Delivery of IPv4 Multicast Services to IPv4 Clients over an IPv6 Multicast Network
draft-ietf-softwire-dslite-multicast-04

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Softwire WG                                                       J. Qin
Internet-Draft                                                     Cisco
Intended status: Standards Track                            M. Boucadair
Expires: April 21, 2013                                     C. Jacquenet
                                                          France Telecom
                                                                  Y. Lee
                                                                 Comcast
                                                                 Q. Wang
                                                           China Telecom
                                                        October 18, 2012

    Delivery of IPv4 Multicast Services to IPv4 Clients over an IPv6
                           Multicast Network
                draft-ietf-softwire-dslite-multicast-04

Abstract

   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 the IPv6 multicast distribution tree to deliver IPv4
   multicast traffic.  The solution is particularly useful for the
   delivery of multicast service offerings to DS-Lite serviced
   customers.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 21, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   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.  Address Mapping  . . . . . . . . . . . . . . . . . . . . . . .  9
     5.1.  Prefix Assignment  . . . . . . . . . . . . . . . . . . . .  9
     5.2.  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  . . . . . . . . . . . . . . . . 11
     6.3.  Fragmentation  . . . . . . . . . . . . . . . . . . . . . . 12
     6.4.  Host built-in mB4 Function . . . . . . . . . . . . . . . . 12
     6.5.  Preserve the Scope . . . . . . . . . . . . . . . . . . . . 12
   7.  Multicast AFTR (mAFTR) . . . . . . . . . . . . . . . . . . . . 12
     7.1.  Routing Considerations . . . . . . . . . . . . . . . . . . 12
     7.2.  Processing PIM Message . . . . . . . . . . . . . . . . . . 13
     7.3.  Switching from Shared Tree to Shortest Path Tree . . . . . 14
     7.4.  Multicast Data Forwarding  . . . . . . . . . . . . . . . . 14
     7.5.  TTL/Scope  . . . . . . . . . . . . . . . . . . . . . . . . 14
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
     8.1.  Firewall Configuration . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     11.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Appendix A.  Use Case: IPTV  . . . . . . . . . . . . . . . . . . . 17
   Appendix B.  Deployment Considerations . . . . . . . . . . . . . . 18
     B.1.  Other operational Modes  . . . . . . . . . . . . . . . . . 18
       B.1.1.  MLD Querier with mAFTR Embedded  . . . . . . . . . . . 18
       B.1.2.  mAFTR embedded in DR . . . . . . . . . . . . . . . . . 18
     B.2.  Older Version of Group Membership management Protocols . . 18
     B.3.  Load-Balancing . . . . . . . . . . . . . . . . . . . . . . 19
     B.4.  RP for IPv4-Embedded IPv6 Multicast Groups . . . . . . . . 19
     B.5.  mAFTR Policy Configuration . . . . . . . . . . . . . . . . 19
     B.6.  Static vs. Dynamic PIM Triggering  . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19

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1.  Introduction

   DS-Lite [RFC6333] is a technique that rationalizes the usage of the
   remaining global IPv4 addresses during the transition period by
   sharing a single IPv4 address with multiple 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.  A more generic problem statement is sketched
   in [I-D.ietf-mboned-v4v6-mcast-ps].

   This document specifies a generic solution for 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).  The solution is however not limited to DS-Lite.

   If customers have to access IPv4 multicast-based services through DS-
   Lite environment, Address Family Transition Router (AFTR) devices
   will have to process all the IGMP Report messages [RFC2236] [RFC3376]
   that have been forwarded by the 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 where
   IPv4 receivers are connected to.

   This kind of DS-Lite environment raises two major issues:

   1.  The IPv6 network loses the benefits of the multicast traffic
       forwarding efficiency 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.

   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 contents.  This
       process may greatly consume AFTR's resources and overload the
       AFTR.

   This document specifies an extension to the DS-Lite model to deliver
   IPv4 multicast services to IPv4 clients over an IPv6 multicast-
   enabled network.

