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Xu 14 Tsinghua University 15 January 23, 2012 17 IPv4-Embedded IPv6 Multicast Address Format 18 draft-boucadair-64-multicast-address-format-00 20 Abstract 22 This document specifies an extension to the IPv6 multicast addressing 23 architecture to be used in the context of IPv4-IPv6 interconnection. 24 In particular, this document defines an address format for IPv4- 25 embedded IPv6 multicast addresses. This address format can be used 26 for IPv4-IPv6 translation or encapsulation schemes. 28 This document updates RFC4291. 30 Requirements Language 32 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 33 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 34 document are to be interpreted as described in RFC 2119 [RFC2119]. 36 Status of this Memo 38 This Internet-Draft is submitted in full conformance with the 39 provisions of BCP 78 and BCP 79. 41 Internet-Drafts are working documents of the Internet Engineering 42 Task Force (IETF). Note that other groups may also distribute 43 working documents as Internet-Drafts. The list of current Internet- 44 Drafts is at http://datatracker.ietf.org/drafts/current/. 46 Internet-Drafts are draft documents valid for a maximum of six months 47 and may be updated, replaced, or obsoleted by other documents at any 48 time. It is inappropriate to use Internet-Drafts as reference 49 material or to cite them other than as "work in progress." 51 This Internet-Draft will expire on July 26, 2012. 53 Copyright Notice 55 Copyright (c) 2012 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents 60 (http://trustee.ietf.org/license-info) in effect on the date of 61 publication of this document. Please review these documents 62 carefully, as they describe your rights and restrictions with respect 63 to this document. Code Components extracted from this document must 64 include Simplified BSD License text as described in Section 4.e of 65 the Trust Legal Provisions and are provided without warranty as 66 described in the Simplified BSD License. 68 Table of Contents 70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 71 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 72 3. IPv4-Embedded IPv6 Multicast Address Format: ASM Mode . . . . 4 73 4. IPv4-Embedded IPv6 Multicast Address Format: SSM Mode . . . . 5 74 5. Textual Representation . . . . . . . . . . . . . . . . . . . . 6 75 6. Multicast PREFIX64 . . . . . . . . . . . . . . . . . . . . . . 6 76 7. Source IPv4 Address in the IPv6 Ream . . . . . . . . . . . . . 7 77 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 78 9. Security Considerations . . . . . . . . . . . . . . . . . . . 7 79 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 80 11. Normative References . . . . . . . . . . . . . . . . . . . . . 8 81 Appendix A. Design Choices . . . . . . . . . . . . . . . . . . . 8 82 A.1. Location of the IPv4 Address . . . . . . . . . . . . . . . 8 83 A.2. Location of the M-bit . . . . . . . . . . . . . . . . . . 8 84 A.3. Encapsulation vs. Translation . . . . . . . . . . . . . . 10 85 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 87 1. Introduction 89 This document specifies an extension to the IPv6 multicast addressing 90 architecture to be used in the context of IPv4-IPv6 interconnection. 91 In particular, this document defines an address format for IPv4- 92 embedded IPv6 multicast addresses. This address format can be used 93 for IPv4-IPv6 translation or encapsulation schemes. 95 This document updates [RFC4291]. 97 This specification can be used in conjunction with other extensions 98 such as building unicast prefix-based multicast IPv6 address 99 [RFC3306] or embedding the rendezvous point [RFC3956]. 101 This document is a companion document to [RFC6052] which focuses 102 exclusively on IPv4-embedded IPv6 unicast addresses. 104 Details about design choices are documented in Appendix A. 106 2. Terminology 108 This document makes use of the following terms: 109 o IPv4-embedded IPv6 multicast address: denotes a multicast IPv6 110 address which includes in 32 bits an IPv4 address. Two types of 111 IPv6 addresses are defined that carry an IPv4 address in the low- 112 order 32 bits of the address. The format to build such addresses 113 is defined in Section 3 for ASM mode and Section 4 for SSM mode. 114 o Multicast Prefix64 (or MPREFIX64 for short) refers to an IPv6 115 multicast prefix to be used to construct IPv4-embedded IPv6 116 multicast addresses. 117 o ASM_MPREFIX64: denotes a multicast Prefix64 used in ASM mode. It 118 follows the format described in Section 3. 119 o SSM_MPREFIX64: denotes a multicast Prefix64 used in SSM mode. It 120 follows the format described in Section 4. 