RFC 3786 (rfc3786) - Page 2 of 14

Extending the Number of Intermediate System to Intermediate System (IS-IS) Link State PDU (LSP) Fragments Beyond the 256 Limit

Alternative Format: Original Text Document

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
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