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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Dave Thaler 3 Internet-Draft Microsoft 4 Expires: July 2004 19 January 2004 6 Unicast-Prefix-based IPv4 Multicast Addresses 7 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 RFC2026. 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 21 documents at any time. It is inappropriate to use Internet- 22 Drafts as reference material or to cite them other than as "work 23 in progress." 25 The list of current Internet-Drafts can be accessed at 26 http://www.ietf.org/ietf/1id-abstracts.txt 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html. 31 Copyright Notice 33 Copyright (C) The Internet Society (2004). All Rights Reserved. 35 Abstract 36 Draft Uni-Prefix-based IPv4 Multicast January 2004 38 This specification defines an extension to the multicast 39 addressing architecture of the IP Version 4 protocol. The 40 extension presented in this document allows for unicast-prefix- 41 based allocation of multicast addresses. By delegating multicast 42 addresses at the same time as unicast prefixes, network operators 43 will be able to identify their multicast addresses without needing 44 to run an inter-domain allocation protocol. 46 1. Introduction 48 RFC 2770 [GLOP] defined an experimental allocation mechanism in 49 233/8 whereby an Autonomous System (AS) number is embedded in the 50 middle 16 bits of an IPv4 multicast address, resulting in 256 51 multicast addresses per AS. Advantages of this mechanism include 52 the ability to get multicast address space without an inter-domain 53 multicast address allocation protocol, and the ease of determining 54 the AS of the owner of an address for debugging and auditing 55 purposes. 57 Some disadvantages of GLOP include: 59 o only 256 addresses are automatically available per AS, and 60 obtaining any more requires administrative effort. 62 o there is work in progress [AS4B] on expanding the size of an 63 AS number to 4 bytes, and GLOP cannot work with such AS's. 65 o when an AS covers multiple sites or organizations, 66 administration of the multicast address space within an AS 67 must be handled by other mechanisms, such as manual 68 administrative effort or MADCAP [MADCAP]. 70 o during debugging, identifying the AS does not immediately 71 identify the owning organization, when an AS covers multiple 72 organizations. 74 More recently, a mechanism [V6UPBM] has been developed for IPv6 75 which provides a multicast range to every IPv6 subnet, which is at 76 a much finer granularity than an AS. As a result, the latter 77 three disadvantages above are avoided (and the first disadvantage 78 does not apply to IPv6 due to the extended size of the address 79 space). 81 Two significant advantages of providing multicast space to every 82 Draft Uni-Prefix-based IPv4 Multicast January 2004 84 subnet (rather than just to an entire AS) are that: 86 o multicast address allocation within the range need only be 87 coordinated within the subnet, and hence can be done with 88 zero configuration. 90 o bidirectional shared tree routing protocols may easily locate 91 the direction to the root by doing a route lookup on a 92 unicast address derived from the multicast group address. 94 This draft specifies a mechanism similar to [V6UPBM], whereby a 95 range of IPv4 multicast address space is provided to most IPv4 96 subnets. A resulting advantage over GLOP is that the mechanisms 97 in IPv4 and IPv6 become more similar. 99 2. Address Space 101 (RFC-editor: replace TBD below with IANA-assigned value, and 102 delete this note.) 104 A multicast address with the prefix TBD/8 indicates that the 105 address is a Unicast-Based Multicast (UBM) address. The 106 remaining 24 bits can be used as follows: 108 Bits: | 8 | Unicast Prefix Length | 24 - Unicast Prefix Length | 109 +-----+-----------------------+----------------------------+ 110 Value: | TBD | Unicast Prefix | Group ID | 111 +-----+-----------------------+----------------------------+ 113 For subnets with a /24 or shorter prefix, the unicast prefix of 114 the subnet is appended to the common /8. Any remaining bits may 115 be locally assigned by hosts within the link (e.g., using manual 116 configuration). Individual subnets with a prefix length longer 117 than 24 do not receive any multicast address space from this 118 mechanism; in such cases, MADCAP may be used. 120 Compared to GLOP, an AS will receive more address space via this 121 mechanism if it has more than a /16 for unicast space. An AS will 122 receive less address space than it does from GLOP if it has less 123 than a /16. 125 The owner of a UBM address can be determined by taking the 126 multicast address, shifting it left by 8 bits, and identifying the 127 owner of the address space covering the resulting unicast address. 129 Draft Uni-Prefix-based IPv4 Multicast January 2004 131 3. IANA Considerations 133 IANA should assign a /8 in the IPv4 multicast address space for 134 this purpose. 136 4. Security Considerations 138 Since dynamic assignment does not cross domain boundaries, the 139 same well known intra-domain security techniques can be applied as 140 with GLOP. Furthermore, the approach described here may have the 141 effect of reduced exposure to denial of space attacks based on 142 dynamic allocation, since the area of dynamic allocation is 143 reduced from an entire AS to only within individual subnets. 145 5. Author's Address 147 Dave Thaler 148 Microsoft Corporation 149 One Microsoft Way 150 Redmond, WA 98052-6399 151 Phone: +1 425 703 8835 152 EMail: dthaler@microsoft.com 154 6. Informative References 156 [AS4B] 157 Vohra, Q. and E. Chen, "BGP support for four-octet AS number 158 space", draft-ietf-idr-as4bytes-07.txt, Work in progress, 159 August 2003. 161 [GLOP] 162 Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", RFC 163 2770, February 2000. 165 [MADCAP] 166 Hanna, S, Patel, B. and M. Shah, "Multicast Address Dynamic 167 Client Allocation Protocol (MADCAP)", RFC 2730, December 168 1999. 170 [V6UPBM] 171 Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 172 Multicast Addresses", RFC 3306, August 2002. 174 Draft Uni-Prefix-based IPv4 Multicast January 2004 176 7. Full Copyright Statement Copyright (C) The Internet Society 177 (2004). All Rights Reserved. 179 This document and translations of it may be copied and furnished 180 to others, and derivative works that comment on or otherwise 181 explain it or assist in its implmentation may be prepared, copied, 182 published and distributed, in whole or in part, without 183 restriction of any kind, provided that the above copyright notice 184 and this paragraph are included on all such copies and derivative 185 works. However, this document itself may not be modified in any 186 way, such as by removing the copyright notice or references to the 187 Internet Society or other Internet organizations, except as needed 188 for the purpose of developing Internet standards in which case the 189 procedures for copyrights defined in the Internet Standards 190 process must be followed, or as required to translate it into 191 languages other than English. 193 The limited permissions granted above are perpetual and will not 194 be revoked by the Internet Society or its successors or assigns. 196 This document and the information contained herein is provided on 197 an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET 198 ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR 199 IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 200 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 201 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.