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Wang 11 China Telecom 12 December 15, 2016 14 Delivery of IPv4 Multicast Services to IPv4 Clients over an IPv6 15 Multicast Network 16 draft-ietf-softwire-dslite-multicast-13 18 Abstract 20 This document specifies a solution for the delivery of IPv4 multicast 21 services to IPv4 clients over an IPv6 multicast network. The 22 solution relies upon a stateless IPv4-in-IPv6 encapsulation scheme 23 and uses the IPv6 multicast distribution tree to deliver IPv4 24 multicast traffic. The solution is particularly useful for the 25 delivery of multicast service offerings to DS-Lite serviced 26 customers. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at http://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on June 18, 2017. 45 Copyright Notice 47 Copyright (c) 2016 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5 67 4.1. IPv4-Embedded IPv6 Prefixes . . . . . . . . . . . . . . . 6 68 4.2. Multicast Distribution Tree Computation . . . . . . . . . 7 69 4.3. Multicast Data Forwarding . . . . . . . . . . . . . . . . 8 70 5. IPv4/IPv6 Address Mapping . . . . . . . . . . . . . . . . . . 8 71 5.1. Prefix Assignment . . . . . . . . . . . . . . . . . . . . 8 72 5.2. Address Translation Algorithm . . . . . . . . . . . . . . 9 73 5.3. Textual Representation . . . . . . . . . . . . . . . . . 9 74 5.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 9 75 6. Multicast B4 (mB4) . . . . . . . . . . . . . . . . . . . . . 10 76 6.1. IGMP-MLD Interworking Function . . . . . . . . . . . . . 10 77 6.2. Multicast Data Forwarding . . . . . . . . . . . . . . . . 11 78 6.3. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 11 79 6.4. Host Built-in mB4 Function . . . . . . . . . . . . . . . 11 80 6.5. Preserve the Scope . . . . . . . . . . . . . . . . . . . 12 81 7. Multicast AFTR (mAFTR) . . . . . . . . . . . . . . . . . . . 12 82 7.1. Routing Considerations . . . . . . . . . . . . . . . . . 12 83 7.2. Processing PIM Messages . . . . . . . . . . . . . . . . . 12 84 7.3. Switching from Shared Tree to Shortest Path Tree . . . . 14 85 7.4. Multicast Data Forwarding . . . . . . . . . . . . . . . . 14 86 7.5. TTL/Scope . . . . . . . . . . . . . . . . . . . . . . . . 14 87 8. Deployment Considerations . . . . . . . . . . . . . . . . . . 15 88 8.1. Other Operational Modes . . . . . . . . . . . . . . . . . 15 89 8.1.1. The MLD Querier is Co-Located with the mAFTR . . . . 15 90 8.1.2. The DR is Co-Located with the mAFTR . . . . . . . . . 15 91 8.2. Load Balancing . . . . . . . . . . . . . . . . . . . . . 15 92 8.3. mAFTR Policy Configuration . . . . . . . . . . . . . . . 15 93 8.4. Static vs. Dynamic PIM Triggering . . . . . . . . . . . . 16 94 9. Security Considerations . . . . . . . . . . . . . . . . . . . 16 95 9.1. Firewall Configuration . . . . . . . . . . . . . . . . . 16 96 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 97 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 98 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 99 12.1. Normative References . . . . . . . . . . . . . . . . . . 17 100 12.2. Informative References . . . . . . . . . . . . . . . . . 18 101 Appendix A. Use Case: IPTV . . . . . . . . . . . . . . . . . . . 19 102 Appendix B. Older Versions of Group Membership Management 103 Protocols . . . . . . . . . . . . . . . . . . . . . 19 104 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 106 1. Introduction 108 DS-Lite [RFC6333] is a technique that rationalizes the usage of the 109 remaining global IPv4 addresses during the transition period by 110 sharing a single IPv4 address with multiple users. A typical DS-Lite 111 scenario is the delivery of an IPv4 service to an IPv4 user over an 112 IPv6 network (denoted as a 4-6-4 scenario). [RFC6333] covers unicast 113 services exclusively. 115 This document specifies a generic solution for the delivery of IPv4 116 multicast services to IPv4 clients over an IPv6 multicast network. 117 The solution was developed with DS-Lite in mind (see more discussion 118 below). The solution is however not limited to DS-Lite; it can be 119 applied in other deployment contexts such as [RFC7596][RFC7597]. 121 If customers have to access IPv4 multicast-based services through a 122 DS-Lite environment, Address Family Transition Router (AFTR) devices 123 will have to process all the Internet Group Management Protocol 124 (IGMP) Report messages [RFC2236] [RFC3376] that have been forwarded 125 by the Customer Premises Equipment (CPE) into the IPv4-in-IPv6 126 tunnels. From that standpoint, AFTR devices are likely to behave as 127 a replication point for downstream multicast traffic, and the 128 multicast packets will be replicated for each tunnel endpoint that 129 IPv4 receivers are connected to. 131 This kind of DS-Lite environment raises two major issues: 133 1. The IPv6 network loses the benefits of the multicast traffic 134 forwarding efficiency because it is unable to deterministically 135 replicate the data as close to the receivers as possible. As a 136 consequence, the downstream bandwidth in the IPv6 network will be 137 vastly consumed by sending multicast data over a unicast 138 infrastructure. 