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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) == Outdated reference: A later version (-04) exists of draft-ietf-mboned-v4v6-mcast-ps-02 == Outdated reference: A later version (-15) exists of draft-ietf-softwire-multicast-prefix-option-03 -- Obsolete informational reference (is this intentional?): RFC 5735 (Obsoleted by RFC 6890) Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Softwire WG J. Qin 3 Internet-Draft Cisco 4 Intended status: Standards Track M. Boucadair 5 Expires: October 17, 2013 C. Jacquenet 6 France Telecom 7 Y. Lee 8 Comcast 9 Q. Wang 10 China Telecom 11 April 15, 2013 13 Delivery of IPv4 Multicast Services to IPv4 Clients over an IPv6 14 Multicast Network 15 draft-ietf-softwire-dslite-multicast-05 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 October 17, 2013. 44 Copyright Notice 46 Copyright (c) 2013 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 . . . . . . . . . 6 68 4.3. Multicast Data Forwarding . . . . . . . . . . . . . . . . 7 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) . . . . . . . . . . . . . . . . . . . . . 9 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 Message . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . 16 95 B.1. Other operational Modes . . . . . . . . . . . . . . . . . 16 96 B.1.1. MLD Querier with mAFTR Embedded . . . . . . . . . . . 16 97 B.1.2. mAFTR embedded in DR . . . . . . . . . . . . . . . . 17 98 B.2. Older Version of Group Membership management Protocols . 17 99 B.3. Load-Balancing . . . . . . . . . . . . . . . . . . . . . 17 100 B.4. RP for IPv4-Embedded IPv6 Multicast Groups . . . . . . . 17 101 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. A more generic problem statement is sketched 113 in [I-D.ietf-mboned-v4v6-mcast-ps]. 115 This document specifies a generic solution for 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. 120 If customers have to access IPv4 multicast-based services through DS- 121 Lite environment, Address Family Transition Router (AFTR) devices 122 will have to process all the IGMP Report messages [RFC2236] [RFC3376] 123 that have been forwarded by the CPE into the IPv4-in-IPv6 tunnels. 124 From that standpoint, AFTR devices are likely to behave as a 125 replication point for downstream multicast traffic. And the 126 multicast packets will be replicated for each tunnel endpoint where 127 IPv4 receivers are connected to. 129 This kind of DS-Lite environment raises two major issues: 131 1. The IPv6 network loses the benefits of the multicast traffic 132 forwarding efficiency because it is unable to deterministically 133 replicate the data as close to the receivers as possible. As a 134 consequence, the downstream bandwidth in the IPv6 network will be 135 vastly consumed by sending multicast data over a unicast 136 infrastructure. 138 2. The AFTR is responsible for replicating multicast traffic and 139 forwarding it into each tunnel endpoint connecting IPv4 receivers 140 that have explicitly asked for the corresponding contents. This 141 process may greatly consume AFTR's resources and overload the 142 AFTR. 144 This document specifies an extension to the DS-Lite model to deliver 145 IPv4 multicast services to IPv4 clients over an IPv6 multicast- 146 enabled network. 148 1.1. Requirements Language 150 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 151 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 152 document are to be interpreted as described in RFC 2119 [RFC2119]. 154 2. Terminology 156 This document makes use of the following terms: 158 o IPv4-embedded IPv6 address: is an IPv6 address which embeds a 32 159 -bit-encoded IPv4 address. An IPv4-embedded IPv6 address can be 160 unicast or multicast. 162 o mPrefix64: is a dedicated multicast IPv6 prefix for constructing 163 IPv4-embedded IPv6 multicast addresses. mPrefix64 can be of two 164 types: ASM_mPrefix64 used in Any Source Multicast (ASM) mode or 165 SSM_mPrefix64 used in Source Specific Multicast (SSM) mode 166 [RFC4607]. 168 o uPrefix64: is a dedicated IPv6 unicast prefix for constructing 169 IPv4-embedded IPv6 unicast addresses [RFC6052]. 