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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Softwire WG Q. Wang 3 Internet-Draft China Telecom 4 Intended status: Standards Track J. Qin 5 Expires: May 3, 2012 ZTE 6 M. Boucadair 7 C. Jacquenet 8 France Telecom 9 Y. Lee 10 Comcast 11 October 31, 2011 13 Multicast Extensions to DS-Lite Technique in Broadband Deployments 14 draft-ietf-softwire-dslite-multicast-01 16 Abstract 18 This document specifies a solution for the delivery of multicast 19 service offerings to DS-Lite serviced customers. The proposed 20 solution relies upon a stateless IPv4-in-IPv6 encapsulation scheme 21 and uses the IPv6 multicast distribution tree to deliver IPv4 22 multicast traffic over an IPv6 multicast-enabled network. 24 Status of this Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on May 3, 2012. 41 Copyright Notice 43 Copyright (c) 2011 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 61 3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 62 4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5 63 4.1. IPv4-embedded IPv6 Prefixes . . . . . . . . . . . . . . . 6 64 4.2. Multicast Distribution Tree Computation . . . . . . . . . 7 65 4.3. Multicast Data Forwarding . . . . . . . . . . . . . . . . 8 66 5. Address Mapping . . . . . . . . . . . . . . . . . . . . . . . 8 67 5.1. Prefix Assignment . . . . . . . . . . . . . . . . . . . . 8 68 5.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 9 69 6. Multicast B4 (mB4) . . . . . . . . . . . . . . . . . . . . . . 9 70 6.1. IGMP-MLD Interworking Function . . . . . . . . . . . . . . 9 71 6.2. Multicast Data Forwarding . . . . . . . . . . . . . . . . 10 72 6.3. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 10 73 6.4. Host built-in mB4 Function . . . . . . . . . . . . . . . . 10 74 7. Multicast AFTR (mAFTR) . . . . . . . . . . . . . . . . . . . . 11 75 7.1. Routing Considerations . . . . . . . . . . . . . . . . . . 11 76 7.2. Processing PIM Message . . . . . . . . . . . . . . . . . . 11 77 7.3. Switching from Shared Tree to Shortest Path Tree . . . . . 12 78 7.4. Multicast Data Forwarding . . . . . . . . . . . . . . . . 12 79 7.5. TTL/Scope . . . . . . . . . . . . . . . . . . . . . . . . 13 80 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 81 8.1. Firewall Configuration . . . . . . . . . . . . . . . . . . 13 82 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 83 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 84 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 85 11.1. Normative References . . . . . . . . . . . . . . . . . . . 14 86 11.2. Informative References . . . . . . . . . . . . . . . . . . 15 87 Appendix A. Use Case: IPTV . . . . . . . . . . . . . . . . . . . 15 88 Appendix B. Deployment Considerations . . . . . . . . . . . . . . 16 89 B.1. Load-Balancing . . . . . . . . . . . . . . . . . . . . . . 16 90 B.2. RP for IPv4-Embedded IPv6 Multicast Groups . . . . . . . . 16 91 B.3. mAFTR Policy Configuration . . . . . . . . . . . . . . . . 16 92 B.4. Static vs. Dynamic PIM Triggering . . . . . . . . . . . . 17 93 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 95 1. Introduction 97 DS-Lite [RFC6333] is a technique that rationalizes the usage of the 98 remaining global IPv4 addresses during the transition period by 99 sharing a single IPv4 address with multiple users. A typical DS-Lite 100 scenario is the delivery of an IPv4 service to an IPv4 user over an 101 IPv6 network (denoted as a 4-6-4 scenario). [RFC6333] covers unicast 102 services exclusively. 104 If customers have to access IPv4 multicast-based services through DS- 105 Lite environment, Address Family Transition Router (AFTR) devices 106 will have to process all the IGMP Report messages [RFC2236] [RFC3376] 107 that have been forwarded by the CPE into the IPv4-in-IPv6 tunnels. 