140 2. The AFTR is responsible for replicating multicast traffic and 141 forwarding it into each tunnel endpoint connecting IPv4 receivers 142 that have explicitly asked for the corresponding contents. This 143 process may significantly consume the AFTR's resources and 144 overload the AFTR. 146 This document specifies an extension to the DS-Lite model to deliver 147 IPv4 multicast services to IPv4 clients over an IPv6 multicast- 148 enabled network. 150 1.1. Requirements Language 152 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 153 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 154 document are to be interpreted as described in RFC 2119 [RFC2119]. 156 2. Terminology 158 This document makes use of the following terms: 160 IPv4-embedded IPv6 address: an IPv6 address which embeds a 32-bit- 161 encoded IPv4 address. An IPv4-embedded IPv6 address can be 162 unicast or multicast. 164 mPrefix64: a dedicated multicast IPv6 prefix for constructing 165 IPv4-embedded IPv6 multicast addresses. mPrefix64 can be of two 166 types: ASM_mPrefix64 used in Any Source Multicast (ASM) mode or 167 SSM_mPrefix64 used in Source Specific Multicast (SSM) mode 168 [RFC4607]. The size of this prefix is /96. 170 Note: "64" is used as an abbreviation for IPv6-IPv4 171 interconnection. 173 uPrefix64: a dedicated IPv6 unicast prefix for constructing 174 IPv4-embedded IPv6 unicast addresses [RFC6052]. 176 Multicast AFTR (mAFTR): a functional entity which supports an 177 IPv4-IPv6 multicast interworking function (refer to Figure 3). It 178 receives and encapsulates the IPv4 multicast packets into IPv4-in- 179 IPv6 packets and behaves as the corresponding IPv6 multicast 180 source for the encapsulated IPv4-in-IPv6 packets. 182 Multicast B4 (mB4): a functional entity which supports an IGMP-MLD 183 interworking function (refer to Section 6.1) that relays 184 information conveyed in IGMP messages by forwarding the 185 corresponding Multicast Listener Discovery (MLD) messages towards 186 the MLD Querier in the IPv6 network. In addition, the mB4 187 decapsulates IPv4-in-IPv6 multicast packets. 189 PIMv4: refers to Protocol Independent Multicast (PIM) when deployed 190 in an IPv4 infrastructure (i.e., IPv4 transport capabilities are 191 used to exchange PIM messages). 193 PIMv6: refers to PIM when deployed in an IPv6 infrastructure (i.e., 194 IPv6 transport capabilities are used to exchange PIM messages). 196 Host portion of the MLD protocol: refers to the part of MLD that 197 applies to all multicast address listeners (Section 6 of 198 [RFC3810]). As a reminder, MLD specifies separate behaviors for 199 multicast address listeners (i.e., hosts or routers that listen to 200 multicast packets) and multicast routers. 202 Router portion of the IGMP protocol: refers to the part of IGMP that 203 is performed by multicast routers (Section 6 of [RFC3376]). 205 3. Scope 207 This document focuses only on the subscription to IPv4 multicast 208 groups and the delivery of IPv4-formatted content to IPv4 receivers 209 over an IPv6-only network. In particular, only the following case is 210 covered: 212 IPv4 receivers access IPv4 multicast contents over IPv6-only 213 multicast-enabled networks. 215 This document does not cover the source/receiver heuristics, where 216 IPv4 receivers can also behave as IPv4 multicast sources. This 217 document assumes that hosts behind the mB4 are IPv4 multicast 218 receivers only. Also, the document covers host built-in mB4 219 function. 221 4. Solution Overview 223 In the DS-Lite specification [RFC6333], an IPv4-in-IPv6 tunnel is 224 used to carry bidirectional IPv4 unicast traffic between a B4 and an 225 AFTR. The solution specified in this document provides an IPv4-in- 226 IPv6 encapsulation scheme to deliver unidirectional IPv4 multicast 227 traffic from an mAFTR to an mB4. 229 An overview of the solution is provided in this section which is 230 intended as an introduction to how it works, but is not normative. 231 For the normative specifications of the two new functional elements: 232 mB4 and mAFTR (Figure 1), refer to Section 6 and Section 7. 