One document matched: draft-xu-softwire-mesh-multicast-02.xml
<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes" symrefs="no" ?>
<rfc docName="draft-xu-softwire-mesh-multicast-02" ipr="pre5378Trust200902">
<front>
<title abbrev="softwire mesh multicast">Softwire Mesh Multicast</title>
<author initials='M.' surname='Xu' fullname='Mingwei Xu'>
<organization abbrev='Tsinghua University'>Tsinghua University</organization>
<address>
<postal>
<street>Department of Computer Science, Tsinghua University</street>
<city>Beijing</city>
<code>100084</code>
<country>P.R. China</country>
</postal>
<phone>+86-10-6278-5822</phone>
<email>xmw@cernet.edu.cn</email>
</address>
</author>
<author initials='Y.' surname='Cui' fullname='Yong Cui'>
<organization abbrev='Tsinghua University'>Tsinghua University</organization>
<address>
<postal>
<street>Department of Computer Science, Tsinghua University</street>
<city>Beijing</city>
<code>100084</code>
<country>P.R. China</country>
</postal>
<phone>+86-10-6278-5822</phone>
<email>cuiyong@tsinghua.edu.cn</email>
</address>
</author>
<author initials='S.' surname='Yang' fullname='Shu Yang'>
<organization abbrev='Tsinghua University'>Tsinghua University</organization>
<address>
<postal>
<street>Department of Computer Science, Tsinghua University</street>
<city>Beijing</city>
<code>100084</code>
<country>P.R. China</country>
</postal>
<phone>+86-10-6278-5822</phone>
<email>yangshu@csnet1.cs.tsinghua.edu.cn</email>
</address>
</author>
<author initials='C.' surname='Metz' fullname='Chris Metz'>
<organization abbrev='Cisco Systems'>Cisco Systems</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<city>San Jose, CA</city>
<code>95134</code>
<country>USA</country>
</postal>
<phone>+1-408-525-3275</phone>
<email>chmetz@cisco.com</email>
</address>
</author>
<author initials='G.' surname='Shepherd' fullname='Greg Shepherd'>
<organization abbrev='Cisco Systems'>Cisco Systems</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<city>San Jose, CA</city>
<code>95134</code>
<country>USA</country>
</postal>
<phone>+1-541-912-9758</phone>
<email>shep@cisco.com</email>
<!-- gjshep@gmail.com -->
</address>
</author>
<date month="July" year="2011" />
<abstract>
<t>The Internet needs support IPv4 and IPv6 packets. Both address
families and their attendant protocol suites support multicast of the
single-source and any-source varieties. As part of the transition to
IPv6, there will be scenarios where a backbone network running one IP
address family internally (referred to as internal IP or I-IP) will
provide transit services to attached client networks running another IP
address family (referred to as external IP or E-IP). It is expected that
the I-IP backbone will offer unicast and multicast transit services to
the client E-IP networks.</t>
<t>Softwires Mesh is a solution for supporting E-IP unicast and
multicast across an I-IP backbone. This document describes the
mechanisms for supporting Internet-style multicast across a set of
E-IP and I-IP networks supporting softwires mesh.</t>
<t></t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t></t>
<t>The Internet needs to support IPv4 and IPv6 packets. Both address
families and their attendant protocol suites support multicast of the
single-source and any-source varieties. As part of the transition to
IPv6, there will be scenarios where a backbone network running one IP
address family internally (referred to as internal IP or I-IP) will
provide transit services to attached client networks running another IP
address family (referred to as external IP or E-IP).</t>
<t>The preferred solution is to leverage the multicast functions,
inherent in the I-IP backbone, to efficiently and scalably tunnel
encapsulated client E-IP multicast packets inside an I-IP core tree
rooted at one or more ingress AFBR nodes and branching out to one or
more egress AFBR leaf nodes.</t>
<t>
<xref target="RFC4925"></xref> outlines the requirements for the
softwires mesh scenario including multicast. It is straightforward to
envisage that client E-IP multicast sources and receivers will reside in
different client E-IP networks connected to an I-IP backbone network.
