IPv6 Prefix Length Recommendation for Forwarding
draft-ietf-v6ops-cidr-prefix-00

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Document Type Active Internet-Draft (v6ops WG)
Last updated 2015-01-20
Replaces draft-boucadair-6man-prefix-routing-reco
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v6ops Working Group                                         M. Boucadair
Internet-Draft                                            France Telecom
Intended status: Best Current Practice                       A. Petrescu
Expires: July 22, 2015                                         CEA, LIST
                                                                F. Baker
                                                           Cisco Systems
                                                        January 18, 2015

            IPv6 Prefix Length Recommendation for Forwarding
                    draft-ietf-v6ops-cidr-prefix-00

Abstract

   IPv6 prefix length, as in IPv4, is a parameter conveyed and used in
   IPv6 routing and forwarding processes in accordance with the
   Classless Inter-domain Routing (CIDR) architecture.  The length of an
   IPv6 prefix may be any number from zero to 128, although subnets
   using stateless address autoconfiguration (SLAAC) for address
   allocation conventionally use a /64 prefix.  Hardware and software
   algorithms should therefore impose no rules on prefix length, but
   implement longest-match-first on prefixes of any valid length.

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.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on July 22, 2015.

Boucadair, et al.         Expires July 22, 2015                 [Page 1]
Internet-Draft                                              January 2015

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Recommendation  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   3
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   Discussions on the 64-bit boundary in IPv6 addressing ([RFC7421])
   revealed a need for a clear recommendation on which bits must be used
   by forwarding decision-making processes.

   Although Section 2.5 of [RFC4291] states "IPv6 unicast addresses are
   aggregatable with prefixes of arbitrary bit-length, similar to IPv4
   addresses under Classless Inter-Domain Routing" (CIDR, [RFC4632]),
   there is still a misinterpretation that IPv6 prefixes can be either
   /127 or any length up to /64.  This (mis)interpretation is mainly
   induced by the 64-bit boundary in IPv6 addressing.

   A detailed analysis of the 64-bit boundary in IPv6 addressing
   together with the implication for end-site prefix assignment are
   documented in [RFC7421], but no recommendation is included in that
   document.

   It is fundamental to not link routing and forwarding to the IPv6
   prefix/address semantics [RFC4291].  This document includes a
   recommendation for that aim.

Boucadair, et al.         Expires July 22, 2015                 [Page 2]
Internet-Draft                                              January 2015

   Forwarding decisions rely on the longest-match-first algorithm, which
   stipulates that, given a choice between two prefixes in the
   Forwarding Information Base (FIB) of different length that match the
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