234 ------------ 235 / \ 236 | IPv4 network | 237 \ / 238 ------------ 239 IPv4 multicast : | ^ PIMv4 Join 240 v | : 241 +-------------+ 242 | mAFTR | 243 +-------------+ 244 IPv6 multicast |:| | ^ PIMv6 Join (PIMv6 245 (IPv4 embedded) |:| | : routers in between) 246 ------------ 247 / \ 248 | IPv6 network | 249 \ / 250 ------------ 251 |:| | ^ MLD Report 252 |v| | : 253 +-----------+ 254 | mB4 | 255 +-----------+ 256 IPv4 multicast : | ^ IGMP Report 257 v | : 258 +-----------+ 259 | IPv4 | 260 | receiver | 261 +-----------+ 263 Figure 1: Functional Architecture 265 4.1. IPv4-Embedded IPv6 Prefixes 267 In order to map the addresses of IPv4 multicast traffic with IPv6 268 multicast addresses, an IPv6 multicast prefix (mPrefix64) and an IPv6 269 unicast prefix (uPrefix64) are provided to the mAFTR and the mB4 270 elements, both of which contribute to the computation and the 271 maintenance of the IPv6 multicast distribution tree that extends the 272 IPv4 multicast distribution tree into the IPv6 multicast network. 273 The IPv4/IPv6 address mapping is stateless. 275 The mAFTR and the mB4 use mPrefix64 to convert an IPv4 multicast 276 address (G4) into an IPv4-embedded IPv6 multicast address (G6). The 277 mAFTR and the mB4 use uPrefix64 to convert an IPv4 multicast source 278 address (S4) into an IPv4-embedded IPv6 address (S6). The mAFTR and 279 the mB4 must use the same mPrefix64 and uPrefix64, and also run the 280 same algorithm for building IPv4-embedded IPv6 addresses. Refer to 281 Section 5 for more details about the address mapping. 283 4.2. Multicast Distribution Tree Computation 285 When an IPv4 receiver connected to the device that embeds the mB4 286 capability wants to subscribe to an IPv4 multicast group, it sends an 287 IGMP Report message towards the mB4. The mB4 creates the IPv6 288 multicast group (G6) address using mPrefix64 and the original IPv4 289 multicast group address. If the receiver sends a source-specific 290 IGMPv3 Report message, the mB4 will create the IPv6 source address 291 (S6) using uPrefix64 and the original IPv4 source address. 293 The mB4 uses the G6 (and both S6 and G6 in SSM) to create the 294 corresponding MLD Report message. The mB4 sends the Report message 295 towards the MLD Querier in the IPv6 network. The MLD Querier (which 296 usually acts as the PIMv6 Designated Router too) receives the MLD 297 Report message and sends the PIMv6 Join to join the IPv6 multicast 298 distribution tree. The MLD Querier can send either PIMv6 Join (*,G6) 299 in ASM or PIMv6 Join (S6,G6) in SSM to the mAFTR. 301 The mAFTR acts as the IPv4 DR to which the uPrefix64-derived S6 is 302 connected. The mAFTR will receive the source-specific PIMv6 Join 303 message (S6,G6) from the IPv6 multicast network. If the mAFTR is the 304 Rendezvous Point (RP) of G6, it will receive the any-source PIMv6 305 Join message (*,G6) from the IPv6 multicast network. If the mAFTR is 306 not the RP of G6, it will send the PIM Register message to the RP of 307 G6 located in the IPv6 multicast network. For the sake of 308 simplicity, it is RECOMMENDED to configure the mAFTR as the RP for 309 the IPv4-embedded IPv6 multicast groups it manages; no registration 310 procedure is required under this configuration. 312 When the mAFTR receives the PIMv6 Join message (*,G6), it will 313 extract the IPv4 multicast group address (G4). If the mAFTR is the 314 RP of G4 in the IPv4 multicast network, it will create a (*,G4) entry 315 (if such entry does not already exist) in its own IPv4 multicast 316 routing table. If the mAFTR is not the RP of G4, it will send the 317 corresponding PIMv4 Join message (*,G4) towards the RP of G4 in the 318 IPv4 multicast network. 320 When the mAFTR receives the PIMv6 Join message (S6,G6), it will 321 extract the IPv4 multicast group address (G4) and IPv4 source address 322 (S4) and send the corresponding (S4,G4) PIMv4 Join message directly 323 to the IPv4 source. 325 A branch of the multicast distribution tree is thus constructed, 326 comprising both an IPv4 part (from the mAFTR upstream) and an IPv6 327 part (from mAFTR downstream towards the mB4). 329 The mAFTR advertises the route of uPrefix64 with an IPv6 Interior 330 Gateway Protocol (IGP), so as to represent the IPv4-embedded IPv6 331 source in the IPv6 multicast network, and to run the Reverse Path 332 Forwarding (RPF) check procedure on incoming multicast traffic. 333 Injecting internal /96 routes is not problematic given the 334 recommendation in [RFC7608] that requires that forwarding processes 335 must be designed to process prefixes of any length up to /128. 337 4.3. Multicast Data Forwarding 339 When the mAFTR receives an IPv4 multicast packet, it will encapsulate 340 the packet into an IPv6 multicast packet using the IPv4-embedded IPv6 341 multicast address as the destination address and an IPv4-embedded 342 IPv6 unicast address as the source address. The encapsulated IPv6 343 multicast packet will be forwarded down the IPv6 multicast 344 distribution tree and the mB4 will eventually receive the packet. 