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Network Working Group                                       B. Carpenter
Internet-Draft                                         Univ. of Auckland
Intended status: Informational                             June 13, 2018
Expires: December 15, 2018


              The Longest Acceptable Prefix for IPv6 Links
                      draft-carpenter-6man-lap-00

Abstract

   This document introduces the concept of a Longest Acceptable Prefix
   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 15, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Longest Acceptable Prefix . . . . . . . . . . . . . . . . . .   2
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   3
   6.  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 purpose is to propose simple terminology to make
   the discussion easier.

2.  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.







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3.  Security Considerations

   As noted in the Security Considerations of
   [I-D.ietf-6man-rfc4291bis], the length of an interface identifier,
   and therefore the length of a LAP, have important implications for
   privacy.  Proposals for adopting LAPs longer than /64 must take
   this into account.

4.  IANA Considerations

   This document makes no request of the IANA.

5.  Acknowledgements

   Useful comments were received from ...

6.  Informative References

   [I-D.bourbaki-6man-classless-ipv6]
              Bourbaki, N., "IPv6 is Classless", draft-bourbaki-6man-
              classless-ipv6-03 (work in progress), March 2018.

   [I-D.ietf-6man-rfc4291bis]
              Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", draft-ietf-6man-rfc4291bis-09 (work in
              progress), July 2017.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <https://www.rfc-editor.org/info/rfc4862>.

   [RFC6164]  Kohno, M., Nitzan, B., Bush, R., Matsuzaki, Y., Colitti,
              L., and T. Narten, "Using 127-Bit IPv6 Prefixes on Inter-
              Router Links", RFC 6164, DOI 10.17487/RFC6164, April 2011,
              <https://www.rfc-editor.org/info/rfc6164>.

   [RFC7136]  Carpenter, B. and S. Jiang, "Significance of IPv6
              Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136,
              February 2014, <https://www.rfc-editor.org/info/rfc7136>.







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   [RFC7608]  Boucadair, M., Petrescu, A., and F. Baker, "IPv6 Prefix
              Length Recommendation for Forwarding", BCP 198, RFC 7608,
              DOI 10.17487/RFC7608, July 2015,
              <https://www.rfc-editor.org/info/rfc7608>.

Appendix A.  Change log [RFC Editor: Please remove]

   draft-carpenter-6man-lap, 2018-06-13:

   Initial version

Author's Address

   Brian Carpenter
   Department of Computer Science
   University of Auckland
   PB 92019
   Auckland  1142
   New Zealand

   Email: brian.e.carpenter@gmail.com






























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