1.1.  Requirements Language

   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].

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2.  Terminology

   This document makes use of the following terms:

   o  IPv4-embedded IPv6 address: is an IPv6 address which embeds a 32-
      bit-encoded IPv4 address.  An IPv4-embedded IPv6 address can be
      unicast or multicast.

   o  mPrefix64: is 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].

   o  uPrefix64: is a dedicated IPv6 unicast prefix for constructing
      IPv4-embedded IPv6 unicast addresses [RFC6052].

   o  Multicast AFTR (mAFTR): is a functional entity which supports
      IPv4-IPv6 multicast interworking function (refer to Figure 3).  It
      receives and encapsulates the IPv4 multicast packets into IPv4-in-
      IPv6 packets and behaves as the corresponding IPv6 multicast
      source for the encapsulated IPv4-in-IPv6 packets.

   o  Multicast B4 (mB4): is a functional entity which supports an IGMP-
      MLD interworking function (refer to Section 6.1) that relays
      information conveyed in IGMP messages by forwarding the
      corresponding MLD messages towards the MLD Querier in the IPv6
      network.  In addition, the mB4 decapsulates IPv4-in-IPv6 multicast
      packets.

   o  PIMv4: refers to PIM when deployed in an IPv4 infrastructure
      (i.e., IPv4 transport capabilities are used to exchange PIM
      messages).

   o  PIMv6: refers to PIM when deployed in an IPv6 infrastructure
      (i.e., IPv6 transport capabilities are used to exchange PIM
      messages).

3.  Scope

   This document focuses only on subscription to an IPv4 multicast group
   and the delivery of IPv4-formatted content to IPv4 receivers over an
   IPv6-only network.  In particular, only the following case is
   covered:

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      An IPv4 receiver accesses IPv4 multicast contents over an IPv6-
      only multicast-enabled network.

   This document does not cover the source/receiver heuristics, where as
   IPv4 receiver can also behave as an IPv4 multicast source.  This
   document assumes that hosts behind the mB4 are IPv4 multicast
   receivers only.

4.  Solution Overview

   In the original 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.

   An overview of the solution is provided in this section which 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 Section 6 and Section 7.

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                             ------------
                           /              \
                          |  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

4.1.  IPv4-Embedded IPv6 Prefixes

   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 mAFTR and 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 mAFTR and mB4 use mPrefix64 to convert an IPv4 multicast address
   (G4) to an IPv4-embedded IPv6 multicast address (G6).  The mAFTR and
   mB4 use uPrefix64 to convert an IPv4 multicast source address (S4) to
   an IPv4-embedded IPv6 address (S6).  The mAFTR and mB4 MUST use the
   same mPrefix64 and uPrefix64, as well as run the same algorithm for
   building IPv4-embedded IPv6 addresses.  Refer to Section 5 for more
   details about the address mapping.

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4.2.  Multicast Distribution Tree Computation

   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 to 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.

   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
   to the MLD Querier in the IPv6 network.  The MLD Querier (typically
   acts as the PIMv6 Designated Router) receives the MLD Report message
   and sends the PIMv6 Join to join the IPv6 multicast distribution
   tree.  The MLD Querier can send either PIMv6 Join (*,G6) in ASM or
   PIMv6 Join (S6,G6) in SSM to the mAFTR.

   The mAFTR acts as the 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.

   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 there is not yet an existing one) 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.

   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.

   A branch of the multicast distribution tree is constructed,
   comprising both an IPv4 part (from the mAFTR upstream) and an IPv6
   part (from mAFTR downstream to the mB4).

   The mAFTR MUST advertise the route of uPrefix64 with an IPv6 IGP, so
   as to represent the IPv4-embedded IPv6 source in the IPv6 multicast
   network, and to pass the Reverse Path Forwarding (RPF) check on
   multicast devices.

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4.3.  Multicast Data Forwarding

   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.

