One document matched: draft-ietf-softwire-dslite-multicast-07.xml
<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc strict="yes"?>
<?rfc toc="yes"?>
<?rfc tocdepth="4"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc category="std" docName="draft-ietf-softwire-dslite-multicast-07"
ipr="trust200902">
<!-- ***** FRONT MATTER ***** -->
<front>
<title abbrev="IPv4 over IPv6 Multicast">Delivery of IPv4 Multicast
Services to IPv4 Clients over an IPv6 Multicast Network</title>
<author fullname="Jacni Qin" initials="J" surname="Qin">
<organization>Cisco</organization>
<address>
<postal>
<street></street>
<city>Shanghai</city>
<region></region>
<code></code>
<country>China</country>
</postal>
<phone></phone>
<email>jacni@jacni.com</email>
</address>
</author>
<author fullname="Mohamed Boucadair" initials="M" surname="Boucadair">
<organization>France Telecom</organization>
<address>
<postal>
<street></street>
<city>Rennes</city>
<region></region>
<code>35000</code>
<country>France</country>
</postal>
<phone></phone>
<email>mohamed.boucadair@orange.com</email>
</address>
</author>
<author fullname="Christian Jacquenet" initials="C" surname="Jacquenet">
<organization>France Telecom</organization>
<address>
<postal>
<street></street>
<city>Rennes</city>
<region></region>
<code>35000</code>
<country>France</country>
</postal>
<phone></phone>
<email>christian.jacquenet@orange.com</email>
</address>
</author>
<author fullname="Yiu L. Lee" initials="Y." surname="Lee">
<organization>Comcast</organization>
<address>
<postal>
<street></street>
<city></city>
<region></region>
<code></code>
<country>U.S.A.</country>
</postal>
<phone></phone>
<email>yiu_lee@cable.comcast.com</email>
<uri>http://www.comcast.com</uri>
</address>
</author>
<author fullname="Qian Wang" initials="Q" surname="Wang">
<organization>China Telecom</organization>
<address>
<postal>
<street>No.118, Xizhimennei</street>
<city>Beijing</city>
<region></region>
<code>100035</code>
<country>China</country>
</postal>
<phone>+86 10 5855 2177</phone>
<email>wangqian@ctbri.com.cn</email>
</address>
</author>
<date day="25" month="March" year="2014" />
<area>Internet</area>
<workgroup>Softwire WG</workgroup>
<keyword>Multicast, DS-Lite, IPv4-IPv6 Interconnection, PREFIX64, SSM,
ASM</keyword>
<abstract>
<t>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.</t>
</abstract>
</front>
<!-- ***** MIDDLE MATTER ***** -->
<middle>
<section title="Introduction">
<t>DS-Lite <xref target="RFC6333"></xref> 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). <xref
target="RFC6333"></xref> covers unicast services exclusively. A more
generic problem statement is sketched in <xref
target="I-D.ietf-mboned-v4v6-mcast-ps"></xref>.</t>
<t>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.</t>
<t>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 <xref
target="RFC2236"></xref> <xref target="RFC3376"></xref> 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.</t>
<t>This kind of DS-Lite environment raises two major issues: <list
style="numbers">
<t>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.</t>
<t>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.</t>
</list></t>
<t>This document specifies an extension to the DS-Lite model to deliver
IPv4 multicast services to IPv4 clients over an IPv6 multicast-enabled
network.</t>
<section title="Requirements Language">
<t>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 <xref
target="RFC2119">RFC 2119</xref>.</t>
</section>
</section>
<section title="Terminology">
<t>This document makes use of the following terms:</t>
<t><list style="symbols">
<t>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.</t>
<t>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 <xref
target="RFC4607"></xref>.</t>
<t>uPrefix64: is a dedicated IPv6 unicast prefix for constructing
IPv4-embedded IPv6 unicast addresses <xref
target="RFC6052"></xref>.</t>
<t>Multicast AFTR (mAFTR): is a functional entity which supports
IPv4-IPv6 multicast interworking function (refer to <xref
target="pim_interworking"></xref>). 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.</t>
<t>Multicast B4 (mB4): is a functional entity which supports an
IGMP-MLD interworking function (refer to <xref
target="igmp_mld_interworking"></xref>) 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.</t>
<t>PIMv4: refers to PIM when deployed in an IPv4 infrastructure
(i.e., IPv4 transport capabilities are used to exchange PIM
messages).</t>
<t>PIMv6: refers to PIM when deployed in an IPv6 infrastructure
(i.e., IPv6 transport capabilities are used to exchange PIM
messages).</t>
</list></t>
</section>
<section title="Scope">
<t>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:</t>
<t><list style="empty">
<t>An IPv4 receiver accesses IPv4 multicast contents over an IPv6-
only multicast-enabled network.</t>
</list></t>
<t>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.</t>
</section>
<section title="Solution Overview">
<t>In the original DS-Lite specification <xref target="RFC6333"></xref>,
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.</t>
<t>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 (<xref target="functional_architecture"></xref>), refer to <xref
target="mb4"></xref> and <xref target="maftr"></xref>.</t>
<figure align="center" anchor="functional_architecture"
title="Functional Architecture">
<artwork align="center"><![CDATA[
------------
/ \
| 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 |
+-----------+
