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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: September 10, 2009 March 9, 2009 6 Unicast-Prefix-based IPv4 Multicast Addresses 7 draft-ietf-mboned-ipv4-uni-based-mcast-06.txt 9 Status of this Memo 11 This Internet-Draft is submitted to IETF in full conformance with the 12 provisions of BCP 78 and BCP 79. 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 months 20 and may be updated, replaced, or obsoleted by other documents at any 21 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 This Internet-Draft will expire on September 10, 2009. 32 Copyright Notice 34 Copyright (c) 2009 IETF Trust and the persons identified as the 35 document authors. All rights reserved. 37 This document is subject to BCP 78 and the IETF Trust's Legal 38 Provisions Relating to IETF Documents in effect on the date of 39 publication of this document (http://trustee.ietf.org/license-info). 40 Please review these documents carefully, as they describe your rights 41 and restrictions with respect to this document. 43 Abstract 45 This specification defines an extension to the multicast addressing 46 architecture of the IP Version 4 protocol. The extension presented 47 in this document allows for unicast-prefix-based assignment of 48 multicast addresses. By delegating multicast addresses at the same 49 time as unicast prefixes, network operators will be able to identify 50 their multicast addresses without needing to run an inter-domain 51 allocation protocol. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. Address Space . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 60 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 61 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5 62 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 63 8.1. Normative References . . . . . . . . . . . . . . . . . . . 6 64 8.2. Informative References . . . . . . . . . . . . . . . . . . 6 65 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 67 1. Introduction 69 RFC 3180 [RFC3180] defined an experimental allocation mechanism 70 (called "GLOP") in 233/8 whereby an Autonomous System (AS) number is 71 embedded in the middle 16 bits of an IPv4 multicast address, 72 resulting in 256 multicast addresses per AS. Advantages of this 73 mechanism include the ability to get multicast address space without 74 an inter-domain multicast address allocation protocol, and the ease 75 of determining the AS that was assigned the address for debugging and 76 auditing purposes. 78 Some disadvantages of GLOP include: 79 o RFC 4893 [RFC4893] expands the size of an AS number to 4 bytes, 80 and GLOP cannot work with 4-byte AS numbers. 81 o When an AS covers multiple sites or organizations, administration 82 of the multicast address space within an AS must be handled by 83 other mechanisms, such as manual administrative effort or MADCAP 84 [RFC2730]. 85 o During debugging, identifying the AS does not immediately identify 86 the correct organization when an AS covers multiple organizations. 87 o Only 256 addresses are automatically available per AS, and 88 obtaining any more requires administrative effort. 90 More recently, a mechanism [RFC3306] has been developed for IPv6 that 91 provides a multicast range to every IPv6 subnet, which is at a much 92 finer granularity than an AS. As a result, the first three 93 disadvantages above are avoided (and the last disadvantage does not 94 apply to IPv6 due to the extended size of the address space). 96 Another advantage of providing multicast space to a subnet, rather 97 than just to an entire AS, is that multicast address assignment 98 within the range need only be coordinated within the subnet. 100 This draft specifies a mechanism similar to [RFC3306], whereby a 101 range of global IPv4 multicast address space is provided to each 102 organization that has unicast address space. A resulting advantage 103 over GLOP is that the mechanisms in IPv4 and IPv6 become more 104 similar. 106 2. Terminology 108 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 109 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 110 document are to be interpreted as described in [RFC2119]. 