Internet Engineering Task Force (IETF) M. Boucadair
Request for Comments: 8114 Orange
Category: Standards Track C. Qin
ISSN: 2070-1721 Cisco
C. Jacquenet
Orange
Y. Lee
Comcast
Q. Wang
China Telecom
March 2017
Internet Engineering Task Force (IETF) M. Boucadair
Request for Comments: 8114 Orange
Category: Standards Track C. Qin
ISSN: 2070-1721 Cisco
C. Jacquenet
Orange
Y. Lee
Comcast
Q. Wang
China Telecom
March 2017
Delivery of IPv4 Multicast Services to IPv4 Clients over an IPv6 Multicast Network
通过IPv6多播网络向IPv4客户端提供IPv4多播服务
Abstract
摘要
This document specifies a solution for the delivery of IPv4 multicast services to IPv4 clients over an IPv6 multicast network. The solution relies upon a stateless IPv4-in-IPv6 encapsulation scheme and uses an IPv6 multicast distribution tree to deliver IPv4 multicast traffic. The solution is particularly useful for the delivery of multicast service offerings to customers serviced by Dual-Stack Lite (DS-Lite).
本文档指定了通过IPv6多播网络向IPv4客户端提供IPv4多播服务的解决方案。该解决方案依赖于无状态IPv4-in-IPv6封装方案，并使用IPv6多播分发树来传递IPv4多播流量。该解决方案对于向由双栈Lite（DS Lite）服务的客户提供多播服务特别有用。
Status of This Memo
关于下段备忘
This is an Internet Standards Track document.
这是一份互联网标准跟踪文件。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。有关互联网标准的更多信息，请参见RFC 7841第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc8114.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc8114.
Copyright Notice
版权公告
Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2017 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 6
4.1. IPv4-Embedded IPv6 Prefixes . . . . . . . . . . . . . . . 7
4.2. Multicast Distribution Tree Computation . . . . . . . . . 8
4.3. Multicast Data Forwarding . . . . . . . . . . . . . . . . 9
5. IPv4/IPv6 Address Mapping . . . . . . . . . . . . . . . . . . 9
5.1. Prefix Assignment . . . . . . . . . . . . . . . . . . . . 9
5.2. Multicast Address Translation Algorithm . . . . . . . . . 10
5.3. Textual Representation . . . . . . . . . . . . . . . . . 10
5.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Multicast B4 (mB4) . . . . . . . . . . . . . . . . . . . . . 11
6.1. IGMP-MLD Interworking Function . . . . . . . . . . . . . 11
6.2. Multicast Data Forwarding . . . . . . . . . . . . . . . . 12
6.3. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 12
6.4. Host Built-In mB4 Function . . . . . . . . . . . . . . . 12
6.5. Preserve the Scope . . . . . . . . . . . . . . . . . . . 13
7. Multicast AFTR (mAFTR) . . . . . . . . . . . . . . . . . . . 13
7.1. Routing Considerations . . . . . . . . . . . . . . . . . 13
7.2. Processing PIM Messages . . . . . . . . . . . . . . . . . 14
7.3. Switching from Shared Tree to Shortest Path Tree . . . . 15
7.4. Multicast Data Forwarding . . . . . . . . . . . . . . . . 15
7.5. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Deployment Considerations . . . . . . . . . . . . . . . . . . 16
8.1. Other Operational Modes . . . . . . . . . . . . . . . . . 16
8.1.1. The IPv6 DR is Co-located with the mAFTR . . . . . . 16
8.1.2. The IPv4 DR is Co-located with the mAFTR . . . . . . 16
8.2. Load Balancing . . . . . . . . . . . . . . . . . . . . . 16
8.3. mAFTR Policy Configuration . . . . . . . . . . . . . . . 16
8.4. Static vs. Dynamic PIM Triggering . . . . . . . . . . . . 17
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
9.1. Firewall Configuration . . . . . . . . . . . . . . . . . 17
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Use Case: IPTV . . . . . . . . . . . . . . . . . . . 21
Appendix B. Older Versions of Group Membership Management
Protocols . . . . . . . . . . . . . . . . . . . . . 22
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 6
4.1. IPv4-Embedded IPv6 Prefixes . . . . . . . . . . . . . . . 7
4.2. Multicast Distribution Tree Computation . . . . . . . . . 8
4.3. Multicast Data Forwarding . . . . . . . . . . . . . . . . 9
5. IPv4/IPv6 Address Mapping . . . . . . . . . . . . . . . . . . 9
5.1. Prefix Assignment . . . . . . . . . . . . . . . . . . . . 9
5.2. Multicast Address Translation Algorithm . . . . . . . . . 10
5.3. Textual Representation . . . . . . . . . . . . . . . . . 10
5.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Multicast B4 (mB4) . . . . . . . . . . . . . . . . . . . . . 11
6.1. IGMP-MLD Interworking Function . . . . . . . . . . . . . 11
6.2. Multicast Data Forwarding . . . . . . . . . . . . . . . . 12
6.3. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 12
6.4. Host Built-In mB4 Function . . . . . . . . . . . . . . . 12
6.5. Preserve the Scope . . . . . . . . . . . . . . . . . . . 13
7. Multicast AFTR (mAFTR) . . . . . . . . . . . . . . . . . . . 13
7.1. Routing Considerations . . . . . . . . . . . . . . . . . 13
7.2. Processing PIM Messages . . . . . . . . . . . . . . . . . 14
7.3. Switching from Shared Tree to Shortest Path Tree . . . . 15
7.4. Multicast Data Forwarding . . . . . . . . . . . . . . . . 15
7.5. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Deployment Considerations . . . . . . . . . . . . . . . . . . 16
8.1. Other Operational Modes . . . . . . . . . . . . . . . . . 16
8.1.1. The IPv6 DR is Co-located with the mAFTR . . . . . . 16
8.1.2. The IPv4 DR is Co-located with the mAFTR . . . . . . 16
8.2. Load Balancing . . . . . . . . . . . . . . . . . . . . . 16
8.3. mAFTR Policy Configuration . . . . . . . . . . . . . . . 16
8.4. Static vs. Dynamic PIM Triggering . . . . . . . . . . . . 17
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
9.1. Firewall Configuration . . . . . . . . . . . . . . . . . 17
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Use Case: IPTV . . . . . . . . . . . . . . . . . . . 21
Appendix B. Older Versions of Group Membership Management
Protocols . . . . . . . . . . . . . . . . . . . . . 22
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
DS-Lite [RFC6333] is an IPv4 address-sharing technique that enables operators to multiplex public IPv4 addresses while provisioning only IPv6 to users. A typical DS-Lite scenario is the delivery of an IPv4 service to an IPv4 user over an IPv6 network (denoted as a 4-6-4 scenario). [RFC6333] covers unicast services exclusively.
DS Lite[RFC6333]是一种IPv4地址共享技术，它使运营商能够多路传输公共IPv4地址，同时只向用户提供IPv6。典型的DS Lite场景是通过IPv6网络向IPv4用户提供IPv4服务（表示为4-6-4场景）。[RFC6333]专门涵盖单播服务。
This document specifies a generic solution for the delivery of IPv4 multicast services to IPv4 clients over an IPv6 multicast network. The solution was developed with DS-Lite in mind (see more discussion below). However, the solution is not limited to DS-Lite; it can also be applied in other deployment contexts, such as the ones described in [RFC7596] and [RFC7597].
本文档指定了通过IPv6多播网络向IPv4客户端提供IPv4多播服务的通用解决方案。该解决方案是在考虑DS Lite的情况下开发的（请参阅下面的更多讨论）。但是，解决方案不限于DS Lite；它还可以应用于其他部署上下文，如[RFC7596]和[RFC7597]中描述的上下文。
If customers have to access IPv4 multicast-based services through a DS-Lite environment, Address Family Transition Router (AFTR) devices will have to process all the Internet Group Management Protocol (IGMP) Report messages [RFC2236] [RFC3376] that have been forwarded by the Customer Premises Equipment (CPE) into the IPv4-in-IPv6 tunnels. From that standpoint, AFTR devices are likely to behave as a replication point for downstream multicast traffic, and the multicast packets will be replicated for each tunnel endpoint that IPv4 receivers are connected to.
