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Xu 14 Tsinghua University 15 February 29, 2012 17 IPv4-Embedded IPv6 Multicast Address Format 18 draft-ietf-mboned-64-multicast-address-format-01 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 September 1, 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 Realm . . . . . . . . . . . . 7 77 8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 78 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 79 10. Security Considerations . . . . . . . . . . . . . . . . . . . 8 80 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 81 12. Normative References . . . . . . . . . . . . . . . . . . . . . 8 82 Appendix A. Design Choices . . . . . . . . . . . . . . . . . . . 9 83 A.1. Location of the IPv4 Address . . . . . . . . . . . . . . . 9 84 A.2. Location of the M-bit . . . . . . . . . . . . . . . . . . 9 85 A.3. Encapsulation vs. Translation . . . . . . . . . . . . . . 11 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 88 1. Introduction 90 This document specifies an extension to the IPv6 multicast addressing 91 architecture to be used in the context of IPv4-IPv6 interconnection. 92 In particular, this document defines an address format for IPv4- 93 embedded IPv6 multicast addresses. This address format can be used 94 for IPv4-IPv6 translation or encapsulation schemes. 96 This document updates [RFC4291]. 98 This specification can be used in conjunction with other extensions 99 such as building unicast prefix-based multicast IPv6 address 100 [RFC3306] or embedding the rendezvous point [RFC3956]. 102 This document is a companion document to [RFC6052] which focuses 103 exclusively on IPv4-embedded IPv6 unicast addresses. 105 Details about design choices are documented in Appendix A. 107 2. Terminology 109 This document makes use of the following terms: 111 o IPv4-embedded IPv6 multicast address: denotes a multicast IPv6 112 address which includes in 32 bits an IPv4 address. Two types of 113 IPv6 addresses are defined that carry an IPv4 address in the low- 114 order 32 bits of the address. The format to build such addresses 115 is defined in Section 3 for ASM mode and Section 4 for SSM mode. 117 o Multicast Prefix64 (or MPREFIX64 for short) refers to an IPv6 118 multicast prefix to be used to construct IPv4-embedded IPv6 119 multicast addresses. 121 o ASM_MPREFIX64: denotes a multicast Prefix64 used in ASM mode. It 122 follows the format described in Section 3. 124 o SSM_MPREFIX64: denotes a multicast Prefix64 used in SSM mode. It 125 follows the format described in Section 4. 127 3. IPv4-Embedded IPv6 Multicast Address Format: ASM Mode 129 To meet the requirements listed in Appendix A.2, the following 130 address format is defined to enclose an IPv4 multicast address when 131 ASM mode is used: 133 | 8 | 4 | 4 | 4 | 76 | 32 | 134 +--------+----+----+----+------------------------------+----------+ 135 |11111111|flgs|scop|64IX| sub-group-id |v4 address| 136 +--------+----+----+----+-----------------------------------------+ 137 +-+-+-+-+ 138 IPv4-IPv6 Interconnection bits (64IX): |M|r|r|r| 139 +-+-+-+-+ 141 Figure 1: IPv4-Embedded IPv6 Multicast Address Format: ASM Mode 143 The description of the fields is as follows: 144 o "flgs" and "scop" fields are defined in [RFC4291]. 145 o 64IX field (IPv4-IPv6 interconnection bits): The first bit is the 146 M-bit. When "M-bit" is set to 1, it indicates that a multicast 147 IPv4 address is embedded in the low-order 32 bits of the multicast 148 IPv6 address. All the remaining bits are reserved and MUST be set 149 to 0. 150 o sub-group-id: This field is configurable according to local 151 policies of the entity managing the IPv4-IPv6 Interconnection 152 Function. This field must follow the recommendations specified in 153 [RFC3306] if unicast-based prefix is used or the recommendations 154 specified in [RFC3956] if embedded-RP is used. The default value 155 is all zeros. 156 o The low-order 32 bits MUST include an IPv4 multicast address when 157 the M-bit is set to 1. The enclosed IPv4 multicast address SHOULD 158 NOT be in 232/8 range. 160 4. IPv4-Embedded IPv6 Multicast Address Format: SSM Mode 162 As mentioned above, any IPv4-embedded IPv6 address used in SSM mode 163 MUST be part of ff3x::/32 [RFC4607]. Figure 2 describes the format 164 of the IPv6 multicast address to be used to enclose an IPv4 multicast 165 address. 167 | 8 | 4 | 4 | 16 | 4 | 60 | 32 | 168 +--------+----+----+-----------+----+------------------+----------+ 169 |11111111|0011|scop|00.......00|64IX| sub-group-id |v4 address| 170 +--------+----+----+-----------+----+------------------+----------+ 171 +-+-+-+-+ 172 IPv4-IPv6 Interconnection bits (64IX): |M|r|r|r| 173 +-+-+-+-+ 175 Figure 2: IPv4-Embedded IPv6 Multicast Address Format: SSM Mode 177 The description of the fields is as follows: 179 o Flags must be set to 0011. 