346 The IPv6 multicast network treats the IPv4-in-IPv6 encapsulated 347 multicast packets as native IPv6 multicast packets. The IPv6 348 multicast routers use the outer IPv6 header to make their forwarding 349 decisions. 351 When the mB4 receives the IPv6 multicast packet (to G6) derived by 352 mPrefix64, it decapsulates it and forwards the original IPv4 353 multicast packet to the receivers subscribing to G4. 355 Note: At this point, only IPv4-in-IPv6 encapsulation is defined; 356 however, other types of encapsulation could be defined in the future. 358 5. IPv4/IPv6 Address Mapping 360 5.1. Prefix Assignment 362 A dedicated IPv6 multicast prefix (mPrefix64) is provisioned to the 363 mAFTR and the mB4. The mAFTR and the mB4 use the mPrefix64 to form 364 an IPv6 multicast group address from an IPv4 multicast group address. 365 The mPrefix64 can be of two types: ASM_mPrefix64 (a mPrefix64 used in 366 ASM mode) or SSM_mPrefix64 (a mPrefix64 used in SSM mode). The 367 mPrefix64 MUST be derived from the corresponding IPv6 multicast 368 address space (e.g., the SSM_mPrefix64 must be in the range of 369 multicast address space specified in [RFC4607]). 371 The IPv6 part of the multicast distribution tree can be seen as an 372 extension of the IPv4 part of the multicast distribution tree. The 373 IPv4 multicast source address MUST be mapped to an IPv6 multicast 374 source address. An IPv6 unicast prefix (uPrefix64) is provisioned to 375 the mAFTR and the mB4. The mAFTR and the mB4 use the uPrefix64 to 376 form an IPv6 multicast source address from an IPv4 multicast source 377 address. The uPrefix-formed IPv6 multicast source address will 378 represent the original IPv4 multicast source in the IPv6 multicast 379 network. The uPrefix64 MUST be derived from the IPv6 unicast address 380 space. 382 The address translation MUST follow the algorithm defined in 383 Section 5.2. 385 The mPrefix64 and uPrefix64 can be configured in the mB4 using a 386 variety of methods, including an out-of-band mechanism, manual 387 configuration, or a dedicated provisioning protocol (e.g., using 388 DHCPv6 [I-D.ietf-softwire-multicast-prefix-option]). 390 5.2. Address Translation Algorithm 392 IPv4-Embedded IPv6 multicast addresses are composed according to the 393 following algorithm: 395 o Concatenate the mPrefix64 96 bits and the 32 bits of the IPv4 396 address to obtain a 128-bit address. 398 The IPv4 multicast addresses are extracted from the IPv4-Embedded 399 IPv6 Multicast Addresses according to the following algorithm: 401 o If the multicast address has a pre-configured mPrefix64, extract 402 the last 32 bits of the IPv6 multicast address. 404 An IPv4 source is represented in the IPv6 realm with its 405 IPv4-converted IPv6 address [RFC6052]. 407 5.3. Textual Representation 409 The embedded IPv4 address in an IPv6 multicast address is included in 410 the last 32 bits; therefore, dotted decimal notation can be used. 412 5.4. Examples 413 Group address mapping example: 415 +---------------------+--------------+----------------------------+ 416 | mPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 417 +---------------------+--------------+----------------------------+ 418 | ff0x::db8:0:0/96 | 233.252.0.1 | ff0x::db8::233.252.0.1 | 419 +---------------------+--------------+----------------------------+ 421 Source address mapping example when a /96 is used: 423 +---------------------+--------------+----------------------------+ 424 | uPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 425 +---------------------+--------------+----------------------------+ 426 | 2001:db8::/96 | 192.0.2.33 | 2001:db8::192.0.2.33 | 427 +---------------------+--------------+----------------------------+ 429 IPv4 and IPv6 addresses used in this example are derived from the 430 IPv4 and IPv6 blocks reserved for documentation, as per [RFC6676]. 431 The unicast IPv4 address of the above example is derived from the 432 documentation address block defined in [RFC6890]. 434 6. Multicast B4 (mB4) 436 6.1. IGMP-MLD Interworking Function 438 The IGMP-MLD Interworking Function combines the IGMP/MLD Proxying 439 function and the address synthesizing operations. The IGMP/MLD 440 Proxying function is specified in [RFC4605]. The address translation 441 is stateless and MUST follow the address mapping specified in 442 Section 5. 