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Wang 10 China Telecom 11 June 8, 2016 13 Delivery of IPv4 Multicast Services to IPv4 Clients over an IPv6 14 Multicast Network 15 draft-ietf-softwire-dslite-multicast-12 17 Abstract 19 This document specifies a solution for the delivery of IPv4 multicast 20 services to IPv4 clients over an IPv6 multicast network. The 21 solution relies upon a stateless IPv4-in-IPv6 encapsulation scheme 22 and uses the IPv6 multicast distribution tree to deliver IPv4 23 multicast traffic. The solution is particularly useful for the 24 delivery of multicast service offerings to DS-Lite serviced 25 customers. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on December 10, 2016. 44 Copyright Notice 46 Copyright (c) 2016 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 62 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 65 4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5 66 4.1. IPv4-Embedded IPv6 Prefixes . . . . . . . . . . . . . . . 6 67 4.2. Multicast Distribution Tree Computation . . . . . . . . . 7 68 4.3. Multicast Data Forwarding . . . . . . . . . . . . . . . . 8 69 5. Address Mapping . . . . . . . . . . . . . . . . . . . . . . . 8 70 5.1. Prefix Assignment . . . . . . . . . . . . . . . . . . . . 8 71 5.2. Address Translation Algorithm . . . . . . . . . . . . . . 9 72 5.3. Textual Representation . . . . . . . . . . . . . . . . . 9 73 5.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 9 74 6. Multicast B4 (mB4) . . . . . . . . . . . . . . . . . . . . . 10 75 6.1. IGMP-MLD Interworking Function . . . . . . . . . . . . . 10 76 6.2. Multicast Data Forwarding . . . . . . . . . . . . . . . . 10 77 6.3. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 11 78 6.4. Host Built-in mB4 Function . . . . . . . . . . . . . . . 11 79 6.5. Preserve the Scope . . . . . . . . . . . . . . . . . . . 11 80 7. Multicast AFTR (mAFTR) . . . . . . . . . . . . . . . . . . . 11 81 7.1. Routing Considerations . . . . . . . . . . . . . . . . . 11 82 7.2. Processing PIM Messages . . . . . . . . . . . . . . . . . 12 83 7.3. Switching from Shared Tree to Shortest Path Tree . . . . 13 84 7.4. Multicast Data Forwarding . . . . . . . . . . . . . . . . 13 85 7.5. TTL/Scope . . . . . . . . . . . . . . . . . . . . . . . . 13 86 8. Security Considerations . . . . . . . . . . . . . . . . . . . 14 87 8.1. Firewall Configuration . . . . . . . . . . . . . . . . . 14 88 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 89 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 90 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 91 11.1. Normative References . . . . . . . . . . . . . . . . . . 14 92 11.2. Informative References . . . . . . . . . . . . . . . . . 15 93 Appendix A. Use Case: IPTV . . . . . . . . . . . . . . . . . . . 16 94 Appendix B. Deployment Considerations . . . . . . . . . . . . . 17 95 B.1. Other Operational Modes . . . . . . . . . . . . . . . . . 17 96 B.1.1. The MLD Querier is Co-Located with the mAFTR . . . . 17 97 B.1.2. The DR is Co-Located with the mAFTR . . . . . . . . . 17 98 B.2. Older Versions of Group Membership Management Protocols . 17 99 B.3. Load Balancing . . . . . . . . . . . . . . . . . . . . . 18 100 B.4. RP for IPv4-Embedded IPv6 Multicast Groups . . . . . . . 18 101 B.5. mAFTR Policy Configuration . . . . . . . . . . . . . . . 18 102 B.6. Static vs. Dynamic PIM Triggering . . . . . . . . . . . . 18 103 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 105 1. Introduction 107 DS-Lite [RFC6333] is a technique that rationalizes the usage of the 108 remaining global IPv4 addresses during the transition period by 109 sharing a single IPv4 address with multiple users. A typical DS-Lite 110 scenario is the delivery of an IPv4 service to an IPv4 user over an 111 IPv6 network (denoted as a 4-6-4 scenario). [RFC6333] covers unicast 112 services exclusively. 114 This document specifies a generic solution for the delivery of IPv4 115 multicast services to IPv4 clients over an IPv6 multicast network. 116 The solution was developed with DS-Lite in mind (see more discussion 117 below). The solution is however not limited to DS-Lite; it can be 118 applied in other deployment contexts such as [RFC7596][RFC7597]. 