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Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-15) exists of draft-ietf-softwire-multicast-prefix-option-12 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Softwire WG M. Boucadair 3 Internet-Draft Orange 4 Intended status: Standards Track C. Qin 5 Expires: July 21, 2017 Cisco 6 C. Jacquenet 7 Orange 8 Y. Lee 9 Comcast 10 Q. Wang 11 China Telecom 12 January 17, 2017 14 Delivery of IPv4 Multicast Services to IPv4 Clients over an IPv6 15 Multicast Network 16 draft-ietf-softwire-dslite-multicast-16 18 Abstract 20 This document specifies a solution for the delivery of IPv4 multicast 21 services to IPv4 clients over an IPv6 multicast network. The 22 solution relies upon a stateless IPv4-in-IPv6 encapsulation scheme 23 and uses an IPv6 multicast distribution tree to deliver IPv4 24 multicast traffic. The solution is particularly useful for the 25 delivery of multicast service offerings to DS-Lite serviced 26 customers. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at http://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on July 21, 2017. 45 Copyright Notice 47 Copyright (c) 2017 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5 67 4.1. IPv4-Embedded IPv6 Prefixes . . . . . . . . . . . . . . . 6 68 4.2. Multicast Distribution Tree Computation . . . . . . . . . 7 69 4.3. Multicast Data Forwarding . . . . . . . . . . . . . . . . 8 70 5. IPv4/IPv6 Address Mapping . . . . . . . . . . . . . . . . . . 8 71 5.1. Prefix Assignment . . . . . . . . . . . . . . . . . . . . 8 72 5.2. Multicast Address Translation Algorithm . . . . . . . . . 9 73 5.3. Textual Representation . . . . . . . . . . . . . . . . . 9 74 5.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 9 75 6. Multicast B4 (mB4) . . . . . . . . . . . . . . . . . . . . . 10 76 6.1. IGMP-MLD Interworking Function . . . . . . . . . . . . . 10 77 6.2. Multicast Data Forwarding . . . . . . . . . . . . . . . . 11 78 6.3. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 11 79 6.4. Host Built-in mB4 Function . . . . . . . . . . . . . . . 11 80 6.5. Preserve the Scope . . . . . . . . . . . . . . . . . . . 12 81 7. Multicast AFTR (mAFTR) . . . . . . . . . . . . . . . . . . . 12 82 7.1. Routing Considerations . . . . . . . . . . . . . . . . . 12 83 7.2. Processing PIM Messages . . . . . . . . . . . . . . . . . 12 84 7.3. Switching from Shared Tree to Shortest Path Tree . . . . 14 85 7.4. Multicast Data Forwarding . . . . . . . . . . . . . . . . 14 86 7.5. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 14 87 8. Deployment Considerations . . . . . . . . . . . . . . . . . . 15 88 8.1. Other Operational Modes . . . . . . . . . . . . . . . . . 15 89 8.1.1. The MLD Querier is Co-Located with the mAFTR . . . . 15 90 8.1.2. The DR is Co-Located with the mAFTR . . . . . . . . . 15 91 8.2. Load Balancing . . . . . . . . . . . . . . . . . . . . . 15 92 8.3. mAFTR Policy Configuration . . . . . . . . . . . . . . . 15 93 8.4. Static vs. Dynamic PIM Triggering . . . . . . . . . . . . 16 94 9. Security Considerations . . . . . . . . . . . . . . . . . . . 16 95 9.1. Firewall Configuration . . . . . . . . . . . . . . . . . 16 96 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 97 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 98 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 99 12.1. Normative References . . . . . . . . . . . . . . . . . . 17 100 12.2. Informative References . . . . . . . . . . . . . . . . . 18 101 Appendix A. Use Case: IPTV . . . . . . . . . . . . . . . . . . . 19 102 Appendix B. Older Versions of Group Membership Management 103 Protocols . . . . . . . . . . . . . . . . . . . . . 19 104 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 106 1. Introduction 108 DS-Lite [RFC6333] is an IPv4 address-sharing technique that enables 109 operators to multiplex public IPv4 addresses while provisioning only 110 IPv6 to users. A typical DS-Lite scenario is the delivery of an IPv4 111 service to an IPv4 user over an IPv6 network (denoted as a 4-6-4 112 scenario). [RFC6333] covers unicast 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 This document describes a stateless translation mechanism that 150 supports either Source Specific Multicast (SSM) or Any Source 151 Multicast (ASM) operation. The recommendation in Section 1 of 152 [RFC4607] is that multicast services use SSM where possible; the 153 operation of the translation mechanism is also simplified when SSM is 154 used, e.g., considerations for placement of the IPv6 the Rendezvous 155 Point (RP) are no longer relevant. 