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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-15) exists of draft-ietf-softwire-multicast-prefix-option-11 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment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 J. Qin 5 Expires: July 16, 2017 Cisco 6 C. Jacquenet 7 Orange 8 Y. Lee 9 Comcast 10 Q. Wang 11 China Telecom 12 January 12, 2017 14 Delivery of IPv4 Multicast Services to IPv4 Clients over an IPv6 15 Multicast Network 16 draft-ietf-softwire-dslite-multicast-15 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 16, 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 . . . . . . . . . . . . . . . . . . . . . . . . 10 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 relays information conveyed in IGMP messages by forwarding 194 the corresponding Multicast Listener Discovery (MLD) messages 195 towards the IPv6 network. In addition, the mB4 decapsulates IPv4- 196 in-IPv6 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 MLD Querier, which usually acts as the 305 PIMv6 Designated Router too, receives the MLD Report message and 306 sends the PIMv6 Join message to join the IPv6 multicast distribution 307 tree. It can send either PIMv6 Join (*,G6) in ASM or PIMv6 Join 308 (S6,G6) in SSM to the mAFTR. 310 The mAFTR acts as the IPv6 DR to which the uPrefix64-derived S6 is 311 connected. The mAFTR will receive the source-specific PIMv6 Join 312 message (S6,G6) from the IPv6 multicast network. If the mAFTR is the 313 Rendezvous Point (RP) of G6, it will receive the any-source PIMv6 314 Join message (*,G6) from the IPv6 multicast network. If the mAFTR is 315 not the RP of G6, it will send the PIM Register message to the RP of 316 G6 located in the IPv6 multicast network. For the sake of 317 simplicity, it is recommended to configure the mAFTR as the RP for 318 the IPv4-embedded IPv6 multicast groups it manages; no registration 319 procedure is required under this configuration. 321 When the mAFTR receives the PIMv6 Join message (*,G6), it will 322 extract the IPv4 multicast group address (G4). If the mAFTR is the 323 RP of G4 in the IPv4 multicast network, it will create a (*,G4) entry 324 (if such entry does not already exist) in its own IPv4 multicast 325 routing table. If the mAFTR is not the RP of G4, it will send the 326 corresponding PIMv4 Join message (*,G4) towards the RP of G4 in the 327 IPv4 multicast network. 329 When the mAFTR receives the PIMv6 Join message (S6,G6), it will 330 extract the IPv4 multicast group address (G4) and IPv4 source address 331 (S4) and send the corresponding (S4,G4) PIMv4 Join message directly 332 to the IPv4 source. 334 A branch of the multicast distribution tree is thus constructed, 335 comprising both an IPv4 part (from the mAFTR upstream) and an IPv6 336 part (from mAFTR downstream towards the mB4). 338 The mAFTR advertises the route of uPrefix64 with an IPv6 Interior 339 Gateway Protocol (IGP), so as to represent the IPv4-embedded IPv6 340 source in the IPv6 multicast network, and to allow IPv6 routers to 341 run the Reverse Path Forwarding (RPF) check procedure on incoming 342 multicast traffic. Injecting internal /96 routes is not problematic 343 given the recommendation in [RFC7608] that requires that forwarding 344 processes must be designed to process prefixes of any length up to 345 /128. 347 4.3. Multicast Data Forwarding 349 When the mAFTR receives an IPv4 multicast packet, it will encapsulate 350 the packet into an IPv6 multicast packet using the IPv4-embedded IPv6 351 multicast address as the destination address and an IPv4-embedded 352 IPv6 unicast address as the source address. The encapsulated IPv6 353 multicast packet will be forwarded down the IPv6 multicast 354 distribution tree and the mB4 will eventually receive the packet. 356 The IPv6 multicast network treats the IPv4-in-IPv6 encapsulated 357 multicast packets as native IPv6 multicast packets. The IPv6 358 multicast routers use the outer IPv6 header to make their forwarding 359 decisions. 