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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: December 2002 29 June 2002 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 (2002). All Rights Reserved. 35 Abstract 36 Draft Uni-Prefix-based IPv4 Multicast June 2002 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 June 2002 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 (e.g., via ZMAAP [ZMAAP]), and 88 hence can be done with 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 IANA should assign a /8 for this Unicast-Based Multicast (UBM) 102 mechanism (e.g., the 225/8 which was previously leased to MASC). 103 The remaining 24 bits will be used as follows: 105 Bits: | 8 | Unicast Prefix Length | 24 - Unicast Prefix Length | 106 +-----+-----------------------+----------------------------+ 107 Value: | 225 | Unicast Prefix | Group ID | 108 +-----+-----------------------+----------------------------+ 110 For subnets with a /24 or shorter prefix, the unicast prefix of 111 the subnet is appended to the common /8. Any remaining bits may 112 be locally assigned by hosts within the link (e.g., using manual 113 configuration, or ZMAAP). Individual subnets with a prefix length 114 longer than 24 do not receive any multicast address space from 115 this mechanism; in such cases, MADCAP may be used. 117 Compared to GLOP, an AS will receive more address space via this 118 mechanism if it has more than a /16 for unicast space. An AS will 119 receive less address space than it does from GLOP if it has less 120 than a /16. 122 The owner of a UBM address can be determined by taking the 123 multicast address, shifting it left by 8 bits, and identifying the 124 owner of the address space covering the resulting unicast address. 126 Draft Uni-Prefix-based IPv4 Multicast June 2002 128 3. Security Considerations 130 Since dynamic assignment does not cross domain boundaries, the 131 same well known intra-domain security techniques can be applied as 132 with GLOP. Furthermore, the approach described here may have the 133 effect of reduced exposure to denial of space attacks based on 134 dynamic allocation, since the area of dynamic allocation is 135 reduced from an entire AS to only within individual subnets. 137 4. Author's Address 139 Dave Thaler 140 Microsoft Corporation 141 One Microsoft Way 142 Redmond, WA 98052-6399 143 Phone: +1 425 703 8835 144 EMail: dthaler@microsoft.com 146 5. References 148 [AS4B] 149 Vohra, Q., and E. Chen, "BGP support for four-octet AS number 150 space", draft-ietf-idr-as4bytes-05.txt, Work in progress, May 151 2002. 153 [GLOP] 154 Meyer, D., and P. Lothberg, "GLOP Addressing in 233/8", RFC 155 2770, February 2000. 157 [MADCAP] 158 Hanna, S, Patel, B., and M. Shah, "Multicast Address Dynamic 159 Client Allocation Protocol (MADCAP)", RFC 2730, December 160 1999. 162 [V6UPBM] 163 Haberman, B., and D. Thaler, "Unicast-Prefix-based IPv6 164 Multicast Addresses", draft-ietf-ipngwg-uni-based- 165 mcast-03.txt, October 2001. 167 [ZMAAP] 168 Catrina, O., Thaler, D., Aboba, B., and E. Guttman, "Zeroconf 169 Multicast Address Allocation Protocol (ZMAAP)", draft-ietf- 170 zeroconf-zmaap-02.txt, October 2001. 172 Draft Uni-Prefix-based IPv4 Multicast June 2002 174 6. Full Copyright Statement Copyright (C) The Internet Society 175 (2002). All Rights Reserved. 177 This document and translations of it may be copied and furnished 178 to others, and derivative works that comment on or otherwise 179 explain it or assist in its implmentation may be prepared, copied, 180 published and distributed, in whole or in part, without 181 restriction of any kind, provided that the above copyright notice 182 and this paragraph are included on all such copies and derivative 183 works. However, this document itself may not be modified in any 184 way, such as by removing the copyright notice or references to the 185 Internet Society or other Internet organizations, except as needed 186 for the purpose of developing Internet standards in which case the 187 procedures for copyrights defined in the Internet Standards 188 process must be followed, or as required to translate it into 189 languages other than English. 191 The limited permissions granted above are perpetual and will not 192 be revoked by the Internet Society or its successors or assigns. 194 This document and the information contained herein is provided on 195 an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET 196 ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR 197 IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 198 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 199 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.