157 1.1. Requirements Language 159 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 160 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 161 document are to be interpreted as described in RFC 2119 [RFC2119]. 163 2. Terminology 165 This document makes use of the following terms: 167 IPv4-embedded IPv6 address: an IPv6 address which embeds a 32-bit- 168 encoded IPv4 address. An IPv4-embedded IPv6 address can be 169 unicast or multicast. 171 mPrefix64: a dedicated multicast IPv6 prefix for constructing 172 IPv4-embedded IPv6 multicast addresses. mPrefix64 can be of two 173 types: ASM_mPrefix64 used in Any Source Multicast (ASM) mode or 174 SSM_mPrefix64 used in Source Specific Multicast (SSM) mode 175 [RFC4607]. The size of this prefix is /96. 177 Note: "64" is used as an abbreviation for IPv6-IPv4 178 interconnection. 180 uPrefix64: a dedicated IPv6 unicast prefix for constructing 181 IPv4-embedded IPv6 unicast addresses [RFC6052]. This prefix may 182 be either the Well-Known Prefix (i.e., 64:ff9b::/96) or a Network- 183 Specific Prefix (NSP). 185 Multicast AFTR (mAFTR): a functional entity which supports an 186 IPv4-IPv6 multicast interworking function (refer to Figure 3). It 187 receives and encapsulates the IPv4 multicast packets into IPv4-in- 188 IPv6 packets. Also, it behaves as the corresponding IPv6 189 multicast source for the encapsulated IPv4-in-IPv6 packets. 191 Multicast Basic Bridging BroadBand (mB4): a functional entity which 192 supports an IGMP-MLD interworking function (refer to Section 6.1) 193 that translates the IGMP messages into the corresponding Multicast 194 Listener Discovery (MLD) messages, and sends the MLD messages to 195 the IPv6 network. In addition, the mB4 decapsulates IPv4-in-IPv6 196 multicast packets. 198 PIMv4: refers to Protocol Independent Multicast (PIM) when deployed 199 in an IPv4 infrastructure (i.e., IPv4 transport capabilities are 200 used to exchange PIM messages). 202 PIMv6: refers to PIM when deployed in an IPv6 infrastructure (i.e., 203 IPv6 transport capabilities are used to exchange PIM messages). 205 Host portion of the MLD protocol: refers to the part of MLD that 206 applies to all multicast address listeners (Section 6 of 207 [RFC3810]). As a reminder, MLD specifies separate behaviors for 208 multicast address listeners (i.e., hosts or routers that listen to 209 multicast packets) and multicast routers. 211 Router portion of the IGMP protocol: refers to the part of IGMP that 212 is performed by multicast routers (Section 6 of [RFC3376]). 214 3. Scope 216 This document focuses only on the subscription to IPv4 multicast 217 groups and the delivery of IPv4-formatted content to IPv4 receivers 218 over an IPv6-only network. In particular, only the following case is 219 covered: 221 IPv4 receivers access IPv4 multicast contents over IPv6-only 222 multicast-enabled networks. 224 This document does not cover the source/receiver heuristics, where 225 IPv4 receivers can also behave as IPv4 multicast sources. This 226 document assumes that hosts behind the mB4 are IPv4 multicast 227 receivers only. Also, the document covers host built-in mB4 228 function. 230 4. Solution Overview 232 In the DS-Lite specification [RFC6333], an IPv4-in-IPv6 tunnel is 233 used to carry bidirectional IPv4 unicast traffic between a B4 and an 234 AFTR. The solution specified in this document provides an IPv4-in- 235 IPv6 encapsulation scheme to deliver unidirectional IPv4 multicast 236 traffic from an mAFTR to an mB4. 238 An overview of the solution is provided in this section which is 239 intended as an introduction to how it works, but is not normative. 240 For the normative specifications of the two new functional elements: 241 mB4 and mAFTR (Figure 1), refer to Sections 6 and 7. 243 ------------ 244 / \ 245 | IPv4 network | 246 \ / 247 ------------ 248 IPv4 multicast : | ^ PIMv4 Join 249 v | : 250 +-------------+ 251 | mAFTR | 252 +-------------+ 253 IPv6 multicast |:| | ^ PIMv6 Join (PIMv6 254 (IPv4 embedded) |:| | : routers in between) 255 ------------ 256 / \ 257 | IPv6 network | 258 \ / 259 ------------ 260 |:| | ^ MLD Report 261 |v| | : 262 +-----------+ 263 | mB4 | 264 +-----------+ 265 IPv4 multicast : | ^ IGMP Report 266 v | : 267 +-----------+ 268 | IPv4 | 269 | receiver | 270 +-----------+ 272 Figure 1: Functional Architecture 274 4.1. IPv4-Embedded IPv6 Prefixes 276 In order to map the addresses of IPv4 multicast traffic with IPv6 277 multicast addresses, an IPv6 multicast prefix (mPrefix64) and an IPv6 278 unicast prefix (uPrefix64) are provided to the mAFTR and the mB4 279 elements, both of which contribute to the computation and the 280 maintenance of the IPv6 multicast distribution tree that extends the 281 IPv4 multicast distribution tree into the IPv6 multicast network. 