112 3. Address Space 114 (RFC-editor: replace TBD in this section and the next with IANA- 115 assigned value, and delete this note.) 117 A multicast address with the prefix TBD/8 indicates that the address 118 is a Unicast-Based Multicast (UBM) address. The remaining 24 bits 119 are used as follows: 121 Bits: | 8 | Unicast Prefix Length | 24 - Unicast Prefix Length | 122 +-----+-----------------------+----------------------------+ 123 Value: | TBD | Unicast Prefix | Group ID | 124 +-----+-----------------------+----------------------------+ 126 For organizations with a /24 or shorter prefix, the unicast prefix of 127 the organization is appended to the common /8. Any remaining bits 128 may be assigned by any mechanism the organization wishes. 130 For example, an organization that has a /16 prefix assigned might 131 choose to assign multicast addresses manually from the /24 multicast 132 prefix derived from the above method. Alternatively, the 133 organization might choose to delegate the use of multicast addresses 134 to individual subnets that have a /24 or shorter unicast prefix, or 135 it might choose some other method. 137 Organizations with a prefix length longer than 24 do not receive any 138 multicast address space from this mechanism; in such cases, another 139 mechanism must be used. 141 Compared to GLOP, an AS will receive more address space via this 142 mechanism if it has more than a /16 for unicast space. An AS will 143 receive less address space than it does from GLOP if it has less than 144 a /16. 146 The organization that is assigned the UBM address can be determined 147 by taking the multicast address, shifting it left by 8 bits, and 148 identifying who has been assigned the address space covering the 149 resulting unicast address. 151 The embedded unicast prefix MUST be a global unicast prefix (i.e., no 152 loopback, multicast, link-local, or private-use IP address space). 153 In addition, since global unicast addresses are not permanently 154 assigned, UBM addresses MUST NOT be hard-coded in applications. 156 4. Examples 158 The following are a few examples of the structure of unicast-prefix 159 based multicast addresses. 160 o Consider an organization that has been assigned the global unicast 161 address space 192.0.2.0/24. This means that organization can use 162 the global multicast address TBD.192.0.2 without coordinating with 163 any other entity. Someone who sees this multicast address and 164 wants to find who is using it can mentally shift the address left 165 by 8 bits to get 192.0.2.0, and then look up who has been assigned 166 unicast address space that includes that address. 167 o Consider an organization has been assigned a larger address space, 168 x.y.0.0/16. This organization can use the global multicast 169 address space TBD.x.y.0/24 without coordinating with any other 170 entity, and can assign addresses within this space by any 171 mechanism the organization wishes. Someone who sees a multicast 172 address (say) TBD.x.y.10, and wants to find who is using it can 173 mentally shift the address left by 8 bits to get x.y.10.0, and can 174 then look up who has been assigned unicast address space that 175 includes that address. 177 5. Security Considerations 179 The same well known intra-domain security techniques can be applied 180 as with GLOP. Furthermore, when dynamic allocation is used within a 181 prefix, the approach described here may have the effect of reduced 182 exposure to denial of space attacks, since the topological area 183 within which nodes compete for addresses within the same prefix is 184 reduced from an entire AS to only within an individual organization 185 or an even smaller area. 187 6. IANA Considerations 189 IANA should assign a /8 in the global IPv4 multicast address space 190 for this purpose. 192 7. Acknowledgments 194 This document was updated based on feedback from the MBoneD working 195 group. In particular, Tim Chown, Toerless Eckert, Prashant Jhingran, 196 Peter Koch, John Linn, Dave Meyer, Pekka Savola, Greg Shepherd, and 197 Stig Venaas provided valuable suggestions on the text. 199 8. References 200 8.1. Normative References 202 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 203 Requirement Levels", BCP 14, RFC 2119, March 1997. 205 8.2. Informative References 207 [RFC2730] Hanna, S., Patel, B., and M. Shah, "Multicast Address 208 Dynamic Client Allocation Protocol (MADCAP)", RFC 2730, 209 December 1999. 211 [RFC3180] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", 212 BCP 53, RFC 3180, September 2001. 214 [RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 215 Multicast Addresses", RFC 3306, August 2002. 217 [RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS 218 Number Space", RFC 4893, May 2007. 220 Author's Address 222 Dave Thaler 223 Microsoft Corporation 224 One Microsoft Way 225 Redmond, WA 98052 226 USA 228 Phone: +1 425 703 8835 229 Email: dthaler@microsoft.com