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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references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) == Outdated reference: A later version (-15) exists of draft-ietf-softwire-multicast-prefix-option-08 Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). 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: March 3, 2016 C. Jacquenet 6 France Telecom 7 Y. Lee 8 Comcast 9 Q. Wang 10 China Telecom 11 August 31, 2015 13 Delivery of IPv4 Multicast Services to IPv4 Clients over an IPv6 14 Multicast Network 15 draft-ietf-softwire-dslite-multicast-10 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 March 3, 2016. 44 Copyright Notice 46 Copyright (c) 2015 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 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 . . . . . . . . . . . 17 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 . . . . . . . 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 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. 119 If customers have to access IPv4 multicast-based services through DS- 120 Lite environment, Address Family Transition Router (AFTR) devices 121 will have to process all the IGMP Report messages [RFC2236] [RFC3376] 122 that have been forwarded by the CPE into the IPv4-in-IPv6 tunnels. 123 From that standpoint, AFTR devices are likely to behave as a 124 replication point for downstream multicast traffic. And the 125 multicast packets will be replicated for each tunnel endpoint where 126 IPv4 receivers are connected to. 128 This kind of DS-Lite environment raises two major issues: 130 1. The IPv6 network loses the benefits of the multicast traffic 131 forwarding efficiency because it is unable to deterministically 132 replicate the data as close to the receivers as possible. As a 133 consequence, the downstream bandwidth in the IPv6 network will be 134 vastly consumed by sending multicast data over a unicast 135 infrastructure. 137 2. The AFTR is responsible for replicating multicast traffic and 138 forwarding it into each tunnel endpoint connecting IPv4 receivers 139 that have explicitly asked for the corresponding contents. This 140 process may greatly consume AFTR's resources and overload the 141 AFTR. 143 This document specifies an extension to the DS-Lite model to deliver 144 IPv4 multicast services to IPv4 clients over an IPv6 multicast- 145 enabled network. 147 1.1. Requirements Language 149 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 150 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 151 document are to be interpreted as described in RFC 2119 [RFC2119]. 153 2. Terminology 155 This document makes use of the following terms: 157 o IPv4-embedded IPv6 address: is an IPv6 address which embeds a 32- 158 bit-encoded IPv4 address. An IPv4-embedded IPv6 address can be 159 unicast or multicast. 161 o mPrefix64: is a dedicated multicast IPv6 prefix for constructing 162 IPv4-embedded IPv6 multicast addresses. mPrefix64 can be of two 163 types: ASM_mPrefix64 used in Any Source Multicast (ASM) mode or 164 SSM_mPrefix64 used in Source Specific Multicast (SSM) mode 165 [RFC4607]. 167 o uPrefix64: is a dedicated IPv6 unicast prefix for constructing 168 IPv4-embedded IPv6 unicast addresses [RFC6052]. 170 o Multicast AFTR (mAFTR): is a functional entity which supports 171 IPv4-IPv6 multicast interworking function (refer to Figure 3). It 172 receives and encapsulates the IPv4 multicast packets into IPv4-in- 173 IPv6 packets and behaves as the corresponding IPv6 multicast 174 source for the encapsulated IPv4-in-IPv6 packets. 176 o Multicast B4 (mB4): is a functional entity which supports an IGMP- 177 MLD interworking function (refer to Section 6.1) that relays 178 information conveyed in IGMP messages by forwarding the 179 corresponding MLD messages towards the MLD Querier in the IPv6 180 network. In addition, the mB4 decapsulates IPv4-in-IPv6 multicast 181 packets. 183 o PIMv4: refers to PIM when deployed in an IPv4 infrastructure 184 (i.e., IPv4 transport capabilities are used to exchange PIM 185 messages). 187 o PIMv6: refers to PIM when deployed in an IPv6 infrastructure 188 (i.e., IPv6 transport capabilities are used to exchange PIM 189 messages). 191 3. Scope 193 This document focuses only on subscription to an IPv4 multicast group 194 and the delivery of IPv4-formatted content to IPv4 receivers over an 195 IPv6-only network. In particular, only the following case is 196 covered: 198 An IPv4 receiver accesses IPv4 multicast contents over an IPv6- 199 only multicast-enabled network. 