Hierarchical IS-IS
draft-li-hierarchical-isis-00

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

                           Hierarchical IS-IS
                     draft-li-hierarchical-isis-00

Abstract

   The IS-IS routing protocol was originally defined with a two level
   hierarchical structure.  This was adequate for the networks at the
   time.  As we continue to expand the scale of our networks, it is
   apparent that additional hierarchy would be a welcome degree of
   flexibility in network design.

   This document defines IS-IS Levels 3 through 8.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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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.  PDU changes . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Circuit Type  . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  PDU Type  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Additional PDUs . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  LAN IS to IS hello PDU (LAN-HELLO-PDU)  . . . . . . . . .   4
     3.2.  Point-to-point IS to IS hello PDU (P2P-HELLO-PDU) . . . .   4
     3.3.  Level n Link State PDU (Ln-LSP-PDU) . . . . . . . . . . .   4
     3.4.  Level n complete sequence numbers PDU (Ln-CSNP-PDU) . . .   5
     3.5.  Level n partial sequence numbers PDU (Ln-PSNP-PDU)  . . .   5
   4.  Inheritance of TLVs . . . . . . . . . . . . . . . . . . . . .   5
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  PDU Type  . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.2.  New PDUs  . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

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.

   Practical considerations, such as the size of an area's link state
   database, cause network designers to restrict the number of routers
   in any given area.  Concurrently, the dominance of scale-out
   architectures based around small routers has created a situation
   where the scalability limits of the protocol are going to become
   critical in the foreseeable future.

   The goal of this document is to enable additional hierarchy within
   IS-IS by creating additional hierarchy.  Each additional level of
   hierarchy has a multiplicative effect on scale, so the addtion of six
   levels should be a significant improvement.  While all six levels may
   not be needed in the short term, it is apparent that the original
   designers of IS-IS reserved enough space for these levels, and
   defining six additional levels is only slightly harder than adding a

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