   The IPv6 multicast network treats the IPv4-in-IPv6 encapsulated
   multicast packets as native.  The IPv6 multicast routers use the
   outer IPv6 header to make forwarding decisions.

   When the mB4 receive the IPv6 multicast packet (to G6) derived by
   mPrefix64, it MUST decapsulate it and forward the original IPv4
   multicast packet to the receivers subscribing to G4.

   Note: At this point, only IPv4-in-IPv6 encapsulation is defined;
   however, other types of encapsulation could be defined in the future.

5.  Address Mapping

5.1.  Prefix Assignment

   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 (a mPrefix64 used in
   ASM mode) or SSM_mPrefix64 (a 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
   multicast address space specified in [RFC4607]).

   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 multicast source address MUST be mapped to an IPv6 multicast
   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 multicast source address from an IPv4 multicast source
   address.  The uPrefix-formed IPv6 multicast source address will
   represent the original IPv4 multicast source in the IPv6 multicast
   network.  The uPrefix64 MUST be derived from the IPv6 unicast address
   space.

   The address translation MUST follow the algorithm defined in
   Section 5.2.

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   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 [I-D.ietf-softwire-multicast-prefix-option]).

5.2.  Address Translation Algorithm

   IPv4-Embedded IPv6 multicast addresses are composed according to the
   following algorithm:

   o  Concatenate the mPrefix64 and the 32 bits of the IPv4 address to
      obtain a 128-bit address.

   The IPv4 multicast addresses are extracted from the IPv4-Embedded
   IPv6 Multicast Addresses according to the following algorithm:

   o  If the multicast address has a pre-configured mPrefix64, extract
      the last 32 bits of the IPv6 multicast address.

   An IPv4 source is represented in the IPv6 realm with its IPv4-
   converted IPv6 address [RFC6052].

5.3.  Textual Representation

   The embedded IPv4 address in an IPv6 multicast address is included in
   the last 32 bits; therefore dotted decimal notation can be used.

5.4.  Examples

    Group address mapping example:

    +---------------------+--------------+----------------------------+
    |      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:

    +---------------------+--------------+----------------------------+
    |      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

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   [RFC5735].

6.  Multicast B4 (mB4)

6.1.  IGMP-MLD Interworking Function

   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.

   The mB4 with the IGMP-MLD Interworking Function embedded relays
   between the IGMP domain and the MLD domain.  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 will
   be forwarded natively towards the MLD Querier located upstream in the
   IPv6 network.  The mB4 also performs the router portion of the IGMP
   protocol on the downstream interface(s).  Refer to [RFC4605] for more
   details

             +----------+   IGMP  +-------+   MLD   +---------+
             |   IPv4   |---------|  mB4  |---------|   MLD   |
             | Receiver |         |       |         | Querier |
             +----------+         +-------+         +---------+

                      Figure 2: IGMP-MLD Interworking

   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 which associates the IPv4-IPv6
   multicast groups with the interfaces (e.g., Wi-Fi and Wired Ethernet)
   facing IPv4 multicast receivers.

6.2.  Multicast Data Forwarding

   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 de-capsulate the IPv6 header and forward the IPv4 multicast
   packet through each relevant interface.  Otherwise, the mB4 MUST drop
   the packet silently.

   As an illustration, if a packet is received from source 2001:db8::
   192.0.2.33 and to be forwarded to group ff3x:1000::233.252.0.1, the

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   mB4 will de-capsulate it into an IPv4 multicast packet using
   192.0.2.33 as the IPv4 multicast source address and using 233.252.0.1
   as the IPv4 destination address.

6.3.  Fragmentation

   Encapsulating IPv4 multicast packets into IPv6 multicast packets that
   will be forwarded by the mAFTR to 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 mAFTR to 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 packet, and forward
   the IPv4 packet to the hosts subscribing the multicast group.
   Further considerations about fragmentation issues are documented in
   [RFC6333].