180 o "scop" is defined in [RFC4291]. 181 o 64IX field (IPv4-IPv6 interconnection bits): Same meaning as 182 Section 3. 183 o sub-group-id: The default value is all zeros. 184 o The low-order 32 bits MUST include an IPv4 multicast address when 185 the M-bit is set to 1. The embedded IPv4 address SHOULD be in the 186 232/8 range [RFC4607]. 232.0.0.1-232.0.0.255 range is being 187 reserved to IANA. 189 5. Textual Representation 191 The embedded IPv4 address in an IPv6 multicast address is included in 192 the last 32 bits; therefore dotted decimal notation can be used. 194 6. Multicast PREFIX64 196 For the delivery of the IPv4-IPv6 multicast interconnection services, 197 a dedicated multicast prefix denoted as MPREFIX64 should be 198 provisioned to any function requiring to build an IPv4-embedded IPv6 199 multicast address based on an IPv4 multicast address. MPREFIX64 can 200 be of ASM or SSM type. When both modes are used, two prefixes are 201 required to be provisioned. 203 The structure of the MPREFIX64 follows the guidelines specified in 204 Section 3 for the ASM mode and Section 4 when SSM mode is used. 206 The RECOMMENDED MPREFIX64 length is /96 (as shown in Figure 3). 208 The format of the MPREFIX64 should follow what is specified in 209 [RFC3306] and [RFC3956] if corresponding mechanisms are used. 211 The format specified in Section 3 uses some reserved bits defined 212 in [RFC3306] and [RFC3956]: the first of the reserved bits now has 213 a meaning, while the remaining bits MUST be set to 0. 215 ASM Mode: 217 | 8 | 4 | 4 | 4 | 76 | 32 | 218 +--------+----+----+----+------------------------------+----------+ 219 |11111111|flgs|scop|64IX| sub-group-id |v4 address| 220 +--------+----+----+----+------------------------------+----------+ 221 | | | 222 v v v 223 +------------------------------------------------------+----------+ 224 | ASM_MPREFIX64 |v4 address| 225 +------------------------------------------------------+----------+ 227 SSM Mode: 229 | 8 | 4 | 4 | 16 | 4 | 60 | 32 | 230 +--------+----+----+-----------+----+------------------+----------+ 231 |11111111|0011|scop|00.......00|64IX| sub-group-id |v4 address| 232 +--------+----+----+-----------+----+------------------+----------+ 233 | | | 234 v v v 235 +------------------------------------------------------+----------+ 236 | SSM_MPREFIX64 |v4 address| 237 +------------------------------------------------------+----------+ 239 Figure 3: MPREFIX64 241 7. Source IPv4 Address in the IPv6 Realm 243 An IPv4 source is represented in the IPv6 realm with its IPv4- 244 converted IPv6 address [RFC6052]. 246 8. Examples 248 Figure 4 provides an example of ASM IPv4-Embedded IPv6 Address while 249 Figure 5 provides an example of SSM IPv4-Embedded IPv6 Address. 251 +---------------------+--------------+----------------------------+ 252 | MPREFIX64 | IPv4 address | IPv4-embedded IPv6 address | 253 +---------------------+--------------+----------------------------+ 254 | ffxx:8000:abc::/96 | 224.1.2.3 | ffxx:8000:abc::224.1.2.3 | 255 +---------------------+--------------+----------------------------+ 257 Figure 4: Example of ASM IPv4-embedded IPv6 address 259 +---------------------+--------------+----------------------------+ 260 | MPREFIX64 | IPv4 address | IPv4-embedded IPv6 address | 261 +---------------------+--------------+----------------------------+ 262 | ff3x:0:8000::/96 | 232.1.2.3 | ff3x:0:8000::232.1.2.3 | 263 +---------------------+--------------+----------------------------+ 265 Figure 5: Example of SSM IPv4-embedded IPv6 address 267 9. IANA Considerations 269 Authors of this document request to reserve: 270 o ff3x:0:8000/33 SSM block to embed an IPv4 multicast address in the 271 last 32 bits. 272 o ffxx:8000/17 ASM block to embed an IPv4 multicast address in the 273 last 32 bits. 275 10. Security Considerations 277 This document defined an address format to embed an IPv4 multicast 278 address in an IPv6 multicast address. The same security 279 considerations as those discussed in [RFC6052] are to be taken into 280 consideration. 282 11. Acknowledgements 284 Many thanks to R. Bonica, B. Sarikaya, P. Savola and T. Tsou for 285 their comments and review. 287 12. Normative References 289 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 290 Requirement Levels", BCP 14, RFC 2119, March 1997. 292 [RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 293 Multicast Addresses", RFC 3306, August 2002. 295 [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous 296 Point (RP) Address in an IPv6 Multicast Address", 297 RFC 3956, November 2004. 