This requires that the client E-IP source-rooted or shared tree will
need to traverse the I-IP backbone network.</t>
<t>One method to accomplish this is to re-use the multicast VPN approach
outlined in <xref target="I-D.ietf-l3vpn-2547bis-mcast"></xref>. MVPN-like schemes can
support the softwire mesh scenario and achieve a "many-to-one" mapping
between the E-IP client multicast trees and transit core multicast
trees. The advantage of this approach is that the number of trees in the
I-IP backbone network scales less than linearly with the number of E-IP
client trees. Corporate enterprise networks and by extension multicast
VPNs have been known to run applications that create a large amount of
(S,G) states. Aggregation at the edge contains the (S,G) states that need
to be maintained by the network operator supporting the customer VPNs.
The disadvantage of this approach is possible inefficient bandwidth and
resource utilization if multicast packets are delivered to a receiver
AFBR with no attached E-IP receiver.</t>
<t>Internet-style multicast is somewhat different in that the trees
tends to be relatively sparse and source-rooted. The need for multicast
aggregation at the edge (where many customer multicast trees are mapped
into a few or one backbone multicast trees) does not exist and to date
has not been identified. Thus the need for a basic or closer alignment
with E-IP and I-IP multicast procedures emerges. </t>
<t>A framework on how to support such methods is described in <xref
target="RFC5565"></xref>. In this document, a more detailed discussion
supporting the "one-to-one" mapping schemes for the IPv6 over IPv4 and
IPv4 over IPv6 scenarios will be discussed.</t>
</section>
<section title="Terminology">
<t>An example of a softwire mesh network supporting multicast is
illustrated in Figure 1. A multicast source S is located in one E-IP
client network, while candidate E-IP group receivers are located in the
same or different E-IP client networks that all share a common I-IP
transit network. When E-IP sources and receivers are not local to each
other, they can only communicate with each other through the I-IP core.
There may be several E-IP sources for some multicast group residing in
different client E-IP networks. In the case of shared trees, the E-IP
sources, receivers and RPs might be located in different client E-IP
networks. In the simple case the resources of the I-IP core are managed
by a single operator although the inter-provider case is not
precluded.</t>
<figure>
<artwork>
<![CDATA[
._._._._. ._._._._.
| | | | --------
| E-IP | | E-IP |--|Source S|
| network | | network | --------
._._._._. ._._._._.
| |
AFBR upstream AFBR
| |
__+____________________+__
/ : : : : \
| : : : : | E-IP Multicast
| : I-IP transit core : | message should
| : : : : | get across the
| : : : : | I-IP transit core
\_._._._._._._._._._._._._./
+ +
downstream AFBR downstream AFBR
| |
._._._._ ._._._._
-------- | | | | --------
|Receiver|-- | E-IP | | E-IP |--|Receiver|
-------- |network | |network | --------
._._._._ ._._._._
]]>
</artwork>
<postamble>Figure 1: Softwire Mesh Multicast Framework</postamble>
</figure>
<t></t>
<t>Terminology used in this document:</t>
<t>o Address Family Border Router (AFBR) - A dual-stack router
interconnecting two or more networks using different IP address
families. In the context of softwire mesh multicast, the AFBR runs E-IP
and I-IP control planes to maintain E-IP and I-IP multicast states
respectively and performs the appropriate encapsulation/decapsulation
of client E-IP multicast packets for transport across the I-IP core. An
AFBR will act as a source and/or receiver in an I-IP multicast
tree.</t>
<t>o Upstream AFBR: The AFBR router that is located at the upstream of
a multicast data flow.</t>
<t>o Downstream AFBR: The AFBR router that is located at the
downstream of a multicast data flow.</t>
<t>o I-IP (Internal IP). This refers to the form of IP (i.e., either
IPv4 or IPv6) that is supported by the core (or backbone)
network. An I-IPv6 core network runs IPv6 and an I-IPv4
core network runs IPv4.</t>
<t>o E-IP (External IP) This refers to the form of IP (i.e. either IPv4
or IPv6) that is supported by the client network(s) attached to the I-IP
transit core. An E-IPv6 client network runs IPv6 and an E-IPv4 client
network runs IPv4.</t>
<t>o I-IP core tree. A single-source or multi-source distribution tree
rooted at one or more AFBR source nodes and branched out to one or more
AFBR leaf nodes. An I-IP core Tree is built using standard IP or MPLS
multicast signaling protocols operating exclusively inside the I-IP core
network. An I-IP core Tree is used to tunnel E-IP multicast packets
belonging to E-IP trees across the I-IP core. Another name for an I-IP
core Tree is multicast or multipoint softwire.</t>
<t>o E-IP client tree. A single-source or multi-source distribution tree
rooted at one or more hosts or routers located inside a client E-IP
network and branched out to one or more leaf nodes located in the same
or different client E-IP networks.</t>
<t></t>
</section>
<section title="Scenarios of Interest">
<t></t>
<t>This section describes the two different scenarios where softwires
mesh multicast will apply.</t>
<section title="IPv4-over-IPv6">
<figure>
<artwork>
<![CDATA[
._._._._. ._._._._.