120 If customers have to access IPv4 multicast-based services through a 121 DS-Lite environment, Address Family Transition Router (AFTR) devices 122 will have to process all the Internet Group Management Protocol 123 (IGMP) Report messages [RFC2236] [RFC3376] that have been forwarded 124 by the Customer Premises Equipment (CPE) into the IPv4-in-IPv6 125 tunnels. From that standpoint, AFTR devices are likely to behave as 126 a replication point for downstream multicast traffic, and the 127 multicast packets will be replicated for each tunnel endpoint that 128 IPv4 receivers are connected to. 130 This kind of DS-Lite environment raises two major issues: 132 1. The IPv6 network loses the benefits of the multicast traffic 133 forwarding efficiency because it is unable to deterministically 134 replicate the data as close to the receivers as possible. As a 135 consequence, the downstream bandwidth in the IPv6 network will be 136 vastly consumed by sending multicast data over a unicast 137 infrastructure. 139 2. The AFTR is responsible for replicating multicast traffic and 140 forwarding it into each tunnel endpoint connecting IPv4 receivers 141 that have explicitly asked for the corresponding contents. This 142 process may significantly consume the AFTR's resources and 143 overload the AFTR. 145 This document specifies an extension to the DS-Lite model to deliver 146 IPv4 multicast services to IPv4 clients over an IPv6 multicast- 147 enabled network. 149 1.1. Requirements Language 151 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 152 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 153 document are to be interpreted as described in RFC 2119 [RFC2119]. 155 2. Terminology 157 This document makes use of the following terms: 159 IPv4-embedded IPv6 address: an IPv6 address which embeds a 32-bit- 160 encoded IPv4 address. An IPv4-embedded IPv6 address can be 161 unicast or multicast. 163 mPrefix64: a dedicated multicast IPv6 prefix for constructing 164 IPv4-embedded IPv6 multicast addresses. mPrefix64 can be of two 165 types: ASM_mPrefix64 used in Any Source Multicast (ASM) mode or 166 SSM_mPrefix64 used in Source Specific Multicast (SSM) mode 167 [RFC4607]. 169 uPrefix64: a dedicated IPv6 unicast prefix for constructing 170 IPv4-embedded IPv6 unicast addresses [RFC6052]. 172 Multicast AFTR (mAFTR): a functional entity which supports an 173 IPv4-IPv6 multicast interworking function (refer to Figure 3). It 174 receives and encapsulates the IPv4 multicast packets into IPv4-in- 175 IPv6 packets and behaves as the corresponding IPv6 multicast 176 source for the encapsulated IPv4-in-IPv6 packets. 178 Multicast B4 (mB4): a functional entity which supports an IGMP-MLD 179 interworking function (refer to Section 6.1) that relays 180 information conveyed in IGMP messages by forwarding the 181 corresponding Multicast Listener Discovery (MLD) messages towards 182 the MLD Querier in the IPv6 network. In addition, the mB4 183 decapsulates IPv4-in-IPv6 multicast packets. 185 PIMv4: refers to Protocol Independent Multicast (PIM) when deployed 186 in an IPv4 infrastructure (i.e., IPv4 transport capabilities are 187 used to exchange PIM messages). 189 PIMv6: refers to PIM when deployed in an IPv6 infrastructure (i.e., 190 IPv6 transport capabilities are used to exchange PIM messages). 192 3. Scope 194 This document focuses only on the subscription to an IPv4 multicast 195 group and the delivery of IPv4-formatted content to IPv4 receivers 196 over an IPv6-only network. In particular, only the following case is 197 covered: 199 An IPv4 receiver accesses IPv4 multicast contents over an IPv6- 200 only multicast-enabled network. 202 This document does not cover the source/receiver heuristics, where an 203 IPv4 receiver can also behave as an IPv4 multicast source. This 204 document assumes that hosts behind the mB4 are IPv4 multicast 205 receivers only. 207 4. Solution Overview 209 In the DS-Lite specification [RFC6333], an IPv4-in-IPv6 tunnel is 210 used to carry bidirectional IPv4 unicast traffic between a B4 and an 211 AFTR. The solution specified in this document provides an IPv4-in- 212 IPv6 encapsulation scheme to deliver unidirectional IPv4 multicast 213 traffic from an mAFTR to an mB4. 215 An overview of the solution is provided in this section which is 216 intended as an introduction to how it works, but is not normative. 217 For the normative specifications of the two new functional elements: 218 mB4 and mAFTR (Figure 1), refer to Section 6 and Section 7. 