299 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 300 Architecture", RFC 4291, February 2006. 302 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 303 IP", RFC 4607, August 2006. 305 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 306 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 307 October 2010. 309 Appendix A. Design Choices 311 A.1. Location of the IPv4 Address 313 There is no strong argument to allow for flexible options to encode 314 the IPv4 address inside the multicast IPv6 address. The option 315 retained by the authors is to encode the multicast IPv4 address in 316 the low-order 32 bits of the IPv6 address. 318 This choice is also motivated by the need to be compliant with 319 [RFC3306] and [RFC3956]. 321 A.2. Location of the M-bit 323 Figure 6 is a reminder of the IPv6 multicast address format as 324 defined in [RFC4291]: 326 | 8 | 4 | 4 | 112 bits | 327 +------ -+----+----+---------------------------------------------+ 328 |11111111|flgs|scop| group ID | 329 +--------+----+----+---------------------------------------------+ 330 +-+-+-+-+ 331 flgs is a set of 4 flags: |0|R|P|T| 332 +-+-+-+-+ 333 * "T-bit" is defined in [RFC4291]; 334 * "P-bit" is defined in [RFC3306] 335 * "R-bit" is defined in [RFC3956] 337 Figure 6: IPv6 Multicast address format as defined in RFC4291 339 It was tempting to use the remaining flag to indicate whether an IPv6 340 address embeds an IPv4 address or not. This choice has been 341 abandoned by the authors for various reasons: 342 o ff3x::/32 is defined as SSM. Defining a new flag would require 343 standards and implementations to also treat ffbx::/32 as SSM. 344 o Prefixes starting with ff7x are defined as embedded-RP, but not 345 prefixes starting with fffx. Below is provided an excerpt from 346 [RFC3956]: 347 " ...the encoding and the protocol mode used when the two high- 348 order bits in "flgs" are set to 11 ("fff0::/12") is 349 intentionally unspecified until such time that the highest- 350 order bit is defined. Without further IETF specification, 351 implementations SHOULD NOT treat the fff0::/12 range as 352 Embedded-RP." 353 as such defining a new flag would require implementations to 354 also treat ff7x::/12 as embedded-RP prefix. 355 o This is the last remaining flag and at this stage we are not sure 356 whether there is other usage scenarios of the flag. 358 As a conclusion, the remaining flag is not used to indicate an IPv6 359 multicast address embeds an IPv4 multicast address. However the 360 following constraints should be met: 362 (1) Belong to ff3x::/32 and be compatible with unicast-based 363 prefix [RFC3306] for SSM. Note that [RFC3306] suggests to set 364 "plen" to 0 and "network-prefix" to 0. 365 (2) Be compatible with embedded-RP [RFC3956] and unicast-based 366 prefix [RFC3306] for ASM; 367 (3) Avoid ff3x::4000:0001-ff3x::7fff:ffff which is reserved for 368 IANA. 369 Meeting (1) and (2) with the same location of the M-bit is not 370 feasible without modifying embedded-RP and unicast-based prefix 371 specifications; this option is avoided. 373 As a consequence, two multicast blocks are proposed to be used when 374 embedding IPv4 address: one block for ASM (Section 3 ) and another 375 one for the SSM (Section 4). 377 A.3. Encapsulation vs. Translation 379 IPv4-IPv6 encapsulator and translator may be embedded in the same 380 device or even implemented with the same software module. In order 381 to help the function whether an encapsulated IPv6 multicast packets 382 or translated IPv6 ones are to be transferred. It was tempting to 383 define an S-bit for that purpose but this choice has been abandoned 384 in favor of the recommendation to use distinct MPREFIX64 for each 385 scheme. 387 As such, there is no need to reserve a bit in the IPv6 multicast 388 address to separate between the translation and the encapsulation 389 schemes. 391 Authors' Addresses 393 Mohamed Boucadair (editor) 394 France Telecom 395 Rennes, 35000 396 France 398 Email: mohamed.boucadair@orange.com 400 Jacni Qin 401 ZTE 402 Shanghai 403 China 405 Email: jacniq@gmail.com 407 Yiu L. Lee 408 Comcast 409 U.S.A 411 Email: yiu_lee@cable.comcast.com 412 Stig Venaas 413 Cisco Systems 414 Tasman Drive 415 San Jose, CA 95134 416 USA 418 Email: stig@cisco.com 420 Xing Li 421 CERNET Center/Tsinghua University 422 Room 225, Main Building, Tsinghua University 423 Beijing, 100084 424 P.R. China 426 Phone: +86 10-62785983 427 Email: xing@cernet.edu.cn 429 Mingwei Xu 430 Tsinghua University 431 Department of Computer Science, Tsinghua University 432 Beijing, 100084 433 P.R.China 435 Phone: +86-10-6278-5822 436 Email: xmw@cernet.edu.cn