171 o Multicast AFTR (mAFTR): is a functional entity which supports 172 IPv4-IPv6 multicast interworking function (refer to Figure 3). It 173 receives and encapsulates the IPv4 multicast packets into IPv4-in- 174 IPv6 packets and behaves as the corresponding IPv6 multicast 175 source for the encapsulated IPv4-in-IPv6 packets. 177 o Multicast B4 (mB4): is a functional entity which supports an IGMP- 178 MLD interworking function (refer to Section 6.1) that relays 179 information conveyed in IGMP messages by forwarding the 180 corresponding MLD messages towards the MLD Querier in the IPv6 181 network. In addition, the mB4 decapsulates IPv4-in-IPv6 multicast 182 packets. 184 o PIMv4: refers to PIM when deployed in an IPv4 infrastructure 185 (i.e., IPv4 transport capabilities are used to exchange PIM 186 messages). 188 o PIMv6: refers to PIM when deployed in an IPv6 infrastructure 189 (i.e., IPv6 transport capabilities are used to exchange PIM 190 messages). 192 3. Scope 194 This document focuses only on subscription to an IPv4 multicast group 195 and the delivery of IPv4-formatted content to IPv4 receivers over an 196 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 as 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 original DS-Lite specification [RFC6333], an IPv4-in-IPv6 210 tunnel is used to carry bidirectional IPv4 unicast traffic between a 211 B4 and an AFTR. The solution specified in this document provides an 212 IPv4-in-IPv6 encapsulation scheme to deliver unidirectional IPv4 213 multicast 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 mAFTR and mB4 elements, 256 both of which contribute to the computation and the maintenance of 257 the IPv6 multicast distribution tree that extends the IPv4 multicast 258 distribution tree into the IPv6 multicast network. 260 The mAFTR and mB4 use mPrefix64 to convert an IPv4 multicast address 261 (G4) to an IPv4-embedded IPv6 multicast address (G6). The mAFTR and 262 mB4 use uPrefix64 to convert an IPv4 multicast source address (S4) to 263 an IPv4-embedded IPv6 address (S6). The mAFTR and mB4 MUST use the 264 same mPrefix64 and uPrefix64, as well as run the same algorithm for 265 building IPv4-embedded IPv6 addresses. Refer to Section 5 for more 266 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 (typically 281 acts as the PIMv6 Designated Router) receives the MLD Report message 282 and sends the PIMv6 Join to join the IPv6 multicast distribution 283 tree. The MLD Querier can send either PIMv6 Join (*,G6) in ASM or 284 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 there is not yet an existing one) 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 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 MUST advertise the route of uPrefix64 with an IPv6 IGP, so 312 as to represent the IPv4-embedded IPv6 source in the IPv6 multicast 313 network, and to pass the Reverse Path Forwarding (RPF) check on 314 multicast devices. 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. The IPv6 multicast routers use the 327 outer IPv6 header to make forwarding decisions. 329 When the mB4 receive the IPv6 multicast packet (to G6) derived by 330 mPrefix64, it MUST decapsulate it and forward the original IPv4 331 multicast packet to the receivers subscribing to G4. 333 Note: At this point, only IPv4-in-IPv6 encapsulation is defined; 334 however, other types of encapsulation could be defined in the future. 336 5. Address Mapping 338 5.1. Prefix Assignment 340 A dedicated IPv6 multicast prefix (mPrefix64) is provisioned to the 341 mAFTR and the mB4. The mAFTR and the mB4 use the mPrefix64 to form 342 an IPv6 multicast group address from an IPv4 multicast group address. 343 The mPrefix64 can be of two types: ASM_mPrefix64 (a mPrefix64 used in 344 ASM mode) or SSM_mPrefix64 (a mPrefix64 used in SSM mode). The 345 mPrefix64 MUST be derived from the corresponding IPv6 multicast 346 address space (e.g., the SSM_mPrefix64 MUST be in the range of 347 multicast address space specified in [RFC4607]). 