220 ------------ 221 / \ 222 | IPv4 network | 223 \ / 224 ------------ 225 IPv4 multicast : | ^ PIMv4 Join 226 v | : 227 +-------------+ 228 | mAFTR | 229 +-------------+ 230 IPv6 multicast |:| | ^ PIMv6 Join (PIMv6 231 (IPv4 embedded) |:| | : routers in between) 232 ------------ 233 / \ 234 | IPv6 network | 235 \ / 236 ------------ 237 |:| | : MLD Report 238 |v| | : 239 +-----------+ 240 | mB4 | 241 +-----------+ 242 IPv4 multicast : | ^ IGMP Report 243 v | : 244 +-----------+ 245 | IPv4 | 246 | receiver | 247 +-----------+ 249 Figure 1: Functional Architecture 251 4.1. IPv4-Embedded IPv6 Prefixes 253 In order to map the addresses of IPv4 multicast traffic with IPv6 254 multicast addresses, an IPv6 multicast prefix (mPrefix64) and an IPv6 255 unicast prefix (uPrefix64) are provided to the mAFTR and the mB4 256 elements, both of which contribute to the computation and the 257 maintenance of the IPv6 multicast distribution tree that extends the 258 IPv4 multicast distribution tree into the IPv6 multicast network. 260 The mAFTR and the mB4 use mPrefix64 to convert an IPv4 multicast 261 address (G4) into an IPv4-embedded IPv6 multicast address (G6). The 262 mAFTR and the mB4 use uPrefix64 to convert an IPv4 multicast source 263 address (S4) into an IPv4-embedded IPv6 address (S6). The mAFTR and 264 the mB4 must use the same mPrefix64 and uPrefix64, and also run the 265 same algorithm for building IPv4-embedded IPv6 addresses. Refer to 266 Section 5 for more details about the address mapping. 268 4.2. Multicast Distribution Tree Computation 270 When an IPv4 receiver connected to the device that embeds the mB4 271 capability wants to subscribe to an IPv4 multicast group, it sends an 272 IGMP Report message to the mB4. The mB4 creates the IPv6 multicast 273 group (G6) address using mPrefix64 and the original IPv4 multicast 274 group address. If the receiver sends a source-specific IGMPv3 Report 275 message, the mB4 will create the IPv6 source address (S6) using 276 uPrefix64 and the original IPv4 source address. 278 The mB4 uses the G6 (and both S6 and G6 in SSM) to create the 279 corresponding MLD Report message. The mB4 sends the Report message 280 to the MLD Querier in the IPv6 network. The MLD Querier (which 281 usually acts as the PIMv6 Designated Router too) receives the MLD 282 Report message and sends the PIMv6 Join to join the IPv6 multicast 283 distribution tree. The MLD Querier can send either PIMv6 Join (*,G6) 284 in ASM or PIMv6 Join (S6,G6) in SSM to the mAFTR. 286 The mAFTR acts as the DR to which the uPrefix64-derived S6 is 287 connected. The mAFTR will receive the source-specific PIMv6 Join 288 message (S6,G6) from the IPv6 multicast network. If the mAFTR is the 289 Rendezvous Point (RP) of G6, it will receive the any-source PIMv6 290 Join message (*,G6) from the IPv6 multicast network. If the mAFTR is 291 not the RP of G6, it will send the PIM Register message to the RP of 292 G6 located in the IPv6 multicast network. 294 When the mAFTR receives the PIMv6 Join message (*,G6), it will 295 extract the IPv4 multicast group address (G4). If the mAFTR is the 296 RP of G4 in the IPv4 multicast network, it will create a (*,G4) entry 297 (if such entry does not already exist) in its own IPv4 multicast 298 routing table. If the mAFTR is not the RP of G4, it will send the 299 corresponding PIMv4 Join message (*,G4) towards the RP of G4 in the 300 IPv4 multicast network. 302 When the mAFTR receives the PIMv6 Join message (S6,G6), it will 303 extract the IPv4 multicast group address (G4) and IPv4 source address 304 (S4) and send the corresponding (S4,G4) PIMv4 Join message directly 305 to the IPv4 source. 307 A branch of the multicast distribution tree is thus constructed, 308 comprising both an IPv4 part (from the mAFTR upstream) and an IPv6 309 part (from mAFTR downstream to the mB4). 311 The mAFTR advertises the route of uPrefix64 with an IPv6 Interior 312 Gateway Protocol (IGP), so as to represent the IPv4-embedded IPv6 313 source in the IPv6 multicast network, and to run the Reverse Path 314 Forwarding (RPF) check procedure on incoming multicast traffic. 316 4.3. Multicast Data Forwarding 318 When the mAFTR receives an IPv4 multicast packet, it will encapsulate 319 the packet into an IPv6 multicast packet using the IPv4-embedded IPv6 320 multicast address as the destination address and an IPv4-embedded 321 IPv6 unicast address as the source address. The encapsulated IPv6 322 multicast packet will be forwarded down the IPv6 multicast 323 distribution tree and the mB4 will eventually receive the packet. 325 The IPv6 multicast network treats the IPv4-in-IPv6 encapsulated 326 multicast packets as native IPv6 multicast packets. The IPv6 327 multicast routers use the outer IPv6 header to make their forwarding 328 decisions. 