361 When the mB4 receives the IPv6 multicast packet (to G6) derived by 362 mPrefix64, it decapsulates it and forwards the original IPv4 363 multicast packet to the receivers subscribing to G4. 365 Note: At this point, only IPv4-in-IPv6 encapsulation is defined; 366 however, other types of encapsulation could be defined in the future. 368 5. IPv4/IPv6 Address Mapping 370 5.1. Prefix Assignment 372 A dedicated IPv6 multicast prefix (mPrefix64) is provisioned to the 373 mAFTR and the mB4. The mAFTR and the mB4 use the mPrefix64 to form 374 an IPv6 multicast group address from an IPv4 multicast group address. 375 The mPrefix64 can be of two types: ASM_mPrefix64 (a mPrefix64 used in 376 ASM mode) or SSM_mPrefix64 (a mPrefix64 used in SSM mode). The 377 mPrefix64 MUST be derived from the corresponding IPv6 multicast 378 address space (e.g., the SSM_mPrefix64 must be in the range of 379 multicast address space specified in [RFC4607]). 381 The IPv6 part of the multicast distribution tree can be seen as an 382 extension of the IPv4 part of the multicast distribution tree. The 383 IPv4 source address MUST be mapped to an IPv6 source address. An 384 IPv6 unicast prefix (uPrefix64) is provisioned to the mAFTR and the 385 mB4. The mAFTR and the mB4 use the uPrefix64 to form an IPv6 source 386 address from an IPv4 source address as specified in [RFC6052]. The 387 uPrefix-formed IPv6 source address will represent the original IPv4 388 source in the IPv6 multicast network. The uPrefix64 MUST be derived 389 from the IPv6 unicast address space. 391 The multicast address translation MUST follow the algorithm defined 392 in Section 5.2. 394 The mPrefix64 and uPrefix64 can be configured in the mB4 using a 395 variety of methods, including an out-of-band mechanism, manual 396 configuration, or a dedicated provisioning protocol (e.g., using 397 DHCPv6 [I-D.ietf-softwire-multicast-prefix-option]). 399 The stateless translation mechanism described in Section 5 does not 400 preclude use of Embedded-RP [RFC3956][RFC7371]. 402 5.2. Multicast Address Translation Algorithm 404 IPv4-embedded IPv6 multicast addresses are composed according to the 405 following algorithm: 407 o Concatenate the mPrefix64 96 bits and the 32 bits of the IPv4 408 address to obtain a 128-bit address. 410 The IPv4 multicast addresses are extracted from the IPv4-embedded 411 IPv6 multicast addresses according to the following algorithm: 413 o If the multicast address has a pre-configured mPrefix64, extract 414 the last 32 bits of the IPv6 multicast address. 416 An IPv4 source is represented in the IPv6 realm with its 417 IPv4-converted IPv6 address [RFC6052]. 419 5.3. Textual Representation 421 The embedded IPv4 address in an IPv6 multicast address is included in 422 the last 32 bits; therefore, dotted decimal notation can be used. 424 5.4. Examples 426 Group address mapping example: 428 +---------------------+--------------+----------------------------+ 429 | mPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 430 +---------------------+--------------+----------------------------+ 431 | ff0x::db8:0:0/96 | 233.252.0.1 | ff0x::db8:233.252.0.1 | 432 +---------------------+--------------+----------------------------+ 434 Source address mapping example when a /96 is used: 436 +---------------------+--------------+----------------------------+ 437 | uPrefix64 | IPv4 address | IPv4-Embedded IPv6 address | 438 +---------------------+--------------+----------------------------+ 439 | 2001:db8::/96 | 192.0.2.33 | 2001:db8::192.0.2.33 | 440 +---------------------+--------------+----------------------------+ 442 IPv4 and IPv6 addresses used in this example are derived from the 443 IPv4 and IPv6 blocks reserved for documentation, as per [RFC6676]. 444 The unicast IPv4 address of the above example is derived from the 445 documentation address block defined in [RFC6890]. 