349 The IPv6 part of the multicast distribution tree can be seen as an 350 extension of the IPv4 part of the multicast distribution tree. The 351 IPv4 multicast source address MUST be mapped to an IPv6 multicast 352 source address. An IPv6 unicast prefix (uPrefix64) is provisioned to 353 the mAFTR and the mB4. The mAFTR and the mB4 use the uPrefix64 to 354 form an IPv6 multicast source address from an IPv4 multicast source 355 address. The uPrefix-formed IPv6 multicast source address will 356 represent the original IPv4 multicast source in the IPv6 multicast 357 network. The uPrefix64 MUST be derived from the IPv6 unicast address 358 space. 360 The address translation MUST follow the algorithm defined in 361 Section 5.2. 363 The mPrefix64 and uPrefix64 can be configured in the mB4 using a 364 variety of methods, including an out-of-band mechanism, manual 365 configuration, or a dedicated provisioning protocol (e.g., using 366 DHCPv6 [I-D.ietf-softwire-multicast-prefix-option]). 368 5.2. Address Translation Algorithm 370 IPv4-Embedded IPv6 multicast addresses are composed according to the 371 following algorithm: 373 o Concatenate the mPrefix64 and the 32 bits of the IPv4 address to 374 obtain a 128-bit address. 376 The IPv4 multicast addresses are extracted from the IPv4-Embedded 377 IPv6 Multicast Addresses according to the following algorithm: 379 o If the multicast address has a pre-configured mPrefix64, extract 380 the last 32 bits of the IPv6 multicast address. 382 An IPv4 source is represented in the IPv6 realm with its 383 IPv4-converted IPv6 address [RFC6052]. 385 5.3. Textual Representation 387 The embedded IPv4 address in an IPv6 multicast address is included in 388 the last 32 bits; therefore dotted decimal notation can be used. 390 5.4. Examples 392 Group address mapping example: 394 +---------------------+--------------+----------------------------+ 395 | mPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 396 +---------------------+--------------+----------------------------+ 397 | ff0x::db8:0:0/96 | 233.252.0.1 | ff0x::db8::233.252.0.1 | 398 +---------------------+--------------+----------------------------+ 400 Source address mapping example when a /96 is used: 402 +---------------------+--------------+----------------------------+ 403 | uPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 404 +---------------------+--------------+----------------------------+ 405 | 2001:db8::/96 | 192.0.2.33 | 2001:db8::192.0.2.33 | 406 +---------------------+--------------+----------------------------+ 408 IPv4 and IPv6 addresses used in this example are derived from the 409 IPv4 and IPv6 blocks reserved for documentation, as per [RFC6676]. 410 The unicast IPv4 address of the above example is derived from 411 [RFC5735]. 413 6. Multicast B4 (mB4) 414 6.1. IGMP-MLD Interworking Function 416 The IGMP-MLD Interworking Function combines the IGMP/MLD Proxying 417 function and the address synthesizing operations. The IGMP/MLD 418 Proxying function is specified in [RFC4605]. The address translation 419 is stateless and MUST follow the address mapping specified in 420 Section 5. 422 The mB4 with the IGMP-MLD Interworking Function embedded relays 423 between the IGMP domain and the MLD domain. The mB4 performs the 424 host portion of the MLD protocol on the upstream interface. The 425 composition of IPv6 membership in this context is constructed through 426 address synthesizing operations and MUST synchronize with the 427 membership database maintained in the IGMP domain. MLD messages will 428 be forwarded natively towards the MLD Querier located upstream in the 429 IPv6 network. The mB4 also performs the router portion of the IGMP 430 protocol on the downstream interface(s). Refer to [RFC4605] for more 431 details 433 +----------+ IGMP +-------+ MLD +---------+ 434 | IPv4 |---------| mB4 |---------| MLD | 435 | Receiver | | | | Querier | 436 +----------+ +-------+ +---------+ 438 Figure 2: IGMP-MLD Interworking 440 If SSM is deployed, the mB4 MUST construct the IPv6 source address 441 (or retrieve the IPv4 source address) using the uPrefix64. The mB4 442 may create a membership database which associates the IPv4-IPv6 443 multicast groups with the interfaces (e.g., Wi-Fi and Wired Ethernet) 444 facing IPv4 multicast receivers. 