IS-IS Route Preference for Extended IP and IPv6 Reachability
RFC 7775

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Internet Engineering Task Force (IETF)                       L. Ginsberg
Request for Comments: 7775                                 Cisco Systems
Updates: 5308                                               S. Litkowski
Category: Standards Track                        Orange Business Service
ISSN: 2070-1721                                               S. Previdi
                                                           Cisco Systems
                                                           February 2016

      IS-IS Route Preference for Extended IP and IPv6 Reachability

Abstract

   In existing specifications, the route preferences for IPv4/IPv6
   Extended Reachability TLVs are not explicitly stated.  There are also
   inconsistencies in the definition of how the up/down bit applies to
   route preference when the prefix advertisement appears in Level 2
   Link State Protocol Data Units (LSPs).  This document addresses these
   issues.

   This document updates RFC 5308.

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 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7775.

Ginsberg, et al.             Standards Track                    [Page 1]
RFC 7775                 IS-IS Route Preference            February 2016

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Use of the Up/Down Bit in Level 2 LSPs  . . . . . . . . . . .   3
   3.  Types of Routes in IS-IS Supported by Extended Reachability
       TLVs  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Types of Routes Supported by TLVs 135 and 235 . . . . . .   4
     3.2.  Types of Routes Supported by TLVs 236 and 237 . . . . . .   6
     3.3.  Order of Preference for All Types of Routes Supported by
           TLVs 135 and 235  . . . . . . . . . . . . . . . . . . . .   7
     3.4.  Order of Preference for All Types of Routes Supported by
           TLVs 236 and 237  . . . . . . . . . . . . . . . . . . . .   8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  Example Interoperability Issue . . . . . . . . . . .  10
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

Ginsberg, et al.             Standards Track                    [Page 2]
RFC 7775                 IS-IS Route Preference            February 2016

1.  Introduction

   [RFC5302] defines the route preference rules as they apply to TLVs
   128 and 130.  [RFC5305] introduced the IP Extended Reachability TLV
   135 but did not explicitly adapt the route preference rules defined
   in [RFC5302] for the new TLV.  [RFC5308] defines the IPv6
   Reachability TLV 236 and does include an explicit statement regarding
   route preference -- but the statement introduces use of the up/down