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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Thaler 3 Internet-Draft Microsoft 4 Expires: August 28, 2008 February 25, 2008 6 Unicast-Prefix-based IPv4 Multicast Addresses 7 draft-ietf-mboned-ipv4-uni-based-mcast-05.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 August 28, 2008. 34 Copyright Notice 36 Copyright (C) The IETF Trust (2008). 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 assignment 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 3. Address Space . . . . . . . . . . . . . . . . . . . . . . . . . 4 53 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 54 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 55 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 56 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5 57 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 58 8.1. Normative References . . . . . . . . . . . . . . . . . . . 6 59 8.2. Informative References . . . . . . . . . . . . . . . . . . 6 60 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 61 Intellectual Property and Copyright Statements . . . . . . . . . . 7 63 1. Introduction 65 RFC 3180 [RFC3180] defined an experimental allocation mechanism 66 (called "GLOP") in 233/8 whereby an Autonomous System (AS) number is 67 embedded in the middle 16 bits of an IPv4 multicast address, 68 resulting in 256 multicast addresses per AS. Advantages of this 69 mechanism include the ability to get multicast address space without 70 an inter-domain multicast address allocation protocol, and the ease 71 of determining the AS that was assigned the address for debugging and 72 auditing purposes. 74 Some disadvantages of GLOP include: 75 o RFC 4893 [RFC4893] expands the size of an AS number to 4 bytes, 76 and GLOP cannot work with 4-byte AS numbers. 77 o When an AS covers multiple sites or organizations, administration 78 of the multicast address space within an AS must be handled by 79 other mechanisms, such as manual administrative effort or MADCAP 80 [RFC2730]. 81 o During debugging, identifying the AS does not immediately identify 82 the correct organization when an AS covers multiple organizations. 83 o Only 256 addresses are automatically available per AS, and 84 obtaining any more requires administrative effort. 86 More recently, a mechanism [RFC3306] has been developed for IPv6 that 87 provides a multicast range to every IPv6 subnet, which is at a much 88 finer granularity than an AS. As a result, the first three 89 disadvantages above are avoided (and the last disadvantage does not 90 apply to IPv6 due to the extended size of the address space). 92 Another advantage of providing multicast space to a subnet, rather 93 than just to an entire AS, is that multicast address assignment 94 within the range need only be coordinated within the subnet. 96 This draft specifies a mechanism similar to [RFC3306], whereby a 97 range of global IPv4 multicast address space is provided to each 98 organization that has unicast address space. A resulting advantage 99 over GLOP is that the mechanisms in IPv4 and IPv6 become more 100 similar. 102 2. Terminology 104 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 105 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 106 document are to be interpreted as described in [RFC2119]. 108 3. Address Space 110 (RFC-editor: replace TBD in this section and the next with IANA- 111 assigned value, and delete this note.) 113 A multicast address with the prefix TBD/8 indicates that the address 114 is a Unicast-Based Multicast (UBM) address. The remaining 24 bits 115 are used as follows: 117 Bits: | 8 | Unicast Prefix Length | 24 - Unicast Prefix Length | 118 +-----+-----------------------+----------------------------+ 119 Value: | TBD | Unicast Prefix | Group ID | 120 +-----+-----------------------+----------------------------+ 122 For organizations with a /24 or shorter prefix, the unicast prefix of 123 the organization is appended to the common /8. Any remaining bits 124 may be assigned by any mechanism the organization wishes. 126 For example, an organization that has a /16 prefix assigned might 127 choose to assign multicast addresses manually from the /24 multicast 128 prefix derived from the above method. Alternatively, the 129 organization might choose to delegate the use of multicast addresses 130 to individual subnets that have a /24 or shorter unicast prefix, or 131 it might choose some other method. 133 Organizations with a prefix length longer than 24 do not receive any 134 multicast address space from this mechanism; in such cases, another 135 mechanism must be used. 137 Compared to GLOP, an AS will receive more address space via this 138 mechanism if it has more than a /16 for unicast space. An AS will 139 receive less address space than it does from GLOP if it has less than 140 a /16. 142 The organization that is assigned the UBM address can be determined 143 by taking the multicast address, shifting it left by 8 bits, and 144 identifying who has been assigned the address space covering the 145 resulting unicast address. 