201 This document does not cover the source/receiver heuristics, where as 202 IPv4 receiver can also behave as an IPv4 multicast source. This 203 document assumes that hosts behind the mB4 are IPv4 multicast 204 receivers only. 206 4. Solution Overview 208 In the original DS-Lite specification [RFC6333], an IPv4-in-IPv6 209 tunnel is used to carry bidirectional IPv4 unicast traffic between a 210 B4 and an AFTR. The solution specified in this document provides an 211 IPv4-in-IPv6 encapsulation scheme to deliver unidirectional IPv4 212 multicast traffic from an mAFTR to an mB4. 214 An overview of the solution is provided in this section which is 215 intended as an introduction to how it works, but is NOT normative. 216 For the normative specifications of the two new functional elements: 217 mB4 and mAFTR (Figure 1), refer to Section 6 and Section 7. 219 ------------ 220 / \ 221 | IPv4 network | 222 \ / 223 ------------ 224 IPv4 multicast : | ^ PIMv4 Join 225 v | : 226 +-------------+ 227 | mAFTR | 228 +-------------+ 229 IPv6 multicast |:| | ^ PIMv6 Join (PIMv6 230 (IPv4 embedded) |:| | : routers in between) 231 ------------ 232 / \ 233 | IPv6 network | 234 \ / 235 ------------ 236 |:| | : MLD Report 237 |v| | : 238 +-----------+ 239 | mB4 | 240 +-----------+ 241 IPv4 multicast : | ^ IGMP Report 242 v | : 243 +-----------+ 244 | IPv4 | 245 | receiver | 246 +-----------+ 248 Figure 1: Functional Architecture 250 4.1. IPv4-Embedded IPv6 Prefixes 252 In order to map the addresses of IPv4 multicast traffic with IPv6 253 multicast addresses, an IPv6 multicast prefix (mPrefix64) and an IPv6 254 unicast prefix (uPrefix64) are provided to mAFTR and mB4 elements, 255 both of which contribute to the computation and the maintenance of 256 the IPv6 multicast distribution tree that extends the IPv4 multicast 257 distribution tree into the IPv6 multicast network. 259 The mAFTR and mB4 use mPrefix64 to convert an IPv4 multicast address 260 (G4) to an IPv4-embedded IPv6 multicast address (G6). The mAFTR and 261 mB4 use uPrefix64 to convert an IPv4 multicast source address (S4) to 262 an IPv4-embedded IPv6 address (S6). The mAFTR and mB4 MUST use the 263 same mPrefix64 and uPrefix64, as well as run the same algorithm for 264 building IPv4-embedded IPv6 addresses. Refer to Section 5 for more 265 details about the address mapping. 267 4.2. Multicast Distribution Tree Computation 269 When an IPv4 receiver connected to the device that embeds the mB4 270 capability wants to subscribe to an IPv4 multicast group, it sends an 271 IGMP Report message to the mB4. The mB4 creates the IPv6 multicast 272 group (G6) address using mPrefix64 and the original IPv4 multicast 273 group address. If the receiver sends a source-specific IGMPv3 Report 274 message, the mB4 will create the IPv6 source address (S6) using 275 uPrefix64 and the original IPv4 source address. 277 The mB4 uses the G6 (and both S6 and G6 in SSM) to create the 278 corresponding MLD Report message. The mB4 sends the Report message 279 to the MLD Querier in the IPv6 network. The MLD Querier (typically 280 acts as the PIMv6 Designated Router) receives the MLD Report message 281 and sends the PIMv6 Join to join the IPv6 multicast distribution 282 tree. The MLD Querier can send either PIMv6 Join (*,G6) in ASM or 283 PIMv6 Join (S6,G6) in SSM to the mAFTR. 285 The mAFTR acts as the DR to which the uPrefix64-derived S6 is 286 connected. The mAFTR will receive the source-specific PIMv6 Join 287 message (S6,G6) from the IPv6 multicast network. If the mAFTR is the 288 Rendezvous Point (RP) of G6, it will receive the any-source PIMv6 289 Join message (*,G6) from the IPv6 multicast network. If the mAFTR is 290 not the RP of G6, it will send the PIM Register message to the RP of 291 G6 located in the IPv6 multicast network. 293 When the mAFTR receives the PIMv6 Join message (*,G6), it will 294 extract the IPv4 multicast group address (G4). If the mAFTR is the 295 RP of G4 in the IPv4 multicast network, it will create a (*,G4) entry 296 (if there is not yet an existing one) in its own IPv4 multicast 297 routing table. If the mAFTR is not the RP of G4, it will send the 298 corresponding PIMv4 Join message (*,G4) towards the RP of G4 in the 299 IPv4 multicast network. 301 When the mAFTR receives the PIMv6 Join message (S6,G6), it will 302 extract the IPv4 multicast group address (G4) and IPv4 source address 303 (S4) and send the corresponding (S4,G4) PIMv4 Join message directly 304 to the IPv4 source. 