330 When the mB4 receives the IPv6 multicast packet (to G6) derived by 331 mPrefix64, it decapsulates it and forwards the original IPv4 332 multicast packet to the receivers subscribing to G4. 334 Note: At this point, only IPv4-in-IPv6 encapsulation is defined; 335 however, other types of encapsulation could be defined in the future. 337 5. Address Mapping 339 5.1. Prefix Assignment 341 A dedicated IPv6 multicast prefix (mPrefix64) is provisioned to the 342 mAFTR and the mB4. The mAFTR and the mB4 use the mPrefix64 to form 343 an IPv6 multicast group address from an IPv4 multicast group address. 344 The mPrefix64 can be of two types: ASM_mPrefix64 (a mPrefix64 used in 345 ASM mode) or SSM_mPrefix64 (a mPrefix64 used in SSM mode). The 346 mPrefix64 MUST be derived from the corresponding IPv6 multicast 347 address space (e.g., the SSM_mPrefix64 must be in the range of 348 multicast address space specified in [RFC4607]). 350 The IPv6 part of the multicast distribution tree can be seen as an 351 extension of the IPv4 part of the multicast distribution tree. The 352 IPv4 multicast source address MUST be mapped to an IPv6 multicast 353 source address. An IPv6 unicast prefix (uPrefix64) is provisioned to 354 the mAFTR and the mB4. The mAFTR and the mB4 use the uPrefix64 to 355 form an IPv6 multicast source address from an IPv4 multicast source 356 address. The uPrefix-formed IPv6 multicast source address will 357 represent the original IPv4 multicast source in the IPv6 multicast 358 network. The uPrefix64 MUST be derived from the IPv6 unicast address 359 space. 361 The address translation MUST follow the algorithm defined in 362 Section 5.2. 364 The mPrefix64 and uPrefix64 can be configured in the mB4 using a 365 variety of methods, including an out-of-band mechanism, manual 366 configuration, or a dedicated provisioning protocol (e.g., using 367 DHCPv6 [I-D.ietf-softwire-multicast-prefix-option]). 369 5.2. Address Translation Algorithm 371 IPv4-Embedded IPv6 multicast addresses are composed according to the 372 following algorithm: 374 o Concatenate the mPrefix64 and the 32 bits of the IPv4 address to 375 obtain a 128-bit address. 377 The IPv4 multicast addresses are extracted from the IPv4-Embedded 378 IPv6 Multicast Addresses according to the following algorithm: 380 o If the multicast address has a pre-configured mPrefix64, extract 381 the last 32 bits of the IPv6 multicast address. 383 An IPv4 source is represented in the IPv6 realm with its 384 IPv4-converted IPv6 address [RFC6052]. 386 5.3. Textual Representation 388 The embedded IPv4 address in an IPv6 multicast address is included in 389 the last 32 bits; therefore, dotted decimal notation can be used. 391 5.4. Examples 393 Group address mapping example: 395 +---------------------+--------------+----------------------------+ 396 | mPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 397 +---------------------+--------------+----------------------------+ 398 | ff0x::db8:0:0/96 | 233.252.0.1 | ff0x::db8::233.252.0.1 | 399 +---------------------+--------------+----------------------------+ 401 Source address mapping example when a /96 is used: 403 +---------------------+--------------+----------------------------+ 404 | uPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 405 +---------------------+--------------+----------------------------+ 406 | 2001:db8::/96 | 192.0.2.33 | 2001:db8::192.0.2.33 | 407 +---------------------+--------------+----------------------------+ 409 IPv4 and IPv6 addresses used in this example are derived from the 410 IPv4 and IPv6 blocks reserved for documentation, as per [RFC6676]. 412 The unicast IPv4 address of the above example is derived from the 413 documentation address block defined in [RFC6890]. 415 6. Multicast B4 (mB4) 417 6.1. IGMP-MLD Interworking Function 419 The IGMP-MLD Interworking Function combines the IGMP/MLD Proxying 420 function and the address synthesizing operations. The IGMP/MLD 421 Proxying function is specified in [RFC4605]. The address translation 422 is stateless and MUST follow the address mapping specified in 423 Section 5. 425 The mB4 performs the host portion of the MLD protocol on the upstream 426 interface. The composition of IPv6 membership in this context is 427 constructed through address synthesizing operations and MUST 428 synchronize with the membership database maintained in the IGMP 429 domain. MLD messages are forwarded natively towards the MLD Querier 430 located upstream in the IPv6 network. The mB4 also performs the 431 router portion of the IGMP protocol on the downstream interface(s). 