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Versions: 00 01 02 03 draft-ietf-v6ops-cidr-prefix

6man Working Group                                          M. Boucadair
Internet-Draft                                            France Telecom
Intended status: Standards Track                             A. Petrescu
Expires: March 28, 2015                                        CEA, LIST
                                                      September 24, 2014


            IPv6 Prefix Length Recommendation for Forwarding
              draft-boucadair-6man-prefix-routing-reco-03

Abstract

   The length of IP prefixes is an information used by forwarding and
   routing processes is policy-based.  As such, no maximum length must
   be assumed by design.

   Discussions on the 64-bit boundary in IPv6 addressing revealed a need
   for a clear recommendation on which bits must be used by forwarding
   decision-making processes.  This document sketches a recommendation
   to be followed by forwarding and routing designs with regards to the
   prefix length.  The aim is to avoid hard-coded routing and forwarding
   designs that exclude some IP prefix lengths.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 28, 2015.






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Copyright Notice

   Copyright (c) 2014 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
   (http://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.

Table of Contents

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

1.  Introduction

   Recent discussions on the 64-bit boundary in IPv6 addressing
   ([I-D.ietf-6man-why64]) revealed a need for a clear recommendation on
   which bits must be used by forwarding decision-making processes.

   A detailed analysis of the 64-bit boundary in IPv6 addressing, and
   the implication for end-site prefix assignment, is documented in
   [I-D.ietf-6man-why64].  No recommendation is included in
   [I-D.ietf-6man-why64].

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

   Forwarding decisions made by routers primarily rely upon a longest
   prefix-match algorithm.  Like in IPv4, the IPv6 prefix-match
   algorithms involve one critical operation which is the comparison of
   a destination address with a prefix present in a routing table (e.g.,
   compare the 2001:db8::1 address with the 2001:db8::/64 prefix).  The




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   recommendation of this document is to be followed by that critical
   operation.

   It is important that the compare operation be a bit-wise comparison,
   and not a byte-wise comparison.

2.  Recommendation

   Forwarding decision-making processes MUST NOT restrict by design the
   length of IPv6 prefixes.  In particular, forwarding processes MUST be
   designed to process prefixes of any length up to /128, by increments
   of 1.

   Obviously, policies can be enforced to restrict the length of IP
   prefixes advertised within a given domain or in a given
   interconnection link.  These policies are deployment-specific and/or
   driven by administrative (interconnection) considerations.

   This recommendation does not conflict with the 64-bit boundary
   involved when IPv6 stateless address autoconfiguration (SLAAC,
   [RFC4862]) is used on links such as Ethernet [RFC2464].

   Some lookup algorithm implementations (find the prefix matching a
   given destination address) may be affected by this recommendation,
   even more so for IPv6 than IPv4.  The performance of some
   implementations may be degraded when prefix lengths are longer than
   /64.

3.  IANA Considerations

   This document does not require any action from IANA.

4.  Security Considerations

   This document does not introduce security issues in addition to what
   is discussed in [RFC4291].

5.  Acknowledgements

   Thanks to Eric Vyncke and Christian Jacquenet for their comments.

   Special thanks to Randy Bush and Brian Carpenter for their support.

6.  References







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6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

6.2.  Informative References

   [I-D.ietf-6man-why64]
              Carpenter, B., Chown, T., Gont, F., Jiang, S., Petrescu,
              A., and A. Yourtchenko, "Analysis of the 64-bit Boundary
              in IPv6 Addressing", draft-ietf-6man-why64-05 (work in
              progress), September 2014.

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, December 1998.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

Authors' Addresses

   Mohamed Boucadair
   France Telecom
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Alexandru Petrescu
   CEA, LIST
   CEA Saclay
   Gif-sur-Yvette, Ile-de-France  91190
   France

   Phone: +33169089223
   Email: Alexandru.Petrescu@cea.fr











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