108 From that standpoint, AFTR devices are likely to behave as a 109 replication point for downstream multicast traffic. And the 110 multicast packets will be replicated for each tunnel endpoint where 111 IPv4 receivers are connected to. 113 This kind of DS-Lite environment raises two major issues: 115 1. The IPv6 network loses the benefits of the multicast traffic 116 forwarding efficiency because it is unable to deterministically 117 replicate the data as close to the receivers as possible. As a 118 consequence, the downstream bandwidth in the IPv6 network will be 119 vastly consumed by sending multicast data over a unicast 120 infrastructure. 122 2. The AFTR is responsible for replicating multicast traffic and 123 forwarding it into each tunnel endpoint connecting IPv4 receivers 124 that have explicitly asked for the corresponding contents. This 125 process may greatly consume AFTR's resources and overload the 126 AFTR. 128 This document specifies an extension to the DS-Lite model to deliver 129 IPv4 multicast services to IPv4 clients over an IPv6 multicast- 130 enabled network. 132 1.1. Requirements Language 134 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 135 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 136 document are to be interpreted as described in RFC 2119 [RFC2119]. 138 2. Terminology 140 This document makes use of the following terms: 142 o IPv4-embedded IPv6 address: is an IPv6 address which embeds a 32- 143 bit-encoded IPv4 address. An IPv4-embedded IPv6 address can be 144 unicast or multicast. 146 o mPrefix64: is a dedicated multicast IPv6 prefix for constructing 147 IPv4-embedded IPv6 multicast addresses 148 [I-D.boucadair-behave-64-multicast-address-format]. mPrefix64 can 149 be of two types: ASM_mPrefix64 used in Any Source Multicast (ASM) 150 mode or SSM_mPrefix64 used in Source Specific Multicast (SSM) mode 151 [RFC4607]. 153 o uPrefix64: is a dedicated IPv6 unicast prefix for constructing 154 IPv4- embedded IPv6 unicast addresses [RFC6052]. 156 o Multicast AFTR (mAFTR): is a functional entity which supports 157 IPv4- IPv6 multicast interworking function (refer to Figure 3). 158 It receives and encapsulates the IPv4 multicast packets into IPv4- 159 in-IPv6 packets and behaves as the corresponding IPv6 multicast 160 source for the encapsulated IPv4-in-IPv6 packets. 162 o Multicast B4 (mB4): is a functional entity embedded in a CPE, 163 which supports an IGMP-MLD interworking function (refer to 164 Section 6.1) that relays information conveyed in IGMP messages by 165 forwarding the corresponding MLD messages towards the MLD Querier 166 in the IPv6 network. In addition, the mB4 decapsulates IPv4-in- 167 IPv6 multicast packets. 169 o PIMv4: refers to PIM when deployed in an IPv4 infrastructure 170 (i.e., IPv4 transfer capabilities are used to exchange PIM 171 messages). 173 o PIMv6: refers to PIM when deployed in an IPv6 infrastructure 174 (i.e., IPv6 transfer capabilities are used to exchange PIM 175 messages). 177 3. Scope 179 This document focuses only on issues raised by a DS-Lite environment: 180 subscription to an IPv4 multicast group and the delivery of IPv4- 181 formatted content to IPv4 receivers over an IPv6-only network. In 182 particular, only the following case is covered: 184 An IPv4 receiver accesses IPv4 multicast contents over an IPv6- 185 only multicast-enabled network. 187 This document does not cover the source/receiver heuristics, where as 188 IPv4 receiver can also behave as an IPv4 multicast source. This 189 document assumes that hosts behind the mB4 are IPv4 multicast 190 receivers only. 192 4. Solution Overview 194 In the original DS-Lite specification [RFC6333], an IPv4-in-IPv6 195 tunnel is used to carry bidirectional IPv4 unicast traffic between a 196 B4 and an AFTR. An extension to DS-Lite is proposed in this document 197 which specifies an IPv4-in-IPv6 encapsulation scheme to deliver 198 unidirectional IPv4 multicast traffic from a mAFTR to a mB4. 200 An overview of the solution is provided in this section which is 201 intended as an introduction to how it works, but is NOT normative. 