432 Refer to [RFC4605] for more details. 434 +----------+ IGMP +-------+ MLD +---------+ 435 | IPv4 |---------| mB4 |---------| MLD | 436 | Receiver | | | | Querier | 437 +----------+ +-------+ +---------+ 439 Figure 2: IGMP-MLD Interworking 441 If SSM is deployed, the mB4 MUST construct the IPv6 source address 442 (or retrieve the IPv4 source address) using the uPrefix64. The mB4 443 may create a membership database which associates the IPv4-IPv6 444 multicast groups with the interfaces (e.g., WLAN and Wired Ethernet) 445 facing IPv4 multicast receivers. 447 6.2. Multicast Data Forwarding 449 When the mB4 receives an IPv6 multicast packet, it MUST check the 450 group address and the source address. If the IPv6 multicast group 451 prefix is mPrefix64 and the IPv6 source prefix is uPrefix64, the mB4 452 MUST decapsulate the IPv6 header and forward the IPv4 multicast 453 packet through each relevant interface. Otherwise, the mB4 MUST 454 silently drop the packet. 456 As an illustration, if a packet is received from source 457 2001:db8::192.0.2.33 and needs to be forwarded to group 458 ff3x:1000::233.252.0.1, the mB4 decapsulates it into an IPv4 459 multicast packet using 192.0.2.33 as the IPv4 multicast source 460 address and using 233.252.0.1 as the IPv4 destination address. 462 6.3. Fragmentation 464 Encapsulating IPv4 multicast packets into IPv6 multicast packets that 465 will be forwarded by the mAFTR to the mB4 along the IPv6 multicast 466 distribution tree reduces the effective MTU size by the size of an 467 IPv6 header. In this specification, the data flow is unidirectional 468 from the mAFTR to the mB4. The mAFTR MUST fragment the oversized 469 IPv6 packet after the encapsulation into two IPv6 packets. The mB4 470 MUST reassemble the IPv6 packets, decapsulate the IPv6 packet, and 471 forward the IPv4 packet to the hosts that have subscribed to the 472 corresponding multicast group. Further considerations about 473 fragmentation issues are documented in [RFC6333]. 475 6.4. Host Built-in mB4 Function 477 If the mB4 function is implemented in the host which is directly 478 connected to an IPv6-only network, the host MUST implement 479 Section 6.1, Section 6.2, and Section 6.3. The host MAY optimize the 480 implementation to provide an Application Programming Interface (API) 481 or kernel module to skip the IGMP-MLD Interworking Function. 482 Optimization considerations are out of scope of this specification. 484 6.5. Preserve the Scope 486 When several mPrefix64s are available, if each enclosed IPv4-embedded 487 IPv6 multicast prefix has a distinct scope, the mB4 MUST select the 488 appropriate IPv4-embedded IPv6 multicast prefix whose scope matches 489 the IPv4 multicast address used to synthesize an IPv4-embedded IPv6 490 multicast address. 492 The mB4 MAY be configured to not preserve the scope when enforcing 493 the address translation algorithm. 495 7. Multicast AFTR (mAFTR) 497 7.1. Routing Considerations 499 The mAFTR is responsible for interconnecting the IPv4 multicast 500 distribution tree with the corresponding IPv6 multicast distribution 501 tree. The mAFTR MUST use the uPrefix64 to build the IPv6 source 502 addresses of the multicast group address derived from mPrefix64. In 503 other words, the mAFTR MUST be the multicast source whose address is 504 derived from uPrefix64. 506 The mAFTR MUST advertise the route towards uPrefix64 with the IPv6 507 IGP. This is needed by the IPv6 multicast routers so that they 508 acquire the routing information to discover the source. 510 7.2. Processing PIM Messages 512 The mAFTR MUST interwork PIM Join/Prune messages for (*, G6) and (S6, 513 G6) on their corresponding (*, G4) and (S4, G4). The following text 514 specifies the expected behavior of the mAFTR for PIM Join messages. 516 +---------+ 517 ---------| mAFTR |--------- 518 PIMv6 |uPrefix64| PIMv4 519 |mPreifx64| 520 +---------+ 522 Figure 3: PIMv6-PIMv4 Interworking Function 524 The mAFTR contains two separate Tree Information Bases (TIBs): the 525 IPv4 Tree Information Base (TIB4) and the IPv6 Tree Information Base 526 (TIB6), which are bridged by one IPv4-in-IPv6 virtual interface. It 527 should be noted that TIB implementations may vary (e.g., some may 528 rely upon a single integrated TIB without any virtual interface), but 529 they should follow this specification for the sake of global and 530 functional consistency. 