122 3. IPv4-Embedded IPv6 Multicast Address Format: ASM Mode 124 To meet the requirements listed in Appendix A.2, the following 125 address format is defined to enclose an IPv4 multicast address when 126 ASM mode is used: 128 | 8 | 4 | 4 | 4 | 76 | 32 | 129 +--------+----+----+----+------------------------------+----------+ 130 |11111111|flgs|scop|64IX| sub-group-id |v4 address| 131 +--------+----+----+----+-----------------------------------------+ 132 +-+-+-+-+ 133 IPv4-IPv6 Interconnection bits (64IX): |M|r|r|r| 134 +-+-+-+-+ 136 Figure 1: IPv4-Embedded IPv6 Multicast Address Format: ASM Mode 138 The description of the fields is as follows: 139 o "flgs" and "scop" fields are defined in [RFC4291]. 140 o 64IX field (IPv4-IPv6 interconnection bits): The first bit is the 141 M-bit. When "M-bit" is set to 1, it indicates that an multicast 142 IPv4 address is embedded in the low-order 32 bits of the multicast 143 IPv6 address. All the remaining bits are reserved and MUST be set 144 to 0. 145 o sub-group-id: This field is configurable according to local 146 policies of the entity managing the IPv4-IPv6 Interconnection 147 Function. This field must follow the recommendations specified in 148 [RFC3306] if unicast-based prefix is used or the recommendations 149 specified in [RFC3956] if embedded-RP is used. The default value 150 is all zeros. 151 o The low-order 32 bits MUST include an IPv4 multicast address when 152 the M-bit is set to 1. The enclosed IPv4 multicast address SHOULD 153 NOT be in 232/8 range. 155 4. IPv4-Embedded IPv6 Multicast Address Format: SSM Mode 157 As mentioned above, any IPv4-embedded IPv6 address used in SSM mode 158 MUST be part of ff3x::/32 [RFC4607]. Figure 2 describes the format 159 of the IPv6 multicast address to be used to enclose an IPv4 multicast 160 address. 162 | 8 | 4 | 4 | 16 | 4 | 60 | 32 | 163 +--------+----+----+-----------+----+------------------+----------+ 164 |11111111|0011|scop|00.......00|64IX| sub-group-id |v4 address| 165 +--------+----+----+-----------+----+------------------+----------+ 166 +-+-+-+-+ 167 IPv4-IPv6 Interconnection bits (64IX): |M|r|r|r| 168 +-+-+-+-+ 170 Figure 2: IPv4-Embedded IPv6 Multicast Address Format: SSM Mode 172 The description of the fields is as follows: 174 o Flags must be set to 0011. 175 o "scop" is defined in [RFC4291]. 176 o 64IX field (IPv4-IPv6 interconnection bits): Same meaning as 177 Section 3. 178 o sub-group-id: The default value is all zeros. 179 o The low-order 32 bits MUST include an IPv4 multicast address when 180 the M-bit is set to 1. The embedded IPv4 address SHOULD be in the 181 232/8 range [RFC4607]. 232.0.0.1-232.0.0.255 range is being 182 reserved to IANA. 184 5. Textual Representation 186 The embedded IPv4 address in an IPv6 multicast address is included in 187 the last 32 bits; therefore dotted decimal notation can be used. 189 6. Multicast PREFIX64 191 For the delivery of the IPv4-IPv6 multicast interconnection services, 192 a dedicated multicast prefix denoted as MPREFIX64 should be 193 provisioned to any function requiring to build an IPv4-embedded IPv6 194 multicast address based on an IPv4 multicast address. MPREFIX64 can 195 be of ASM or SSM type. When both modes are used, two prefixes are 196 required to be provisioned. 198 The structure of the MPREFIX64 follows the guidelines specified in 199 Section 3 for the ASM mode and Section 4 when SSM mode is used. 201 The RECOMMENDED MPREFIX64 length is /96 (as shown in Figure 3). 203 The format of the MPREFIX64 should be compatible with what is 204 specified in [RFC3306] and [RFC3956] if corresponding mechanisms are 205 used. 207 ASM Mode: 209 | 8 | 4 | 4 | 4 | 76 | 32 | 210 +--------+----+----+----+------------------------------+----------+ 211 |11111111|flgs|scop|64IX| sub-group-id |v4 address| 212 +--------+----+----+----+------------------------------+----------+ 213 | | | 214 v v v 215 +------------------------------------------------------+----------+ 216 | ASM_MPREFIX64 |v4 address| 217 +------------------------------------------------------+----------+ 219 SSM Mode: 221 | 8 | 4 | 4 | 16 | 4 | 60 | 32 | 222 +--------+----+----+-----------+----+------------------+----------+ 223 |11111111|0011|scop|00.......00|64IX| sub-group-id |v4 address| 224 +--------+----+----+-----------+----+------------------+----------+ 225 | | | 226 v v v 227 +------------------------------------------------------+----------+ 228 | SSM_MPREFIX64 |v4 address| 229 +------------------------------------------------------+----------+ 231 Figure 3: MPREFIX64 233 7. Source IPv4 Address in the IPv6 Ream 235 An IPv4 source is represented in the IPv6 realm with its IPv4- 236 converted IPv6 address [RFC6052]. 238 8. IANA Considerations 240 Authors of this document request to reserve: 241 o ff3x:0:8000/33 SSM block to embed an IPv4 multicast address in the 242 last 32 bits. 243 o ffxx:8000/17 ASM block to embed an IPv4 multicast address in the 244 last 32 bits. 246 9. Security Considerations 248 This document defined an address format to embed an IPv4 multicast 249 address in an IPv6 multicast address. The same security 250 considerations as those discussed in [RFC6052] are to be taken into 251 consideration. 253 10. Acknowledgements 255 Many thanks to R. Bonica, B. Sarikaya, P. Savola and T. Tsou for 256 their comments and review. 