202 For the normative specifications of the two new functional elements: 203 mB4 and mAFTR (Figure 1), refer to Section 6 and Section 7. 205 ------------ 206 / \ 207 | IPv4 network | 208 \ / 209 ------------ 210 IPv4 multicast : | ^ PIMv4 Join 211 v | : 212 +-------------+ 213 | mAFTR | 214 +-------------+ 215 IPv6 multicast |:| | ^ PIMv6 Join (PIMv6 216 (IPv4 embedded) |:| | : routers in between) 217 ------------ 218 / \ 219 | IPv6 network | 220 \ / 221 ------------ 222 |:| | : MLD Report 223 |v| | : 224 +-----------+ 225 | mB4 | 226 +-----------+ 227 IPv4 multicast : | ^ IGMP Report 228 v | : 229 +-----------+ 230 | IPv4 | 231 | receiver | 232 +-----------+ 234 Figure 1: Functional Architecture 236 4.1. IPv4-embedded IPv6 Prefixes 238 In order to map the addresses of IPv4 multicast traffic with IPv6 239 multicast addresses, an IPv6 multicast prefix (mPrefix64) and an IPv6 240 unicast prefix (uPrefix64) are provided to mAFTR and mB4 elements, 241 both of which contribute to the computation and the maintenance of 242 the IPv6 multicast distribution tree that extends the IPv4 multicast 243 distribution tree into the IPv6 multicast network. 245 The mAFTR and mB4 use mPrefix64 to convert an IPv4 multicast address 246 (G4) to an IPv4-embedded IPv6 multicast address (G6). The mAFTR and 247 mB4 use uPrefix64 to convert an IPv4 multicast source address (S4) to 248 an IPv4-embedded IPv6 address (S6). The mAFTR and mB4 MUST use the 249 same mPrefix64 and uPrefix64, as well as run the same algorithm for 250 building IPv4-embedded IPv6 addresses. Refer to Section 5 for more 251 details about the address mapping. 253 4.2. Multicast Distribution Tree Computation 255 When an IPv4 receiver connected to the CPE that embeds mB4 wants to 256 subscribe to an IPv4 multicast group, it sends an IGMP Report message 257 to the mB4. The mB4 creates the IPv6 multicast group (G6) address 258 using mPrefix64 and the original IPv4 multicast gorup address. If 259 the receiver sends a source-specific IGMPv3 Report message, the mB4 260 will create the IPv6 source address (S6) using uPrefix64 and the 261 original IPv4 source address. 263 The mB4 uses the G6 (and both S6 and G6 in SSM) to create the 264 corresponding MLD Report message. The mB4 sends the Report message 265 to the MLD Querier in the IPv6 network. The MLD Querier (typically 266 acts as the PIMv6 Designated Router) receives the MLD Report message 267 and sends the PIMv6 Join to join the IPv6 multicast distribution 268 tree. The MLD Querier can send either PIMv6 Join (*,G6) in ASM or 269 PIMv6 Join (S6,G6) in SSM to the mAFTR. 271 The mAFTR acts as the DR to which the uPrefix64-derived S6 is 272 connected. The mAFTR will receive the source-specific PIMv6 Join 273 message (S6,G6) from the IPv6 multicast network. If the mAFTR is the 274 Rendezvous Point (RP) of G6, it will receive the any-source PIMv6 275 Join message (*,G6) from the IPv6 multicast network. If the mAFTR is 276 not the RP of G6, it will send the PIM Register message to the RP of 277 G6 located in the IPv6 multicast network. 279 When the mAFTR receives the PIMv6 Join message (*,G6), it will 280 extract the IPv4 multicast group address (G4). If the mAFTR is the 281 RP of G4 in the IPv4 multicast network, it will create a (*,G4) entry 282 (if there is not yet an existing one) in its own IPv4 multicast 283 routing table. If the mAFTR is not the RP of G4, it will send the 284 corresponding PIMv4 Join message (*,G4) towards the RP of G4 in the 285 IPv4 multicast network. 287 When the mAFTR receives the PIMv6 Join message (S6,G6), it will 288 extract the IPv4 multicast group address (G4) and IPv4 source address 289 (S4) and send the corresponding (S4,G4) PIMv4 Join message directly 290 to the IPv4 source. 292 A branch of the multicast distribution tree is then grafted, 293 comprising both an IPv4 part (from the mAFTR upstream) and an IPv6 294 part (from mAFTR downstream to the mB4). 296 The mAFTR MUST advertise the route of uPrefix64 with an IPv6 IGP, so 297 as to represent the IPv4-embedded IPv6 source in the IPv6 multicast 298 network. 