444 The mB4 performs the host portion of the MLD protocol on the upstream 445 interface. The composition of IPv6 membership in this context is 446 constructed through address synthesizing operations and MUST 447 synchronize with the membership database maintained in the IGMP 448 domain. MLD messages are forwarded natively towards the MLD Querier 449 located upstream in the IPv6 network (i.e., the first hop IPv6 450 router). The mB4 also performs the router portion of the IGMP 451 protocol on the downstream interface(s). Refer to [RFC4605] for more 452 details. 454 +----------+ IGMP +-------+ MLD +---------+ 455 | IPv4 |---------| mB4 |---------| MLD | 456 | Receiver | | | | Querier | 457 +----------+ +-------+ +---------+ 459 Figure 2: IGMP-MLD Interworking 461 If SSM is deployed, the mB4 MUST construct the IPv6 source address 462 (or retrieve the IPv4 source address) using the uPrefix64. The mB4 463 may create a membership database which associates the IPv4-IPv6 464 multicast groups with the interfaces (e.g., WLAN and Wired Ethernet) 465 facing IPv4 multicast receivers. 467 6.2. Multicast Data Forwarding 469 When the mB4 receives an IPv6 multicast packet, it MUST check the 470 group address and the source address. If the IPv6 multicast group 471 prefix is mPrefix64 and the IPv6 source prefix is uPrefix64, the mB4 472 MUST decapsulate the IPv6 header; the decapsulated IPv4 multicast 473 packet will be forwarded through each relevant interface following 474 standard IPv4 multicast forwarding procedure. Otherwise, the mB4 475 MUST silently drop the packet. 477 As an illustration, if a packet is received from source 478 2001:db8::192.0.2.33 and needs to be forwarded to group 479 ff3x:1000::233.252.0.1, the mB4 decapsulates it into an IPv4 480 multicast packet using 192.0.2.33 as the IPv4 source address and 481 using 233.252.0.1 as the IPv4 destination multicast group. 483 6.3. Fragmentation 485 Encapsulating IPv4 multicast packets into IPv6 multicast packets that 486 will be forwarded by the mAFTR towards the mB4 along the IPv6 487 multicast distribution tree reduces the effective MTU size by the 488 size of an IPv6 header. In this specification, the data flow is 489 unidirectional from the mAFTR to the mB4. The mAFTR MUST fragment 490 the oversized IPv6 packet after the encapsulation into two IPv6 491 packets. The mB4 MUST reassemble the IPv6 packets, decapsulate the 492 IPv6 packet, and forward the IPv4 packet to the hosts that have 493 subscribed to the corresponding multicast group. Further 494 considerations about fragmentation issues are documented in 495 [RFC6333]. 497 6.4. Host Built-in mB4 Function 499 If the mB4 function is implemented in the host which is directly 500 connected to an IPv6-only network, the host MUST implement 501 Section 6.1, Section 6.2, and Section 6.3. The host MAY optimize the 502 implementation to provide an Application Programming Interface (API) 503 or kernel module to skip the IGMP-MLD Interworking Function. 504 Optimization considerations are out of scope of this specification. 506 6.5. Preserve the Scope 508 When several mPrefix64s are available, if each enclosed IPv4-embedded 509 IPv6 multicast prefix has a distinct scope, the mB4 MUST select the 510 appropriate IPv4-embedded IPv6 multicast prefix whose scope matches 511 the IPv4 multicast address used to synthesize an IPv4-embedded IPv6 512 multicast address (Section 8 of [RFC2365]). 514 The mB4 MAY be configured to not preserve the scope when enforcing 515 the address translation algorithm. 517 Consider that an mB4 is configured with two mPrefix64s 518 ff0e::db8:0:0/96 (Global scope) and ff08::db8:0:0/96 (Organization 519 scope). If the mB4 receives an IGMP report from an IPv4 receiver to 520 subscribe to 233.252.0.1, it checks which mPrefix64 to use in order 521 to preserve the scope of the requested IPv4 multicast group. In this 522 example, given that 233.252.0.1 is intended for global use, the mB4 523 creates the IPv6 multicast group (G6) address using ff0e::db8:0:0/96 524 and the original IPv4 multicast group address (233.252.0.1): 525 ff0e::db8::233.252.0.1. 527 7. Multicast AFTR (mAFTR) 529 7.1. Routing Considerations 531 The mAFTR is responsible for interconnecting the IPv4 multicast 532 distribution tree with the corresponding IPv6 multicast distribution 533 tree. The mAFTR MUST use the uPrefix64 to build the IPv6 source 534 addresses of the multicast group address derived from mPrefix64. In 535 other words, the mAFTR MUST be the multicast source whose address is 536 derived from uPrefix64. 538 The mAFTR MUST advertise the route towards uPrefix64 with the IPv6 539 IGP. This is needed by the IPv6 multicast routers so that they 540 acquire the routing information to discover the source. 542 7.2. Processing PIM Messages 544 The mAFTR MUST interwork PIM Join/Prune messages for (*, G6) and (S6, 545 G6) on their corresponding (*, G4) and (S4, G4). The following text 546 specifies the expected behavior of the mAFTR for PIM Join messages. 