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

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Table of Contents

• 1. Introduction
• 2. Definition of Longest Acceptable Prefix
• 3. Security Considerations
• 4. IANA Considerations
• 5. Acknowledgements
• 6. Informative References
• Appendix A. Change log [RFC Editor: Please remove]
• Author's Address

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. 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.

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

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

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

Initial version

Author's Address