300 4.3. Multicast Data Forwarding 302 When the mAFTR receives an IPv4 multicast packet, it will encapsulate 303 the packet into an IPv6 multicast packet using the IPv4-embedded IPv6 304 multicast address as the destination address and an IPv4-embedded 305 IPv6 unicast address as the source address. The encapsulated IPv6 306 multicast packet will be forwarded down the IPv6 multicast 307 distribution tree and the mB4 will eventually receive the packet. 309 The IPv6 multicast network treats the IPv4-in-IPv6 encapsulated 310 multicast packets as native. The IPv6 multicast routers use the 311 outer IPv6 header to make forwarding decisions. 313 When the mB4 receive the IPv6 multicast packet (to G6) derived by 314 mPrefix64, it MUST decapsulate it and forward the original IPv4 315 multicast packet to the receivers subscribing to G4. 317 5. Address Mapping 319 5.1. Prefix Assignment 321 A dedicated IPv6 multicast prefix (mPrefix64) is provisioned to the 322 mAFTR and the mB4. The mAFTR and the mB4 use the mPrefix64 to form 323 an IPv6 multicast group address from an IPv4 multicast group address. 324 The mPrefix64 can be of two types: ASM_mPrefix64 (a mPrefix64 used in 325 ASM mode) or SSM_mPrefix64 (a mPrefix64 used in SSM mode). The 326 mPrefix64 Must be derived from the corresponding IPv6 multicast 327 address space (e.g., the SSM_mPrefix64 MUST be in the range of 328 multicast address space specified in [RFC4607]). 330 The IPv6 part of the multicast distribution tree can be seen as an 331 extension of the IPv4 part of the multicast distribution tree. The 332 IPv4 multicast source address MUST be mapped to an IPv6 multicast 333 source address. An IPv6 unicast prefix (uPrefix64) is provisioned to 334 the mAFTR and the mB4. The mAFTR and the mB4 use the uPrefix64 to 335 form an IPv6 multicast source address from an IPv4 multicast source 336 address. The uPrefix-formed IPv6 multicast source address will 337 represent the original IPv4 multicast source in the IPv6 multicast 338 network. The uPrefix64 MUST be derived from the IPv6 unicast address 339 space. 341 The address format to be used is left to the responsibility of the 342 network provider. The address synthesizing MUST follow 343 [I-D.boucadair-behave-64-multicast-address-format] and [RFC6052]. 345 The mPrefix64 and uPrefix64 can be configured in the mB4 using a 346 variety of methods, including an out-of-band mechanism, manual 347 configuration, or a dedicated provisioning protocol (e.g., using 348 DHCPv6 [I-D.qin-softwire-multicast-prefix-option]). 350 5.2. Examples 352 Group address mapping example when a /96 is used: 354 +---------------------+--------------+----------------------------+ 355 | mPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 356 +---------------------+--------------+----------------------------+ 357 | ffxx:abc::/96 | 230.1.2.3 | ffxx:abc::230.1.2.3 | 358 +---------------------+--------------+----------------------------+ 360 Source address mapping example when a /96 is used: 362 +---------------------+--------------+----------------------------+ 363 | uPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 364 +---------------------+--------------+----------------------------+ 365 | 2001:db8::/96 | 192.1.2.3 | 2001:db8::192.1.2.3 | 366 +---------------------+--------------+----------------------------+ 368 6. Multicast B4 (mB4) 370 6.1. IGMP-MLD Interworking Function 372 The IGMP-MLD Interworking Function combines the IGMP/MLD Proxying 373 function and the IGMP/MLD translation function. The IGMP/MLD 374 Proxying function is specified in [RFC4605]. The IGMP/MLD 375 translation function translates the contents of IGMP messages into 376 MLD messages by using a stateless algorithm. The address 377 synthesizing MUST comply with the rules documented in Section 5. MLD 378 messages will be forwarded natively towards the MLD Querier located 379 upstream in the IPv6 network. The mB4 performs the IGMP-MLD 380 Interworking Function to relay between the IGMP messages and the MLD 381 messages. 