306 A branch of the multicast distribution tree is constructed, 307 comprising both an IPv4 part (from the mAFTR upstream) and an IPv6 308 part (from mAFTR downstream to the mB4). 310 The mAFTR MUST advertise the route of uPrefix64 with an IPv6 IGP, so 311 as to represent the IPv4-embedded IPv6 source in the IPv6 multicast 312 network, and to pass the Reverse Path Forwarding (RPF) check on 313 multicast devices. 315 4.3. Multicast Data Forwarding 317 When the mAFTR receives an IPv4 multicast packet, it will encapsulate 318 the packet into an IPv6 multicast packet using the IPv4-embedded IPv6 319 multicast address as the destination address and an IPv4-embedded 320 IPv6 unicast address as the source address. The encapsulated IPv6 321 multicast packet will be forwarded down the IPv6 multicast 322 distribution tree and the mB4 will eventually receive the packet. 324 The IPv6 multicast network treats the IPv4-in-IPv6 encapsulated 325 multicast packets as native. The IPv6 multicast routers use the 326 outer IPv6 header to make forwarding decisions. 328 When the mB4 receive the IPv6 multicast packet (to G6) derived by 329 mPrefix64, it MUST decapsulate it and forward the original IPv4 330 multicast packet to the receivers subscribing to G4. 332 Note: At this point, only IPv4-in-IPv6 encapsulation is defined; 333 however, other types of encapsulation could be defined in the future. 335 5. Address Mapping 337 5.1. Prefix Assignment 339 A dedicated IPv6 multicast prefix (mPrefix64) is provisioned to the 340 mAFTR and the mB4. The mAFTR and the mB4 use the mPrefix64 to form 341 an IPv6 multicast group address from an IPv4 multicast group address. 342 The mPrefix64 can be of two types: ASM_mPrefix64 (a mPrefix64 used in 343 ASM mode) or SSM_mPrefix64 (a mPrefix64 used in SSM mode). The 344 mPrefix64 MUST be derived from the corresponding IPv6 multicast 345 address space (e.g., the SSM_mPrefix64 MUST be in the range of 346 multicast address space specified in [RFC4607]). 348 The IPv6 part of the multicast distribution tree can be seen as an 349 extension of the IPv4 part of the multicast distribution tree. The 350 IPv4 multicast source address MUST be mapped to an IPv6 multicast 351 source address. An IPv6 unicast prefix (uPrefix64) is provisioned to 352 the mAFTR and the mB4. The mAFTR and the mB4 use the uPrefix64 to 353 form an IPv6 multicast source address from an IPv4 multicast source 354 address. The uPrefix-formed IPv6 multicast source address will 355 represent the original IPv4 multicast source in the IPv6 multicast 356 network. The uPrefix64 MUST be derived from the IPv6 unicast address 357 space. 359 The address translation MUST follow the algorithm defined in 360 Section 5.2. 362 The mPrefix64 and uPrefix64 can be configured in the mB4 using a 363 variety of methods, including an out-of-band mechanism, manual 364 configuration, or a dedicated provisioning protocol (e.g., using 365 DHCPv6 [I-D.ietf-softwire-multicast-prefix-option]). 367 5.2. Address Translation Algorithm 369 IPv4-Embedded IPv6 multicast addresses are composed according to the 370 following algorithm: 372 o Concatenate the mPrefix64 and the 32 bits of the IPv4 address to 373 obtain a 128-bit address. 375 The IPv4 multicast addresses are extracted from the IPv4-Embedded 376 IPv6 Multicast Addresses according to the following algorithm: 378 o If the multicast address has a pre-configured mPrefix64, extract 379 the last 32 bits of the IPv6 multicast address. 381 An IPv4 source is represented in the IPv6 realm with its 382 IPv4-converted IPv6 address [RFC6052]. 384 5.3. Textual Representation 386 The embedded IPv4 address in an IPv6 multicast address is included in 387 the last 32 bits; therefore dotted decimal notation can be used. 389 5.4. Examples 391 Group address mapping example: 393 +---------------------+--------------+----------------------------+ 394 | mPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 395 +---------------------+--------------+----------------------------+ 396 | ff0x::db8:0:0/96 | 233.252.0.1 | ff0x::db8::233.252.0.1 | 397 +---------------------+--------------+----------------------------+ 399 Source address mapping example when a /96 is used: 401 +---------------------+--------------+----------------------------+ 402 | uPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 403 +---------------------+--------------+----------------------------+ 404 | 2001:db8::/96 | 192.0.2.33 | 2001:db8::192.0.2.33 | 405 +---------------------+--------------+----------------------------+ 407 IPv4 and IPv6 addresses used in this example are derived from the 408 IPv4 and IPv6 blocks reserved for documentation, as per [RFC6676]. 