532 When a mAFTR receives a PIMv6 Join message (*,G6) with an IPv6 533 multicast group address (G6) that is derived from the mPrefix64, it 534 MUST check its IPv6 Tree Information Base (TIB6). If there is an 535 entry for this G6 address, it MUST check whether the interface 536 through which the PIMv6 Join message has been received is in the 537 outgoing interface (oif) list. If not, the mAFTR MUST add the 538 interface to the oif list. If there is no entry in the TIB6, the 539 mAFTR MUST create a new entry (*,G6) for the multicast group. 540 Whether or not the IPv4-in-IPv6 virtual interface is set as the 541 incoming interface of the newly created entry is up to the 542 implementation but it should comply with the mAFTR's multicast data 543 forwarding behavior, see Section 7.4. 545 The mAFTR MUST extract the IPv4 multicast group address (G4) from the 546 IPv4-embedded IPv6 multicast address (G6) contained in the PIMv6 Join 547 message. The mAFTR MUST check its IPv4 Tree Information Base (TIB4). 548 If there is an entry for G4, it MUST check whether the IPv4-in-IPv6 549 virtual interface is in the outgoing interface list. If not, the 550 mAFTR MUST add the interface to the oif list. If there is no entry 551 for G4, the mAFTR MUST create a new (*,G4) entry in its TIB4 and 552 initiate the procedure for building the shared tree in the IPv4 553 multicast network without any additional requirement. 555 If the mAFTR receives a source-specific Join message, the (S6, G6) is 556 processed rather than (*,G6). The procedures of processing (S6,G6) 557 and (*,G6) are almost the same. Differences have been detailed in 558 [RFC7761]. 560 7.3. Switching from Shared Tree to Shortest Path Tree 562 When the mAFTR receives the first IPv4 multicast packet, it may 563 extract the multicast source address (S4) from the packet and send an 564 Explicit PIMv4 (S4,G4) Join message directly to S4. The mAFTR 565 switches from the shared Rendezvous Point Tree (RPT) to the Shortest 566 Path Tree (SPT) for G4. 568 For IPv6 multicast routers to switch to the SPT, there is no new 569 requirement. IPv6 multicast routers may send an Explicit PIMv6 Join 570 to the mAFTR once the first (S6,G6) multicast packet arrives from 571 upstream multicast routers. 573 7.4. Multicast Data Forwarding 575 When the mAFTR receives an IPv4 multicast packet, it checks its TIB4 576 to find a matching entry and then forwards the packet to the 577 interface(s) listed in the outgoing interface list. If the IPv4-in- 578 IPv6 virtual interface also belongs to this list, the packet is 579 encapsulated with the mPrefix64-derived and uPrefix64-derived 580 IPv4-embedded IPv6 addresses to form an IPv6 multicast packet. Then 581 another lookup is made by the mAFTR to find a matching entry in the 582 TIB6. Whether the RPF check for the second lookup is performed or 583 not is up to the implementation and is out of the scope of this 584 document. The IPv6 multicast packet is then forwarded along the IPv6 585 multicast distribution tree, based upon the outgoing interface list 586 of the matching entry in the TIB6. 588 As an illustration, if a packet is received from source 192.0.2.33 589 and needs to be forwarded to group 233.252.0.1, the mAFTR 590 encapsulates it into an IPv6 multicast packet using 591 ff3x:1000::233.252.0.1 as the IPv6 destination address and using 592 2001:db8::192.0.2.33 as the IPv6 multicast source address. 594 7.5. TTL/Scope 596 The Scope field of IPv4-in-IPv6 multicast addresses should be valued 597 accordingly (e.g, to "E", Global scope;) in the deployment 598 environment. This specification does not discuss the scope value 599 that should be used. 601 Nevertheless, when several mPrefix64s are available, if each enclosed 602 IPv4-embedded IPv6 multicast prefix has a distinct scope, the mAFTR 603 MUST select the appropriate IPv4-embedded IPv6 multicast prefix whose 604 scope matches the IPv4 multicast address used to synthesize an 605 IPv4-embedded IPv6 multicast address. 607 An mAFTR MAY be configured to not preserve the scope when enforcing 608 the address translation algorithm. 610 8. Security Considerations 612 Besides multicast scoping considerations (see Section 6.5 and 613 Section 7.5), this document does not introduce any new security 614 concern in addition to what is discussed in Section 5 of [RFC6052], 615 Section 10 of [RFC3810] and Section 6 of [RFC7761]. 