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.
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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
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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
Boucadair, et al. Expires July 22, 2015 [Page 5]