6.4.  Host built-in mB4 Function

   If the mB4 function is implemented in the host which is directly
   connected to an IPv6-only network, the host MUST implement
   Section 6.1, Section 6.2, and Section 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.  The
   optimization is out of scope of the specification.

6.5.  Preserve the Scope

   When several mPrefix64s are available, if each enclosed IPv4-embedded
   IPv6 multicast prefix has a distinct scope, mB4 MUST select the
   appropriate IPv4-embedded IPv6 multicast prefix having a scope
   matching the IPv4 multicast address used to synthesize an IPv4-
   embedded IPv6 multicast address.

   The mB4 MAY be configured to not preserve the scope when enforcing
   the address translation algorithm.

7.  Multicast AFTR (mAFTR)

7.1.  Routing Considerations

   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 derived from
   uPrefix64.

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   The mAFTR MUST advertise the route of uPrefix64 to the IPv6 IGP.
   This is needed for the IPv6 multicast routers to have routing
   information to discover the source.

7.2.  Processing PIM Message

   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 mAFTR for PIM Join message.

                                +---------+
                       ---------|  mAFTR  |---------
                         PIMv6  |uPrefix64|  PIMv4
                                |mPreifx64|
                                +---------+

                Figure 3: PIMv6-PIMv4 Interworking Function

   The mAFTR contains two separate Tree Information Base (TIB): IPv4
   Tree Information Base (TIB4) and IPv6 Tree Information Base (TIB6),
   which are bridged by one IPv4-in-IPv6 virtual interface.  It should
   be noted that the implementations may vary (e.g., using one
   integrated TIB without any virtual interface), while they should
   follow the specification herein for the consistency of overall
   functionality.

   When a 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, it MUST check whether the interface through which
   the PIMv6 Join message has been received is on the outgoing interface
   list.  If not, the mAFTR MUST add the interface to the outgoing
   interface list.  If there is no entry in the TIB6, the mAFTR MUST
   create a new entry (*,G6) for the multicast group.  While, whether or
   not to set the IPv4-in-IPv6 virtual interface as the incoming
   interface of the newly created entry is up to the implementation but
   should comply with the mAFTR's behavior of multicast data forwarding,
   see Section 7.4.

   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 on the outgoing interface list.  If not, the
   mAFTR MUST add the interface to the outgoing interface 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

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   the IPv4 multicast network without any additional requirement.

   If mAFTR receives a source-specific Join message, the (S6, G6) will
   be processed rather than (*,G6).  The procedures of processing
   (S6,G6) and (*,G6) are almost the same.  Differences have been
   detailed in [RFC4601].

7.3.  Switching from Shared Tree to Shortest Path Tree

   When the mAFTR receives the first IPv4 multicast packet, it may
   extract the multicast source address (S4) from the packet and send an
   Explicit PIMv4 (S4,G4) Join message directly to S4.  The mAFTR will
   switch from the shared Rendezvous Point Tree (RPT) to the Shortest
   Path Tree (SPT) for G4.

   For IPv6 multicast routers to switch to the SPT, there is no new
   requirement.  IPv6 multicast routers may send an Explicit PIMv6 Join
   to mAFTR once the first (S6,G6) multicast packet arrives from
   upstream multicast routers.

7.4.  Multicast Data Forwarding

   When the mAFTR receives an IPv4 multicast packet, it will look up the
   TIB4 to find a matching entry and then forward the packet to the
   interface(s) on the outgoing interface list.  If the IPv4-in-IPv6
   virtual interface also belongs to this list, the packet will be
   encapsulated with the mPrefix64-derived and uPrefix64-derived IPv4-
   embedded IPv6 addresses to form an IPv6 multicast packet.  Then
   another lookup is executed to find a matching entry in the TIB6,
   while whether or not to perform RPF check for the second lookup is up
   to the implementation and is out of the scope of this document.  The
   IPv6 multicast packet is forwarded along the IPv6 multicast
   distribution tree, based upon the outgoing interface list of the
   matching entry in the TIB6.

