Level 1 Area Abstraction for IS-IS
draft-li-area-abstraction-00

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Last updated 2018-06-29
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Internet Engineering Task Force                                    T. Li
Internet-Draft                                           Arista Networks
Intended status: Informational                             June 28, 2018
Expires: December 30, 2018

                   Level 1 Area Abstraction for IS-IS
                      draft-li-area-abstraction-00

Abstract

   Link state routing protocols have hierarchical abstraction already
   built into them.  However, when lower levels are used for transit,
   they must expose their internal topologies, leading to scale issues.

   To avoid this, this document discusses extensions to the IS-IS
   routing protocol that would allow level 1 areas to provide transit,
   yet only inject an abstraction of the topology into level 2.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on December 30, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Area Abstraction  . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Area Leader Election  . . . . . . . . . . . . . . . . . .   4
     2.2.  LSP Generation  . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Redundancy  . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Area Pseudonode TLV . . . . . . . . . . . . . . . . . . . . .   5
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The IS-IS routing protocol IS-IS [ISO10589] currently supports a two
   level hierarchy of abstraction.  The fundamental unit of abstraction
   is the 'area', which is a (hopefully) connected set of systems
   running IS-IS at the same level.  Level 1, the lowest level, is
   abstracted by routers that participate in both Level 1 and Level 2,
   and they inject area information into Level 2.  Level 2 systems
   seeking to access Level 1, use this abstraction to compute the
   shortest path to the Level 1 area.  The full topology database of
   Level 1 is not injected into Level 2, only a summary of the address
   space contained within the area, so the scalability of the Level 2
   link state database is protected.

   This works well if the Level 1 area is tangential to the Level 2
   area.  This also works well if there are a number of routers in both
   Level 1 and Level 2 and they are adjacent, so Level 2 traffic will
   never need to transit Level 1 only routers.  Level 1 will not contain
   any Level 2 topology, and Level 2 will only contain area abstractions
   for Level 1.

   Unfortunately, this scheme does not work so well if the Level 1 area
   needs to provide transit for Level 2 traffic.  For Level 2 shortest
   path first (SPF) computations to work correctly, the transit topology
   must also appear in the Level 2 link state database.  This implies
   that all routers that could possibly provide transit, plus any links
   that might also provide Level 2 transit must also become part of the

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