]]></artwork>
<postamble></postamble>
</figure>
<section title="IPv4-Embedded IPv6 Prefixes">
<t>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.</t>
<t>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 <xref
target="maddress"></xref> for more details about the address
mapping.</t>
</section>
<section anchor="mcast_tree"
title="Multicast Distribution Tree Computation">
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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).</t>
<t>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.</t>
</section>
<section anchor="mcast_forwarding" title="Multicast Data Forwarding">
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>Note: At this point, only IPv4-in-IPv6 encapsulation is defined;
however, other types of encapsulation could be defined in the
future.</t>
</section>
</section>
<section anchor="maddress" title="Address Mapping">
<section title="Prefix Assignment">
<t>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 <xref target="RFC4607"></xref>).</t>
<t>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.</t>
<t>The address translation MUST follow the algorithm defined in <xref
target="algo"></xref>.</t>
<t>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 <xref
target="I-D.ietf-softwire-multicast-prefix-option"></xref>).</t>
</section>
<section anchor="algo" title="Address Translation Algorithm">
<t>IPv4-Embedded IPv6 multicast addresses are composed according to
the following algorithm:<list style="symbols">
<t>Concatenate the mPrefix64 and the 32 bits of the IPv4 address
to obtain a 128-bit address.</t>
</list></t>
<t>The IPv4 multicast addresses are extracted from the IPv4-Embedded
IPv6 Multicast Addresses according to the following algorithm:<list
style="symbols">
<t>If the multicast address has a pre-configured mPrefix64,
extract the last 32 bits of the IPv6 multicast address.</t>
</list></t>
<t>An IPv4 source is represented in the IPv6 realm with its
IPv4-converted IPv6 address <xref target="RFC6052"></xref>.</t>
</section>
<section title="Textual Representation">
<t>The embedded IPv4 address in an IPv6 multicast address is included
in the last 32 bits; therefore dotted decimal notation can be
used.</t>
</section>
<section title="Examples">
<figure align="center">
<artwork align="center"><![CDATA[
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 |
+---------------------+--------------+----------------------------+
]]></artwork>
</figure>
<t>IPv4 and IPv6 addresses used in this example are derived from the
IPv4 and IPv6 blocks reserved for documentation, as per <xref
target="RFC6676"></xref>. The unicast IPv4 address of the above
example is derived from <xref target="RFC5735"></xref>.</t>
</section>
</section>
<section anchor="mb4" title="Multicast B4 (mB4)">
<section anchor="igmp_mld_interworking"
title="IGMP-MLD Interworking Function">
<t>The IGMP-MLD Interworking Function combines the IGMP/MLD Proxying
function and the address synthesizing operations. The IGMP/MLD
Proxying function is specified in <xref target="RFC4605"></xref>. The
address translation is stateless and MUST follow the address mapping
specified in <xref target="maddress"></xref>.</t>
<t>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 <xref target="RFC4605"></xref> for
more details</t>
<figure align="center" anchor="IGMP_MLD_Interworking"
title="IGMP-MLD Interworking">
<artwork align="center"><![CDATA[
+----------+ IGMP +-------+ MLD +---------+
| IPv4 |---------| mB4 |---------| MLD |
| Receiver | | | | Querier |
+----------+ +-------+ +---------+
]]></artwork>
<postamble></postamble>
</figure>
<t>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.</t>
</section>
<section anchor="forwarding" title="Multicast Data Forwarding">
<t>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.</t>
<t>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 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.</t>
</section>
<section anchor="frag" title="Fragmentation">
<t>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 <xref target="RFC6333"></xref>.</t>
</section>
<section title="Host built-in mB4 Function">
<t>If the mB4 function is implemented in the host which is directly
connected to an IPv6-only network, the host MUST implement <xref
target="igmp_mld_interworking"></xref>, <xref
target="forwarding"></xref>, and <xref target="frag"></xref>. 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.</t>
</section>
<section anchor="scopemb4" title="Preserve the Scope">
<t>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.</t>
<t>The mB4 MAY be configured to not preserve the scope when enforcing
the address translation algorithm.</t>
</section>
</section>
<section anchor="maftr" title="Multicast AFTR (mAFTR)">
<section anchor="rpf" title="Routing Considerations">
<t>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.</t>
<t>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.</t>
</section>
<section title="Processing PIM Message">
<t>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.</t>
<t><figure align="center" anchor="pim_interworking"
title="PIMv6-PIMv4 Interworking Function">
<artwork align="center"><![CDATA[
+---------+
---------| mAFTR |---------
PIMv6 |uPrefix64| PIMv4
|mPreifx64|
+---------+
]]></artwork>
<postamble></postamble>
</figure></t>
<t>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.</t>
<t>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 <xref target="multicast_forwarding"></xref>.</t>