446 6.2. Multicast Data Forwarding 448 When the mB4 receives an IPv6 multicast packet, it MUST check the 449 group address and the source address. If the IPv6 multicast group 450 prefix is mPrefix64 and the IPv6 source prefix is uPrefix64, the mB4 451 MUST de-capsulate the IPv6 header and forward the IPv4 multicast 452 packet through each relevant interface. Otherwise, the mB4 MUST drop 453 the packet silently. 455 As an illustration, if a packet is received from source 456 2001:db8::192.0.2.33 and to be forwarded to group 457 ff3x:1000::233.252.0.1, the mB4 will de-capsulate it into an IPv4 458 multicast packet using 192.0.2.33 as the IPv4 multicast source 459 address and using 233.252.0.1 as the IPv4 destination address. 461 6.3. Fragmentation 463 Encapsulating IPv4 multicast packets into IPv6 multicast packets that 464 will be forwarded by the mAFTR to the mB4 along the IPv6 multicast 465 distribution tree reduces the effective MTU size by the size of an 466 IPv6 header. In this specification, the data flow is unidirectional 467 from mAFTR to mB4, the mAFTR MUST fragment the oversized IPv6 packet 468 after the encapsulation into two IPv6 packets. The mB4 MUST 469 reassemble the IPv6 packets, decapsulate the IPv6 packet, and forward 470 the IPv4 packet to the hosts subscribing the multicast group. 471 Further considerations about fragmentation issues are documented in 472 [RFC6333]. 474 6.4. Host built-in mB4 Function 476 If the mB4 function is implemented in the host which is directly 477 connected to an IPv6-only network, the host MUST implement 478 Section 6.1, Section 6.2, and Section 6.3. The host MAY optimize the 479 implementation to provide an Application Programming Interface (API) 480 or kernel module to skip the IGMP-MLD Interworking Function. The 481 optimization is out of scope of the specification. 483 6.5. Preserve the Scope 485 When several mPrefix64s are available, if each enclosed IPv4-embedded 486 IPv6 multicast prefix has a distinct scope, mB4 MUST select the 487 appropriate IPv4-embedded IPv6 multicast prefix having a scope 488 matching the IPv4 multicast address used to synthesize an 489 IPv4-embedded IPv6 multicast address. 491 The mB4 MAY be configured to not preserve the scope when enforcing 492 the address translation algorithm. 494 7. Multicast AFTR (mAFTR) 496 7.1. Routing Considerations 498 The mAFTR is responsible for interconnecting the IPv4 multicast 499 distribution tree with the corresponding IPv6 multicast distribution 500 tree. The mAFTR MUST use the uPrefix64 to build the IPv6 source 501 addresses of the multicast group address derived from mPrefix64. In 502 other words, the mAFTR MUST be the multicast source derived from 503 uPrefix64. 505 The mAFTR MUST advertise the route of uPrefix64 to the IPv6 IGP. 506 This is needed for the IPv6 multicast routers to have routing 507 information to discover the source. 509 7.2. Processing PIM Message 511 The mAFTR MUST interwork PIM Join/Prune messages for (*, G6) and (S6, 512 G6) on their corresponding (*, G4) and (S4, G4). The following text 513 specifies the expected behavior of mAFTR for PIM Join message. 515 +---------+ 516 ---------| mAFTR |--------- 517 PIMv6 |uPrefix64| PIMv4 518 |mPreifx64| 519 +---------+ 521 Figure 3: PIMv6-PIMv4 Interworking Function 523 The mAFTR contains two separate Tree Information Base (TIB): IPv4 524 Tree Information Base (TIB4) and IPv6 Tree Information Base (TIB6), 525 which are bridged by one IPv4-in-IPv6 virtual interface. It should 526 be noted that the implementations may vary (e.g., using one 527 integrated TIB without any virtual interface), while they should 528 follow the specification herein for the consistency of overall 529 functionality. 531 When a mAFTR receives a PIMv6 Join message (*,G6) with an IPv6 532 multicast group address (G6) that is derived from the mPrefix64, it 533 MUST check its IPv6 Tree Information Base (TIB6). If there is an 534 entry for this G6, it MUST check whether the interface through which 535 the PIMv6 Join message has been received is on the outgoing interface 536 list. If not, the mAFTR MUST add the interface to the outgoing 537 interface list. If there is no entry in the TIB6, the mAFTR MUST 538 create a new entry (*,G6) for the multicast group. While, whether or 539 not to set the IPv4-in-IPv6 virtual interface as the incoming 540 interface of the newly created entry is up to the implementation but 541 should comply with the mAFTR's behavior of multicast data forwarding, 542 see Section 7.4. 