Internet DRAFT - draft-carpenter-6man-lap
draft-carpenter-6man-lap
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
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This Internet-Draft will expire on December 22, 2018.
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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.
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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,
LAP + SAIL <= 128
Currently, a site or link that uses SLAAC has a SAIL of 64.
Situations in which other SAILs might be used should be defined in
other documents, with particular attention to security and privacy
issues.
4. Security Considerations
As noted in the Security Considerations of
[I-D.ietf-6man-rfc4291bis], the length of a SAIL, and therefore the
length of a LAP, have important implications for privacy. Proposals
for adopting LAPs longer than /64 must take this into account.
Additionally, the length of a SAIL has important implications for the
feasability of network reconnaissance by scanning attacks [RFC7707].
5. IANA Considerations
This document makes no request of the IANA.
6. Acknowledgements
The term SAIL is directly based on a suggestion by Mark Smith.
7. 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>.
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[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>.
[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>.
[RFC7707] Gont, F. and T. Chown, "Network Reconnaissance in IPv6
Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,
<https://www.rfc-editor.org/info/rfc7707>.
Appendix A. Change log [RFC Editor: Please remove]
draft-carpenter-6man-lap-00, 2018-06-13:
Initial version
draft-carpenter-6man-lap-01, 2018-06-20:
Added SAIL, minor clarifications
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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