a system to originate more than 256 Link State PDU (LSP) fragments, a limit set by the original Intermediate System to Intermediate System (IS-IS) Routing protocol, as described in ISO/IEC 10589. This mechanism can be used in IP-only, OSI-only, and dual routers. Table of Contents 1. Introduction ................................................. 2 1.1. Keywords ............................................... 2 1.2. Definitions of Commonly Used Terms ..................... 2 1.3. Operation Modes ........................................ 3 1.4. Overview ............................................... 4 2. IS Alias ID TLV (IS-A) ....................................... 5 3. Generating LSPs .............................................. 6 3.1. Both Operation Modes ................................... 6 3.2. Operation Mode 1 Additives ............................. 8 4. Purging Extended LSP Fragments ............................... 10 5. Modifications to LSP handling in SPF ......................... 10 6. Forming Adjacencies .......................................... 11 7. Interoperating between extension-capable and non-capable ISs . 11 8. Security Considerations ...................................... 12 9. Acknowledgements ............................................. 12 Hermelin, et al. Informational [Page 1] RFC 3786 IS-IS LSP Fragments May 2004 10. References ................................................... 12 11. Authors' Addresses ........................................... 13 12. Full Copyright Statement ..................................... 14 1. Introduction In the Intermediate System to Intermediate System (IS-IS) protocol, a system floods its link-state information in Link State PDU (LSP) Data Units, or LSPs for short. These logical LSPs can become quite large, therefore the protocol specifies a means of fragmenting this information into multiple LSP fragments. The number of fragments a system can generate is limited by ISO/IEC 10589 [ISIS-ISO] to 256 fragments, where each fragment's size is also limited. Hence, there is a limit on the amount of link-state information a system can generate. A number of factors can contribute to exceeding this limit: - Introduction of new TLVs and sub-TLVs to be included in LSPs. - The use of LSPs to propagate various types of information (such as traffic-engineering information). - The increasing number of destinations and AS topologies. - Finer granularity routing, and the ability to inject external routes into areas [DOMAIN-WIDE]. - Other emerging technologies, such as optical, IPv6, etc. This document describes mechanisms to relax the limit on the number of LSP fragments. 1.1. Keywords 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 BCP 14, RFC 2119 [BCP14]. 1.2. Definitions of Commonly Used Terms This section provides definitions for terms that are used throughout the text. Originating System A router physically running the IS-IS protocol. As this document describes methods allowing a single IS-IS process to advertise its LSPs as multiple "virtual" routers, the Originating System represents the single "physical" IS-IS process. Hermelin, et al. Informational [Page 2] RFC 3786 IS-IS LSP Fragments May 2004 Normal system-id The system-id of an Originating System. Additional system-id An Additional system-id that is assigned by the network administrator. Each Additional system-id allows generation of 256 additional, or extended, LSP fragments. The AdditionalShow full document text