   As an illustration, if a packet is received from source 192.0.2.33
   and to be forwarded to group 233.252.0.1, the mAFTR encapsulates it
   into an IPv6 multicast packet using ff3x:1000::233.252.0.1 as the
   IPv6 destination address and using 2001:db8::192.0.2.33 as the IPv6
   multicast source address.

7.5.  TTL/Scope

   The Scope field of IPv4-in-IPv6 multicast addresses should be valued
   accordingly (e.g, to "E", Global scope;) in the deployment
   environment.  This specification does not discuss the scope value
   that should be used.

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   Nevertheless, when several mPrefix64s are available, if each enclosed
   IPv4-embedded IPv6 multicast prefix has a distinct scope, mAFTR MUST
   select the appropriate IPv4-embedded IPv6 multicast prefix having a
   scope matching the IPv4 multicast address used to synthesize an IPv4-
   embedded IPv6 multicast address.

   mAFTR MAY be configured to not preserve the scope when enforcing the
   address translation algorithm.

8.  Security Considerations

   A part for multicast scoping considerations (see Section 6.5 and
   Section 7.5), this document does not introduce any new security
   concern in addition to what is discussed in Section 5 of [RFC6052],
   Section 10 of [RFC3810] and Section 6 of [RFC4601].

   mB4 SHOULD be provided with appropriate configuration to enable
   preserving the scope of a multicast message when mapping an IPv4
   multicast address into an IPv4-embedded IPv6 multicast address and
   vice versa.

8.1.  Firewall Configuration

   The CPE that embeds the mB4 function SHOULD be configured to accept
   incoming MLD messages and traffic forwarded to multicast groups
   subscribed by receivers located in the customer premises.

9.  Acknowledgements

   The authors would like to thank Dan Wing for his guidance in the
   early discussions which 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 S. Venaas for
   their valuable comments.

10.  IANA Considerations

   This document includes no request to IANA.

11.  References

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11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, October 2002.

   [RFC3810]  Vida, R. and L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601, August 2006.

   [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, August 2006.

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, August 2006.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

11.2.  Informative References

   [I-D.ietf-mboned-multiaaa-framework]
              Satou, H., Ohta, H., Hayashi, T., Jacquenet, C., and H.
              He, "AAA and Admission Control Framework for
              Multicasting", draft-ietf-mboned-multiaaa-framework-12
              (work in progress), August 2010.

   [I-D.ietf-mboned-v4v6-mcast-ps]
              Jacquenet, C., Boucadair, M., Lee, Y., Qin, J., Tsou, T.,
              and Q. Sun, "IPv4-IPv6 Multicast: Problem Statement and
              Use Cases", draft-ietf-mboned-v4v6-mcast-ps-00 (work in
              progress), May 2012.

   [I-D.ietf-softwire-multicast-prefix-option]
              Boucadair, M., Qin, J., Tsou, T., and X. Deng, "DHCPv6

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              Option for IPv4-Embedded Multicast and Unicast IPv6
              Prefixes", draft-ietf-softwire-multicast-prefix-option-02
              (work in progress), October 2012.

   [RFC2236]  Fenner, W., "Internet Group Management Protocol, Version
              2", RFC 2236, November 1997.

   [RFC5735]  Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
              BCP 153, RFC 5735, January 2010.

   [RFC6676]  Venaas, S., Parekh, R., Van de Velde, G., Chown, T., and
              M. Eubanks, "Multicast Addresses for Documentation",
              RFC 6676, August 2012.

Appendix A.  Use Case: IPTV

   IPTV generally includes two categories of service offerings:

   o  Video on Demand (VoD) that unicast video content to receivers.

   o  Multicast live TV broadcast services.

   Two players intervene in the delivery of this service:

   o  Content Providers, who usually own the contents that is multicast
      to receivers.  Content providers may contractually define an
      agreement with network providers to deliver contents to receivers.

   o  Network Providers, who provide network connectivity services
      (e.g., network providers are responsible for carrying multicast
      flows from head-ends to receivers).  Refer to
      [I-D.ietf-mboned-multiaaa-framework].