如果客户必须通过DS Lite环境访问基于IPv4多播的服务，地址族转换路由器（AFTR）设备将必须处理所有已由客户场所设备（CPE）转发到IPv4-in-IPv6隧道中的Internet组管理协议（IGMP）报告消息[RFC2236][RFC3376]。从这个角度来看，AFTR设备可能充当下游多播流量的复制点，并且将为IPv4接收器连接到的每个隧道端点复制多播数据包。
This kind of DS-Lite environment raises two major issues:
这种DS-Lite环境引发了两个主要问题：
1. The IPv6 network loses the benefits of efficient multicast traffic forwarding because it is unable to deterministically replicate the data as close to the receivers as possible. As a consequence, the downstream bandwidth in the IPv6 network will be vastly consumed by sending multicast data over a unicast infrastructure.
1. IPv6网络失去了高效多播流量转发的好处，因为它无法确定地将数据复制到尽可能靠近接收器的位置。因此，通过单播基础设施发送多播数据将极大地消耗IPv6网络中的下游带宽。
2. The AFTR is responsible for replicating multicast traffic and forwarding it into each tunnel endpoint connecting IPv4 receivers that have explicitly asked for the corresponding content. This process may significantly consume the AFTR's resources and overload the AFTR.
2. AFTR负责复制多播流量，并将其转发到连接IPv4接收器的每个隧道端点中，IPv4接收器已明确请求相应的内容。此过程可能会严重消耗AFTR的资源并使AFTR过载。
This document specifies an extension to the DS-Lite model to deliver IPv4 multicast services to IPv4 clients over an IPv6 multicast-enabled network.
本文档指定DS Lite模型的扩展，以通过支持IPv6多播的网络向IPv4客户端提供IPv4多播服务。
This document describes a stateless translation mechanism that supports either Source-Specific Multicast (SSM) or Any-Source Multicast (ASM) operation. The recommendation in Section 1 of [RFC4607] is that multicast services use SSM where possible; the operation of the translation mechanism is also simplified when SSM is used, e.g., considerations for placement of the IPv6 Rendezvous Point (RP) are no longer relevant.
本文档描述了一种无状态转换机制，它支持源特定多播（SSM）或任何源多播（ASM）操作。[RFC4607]第1节中的建议是，多播服务在可能的情况下使用SSM；当使用SSM时，转换机制的操作也被简化，例如，IPv6集合点（RP）的放置考虑不再相关。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
本文件中的关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[RFC2119]中所述进行解释。
This document makes use of the following terms:
本文件使用了以下术语：
IPv4-embedded IPv6 address: an IPv6 address that embeds a 32-bit-encoded IPv4 address. An IPv4-embedded IPv6 address can be unicast or multicast.
IPv4嵌入IPv6地址：嵌入32位编码IPv4地址的IPv6地址。IPv4嵌入IPv6地址可以是单播或多播。
mPrefix64: a dedicated multicast IPv6 prefix for constructing IPv4-embedded IPv6 multicast addresses. mPrefix64 can be of two types: ASM_mPrefix64 used in Any-Source Multicast (ASM) mode or SSM_mPrefix64 used in Source-Specific Multicast (SSM) mode [RFC4607]. The size of this prefix is /96.
mPrefix64：用于构造IPv4嵌入式IPv6多播地址的专用多播IPv6前缀。mPrefix64可以有两种类型：任何源多播（ASM）模式中使用的ASM_mPrefix64或源特定多播（SSM）模式中使用的SSM_mPrefix64[RFC4607]。此前缀的大小为/96。
Note: "64" is used as an abbreviation for IPv6-IPv4 interconnection.
注：“64”用作IPv6-IPv4互连的缩写。
uPrefix64: a dedicated IPv6 unicast prefix for constructing IPv4-embedded IPv6 unicast addresses [RFC6052]. This prefix may be either the Well-Known Prefix (i.e., 64:ff9b::/96) or a Network-Specific Prefix (NSP).
uPrefix64：用于构造IPv4嵌入式IPv6单播地址的专用IPv6单播前缀[RFC6052]。该前缀可以是众所周知的前缀（即64:ff9b:：/96）或网络特定前缀（NSP）。
Multicast AFTR (mAFTR): a functional entity that supports an IPv4-IPv6 multicast interworking function (refer to Figure 3). It receives and encapsulates the IPv4 multicast packets into IPv4-in-IPv6 packets. Also, it behaves as the corresponding IPv6 multicast source for the encapsulated IPv4-in-IPv6 packets.
多播AFTR（mAFTR）：支持IPv4-IPv6多播互通功能的功能实体（参见图3）。它接收IPv4多播数据包并将其封装为IPv4-in-IPv6数据包。此外，它还充当封装的IPv4-in-IPv6数据包的相应IPv6多播源。
Multicast Basic Bridging BroadBand (mB4): a functional entity that supports an IGMP-MLD Interworking function (refer to Section 6.1) that translates the IGMP messages into the corresponding Multicast Listener Discovery (MLD) messages and sends the MLD messages to the IPv6 network. In addition, the mB4 decapsulates IPv4-in-IPv6 multicast packets.
多播基本桥接宽带（mB4）：支持IGMP-MLD互通功能（参考第6.1节）的功能实体，该功能实体将IGMP消息转换为相应的多播侦听器发现（MLD）消息，并将MLD消息发送到IPv6网络。此外，mB4将IPv4-In-IPv6多播数据包解除封装。
PIMv4: refers to Protocol Independent Multicast (PIM) when deployed in an IPv4 infrastructure (i.e., IPv4 transport capabilities are used to exchange PIM messages).
PIMv4：当部署在IPv4基础设施中时，指协议独立多播（PIM）（即，IPv4传输功能用于交换PIM消息）。
PIMv6: refers to PIM when deployed in an IPv6 infrastructure (i.e., IPv6 transport capabilities are used to exchange PIM messages).
PIMv6：指部署在IPv6基础设施中时的PIM（即，IPv6传输功能用于交换PIM消息）。
Host portion of the MLD protocol: refers to the part of MLD that applies to all multicast address listeners (Section 6 of [RFC3810]). As a reminder, MLD specifies separate behaviors for multicast address listeners (i.e., hosts or routers that listen to multicast packets) and multicast routers.
MLD协议的主机部分：指适用于所有多播地址侦听器的MLD部分（RFC3810第6节）。作为提醒，MLD为多播地址侦听器（即侦听多播数据包的主机或路由器）和多播路由器指定了单独的行为。
Router portion of IGMP: refers to the part of IGMP that is performed by multicast routers (Section 6 of [RFC3376]).
IGMP的路由器部分：指由多播路由器执行的IGMP部分（RFC3376第6节）。
DR: refers to the Designated Router as defined in [RFC7761].
DR：指[RFC7761]中定义的指定路由器。
This document focuses only on the subscription to IPv4 multicast groups and the delivery of IPv4-formatted content to IPv4 receivers over an IPv6-only network. In particular, only the following case is covered:
本文档仅关注IPv4多播组的订阅以及通过仅限IPv6的网络将IPv4格式的内容传递给IPv4接收器。特别是，仅涵盖以下情况：
IPv4 receivers access IPv4 multicast content over IPv6-only multicast-enabled networks.
IPv4接收器通过仅支持IPv6的多播网络访问IPv4多播内容。
This document does not cover the source/receiver heuristics, where IPv4 receivers can also behave as IPv4 multicast sources. This document assumes that hosts behind the mB4 are IPv4 multicast receivers only. Also, the document covers the host built-in mB4 function.
本文档不包括源/接收器试探法，其中IPv4接收器也可以作为IPv4多播源。本文档假设mB4后面的主机仅为IPv4多播接收器。此外，本文档还介绍了主机内置的mB4功能。
In the DS-Lite specification [RFC6333], an IPv4-in-IPv6 tunnel is used to carry bidirectional IPv4 unicast traffic between a B4 and an AFTR. The solution specified in this document provides an IPv4-in-IPv6 encapsulation scheme to deliver unidirectional IPv4 multicast traffic from an mAFTR to an mB4.
在DS Lite规范[RFC6333]中，IPv6隧道中的IPv4用于承载B4和AFTR之间的双向IPv4单播流量。本文档中指定的解决方案提供了IPv4-in-IPv6封装方案，用于将单向IPv4多播流量从mAFTR传输到mB4。
An overview of the solution is provided in this section; it is intended as an introduction to how it works but is not normative. For the normative specifications of the two new functional elements, mB4 and mAFTR (Figure 1), refer to Sections 6 and 7.