447 6. Multicast B4 (mB4) 449 6.1. IGMP-MLD Interworking Function 451 The IGMP-MLD Interworking Function combines the IGMP/MLD Proxying 452 function and the address synthesizing operations. The IGMP/MLD 453 Proxying function is specified in [RFC4605]. The address translation 454 is stateless and MUST follow the address mapping specified in 455 Section 5. 457 The mB4 performs the host portion of the MLD protocol on the upstream 458 interface. The composition of IPv6 membership in this context is 459 constructed through address synthesizing operations and MUST 460 synchronize with the membership database maintained in the IGMP 461 domain. MLD messages are forwarded natively towards the MLD Querier 462 located upstream in the IPv6 network (i.e., the first hop IPv6 463 router). The mB4 also performs the router portion of the IGMP 464 protocol on the downstream interface(s). Refer to [RFC4605] for more 465 details. 467 +----------+ IGMP +-------+ MLD +---------+ 468 | IPv4 |---------| mB4 |---------| MLD | 469 | Receiver | | | | Querier | 470 +----------+ +-------+ +---------+ 472 Figure 2: IGMP-MLD Interworking 474 If SSM is deployed, the mB4 MUST construct the IPv6 source address 475 (or retrieve the IPv4 source address) using the uPrefix64. The mB4 476 MAY create a membership database which associates the IPv4-IPv6 477 multicast groups with the interfaces (e.g., WLAN and Wired Ethernet) 478 facing IPv4 multicast receivers. 480 6.2. Multicast Data Forwarding 482 When the mB4 receives an IPv6 multicast packet, it MUST check the 483 group address and the source address. If the IPv6 multicast group 484 prefix is mPrefix64 and the IPv6 source prefix is uPrefix64, the mB4 485 MUST decapsulate the IPv6 header [RFC2473]; the decapsulated IPv4 486 multicast packet will be forwarded through each relevant interface 487 following standard IPv4 multicast forwarding procedure. Otherwise, 488 the mB4 MUST silently drop the packet. 490 As an illustration, if a packet is received from source 491 2001:db8::192.0.2.33 and needs to be forwarded to group 492 ff3x:20:2001:db8::233.252.0.1, the mB4 decapsulates it into an IPv4 493 multicast packet using 192.0.2.33 as the IPv4 source address and 494 using 233.252.0.1 as the IPv4 destination multicast group. 496 6.3. Fragmentation 498 Encapsulating IPv4 multicast packets into IPv6 multicast packets that 499 will be forwarded by the mAFTR towards the mB4 along the IPv6 500 multicast distribution tree reduces the effective MTU size by the 501 size of an IPv6 header. In this specification, the data flow is 502 unidirectional from the mAFTR to the mB4. The mAFTR MUST fragment 503 the oversized IPv6 packet after the encapsulation into two IPv6 504 packets. The mB4 MUST reassemble the IPv6 packets, decapsulate the 505 IPv6 header, and forward the IPv4 packet to the hosts that have 506 subscribed to the corresponding multicast group. Further 507 considerations about fragmentation issues are documented in 508 [RFC6333]. 510 6.4. Host Built-in mB4 Function 512 If the mB4 function is implemented in the host which is directly 513 connected to an IPv6-only network, the host MUST implement the 514 behaviors specified in Sections 6.1, 6.2, and 6.3. The host MAY 515 optimize the implementation to provide an Application Programming 516 Interface (API) or kernel module to skip the IGMP-MLD Interworking 517 Function. Optimization considerations are out of scope of this 518 specification. 520 6.5. Preserve the Scope 522 When several mPrefix64s are available, if each enclosed IPv4-embedded 523 IPv6 multicast prefix has a distinct scope, the mB4 MUST select the 524 appropriate IPv4-embedded IPv6 multicast prefix whose scope matches 525 the IPv4 multicast address used to synthesize an IPv4-embedded IPv6 526 multicast address (Section 8 of [RFC2365]). 528 The mB4 MAY be configured to not preserve the scope when enforcing 529 the address translation algorithm. 