282 The IPv4/IPv6 address mapping is stateless. 284 The mAFTR and the mB4 use mPrefix64 to convert an IPv4 multicast 285 address (G4) into an IPv4-embedded IPv6 multicast address (G6). The 286 mAFTR and the mB4 use uPrefix64 to convert an IPv4 source address 287 (S4) into an IPv4-embedded IPv6 address (S6). The mAFTR and the mB4 288 must use the same mPrefix64 and uPrefix64, and also run the same 289 algorithm for building IPv4-embedded IPv6 addresses. Refer to 290 Section 5 for more details about the address mapping. 292 4.2. Multicast Distribution Tree Computation 294 When an IPv4 receiver connected to the device that embeds the mB4 295 capability wants to subscribe to an IPv4 multicast group, it sends an 296 IGMP Report message towards the mB4. The mB4 creates the IPv6 297 multicast group (G6) address using mPrefix64 and the original IPv4 298 multicast group address. If the receiver sends a source-specific 299 IGMPv3 Report message, the mB4 will create the IPv6 source address 300 (S6) using uPrefix64 and the original IPv4 source address. 302 The mB4 uses the G6 (and both S6 and G6 in SSM) to create the 303 corresponding MLD Report message. The mB4 sends the Report message 304 towards the IPv6 network. The PIMv6 Designated Router receives the 305 MLD Report message and sends the PIMv6 Join message to join the IPv6 306 multicast distribution tree. It can send either PIMv6 Join (*,G6) in 307 ASM or PIMv6 Join (S6,G6) in SSM to the mAFTR. 309 The mAFTR acts as the IPv6 DR to which the uPrefix64-derived S6 is 310 connected. The mAFTR will receive the source-specific PIMv6 Join 311 message (S6,G6) from the IPv6 multicast network. If the mAFTR is the 312 Rendezvous Point (RP) of G6, it will receive the any-source PIMv6 313 Join message (*,G6) from the IPv6 multicast network. If the mAFTR is 314 not the RP of G6, it will send the PIM Register message to the RP of 315 G6 located in the IPv6 multicast network. For the sake of 316 simplicity, it is recommended to configure the mAFTR as the RP for 317 the IPv4-embedded IPv6 multicast groups it manages; no registration 318 procedure is required under this configuration. 320 When the mAFTR receives the PIMv6 Join message (*,G6), it will 321 extract the IPv4 multicast group address (G4). If the mAFTR is the 322 RP of G4 in the IPv4 multicast network, it will create a (*,G4) entry 323 (if such entry does not already exist) in its own IPv4 multicast 324 routing table. If the mAFTR is not the RP of G4, it will send the 325 corresponding PIMv4 Join message (*,G4) towards the RP of G4 in the 326 IPv4 multicast network. 328 When the mAFTR receives the PIMv6 Join message (S6,G6), it will 329 extract the IPv4 multicast group address (G4) and IPv4 source address 330 (S4) and send the corresponding (S4,G4) PIMv4 Join message directly 331 to the IPv4 source. 333 A branch of the multicast distribution tree is thus constructed, 334 comprising both an IPv4 part (from the mAFTR upstream) and an IPv6 335 part (from mAFTR downstream towards the mB4). 337 The mAFTR advertises the route of uPrefix64 with an IPv6 Interior 338 Gateway Protocol (IGP), so as to represent the IPv4-embedded IPv6 339 source in the IPv6 multicast network, and to allow IPv6 routers to 340 run the Reverse Path Forwarding (RPF) check procedure on incoming 341 multicast traffic. Injecting internal /96 routes is not problematic 342 given the recommendation in [RFC7608] that requires that forwarding 343 processes must be designed to process prefixes of any length up to 344 /128. 346 4.3. Multicast Data Forwarding 348 When the mAFTR receives an IPv4 multicast packet, it will encapsulate 349 the packet into an IPv6 multicast packet using the IPv4-embedded IPv6 350 multicast address as the destination address and an IPv4-embedded 351 IPv6 unicast address as the source address. The encapsulated IPv6 352 multicast packet will be forwarded down the IPv6 multicast 353 distribution tree and the mB4 will eventually receive the packet. 355 The IPv6 multicast network treats the IPv4-in-IPv6 encapsulated 356 multicast packets as native IPv6 multicast packets. The IPv6 357 multicast routers use the outer IPv6 header to make their forwarding 358 decisions. 360 When the mB4 receives the IPv6 multicast packet (to G6) derived by 361 mPrefix64, it decapsulates it and forwards the original IPv4 362 multicast packet to the receivers subscribing to G4. 364 Note: At this point, only IPv4-in-IPv6 encapsulation is defined; 365 however, other types of encapsulation could be defined in the future. 367 5. IPv4/IPv6 Address Mapping 369 5.1. Prefix Assignment 371 A dedicated IPv6 multicast prefix (mPrefix64) is provisioned to the 372 mAFTR and the mB4. The mAFTR and the mB4 use the mPrefix64 to form 373 an IPv6 multicast group address from an IPv4 multicast group address. 