本节概述了解决方案；本手册旨在介绍其工作原理，但不具有规范性。有关两个新功能元件mB4和mAFTR（图1）的标准规范，请参阅第6节和第7节。
------------
/ \
| IPv4 network |
\ /
------------
IPv4 multicast : | ^ PIMv4 Join
v | :
+-------------+
| mAFTR |
+-------------+
IPv6 multicast |:| | ^ PIMv6 Join (PIMv6
(IPv4 embedded) |:| | : routers in between)
------------
/ \
| IPv6 network |
\ /
------------
|:| | ^ MLD Report
|v| | :
+-----------+
| mB4 |
+-----------+
IPv4 multicast : | ^ IGMP Report
v | :
+-----------+
| IPv4 |
| receiver |
+-----------+
------------
/ \
| IPv4 network |
\ /
------------
IPv4 multicast : | ^ PIMv4 Join
v | :
+-------------+
| mAFTR |
+-------------+
IPv6 multicast |:| | ^ PIMv6 Join (PIMv6
(IPv4 embedded) |:| | : routers in between)
------------
/ \
| IPv6 network |
\ /
------------
|:| | ^ MLD Report
|v| | :
+-----------+
| mB4 |
+-----------+
IPv4 multicast : | ^ IGMP Report
v | :
+-----------+
| IPv4 |
| receiver |
+-----------+
Figure 1: Functional Architecture
图1：功能架构
In order to map the addresses of IPv4 multicast traffic with IPv6 multicast addresses, an IPv6 multicast prefix (mPrefix64) and an IPv6 unicast prefix (uPrefix64) are provided to the mAFTR and the mB4 elements, both of which contribute to the computation and the maintenance of the IPv6 multicast distribution tree that extends the IPv4 multicast distribution tree into the IPv6 multicast network. The IPv4/IPv6 address mapping is stateless.
为了将IPv4多播通信的地址映射到IPv6多播地址，向mAFTR和mB4元素提供IPv6多播前缀（mPrefix64）和IPv6单播前缀（uPrefix64），这两者都有助于IPv6多播分发树的计算和维护，从而将IPv4多播分发树扩展到IPv6多播网络。IPv4/IPv6地址映射是无状态的。
The mAFTR and the mB4 use mPrefix64 to convert an IPv4 multicast address (G4) into an IPv4-embedded IPv6 multicast address (G6). The mAFTR and the mB4 use uPrefix64 to convert an IPv4 source address (S4) into an IPv4-embedded IPv6 address (S6). The mAFTR and the mB4 must use the same mPrefix64 and uPrefix64; they also run the same algorithm for building IPv4-embedded IPv6 addresses. Refer to Section 5 for more details about the address mapping.
mAFTR和mB4使用mPrefix64将IPv4多播地址（G4）转换为IPv4嵌入式IPv6多播地址（G6）。mAFTR和mB4使用uPrefix64将IPv4源地址（S4）转换为IPv4嵌入式IPv6地址（S6）。mAFTR和mB4必须使用相同的mPrefix64和uPrefix64；它们还运行相同的算法来构建IPv4嵌入式IPv6地址。有关地址映射的更多详细信息，请参阅第5节。
When an IPv4 receiver connected to the device that embeds the mB4 capability wants to subscribe to an IPv4 multicast group, it sends an IGMP Report message towards the mB4. The mB4 creates the IPv6 multicast group (G6) address using mPrefix64 and the original IPv4 multicast group address. If the receiver sends a source-specific IGMPv3 Report message, the mB4 will create the IPv6 source address (S6) using uPrefix64 and the original IPv4 source address.
当连接到嵌入mB4功能的设备的IPv4接收器想要订阅IPv4多播组时，它会向mB4发送IGMP报告消息。mB4使用mPrefix64和原始IPv4多播组地址创建IPv6多播组（G6）地址。如果接收器发送特定于源的IGMPv3报告消息，mB4将使用uPrefix64和原始IPv4源地址创建IPv6源地址（S6）。
The mB4 uses the G6 (and both S6 and G6 in SSM) to create the corresponding MLD Report message. The mB4 sends the Report message towards the IPv6 network. The PIMv6 DR receives the MLD Report message and sends the PIMv6 Join message to join the IPv6 multicast distribution tree. It can send either PIMv6 Join (*,G6) in ASM or PIMv6 Join (S6,G6) in SSM to the mAFTR.
mB4使用G6（以及SSM中的S6和G6）创建相应的MLD报告消息。mB4向IPv6网络发送报告消息。PIMv6 DR接收MLD报告消息并发送PIMv6加入消息以加入IPv6多播分发树。它可以将ASM中的PIMv6连接（*，G6）或SSM中的PIMv6连接（S6，G6）发送到mAFTR。
The mAFTR acts as the IPv6 DR to which the uPrefix64-derived S6 is connected. The mAFTR will receive the source-specific PIMv6 Join message (S6,G6) from the IPv6 multicast network. If the mAFTR is the Rendezvous Point (RP) of G6, it will receive the any-source PIMv6 Join message (*,G6) from the IPv6 multicast network. If the mAFTR is not the RP of G6, it will send the PIM Register message to the RP of G6 located in the IPv6 multicast network. For the sake of simplicity, it is recommended to configure the mAFTR as the RP for the IPv4-embedded IPv6 multicast groups it manages; no registration procedure is required under this configuration.
mAFTR充当uPrefix64衍生S6连接到的IPv6 DR。mAFTR将从IPv6多播网络接收特定于源的PIMv6加入消息（S6、G6）。如果mAFTR是G6的集合点（RP），它将从IPv6多播网络接收任何源PIMv6连接消息（*，G6）。如果mAFTR不是G6的RP，它将向位于IPv6多播网络中的G6 RP发送PIM注册消息。为简单起见，建议将mAFTR配置为其管理的IPv4嵌入式IPv6多播组的RP；在此配置下不需要注册过程。
When the mAFTR receives the PIMv6 Join message (*,G6), it will extract the IPv4 multicast group address (G4). If the mAFTR is the RP of G4 in the IPv4 multicast network, it will create a (*,G4) entry (if such entry does not already exist) in its own IPv4 multicast routing table. If the mAFTR is not the RP of G4, it will send the corresponding PIMv4 Join message (*,G4) towards the RP of G4 in the IPv4 multicast network.
当mAFTR接收到PIMv6加入消息（*，G6）时，它将提取IPv4多播组地址（G4）。如果mAFTR是IPv4多播网络中G4的RP，它将在其自己的IPv4多播路由表中创建（*，G4）条目（如果该条目不存在）。如果mAFTR不是G4的RP，它将向IPv4多播网络中G4的RP发送相应的PIMv4加入消息（*，G4）。
When the mAFTR receives the PIMv6 Join message (S6,G6), it will extract the IPv4 multicast group address (G4) and IPv4 source address (S4) and send the corresponding (S4,G4) PIMv4 Join message directly to the IPv4 source.
当mAFTR接收到PIMv6加入消息（S6，G6）时，它将提取IPv4多播组地址（G4）和IPv4源地址（S4），并将相应的（S4，G4）PIMv4加入消息直接发送到IPv4源。
A branch of the multicast distribution tree is thus constructed, comprising both an IPv4 part (from the mAFTR upstream) and an IPv6 part (from mAFTR downstream towards the mB4).
由此构造多播分发树的分支，包括IPv4部分（从mAFTR上游）和IPv6部分（从mAFTR下游到mB4）。
The mAFTR advertises the route of uPrefix64 with an IPv6 Interior Gateway Protocol (IGP), so as to represent the IPv4-embedded IPv6 source in the IPv6 multicast network and to allow IPv6 routers to run
mAFTR使用IPv6内部网关协议（IGP）公布uPrefix64的路由，以表示IPv6多播网络中的IPv4嵌入式IPv6源，并允许IPv6路由器运行
the Reverse Path Forwarding (RPF) check procedure on incoming multicast traffic. Injecting internal /96 routes is not problematic given the recommendation in [RFC7608] that requires that forwarding processes must be designed to process prefixes of any length up to /128.
传入多播流量的反向路径转发（RPF）检查过程。鉴于[RFC7608]中的建议要求转发进程必须设计为处理长度不超过/128的前缀，注入内部/96路由没有问题。
When the mAFTR receives an IPv4 multicast packet, it will encapsulate the packet into an IPv6 multicast packet using the IPv4-embedded IPv6 multicast address as the destination address and an IPv4-embedded IPv6 unicast address as the source address. The encapsulated IPv6 multicast packet will be forwarded down the IPv6 multicast distribution tree, and the mB4 will eventually receive the packet.
