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Petrescu 3 Internet-Draft CEA, LIST 4 Intended status: Standards Track September 24, 2018 5 Expires: March 28, 2019 7 The length of the IPv6 link-local prefix 8 draft-petrescu-6man-ll-prefix-len-02 10 Abstract 12 The length of the IPv6 link-local prefix is 64 decimal. 14 Status of This Memo 16 This Internet-Draft is submitted in full conformance with the 17 provisions of BCP 78 and BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF). Note that other groups may also distribute 21 working documents as Internet-Drafts. The list of current Internet- 22 Drafts is at https://datatracker.ietf.org/drafts/current/. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 This Internet-Draft will expire on March 28, 2019. 31 Copyright Notice 33 Copyright (c) 2018 IETF Trust and the persons identified as the 34 document authors. All rights reserved. 36 This document is subject to BCP 78 and the IETF Trust's Legal 37 Provisions Relating to IETF Documents 38 (https://trustee.ietf.org/license-info) in effect on the date of 39 publication of this document. Please review these documents 40 carefully, as they describe your rights and restrictions with respect 41 to this document. Code Components extracted from this document must 42 include Simplified BSD License text as described in Section 4.e of 43 the Trust Legal Provisions and are provided without warranty as 44 described in the Simplified BSD License. 46 Table of Contents 48 1. Statement . . . . . . . . . . . . . . . . . . . . . . . . . . 2 49 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 50 3. Context . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 51 4. Security Considerations . . . . . . . . . . . . . . . . . . . 3 52 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 53 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 4 54 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 55 8. Normative References . . . . . . . . . . . . . . . . . . . . 4 56 Appendix A. ChangeLog . . . . . . . . . . . . . . . . . . . . . 4 57 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 59 1. Statement 61 The length of the IPv6 link-local prefix is 64 decimal. 63 The IPv6 link-local prefix is represented textually "fe80::/64". 65 The illustration of the IPv6 link-local prefix is: 67 | 68 | 64 bits, the link-local prefix | 64 bits | 69 +----------+-------------------------+----------------------------+ 70 |1111111010000000000000...00000000000| interface ID | 71 +----------+-------------------------+----------------------------+ 73 Figure 1: The IPv6 link-local prefix 75 2. Terminology 77 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 78 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 79 document are to be interpreted as described in RFC 2119 [RFC2119]. 81 prefix: a contiguous string of bits valid for forwarding operations 82 and for subnet formation. 84 textual representation of a prefix: e.g. fe80::/64. 86 n leading bits: the first n bits in a string of bits read from left 87 to right in a writing system that is read left-to-right. E.g. the 10 88 leading bits of the fe80::/64 textual representation of the IPv6 89 link-local prefix are 1111111010. 91 3. Context 93 The RFC "IPv6 Address Archi" illustrates the format of the link-local 94 addresses. From the illustration it MAY be understood that the 95 length of the link-local prefix is 10 bits of value 1111111010 and 54 96 0 bits. 98 IANA lists the "IPv6 prefix", and "Address Block", to be "fe80::/10" 99 on its website. It is possible that in the future the IETF could 100 decide to use the bits 11-53. 102 The RFC 2464 "IPv6-over-Ethernet" states that the prefix for link- 103 local addresses is "fe80::/64". 105 RFC 6874, "Representing IPv6 Zone Identifiers in Address Literals and 106 Uniform Resource Identifiers" specifies the link-local addresses to 107 be under prefix "fe80::/10". 109 Several knowledgeable interpretations state that, generally speaking, 110 the prefix length of link-local addresses is 10, but it is 64 in the 111 particular case of Stateless Address-Autoconfiguration (SLAAC). In 112 this latter case, the prefix is named a "subnet prefix", or "prefix 113 on a link", and it is "fe80::/64". 115 Implementations of an IPv6 stack in a particular operating system 116 allow for the manual configuration of both prefix lengths 64 and 10 117 for link-local addresses. In another operating system the prefix 118 length for link-local addresses can not be explicitely specified by 119 the end user, but may be indirectly derived from two distinct textual 120 formats by using an unspecified rule. 122 Misconfigurations and lack of interoperability MAY arise between 123 computers that use mixed prefix lengths for link-local addresses. 125 A memo describes the use of IPv6 link-local addresses in 126 applications. The filename of the Internet Draft is draft-smith- 127 ipv6-link-locals-apps-00. 129 Historical note: earlier, the link-local prefix fe80::/10 and site- 130 local prefix fec0::/10 were grouped into a common fe80::/9. If bits 131 10-64 were 0 then the prefix was a link-local, otherwise a site- 132 local. The site-local addresses were later deprecated by RFC 3879. 134 4. Security Considerations 136 The clarification of the definition of the prefix length of the IPv6 137 link-local prefix at IANA is: call it 'leading bits' and not 138 'prefix', or state that the IPv6 prefix length of link-local 139 addresses is 10 decimal. This clarification has beneficial impact in 140 the algorithm implementation for calculation of the opaque and stable 141 Interface Identifiers for IPv6 link-local addresses. It also 142 positively impacts some implementations of IPv6 forwarding. 144 5. IANA Considerations 146 IANA is requested to change the name of the column head in the table 147 that depicts the "Internet Protocol Version 6 Address Space". The 148 name should be "The n leading bits of an address" instead of "IPv6 149 Prefix". 151 The desired effect of this change is that the IPv6 link-local prefix 152 be "fe80::/64" and that the 10 leading bits of this prefix be 153 1111111010. A second effect is that the textual representation 154 "fe80::/10" as an IPv6 link-local prefix should disappear from that 155 IANA page, because it is wrong. 157 6. Contributors 159 Listed from 6man WG discussion. 161 7. Acknowledgements 163 The following persons are acknowledged for the discussion that is 164 reflected in this draft. Not all points are reflected. Some points 165 are copied almost entirely. 167 Ole Troan, Scott Timothy Morizot, Brian Carpenter, Fred Baker, Mark 168 Smith, Peter Occil, Philip Homburg, Albert Manfredi, _–3/4 169 ’BAE (TATUYA Jinmei), Fernando Gont, Christian Huitema. 171 8. Normative References 173 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 174 Requirement Levels", BCP 14, RFC 2119, 175 DOI 10.17487/RFC2119, March 1997, 176 . 178 Appendix A. ChangeLog 180 The changes are listed in reverse chronological order, most recent 181 changes appearing at the top of the list. 183 -02: corrected a typo in "fe80::/1" and added a 7-bit encoding for 184 one persons name (in addition to the japanese-shift-jis encoding 185 which is not understood by xml2rfc.) 187 Author's Address 189 Alexandre Petrescu 190 CEA, LIST 191 CEA Saclay 192 Gif-sur-Yvette , Ile-de-France 91190 193 France 195 Phone: +33169089223 196 Email: Alexandre.Petrescu@cea.fr