374 The mPrefix64 can be of two types: ASM_mPrefix64 (a mPrefix64 used in 375 ASM mode) or SSM_mPrefix64 (a mPrefix64 used in SSM mode). The 376 mPrefix64 MUST be derived from the corresponding IPv6 multicast 377 address space (e.g., the SSM_mPrefix64 must be in the range of 378 multicast address space specified in [RFC4607]). 380 The IPv6 part of the multicast distribution tree can be seen as an 381 extension of the IPv4 part of the multicast distribution tree. The 382 IPv4 source address MUST be mapped to an IPv6 source address. An 383 IPv6 unicast prefix (uPrefix64) is provisioned to the mAFTR and the 384 mB4. The mAFTR and the mB4 use the uPrefix64 to form an IPv6 source 385 address from an IPv4 source address as specified in [RFC6052]. The 386 uPrefix-formed IPv6 source address will represent the original IPv4 387 source in the IPv6 multicast network. The uPrefix64 MUST be derived 388 from the IPv6 unicast address space. 390 The multicast address translation MUST follow the algorithm defined 391 in Section 5.2. 393 The mPrefix64 and uPrefix64 can be configured in the mB4 using a 394 variety of methods, including an out-of-band mechanism, manual 395 configuration, or a dedicated provisioning protocol (e.g., using 396 DHCPv6 [I-D.ietf-softwire-multicast-prefix-option]). 398 The stateless translation mechanism described in Section 5 does not 399 preclude use of Embedded-RP [RFC3956][RFC7371]. 401 5.2. Multicast Address Translation Algorithm 403 IPv4-embedded IPv6 multicast addresses are composed according to the 404 following algorithm: 406 o Concatenate the mPrefix64 96 bits and the 32 bits of the IPv4 407 address to obtain a 128-bit address. 409 The IPv4 multicast addresses are extracted from the IPv4-embedded 410 IPv6 multicast addresses according to the following algorithm: 412 o If the multicast address has a pre-configured mPrefix64, extract 413 the last 32 bits of the IPv6 multicast address. 415 An IPv4 source is represented in the IPv6 realm with its 416 IPv4-converted IPv6 address [RFC6052]. 418 5.3. Textual Representation 420 The embedded IPv4 address in an IPv6 multicast address is included in 421 the last 32 bits; therefore, dotted decimal notation can be used. 423 5.4. Examples 424 Group address mapping example: 426 +---------------------+--------------+----------------------------+ 427 | mPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 428 +---------------------+--------------+----------------------------+ 429 | ff0x::db8:0:0/96 | 233.252.0.1 | ff0x::db8:233.252.0.1 | 430 +---------------------+--------------+----------------------------+ 432 Source address mapping example when a /96 is used: 434 +---------------------+--------------+----------------------------+ 435 | uPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 436 +---------------------+--------------+----------------------------+ 437 | 2001:db8::/96 | 192.0.2.33 | 2001:db8::192.0.2.33 | 438 +---------------------+--------------+----------------------------+ 440 IPv4 and IPv6 addresses used in this example are derived from the 441 IPv4 and IPv6 blocks reserved for documentation, as per [RFC6676]. 442 The unicast IPv4 address of the above example is derived from the 443 documentation address block defined in [RFC6890]. 445 6. Multicast B4 (mB4) 447 6.1. IGMP-MLD Interworking Function 449 The IGMP-MLD Interworking Function combines the IGMP/MLD Proxying 450 function and the address synthesizing operations. The IGMP/MLD 451 Proxying function is specified in [RFC4605]. The address translation 452 is stateless and MUST follow the address mapping specified in 453 Section 5. 455 The mB4 performs the host portion of the MLD protocol on the upstream 456 interface. The composition of IPv6 membership in this context is 457 constructed through address synthesizing operations and MUST 458 synchronize with the membership database maintained in the IGMP 459 domain. MLD messages are sent natively to the directly connected 460 IPv6 multicast routers (it will be processed by the PIM DR). The mB4 461 also performs the router portion of the IGMP protocol on the 462 downstream interface(s). Refer to [RFC4605] for more details. 464 +----------+ IGMP +-------+ MLD +---------+ 465 | IPv4 |---------| mB4 |---------| PIM | 466 | Receiver | | | | DR | 467 +----------+ +-------+ +---------+ 469 Figure 2: IGMP-MLD Interworking 471 If SSM is deployed, the mB4 MUST construct the IPv6 source address 472 (or retrieve the IPv4 source address) using the uPrefix64. The mB4 473 MAY create a membership database which associates the IPv4-IPv6 474 multicast groups with the interfaces (e.g., WLAN and Wired Ethernet) 475 facing IPv4 multicast receivers. 