| IPv4 | | IPv4 | --------
| Client | | Client |--|Source S|
| network | | network | --------
._._._._. ._._._._.
| |
AFBR upstream AFBR(A)
| |
__+____________________+__
/ : : : : \
| : : : : |
| : IPv6 transit core : |
| : : : : |
| : : : : |
\_._._._._._._._._._._._._./
+ +
downstream AFBR(C) downstream AFBR(D)
| |
._._._._ ._._._._
-------- | IPv4 | | IPv4 | --------
|Receiver|-- | Client | | Client |--|Receiver|
-------- |network | | network| --------
._._._._ ._._._._
]]>
</artwork>
<postamble>Figure 2: IPv4-over-IPv6 Scenario</postamble>
</figure>
<t>In this scenario, the E-IP client networks run IPv4 and I-IP core
runs IPv6. This scenario is illustrated in Figure 2.</t>
<t>Because of the much larger IPv6 group address space, it will not be
a problem to map individual client E-IPv4 tree to a specific I-IPv6
core tree. This simplifies operations on the AFBR because it becomes
possible to algorithmically map an IPv4 group/source address to an
IPv6 group/source address and vice-versa. </t>
<t>The IPv4-over-IPv6 scenario is an emerging requirement as network
operators build out native IPv6 backbone networks. These networks
naturally support native IPv6 services and applications but it is
with near 100% certainty that legacy IPv4 networks handling unicast
and multicast will need to be accommodated. </t>
<t></t>
</section>
<section title="IPv6-over-IPv4 ">
<figure>
<artwork>
<![CDATA[
._._._._. ._._._._.
| IPv6 | | IPv6 | --------
| Client | | Client |--|Source S|
| network | | network | --------
._._._._. ._._._._.
| |
AFBR upstream AFBR
| |
__+____________________+__
/ : : : : \
| : : : : |
| : IPv4 transit core : |
| : : : : |
| : : : : |
\_._._._._._._._._._._._._./
+ +
downstream AFBR downstream AFBR
| |
._._._._ ._._._._
-------- | IPv6 | | IPv6 | --------
|Receiver|-- | Client | | Client |--|Receiver|
-------- |network | | network| --------
._._._._ ._._._._
]]>
</artwork>
<postamble>Figure 3: IPv6-over-IPv4 Scenario</postamble>
</figure>
<t>In this scenario, the E-IP Client Networks run IPv6 while the I-IP
core runs IPv4 and is illustrated in Figure 3.</t>
<t>IPv6 multicast group addresses are longer than IPv4 multicast group
addresses. It will not be possible to perform an algorithmic IPv6 - to
- IPv4 address mapping without the risk of multiple IPv6 group
addresses mapped to the same IPv4 address resulting in unnecessary
bandwidth and resource consumption. Therefore additional efforts will
be required to ensure that client E-IPv6 multicast packets can be
injected into the correct I-IPv4 multicast trees
at the AFBRs. This clear mismatch in IPv6 and IPv4 group address
lengths means that it will not be possible to perform a one-to-one
mapping between IPv6 and IPv4 group addresses unless the IPv6 group
address is scoped.</t>
<t>As mentioned earlier this scenario is common in the MVPN environment.