当mAFTR接收到IPv4多播数据包时，它将使用IPv4嵌入式IPv6多播地址作为目标地址和IPv4嵌入式IPv6单播地址作为源地址，将数据包封装到IPv6多播数据包中。封装的IPv6多播数据包将沿着IPv6多播分发树向下转发，mB4最终将接收该数据包。
The IPv6 multicast network treats the IPv4-in-IPv6 encapsulated multicast packets as native IPv6 multicast packets. The IPv6 multicast routers use the outer IPv6 header to make their forwarding decisions.
IPv6多播网络将IPv4-in-IPv6封装的多播数据包视为本机IPv6多播数据包。IPv6多播路由器使用外部IPv6报头来做出转发决策。
When the mB4 receives the IPv6 multicast packet (to G6) derived by mPrefix64, it decapsulates it and forwards the original IPv4 multicast packet towards the receivers subscribing to G4.
当mB4接收到由mPrefix64派生的IPv6多播数据包（到G6）时，它将其解封并将原始IPv4多播数据包转发给订阅G4的接收器。
Note: At this point, only IPv4-in-IPv6 encapsulation is defined; however, other types of encapsulation could be defined in the future.
注意：此时只定义了IPv4-in-IPv6封装；但是，将来可以定义其他类型的封装。
A dedicated IPv6 multicast prefix (mPrefix64) is provisioned to the mAFTR and the mB4. The mAFTR and the mB4 use the mPrefix64 to form an IPv6 multicast group address from an IPv4 multicast group address. The mPrefix64 can be of two types: ASM_mPrefix64 (an mPrefix64 used in ASM mode) or SSM_mPrefix64 (an mPrefix64 used in SSM mode). The mPrefix64 MUST be derived from the corresponding IPv6 multicast address space (e.g., the SSM_mPrefix64 must be in the range of the multicast address space specified in [RFC4607]).
向mAFTR和mB4提供专用IPv6多播前缀（mPrefix64）。mAFTR和mB4使用mPrefix64从IPv4多播组地址形成IPv6多播组地址。mPrefix64可以有两种类型：ASM_mPrefix64（ASM模式下使用的mPrefix64）或SSM_mPrefix64（SSM模式下使用的mPrefix64）。mPrefix64必须从相应的IPv6多播地址空间派生（例如，SSM_mPrefix64必须在[RFC4607]中指定的多播地址空间范围内）。
The IPv6 part of the multicast distribution tree can be seen as an extension of the IPv4 part of the multicast distribution tree. The IPv4 source address MUST be mapped to an IPv6 source address. An IPv6 unicast prefix (uPrefix64) is provisioned to the mAFTR and the mB4. The mAFTR and the mB4 use the uPrefix64 to form an IPv6 source address from an IPv4 source address as specified in [RFC6052]. The
多播分发树的IPv6部分可以看作是多播分发树的IPv4部分的扩展。IPv4源地址必须映射到IPv6源地址。向mAFTR和mB4提供IPv6单播前缀（uPrefix64）。mAFTR和mB4使用uPrefix64从[RFC6052]中指定的IPv4源地址形成IPv6源地址。这个
uPrefix-formed IPv6 source address will represent the original IPv4 source in the IPv6 multicast network. The uPrefix64 MUST be derived from the IPv6 unicast address space.
uPrefix格式的IPv6源地址将表示IPv6多播网络中的原始IPv4源。uPrefix64必须从IPv6单播地址空间派生。
The multicast address translation MUST follow the algorithm defined in Section 5.2.
多播地址转换必须遵循第5.2节中定义的算法。
The mPrefix64 and uPrefix64 can be configured in the mB4 using a variety of methods, including an out-of-band mechanism, manual configuration, or a dedicated provisioning protocol (e.g., using DHCPv6 [RFC8115]).
mPrefix64和uPrefix64可以使用多种方法在mB4中配置，包括带外机制、手动配置或专用配置协议（例如，使用DHCPv6[RFC8115]）。
The stateless translation mechanism described in Section 5 does not preclude use of Embedded-RP [RFC3956] [RFC7371].
第5节中描述的无状态转换机制并不排除使用嵌入式RP[RFC3956][RFC7371]。
IPv4-embedded IPv6 multicast addresses are composed according to the following algorithm:
IPv4嵌入式IPv6多播地址根据以下算法组成：
o Concatenate the 96 bits of the mPrefix64 and the 32 bits of the IPv4 address to obtain a 128-bit address.
o 连接mPrefix64的96位和IPv4地址的32位，以获得128位地址。
The IPv4 multicast addresses are extracted from the IPv4-embedded IPv6 multicast addresses according to the following algorithm:
IPv4多播地址根据以下算法从IPv4嵌入式IPv6多播地址中提取：
o If the multicast address has a pre-configured mPrefix64, extract the last 32 bits of the IPv6 multicast address.
o 如果多播地址具有预配置的mPrefix64，则提取IPv6多播地址的最后32位。
An IPv4 source is represented in the IPv6 realm with its IPv4-converted IPv6 address [RFC6052].
IPv4源在IPv6域中以其IPv4转换的IPv6地址[RFC6052]表示。
The embedded IPv4 address in an IPv6 multicast address is included in the last 32 bits; therefore, dotted decimal notation can be used.
IPv6多播地址中嵌入的IPv4地址包含在最后32位中；因此，可以使用点十进制表示法。
Group address mapping example:
组地址映射示例：
+---------------------+--------------+----------------------------+
| mPrefix64 | IPv4 address | IPv4-Embedded IPv6 address |
+---------------------+--------------+----------------------------+
| ff0x::db8:0:0/96 | 233.252.0.1 | ff0x::db8:233.252.0.1 |
+---------------------+--------------+----------------------------+
+---------------------+--------------+----------------------------+
| mPrefix64 | IPv4 address | IPv4-Embedded IPv6 address |
+---------------------+--------------+----------------------------+
| ff0x::db8:0:0/96 | 233.252.0.1 | ff0x::db8:233.252.0.1 |
+---------------------+--------------+----------------------------+
Source address mapping example when a /96 is used:
使用a/96时的源地址映射示例：
+---------------------+--------------+----------------------------+
| uPrefix64 | IPv4 address | IPv4-Embedded IPv6 address |
+---------------------+--------------+----------------------------+
| 2001:db8::/96 | 192.0.2.33 | 2001:db8::192.0.2.33 |
+---------------------+--------------+----------------------------+
+---------------------+--------------+----------------------------+
| uPrefix64 | IPv4 address | IPv4-Embedded IPv6 address |
+---------------------+--------------+----------------------------+
| 2001:db8::/96 | 192.0.2.33 | 2001:db8::192.0.2.33 |
+---------------------+--------------+----------------------------+
IPv4 and IPv6 addresses used in this example are derived from the IPv4 and IPv6 blocks reserved for documentation, as per [RFC6676]. The unicast IPv4 address of the above example is derived from the documentation address block defined in [RFC6890].
根据[RFC6676]，本例中使用的IPv4和IPv6地址源自为文档保留的IPv4和IPv6块。上述示例的单播IPv4地址源自[RFC6890]中定义的文档地址块。
The IGMP-MLD Interworking function combines the IGMP/MLD Proxying function and the address-synthesizing operations. The IGMP/MLD Proxying function is specified in [RFC4605]. The address translation is stateless and MUST follow the address mapping specified in Section 5.
IGMP-MLD互通功能结合了IGMP/MLD代理功能和地址合成操作。[RFC4605]中规定了IGMP/MLD代理功能。地址转换是无状态的，必须遵循第5节中指定的地址映射。
The mB4 performs the host portion of the MLD protocol on the upstream interface. The composition of IPv6 membership in this context is constructed through address-synthesizing operations and MUST synchronize with the membership database maintained in the IGMP domain. MLD messages are sent natively to the direct-connected IPv6 multicast routers (they will be processed by the PIM DR). The mB4 also performs the router portion of IGMP on the downstream interface(s). Refer to [RFC4605] for more details.
mB4在上游接口上执行MLD协议的主机部分。在此上下文中，IPv6成员资格的组合是通过地址合成操作构建的，必须与IGMP域中维护的成员资格数据库同步。MLD消息以本机方式发送到直接连接的IPv6多播路由器（它们将由PIM DR处理）。mB4还在下游接口上执行IGMP的路由器部分。有关更多详细信息，请参阅[RFC4605]。
+----------+ IGMP +-------+ MLD +---------+
| IPv4 |---------| mB4 |---------| PIM |
| Receiver | | | | DR |
+----------+ +-------+ +---------+
+----------+ IGMP +-------+ MLD +---------+
| IPv4 |---------| mB4 |---------| PIM |
| Receiver | | | | DR |
+----------+ +-------+ +---------+
Figure 2: IGMP-MLD Interworking
图2:IGMP-MLD互通
If SSM is deployed, the mB4 MUST construct the IPv6 source address (or retrieve the IPv4 source address) using the uPrefix64. The mB4 MAY create a membership database that associates the IPv4-IPv6 multicast groups with the interfaces (e.g., WLAN and Wired Ethernet) facing IPv4 multicast receivers.