410 The unicast IPv4 address of the above example is derived from the 411 documentation address block defined in [RFC6890]. 413 6. Multicast B4 (mB4) 415 6.1. IGMP-MLD Interworking Function 417 The IGMP-MLD Interworking Function combines the IGMP/MLD Proxying 418 function and the address synthesizing operations. The IGMP/MLD 419 Proxying function is specified in [RFC4605]. The address translation 420 is stateless and MUST follow the address mapping specified in 421 Section 5. 423 The mB4 with the IGMP-MLD Interworking Function embedded relays 424 between the IGMP domain and the MLD domain. The mB4 performs the 425 host portion of the MLD protocol on the upstream interface. The 426 composition of IPv6 membership in this context is constructed through 427 address synthesizing operations and MUST synchronize with the 428 membership database maintained in the IGMP domain. MLD messages will 429 be forwarded natively towards the MLD Querier located upstream in the 430 IPv6 network. The mB4 also performs the router portion of the IGMP 431 protocol on the downstream interface(s). Refer to [RFC4605] for more 432 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., Wi-Fi 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 de-capsulate the IPv6 header and forward the IPv4 multicast 453 packet through each relevant interface. Otherwise, the mB4 MUST drop 454 the packet silently. 456 As an illustration, if a packet is received from source 457 2001:db8::192.0.2.33 and to be forwarded to group 458 ff3x:1000::233.252.0.1, the mB4 will de-capsulate 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 mAFTR to mB4, the mAFTR MUST fragment the oversized IPv6 packet 469 after the encapsulation into two IPv6 packets. The mB4 MUST 470 reassemble the IPv6 packets, decapsulate the IPv6 packet, and forward 471 the IPv4 packet to the hosts subscribing the multicast group. 472 Further considerations about fragmentation issues are documented in 473 [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. The 482 optimization is out of scope of the 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, mB4 MUST select the 488 appropriate IPv4-embedded IPv6 multicast prefix having a scope 489 matching the IPv4 multicast address used to synthesize an 490 IPv4-embedded IPv6 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 derived from 504 uPrefix64. 506 The mAFTR MUST advertise the route of uPrefix64 to the IPv6 IGP. 507 This is needed for the IPv6 multicast routers to have routing 508 information to discover the source. 510 7.2. Processing PIM Message 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 mAFTR for PIM Join message. 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 Base (TIB): IPv4 525 Tree Information Base (TIB4) and IPv6 Tree Information Base (TIB6), 526 which are bridged by one IPv4-in-IPv6 virtual interface. It should 527 be noted that the implementations may vary (e.g., using one 528 integrated TIB without any virtual interface), while they should 529 follow the specification herein for the consistency of overall 530 functionality. 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, it MUST check whether the interface through which 536 the PIMv6 Join message has been received is on the outgoing interface 537 list. If not, the mAFTR MUST add the interface to the outgoing 538 interface list. If there is no entry in the TIB6, the mAFTR MUST 539 create a new entry (*,G6) for the multicast group. While, whether or 540 not to set the IPv4-in-IPv6 virtual interface as the incoming 541 interface of the newly created entry is up to the implementation but 542 should comply with the mAFTR's behavior of multicast data forwarding, 543 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 on the outgoing interface list. If not, the 550 mAFTR MUST add the interface to the outgoing interface list. If 551 there is no entry for G4, the mAFTR MUST create a new (*,G4) entry in 552 its TIB4 and initiate the procedure for building the shared tree in 553 the IPv4 multicast network without any additional requirement. 555 If mAFTR receives a source-specific Join message, the (S6, G6) will 556 be processed rather than (*,G6). The procedures of processing 557 (S6,G6) and (*,G6) are almost the same. Differences have been 558 detailed in [RFC4601]. 