548 +---------+ 549 ---------| mAFTR |--------- 550 PIMv6 |uPrefix64| PIMv4 551 |mPreifx64| 552 +---------+ 554 Figure 3: PIMv6-PIMv4 Interworking Function 556 The mAFTR contains two separate Tree Information Bases (TIBs): the 557 IPv4 Tree Information Base (TIB4) and the IPv6 Tree Information Base 558 (TIB6), which are bridged by one IPv4-in-IPv6 virtual interface. It 559 should be noted that TIB implementations may vary (e.g., some may 560 rely upon a single integrated TIB without any virtual interface), but 561 they should follow this specification for the sake of global and 562 functional consistency. 564 When a mAFTR receives a PIMv6 Join message (*,G6) with an IPv6 565 multicast group address (G6) that is derived from the mPrefix64, it 566 MUST check its IPv6 Tree Information Base (TIB6). If there is an 567 entry for this G6 address, it MUST check whether the interface 568 through which the PIMv6 Join message has been received is in the 569 outgoing interface (oif) list. If not, the mAFTR MUST add the 570 interface to the oif list. If there is no entry in the TIB6, the 571 mAFTR MUST create a new entry (*,G6) for the multicast group. 572 Whether or not the IPv4-in-IPv6 virtual interface is set as the 573 incoming interface of the newly created entry is up to the 574 implementation but it should comply with the mAFTR's multicast data 575 forwarding behavior, see Section 7.4. 577 The mAFTR MUST extract the IPv4 multicast group address (G4) from the 578 IPv4-embedded IPv6 multicast address (G6) contained in the PIMv6 Join 579 message. The mAFTR MUST check its IPv4 Tree Information Base (TIB4). 580 If there is an entry for G4, it MUST check whether the IPv4-in-IPv6 581 virtual interface is in the outgoing interface list. If not, the 582 mAFTR MUST add the interface to the oif list. If there is no entry 583 for G4, the mAFTR MUST create a new (*,G4) entry in its TIB4 and 584 initiate the procedure for building the shared tree in the IPv4 585 multicast network without any additional requirement. 587 If the mAFTR receives a source-specific Join message, the (S6, G6) is 588 processed rather than (*,G6). The procedures of processing (S6,G6) 589 and (*,G6) are almost the same. Differences have been detailed in 590 [RFC7761]. 592 7.3. Switching from Shared Tree to Shortest Path Tree 594 When the mAFTR receives the first IPv4 multicast packet, it may 595 extract the multicast source address (S4) from the packet and send an 596 Explicit PIMv4 (S4,G4) Join message directly to S4. The mAFTR 597 switches from the shared Rendezvous Point Tree (RPT) to the Shortest 598 Path Tree (SPT) for G4. 600 For IPv6 multicast routers to switch to the SPT, there is no new 601 requirement. IPv6 multicast routers may send an Explicit PIMv6 Join 602 to the mAFTR once the first (S6,G6) multicast packet arrives from 603 upstream multicast routers. 605 7.4. Multicast Data Forwarding 607 When the mAFTR receives an IPv4 multicast packet, it checks its TIB4 608 to find a matching entry and then forwards the packet to the 609 interface(s) listed in the outgoing interface list. If the IPv4-in- 610 IPv6 virtual interface also belongs to this list, the packet is 611 encapsulated with the mPrefix64-derived and uPrefix64-derived 612 IPv4-embedded IPv6 addresses to form an IPv6 multicast packet. Then 613 another lookup is made by the mAFTR to find a matching entry in the 614 TIB6. Whether the RPF check for the second lookup is performed or 615 not is up to the implementation and is out of the scope of this 616 document. The IPv6 multicast packet is then forwarded along the IPv6 617 multicast distribution tree, based upon the outgoing interface list 618 of the matching entry in the TIB6. 620 As an illustration, if a packet is received from source 192.0.2.33 621 and needs to be forwarded to group 233.252.0.1, the mAFTR 622 encapsulates it into an IPv6 multicast packet using 623 ff3x:1000::233.252.0.1 as the IPv6 destination multicast group and 624 using 2001:db8::192.0.2.33 as the IPv6 source address. 626 7.5. TTL/Scope 628 The Scope field of IPv4-in-IPv6 multicast addresses should be valued 629 accordingly (e.g, to "E", Global scope;) in the deployment 630 environment. This specification does not discuss the scope value 631 that should be used. 633 Nevertheless, when several mPrefix64s are available, if each enclosed 634 IPv4-embedded IPv6 multicast prefix has a distinct scope, the mAFTR 635 MUST select the appropriate IPv4-embedded IPv6 multicast prefix whose 636 scope matches the IPv4 multicast address used to synthesize an 637 IPv4-embedded IPv6 multicast address. 639 An mAFTR MAY be configured to not preserve the scope when enforcing 640 the address translation algorithm. 