如果部署了SSM，mB4必须使用uPrefix64构造IPv6源地址（或检索IPv4源地址）。mB4可以创建将IPv4-IPv6多播组与面向IPv4多播接收器的接口（例如，WLAN和有线以太网）相关联的成员数据库。
When the mB4 receives an IPv6 multicast packet, it MUST check the group address and the source address. If the IPv6 multicast group prefix is mPrefix64 and the IPv6 source prefix is uPrefix64, the mB4 MUST decapsulate the IPv6 header [RFC2473]; the decapsulated IPv4 multicast packet will be forwarded through each relevant interface following standard IPv4 multicast forwarding procedures. Otherwise, the mB4 MUST silently drop the packet.
当mB4接收到IPv6多播数据包时，它必须检查组地址和源地址。如果IPv6多播组前缀为mPrefix64且IPv6源前缀为uPrefix64，则mB4必须解除对IPv6标头的封装[RFC2473]；解除封装的IPv4多播数据包将按照标准IPv4多播转发程序通过每个相关接口转发。否则，mB4必须静默地丢弃该分组。
As an illustration, if a packet is received from source 2001:db8::192.0.2.33 and needs to be forwarded to group ff3x:20:2001:db8::233.252.0.1, the mB4 decapsulates it into an IPv4 multicast packet using 192.0.2.33 as the IPv4 source address and using 233.252.0.1 as the IPv4 destination multicast group. This example assumes that the mB4 is provisioned with uPrefix64 (2001:db8::/96) and mPrefix64 (ff3x:20:2001:db8::/96).
举例说明，如果从源2001:db8:：192.0.2.33接收到数据包，并且需要转发到组ff3x:20:2001:db8:：233.252.0.1，则mB4使用192.0.2.33作为IPv4源地址，并使用233.252.0.1作为IPv4目标多播组，将其解封为IPv4多播数据包。本例假设mB4配置了uPrefix64（2001:db8:：/96）和mPrefix64（ff3x:20:2001:db8:：/96）。
Encapsulating IPv4 multicast packets into IPv6 multicast packets that will be forwarded by the mAFTR towards the mB4 along the IPv6 multicast distribution tree reduces the effective MTU size by the size of an IPv6 header. In this specification, the data flow is unidirectional from the mAFTR to the mB4. The mAFTR MUST fragment the oversized IPv6 packet after the encapsulation into two IPv6 packets. The mB4 MUST reassemble the IPv6 packets, decapsulate the IPv6 header, and forward the IPv4 packet to the hosts that have subscribed to the corresponding multicast group. Further considerations about fragmentation issues are documented in Sections 5.3 and 6.3 of [RFC6333].
将IPv4多播数据包封装到IPv6多播数据包中，这些数据包将由mAFTR沿着IPv6多播分发树转发到mB4，从而将有效MTU大小减少IPv6报头的大小。在本规范中，从mAFTR到mB4的数据流是单向的。mAFTR必须在封装后将超大的IPv6数据包分割为两个IPv6数据包。mB4必须重新组装IPv6数据包，解除IPv6报头的封装，并将IPv4数据包转发给已订阅相应多播组的主机。[RFC6333]第5.3节和第6.3节记录了关于碎片问题的进一步考虑。
If the mB4 function is implemented in the host that is directly connected to an IPv6-only network, the host MUST implement the behaviors specified in Sections 6.1, 6.2, and 6.3. The host MAY optimize the implementation to provide an Application Programming Interface (API) or kernel module to skip the IGMP-MLD Interworking function. Optimization considerations are out of scope of this specification.
如果mB4功能在直接连接到纯IPv6网络的主机中实现，则主机必须实现第6.1、6.2和6.3节中规定的行为。主机可优化实现以提供应用程序编程接口（API）或内核模块，以跳过IGMP-MLD互通功能。优化考虑超出了本规范的范围。
When several mPrefix64s are available, if each enclosed IPv4-embedded IPv6 multicast prefix has a distinct scope, the mB4 MUST select the appropriate IPv4-embedded IPv6 multicast prefix whose scope matches the IPv4 multicast address used to synthesize an IPv4-embedded IPv6 multicast address (specific mappings are listed in Section 8 of [RFC2365]). Mapping is achieved such that the scope of the selected IPv6 multicast prefix does not exceed the original IPv4 multicast scope. If the mB4 is instructed to preserve the scope but no IPv6 multicast prefix that matches the IPv4 multicast scope is found, IPv6 multicast address mapping SHOULD fail.
当多个MPREFIX64可用时，如果每个封闭的IPv4嵌入式IPv6多播前缀具有不同的作用域，则mB4必须选择适当的IPv4嵌入式IPv6多播前缀，其作用域与用于合成IPv4嵌入式IPv6多播地址的IPv4多播地址相匹配（具体映射在[RFC2365]的第8节中列出）. 实现映射时，所选IPv6多播前缀的作用域不会超过原始IPv4多播作用域。如果指示mB4保留作用域，但未找到与IPv4多播作用域匹配的IPv6多播前缀，则IPv6多播地址映射应失败。
The mB4 MAY be configured to not preserve the scope when enforcing the address translation algorithm.
mB4可被配置为在实施地址转换算法时不保留作用域。
Consider that an mB4 is configured with two mPrefix64s, ff0e::db8:0:0/96 (global scope) and ff08::db8:0:0/96 (organization scope). If the mB4 receives an IGMP Report message from an IPv4 receiver to subscribe to 233.252.0.1, it checks which mPrefix64 to use in order to preserve the scope of the requested IPv4 multicast group. In this example, given that 233.252.0.1 is intended for global use, the mB4 creates the IPv6 multicast group (G6) address using ff0e::db8:0:0/96 and the original IPv4 multicast group address (233.252.0.1): ff0e::db8:233.252.0.1.
考虑到一个Mb4被配置为两个MPROFIX64、FF0E::D8:0:0/0/ 96（全局范围）和FF08：：D8:0:0/0/ 96（组织范围）。如果mB4从IPv4接收器接收到要订阅233.252.0.1的IGMP报告消息，它将检查要使用的mPrefix64，以保留请求的IPv4多播组的范围。在本例中，假设233.252.0.1用于全局使用，mB4使用ff0e:：db8:0:0/96和原始IPv4多播组地址（233.252.0.1）：ff0e:：db8:233.252.0.1创建IPv6多播组（G6）地址。
The mAFTR is responsible for interconnecting the IPv4 multicast distribution tree with the corresponding IPv6 multicast distribution tree. The mAFTR MUST use the uPrefix64 to build the IPv6 source addresses of the multicast group address derived from mPrefix64. In other words, the mAFTR MUST be the multicast source whose address is derived from uPrefix64.
mAFTR负责将IPv4多播分发树与相应的IPv6多播分发树互连。mAFTR必须使用uPrefix64来构建从mPrefix64派生的多播组地址的IPv6源地址。换句话说，mAFTR必须是地址从uPrefix64派生的多播源。
The mAFTR MUST advertise the route towards uPrefix64 with the IPv6 IGP. This is needed by the IPv6 multicast routers so that they acquire the routing information to discover the source.
mAFTR必须使用IPv6 IGP公布通向uPrefix64的路由。这是IPv6多播路由器所需要的，以便它们获取路由信息以发现源。
The mAFTR MUST interwork PIM Join/Prune messages for (*,G6) and (S6,G6) on their corresponding (*,G4) and (S4,G4). The following text specifies the expected behavior of the mAFTR for PIM Join messages.
mAFTR必须在对应的（*，G4）和（S4，G4）上互通（*，G6）和（S6，G6）的PIM连接/删除消息。以下文本指定PIM联接消息的mAFTR的预期行为。
+---------+
---------| mAFTR |---------
PIMv6 |uPrefix64| PIMv4
|mPrefix64|
+---------+
+---------+
---------| mAFTR |---------
PIMv6 |uPrefix64| PIMv4
|mPrefix64|
+---------+
Figure 3: PIMv6-PIMv4 Interworking Function
图3:PIMv6-PIMv4互通功能
The mAFTR contains two separate Tree Information Bases (TIBs): the IPv4 Tree Information Base (TIB4) and the IPv6 Tree Information Base (TIB6), which are bridged by one IPv4-in-IPv6 virtual interface. It should be noted that TIB implementations may vary (e.g., some may rely upon a single integrated TIB without any virtual interface), but they should follow this specification for the sake of global and functional consistency.