531 Consider that an mB4 is configured with two mPrefix64s 532 ff0e::db8:0:0/96 (Global scope) and ff08::db8:0:0/96 (Organization 533 scope). If the mB4 receives an IGMP report from an IPv4 receiver to 534 subscribe to 233.252.0.1, it checks which mPrefix64 to use in order 535 to preserve the scope of the requested IPv4 multicast group. In this 536 example, given that 233.252.0.1 is intended for global use, the mB4 537 creates the IPv6 multicast group (G6) address using ff0e::db8:0:0/96 538 and the original IPv4 multicast group address (233.252.0.1): 539 ff0e::db8:233.252.0.1. 541 7. Multicast AFTR (mAFTR) 543 7.1. Routing Considerations 545 The mAFTR is responsible for interconnecting the IPv4 multicast 546 distribution tree with the corresponding IPv6 multicast distribution 547 tree. The mAFTR MUST use the uPrefix64 to build the IPv6 source 548 addresses of the multicast group address derived from mPrefix64. In 549 other words, the mAFTR MUST be the multicast source whose address is 550 derived from uPrefix64. 552 The mAFTR MUST advertise the route towards uPrefix64 with the IPv6 553 IGP. This is needed by the IPv6 multicast routers so that they 554 acquire the routing information to discover the source. 556 7.2. Processing PIM Messages 558 The mAFTR MUST interwork PIM Join/Prune messages for (*,G6) and 559 (S6,G6) on their corresponding (*,G4) and (S4,G4). The following 560 text specifies the expected behavior of the mAFTR for PIM Join 561 messages. 563 +---------+ 564 ---------| mAFTR |--------- 565 PIMv6 |uPrefix64| PIMv4 566 |mPrefix64| 567 +---------+ 569 Figure 3: PIMv6-PIMv4 Interworking Function 571 The mAFTR contains two separate Tree Information Bases (TIBs): the 572 IPv4 Tree Information Base (TIB4) and the IPv6 Tree Information Base 573 (TIB6), which are bridged by one IPv4-in-IPv6 virtual interface. It 574 should be noted that TIB implementations may vary (e.g., some may 575 rely upon a single integrated TIB without any virtual interface), but 576 they should follow this specification for the sake of global and 577 functional consistency. 579 When a mAFTR receives a PIMv6 Join message (*,G6) with an IPv6 580 multicast group address (G6) that is derived from the mPrefix64, it 581 MUST check its IPv6 Tree Information Base (TIB6). If there is an 582 entry for this G6 address, it MUST check whether the interface 583 through which the PIMv6 Join message has been received is in the 584 outgoing interface (oif) list. If not, the mAFTR MUST add the 585 interface to the oif list. If there is no entry in the TIB6, the 586 mAFTR MUST create a new entry (*,G6) for the multicast group. 587 Whether or not the IPv4-in-IPv6 virtual interface is set as the 588 incoming interface of the newly created entry is up to the 589 implementation but it should comply with the mAFTR's multicast data 590 forwarding behavior, see Section 7.4. 592 The mAFTR MUST extract the IPv4 multicast group address (G4) from the 593 IPv4-embedded IPv6 multicast address (G6) contained in the PIMv6 Join 594 message. The mAFTR MUST check its IPv4 Tree Information Base (TIB4). 595 If there is an entry for G4, it MUST check whether the IPv4-in-IPv6 596 virtual interface is in the outgoing interface list. If not, the 597 mAFTR MUST add the interface to the oif list. If there is no entry 598 for G4, the mAFTR MUST create a new (*,G4) entry in its TIB4 and 599 initiate the procedure for building the shared tree in the IPv4 600 multicast network without any additional requirement. 602 If the mAFTR receives a source-specific Join message, the (S6,G6) is 603 processed rather than (*,G6). The procedures of processing (S6,G6) 604 and (*,G6) are almost the same. Differences have been detailed in 605 [RFC7761]. 607 7.3. Switching from Shared Tree to Shortest Path Tree 609 When the mAFTR receives the first IPv4 multicast packet, it may 610 extract the source address (S4) from the packet and send an Explicit 611 PIMv4 (S4,G4) Join message directly to S4. The mAFTR switches from 612 the shared Rendezvous Point Tree (RPT) to the Shortest Path Tree 613 (SPT) for G4. 