The Longest Acceptable Prefix for IPv6 Links
draft-carpenter-6man-lap-01

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Network Working Group                                       B. Carpenter
Internet-Draft                                         Univ. of Auckland
Intended status: Informational                             June 20, 2018
Expires: December 22, 2018

              The Longest Acceptable Prefix for IPv6 Links
                      draft-carpenter-6man-lap-01

Abstract

   This document introduces the concepts of a Longest Acceptable Prefix
   (LAP) and a Shortest Acceptable Identifier Length (SAIL) for an IPv6
   link.

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 December 22, 2018.

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Carpenter               Expires December 22, 2018               [Page 1]
Internet-Draft          Longest Acceptable Prefix              June 2018

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definition of Longest Acceptable Prefix . . . . . . . . . . .   2
   3.  Definition of Shortest Acceptable Identifier Length . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   3
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   3
   Appendix A.  Change log [RFC Editor: Please remove] . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   The IPv6 addressing architecture [RFC4291] clearly separates an
   address into a routing prefix of length n bits and an interface
   identifier of length 128-n bits.  IPv6 routers are required by BCP
   198 [RFC7608] to support any length of routing prefix.  For
   operational reasons, routing prefixes up to 127 bits have been
   recommended [RFC6164].

   Stateless Address Autoconfiguration (SLAAC) [RFC4862] requires a
   fixed prefix length for each Layer 2 medium, and for largely
   historical reasons [RFC7136] this has been fixed for all media as 64
   bits by the addressing architecture.

   Efforts to update the addressing architecture
   [I-D.ietf-6man-rfc4291bis] have shown that there are contradictory
   opinions about retaining this fixed length for all purposes, not just
   for SLAAC.  See for example [I-D.bourbaki-6man-classless-ipv6].

   This document does not aim to rehash those opinions and the arguments
   behind them.  Its only purpose is to propose simple terminology to
   make the discussion easier.  Both the terms introduced include the
   word "Acceptable" to make it clear that they are human operational
   choices.

2.  Definition of Longest Acceptable Prefix

   As noted above, any prefix length up to /128 is treated identically
   by routing protocols.  However, for a given network, end site, or
   link, there always exists a Longest Acceptable Prefix (LAP), whose
   length is locally determined.  Currently, a site or link that uses
   SLAAC has a LAP of /64, and will not work with a longer one.  A
   point-to-point link may have a LAP of /127, according to [RFC6164].
   Situations in which other LAPs might be used should be defined in
   other documents.

Carpenter               Expires December 22, 2018               [Page 2]
Internet-Draft          Longest Acceptable Prefix              June 2018

3.  Definition of Shortest Acceptable Identifier Length

   The interface identifier is used to identify a given interface on a
   given link, and is therefore only of local significance, even though
   it is globally visible as part of an address.  For a given link,
   there always exists a Shortest Acceptable Identifier Length (SAIL).
   By definition,
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