mAFTR包含两个独立的树信息库（TIB）：IPv4树信息库（TIB4）和IPv6树信息库（TIB6），它们由一个IPv4-in-IPv6虚拟接口桥接。应该注意的是，TIB实现可能会有所不同（例如，一些可能依赖于单个集成的TIB，而没有任何虚拟接口），但出于全局和功能一致性的考虑，它们应该遵循本规范。
When an mAFTR receives a PIMv6 Join message (*,G6) with an IPv6 multicast group address (G6) that is derived from the mPrefix64, it MUST check its IPv6 Tree Information Base (TIB6). If there is an entry for this G6 address, it MUST check whether the interface through which the PIMv6 Join message has been received is in the outgoing interface (oif) list. If not, the mAFTR MUST add the interface to the oif list. If there is no entry in the TIB6, the mAFTR MUST create a new entry (*,G6) for the multicast group. Whether or not the IPv4-in-IPv6 virtual interface is set as the incoming interface of the newly created entry is up to the implementation, but it should comply with the mAFTR's multicast data forwarding behavior (see Section 7.4).
当mAFTR接收到一条PIMv6加入消息（*，G6），该消息带有从mPrefix64派生的IPv6多播组地址（G6），它必须检查其IPv6树信息库（TIB6）。如果有此G6地址的条目，则必须检查接收PIMv6加入消息的接口是否在传出接口（oif）列表中。如果没有，mAFTR必须将接口添加到oif列表中。如果TIB6中没有条目，mAFTR必须为多播组创建一个新条目（*，G6）。是否将IPv4-in-IPv6虚拟接口设置为新创建条目的传入接口取决于实现，但它应符合mAFTR的多播数据转发行为（参见第7.4节）。
The mAFTR MUST extract the IPv4 multicast group address (G4) from the IPv4-embedded IPv6 multicast address (G6) contained in the PIMv6 Join message. The mAFTR MUST check its IPv4 Tree Information Base (TIB4). If there is an entry for G4, it MUST check whether the IPv4-in-IPv6 virtual interface is in the outgoing interface list. If not, the mAFTR MUST add the interface to the oif list. If there is no entry for G4, the mAFTR MUST create a new (*,G4) entry in its TIB4 and initiate the procedure for building the shared tree in the IPv4 multicast network without any additional requirement.
mAFTR必须从PIMv6加入消息中包含的IPv4嵌入式IPv6多播地址（G6）中提取IPv4多播组地址（G4）。mAFTR必须检查其IPv4树信息库（TIB4）。如果有G4条目，则必须检查IPv4-in-IPv6虚拟接口是否在传出接口列表中。如果没有，mAFTR必须将接口添加到oif列表中。如果没有G4条目，mAFTR必须在其TIB4中创建一个新的（*，G4）条目，并启动在IPv4多播网络中构建共享树的过程，而无需任何附加要求。
If the mAFTR receives a source-specific Join message, the (S6,G6) is processed rather than (*,G6). The procedures of processing (S6,G6) and (*,G6) are almost the same. Differences have been detailed in [RFC7761].
如果mAFTR接收到特定于源的连接消息，则处理（S6，G6）而不是（*，G6）。处理程序（S6，G6）和（*，G6）几乎相同。差异详见[RFC7761]。
When the mAFTR receives the first IPv4 multicast packet, it may extract the source address (S4) from the packet and send an Explicit PIMv4 (S4,G4) Join message directly to S4. The mAFTR switches from the shared Rendezvous Point Tree (RPT) to the Shortest Path Tree (SPT) for G4.
当mAFTR接收到第一个IPv4多播分组时，它可以从分组中提取源地址（S4），并直接向S4发送显式PIMv4（S4，G4）加入消息。mAFTR从G4的共享交会点树（RPT）切换到最短路径树（SPT）。
For IPv6 multicast routers to switch to the SPT, there is no new requirement. IPv6 multicast routers may send an Explicit PIMv6 Join to the mAFTR once the first (S6,G6) multicast packet arrives from upstream multicast routers.
对于IPv6多播路由器切换到SPT，没有新的要求。一旦第一个（S6，G6）多播分组从上游多播路由器到达，IPv6多播路由器可向mAFTR发送显式PIMv6加入。
When the mAFTR receives an IPv4 multicast packet, it checks its TIB4 to find a matching entry and then forwards the packet to the interface(s) listed in the outgoing interface list. If the IPv4-in-IPv6 virtual interface also belongs to this list, the packet is encapsulated with the mPrefix64-derived and uPrefix64-derived IPv4-embedded IPv6 addresses to form an IPv6 multicast packet [RFC2473]. Then another lookup is made by the mAFTR to find a matching entry in the TIB6. Whether or not the RPF check for the second lookup is performed is up to the implementation and is out of the scope of this document. The IPv6 multicast packet is then forwarded along the IPv6 multicast distribution tree, based upon the outgoing interface list of the matching entry in the TIB6.
当mAFTR接收到IPv4多播数据包时，它会检查其TIB4以找到匹配的条目，然后将数据包转发到传出接口列表中列出的接口。如果IPv4-in-IPv6虚拟接口也属于此列表，则使用mPrefix64派生和uPrefix64派生的IPv4嵌入IPv6地址封装数据包，以形成IPv6多播数据包[RFC2473]。然后，mAFTR进行另一次查找，以在TIB6中找到匹配的条目。是否执行第二次查找的RPF检查取决于实现，不在本文档的范围内。然后，基于TIB6中匹配条目的传出接口列表，沿着IPv6多播分发树转发IPv6多播数据包。
As an illustration, if a packet is received from source 192.0.2.33 and needs to be forwarded to group 233.252.0.1, the mAFTR encapsulates it into an IPv6 multicast packet using ff3x:20:2001:db8::233.252.0.1 as the IPv6 destination multicast group and using 2001:db8::192.0.2.33 as the IPv6 source address.
作为说明，如果从源192.0.2.33接收到数据包并需要转发到组233.252.0.1，则mAFTR使用ff3x:20:2001:db8:：233.252.0.1作为IPv6目标多播组并使用2001:db8:：192.0.2.33作为IPv6源地址将其封装到IPv6多播数据包中。
The Scope field of IPv4-in-IPv6 multicast addresses should be valued accordingly (e.g., to "E" for global scope) in the deployment environment. This specification does not discuss the scope value that should be used.
在部署环境中，IPv4-in-IPv6多播地址的作用域字段应相应地取值（例如，全局作用域为“e”）。本规范不讨论应使用的范围值。
The considerations in Section 6.5 are to be followed by the mAFTR.
mAFTR应遵循第6.5节中的注意事项。
The mAFTR can embed the MLD Querier function (as well as the PIMv6 DR) for optimization purposes. When the mB4 sends an MLD Report message to this mAFTR, the mAFTR should process the MLD Report message that contains the IPv4-embedded IPv6 multicast group address and then send the corresponding PIMv4 Join message (Figure 4).
mAFTR可以嵌入MLD查询器函数（以及PIMv6 DR）以进行优化。当mB4向该mAFTR发送MLD报告消息时，mAFTR应处理包含IPv4嵌入IPv6多播组地址的MLD报告消息，然后发送相应的PIMv4加入消息（图4）。
+---------+
---------| mAFTR |---------
MLD |uPrefix64| PIMv4
|mPrefix64|
+---------+
+---------+
---------| mAFTR |---------
MLD |uPrefix64| PIMv4
|mPrefix64|
+---------+
Figure 4: MLD-PIMv4 Interworking Function
图4:MLD-PIMv4互通功能
Discussions about the location of the mAFTR capability and related ASM or SSM multicast design considerations are out of the scope of this document.
关于mAFTR功能位置和相关ASM或SSM多播设计注意事项的讨论不在本文档范围内。
If the mAFTR is co-located with the IPv4 DR connected to the original IPv4 source, it may simply use the uPrefix64 and mPrefix64 prefixes to build the IPv4-embedded IPv6 multicast packets, and the sending of PIMv4 Join messages becomes unnecessary.