642 8. Deployment Considerations 644 8.1. Other Operational Modes 646 8.1.1. The MLD Querier is Co-Located with the mAFTR 648 The mAFTR can embed the MLD Querier function (as well as the PIMv6 649 DR) for optimization purposes. When the mB4 sends a MLD Report 650 message to this mAFTR, the mAFTR should process the MLD Report 651 message that contains the IPv4-embedded IPv6 multicast group address 652 and then send the corresponding PIMv4 Join message. (Figure 4) 654 +---------+ 655 ---------| mAFTR |--------- 656 MLD |uPrefix64| PIMv4 657 |mPreifx64| 658 +---------+ 660 Figure 4: MLD-PIMv4 Interworking Function 662 Discussions about the location of the mAFTR capability and related 663 ASM or SSM multicast design considerations are out of the scope of 664 this document. 666 8.1.2. The DR is Co-Located with the mAFTR 668 If the mAFTR is co-located with the DR connected to the original IPv4 669 source, it may simply use the uPrefix64 and mPrefix64 prefixes to 670 build the IPv4-embedded IPv6 multicast packets, and the sending of 671 PIMv4 Join messages becomes unnecessary. 673 8.2. Load Balancing 675 For robustness and load distribution purposes, several nodes in the 676 network can embed the mAFTR function. In such case, the same IPv6 677 prefixes (i.e., mPrefix64 and uPrefix64) and algorithm to build 678 IPv4-embedded IPv6 addresses must be configured on those nodes. 680 8.3. mAFTR Policy Configuration 682 The mAFTR may be configured with a list of IPv4 multicast groups and 683 sources. Only multicast flows bound to the configured addresses 684 should be handled by the mAFTR. Otherwise, packets are silently 685 dropped. 687 8.4. Static vs. Dynamic PIM Triggering 689 To optimize the usage of network resources in current deployments, 690 all multicast streams are conveyed in the core network while only the 691 most popular ones are forwarded in the aggregation/access networks 692 (static mode). Less popular streams are forwarded in the access 693 network upon request (dynamic mode). Depending on the location of 694 the mAFTR in the network, two modes can be envisaged: static and 695 dynamic. 697 Static Mode: the mAFTR is configured to instantiate permanent (S6, 698 G6) and (*, G6) entries in its TIB6 using a pre-configured (S4, 699 G4) list. 701 Dynamic Mode: the instantiation or withdrawal of (S6, G6) or (*, G6) 702 entries is triggered by the receipt of PIMv6 messages. 704 9. Security Considerations 706 Besides multicast scoping considerations (see Section 6.5 and 707 Section 7.5), this document does not introduce any new security 708 concern in addition to what is discussed in Section 5 of [RFC6052], 709 Section 10 of [RFC3810] and Section 6 of [RFC7761]. 711 An mB4 SHOULD be provided with appropriate configuration information 712 to preserve the scope of a multicast message when mapping an IPv4 713 multicast address into an IPv4-embedded IPv6 multicast address and 714 vice versa. 716 9.1. Firewall Configuration 718 The CPE that embeds the mB4 function SHOULD be configured to accept 719 incoming MLD messages and traffic forwarded to multicast groups 720 subscribed by receivers located in the customer premises. 722 10. Acknowledgements 724 The authors would like to thank Dan Wing for his guidance in the 725 early discussions which initiated this work. We also thank Peng Sun, 726 Jie Hu, Qiong Sun, Lizhong Jin, Alain Durand, Dean Cheng, Behcet 727 Sarikaya, Tina Tsou, Rajiv Asati, Xiaohong Deng, and Stig Venaas for 728 their valuable comments. 730 Many thanks to Ian Farrer for the review. 732 Thanks to Zhen Cao and Tim Chown for the INT directorate review. 734 11. IANA Considerations 736 This document includes no request to IANA. 738 12. References 740 12.1. Normative References 742 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 743 Requirement Levels", BCP 14, RFC 2119, 744 DOI 10.17487/RFC2119, March 1997, 745 . 747 [RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23, 748 RFC 2365, DOI 10.17487/RFC2365, July 1998, 749 . 751 [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 752 Thyagarajan, "Internet Group Management Protocol, Version 753 3", RFC 3376, DOI 10.17487/RFC3376, October 2002, 754 . 756 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 757 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 758 DOI 10.17487/RFC3810, June 2004, 759 . 761 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 762 "Internet Group Management Protocol (IGMP) / Multicast 763 Listener Discovery (MLD)-Based Multicast Forwarding 764 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 765 August 2006, . 767 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 768 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 769 . 