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Carpenter 3 Internet-Draft Univ. of Auckland 4 Intended status: Informational June 20, 2018 5 Expires: December 22, 2018 7 The Longest Acceptable Prefix for IPv6 Links 8 draft-carpenter-6man-lap-01 10 Abstract 12 This document introduces the concepts of a Longest Acceptable Prefix 13 (LAP) and a Shortest Acceptable Identifier Length (SAIL) for an IPv6 14 link. 16 Status of This Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF). Note that other groups may also distribute 23 working documents as Internet-Drafts. The list of current Internet- 24 Drafts is at https://datatracker.ietf.org/drafts/current/. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 This Internet-Draft will expire on December 22, 2018. 33 Copyright Notice 35 Copyright (c) 2018 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (https://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. Code Components extracted from this document must 44 include Simplified BSD License text as described in Section 4.e of 45 the Trust Legal Provisions and are provided without warranty as 46 described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 51 2. Definition of Longest Acceptable Prefix . . . . . . . . . . . 2 52 3. Definition of Shortest Acceptable Identifier Length . . . . . 3 53 4. Security Considerations . . . . . . . . . . . . . . . . . . . 3 54 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 55 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 3 56 7. Informative References . . . . . . . . . . . . . . . . . . . 3 57 Appendix A. Change log [RFC Editor: Please remove] . . . . . . . 4 58 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4 60 1. Introduction 62 The IPv6 addressing architecture [RFC4291] clearly separates an 63 address into a routing prefix of length n bits and an interface 64 identifier of length 128-n bits. IPv6 routers are required by BCP 65 198 [RFC7608] to support any length of routing prefix. For 66 operational reasons, routing prefixes up to 127 bits have been 67 recommended [RFC6164]. 69 Stateless Address Autoconfiguration (SLAAC) [RFC4862] requires a 70 fixed prefix length for each Layer 2 medium, and for largely 71 historical reasons [RFC7136] this has been fixed for all media as 64 72 bits by the addressing architecture. 74 Efforts to update the addressing architecture 75 [I-D.ietf-6man-rfc4291bis] have shown that there are contradictory 76 opinions about retaining this fixed length for all purposes, not just 77 for SLAAC. See for example [I-D.bourbaki-6man-classless-ipv6]. 79 This document does not aim to rehash those opinions and the arguments 80 behind them. Its only purpose is to propose simple terminology to 81 make the discussion easier. Both the terms introduced include the 82 word "Acceptable" to make it clear that they are human operational 83 choices. 85 2. Definition of Longest Acceptable Prefix 87 As noted above, any prefix length up to /128 is treated identically 88 by routing protocols. However, for a given network, end site, or 89 link, there always exists a Longest Acceptable Prefix (LAP), whose 90 length is locally determined. Currently, a site or link that uses 91 SLAAC has a LAP of /64, and will not work with a longer one. A 92 point-to-point link may have a LAP of /127, according to [RFC6164]. 93 Situations in which other LAPs might be used should be defined in 94 other documents. 96 3. Definition of Shortest Acceptable Identifier Length 98 The interface identifier is used to identify a given interface on a 99 given link, and is therefore only of local significance, even though 100 it is globally visible as part of an address. For a given link, 101 there always exists a Shortest Acceptable Identifier Length (SAIL). 102 By definition, 104 LAP + SAIL <= 128 106 Currently, a site or link that uses SLAAC has a SAIL of 64. 107 Situations in which other SAILs might be used should be defined in 108 other documents, with particular attention to security and privacy 109 issues. 111 4. Security Considerations 113 As noted in the Security Considerations of 114 [I-D.ietf-6man-rfc4291bis], the length of a SAIL, and therefore the 115 length of a LAP, have important implications for privacy. Proposals 116 for adopting LAPs longer than /64 must take this into account. 118 Additionally, the length of a SAIL has important implications for the 119 feasability of network reconnaissance by scanning attacks [RFC7707]. 121 5. IANA Considerations 123 This document makes no request of the IANA. 125 6. Acknowledgements 127 The term SAIL is directly based on a suggestion by Mark Smith. 129 7. Informative References 131 [I-D.bourbaki-6man-classless-ipv6] 132 Bourbaki, N., "IPv6 is Classless", draft-bourbaki-6man- 133 classless-ipv6-03 (work in progress), March 2018. 135 [I-D.ietf-6man-rfc4291bis] 136 Hinden, R. and S. Deering, "IP Version 6 Addressing 137 Architecture", draft-ietf-6man-rfc4291bis-09 (work in 138 progress), July 2017. 140 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 141 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 142 2006, . 144 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 145 Address Autoconfiguration", RFC 4862, 146 DOI 10.17487/RFC4862, September 2007, 147 . 149 [RFC6164] Kohno, M., Nitzan, B., Bush, R., Matsuzaki, Y., Colitti, 150 L., and T. Narten, "Using 127-Bit IPv6 Prefixes on Inter- 151 Router Links", RFC 6164, DOI 10.17487/RFC6164, April 2011, 152 . 154 [RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6 155 Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136, 156 February 2014, . 158 [RFC7608] Boucadair, M., Petrescu, A., and F. Baker, "IPv6 Prefix 159 Length Recommendation for Forwarding", BCP 198, RFC 7608, 160 DOI 10.17487/RFC7608, July 2015, 161 . 163 [RFC7707] Gont, F. and T. Chown, "Network Reconnaissance in IPv6 164 Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016, 165 . 167 Appendix A. Change log [RFC Editor: Please remove] 169 draft-carpenter-6man-lap-00, 2018-06-13: 171 Initial version 173 draft-carpenter-6man-lap-01, 2018-06-20: 175 Added SAIL, minor clarifications 177 Author's Address 179 Brian Carpenter 180 Department of Computer Science 181 University of Auckland 182 PB 92019 183 Auckland 1142 184 New Zealand 186 Email: brian.e.carpenter@gmail.com