617 An mB4 SHOULD be provided with appropriate configuration information 618 to preserve the scope of a multicast message when mapping an IPv4 619 multicast address into an IPv4-embedded IPv6 multicast address and 620 vice versa. 622 8.1. Firewall Configuration 624 The CPE that embeds the mB4 function SHOULD be configured to accept 625 incoming MLD messages and traffic forwarded to multicast groups 626 subscribed by receivers located in the customer premises. 628 9. Acknowledgements 630 The authors would like to thank Dan Wing for his guidance in the 631 early discussions which initiated this work. We also thank Peng Sun, 632 Jie Hu, Qiong Sun, Lizhong Jin, Alain Durand, Dean Cheng, Behcet 633 Sarikaya, Tina Tsou, Rajiv Asati, Xiaohong Deng, and Stig Venaas for 634 their valuable comments. 636 Many thanks to Ian Farrer for the review. 638 10. IANA Considerations 640 This document includes no request to IANA. 642 11. References 644 11.1. Normative References 646 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 647 Requirement Levels", BCP 14, RFC 2119, 648 DOI 10.17487/RFC2119, March 1997, 649 . 651 [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 652 Thyagarajan, "Internet Group Management Protocol, Version 653 3", RFC 3376, DOI 10.17487/RFC3376, October 2002, 654 . 656 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 657 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 658 DOI 10.17487/RFC3810, June 2004, 659 . 661 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 662 "Internet Group Management Protocol (IGMP) / Multicast 663 Listener Discovery (MLD)-Based Multicast Forwarding 664 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 665 August 2006, . 667 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 668 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 669 . 671 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 672 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 673 DOI 10.17487/RFC6052, October 2010, 674 . 676 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 677 Stack Lite Broadband Deployments Following IPv4 678 Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011, 679 . 681 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 682 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 683 Multicast - Sparse Mode (PIM-SM): Protocol Specification 684 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 685 2016, . 687 11.2. Informative References 689 [I-D.ietf-softwire-multicast-prefix-option] 690 Boucadair, M., Qin, J., Tsou, T., and X. Deng, "DHCPv6 691 Option for IPv4-Embedded Multicast and Unicast IPv6 692 Prefixes", draft-ietf-softwire-multicast-prefix-option-10 693 (work in progress), February 2016. 695 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 696 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 697 . 699 [RFC6676] Venaas, S., Parekh, R., Van de Velde, G., Chown, T., and 700 M. Eubanks, "Multicast Addresses for Documentation", 701 RFC 6676, DOI 10.17487/RFC6676, August 2012, 702 . 704 [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, 705 "Special-Purpose IP Address Registries", BCP 153, 706 RFC 6890, DOI 10.17487/RFC6890, April 2013, 707 . 709 [RFC7596] Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I. 710 Farrer, "Lightweight 4over6: An Extension to the Dual- 711 Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596, 712 July 2015, . 714 [RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S., 715 Murakami, T., and T. Taylor, Ed., "Mapping of Address and 716 Port with Encapsulation (MAP-E)", RFC 7597, 717 DOI 10.17487/RFC7597, July 2015, 718 . 720 Appendix A. Use Case: IPTV 722 IPTV generally includes two categories of service offerings: 724 o Video on Demand (VoD) that unicast video content to receivers. 726 o Multicast live TV broadcast services. 728 Two players intervene in the delivery of this service: 730 o Content Providers, who usually own the contents that is multicast 731 to receivers. Content providers may contractually define an 732 agreement with network providers to deliver contents to receivers. 734 o Network Providers, who provide network connectivity services 735 (e.g., network providers are responsible for carrying multicast 736 flows from head-ends to receivers). 738 Note that some contract agreements prevent a network provider from 739 altering the content as sent by the content provider for various 740 reasons. Depending on these contract agreements, multicast streams 741 should be delivered unaltered to the requesting users. 