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Thaler 3 Internet-Draft Microsoft 4 Expires: January 27, 2008 July 26, 2007 6 Unicast-Prefix-based IPv4 Multicast Addresses 7 draft-ietf-mboned-ipv4-uni-based-mcast-04.txt 9 Status of this Memo 11 By submitting this Internet-Draft, each author represents that any 12 applicable patent or other IPR claims of which he or she is aware 13 have been or will be disclosed, and any of which he or she becomes 14 aware will be disclosed, in accordance with Section 6 of BCP 79. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt. 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 This Internet-Draft will expire on January 27, 2008. 34 Copyright Notice 36 Copyright (C) The IETF Trust (2007). 38 Abstract 40 This specification defines an extension to the multicast addressing 41 architecture of the IP Version 4 protocol. The extension presented 42 in this document allows for unicast-prefix-based allocation of 43 multicast addresses. By delegating multicast addresses at the same 44 time as unicast prefixes, network operators will be able to identify 45 their multicast addresses without needing to run an inter-domain 46 allocation protocol. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 51 2. Address Space . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 53 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 54 5. Informative References . . . . . . . . . . . . . . . . . . . . 5 55 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5 56 Intellectual Property and Copyright Statements . . . . . . . . . . 6 58 1. Introduction 60 RFC 3180 [RFC3180] defined an experimental allocation mechanism 61 (called "GLOP") in 233/8 whereby an Autonomous System (AS) number is 62 embedded in the middle 16 bits of an IPv4 multicast address, 63 resulting in 256 multicast addresses per AS. Advantages of this 64 mechanism include the ability to get multicast address space without 65 an inter-domain multicast address allocation protocol, and the ease 66 of determining the AS of the owner of an address for debugging and 67 auditing purposes. 69 Some disadvantages of GLOP include: 70 o RFC 4893 [RFC4893] expands the size of an AS number to 4 bytes, 71 and GLOP cannot work with 4-byte AS numbers. 72 o When an AS covers multiple sites or organizations, administration 73 of the multicast address space within an AS must be handled by 74 other mechanisms, such as manual administrative effort or MADCAP 75 [RFC2730]. 76 o During debugging, identifying the AS does not immediately identify 77 the owning organization when an AS covers multiple organizations. 78 o Only 256 addresses are automatically available per AS, and 79 obtaining any more requires administrative effort. 81 More recently, a mechanism [RFC3306] has been developed for IPv6 that 82 provides a multicast range to every IPv6 subnet, which is at a much 83 finer granularity than an AS. As a result, the first three 84 disadvantages above are avoided (and the last disadvantage does not 85 apply to IPv6 due to the extended size of the address space). 87 Another advantage of providing multicast space to a subnet, rather 88 than just to an entire AS, is that multicast address allocation 89 within the range need only be coordinated within the subnet. 91 This draft specifies a mechanism similar to [RFC3306], whereby a 92 range of IPv4 multicast address space is provided to each 93 organization that has unicast address space. A resulting advantage 94 over GLOP is that the mechanisms in IPv4 and IPv6 become more 95 similar. 97 This document proposes an experimental method of statically 98 allocating multicast address ranges with global scope. As described 99 in section Section 4, this experiment will last for a period of one 100 year, but may be extended. 102 2. Address Space 104 (RFC-editor: replace TBD below with IANA-assigned value, and delete 105 this note.) 107 A multicast address with the prefix TBD/8 indicates that the address 108 is a Unicast-Based Multicast (UBM) address. The remaining 24 bits 109 are used as follows: 111 Bits: | 8 | Unicast Prefix Length | 24 - Unicast Prefix Length | 112 +-----+-----------------------+----------------------------+ 113 Value: | TBD | Unicast Prefix | Group ID | 114 +-----+-----------------------+----------------------------+ 116 For organizations with a /24 or shorter prefix, the unicast prefix of 117 the organization is appended to the common /8. Any remaining bits 118 may be assigned by any mechanism the organization wishes. For 119 example, an organization that has a subnet with a /24 or shorter 120 prefix assigned to a link may wish to embed the entire subnet prefix 121 within the multicast address, with the remaining bits assigned by 122 hosts within the link (e.g., using manual configuration). 123 Organizations with a prefix length longer than 24 do not receive any 124 multicast address space from this mechanism; in such cases, another 125 mechanism must be used. 127 Compared to GLOP, an AS will receive more address space via this 128 mechanism if it has more than a /16 for unicast space. An AS will 129 receive less address space than it does from GLOP if it has less than 130 a /16. 132 The owner of a UBM address can be determined by taking the multicast 133 address, shifting it left by 8 bits, and identifying the owner of the 134 address space covering the resulting unicast address. 136 3. Security Considerations 138 The same well known intra-domain security techniques can be applied 139 as with GLOP. Furthermore, when dynamic allocation is used within a 140 prefix, the approach described here may have the effect of reduced 141 exposure to denial of space attacks, since the topological area 142 within which nodes compete for addresses within the same prefix is 143 reduced from an entire AS to only within an individual organization 144 or an even smaller area. 146 4. IANA Considerations 148 IANA should assign a /8 in the IPv4 multicast address space for this 149 purpose. 151 This assignment should time out one year after the assignment is 152 made. The assignment may be renewed at that time. 154 5. Informative References 156 [RFC2730] Hanna, S., Patel, B., and M. Shah, "Multicast Address 157 Dynamic Client Allocation Protocol (MADCAP)", RFC 2730, 158 December 1999. 160 [RFC3180] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", 161 BCP 53, RFC 3180, September 2001. 163 [RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 164 Multicast Addresses", RFC 3306, August 2002. 166 [RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS 167 Number Space", RFC 4893, May 2007. 169 Author's Address 171 Dave Thaler 172 Microsoft Corporation 173 One Microsoft Way 174 Redmond, WA 98052 175 USA 177 Phone: +1 425 703 8835 178 Email: dthaler@microsoft.com 180 Full Copyright Statement 182 Copyright (C) The IETF Trust (2007). 184 This document is subject to the rights, licenses and restrictions 185 contained in BCP 78, and except as set forth therein, the authors 186 retain all their rights. 188 This document and the information contained herein are provided on an 189 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 190 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 191 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 192 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 193 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 194 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 196 Intellectual Property 198 The IETF takes no position regarding the validity or scope of any 199 Intellectual Property Rights or other rights that might be claimed to 200 pertain to the implementation or use of the technology described in 201 this document or the extent to which any license under such rights 202 might or might not be available; nor does it represent that it has 203 made any independent effort to identify any such rights. Information 204 on the procedures with respect to rights in RFC documents can be 205 found in BCP 78 and BCP 79. 207 Copies of IPR disclosures made to the IETF Secretariat and any 208 assurances of licenses to be made available, or the result of an 209 attempt made to obtain a general license or permission for the use of 210 such proprietary rights by implementers or users of this 211 specification can be obtained from the IETF on-line IPR repository at 212 http://www.ietf.org/ipr. 214 The IETF invites any interested party to bring to its attention any 215 copyrights, patents or patent applications, or other proprietary 216 rights that may cover technology that may be required to implement 217 this standard. Please address the information to the IETF at 218 ietf-ipr@ietf.org. 220 Acknowledgment 222 Funding for the RFC Editor function is provided by the IETF 223 Administrative Support Activity (IASA).