383 +----------+ IGMP +-------+ MLD +---------+ 384 | IPv4 |---------| mB4 |---------| MLD | 385 | Receiver | | | | Querier | 386 +----------+ +-------+ +---------+ 388 Figure 2: IGMP-MLD Interworking 390 When the mB4 receives an IGMP Report message from a receiver to 391 subscribe to multicast group (and optionally associated to a source 392 in SSM mode), it MUST translate the IGMP Report message into a MLD 393 Report message and send to the MLD Querier. The mB4 MUST construct 394 the IPv6 multicast group address using the mPrefix64. 396 When the mB4 receives an MLD Listener Query message from the MLD 397 Querier, it MUST convert the MLD listener Query message to the IGMP 398 Query message and send it to the IPv4 receiver(s). The mB4 MUST 399 retrieve the IPv4 multicast group address using the mPrefix64. 401 If SSM is deployed, the mB4 MUST construct the IPv6 source address 402 (or retrieve the IPv4 source address) using the uPrefix64. The mB4 403 may create a membership database which associates the IPv4-IPv6 404 multicast groups with the interfaces (e.g., Wi-Fi and Wired Ethernet) 405 facing IPv4 multicast receivers. 407 6.2. Multicast Data Forwarding 409 When the mB4 receives an IPv6 multicast packet, it MUST check the 410 group address and the source address. If the IPv6 multicast group 411 prefix is mPrefix64 and the IPv6 source prefix is uPrefix64, the mB4 412 MUST de-capsulate the IPv6 header and forward the IPv4 multicast 413 packet through each relevant interface. Otherwise, the mB4 MUST drop 414 the packet silently. 416 As an illustration, if a packet is received from source 2001:db8:: 417 192.1.2.3 and to be forwarded to group ffxx:abc::230.1.2.3, the mB4 418 will de-capsulate it into an IPv4 multicast packet using 192.1.2.3 as 419 the IPv4 multicast source address and using 230.1.2.3 as the IPv4 420 destination address. 422 6.3. Fragmentation 424 Encapsulating IPv4 multicast packets into IPv6 multicast packets that 425 will be forwarded by the mAFTR to the mB4 along the IPv6 multicast 426 distribution tree reduces the effective MTU size by the size of an 427 IPv6 header. In this specification, the data flow is unidirection 428 from mAFTR to mB4, the mAFTR must fragment the oversized IPv6 packet 429 after the encapsulation into two IPv6 packets. The mB4 MUST 430 reassemable the IPv6 packets, decapsulate the IPv6 packet, and 431 forward the IPv4 packet to the hosts subscribing the multicast group. 432 Further considerations about fragmentation issues are documented in 433 [RFC6333]. 435 6.4. Host built-in mB4 Function 437 If the mB4 function is implemented in the host which is directly 438 connected to an IPv6-only network. If an IPv4 application running in 439 the host requests to subscribe an IPv4 multicast stream, the host 440 MUST implement Section 6.1, Section 6.2, and Section 6.3. The host 441 MAY optimize the implemntation to provide an Application Programming 442 Interface (API) or kernel module to skip the IGMP-MLD Interworking 443 Function. The optimization is out of scope of the specification. 445 7. Multicast AFTR (mAFTR) 447 7.1. Routing Considerations 449 The mAFTR is responsible for interconnecting the IPv4 multicast 450 distribution tree with the corresponding IPv6 multicast distribution 451 tree. The mAFTR MUST use the uPrefix64 to build the IPv6 source 452 addresses of the multicast group address derived from mPrefix64. In 453 other words, the mAFTR MUST be the multicast source derived from 454 mPrefix64. 456 The mAFTR MUST advertise the route of uPrefix64 to the IPv6 IGP. 457 This is needed for the IPv6 multicast router to have routing 458 information to discover the source. In order to pass the Reverse 459 Path Forwarding (RPF) check, the IPv6 routers MUST enable PIM on the 460 interfaces which has the shortest path to the uPrefix64. 