771 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 772 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 773 DOI 10.17487/RFC6052, October 2010, 774 . 776 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 777 Stack Lite Broadband Deployments Following IPv4 778 Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011, 779 . 781 [RFC7608] Boucadair, M., Petrescu, A., and F. Baker, "IPv6 Prefix 782 Length Recommendation for Forwarding", BCP 198, RFC 7608, 783 DOI 10.17487/RFC7608, July 2015, 784 . 786 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 787 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 788 Multicast - Sparse Mode (PIM-SM): Protocol Specification 789 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 790 2016, . 792 12.2. Informative References 794 [I-D.ietf-softwire-multicast-prefix-option] 795 Boucadair, M., Qin, J., Tsou, T., and X. Deng, "DHCPv6 796 Option for IPv4-Embedded Multicast and Unicast IPv6 797 Prefixes", draft-ietf-softwire-multicast-prefix-option-11 798 (work in progress), June 2016. 800 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 801 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 802 . 804 [RFC6676] Venaas, S., Parekh, R., Van de Velde, G., Chown, T., and 805 M. Eubanks, "Multicast Addresses for Documentation", 806 RFC 6676, DOI 10.17487/RFC6676, August 2012, 807 . 809 [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, 810 "Special-Purpose IP Address Registries", BCP 153, 811 RFC 6890, DOI 10.17487/RFC6890, April 2013, 812 . 814 [RFC7596] Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I. 815 Farrer, "Lightweight 4over6: An Extension to the Dual- 816 Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596, 817 July 2015, . 819 [RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S., 820 Murakami, T., and T. Taylor, Ed., "Mapping of Address and 821 Port with Encapsulation (MAP-E)", RFC 7597, 822 DOI 10.17487/RFC7597, July 2015, 823 . 825 Appendix A. Use Case: IPTV 827 IPTV generally includes two categories of service offerings: 829 o Video on Demand (VoD) that unicast video content to receivers. 831 o Multicast live TV broadcast services. 833 Two types of provider are involved in the delivery of this service: 835 o Content Providers, who usually own the contents that is multicast 836 to receivers. Content providers may contractually define an 837 agreement with network providers to deliver contents to receivers. 839 o Network Providers, who provide network connectivity services 840 (e.g., network providers are responsible for carrying multicast 841 flows from head-ends to receivers). 843 Note that some contract agreements prevent a network provider from 844 altering the content as sent by the content provider for various 845 reasons. Depending on these contract agreements, multicast streams 846 should be delivered unaltered to the requesting users. 848 Many current IPTV contents are likely to remain IPv4-formatted and 849 out of control of the network providers. Additionally, there are 850 numerous legacy receivers (e.g., IPv4-only Set Top Boxes (STB)) that 851 can't be upgraded or be easily replaced to support IPv6. As a 852 consequence, IPv4 service continuity must be guaranteed during the 853 transition period, including the delivery of multicast services such 854 as Live TV Broadcasting to users. 856 Appendix B. Older Versions of Group Membership Management Protocols 858 Given the multiple versions of group membership management protocols, 859 mismatch issues may arise at the mB4 (refer to Section 6.1). 861 If IGMPv2 operates on the IPv4 receivers while MLDv2 operates on the 862 MLD Querier, or if IGMPv3 operates on the IPv4 receivers while MLDv1 863 operates on the MLD Querier, the version mismatch issue will be 864 encountered. To solve this problem, the mB4 should perform the 865 router portion of IGMP which is similar to the corresponding MLD 866 version (IGMPv2 as of MLDv1, or IGMPv3 as of MLDv2) operating in the 867 IPv6 domain. Then, the protocol interaction approach specified in 868 Section 7 of [RFC3376] can be applied to exchange signaling messages 869 with the IPv4 receivers on which the different version of IGMP is 870 operating. 872 Authors' Addresses 874 Mohamed Boucadair 875 Orange 876 Rennes 35000 877 France 879 Email: mohamed.boucadair@orange.com 881 Jacni Qin 882 Cisco 883 Shanghai 884 China 886 Email: jacni@jacni.com 888 Christian Jacquenet 889 Orange 890 Rennes 35000 891 France 893 Email: christian.jacquenet@orange.com 895 Yiu L. Lee 896 Comcast 897 U.S.A. 899 Email: yiu_lee@cable.comcast.com 900 URI: http://www.comcast.com 902 Qian Wang 903 China Telecom 904 China 906 Phone: +86 10 58502462 907 Email: 13301168516@189.cn