<t>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
the IPv4 multicast network without any additional requirement.</t>
<t>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
<xref target="RFC4601"></xref>.</t>
</section>
<section title="Switching from Shared Tree to Shortest Path Tree">
<t>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.</t>
<t>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.</t>
</section>
<section anchor="multicast_forwarding" title="Multicast Data Forwarding">
<t>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.</t>
<t>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.</t>
</section>
<section anchor="scopemaftr" title="TTL/Scope">
<t>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.</t>
<t>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.</t>
<t>mAFTR MAY be configured to not preserve the scope when enforcing
the address translation algorithm.</t>
</section>
</section>
<section anchor="Security" title="Security Considerations">
<t>A part for multicast scoping considerations (see <xref
target="scopemb4"></xref> and <xref target="scopemaftr"></xref>), this
document does not introduce any new security concern in addition to what
is discussed in Section 5 of <xref target="RFC6052"></xref>, Section 10
of <xref target="RFC3810"></xref> and Section 6 of <xref
target="RFC4601"></xref>.</t>
<t>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.</t>
<section title="Firewall Configuration">
<t>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.</t>
</section>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>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.</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This document includes no request to IANA.</t>
</section>
</middle>
<!-- *****BACK MATTER ***** -->
<back>
<references title="Normative References">
<?rfc include='reference.RFC.6333'?>
<?rfc include='reference.RFC.2119'?>
<?rfc include='reference.RFC.4605'?>
<?rfc include='reference.RFC.6052'?>
<?rfc include='reference.RFC.4607'?>
<?rfc include='reference.RFC.4601'?>
<?rfc include='reference.RFC.3376'?>
<?rfc include='reference.RFC.3810'?>
</references>
<references title="Informative References">
<?rfc include='reference.RFC.2236'?>
<?rfc include='reference.RFC.6676'?>
<?rfc include='reference.RFC.5735'?>
<?rfc include='reference.I-D.ietf-mboned-multiaaa-framework'?>
<?rfc include='reference.I-D.ietf-mboned-v4v6-mcast-ps'?>
<?rfc include='reference.I-D.ietf-softwire-multicast-prefix-option'?>
</references>
<section title="Use Case: IPTV">
<t>IPTV generally includes two categories of service offerings:</t>
<t><list style="symbols">
<t>Video on Demand (VoD) that unicast video content to
receivers.</t>
<t>Multicast live TV broadcast services.</t>
</list></t>
<t>Two players intervene in the delivery of this service:</t>
<t><list style="symbols">
<t>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.</t>
<t>Network Providers, who provide network connectivity services
(e.g., network providers are responsible for carrying multicast
flows from head-ends to receivers). Refer to <xref
target="I-D.ietf-mboned-multiaaa-framework"></xref>.</t>
</list></t>
<t>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.</t>
<t>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.</t>
</section>
<section title="Deployment Considerations">
<section title="Other operational Modes">
<section anchor="mld_maftr" title="MLD Querier with mAFTR Embedded">
<t>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. (<xref
target="mld_pimv4_interworking"></xref>)</t>
<t><figure align="center" anchor="mld_pimv4_interworking"
title="MLD-PIMv4 Interworking Function">
<artwork align="center"><![CDATA[
+---------+
---------| mAFTR |---------
MLD |uPrefix64| PIMv4
|mPreifx64|
+---------+
]]></artwork>
<postamble></postamble>
</figure></t>
<t>Discussions about the location of the mAFTR capability and
related ASM or SSM multicast design considerations are out of the
scope of this document.</t>
</section>
<section anchor="dr_maftr" title="mAFTR embedded in DR">
<t>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.</t>
</section>
</section>
<section title="Older Version of Group Membership management Protocols">
<t>Given the multiple versions of group membership management
protocols, mismatch issues may be raised in the mB4 Function (refer to
<xref target="igmp_mld_interworking"></xref>).</t>
<t>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 <xref target="RFC3376"></xref> can be used to exchange signaling
messages with the IPv4 receivers on which the different version of
IGMP is operating.</t>
</section>
<section title="Load-Balancing">
<t>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.</t>
</section>
<section title="RP for IPv4-Embedded IPv6 Multicast Groups">
<t>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.</t>
</section>
<section title="mAFTR Policy Configuration">
<t>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.</t>
</section>
<section title="Static vs. Dynamic PIM Triggering">
<t>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.
<list style="symbols">
<t>Static Mode: the mAFTR is configured to instantiate permanent
(S6, G6) and (*, G6) entries in its TIB6 using a pre-configured
(S4, G4) list.</t>
<t>Dynamic Mode: the instantiation and deletion of (S6, g6) or (*,
G6) is triggered by the receipt of PIMv6 messages.</t>
</list></t>
</section>
</section>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 10:04:20 |