As native IPv6 deployments and multicast applications emerge from the
outer reaches of the greater public IPv4 Internet, it is envisaged
that the IPv6 over IPv4 softwire mesh multicast scenario will be a
necessary feature supported by network operators. </t>
</section>
</section>
<section title="IPv4-over-IPv6 ">
<section title="Mechanism">
<t>Routers in the client E-IPv4 networks contain routes to all other
client E-IPv4 networks. Through the set of known and deployed
mechanisms, E-IPv4 hosts and routers have discovered or learned of
(S,G) or (*,G) IPv4 addresses. Any I-IP multicast state instantiated
in the core is referred to as (S',G') or (*,G') and is of course
separated from E-IP multicast state.</t>
<t>Suppose a downstream AFBR receives an E-IPv4 PIM Join/Prune
message from the E-IPv4 network for either an (S,G) tree or a (*,G)
tree. The AFBR can translate the E-IPv4 PIM message into an
I-IPv6 PIM message with the latter being directed towards I-IP IPv6
address of the upstream AFBR. When the I-IPv6 PIM message arrives at
the upstream AFBR, it should be translated back into an
E-IPv4 PIM message. The result of these actions is the construction
of E-IPv4 trees and a corresponding I-IP tree in the I-IP network.</t>
<t>In this case it is incumbent upon the AFBR routers to perform PIM
message conversions in the control plane and IP group
address conversions or mappings in the data plane. It becomes possible to
devise an algorithmic one-to-one IPv4-to-IPv6 address mapping at AFBRs.
</t>
</section>
<section title="Source Address Mapping">
<t>There are two kinds of multicast --- ASM and SSM. It's possible for I-IP network
and E-IP network to support different kinds of multicast, and the source address translation
rules may vary a lot. There are four scenarios to be discussed in detail:</t>
<t>
<list style="symbols">
<t>E-IP network supports SSM, I-IP network supports SSM<vspace/>
One possible way to make sure that the translated I-IPv6 PIM message reaches
upstream AFBR is to set S' to a virtual IPv6 address that leads to
the upstream AFBR. Figure 4 is the recommended address
format based on <xref target="RFC6052"></xref>:<vspace/>
<figure>
<artwork>
<![CDATA[
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0-------------32--40--48--56--64--72--80--88--96--104---------|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| prefix |v4(32) | u | suffix |source address |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
]]>
</artwork>
<postamble>Figure 4: IPv4-Embedded IPv6 Virtual Source Address Format</postamble>
</figure>
<vspace/>
In this address format, the "prefix" field contains a "Well-Known"
prefix or a ISP-defined prefix. An existing "Well-Known" prefix is
64:ff9b, which is defined in <xref target="RFC6052"></xref>; "v4" field is
the IP address of one of upstream AFBR's E-IPv4 interface; "u"
field is defined in <xref target="RFC4291"></xref>, and MUST be
set to zero; "suffix" field is reserved for future extensions
and SHOULD be set to zero; "source address" field stores the original
S.<vspace/>
To make it feasible, the /32 prefix must be known to every AFBR,
and AFBRs should not only announce the /96 prefixes of
S' to the I-IPv6 network, but also announce the IP addresses of upstream
AFBRs' E-IPv4 interface presented in the "v4" field to other AFBRs by MPBGP. In this way,
when a downstream AFBR receives a (S,G) message, it can translate
it into (S',G') by looking up the IP address of the corresponding AFBR's E-IPv4 interface.
Since S' is globally unique and the /96 prefix of S' is known to every router
in I-IPv6 network, the translated message will eventually arrive at the
corresponding upstream AFBR, and the upstream AFBR can translate the message
back to (S,G).</t>
<t>E-IP network supports SSM, I-IP network supports ASM<vspace/>
Since any network that supports ASM should also support SSM, we can
construct a SSM tree in I-IP network. The operation in this
scenario is the same as that in the first scenario.