462 7.2. Processing PIM Message 464 The mAFTR MUST interwork PIM Join/Prune messages for (*, G6) and (S6, 465 G6) on their corresponding (*, G4) and (S4, G4). The following text 466 specifies the expected behavior of mAFTR for PIM Join message. 468 +---------+ 469 ---------| mAFTR |--------- 470 PIMv6 |uPrefix64| PIMv4 471 |mPreifx64| 472 +---------+ 474 Figure 3: PIMv6-PIMv4 Interworking Function 476 The mAFTR contains two separate multicast routing table (mRIB): IPv4 477 multicast routing table (mRIB4) and IPv6 multicast routing table 478 (mRIB6), which are bridged by one IPv4-in-IPv6 virtual interface. It 479 should be noted that the implementations may vary (e.g., using one 480 integrated mRIB without any virtual interface), while they should 481 follow the specification herein for the consistency of overall 482 functionality. 484 When a mAFTR receives a PIMv6 Join message (*,G6) with an IPv6 485 multicast group address (G6) that is derived from the mPrefix64, it 486 MUST check its IPv6 multicast routing table (mRIB6). If there is an 487 entry for this G6, it MUST check whether the interface through which 488 the PIMv6 Join message has been received is on the outgoing interface 489 list. If not, the mAFTR MUST add the interface to the outgoing 490 interface list. If there is no entry in the mRIB6, the mAFTR MUST 491 create a new entry (*,G6) for the multicast group. While, whether or 492 not to set the IPv4-in-IPv6 virtual interface as the incoming 493 interface of the newly created entry is up to the implementation but 494 should comply with the mAFTR's behavior of multicast data forwarding, 495 see Section 7.4. 497 The mAFTR MUST extract the IPv4 multicast group address (G4) from the 498 IPv4-embedded IPv6 multicast address (G6) contained in the PIMv6 Join 499 message. The mAFTR MUST check its IPv4 multicast routing table 500 (mRIB4). If there is an entry for G4, it MUST check whether the 501 IPv4-in-IPv6 virtual interface is on the outgoing interface list. If 502 not, the mAFTR MUST add the interface to the outgoing interface list. 503 If there is no entry for G4, the mAFTR MUST create a new (*,G4) entry 504 in its mRIB4 and initiate the procedure for building the shared tree 505 in the IPv4 multicast network without any additional requirement. 507 If mAFTR receives a source-specific Join message, the (S6, G6) will 508 be processed rather than (*,G6). The procedures of processing 509 (S6,G6) and (*,G6) are almost the same. Differences have been 510 detailed in [RFC4601]. 512 7.3. Switching from Shared Tree to Shortest Path Tree 514 When the mAFTR receives the first IPv4 multicast packet, it may 515 extract the multicast source address (S4) from the packet and send an 516 Explicit PIMv4 (S4,G4) Join message directly to S4. The mAFTR will 517 switch from the shared Rendezvous Point Tree (RPT) to the Shortest 518 Path Tree (SPT) for G4. 520 For IPv6 multicast routers to switch to the SPT, there is no new 521 requirement. IPv6 multicast routers may send an Explicit PIMv6 Join 522 to mAFTR once the first (S6,G6) multicast packet arrives from 523 upstream multicast routers. 525 7.4. Multicast Data Forwarding 527 When the mAFTR receives an IPv4 multicast packet, it will look up the 528 mRIB4 to find a matching entry and then forward the packet to the 529 interface(s) on the outgoing interface list. If the IPv4-in-IPv6 530 virtual interface also belongs to this list, the packet will be 531 encapsulated with the mPrefix64-derived and uPrefix64-derived IPv4- 532 embedded IPv6 addresses to form an IPv6 multicast packet. Then 533 another lookup is executed to find a matching entry in the mRIB6, 534 while whether or not to perform RPF check for the second lookup is up 535 to the implementation and is out of the scope of this document. The 536 IPv6 multicast packet is forwarded along the IPv6 multicast 537 distribution tree, based upon the outgoing interface list of the 538 matching entry in the mRIB6. 