743 Many current IPTV contents are likely to remain IPv4-formatted and 744 out of control of the network providers. Additionally, there are 745 numerous legacy receivers (e.g., IPv4-only Set Top Boxes (STB)) that 746 can't be upgraded or be easily replaced to support IPv6. As a 747 consequence, IPv4 service continuity must be guaranteed during the 748 transition period, including the delivery of multicast services such 749 as Live TV Broadcasting to users. 751 Appendix B. Deployment Considerations 753 B.1. Other Operational Modes 755 B.1.1. The MLD Querier is Co-Located with the mAFTR 757 The mAFTR can embed the MLD Querier function (as well as the PIMv6 758 DR) for optimization purposes. When the mB4 sends a MLD Report 759 message to this mAFTR, the mAFTR should process the MLD Report 760 message that contains the IPv4-embedded IPv6 multicast group address 761 and then send the corresponding PIMv4 Join message. (Figure 4) 763 +---------+ 764 ---------| mAFTR |--------- 765 MLD |uPrefix64| PIMv4 766 |mPreifx64| 767 +---------+ 769 Figure 4: MLD-PIMv4 Interworking Function 771 Discussions about the location of the mAFTR capability and related 772 ASM or SSM multicast design considerations are out of the scope of 773 this document. 775 B.1.2. The DR is Co-Located with the mAFTR 777 If the mAFTR is co-located with the DR connected to the original IPv4 778 source, it may simply use the uPrefix64 and mPrefix64 prefixes to 779 build the IPv4-embedded IPv6 multicast packets, and the sending of 780 PIMv4 Join messages becomes unnecessary. 782 B.2. Older Versions of Group Membership Management Protocols 784 Given the multiple versions of group membership management protocols, 785 mismatch issues may arise at the mB4 (refer to Section 6.1). 787 If IGMPv2 operates on the IPv4 receivers while MLDv2 operates on the 788 MLD Querier, or if IGMPv3 operates on the IPv4 receivers while MLDv1 789 operates on the MLD Querier, the issue mentioned above will be 790 encountered. To solve this problem, the mB4 should perform the 791 router portion of IGMP which is similar to the corresponding MLD 792 version (IGMPv2 as of MLDv1, or IGMPv3 as of MLDv2) operating in the 793 IPv6 domain. Then, the protocol interaction approach specified in 794 Section 7 of [RFC3376] can be applied to exchange signaling messages 795 with the IPv4 receivers on which the different version of IGMP is 796 operating. 798 B.3. Load Balancing 800 For robustness and load distribution purposes, several nodes in the 801 network can embed the mAFTR function. In such case, the same IPv6 802 prefixes (i.e., mPrefix64 and uPrefix64) and algorithm to build IPv4- 803 embedded IPv6 addresses must be configured on those nodes. 805 B.4. RP for IPv4-Embedded IPv6 Multicast Groups 807 For the sake of simplicity, it is recommended to configure the mAFTR 808 as the RP for the IPv4-embedded IPv6 multicast groups it manages. No 809 registration procedure is required under this configuration. 811 B.5. mAFTR Policy Configuration 813 The mAFTR may be configured with a list of IPv4 multicast groups and 814 sources. Only multicast flows bound to the configured addresses 815 should be handled by the mAFTR. Otherwise, packets are silently 816 dropped. 818 B.6. Static vs. Dynamic PIM Triggering 820 To optimize the usage of network resources in current deployments, 821 all multicast streams are conveyed in the core network while only the 822 most popular ones are forwarded in the aggregation/access networks 823 (static mode). Less popular streams are forwarded in the access 824 network upon request (dynamic mode). Depending on the location of 825 the mAFTR in the network, two modes can be envisaged: static and 826 dynamic. 828 Static Mode: the mAFTR is configured to instantiate permanent (S6, 829 G6) and (*, G6) entries in its TIB6 using a pre-configured (S4, 830 G4) list. 832 Dynamic Mode: the instantiation or withdrawal of (S6, G6) or (*, G6) 833 entries is triggered by the receipt of PIMv6 messages. 835 Authors' Addresses 837 Jacni Qin 838 Cisco 839 Shanghai 840 China 842 Email: jacni@jacni.com 843 Mohamed Boucadair 844 Orange 845 Rennes 35000 846 France 848 Email: mohamed.boucadair@orange.com 850 Christian Jacquenet 851 Orange 852 Rennes 35000 853 France 855 Email: christian.jacquenet@orange.com 857 Yiu L. Lee 858 Comcast 859 U.S.A. 861 Email: yiu_lee@cable.comcast.com 862 URI: http://www.comcast.com 864 Qian Wang 865 China Telecom 866 China 868 Phone: +86 10 58502462 869 Email: wangqian@chinatelecom.cn