</t>
<t>E-IP network supports ASM, I-IP network supports SSM<vspace/>
ASM and SSM have the same PIM message format. The main differences
between ASM and SSM are RP and (*,G) messages. To make this scenario
feasible, we must be able to translate (*,G) messages into (S',G')
messages at downstream AFBRs, and translate it back at upstream
AFBRs. Assume RP' is the upstream AFBR
that locates between RP and the downstream AFBR. When downstream AFBR
receives an E-IPv4 PIM (*,G) message, S' can be generated
according to the format specified in Figure 4, with "v4" field
setting to the IP address of one of RP's E-IPv4 interface and "source
address" field setting to *(the IPv4 address of RP). The translated
message will eventually arrive at RP'. RP' checks the "source
address" field and find the IPv4 address of RP, so RP' judges that this is
originally a (*,G) message, then it translates the message
back to (*,G) message and forward it to RP.<vspace/>
Traveling all the way from sources to the RP, and then back down the shared tree
may result in the multicast data packets passing through RP' twice,
which brings about undesirable increased latency or bandwidth
consumption. For this reason, RP' MAY perform a "cut-through",
namely when RP' receives multicast data packets sent from sources
to RP, it not only forwards them to RP, but also forwards them directly
onto the multicast tree built in the I-IPv6 network. (S,G,rpt) messages should
be sent towards RP to avoid reduplication.
</t>
<t>E-IP network supports ASM, I-IP network supports ASM<vspace/>
To keep it as simple as possible, we treat I-IP network as SSM and
the solution is the same as the third scenario.</t>
</list>
</t>
</section>
<section title="Group Address Mapping">
<t>For IPv4-over-IPv6 scenario, a simple algorithmic mapping between
IPv4 multicast group addresses and IPv6 group addresses is supported.
<xref target="I-D.boucadair-behave-64-multicast-address-format"></xref> has
already defined an applicable format. Figure 5 is a reminder of the format:</t>
<figure>
<artwork>
<![CDATA[
| 8 | 4 | 4 | 16 | 4 | 60 | 32 |
+--------+----+----+-----------+----+------------------+----------+
|11111111|0011|scop|00.......00|64IX| sub-group-id |v4 address|
+--------+----+----+-----------+----+------------------+----------+
+-+-+-+-+
IPv4-IPv6 Interconnection bits (64IX): |M|r|r|r|
+-+-+-+-+
]]>
</artwork>
<postamble>Figure 5: IPv4-Embedded IPv6 Multicast Address Format: SSM Mode</postamble>
</figure>
<t>The high order bits of the I-IPv6 address range will be fixed for
mapping purposes.
With this scheme, each IPv4 multicast address can be mapped into an
IPv6 multicast address(with the assigned prefix), and each IPv6
multicast address with the assigned prefix can be mapped into IPv4
multicast address.</t>
</section>
<section title="Actions performed by AFBR">
<t>The following actions are performed by AFBRs:</t>
<t>
<list style="symbols">
<t>Receive E-IPv4 PIM messages<vspace/>
When a downstream AFBR receives an E-IPv4 PIM message, it should check
the address family of the next-hop towards the destination. If the
address family is IPv4, the AFBR should forward the message without
any translation; otherwise it should take the following operation.</t>
<t>Translate E-IPv4 PIM messages into I-IPv6 PIM messages<vspace/>
E-IPv4 PIM message with S(or *) and G is translated into I-IPv6
PIM message with S' and G' following the rules specified above.</t>
<t>Transmit I-IPv6 PIM messages<vspace/>
The downstream AFBR sends the I-IPv6 PIM message to the upstream AFBR.
When the upstream AFBR receives this I-IPv6 PIM message, it checks the
prefix of the source address and judges that the message is a translated
message, then translates the message back to E-IPv4 PIM message
and sends it towards source or RP.</t>
<t>Process and forward multicast data<vspace/>
On receiving multicast data from upstream routers, the AFBR looks up its
forwarding table to check the IP address of each outgoing interface. If there
exists at least one outgoing interface whose IP address family is different
from the incoming interface, the AFBR should encapsulate/decapsulate this
packet and forward it to the outgoing interface(s), and then forward
the data to the other outgoing interfaces without encapsulation/decapsulation.</t>
</list>
</t>
</section>
</section>
<section title="IPv6-over-IPv4">
<section title="Mechanism">
<t></t>
<t>Routers in the client E-IPv6 networks contain routes to all other
client E-IPv6 networks. Through the set of known and deployed
mechanisms, E-IPv6 hosts and routers have discovered or learned of
(S,G) or (*,G) IPv6 addresses. Any I-IP multicast state instantiated
in the core is referred to as (S',G') or (*,G') and is of course
separated from E-IP multicast state.</t>
<t>This particular scenario introduces unique challenges. Unlike the
IPv4-over-IPv6 scenario, it's impossible to map all of the IPv6
multicast address space into the IPv4 address space to address the
one-to-one Softwire Multicast requirement. To coordinate with the
"IPv4-over-IPv6" scenario and keep the solution as simple as possible,
one possible solution to this problem is to limit the scope of the
E-IPv6 source addresses for mapping, such as applying a "Well-Known"
prefix or a ISP-defined prefix.
