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Versions: (draft-boucadair-6man-prefix-routing-reco) 00 01 02 03 RFC 7608

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
   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 July 22, 2015.






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Copyright Notice

   Copyright (c) 2015 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  . . . . . . . . . . . . . . . . . . . . . . . . .   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.



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   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
   destination address in each bit up to their respective lengths, the
   longer prefix is used.  This document's recommendation is that IPv6
   forwarding must follow the longest-match-first rule, regardless of
   prefix length, barring the configuration of some overriding policy.

   A historical reminder of CIDR is documented in [RFC1380] and
   Section 2 of [RFC4632].

2.  Recommendation

   IPv6 MUST conform to the rules specified in Section 5.1 of [RFC4632].

   Forwarding decision-making processes MUST NOT restrict the length of
   IPv6 prefixes by design.  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 for
   some IPv6 stateless address autoconfiguration (SLAAC, [RFC4862])
   based schemes such as [RFC2464].

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, Christian Jacquenet, Brian Carpenter, Fernando
   Gont, Tatuya Jinmei, Lorenzo Colitti, and Ross Chandler for their
   comments.

   Special thanks to Randy Bush for his support.






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6.  References

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.

   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
              (CIDR): The Internet Address Assignment and Aggregation
              Plan", BCP 122, RFC 4632, August 2006.

6.2.  Informative References

   [RFC1380]  Gross, P. and P. Almquist, "IESG Deliberations on Routing
              and Addressing", RFC 1380, November 1992.

   [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.

   [RFC7421]  Carpenter, B., Chown, T., Gont, F., Jiang, S., Petrescu,
              A., and A. Yourtchenko, "Analysis of the 64-bit Boundary
              in IPv6 Addressing", RFC 7421, January 2015.

Authors' Addresses

   Mohamed Boucadair
   France Telecom
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


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

   Phone: +33169089223
   Email: alexandre.petrescu@cea.fr




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   Fred Baker
   Cisco Systems
   Santa Barbara, California  93117
   USA

   Email: fred@cisco.com













































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