147 The embedded unicast prefix MUST be a global unicast prefix (i.e., no 148 loopback, multicast, link-local, or private-use IP address space). 149 In addition, since global unicast addresses are not permanently 150 assigned, UBM addresses MUST NOT be hard-coded in applications. 152 4. Examples 154 The following are a few examples of the structure of unicast-prefix 155 based multicast addresses. 156 o Consider an organization that has been assigned the global unicast 157 address space 192.0.2.0/24. This means that organization can use 158 the global multicast address TBD.192.0.2 without coordinating with 159 any other entity. Someone who sees this multicast address and 160 wants to find who is using it can mentally shift the address left 161 by 8 bits to get 192.0.2.0, and then look up who has been assigned 162 unicast address space that includes that address. 163 o Consider an organization has been assigned a larger address space, 164 x.y.0.0/16. This organization can use the global multicast 165 address space TBD.x.y.0/24 without coordinating with any other 166 entity, and can assign addresses within this space by any 167 mechanism the organization wishes. Someone who sees a multicast 168 address (say) TBD.x.y.10, and wants to find who is using it can 169 mentally shift the address left by 8 bits to get x.y.10.0, and can 170 then look up who has been assigned unicast address space that 171 includes that address. 173 5. Security Considerations 175 The same well known intra-domain security techniques can be applied 176 as with GLOP. Furthermore, when dynamic allocation is used within a 177 prefix, the approach described here may have the effect of reduced 178 exposure to denial of space attacks, since the topological area 179 within which nodes compete for addresses within the same prefix is 180 reduced from an entire AS to only within an individual organization 181 or an even smaller area. 183 6. IANA Considerations 185 IANA should assign a /8 in the global IPv4 multicast address space 186 for this purpose. 188 7. Acknowledgments 190 This document was updated based on feedback from the MBoneD working 191 group. In particular, Tim Chown, Toerless Eckert, Prashant Jhingran, 192 Peter Koch, John Linn, Dave Meyer, Pekka Savola, Greg Shepherd, and 193 Stig Venaas provided valuable suggestions on the text. 195 8. References 196 8.1. Normative References 198 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 199 Requirement Levels", BCP 14, RFC 2119, March 1997. 201 8.2. Informative References 203 [RFC2730] Hanna, S., Patel, B., and M. Shah, "Multicast Address 204 Dynamic Client Allocation Protocol (MADCAP)", RFC 2730, 205 December 1999. 207 [RFC3180] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", 208 BCP 53, RFC 3180, September 2001. 210 [RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 211 Multicast Addresses", RFC 3306, August 2002. 213 [RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS 214 Number Space", RFC 4893, May 2007. 216 Author's Address 218 Dave Thaler 219 Microsoft Corporation 220 One Microsoft Way 221 Redmond, WA 98052 222 USA 224 Phone: +1 425 703 8835 225 Email: dthaler@microsoft.com 227 Full Copyright Statement 229 Copyright (C) The IETF Trust (2008). 231 This document is subject to the rights, licenses and restrictions 232 contained in BCP 78, and except as set forth therein, the authors 233 retain all their rights. 235 This document and the information contained herein are provided on an 236 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 237 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 238 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 239 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 240 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 241 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 243 Intellectual Property 245 The IETF takes no position regarding the validity or scope of any 246 Intellectual Property Rights or other rights that might be claimed to 247 pertain to the implementation or use of the technology described in 248 this document or the extent to which any license under such rights 249 might or might not be available; nor does it represent that it has 250 made any independent effort to identify any such rights. Information 251 on the procedures with respect to rights in RFC documents can be 252 found in BCP 78 and BCP 79. 254 Copies of IPR disclosures made to the IETF Secretariat and any 255 assurances of licenses to be made available, or the result of an 256 attempt made to obtain a general license or permission for the use of 257 such proprietary rights by implementers or users of this 258 specification can be obtained from the IETF on-line IPR repository at 259 http://www.ietf.org/ipr. 261 The IETF invites any interested party to bring to its attention any 262 copyrights, patents or patent applications, or other proprietary 263 rights that may cover technology that may be required to implement 264 this standard. Please address the information to the IETF at 265 ietf-ipr@ietf.org. 267 Acknowledgment 269 Funding for the RFC Editor function is provided by the IETF 270 Administrative Support Activity (IASA).