</t>
</section>
<section title="Source Address Mapping">
<t>There are two kinds of multicast --- ASM and SSM. It's possible for I-IP network
and E-IP network to support different kind of multicast, and the source address translation
rules may vary a lot. There are four scenarios to be discussed in detail:</t>
<t>
<list style="symbols">
<t>E-IP network supports SSM, I-IP network supports SSM<vspace/>
To make sure that the translated I-IPv4 PIM
message reaches the upstream AFBR, we need to set S' to an IPv4
address that leads to the upstream AFBR. But due to the non-"one-to-one"
mapping of E-IPv6 to I-IPv4 unicast address, the
upstream AFBR is unable to remap the I-IPv4 source address to the
original E-IPv6 source address without any constraints.<vspace/>
We apply a fixed IPv6 prefix and static mapping to solve this
problem. A recommended source address format is defined in
<xref target="RFC6052"></xref>. Figure 6 is a reminder of the
format:<vspace/>
<figure>
<artwork>
<![CDATA[
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0-------------32--40--48--56--64--72--80--88--96--104---------|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| prefix(96) | v4(32) |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
]]>
</artwork>
<postamble>Figure 6: IPv4-Embedded IPv6 Source Address Format</postamble>
</figure>
<vspace blankLines='1'/>
In this address format, the "prefix" field contains a "Well-Known"
prefix or a ISP-defined prefix. An existing "Well-Known" prefix is
64:ff9b, which is defined in <xref target="RFC6052"></xref>; "v4" field is
the corresponding I-IPv4 source address.<vspace/>
To make it feasible, the /96 prefix must be known to every AFBR,
every E-IPv6 address of sources that support mesh
multicast MUST follow the format specified in Figure 6, and the corresponding
upstream AFBR should announce the I-IPv4 address in "v4" field to
the I-IPv4 network. In this way, when a downstream AFBR receives a
(S,G) message, it can translate it into (S',G') by simply take off the prefix
in S. Since S' is known to every router in I-IPv4 network, the translated
message will eventually arrive at the corresponding upstream AFBR, and the
upstream AFBR can translate the message back to (S,G) by appending the prefix to S'.
</t>
<t>E-IP network supports SSM, I-IP network supports ASM<vspace/>
Since any network that supports ASM should also support SSM, we can
construct a SSM tree in I-IP network. The operation in this
scenario is the same as that in the first scenario.</t>
<t>E-IP network supports ASM, I-IP network supports SSM<vspace/>
ASM and SSM have the same PIM message format. The main differences
between ASM and SSM are RP and (*,G) messages. To make this scenario
feasible, we must be able to translate (*,G) messages into (S',G')
messages at downstream AFBRs and translate it back at upstream AFBRs. Here, the E-IPv6 address of RP MUST
follow the format specified in Figure 6. Assume RP' is the upstream AFBR
that locates between RP and the downstream AFBR. When a downstream AFBR receives a
(*,G) message, it can translate it into (S',G') by simply take off the prefix
in *(the E-IPv6 address of RP). Since S' is known to every router
in I-IPv4 network, the translated message will eventually arrive at RP'.
RP' knows that S' is the mapped I-IPv4 address of RP, so RP' will
translate the message back to (*,G) by appending the prefix to S'
and forward it to RP.