544 The mAFTR MUST extract the IPv4 multicast group address (G4) from the 545 IPv4-embedded IPv6 multicast address (G6) contained in the PIMv6 Join 546 message. The mAFTR MUST check its IPv4 Tree Information Base (TIB4). 547 If there is an entry for G4, it MUST check whether the IPv4-in-IPv6 548 virtual interface is on the outgoing interface list. If not, the 549 mAFTR MUST add the interface to the outgoing interface list. If 550 there is no entry for G4, the mAFTR MUST create a new (*,G4) entry in 551 its TIB4 and initiate the procedure for building the shared tree in 552 the IPv4 multicast network without any additional requirement. 554 If mAFTR receives a source-specific Join message, the (S6, G6) will 555 be processed rather than (*,G6). The procedures of processing 556 (S6,G6) and (*,G6) are almost the same. Differences have been 557 detailed in [RFC4601]. 559 7.3. Switching from Shared Tree to Shortest Path Tree 561 When the mAFTR receives the first IPv4 multicast packet, it may 562 extract the multicast source address (S4) from the packet and send an 563 Explicit PIMv4 (S4,G4) Join message directly to S4. The mAFTR will 564 switch from the shared Rendezvous Point Tree (RPT) to the Shortest 565 Path Tree (SPT) for G4. 567 For IPv6 multicast routers to switch to the SPT, there is no new 568 requirement. IPv6 multicast routers may send an Explicit PIMv6 Join 569 to mAFTR once the first (S6,G6) multicast packet arrives from 570 upstream multicast routers. 572 7.4. Multicast Data Forwarding 574 When the mAFTR receives an IPv4 multicast packet, it will look up the 575 TIB4 to find a matching entry and then forward the packet to the 576 interface(s) on the outgoing interface list. If the IPv4-in-IPv6 577 virtual interface also belongs to this list, the packet will be 578 encapsulated with the mPrefix64-derived and uPrefix64-derived 579 IPv4-embedded IPv6 addresses to form an IPv6 multicast packet. Then 580 another lookup is executed to find a matching entry in the TIB6, 581 while whether or not to perform RPF check for the second lookup is up 582 to the implementation and is out of the scope of this document. The 583 IPv6 multicast packet is forwarded along the IPv6 multicast 584 distribution tree, based upon the outgoing interface list of the 585 matching entry in the TIB6. 587 As an illustration, if a packet is received from source 192.0.2.33 588 and to be forwarded to group 233.252.0.1, the mAFTR encapsulates it 589 into an IPv6 multicast packet using ff3x:1000::233.252.0.1 as the 590 IPv6 destination address and using 2001:db8::192.0.2.33 as the IPv6 591 multicast source address. 593 7.5. TTL/Scope 595 The Scope field of IPv4-in-IPv6 multicast addresses should be valued 596 accordingly (e.g, to "E", Global scope;) in the deployment 597 environment. This specification does not discuss the scope value 598 that should be used. 600 Nevertheless, when several mPrefix64s are available, if each enclosed 601 IPv4-embedded IPv6 multicast prefix has a distinct scope, mAFTR MUST 602 select the appropriate IPv4-embedded IPv6 multicast prefix having a 603 scope matching the IPv4 multicast address used to synthesize an 604 IPv4-embedded IPv6 multicast address. 606 mAFTR MAY be configured to not preserve the scope when enforcing the 607 address translation algorithm. 609 8. Security Considerations 611 A part for multicast scoping considerations (see Section 6.5 and 612 Section 7.5), this document does not introduce any new security 613 concern in addition to what is discussed in Section 5 of [RFC6052], 614 Section 10 of [RFC3810] and Section 6 of [RFC4601]. 616 mB4 SHOULD be provided with appropriate configuration to enable 617 preserving the scope of a multicast message when mapping an IPv4 618 multicast address into an IPv4-embedded IPv6 multicast address and 619 vice versa. 