IS-IS Routing with Reverse Metric
RFC 8500

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Internet Engineering Task Force (IETF)                           N. Shen
Request for Comments: 8500                                 Cisco Systems
Category: Standards Track                                      S. Amante
ISSN: 2070-1721                                               Apple Inc.
                                                          M. Abrahamsson
                                                        T-Systems Nordic
                                                           February 2019

                   IS-IS Routing with Reverse Metric

Abstract

   This document describes a mechanism to allow IS-IS routing to quickly
   and accurately shift traffic away from either a point-to-point or
   multi-access LAN interface during network maintenance or other
   operational events.  This is accomplished by signaling adjacent IS-IS
   neighbors with a higher reverse metric, i.e., the metric towards the
   signaling IS-IS router.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8500.

Copyright Notice

   Copyright (c) 2019 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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Shen, et al.                 Standards Track                    [Page 1]
RFC 8500                  IS-IS Reverse Metric             February 2019

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Node and Link Isolation . . . . . . . . . . . . . . . . .   2
     1.2.  Distributed Forwarding Planes . . . . . . . . . . . . . .   3
     1.3.  Spine-Leaf Applications . . . . . . . . . . . . . . . . .   3
     1.4.  LDP IGP Synchronization . . . . . . . . . . . . . . . . .   3
     1.5.  IS-IS Reverse Metric  . . . . . . . . . . . . . . . . . .   3
     1.6.  Specification of Requirements . . . . . . . . . . . . . .   4
   2.  IS-IS Reverse Metric TLV  . . . . . . . . . . . . . . . . . .   4
   3.  Elements of Procedure . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Processing Changes to Default Metric  . . . . . . . . . .   6
     3.2.  Multi-Topology IS-IS Support on Point-to-Point Links  . .   7
     3.3.  Multi-access LAN Procedures . . . . . . . . . . . . . . .   7
     3.4.  LDP/IGP Synchronization on LANs . . . . . . . . . . . . .   8
     3.5.  Operational Guidelines  . . . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Appendix A.  Node Isolation Challenges  . . . . . . . . . . . . .  13
   Appendix B.  Link Isolation Challenges  . . . . . . . . . . . . .  13
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  15
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   The IS-IS [ISO10589] routing protocol has been widely used in
   Internet Service Provider IP/MPLS networks.  Operational experience
   with the protocol combined with ever increasing requirements for
   lossless operations have demonstrated some operational issues.  This
   document describes the issues and a mechanism for mitigating them.

   This document defines the IS-IS "Reverse Metric" mechanism that
   allows an IS-IS node to send a Reverse Metric TLV through the IS-IS
   Hello (IIH) PDU to the neighbor or pseudonode to adjust the routing
   metric on the inbound direction.

1.1.  Node and Link Isolation

   The IS-IS routing mechanism has the overload bit, which can be used
   by operators to perform disruptive maintenance on the router.  But in
   many operational maintenance cases, it is not necessary to divert all