258 11. Normative References 260 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 261 Requirement Levels", BCP 14, RFC 2119, March 1997. 263 [RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 264 Multicast Addresses", RFC 3306, August 2002. 266 [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous 267 Point (RP) Address in an IPv6 Multicast Address", 268 RFC 3956, November 2004. 270 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 271 Architecture", RFC 4291, February 2006. 273 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 274 IP", RFC 4607, August 2006. 276 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 277 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 278 October 2010. 280 Appendix A. Design Choices 282 A.1. Location of the IPv4 Address 284 There is no strong argument to allow for flexible options to encode 285 the IPv4 address inside the multicast IPv6 address. The option 286 retained by the authors is to encode the multicast IPv4 address in 287 the low-order 32 bits of the IPv6 address. 289 This choice is also motivated by the need to be compliant with 290 [RFC3306] and [RFC3956]. 292 A.2. Location of the M-bit 294 Figure 4 is a reminder of the IPv6 multicast address format as 295 defined in [RFC4291]: 297 | 8 | 4 | 4 | 112 bits | 298 +------ -+----+----+---------------------------------------------+ 299 |11111111|flgs|scop| group ID | 300 +--------+----+----+---------------------------------------------+ 301 +-+-+-+-+ 302 flgs is a set of 4 flags: |0|R|P|T| 303 +-+-+-+-+ 304 * "T-bit" is defined in [RFC4291]; 305 * "P-bit" is defined in [RFC3306] 306 * "R-bit" is defined in [RFC3956] 308 Figure 4: IPv6 Multicast address format as defined in RFC4291 310 It was tempting to use the remaining flag to indicate whether an IPv6 311 address embeds an IPv4 address or not. This choice has been 312 abandoned by the authors for various reasons: 313 o ff3x::/32 is defined as SSM. Defining a new flag would require 314 standards and implementations to also treat ffbx::/32 as SSM. 315 o Prefixes starting with ff7x are defined as embedded-RP, but not 316 prefixes starting with fffx. Blow is provided an excerpt from 317 [RFC3956]: 318 " ...the encoding and the protocol mode used when the two high- 319 order bits in "flgs" are set to 11 ("fff0::/12") is 320 intentionally unspecified until such time that the highest- 321 order bit is defined. Without further IETF specification, 322 implementations SHOULD NOT treat the fff0::/12 range as 323 Embedded-RP." 324 as such defining a new flag would require implementations to 325 also treat ff7x::/12 as embedded-RP prefix. 326 o This is the last remaining flag and at this stage we are not sure 327 whether there is other usage scenarios of the flag. 329 As a conclusion, the remaining flag is not used to indicate an IPv6 330 multicast address embeds an IPv4 multicast address. However the 331 following constraints should be met: 333 (1) Belong to ff3x::/32 and be compatible with unicast-based 334 prefix [RFC3306] for SSM. Note that [RFC3306] suggests to set 335 "plen" to 0 and "network-prefix" to 0. 336 (2) Be compatible with embedded-RP [RFC3956] and unicast-based 337 prefix [RFC3306] for ASM; 338 (3) Avoid ff3x::4000:0001-ff3x::7fff:ffff which is reserved for 339 IANA. 340 Meeting (1) and (2) with the same location of the M-bit is not 341 feasible without modifying embedded-RP and unicast-based prefix 342 specifications; this option is avoided. 344 As a consequence, two multicast blocks are proposed to be used when 345 embedding IPv4 address: one block for ASM (Section 3 ) and another 346 one for the SSM (Section 4). 348 A.3. Encapsulation vs. Translation 350 IPv4-IPv6 encapsulator and translator may be embedded in the same 351 device or even implemented with the same software module. In order 352 to help the function whether an encapsulated IPv6 multicast packets 353 or translated IPv6 ones are to be transferred. It was tempting to 354 define an S-bit for that purpose but this choice has been abandoned 355 in favor of the recommendation to use distinct MPREFIX64 for each 356 scheme. 358 As such, there is no need to reserve a bit in the IPv6 multicast 359 address to separate between the translation and the encapsulation 360 schemes. 362 Authors' Addresses 364 Mohamed Boucadair (editor) 365 France Telecom 366 Rennes, 35000 367 France 369 Email: mohamed.boucadair@orange.com 371 Jacni Qin 372 ZTE 373 Shanghai 374 China 376 Email: jacniq@gmail.com 378 Yiu L. Lee 379 Comcast 380 U.S.A 382 Email: yiu_lee@cable.comcast.com 383 Stig Venaas 384 Cisco Systems 385 Tasman Drive 386 San Jose, CA 95134 387 USA 389 Email: stig@cisco.com 391 Xing Li 392 CERNET Center/Tsinghua University 393 Room 225, Main Building, Tsinghua University 394 Beijing, 100084 395 P.R. China 397 Phone: +86 10-62785983 398 Email: xing@cernet.edu.cn 400 Mingwei Xu 401 Tsinghua University 402 Department of Computer Science, Tsinghua University 403 Beijing, 100084 404 P.R.China 406 Phone: +86-10-6278-5822 407 Email: xmw@cernet.edu.cn