477 6.2. Multicast Data Forwarding 479 When the mB4 receives an IPv6 multicast packet, it MUST check the 480 group address and the source address. If the IPv6 multicast group 481 prefix is mPrefix64 and the IPv6 source prefix is uPrefix64, the mB4 482 MUST decapsulate the IPv6 header [RFC2473]; the decapsulated IPv4 483 multicast packet will be forwarded through each relevant interface 484 following standard IPv4 multicast forwarding procedure. Otherwise, 485 the mB4 MUST silently drop the packet. 487 As an illustration, if a packet is received from source 488 2001:db8::192.0.2.33 and needs to be forwarded to group 489 ff3x:20:2001:db8::233.252.0.1, the mB4 decapsulates it into an IPv4 490 multicast packet using 192.0.2.33 as the IPv4 source address and 491 using 233.252.0.1 as the IPv4 destination multicast group. 493 6.3. Fragmentation 495 Encapsulating IPv4 multicast packets into IPv6 multicast packets that 496 will be forwarded by the mAFTR towards the mB4 along the IPv6 497 multicast distribution tree reduces the effective MTU size by the 498 size of an IPv6 header. In this specification, the data flow is 499 unidirectional from the mAFTR to the mB4. The mAFTR MUST fragment 500 the oversized IPv6 packet after the encapsulation into two IPv6 501 packets. The mB4 MUST reassemble the IPv6 packets, decapsulate the 502 IPv6 header, and forward the IPv4 packet to the hosts that have 503 subscribed to the corresponding multicast group. Further 504 considerations about fragmentation issues are documented in 505 [RFC6333]. 507 6.4. Host Built-in mB4 Function 509 If the mB4 function is implemented in the host which is directly 510 connected to an IPv6-only network, the host MUST implement the 511 behaviors specified in Sections 6.1, 6.2, and 6.3. The host MAY 512 optimize the implementation to provide an Application Programming 513 Interface (API) or kernel module to skip the IGMP-MLD Interworking 514 Function. Optimization considerations are out of scope of this 515 specification. 517 6.5. Preserve the Scope 519 When several mPrefix64s are available, if each enclosed IPv4-embedded 520 IPv6 multicast prefix has a distinct scope, the mB4 MUST select the 521 appropriate IPv4-embedded IPv6 multicast prefix whose scope matches 522 the IPv4 multicast address used to synthesize an IPv4-embedded IPv6 523 multicast address (Section 8 of [RFC2365]). 525 The mB4 MAY be configured to not preserve the scope when enforcing 526 the address translation algorithm. 528 Consider that an mB4 is configured with two mPrefix64s 529 ff0e::db8:0:0/96 (Global scope) and ff08::db8:0:0/96 (Organization 530 scope). If the mB4 receives an IGMP report from an IPv4 receiver to 531 subscribe to 233.252.0.1, it checks which mPrefix64 to use in order 532 to preserve the scope of the requested IPv4 multicast group. In this 533 example, given that 233.252.0.1 is intended for global use, the mB4 534 creates the IPv6 multicast group (G6) address using ff0e::db8:0:0/96 535 and the original IPv4 multicast group address (233.252.0.1): 536 ff0e::db8:233.252.0.1. 538 7. Multicast AFTR (mAFTR) 540 7.1. Routing Considerations 542 The mAFTR is responsible for interconnecting the IPv4 multicast 543 distribution tree with the corresponding IPv6 multicast distribution 544 tree. The mAFTR MUST use the uPrefix64 to build the IPv6 source 545 addresses of the multicast group address derived from mPrefix64. In 546 other words, the mAFTR MUST be the multicast source whose address is 547 derived from uPrefix64. 549 The mAFTR MUST advertise the route towards uPrefix64 with the IPv6 550 IGP. This is needed by the IPv6 multicast routers so that they 551 acquire the routing information to discover the source. 553 7.2. Processing PIM Messages 555 The mAFTR MUST interwork PIM Join/Prune messages for (*,G6) and 556 (S6,G6) on their corresponding (*,G4) and (S4,G4). The following 557 text specifies the expected behavior of the mAFTR for PIM Join 558 messages. 560 +---------+ 561 ---------| mAFTR |--------- 562 PIMv6 |uPrefix64| PIMv4 563 |mPrefix64| 564 +---------+ 566 Figure 3: PIMv6-PIMv4 Interworking Function 568 The mAFTR contains two separate Tree Information Bases (TIBs): the 569 IPv4 Tree Information Base (TIB4) and the IPv6 Tree Information Base 570 (TIB6), which are bridged by one IPv4-in-IPv6 virtual interface. It 571 should be noted that TIB implementations may vary (e.g., some may 572 rely upon a single integrated TIB without any virtual interface), but 573 they should follow this specification for the sake of global and 574 functional consistency. 