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 will 565 switch 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 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 will look up the 576 TIB4 to find a matching entry and then forward the packet to the 577 interface(s) on the outgoing interface list. If the IPv4-in-IPv6 578 virtual interface also belongs to this list, the packet will be 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 executed to find a matching entry in the TIB6, 582 while whether or not to perform RPF check for the second lookup is up 583 to the implementation and is out of the scope of this document. The 584 IPv6 multicast packet is forwarded along the IPv6 multicast 585 distribution tree, based upon the outgoing interface list of the 586 matching entry in the TIB6. 588 As an illustration, if a packet is received from source 192.0.2.33 589 and to be forwarded to group 233.252.0.1, the mAFTR encapsulates it 590 into an IPv6 multicast packet using ff3x:1000::233.252.0.1 as the 591 IPv6 destination address and using 2001:db8::192.0.2.33 as the IPv6 592 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, mAFTR MUST 603 select the appropriate IPv4-embedded IPv6 multicast prefix having a 604 scope matching the IPv4 multicast address used to synthesize an 605 IPv4-embedded IPv6 multicast address. 607 mAFTR MAY be configured to not preserve the scope when enforcing the 608 address translation algorithm. 610 8. Security Considerations 612 A part for 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 [RFC4601]. 617 mB4 SHOULD be provided with appropriate configuration to enable 618 preserving 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 S. Venaas for 634 their valuable comments. 636 10. IANA Considerations 638 This document includes no request to IANA. 640 11. References 642 11.1. Normative References 644 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 645 Requirement Levels", BCP 14, RFC 2119, 646 DOI 10.17487/RFC2119, March 1997, 647 . 649 [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 650 Thyagarajan, "Internet Group Management Protocol, Version 651 3", RFC 3376, DOI 10.17487/RFC3376, October 2002, 652 . 654 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 655 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 656 DOI 10.17487/RFC3810, June 2004, 657 . 659 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 660 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 661 Protocol Specification (Revised)", RFC 4601, 662 DOI 10.17487/RFC4601, August 2006, 663 . 665 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 666 "Internet Group Management Protocol (IGMP) / Multicast 667 Listener Discovery (MLD)-Based Multicast Forwarding 668 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 669 August 2006, . 671 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 672 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 673 . 675 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 676 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 677 DOI 10.17487/RFC6052, October 2010, 678 . 680 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 681 Stack Lite Broadband Deployments Following IPv4 682 Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011, 683 . 685 11.2. Informative References 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-08 691 (work in progress), March 2015. 693 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 694 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 695 . 697 [RFC6676] Venaas, S., Parekh, R., Van de Velde, G., Chown, T., and 698 M. Eubanks, "Multicast Addresses for Documentation", 699 RFC 6676, DOI 10.17487/RFC6676, August 2012, 700 . 702 [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, 703 "Special-Purpose IP Address Registries", BCP 153, 704 RFC 6890, DOI 10.17487/RFC6890, April 2013, 705 . 707 Appendix A. Use Case: IPTV 709 IPTV generally includes two categories of service offerings: 711 o Video on Demand (VoD) that unicast video content to receivers. 713 o Multicast live TV broadcast services. 715 Two players intervene in the delivery of this service: 717 o Content Providers, who usually own the contents that is multicast 718 to receivers. Content providers may contractually define an 719 agreement with network providers to deliver contents to receivers. 721 o Network Providers, who provide network connectivity services 722 (e.g., network providers are responsible for carrying multicast 723 flows from head-ends to receivers). 725 Note that some contract agreements prevent a network provider from 726 altering the content as sent by the content provider for various 727 reasons. Under the contract, multicast streams should be delivered 728 unaltered to the requesting users. 