Avoiding Traffic Black-Holes for Route Aggregation in IS-IS
draft-chen-isis-black-hole-avoid-01

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Network Working Group                                            Z. Chen
Internet-Draft                                                     X. Xu
Intended status: Standards Track                     Huawei Technologies
Expires: March 17, 2018                               September 13, 2017

      Avoiding Traffic Black-Holes for Route Aggregation in IS-IS
                  draft-chen-isis-black-hole-avoid-01

Abstract

   When the Intermediate System to Intermediate System (IS-IS) routing
   protocol is adopted by a highly symmetric network such as the Leaf-
   Spine or Fat-Tree network, the Leaf nodes (e.g., Top of Rack switches
   in datacenters) are recommended to be prevented from receiving other
   nodes' explicit routes in order to achieve scalability.  However,
   such a setup would cause traffic black-holes or suboptimal routing if
   link failure happens in the network.  This document extends IS-IS to
   solve this problem.

Requirements Language

   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 [RFC2119].

Status of This Memo

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

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   This Internet-Draft will expire on March 17, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Chen & Xu                Expires March 17, 2018                 [Page 1]
Internet-Draft          IS-IS Black-Hole Avoiding         September 2017

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem Description . . . . . . . . . . . . . . . . . . . . .   3
   3.  IS-IS Extensions  . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  TLV Encoding  . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Unreachable Prefixes Advertisement  . . . . . . . . . . .   5
   4.  Alternative Solution  . . . . . . . . . . . . . . . . . . . .   6
   5.  IPv6 Support  . . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   When running the Intermediate System to Intermediate System (IS-IS)
   routing protocol in a highly symmetric network such as the Leaf-Spine
   or Fat-Tree network, the Leaf nodes (e.g., Top of Rack switches in
   datacenters) are recommended to be prevented from receiving other
   nodes' explicit routes in order to achieve scalability, as proposed
   in [IS-IS-SL-Extension], [IS-IS-Overhead-Reduction], [RIFT], and
   [OpenFabric].  In particular, each Leaf node SHOULD simply maintain a
   default (or aggregated) route (e.g., 0.0.0.0/0) in its routing table,
   of which the next hop SHOULD be an Equal Cost Multi Path (ECMP) group
   including all Spines nodes that the Leaf node connects to.  However,
   such a setup would cause traffic black-holes or suboptimal routing if
   link failure happens in the network, since the Leaf nodes are not
   aware of any topology information.

   To solve this problem, this document extends IS-IS to advertise
   unreachable prefixes, which are defined as the prefixes that a
   default (or aggregated) route's next hop can no longer reach.  When
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