576 When an mAFTR receives a PIMv6 Join message (*,G6) with an IPv6 577 multicast group address (G6) that is derived from the mPrefix64, it 578 MUST check its IPv6 Tree Information Base (TIB6). If there is an 579 entry for this G6 address, it MUST check whether the interface 580 through which the PIMv6 Join message has been received is in the 581 outgoing interface (oif) list. If not, the mAFTR MUST add the 582 interface to the oif list. If there is no entry in the TIB6, the 583 mAFTR MUST create a new entry (*,G6) for the multicast group. 584 Whether or not the IPv4-in-IPv6 virtual interface is set as the 585 incoming interface of the newly created entry is up to the 586 implementation but it should comply with the mAFTR's multicast data 587 forwarding behavior, see Section 7.4. 589 The mAFTR MUST extract the IPv4 multicast group address (G4) from the 590 IPv4-embedded IPv6 multicast address (G6) contained in the PIMv6 Join 591 message. The mAFTR MUST check its IPv4 Tree Information Base (TIB4). 592 If there is an entry for G4, it MUST check whether the IPv4-in-IPv6 593 virtual interface is in the outgoing interface list. If not, the 594 mAFTR MUST add the interface to the oif list. If there is no entry 595 for G4, the mAFTR MUST create a new (*,G4) entry in its TIB4 and 596 initiate the procedure for building the shared tree in the IPv4 597 multicast network without any additional requirement. 599 If the mAFTR receives a source-specific Join message, the (S6,G6) is 600 processed rather than (*,G6). The procedures of processing (S6,G6) 601 and (*,G6) are almost the same. Differences have been detailed in 602 [RFC7761]. 604 7.3. Switching from Shared Tree to Shortest Path Tree 606 When the mAFTR receives the first IPv4 multicast packet, it may 607 extract the source address (S4) from the packet and send an Explicit 608 PIMv4 (S4,G4) Join message directly to S4. The mAFTR switches from 609 the shared Rendezvous Point Tree (RPT) to the Shortest Path Tree 610 (SPT) for G4. 612 For IPv6 multicast routers to switch to the SPT, there is no new 613 requirement. IPv6 multicast routers may send an Explicit PIMv6 Join 614 to the mAFTR once the first (S6,G6) multicast packet arrives from 615 upstream multicast routers. 617 7.4. Multicast Data Forwarding 619 When the mAFTR receives an IPv4 multicast packet, it checks its TIB4 620 to find a matching entry and then forwards the packet to the 621 interface(s) listed in the outgoing interface list. If the IPv4-in- 622 IPv6 virtual interface also belongs to this list, the packet is 623 encapsulated with the mPrefix64-derived and uPrefix64-derived 624 IPv4-embedded IPv6 addresses to form an IPv6 multicast packet 625 [RFC2473]. Then another lookup is made by the mAFTR to find a 626 matching entry in the TIB6. Whether the RPF check for the second 627 lookup is performed or not is up to the implementation and is out of 628 the scope of this document. The IPv6 multicast packet is then 629 forwarded along the IPv6 multicast distribution tree, based upon the 630 outgoing interface list of the matching entry in the TIB6. 632 As an illustration, if a packet is received from source 192.0.2.33 633 and needs to be forwarded to group 233.252.0.1, the mAFTR 634 encapsulates it into an IPv6 multicast packet using 635 ff3x:20:2001:db8::233.252.0.1 as the IPv6 destination multicast group 636 and using 2001:db8::192.0.2.33 as the IPv6 source address. 638 7.5. Scope 640 The Scope field of IPv4-in-IPv6 multicast addresses should be valued 641 accordingly (e.g, to "E" for Global scope) in the deployment 642 environment. This specification does not discuss the scope value 643 that should be used. 645 Nevertheless, when several mPrefix64s are available, if each enclosed 646 IPv4-embedded IPv6 multicast prefix has a distinct scope, the mAFTR 647 MUST select the appropriate IPv4-embedded IPv6 multicast prefix whose 648 scope matches the IPv4 multicast address used to synthesize an 649 IPv4-embedded IPv6 multicast address. 651 An mAFTR MAY be configured to not preserve the scope when enforcing 652 the address translation algorithm. 654 8. Deployment Considerations 656 8.1. Other Operational Modes 658 8.1.1. The MLD Querier is Co-Located with the mAFTR 660 The mAFTR can embed the MLD Querier function (as well as the PIMv6 661 DR) for optimization purposes. When the mB4 sends a MLD Report 662 message to this mAFTR, the mAFTR should process the MLD Report 663 message that contains the IPv4-embedded IPv6 multicast group address 664 and then send the corresponding PIMv4 Join message (Figure 4). 666 +---------+ 667 ---------| mAFTR |--------- 668 MLD |uPrefix64| PIMv4 669 |mPrefix64| 670 +---------+ 672 Figure 4: MLD-PIMv4 Interworking Function 674 Discussions about the location of the mAFTR capability and related 675 ASM or SSM multicast design considerations are out of the scope of 676 this document. 