615 For IPv6 multicast routers to switch to the SPT, there is no new 616 requirement. IPv6 multicast routers may send an Explicit PIMv6 Join 617 to the mAFTR once the first (S6,G6) multicast packet arrives from 618 upstream multicast routers. 620 7.4. Multicast Data Forwarding 622 When the mAFTR receives an IPv4 multicast packet, it checks its TIB4 623 to find a matching entry and then forwards the packet to the 624 interface(s) listed in the outgoing interface list. If the IPv4-in- 625 IPv6 virtual interface also belongs to this list, the packet is 626 encapsulated with the mPrefix64-derived and uPrefix64-derived 627 IPv4-embedded IPv6 addresses to form an IPv6 multicast packet 628 [RFC2473]. Then another lookup is made by the mAFTR to find a 629 matching entry in the TIB6. Whether the RPF check for the second 630 lookup is performed or not is up to the implementation and is out of 631 the scope of this document. The IPv6 multicast packet is then 632 forwarded along the IPv6 multicast distribution tree, based upon the 633 outgoing interface list of the matching entry in the TIB6. 635 As an illustration, if a packet is received from source 192.0.2.33 636 and needs to be forwarded to group 233.252.0.1, the mAFTR 637 encapsulates it into an IPv6 multicast packet using 638 ff3x:20:2001:db8::233.252.0.1 as the IPv6 destination multicast group 639 and using 2001:db8::192.0.2.33 as the IPv6 source address. 641 7.5. Scope 643 The Scope field of IPv4-in-IPv6 multicast addresses should be valued 644 accordingly (e.g, to "E" for Global scope) in the deployment 645 environment. This specification does not discuss the scope value 646 that should be used. 648 Nevertheless, when several mPrefix64s are available, if each enclosed 649 IPv4-embedded IPv6 multicast prefix has a distinct scope, the mAFTR 650 MUST select the appropriate IPv4-embedded IPv6 multicast prefix whose 651 scope matches the IPv4 multicast address used to synthesize an 652 IPv4-embedded IPv6 multicast address. 654 An mAFTR MAY be configured to not preserve the scope when enforcing 655 the address translation algorithm. 657 8. Deployment Considerations 659 8.1. Other Operational Modes 661 8.1.1. The MLD Querier is Co-Located with the mAFTR 663 The mAFTR can embed the MLD Querier function (as well as the PIMv6 664 DR) for optimization purposes. When the mB4 sends a MLD Report 665 message to this mAFTR, the mAFTR should process the MLD Report 666 message that contains the IPv4-embedded IPv6 multicast group address 667 and then send the corresponding PIMv4 Join message. (Figure 4) 669 +---------+ 670 ---------| mAFTR |--------- 671 MLD |uPrefix64| PIMv4 672 |mPrefix64| 673 +---------+ 675 Figure 4: MLD-PIMv4 Interworking Function 677 Discussions about the location of the mAFTR capability and related 678 ASM or SSM multicast design considerations are out of the scope of 679 this document. 681 8.1.2. The DR is Co-Located with the mAFTR 683 If the mAFTR is co-located with the DR connected to the original IPv4 684 source, it may simply use the uPrefix64 and mPrefix64 prefixes to 685 build the IPv4-embedded IPv6 multicast packets, and the sending of 686 PIMv4 Join messages becomes unnecessary. 688 8.2. Load Balancing 690 For robustness and load distribution purposes, several nodes in the 691 network can embed the mAFTR function. In such case, the same IPv6 692 prefixes (i.e., mPrefix64 and uPrefix64) and algorithm to build 693 IPv4-embedded IPv6 addresses must be configured on those nodes. 695 8.3. mAFTR Policy Configuration 697 The mAFTR may be configured with a list of IPv4 multicast groups and 698 sources. Only multicast flows bound to the configured addresses 699 should be handled by the mAFTR. Otherwise, packets are silently 700 dropped. 