   Note that some contract agreements prevent a network provider from
   altering the content as sent by the content provider for various
   reasons.  Under the contract, multicast streams should be delivered
   unaltered to the requesting users.

   Many current IPTV contents are likely to remain IPv4-formatted and
   out of control of the network providers.  Additionally, there are
   numerous legacy receivers (e.g., IPv4-only Set Top Boxes (STB)) that
   can't be upgraded or be 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.

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Appendix B.  Deployment Considerations

B.1.  Other operational Modes

B.1.1.  MLD Querier with mAFTR Embedded

   mAFTR can embed the MLD Querier function (as well as the PIMv6 DR)
   for optimization.  When mB4 sends MLD Report message to this mAFTR,
   the mAFTR should process the MLD Report message that contain IPv4-
   embedded IPv6 multicast group subscription information then send the
   corresponding PIMv4 Join message.  (Figure 4)

                                +---------+
                       ---------|  mAFTR  |---------
                          MLD   |uPrefix64|  PIMv4
                                |mPreifx64|
                                +---------+

                 Figure 4: MLD-PIMv4 Interworking Function

   Discussions about the location of the mAFTR capability and related
   ASM or SSM multicast design considerations are out of the scope of
   this document.

B.1.2.  mAFTR embedded in DR

   If mAFTR is the DR of the original IPv4 source, it may simply use the
   uPrefix64 and mPrefix64 to build the IPv4-embedded IPv6 multicast
   traffic, the sending of PIMv4 Join message is not necessary.

B.2.  Older Version of Group Membership management Protocols

   Given the multiple versions of group membership management protocols,
   mismatch issues may be raised in the mB4 Function (refer to
   Section 6.1).

   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, the issue mentioned above will be
   encountered.  To solve this problem, the mB4 SHOULD perform the
   router portion of IGMP which is of the same as the corresponding MLD
   version (IGMPv2 as of MLDv1, or IGMPv3 as of MLDv2) operating in the
   IPv6 domain, then the protocol interaction approach specified in
   Section 7 of [RFC3376] can be used to exchange signaling messages
   with the IPv4 receivers on which the different version of IGMP is
   operating.

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B.3.  Load-Balancing

   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.

B.4.  RP for IPv4-Embedded IPv6 Multicast Groups

   For the sake of simplicity, it is RECOMMENDED to configure mAFTR as
   the RP for the IPv4-embedded IPv6 multicast groups it manages.  No
   registration procedure is required under this configuration.

B.5.  mAFTR Policy Configuration

   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
   drooped.

B.6.  Static vs. Dynamic PIM Triggering

   To optimize the usage of network resources in current deployments,
   all multicast streams are conveyed in the core network while only
   popular ones are continuously conveyed in the aggregation/access
   network (static mode).  Non-popular streams are conveyed 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.

   o  Static Mode: the mAFTR is configured to instantiate permanent (S6,
      G6) and (*, G6) entries in its TIB6 using a pre-configured (S4,
      G4) list.

   o  Dynamic Mode: the instantiation and deletion of (S6, g6) or (*,
      G6) is triggered by the receipt of PIMv6 messages.

Authors' Addresses

   Jacni Qin
   Cisco
   Shanghai,
   China

   Phone:
   Email: jacni@jacni.com

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   Mohamed Boucadair
   France Telecom
   Rennes,   35000
   France

   Phone:
   Email: mohamed.boucadair@orange.com

   Christian Jacquenet
   France Telecom
   Rennes,   35000
   France

   Phone:
   Email: christian.jacquenet@orange.com

   Yiu L. Lee
   Comcast
   U.S.A.

   Phone:
   Email: yiu_lee@cable.comcast.com
   URI:   http://www.comcast.com

   Qian Wang
   China Telecom
   No.118, Xizhimennei
   Beijing,   100035
   China

   Phone: +86 10 5855 2177
   Email: wangqian@ctbri.com.cn

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