678 8.1.2. The DR is Co-Located with the mAFTR 680 If the mAFTR is co-located with the DR connected to the original IPv4 681 source, it may simply use the uPrefix64 and mPrefix64 prefixes to 682 build the IPv4-embedded IPv6 multicast packets, and the sending of 683 PIMv4 Join messages becomes unnecessary. 685 8.2. Load Balancing 687 For robustness and load distribution purposes, several nodes in the 688 network can embed the mAFTR function. In such case, the same IPv6 689 prefixes (i.e., mPrefix64 and uPrefix64) and algorithm to build 690 IPv4-embedded IPv6 addresses must be configured on those nodes. 692 8.3. mAFTR Policy Configuration 694 The mAFTR may be configured with a list of IPv4 multicast groups and 695 sources. Only multicast flows bound to the configured addresses 696 should be handled by the mAFTR. Otherwise, packets are silently 697 dropped. 699 8.4. Static vs. Dynamic PIM Triggering 701 To optimize the usage of network resources in current deployments, 702 all multicast streams are conveyed in the core network while only the 703 most popular ones are forwarded in the aggregation/access networks 704 (static mode). Less popular streams are forwarded in the access 705 network upon request (dynamic mode). Depending on the location of 706 the mAFTR in the network, two modes can be envisaged: static and 707 dynamic. 709 Static Mode: the mAFTR is configured to instantiate permanent 710 (S6,G6) and (*,G6) entries in its TIB6 using a pre-configured 711 (S4,G4) list. 713 Dynamic Mode: the instantiation or withdrawal of (S6,G6) or (*,G6) 714 entries is triggered by the receipt of PIMv6 messages. 716 9. Security Considerations 718 Besides multicast scoping considerations (see Section 6.5 and 719 Section 7.5), this document does not introduce any new security 720 concern in addition to what is discussed in Section 5 of [RFC6052], 721 Section 10 of [RFC3810] and Section 6 of [RFC7761]. 723 An mB4 SHOULD be provided with appropriate configuration information 724 to preserve the scope of a multicast message when mapping an IPv4 725 multicast address into an IPv4-embedded IPv6 multicast address and 726 vice versa. 728 9.1. Firewall Configuration 730 The CPE that embeds the mB4 function SHOULD be configured to accept 731 incoming MLD messages and traffic forwarded to multicast groups 732 subscribed by receivers located in the customer premises. 734 10. Acknowledgments 736 The authors would like to thank Dan Wing for his guidance in the 737 early discussions which initiated this work. We also thank Peng Sun, 738 Jie Hu, Qiong Sun, Lizhong Jin, Alain Durand, Dean Cheng, Behcet 739 Sarikaya, Tina Tsou, Rajiv Asati, Xiaohong Deng, and Stig Venaas for 740 their valuable comments. 742 Many thanks to Ian Farrer for the review. 744 Thanks to Zhen Cao, Tim Chown, Francis Dupont, Jouni Korhonen, and 745 Stig Venaas for the directorates review. 747 11. IANA Considerations 749 This document includes no request to IANA. 751 12. References 753 12.1. Normative References 755 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 756 Requirement Levels", BCP 14, RFC 2119, 757 DOI 10.17487/RFC2119, March 1997, 758 . 760 [RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23, 761 RFC 2365, DOI 10.17487/RFC2365, July 1998, 762 . 764 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 765 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 766 December 1998, . 768 [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 769 Thyagarajan, "Internet Group Management Protocol, Version 770 3", RFC 3376, DOI 10.17487/RFC3376, October 2002, 771 . 773 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 774 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 775 DOI 10.17487/RFC3810, June 2004, 776 . 778 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 779 "Internet Group Management Protocol (IGMP) / Multicast 780 Listener Discovery (MLD)-Based Multicast Forwarding 781 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 782 August 2006, . 784 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 785 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 786 . 788 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 789 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 790 DOI 10.17487/RFC6052, October 2010, 791 . 793 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 794 Stack Lite Broadband Deployments Following IPv4 795 Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011, 796 . 798 [RFC7608] Boucadair, M., Petrescu, A., and F. Baker, "IPv6 Prefix 799 Length Recommendation for Forwarding", BCP 198, RFC 7608, 800 DOI 10.17487/RFC7608, July 2015, 801 . 