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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (April 28, 1999) is 9130 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Missing reference section? '1' on line 13 looks like a reference -- Missing reference section? '2' on line 41 looks like a reference -- Missing reference section? '3' on line 44 looks like a reference -- Missing reference section? '4' on line 91 looks like a reference Summary: 5 errors (**), 0 flaws (~~), 2 warnings (==), 6 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPng Working Group R. Draves 3 Internet Draft Microsoft Research 4 Document: draft-draves-ipngwg-simple-srcaddr-00.txt April 28, 1999 5 Category: Standards Track 7 Simple Source Address Selection for IPv6 9 Status of this Memo 11 This document is an Internet-Draft and is in full conformance with 12 all provisions of Section 10 of RFC 2026 [1]. 14 Internet-Drafts are working documents of the Internet Engineering 15 Task Force (IETF), its areas, and its working groups. Note that 16 other groups may also distribute working documents as Internet- 17 Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six 20 months and may be updated, replaced, or obsoleted by other documents 21 at any time. It is inappropriate to use Internet-Drafts as reference 22 material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at 25 http://www.ietf.org/ietf/1id-abstracts.txt. 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html. 30 1. Abstract 32 This document describes a simple algorithm by which IPv6 33 implementations can choose an appropriate source address to use for 34 communication with a specified destination address. 36 2. Conventions used in this document 38 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 39 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 40 this document are to be interpreted as described in RFC-2119 [2]. 42 3. Introduction 44 The IPv6 addressing architecture [3] allows multiple addresses to be 45 assigned to interfaces. These addresses may have different 46 reachability scopes (link-local, site-local, or global). 47 Furthermore, addresses assigned via IPv6's auto-configuration 48 mechanisms [4] may be "preferred" or "deprecated". 50 Draves Standards Track - Expires November 1999 1 51 Simple Source Address Selection for IPv6 April 28, 1999 53 On occasion, an IPv6 implementation must choose from a set of 54 available addresses an appropriate source address to use for a given 55 destination address. This document specifies a simple set of rules 56 for choosing a source address of appropriate scope and configuration 57 status (preferred or deprecated). Furthermore, this document 58 suggests a preferred method, longest matching prefix, for choosing 59 among otherwise equivalent source addresses in the absence of better 60 information. 62 This document does not address the more general problem of choosing 63 the "best" destination address / source address pair for 64 communication with another node, given a set of possible destination 65 addresses and a set of possible source addresses. 67 This document does not specify a "strong host" or "weak host" model 68 for source address selection [5, section 3.3.4.2]. It merely assumes 69 that the implementation has a set of candidate source addresses from 70 which one must be chosen. If the implementation uses the strong host 71 model, this MAY be the set of addresses assigned to the outgoing 72 interface that will be used for the destination address. If the 73 implementation uses the weak host model, this MAY be the set of all 74 addresses assigned to the node's interfaces. 76 The rules specified in this document MUST NOT be construed to 77 override an application's explicit choice of source address. 79 4. Source Address Selection 81 This document specifies a pair-wise source address selection 82 algorithm. Given a destination address and a pair of possible source 83 addresses SA and SB (SA not equal to SB), it chooses a source 84 address. Obviously, any pair-wise algorithm may be extended to 85 select an address from a set of candidate source addresses. 87 When comparing scopes, we say that link-local scope is smaller than 88 site-local scope, which is smaller than global scope. 90 Addresses that are manually configured (or otherwise not auto- 91 configured according to [4]), we treat as having "preferred" 92 configuration status. 94 The algorithm consists of four rules, which MUST be applied in 95 order. If a rule chooses a source address, then the remaining rules 96 are not relevant and MUST be ignored. Subsequent rules act as tie- 97 breakers for earlier rules. If the four rules fail to choose a 98 source address, some unspecified tie-breaker MUST be used. 100 Rule 1: If one of the source addresses is equal to the destination 101 address, an implementation MUST choose that source address. 