540 As an illustration, if a packet is received from source 192.1.2.3 and 541 to be forwarded to group 230.1.2.3, the mAFTR encapsulates it into an 542 IPv6 multicast packet using ffxx:abc::230.1.2.3 as the IPv6 543 destination address and using 2001:db8::192.1.2.3 as the IPv6 544 multicast source address. 546 7.5. TTL/Scope 548 The Scope field of IPv4-in-IPv6 multicast addresses can be valued to 549 "E" (Global scope) or to "8" (Organization-local scope). This 550 specification does not discuss the scope value that should be used. 552 8. Security Considerations 554 This document does not introduce any new security concern in addition 555 to what is discussed in Section 5 of [RFC6052], Section 10 of 556 [RFC3810] and Section 6 of [RFC4601]. 558 8.1. Firewall Configuration 560 The CPE should be configured to accept incoming MLD messages and 561 traffic forwarded to multicast groups subscribed by receivers located 562 in the customer premises. 564 9. Acknowledgements 566 The authors would like to thank Dan Wing for his guidance in the 567 early discussions which initiated this work. We also thank Peng Sun, 568 Jie Hu, Qiong Sun, Lizhong Jin, Alain Durand, Dean Cheng, Behcet 569 Sarikaya, Tina Tsou, Rajiv Asati, and Xiaohong Deng for their 570 valuable comments. 572 10. IANA Considerations 574 This document includes no request to IANA. 576 11. References 577 11.1. Normative References 579 [I-D.boucadair-behave-64-multicast-address-format] 580 Boucadair, M., Qin, J., Lee, Y., Venaas, S., Li, X., and 581 M. Xu, "IPv4-Embedded IPv6 Multicast Address Format", 582 draft-boucadair-behave-64-multicast-address-format-03 583 (work in progress), October 2011. 585 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 586 Requirement Levels", BCP 14, RFC 2119, March 1997. 588 [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast 589 Listener Discovery (MLD) for IPv6", RFC 2710, 590 October 1999. 592 [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 593 Thyagarajan, "Internet Group Management Protocol, Version 594 3", RFC 3376, October 2002. 596 [RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery 597 Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. 599 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 600 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 601 Protocol Specification (Revised)", RFC 4601, August 2006. 603 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 604 "Internet Group Management Protocol (IGMP) / Multicast 605 Listener Discovery (MLD)-Based Multicast Forwarding 606 ("IGMP/MLD Proxying")", RFC 4605, August 2006. 608 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 609 IP", RFC 4607, August 2006. 611 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 612 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 613 October 2010. 615 [RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation 616 Algorithm", RFC 6145, April 2011. 618 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 619 Stack Lite Broadband Deployments Following IPv4 620 Exhaustion", RFC 6333, August 2011. 622 11.2. Informative References 624 [I-D.ietf-mboned-multiaaa-framework] 625 Satou, H., Ohta, H., Hayashi, T., Jacquenet, C., and H. 626 He, "AAA and Admission Control Framework for 627 Multicasting", draft-ietf-mboned-multiaaa-framework-12 628 (work in progress), August 2010. 630 [I-D.jaclee-behave-v4v6-mcast-ps] 631 Jacquenet, C., Boucadair, M., Lee, Y., Qin, J., and T. 632 ZOU), "IPv4-IPv6 Multicast: Problem Statement and Use 633 Cases", draft-jaclee-behave-v4v6-mcast-ps-02 (work in 634 progress), June 2011. 636 [I-D.qin-softwire-multicast-prefix-option] 637 Qin, J., Boucadair, M., and T. Tsou, "DHCPv6 Options for 638 IPv6 DS-Lite Multicast Prefix", 639 draft-qin-softwire-multicast-prefix-option-01 (work in 640 progress), October 2011. 642 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 643 2", RFC 2236, November 1997. 645 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 646 IPv6 Specification", RFC 2473, December 1998. 