730 Many current IPTV contents are likely to remain IPv4-formatted and 731 out of control of the network providers. Additionally, there are 732 numerous legacy receivers (e.g., IPv4-only Set Top Boxes (STB)) that 733 can't be upgraded or be easily replaced to support IPv6. As a 734 consequence, IPv4 service continuity MUST be guaranteed during the 735 transition period, including the delivery of multicast services such 736 as Live TV Broadcasting to users. 738 Appendix B. Deployment Considerations 740 B.1. Other operational Modes 741 B.1.1. MLD Querier with mAFTR Embedded 743 mAFTR can embed the MLD Querier function (as well as the PIMv6 DR) 744 for optimization. When mB4 sends MLD Report message to this mAFTR, 745 the mAFTR should process the MLD Report message that contain 746 IPv4-embedded IPv6 multicast group subscription information then send 747 the corresponding PIMv4 Join message. (Figure 4) 749 +---------+ 750 ---------| mAFTR |--------- 751 MLD |uPrefix64| PIMv4 752 |mPreifx64| 753 +---------+ 755 Figure 4: MLD-PIMv4 Interworking Function 757 Discussions about the location of the mAFTR capability and related 758 ASM or SSM multicast design considerations are out of the scope of 759 this document. 761 B.1.2. mAFTR embedded in DR 763 If mAFTR is the DR of the original IPv4 source, it may simply use the 764 uPrefix64 and mPrefix64 to build the IPv4-embedded IPv6 multicast 765 traffic, the sending of PIMv4 Join message is not necessary. 767 B.2. Older Version of Group Membership management Protocols 769 Given the multiple versions of group membership management protocols, 770 mismatch issues may be raised in the mB4 Function (refer to 771 Section 6.1). 773 If IGMPv2 operates on the IPv4 receivers while MLDv2 operates on the 774 MLD Querier, or if IGMPv3 operates on the IPv4 receivers while MLDv1 775 operates on the MLD Querier, the issue mentioned above will be 776 encountered. To solve this problem, the mB4 SHOULD perform the 777 router portion of IGMP which is of the same as the corresponding MLD 778 version (IGMPv2 as of MLDv1, or IGMPv3 as of MLDv2) operating in the 779 IPv6 domain, then the protocol interaction approach specified in 780 Section 7 of [RFC3376] can be used to exchange signaling messages 781 with the IPv4 receivers on which the different version of IGMP is 782 operating. 784 B.3. Load-Balancing 786 For robustness and load distribution purposes, several nodes in the 787 network can embed the mAFTR function. In such case, the same IPv6 788 prefixes (i.e., mPrefix64 and uPrefix64) and algorithm to build IPv4- 789 embedded IPv6 addresses MUST be configured on those nodes. 791 B.4. RP for IPv4-Embedded IPv6 Multicast Groups 793 For the sake of simplicity, it is RECOMMENDED to configure mAFTR as 794 the RP for the IPv4-embedded IPv6 multicast groups it manages. No 795 registration procedure is required under this configuration. 797 B.5. mAFTR Policy Configuration 799 mAFTR may be configured with a list of IPv4 multicast groups and 800 sources. Only multicast flows bound to the configured addresses 801 should be handled by the mAFTR. Otherwise, packets are silently 802 drooped. 804 B.6. Static vs. Dynamic PIM Triggering 806 To optimize the usage of network resources in current deployments, 807 all multicast streams are conveyed in the core network while only 808 popular ones are continuously conveyed in the aggregation/access 809 network (static mode). Non-popular streams are conveyed in the 810 access network upon request (dynamic mode). Depending on the 811 location of the mAFTR in the network, two modes can be envisaged: 812 static and dynamic. 814 o Static Mode: the mAFTR is configured to instantiate permanent (S6, 815 G6) and (*, G6) entries in its TIB6 using a pre-configured (S4, 816 G4) list. 818 o Dynamic Mode: the instantiation and deletion of (S6, g6) or (*, 819 G6) is triggered by the receipt of PIMv6 messages. 821 Authors' Addresses 823 Jacni Qin 824 Cisco 825 Shanghai 826 China 828 Email: jacni@jacni.com 829 Mohamed Boucadair 830 France Telecom 831 Rennes 35000 832 France 834 Email: mohamed.boucadair@orange.com 836 Christian Jacquenet 837 France Telecom 838 Rennes 35000 839 France 841 Email: christian.jacquenet@orange.com 843 Yiu L. Lee 844 Comcast 845 U.S.A. 847 Email: yiu_lee@cable.comcast.com 848 URI: http://www.comcast.com 850 Qian Wang 851 China Telecom 852 No.118, Xizhimennei 853 Beijing 100035 854 China 856 Phone: +86 10 5855 2177 857 Email: wangqian@ctbri.com.cn