如果mAFTR与连接到原始IPv4源的IPv4 DR位于同一位置，则它可以简单地使用uPrefix64和mPrefix64前缀来构建IPv4嵌入的IPv6多播数据包，并且不需要发送PIMv4加入消息。
For robustness and load distribution purposes, several nodes in the network can embed the mAFTR function. In such case, the same IPv6 prefixes (i.e., mPrefix64 and uPrefix64) and algorithm to build IPv4-embedded IPv6 addresses must be configured on those nodes.
出于健壮性和负载分配的目的，网络中的多个节点可以嵌入mAFTR功能。在这种情况下，必须在这些节点上配置相同的IPv6前缀（即mPrefix64和uPrefix64）和用于构建IPv4嵌入式IPv6地址的算法。
The mAFTR may be configured with a list of IPv4 multicast groups and sources. Only multicast flows bound to the configured addresses should be handled by the mAFTR. Otherwise, packets are silently dropped.
mAFTR可以配置IPv4多播组和源的列表。mAFTR只能处理绑定到配置地址的多播流。否则，数据包将被静默丢弃。
To optimize the usage of network resources in current deployments, all multicast streams are conveyed in the core network while only the most popular ones are forwarded in the aggregation/access networks (static mode). Less popular streams are forwarded in the access network upon request (dynamic mode). Depending on the location of the mAFTR in the network, two modes can be envisaged: static and dynamic.
为了在当前部署中优化网络资源的使用，所有多播流都在核心网络中传输，而只有最流行的多播流在聚合/访问网络中转发（静态模式）。不太流行的流根据请求在接入网络中转发（动态模式）。根据mAFTR在网络中的位置，可以设想两种模式：静态和动态。
Static Mode: The mAFTR is configured to instantiate permanent (S6,G6) and (*,G6) entries in its TIB6 using a pre-configured (S4,G4) list.
静态模式：mAFTR配置为使用预配置（S4，G4）列表实例化其TIB6中的永久（S6，G6）和（*，G6）条目。
Dynamic Mode: The instantiation or withdrawal of (S6,G6) or (*,G6) entries is triggered by the receipt of PIMv6 messages.
动态模式：通过接收PIMv6消息触发（S6，G6）或（*，G6）条目的实例化或撤销。
Besides multicast scoping considerations (see Sections 6.5 and 7.5), this document does not introduce any new security concerns in addition to those discussed in Section 5 of [RFC6052], Section 10 of [RFC3810], and Section 6 of [RFC7761].
除了多播作用域注意事项（参见第6.5节和第7.5节），本文件除[RFC6052]第5节、[RFC3810]第10节和[RFC7761]第6节中讨论的安全问题外，未引入任何新的安全问题。
Unlike solutions that map IPv4 multicast flows to IPv6 unicast flows, this document does not exacerbate Denial-of-Service (DoS) attacks.
与将IPv4多播流映射到IPv6单播流的解决方案不同，本文档不会加剧拒绝服务（DoS）攻击。
An mB4 SHOULD be provided with appropriate configuration information to preserve the scope of a multicast message when mapping an IPv4 multicast address into an IPv4-embedded IPv6 multicast address and vice versa.
mB4应提供适当的配置信息，以便在将IPv4多播地址映射到IPv4嵌入式IPv6多播地址时保留多播消息的范围，反之亦然。
The CPE that embeds the mB4 function SHOULD be configured to accept incoming MLD messages and traffic forwarded to multicast groups subscribed to by receivers located in the customer premises.
嵌入mB4功能的CPE应配置为接受传入的MLD消息和转发到多播组的流量，多播组由位于客户场所的接收器订阅。
This document does not require any IANA actions.
本文件不要求IANA采取任何行动。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，DOI 10.17487/RFC2119，1997年3月<http://www.rfc-editor.org/info/rfc2119>.
[RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23, RFC 2365, DOI 10.17487/RFC2365, July 1998, <http://www.rfc-editor.org/info/rfc2365>.
[RFC2365]Meyer，D.，“管理范围的IP多播”，BCP 23，RFC 2365，DOI 10.17487/RFC2365，1998年7月<http://www.rfc-editor.org/info/rfc2365>.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, December 1998, <http://www.rfc-editor.org/info/rfc2473>.
[RFC2473]Conta，A.和S.Deering，“IPv6规范中的通用数据包隧道”，RFC 2473，DOI 10.17487/RFC2473，1998年12月<http://www.rfc-editor.org/info/rfc2473>.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. Thyagarajan, "Internet Group Management Protocol, Version 3", RFC 3376, DOI 10.17487/RFC3376, October 2002, <http://www.rfc-editor.org/info/rfc3376>.
[RFC3376]Cain，B.，Deering，S.，Kouvelas，I.，Fenner，B.，和A.Thyagarajan，“互联网组管理协议，版本3”，RFC 3376，DOI 10.17487/RFC3376，2002年10月<http://www.rfc-editor.org/info/rfc3376>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", RFC 3810, DOI 10.17487/RFC3810, June 2004, <http://www.rfc-editor.org/info/rfc3810>.
[RFC3810]Vida，R.，Ed.和L.Costa，Ed.，“IPv6的多播侦听器发现版本2（MLDv2）”，RFC 3810，DOI 10.17487/RFC3810，2004年6月<http://www.rfc-editor.org/info/rfc3810>.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet Group Management Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, August 2006, <http://www.rfc-editor.org/info/rfc4605>.
[RFC4605]Fenner，B.，He，H.，Haberman，B.，和H.Sandick，“基于Internet组管理协议（IGMP）/多播侦听器发现（MLD）的多播转发（“IGMP/MLD代理”）”，RFC 4605，DOI 10.17487/RFC4605，2006年8月<http://www.rfc-editor.org/info/rfc4605>.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, <http://www.rfc-editor.org/info/rfc4607>.
[RFC4607]Holbrook，H.和B.Cain，“IP的源特定多播”，RFC 4607，DOI 10.17487/RFC4607，2006年8月<http://www.rfc-editor.org/info/rfc4607>.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, DOI 10.17487/RFC6052, October 2010, <http://www.rfc-editor.org/info/rfc6052>.
[RFC6052]Bao，C.，Huitema，C.，Bagnulo，M.，Boucadair，M.，和X.Li，“IPv4/IPv6转换器的IPv6寻址”，RFC 6052，DOI 10.17487/RFC6052，2010年10月<http://www.rfc-editor.org/info/rfc6052>.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011, <http://www.rfc-editor.org/info/rfc6333>.
[RFC6333]Durand，A.，Droms，R.，Woodyatt，J.，和Y.Lee，“IPv4耗尽后的双栈Lite宽带部署”，RFC 6333，DOI 10.17487/RFC6333，2011年8月<http://www.rfc-editor.org/info/rfc6333>.
[RFC7608] Boucadair, M., Petrescu, A., and F. Baker, "IPv6 Prefix Length Recommendation for Forwarding", BCP 198, RFC 7608, DOI 10.17487/RFC7608, July 2015, <http://www.rfc-editor.org/info/rfc7608>.
[RFC7608]Boucadair，M.，Petrescu，A.，和F.Baker，“转发的IPv6前缀长度建议”，BCP 198，RFC 7608，DOI 10.17487/RFC7608，2015年7月<http://www.rfc-editor.org/info/rfc7608>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 2016, <http://www.rfc-editor.org/info/rfc7761>.
[RFC7761]Fenner，B.，Handley，M.，Holbrook，H.，Kouvelas，I.，Parekh，R.，Zhang，Z.，和L.Zheng，“协议独立多播-稀疏模式（PIM-SM）：协议规范（修订版）”，STD 83，RFC 7761，DOI 10.17487/RFC7761，2016年3月<http://www.rfc-editor.org/info/rfc7761>.
[RFC2236] Fenner, W., "Internet Group Management Protocol, Version 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, <http://www.rfc-editor.org/info/rfc2236>.
[RFC2236]Fenner，W.，“互联网组管理协议，第2版”，RFC 2236，DOI 10.17487/RFC2236，1997年11月<http://www.rfc-editor.org/info/rfc2236>.
[RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address", RFC 3956, DOI 10.17487/RFC3956, November 2004, <http://www.rfc-editor.org/info/rfc3956>.
[RFC3956]Savola，P.和B.Haberman，“将集合点（RP）地址嵌入IPv6多播地址”，RFC 3956，DOI 10.17487/RFC3956，2004年11月<http://www.rfc-editor.org/info/rfc3956>.
[RFC6676] Venaas, S., Parekh, R., Van de Velde, G., Chown, T., and M. Eubanks, "Multicast Addresses for Documentation", RFC 6676, DOI 10.17487/RFC6676, August 2012, <http://www.rfc-editor.org/info/rfc6676>.