702 8.4. Static vs. Dynamic PIM Triggering 704 To optimize the usage of network resources in current deployments, 705 all multicast streams are conveyed in the core network while only the 706 most popular ones are forwarded in the aggregation/access networks 707 (static mode). Less popular streams are forwarded in the access 708 network upon request (dynamic mode). Depending on the location of 709 the mAFTR in the network, two modes can be envisaged: static and 710 dynamic. 712 Static Mode: the mAFTR is configured to instantiate permanent 713 (S6,G6) and (*,G6) entries in its TIB6 using a pre-configured 714 (S4,G4) list. 716 Dynamic Mode: the instantiation or withdrawal of (S6,G6) or (*,G6) 717 entries is triggered by the receipt of PIMv6 messages. 719 9. Security Considerations 721 Besides multicast scoping considerations (see Section 6.5 and 722 Section 7.5), this document does not introduce any new security 723 concern in addition to what is discussed in Section 5 of [RFC6052], 724 Section 10 of [RFC3810] and Section 6 of [RFC7761]. 726 An mB4 SHOULD be provided with appropriate configuration information 727 to preserve the scope of a multicast message when mapping an IPv4 728 multicast address into an IPv4-embedded IPv6 multicast address and 729 vice versa. 731 9.1. Firewall Configuration 733 The CPE that embeds the mB4 function SHOULD be configured to accept 734 incoming MLD messages and traffic forwarded to multicast groups 735 subscribed by receivers located in the customer premises. 737 10. Acknowledgments 739 The authors would like to thank Dan Wing for his guidance in the 740 early discussions which initiated this work. We also thank Peng Sun, 741 Jie Hu, Qiong Sun, Lizhong Jin, Alain Durand, Dean Cheng, Behcet 742 Sarikaya, Tina Tsou, Rajiv Asati, Xiaohong Deng, and Stig Venaas for 743 their valuable comments. 745 Many thanks to Ian Farrer for the review. 747 Thanks to Zhen Cao, Tim Chown, Francis Dupont, Jouni Korhonen, and 748 Stig Venaas for the directorates review. 750 11. IANA Considerations 752 This document includes no request to IANA. 754 12. References 756 12.1. Normative References 758 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 759 Requirement Levels", BCP 14, RFC 2119, 760 DOI 10.17487/RFC2119, March 1997, 761 . 763 [RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23, 764 RFC 2365, DOI 10.17487/RFC2365, July 1998, 765 . 767 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 768 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 769 December 1998, . 771 [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 772 Thyagarajan, "Internet Group Management Protocol, Version 773 3", RFC 3376, DOI 10.17487/RFC3376, October 2002, 774 . 776 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 777 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 778 DOI 10.17487/RFC3810, June 2004, 779 . 781 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 782 "Internet Group Management Protocol (IGMP) / Multicast 783 Listener Discovery (MLD)-Based Multicast Forwarding 784 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 785 August 2006, . 787 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 788 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 789 . 791 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 792 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 793 DOI 10.17487/RFC6052, October 2010, 794 . 796 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 797 Stack Lite Broadband Deployments Following IPv4 798 Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011, 799 . 801 [RFC7608] Boucadair, M., Petrescu, A., and F. Baker, "IPv6 Prefix 802 Length Recommendation for Forwarding", BCP 198, RFC 7608, 803 DOI 10.17487/RFC7608, July 2015, 804 . 806 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 807 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 808 Multicast - Sparse Mode (PIM-SM): Protocol Specification 809 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 810 2016, . 