<vspace/>
Traveling all the way from sources to the RP, and then back down the shared tree
may result in the multicast data packets passing through RP' twice,
which brings about undesirable increased latency or bandwidth
consumption. For this reason, RP' MAY perform a "cut-through",
namely when RP' receives multicast data packets sent from sources
to RP, it not only forwards them to RP, but also forwards them directly
onto the multicast tree built in the I-IPv6 network. (S,G,rpt) messages should
be sent towards RP to avoid reduplication.</t>
<t>E-IP network supports ASM, I-IP network supports ASM<vspace/>
To keep it as simple as possible, we treat I-IP network as SSM and
the solution is the same as the third scenario.</t>
</list>
</t>
</section>
<section title="Group Address Mapping">
<t>To keep one-to-one group address mapping simple, the group address
range of E-IP IPv6 can be reduced in a number
of ways to limit the scope of addresses that need to be mapped into
the I-IP IPv4 space.</t>
<t>A recommended multicast address format is defined
in <xref target="I-D.boucadair-behave-64-multicast-address-format"></xref>.
The high order bits of the E-IPv6 address range will be fixed for
mapping purposes.
With this scheme, each IPv4 multicast address can be mapped into an
IPv6 multicast address(with the assigned prefix), and each IPv6
multicast address with the assigned prefix can be mapped into IPv4
multicast address.</t>
</section>
<section title="Actions performed by AFBR">
<t>The following actions are performed by AFBRs</t>
<t>
<list style="symbols">
<t>Receive E-IPv6 PIM messages<vspace/>
When a downstream AFBR receives an E-IPv6 PIM message, it should check
the address family of the upstream router. If the address family is
IPv6, the AFBR should not translate this message; otherwise it should
take the following operation.</t>
<t>Translate E-IPv6 PIM messages into I-IPv4 PIM messages<vspace/>
E-IPv6 PIM message with S(or *) and G is translated into I-IPv4
PIM message with S' and G' following the rules specified above.</t>
<t>Transmit I-IPv4 PIM messages<vspace/>
The downstream AFBR sends the I-IPv4 PIM message to the upstream
AFBR. When the upstream AFBR receives this I-IPv4 PIM message, it
checks the source address and judges that the message
is a translated message, then translates the message back to
E-IPv6 PIM message and sends it towards source or RP.</t>
<t>Process and forward multicast data<vspace/>
On receiving multicast data from upstream routers, the AFBR looks up its
forwarding table to check the IP address of each outgoing interface. If there
exists at least one outgoing interface whose IP address family is different
from the incoming interface, the AFBR should encapsulate/decapsulate this
packet and forward it to the outgoing interface(s), and then forward
the data to the other outgoing interfaces without encapsulation/decapsulation.
</t>
</list>
</t>
</section>
</section>
<section title="Security Considerations">
<t>The AFBR routers could maintain secure communications through the use
of Security Architecture for the Internet Protocol as described
in[RFC4301]. But when adopting some schemes that will cause heavy burden
on routers, some attacker may use it as a tool for DDoS attack.</t>
</section>
<section title="IANA Considerations">
<t>When AFBRs perform address mapping, they should
follow some predefined rules, especially the IPv6 prefix for source
address mapping should be predefined, so that ingress AFBR and egress
AFBR can finish the mapping procedure correctly. The IPv6
prefix for translation can be unified within only the transit core, or
within global area. In the later condition, the prefix should be
assigned by IANA.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2784" ?>
<?rfc include="reference.RFC.3991" ?>
<?rfc include="reference.RFC.2373" ?>
<?rfc include="reference.RFC.4291" ?>
<?rfc include="reference.RFC.4601" ?>
<?rfc include="reference.RFC.4925" ?>
<?rfc include="reference.RFC.5496" ?>
<?rfc include="reference.RFC.5565" ?>
<?rfc include="reference.RFC.6052" ?>
</references>
<references title="Informative References">
<?rfc include="reference.I-D.ietf-l3vpn-2547bis-mcast" ?>
<?rfc include="reference.I-D.draft-boucadair-behave-64-multicast-address-format-02" ?>
</references>
<section title="Acknowledgements">
<t>Wenlong Chen, Xuan Chen, Alain Durand, Yiu Lee, Jacni Qin and Stig Venaas
provided useful input into this document.</t>
</section>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 10:07:42 |