[RFC6676]Venaas，S.，Parekh，R.，Van de Velde，G.，Chown，T.，和M.Eubanks，“文档的多播地址”，RFC 6676，DOI 10.17487/RFC6676，2012年8月<http://www.rfc-editor.org/info/rfc6676>.
[RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, "Special-Purpose IP Address Registries", BCP 153, RFC 6890, DOI 10.17487/RFC6890, April 2013, <http://www.rfc-editor.org/info/rfc6890>.
[RFC6890]Cotton，M.，Vegoda，L.，Bonica，R.，Ed.，和B.Haberman，“特殊用途IP地址注册”，BCP 153，RFC 6890，DOI 10.17487/RFC6890，2013年4月<http://www.rfc-editor.org/info/rfc6890>.
[RFC7371] Boucadair, M. and S. Venaas, "Updates to the IPv6 Multicast Addressing Architecture", RFC 7371, DOI 10.17487/RFC7371, September 2014, <http://www.rfc-editor.org/info/rfc7371>.
[RFC7371]Boucadair，M.和S.Venaas，“IPv6多播寻址体系结构的更新”，RFC 7371，DOI 10.17487/RFC7371，2014年9月<http://www.rfc-editor.org/info/rfc7371>.
[RFC7596] Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I. Farrer, "Lightweight 4over6: An Extension to the Dual-Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596, July 2015, <http://www.rfc-editor.org/info/rfc7596>.
[RFC7596]Cui，Y.，Sun，Q.，Boucadair，M.，Tsou，T.，Lee，Y.，和I.Farrer，“轻量级4over6：双栈精简架构的扩展”，RFC 7596，DOI 10.17487/RFC75962015年7月<http://www.rfc-editor.org/info/rfc7596>.
[RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S., Murakami, T., and T. Taylor, Ed., "Mapping of Address and Port with Encapsulation (MAP-E)", RFC 7597, DOI 10.17487/RFC7597, July 2015, <http://www.rfc-editor.org/info/rfc7597>.
[RFC7597]Troan，O.，Ed.，Dec，W.，Li，X.，Bao，C.，Matsushima，S.，Murakami，T.，和T.Taylor，Ed.，“地址和端口的封装映射（MAP-E）”，RFC 7597，DOI 10.17487/RFC7597，2015年7月<http://www.rfc-editor.org/info/rfc7597>.
[RFC8115] Boucadair, M., Qin, J., Tsou, T., and X. Deng, "DHCPv6 Option for IPv4-Embedded Multicast and Unicast IPv6 Prefixes", RFC 8115, DOI 10.17487/RFC8115, March 2017, <http://www.rfc-editor.org/info/rfc8115>.
[RFC8115]Boucadair，M.，Qin，J.，Tsou，T.，和X.Deng，“IPv4嵌入式多播和单播IPv6前缀的DHCPv6选项”，RFC 8115，DOI 10.17487/RFC8115，2017年3月<http://www.rfc-editor.org/info/rfc8115>.
Appendix A. Use Case: IPTV
附录A.用例：IPTV
IPTV generally includes two categories of service offerings:
IPTV通常包括两类服务：
o Video on Demand (VoD) that streams unicast video content to receivers.
o 视频点播（VoD），将单播视频内容流到接收器。
o Multicast live TV broadcast services.
o 多播电视直播服务。
Two types of provider are involved in the delivery of this service:
本服务的提供涉及两类提供商：
o Content Providers, who usually own the content that is multicast to receivers. Content providers may contractually define an agreement with network providers to deliver content to receivers.
o 内容提供商，通常拥有多播到接收者的内容。内容提供商可以通过合同与网络提供商签订协议，将内容交付给接收者。
o Network Providers, who provide network connectivity services (e.g., network providers are responsible for carrying multicast flows from head-ends to receivers).
o 提供网络连接服务的网络提供商（例如，网络提供商负责将多播流从前端传送到接收器）。
Note that some contract agreements prevent a network provider from altering the content as sent by the content provider for various reasons. Depending on these contract agreements, multicast streams should be delivered unaltered to the requesting users.
请注意，某些合同协议阻止网络提供商出于各种原因更改内容提供商发送的内容。根据这些契约协议，多播流应该不加更改地交付给请求用户。
Most current IPTV content is likely to remain IPv4-formatted and out of the control of network providers. Additionally, there are numerous legacy receivers (e.g., IPv4-only Set-Top Boxes (STBs)) that can't be upgraded or easily replaced to support IPv6. As a consequence, IPv4 service continuity must be guaranteed during the transition period, including the delivery of multicast services such as Live TV Broadcasting to users.
大多数当前IPTV内容可能保持IPv4格式，不受网络提供商的控制。此外，还有许多传统接收器（例如，仅限IPv4的机顶盒（STB））无法升级或轻松更换以支持IPv6。因此，在过渡期间必须保证IPv4服务的连续性，包括向用户提供直播电视广播等多播服务。
Given the multiple versions of group membership management protocols, mismatch issues may arise at the mB4 (refer to Section 6.1).
鉴于集团成员资格管理协议的多个版本，mB4可能会出现不匹配问题（请参阅第6.1节）。
If IGMPv2 operates on the IPv4 receivers while MLDv2 operates on the MLD Querier, or if IGMPv3 operates on the IPv4 receivers while MLDv1 operates on the MLD Querier, a version mismatch issue will be encountered. To solve this problem, the mB4 should perform the router portion of IGMP, which is similar to the corresponding MLD version (IGMPv2 for MLDv1 or IGMPv3 for MLDv2) operating in the IPv6 domain. Then, the protocol interaction approach specified in Section 7 of [RFC3376] can be applied to exchange signaling messages with the IPv4 receivers on which the different version of IGMP is operating.
如果IGMPv2在IPv4接收器上运行，而MLDv2在MLD查询器上运行，或者如果IGMPv3在IPv4接收器上运行，而MLDv1在MLD查询器上运行，则将遇到版本不匹配问题。为了解决这个问题，mB4应该执行IGMP的路由器部分，这类似于在IPv6域中运行的相应MLD版本（针对MLDv1的IGMPv2或针对MLDv2的IGMPv3）。然后，[RFC3376]第7节中规定的协议交互方法可用于与运行不同版本IGMP的IPv4接收器交换信令消息。
Note that the support of IPv4 SSM requires MLDv2 to be enabled in the IPv6 network.
请注意，支持IPv4 SSM需要在IPv6网络中启用MLDv2。
Acknowledgements
致谢
The authors would like to thank Dan Wing for his guidance in the early discussions that initiated this work. We also thank Peng Sun, Jie Hu, Qiong Sun, Lizhong Jin, Alain Durand, Dean Cheng, Behcet Sarikaya, Tina Tsou, Rajiv Asati, Xiaohong Deng, and Stig Venaas for their valuable comments.
作者要感谢Dan Wing在发起这项工作的早期讨论中的指导。我们还感谢孙鹏、胡杰、孙琼、金立中、阿兰·杜兰德、程院长、白塞特·萨里卡亚、邹天娜、拉吉夫·阿萨蒂、邓晓红和斯蒂格·维纳斯的宝贵意见。
Many thanks to Ian Farrer for the review.
非常感谢伊恩·法勒的评论。
Thanks to Zhen Cao, Tim Chown, Francis Dupont, Jouni Korhonen, and Stig Venaas for the directorates review.
感谢曹震、周天恩、弗朗西斯·杜邦、朱尼·科霍宁和斯蒂格·维纳斯参与董事会审查。
Authors' Addresses
作者地址
Mohamed Boucadair Orange Rennes 35000 France
穆罕默德·布卡代尔·奥兰治·雷恩35000法国
Email: mohamed.boucadair@orange.com
Email: mohamed.boucadair@orange.com
Chao Qin Cisco Shanghai China
赵琴思科中国上海
Email: jacni@jacni.com
Email: jacni@jacni.com
Christian Jacquenet Orange Rennes 35000 France
克里斯蒂安·雅克内特·奥兰治·雷恩35000法国
Email: christian.jacquenet@orange.com
Email: christian.jacquenet@orange.com
Yiu L. Lee Comcast United States of America
Yiu L.Lee Comcast美利坚合众国
Email: yiu_lee@cable.comcast.com
URI: http://www.comcast.com
Email: yiu_lee@cable.comcast.com
URI: http://www.comcast.com
Qian Wang China Telecom China
钱旺中国电信
Phone: +86 10 58502462
Email: 13301168516@189.cn
Phone: +86 10 58502462
Email: 13301168516@189.cn