803 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 804 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 805 Multicast - Sparse Mode (PIM-SM): Protocol Specification 806 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 807 2016, . 809 12.2. Informative References 811 [I-D.ietf-softwire-multicast-prefix-option] 812 Boucadair, M., Qin, J., Tsou, T., and X. Deng, "DHCPv6 813 Option for IPv4-Embedded Multicast and Unicast IPv6 814 Prefixes", draft-ietf-softwire-multicast-prefix-option-12 815 (work in progress), January 2017. 817 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 818 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 819 . 821 [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous 822 Point (RP) Address in an IPv6 Multicast Address", 823 RFC 3956, DOI 10.17487/RFC3956, November 2004, 824 . 826 [RFC6676] Venaas, S., Parekh, R., Van de Velde, G., Chown, T., and 827 M. Eubanks, "Multicast Addresses for Documentation", 828 RFC 6676, DOI 10.17487/RFC6676, August 2012, 829 . 831 [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, 832 "Special-Purpose IP Address Registries", BCP 153, 833 RFC 6890, DOI 10.17487/RFC6890, April 2013, 834 . 836 [RFC7371] Boucadair, M. and S. Venaas, "Updates to the IPv6 837 Multicast Addressing Architecture", RFC 7371, 838 DOI 10.17487/RFC7371, September 2014, 839 . 841 [RFC7596] Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I. 842 Farrer, "Lightweight 4over6: An Extension to the Dual- 843 Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596, 844 July 2015, . 846 [RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S., 847 Murakami, T., and T. Taylor, Ed., "Mapping of Address and 848 Port with Encapsulation (MAP-E)", RFC 7597, 849 DOI 10.17487/RFC7597, July 2015, 850 . 852 Appendix A. Use Case: IPTV 854 IPTV generally includes two categories of service offerings: 856 o Video on Demand (VoD) that unicast video content to receivers. 858 o Multicast live TV broadcast services. 860 Two types of provider are involved in the delivery of this service: 862 o Content Providers, who usually own the contents that is multicast 863 to receivers. Content providers may contractually define an 864 agreement with network providers to deliver contents to receivers. 866 o Network Providers, who provide network connectivity services 867 (e.g., network providers are responsible for carrying multicast 868 flows from head-ends to receivers). 870 Note that some contract agreements prevent a network provider from 871 altering the content as sent by the content provider for various 872 reasons. Depending on these contract agreements, multicast streams 873 should be delivered unaltered to the requesting users. 875 Many current IPTV contents are likely to remain IPv4-formatted and 876 out of control of the network providers. Additionally, there are 877 numerous legacy receivers (e.g., IPv4-only Set Top Boxes (STB)) that 878 can't be upgraded or be easily replaced to support IPv6. As a 879 consequence, IPv4 service continuity must be guaranteed during the 880 transition period, including the delivery of multicast services such 881 as Live TV Broadcasting to users. 883 Appendix B. Older Versions of Group Membership Management Protocols 885 Given the multiple versions of group membership management protocols, 886 mismatch issues may arise at the mB4 (refer to Section 6.1). 888 If IGMPv2 operates on the IPv4 receivers while MLDv2 operates on the 889 MLD Querier, or if IGMPv3 operates on the IPv4 receivers while MLDv1 890 operates on the MLD Querier, the version mismatch issue will be 891 encountered. To solve this problem, the mB4 should perform the 892 router portion of IGMP which is similar to the corresponding MLD 893 version (IGMPv2 as of MLDv1, or IGMPv3 as of MLDv2) operating in the 894 IPv6 domain. Then, the protocol interaction approach specified in 895 Section 7 of [RFC3376] can be applied to exchange signaling messages 896 with the IPv4 receivers on which the different version of IGMP is 897 operating. 899 Noet that the support of IPv4 SSM requires to enable MLDv2 in the 900 IPv6 network. 902 Authors' Addresses 904 Mohamed Boucadair 905 Orange 906 Rennes 35000 907 France 909 Email: mohamed.boucadair@orange.com 911 Chao Qin 912 Cisco 913 Shanghai 914 P.R. China 916 Email: jacni@jacni.com 918 Christian Jacquenet 919 Orange 920 Rennes 35000 921 France 923 Email: christian.jacquenet@orange.com 925 Yiu L. Lee 926 Comcast 927 United States of America 929 Email: yiu_lee@cable.comcast.com 930 URI: http://www.comcast.com 931 Qian Wang 932 China Telecom 933 P.R. China 935 Phone: +86 10 58502462 936 Email: 13301168516@189.cn