621 8.1. Firewall Configuration 623 The CPE that embeds the mB4 function SHOULD be configured to accept 624 incoming MLD messages and traffic forwarded to multicast groups 625 subscribed by receivers located in the customer premises. 627 9. Acknowledgements 629 The authors would like to thank Dan Wing for his guidance in the 630 early discussions which initiated this work. We also thank Peng Sun, 631 Jie Hu, Qiong Sun, Lizhong Jin, Alain Durand, Dean Cheng, Behcet 632 Sarikaya, Tina Tsou, Rajiv Asati, Xiaohong Deng and S. Venaas for 633 their valuable comments. 635 10. IANA Considerations 637 This document includes no request to IANA. 639 11. References 641 11.1. Normative References 643 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 644 Requirement Levels", BCP 14, RFC 2119, March 1997. 646 [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 647 Thyagarajan, "Internet Group Management Protocol, Version 648 3", RFC 3376, October 2002. 650 [RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery 651 Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. 653 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 654 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 655 Protocol Specification (Revised)", RFC 4601, August 2006. 657 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 658 "Internet Group Management Protocol (IGMP) / Multicast 659 Listener Discovery (MLD)-Based Multicast Forwarding ("IGMP 660 /MLD Proxying")", RFC 4605, August 2006. 662 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 663 IP", RFC 4607, August 2006. 665 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 666 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 667 October 2010. 669 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 670 Stack Lite Broadband Deployments Following IPv4 671 Exhaustion", RFC 6333, August 2011. 673 11.2. Informative References 675 [I-D.ietf-mboned-multiaaa-framework] 676 Satou, H., Ohta, H., Hayashi, T., Jacquenet, C., and H. 677 He, "AAA and Admission Control Framework for 678 Multicasting", draft-ietf-mboned-multiaaa-framework-12 679 (work in progress), August 2010. 681 [I-D.ietf-mboned-v4v6-mcast-ps] 682 Jacquenet, C., Boucadair, M., Lee, Y., Qin, J., Tsou, T., 683 and Q. Sun, "IPv4-IPv6 Multicast: Problem Statement and 684 Use Cases", draft-ietf-mboned-v4v6-mcast-ps-02 (work in 685 progress), March 2013. 687 [I-D.ietf-softwire-multicast-prefix-option] 688 Boucadair, M., Qin, J., Tsou, T., and X. Deng, "DHCPv6 689 Option for IPv4-Embedded Multicast and Unicast IPv6 690 Prefixes", draft-ietf-softwire-multicast-prefix-option-03 691 (work in progress), October 2012. 693 [RFC2236] Fenner, W.C., "Internet Group Management Protocol, Version 694 2", RFC 2236, November 1997. 696 [RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses", 697 BCP 153, RFC 5735, January 2010. 699 [RFC6676] Venaas, S., Parekh, R., Van de Velde, G., Chown, T., and 700 M. Eubanks, "Multicast Addresses for Documentation", RFC 701 6676, August 2012. 703 Appendix A. Use Case: IPTV 705 IPTV generally includes two categories of service offerings: 707 o Video on Demand (VoD) that unicast video content to receivers. 709 o Multicast live TV broadcast services. 711 Two players intervene in the delivery of this service: 713 o Content Providers, who usually own the contents that is multicast 714 to receivers. Content providers may contractually define an 715 agreement with network providers to deliver contents to receivers. 717 o Network Providers, who provide network connectivity services 718 (e.g., network providers are responsible for carrying multicast 719 flows from head-ends to receivers). Refer to 720 [I-D.ietf-mboned-multiaaa-framework]. 722 Note that some contract agreements prevent a network provider from 723 altering the content as sent by the content provider for various 724 reasons. Under the contract, multicast streams should be delivered 725 unaltered to the requesting users. 727 Many current IPTV contents are likely to remain IPv4-formatted and 728 out of control of the network providers. Additionally, there are 729 numerous legacy receivers (e.g., IPv4-only Set Top Boxes (STB)) that 730 can't be upgraded or be easily replaced to support IPv6. As a 731 consequence, IPv4 service continuity MUST be guaranteed during the 732 transition period, including the delivery of multicast services such 733 as Live TV Broadcasting to users. 