103 Rule 2: If the source addresses SA and SB have different scope, then 104 an implementation MUST choose the source address as follows. Without 105 loss of generality, assume that SA has smaller scope than SB. If the 107 Draves Standards Track - Expires November 1999 2 108 Simple Source Address Selection for IPv6 April 28, 1999 110 destination address scope is smaller than or equal to SA's scope, 111 then choose SA. Otherwise choose SB. 113 Rule 3: The two source addresses have the same scope. If one of the 114 source addresses is "preferred" and one of them is "deprecated", an 115 implementation MUST choose the one that is preferred. 117 Rule 4: The two source addresses have the same scope and the same 118 configuration status (both preferred or both deprecated). If one of 119 the source addresses has a longer prefix matching the destination 120 address, an implementation SHOULD choose the source address with the 121 longer matching prefix. 123 The fourth rule MAY be superceded if the implementation has other 124 means of choosing among source addresses. For example, if the 125 implementation somehow knows which source address will result in the 126 "best" communications performance. 128 5. Multicast Destination Addresses 130 Multicast destination addresses have a 4-bit scope field that 131 controls the propagation of the multicast packet. The IPv6 132 addressing architecture defines scope field values for node-local 133 (0x1), link-local (0x2), site-local (0x5), organization-local (0x8), 134 and global (0xE) scopes. 136 Application of the source address selection algorithm to a multicast 137 destination address requires the comparison of a unicast source 138 address scope with a multicast destination address scope. We map 139 unicast link-local to multicast link-local, unicast site-local to 140 multicast site-local, and unicast global scope to multicast global 141 scope. This mapping implicitly conflates unicast site boundaries and 142 multicast site boundaries. 144 6. IPv4-Compatible Addresses 146 For the purposes of this document, IPv4-compatible addresses have 147 global scope and "preferred" configuration status. 149 7. Other Format Prefixes 151 This document does not specify source address selection in the 152 presence of NSAP addresses, IPX addresses, or addresses with as-yet- 153 undefined format prefixes. 155 5. Security Considerations 157 This document has no direct impact on Internet infrastructure 158 security. 160 Draves Standards Track - Expires November 1999 3 161 Simple Source Address Selection for IPv6 April 28, 1999 163 6. References 165 1 S. Bradner, "The Internet Standards Process -- Revision 3", BCP 166 9, RFC 2026, October 1996. 168 2 S. Bradner, "Key words for use in RFCs to Indicate Requirement 169 Levels", BCP 14, RFC 2119, March 1997. 171 3 R. Hinden, S. Deering, "IP Version 6 Addressing Architecture", 172 RFC 2373, July 1998. 174 4 S. Thompson, T. Narten, "IPv6 Stateless Address 175 Autoconfiguration", RFC 2462 , December 1998. 177 5 R. Braden, editor, "Requirements for Internet Hosts - 178 Communication Layers", RFC 1122 , October 1989. 180 7. Acknowledgments 182 The author would like to acknowledge the contributions of the IPng 183 Working Group, and in particular, Robert Elz and Jack McCann. 185 8. Author's Address 187 Richard Draves 188 Microsoft Research 189 One Microsoft Way 190 Redmond, WA 98052 191 Email: richdr@microsoft.com 193 Draves Standards Track - Expires November 1999 4 194 Simple Source Address Selection for IPv6 April 28, 1999 196 Full Copyright Statement 198 Copyright (C) The Internet Society (1999). All Rights Reserved. 199 This document and translations of it may be copied and furnished to 200 others, and derivative works that comment on or otherwise explain it 201 or assist in its implementation may be prepared, copied, published 202 and distributed, in whole or in part, without restriction of any 203 kind, provided that the above copyright notice and this paragraph 204 are included on all such copies and derivative works. However, this 205 document itself may not be modified in any way, such as by removing 206 the copyright notice or references to the Internet Society or other 207 Internet organizations, except as needed for the purpose of 208 developing Internet standards in which case the procedures for 209 copyrights defined in the Internet Standards process must be 210 followed, or as required to translate it into languages other than 211 English. 213 The limited permissions granted above are perpetual and will not be 214 revoked by the Internet Society or its successors or assigns. 216 This document and the information contained herein is provided on an 217 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 218 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 219 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 220 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 221 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 223 Draves Standards Track - Expires November 1999 5