648 [RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet 649 Group Management Protocol Version 3 (IGMPv3) and Multicast 650 Listener Discovery Protocol Version 2 (MLDv2) for Source- 651 Specific Multicast", RFC 4604, August 2006. 653 [RFC4608] Meyer, D., Rockell, R., and G. Shepherd, "Source-Specific 654 Protocol Independent Multicast in 232/8", BCP 120, 655 RFC 4608, August 2006. 657 Appendix A. Use Case: IPTV 659 IPTV generally includes two categories of service offerings: 661 o Video on Demand (VoD) that unicast video content to receivers. 663 o Multicast live TV broadcast services. 665 Two players intervene in the delivery of this service: 667 o Content Providers, who usually own the contents that is multicast 668 to receivers. Content providers may contractually define an 669 agreement with network providers to deliver contents to receivers. 671 o Network Providers, who provide network connectivity services 672 (e.g., network providers are responsible for carrying multicast 673 flows from head-ends to receivers). Refer to 674 [I-D.ietf-mboned-multiaaa-framework]. 676 Note that some contract agreements prevent a network provider from 677 altering the content as sent by the content provider for various 678 reasons. Under the contract, multicast streams should be delivered 679 unaltered to the requesting users. 681 Many current IPTV contents are likely to remain IPv4-formatted and 682 out of control of the network providers. Additionally, there are 683 numerous legacy receivers (e.g., IPv4-only Set Top Boxes (STB)) that 684 can't be upgraded or be easily replaced to support IPv6. As a 685 consequence, IPv4 service continuity MUST be guaranteed during the 686 transition period, including the delivery of multicast services such 687 as Live TV Broadcasting to users. 689 Appendix B. Deployment Considerations 691 B.1. Load-Balancing 693 For robustness and load distribution purposes, several nodes in the 694 network can embed the mAFTR function. In such case, the same IPv6 695 prefixes (i.e., mPrefix64 and uPrefix64) and algorithm to build IPv4- 696 embedded IPv6 addresses MUST be configured on those nodes. 698 B.2. RP for IPv4-Embedded IPv6 Multicast Groups 700 For the sake of simplicity, it is RECOMMENDED to configure mAFTR as 701 the RP for the IPv4-embedded IPv6 multicast groups it manages. No 702 registration procedure is required under this configuration. 704 B.3. mAFTR Policy Configuration 706 mAFTR may be configured with a list of IPv4 multicast groups and 707 sources. Only multicast flows bound to the configured addresses 708 should be handled by the mAFTR. Otherwise, packets are silently 709 drooped. 711 B.4. Static vs. Dynamic PIM Triggering 713 To optimize the usage of network resources in current deployments, 714 all multicast streams are conveyed in the core network while only 715 popular ones are continuously conveyed in the aggregation/access 716 network (static mode). Non-popular streams are conveyed in the 717 access network upon request (dynamic mode). Depending on the 718 location of the mAFTR in the network, two modes can be envisaged: 719 static and dynamic. 721 o Static Mode: the mAFTR is configured to instantiate permanent (S6, 722 G6) and (*, G6) entries in its MRIBv6 using a pre-configured (S4, 723 G4) list. 725 o Dynamic Mode: the instantiation and deletion of (S6, g6) or (*, 726 G6) is triggered by the receipt of PIMv6 messages. 728 Authors' Addresses 730 Qian Wang 731 China Telecom 732 No.118, Xizhimennei 733 Beijing, 100035 734 China 736 Phone: +86 10 5855 2177 737 Email: wangqian@ctbri.com.cn 739 Jacni Qin 740 ZTE 741 Shanghai, 742 China 744 Phone: +86 1391 8619 913 745 Email: jacni@jacni.com 747 Mohamed Boucadair 748 France Telecom 749 Rennes, 35000 750 France 752 Phone: 753 Email: mohamed.boucadair@orange.com 754 Christian Jacquenet 755 France Telecom 756 Rennes, 35000 757 France 759 Phone: 760 Email: christian.jacquenet@orange.com 762 Yiu L. Lee 763 Comcast 764 U.S.A. 766 Phone: 767 Email: yiu_lee@cable.comcast.com 768 URI: http://www.comcast.com