735 Appendix B. Deployment Considerations 737 B.1. Other operational Modes 739 B.1.1. MLD Querier with mAFTR Embedded 741 mAFTR can embed the MLD Querier function (as well as the PIMv6 DR) 742 for optimization. When mB4 sends MLD Report message to this mAFTR, 743 the mAFTR should process the MLD Report message that contain 744 IPv4-embedded IPv6 multicast group subscription information then send 745 the corresponding PIMv4 Join message. (Figure 4) 746 +---------+ 747 ---------| mAFTR |--------- 748 MLD |uPrefix64| PIMv4 749 |mPreifx64| 750 +---------+ 752 Figure 4: MLD-PIMv4 Interworking Function 754 Discussions about the location of the mAFTR capability and related 755 ASM or SSM multicast design considerations are out of the scope of 756 this document. 758 B.1.2. mAFTR embedded in DR 760 If mAFTR is the DR of the original IPv4 source, it may simply use the 761 uPrefix64 and mPrefix64 to build the IPv4-embedded IPv6 multicast 762 traffic, the sending of PIMv4 Join message is not necessary. 764 B.2. Older Version of Group Membership management Protocols 766 Given the multiple versions of group membership management protocols, 767 mismatch issues may be raised in the mB4 Function (refer to 768 Section 6.1). 770 If IGMPv2 operates on the IPv4 receivers while MLDv2 operates on the 771 MLD Querier, or if IGMPv3 operates on the IPv4 receivers while MLDv1 772 operates on the MLD Querier, the issue mentioned above will be 773 encountered. To solve this problem, the mB4 SHOULD perform the 774 router portion of IGMP which is of the same as the corresponding MLD 775 version (IGMPv2 as of MLDv1, or IGMPv3 as of MLDv2) operating in the 776 IPv6 domain, then the protocol interaction approach specified in 777 Section 7 of [RFC3376] can be used to exchange signaling messages 778 with the IPv4 receivers on which the different version of IGMP is 779 operating. 781 B.3. Load-Balancing 783 For robustness and load distribution purposes, several nodes in the 784 network can embed the mAFTR function. In such case, the same IPv6 785 prefixes (i.e., mPrefix64 and uPrefix64) and algorithm to build IPv4- 786 embedded IPv6 addresses MUST be configured on those nodes. 788 B.4. RP for IPv4-Embedded IPv6 Multicast Groups 790 For the sake of simplicity, it is RECOMMENDED to configure mAFTR as 791 the RP for the IPv4-embedded IPv6 multicast groups it manages. No 792 registration procedure is required under this configuration. 794 B.5. mAFTR Policy Configuration 796 mAFTR may be configured with a list of IPv4 multicast groups and 797 sources. Only multicast flows bound to the configured addresses 798 should be handled by the mAFTR. Otherwise, packets are silently 799 drooped. 801 B.6. Static vs. Dynamic PIM Triggering 803 To optimize the usage of network resources in current deployments, 804 all multicast streams are conveyed in the core network while only 805 popular ones are continuously conveyed in the aggregation/access 806 network (static mode). Non-popular streams are conveyed in the 807 access network upon request (dynamic mode). Depending on the 808 location of the mAFTR in the network, two modes can be envisaged: 809 static and dynamic. 811 o Static Mode: the mAFTR is configured to instantiate permanent (S6, 812 G6) and (*, G6) entries in its TIB6 using a pre-configured (S4, 813 G4) list. 815 o Dynamic Mode: the instantiation and deletion of (S6, g6) or (*, 816 G6) is triggered by the receipt of PIMv6 messages. 818 Authors' Addresses 820 Jacni Qin 821 Cisco 822 Shanghai 823 China 825 Email: jacni@jacni.com 827 Mohamed Boucadair 828 France Telecom 829 Rennes 35000 830 France 832 Email: mohamed.boucadair@orange.com 834 Christian Jacquenet 835 France Telecom 836 Rennes 35000 837 France 839 Email: christian.jacquenet@orange.com 840 Yiu L. Lee 841 Comcast 842 U.S.A. 844 Email: yiu_lee@cable.comcast.com 845 URI: http://www.comcast.com 847 Qian Wang 848 China Telecom 849 No.118, Xizhimennei 850 Beijing 100035 851 China 853 Phone: +86 10 5855 2177 854 Email: wangqian@ctbri.com.cn