812 12.2. Informative References 814 [I-D.ietf-softwire-multicast-prefix-option] 815 Boucadair, M., Qin, J., Tsou, T., and X. Deng, "DHCPv6 816 Option for IPv4-Embedded Multicast and Unicast IPv6 817 Prefixes", draft-ietf-softwire-multicast-prefix-option-11 818 (work in progress), June 2016. 820 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 821 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 822 . 824 [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous 825 Point (RP) Address in an IPv6 Multicast Address", 826 RFC 3956, DOI 10.17487/RFC3956, November 2004, 827 . 829 [RFC6676] Venaas, S., Parekh, R., Van de Velde, G., Chown, T., and 830 M. Eubanks, "Multicast Addresses for Documentation", 831 RFC 6676, DOI 10.17487/RFC6676, August 2012, 832 . 834 [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, 835 "Special-Purpose IP Address Registries", BCP 153, 836 RFC 6890, DOI 10.17487/RFC6890, April 2013, 837 . 839 [RFC7371] Boucadair, M. and S. Venaas, "Updates to the IPv6 840 Multicast Addressing Architecture", RFC 7371, 841 DOI 10.17487/RFC7371, September 2014, 842 . 844 [RFC7596] Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I. 845 Farrer, "Lightweight 4over6: An Extension to the Dual- 846 Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596, 847 July 2015, . 849 [RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S., 850 Murakami, T., and T. Taylor, Ed., "Mapping of Address and 851 Port with Encapsulation (MAP-E)", RFC 7597, 852 DOI 10.17487/RFC7597, July 2015, 853 . 855 Appendix A. Use Case: IPTV 857 IPTV generally includes two categories of service offerings: 859 o Video on Demand (VoD) that unicast video content to receivers. 861 o Multicast live TV broadcast services. 863 Two types of provider are involved in the delivery of this service: 865 o Content Providers, who usually own the contents that is multicast 866 to receivers. Content providers may contractually define an 867 agreement with network providers to deliver contents to receivers. 869 o Network Providers, who provide network connectivity services 870 (e.g., network providers are responsible for carrying multicast 871 flows from head-ends to receivers). 873 Note that some contract agreements prevent a network provider from 874 altering the content as sent by the content provider for various 875 reasons. Depending on these contract agreements, multicast streams 876 should be delivered unaltered to the requesting users. 878 Many current IPTV contents are likely to remain IPv4-formatted and 879 out of control of the network providers. Additionally, there are 880 numerous legacy receivers (e.g., IPv4-only Set Top Boxes (STB)) that 881 can't be upgraded or be easily replaced to support IPv6. As a 882 consequence, IPv4 service continuity must be guaranteed during the 883 transition period, including the delivery of multicast services such 884 as Live TV Broadcasting to users. 886 Appendix B. Older Versions of Group Membership Management Protocols 888 Given the multiple versions of group membership management protocols, 889 mismatch issues may arise at the mB4 (refer to Section 6.1). 891 If IGMPv2 operates on the IPv4 receivers while MLDv2 operates on the 892 MLD Querier, or if IGMPv3 operates on the IPv4 receivers while MLDv1 893 operates on the MLD Querier, the version mismatch issue will be 894 encountered. To solve this problem, the mB4 should perform the 895 router portion of IGMP which is similar to the corresponding MLD 896 version (IGMPv2 as of MLDv1, or IGMPv3 as of MLDv2) operating in the 897 IPv6 domain. Then, the protocol interaction approach specified in 898 Section 7 of [RFC3376] can be applied to exchange signaling messages 899 with the IPv4 receivers on which the different version of IGMP is 900 operating. 902 Authors' Addresses 904 Mohamed Boucadair 905 Orange 906 Rennes 35000 907 France 909 Email: mohamed.boucadair@orange.com 911 Jacni 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