One document matched: draft-xu-softwire-mesh-multicast-00.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-00" ipr="pre5378Trust200902">
<front>
<title abbrev="softwire mcast framework">Softwire Mesh Multicast</title>
<author fullname="Mingwei Xu" initials="M" surname="Xu">
<organization>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 fullname="Yong Cui" initials="Y" surname="Cui">
<organization>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 fullname="Shu Yang" initials="Shu" surname="Yang">
<organization>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>yangshu1988@gmail.com</email>
</address>
</author>
<author fullname="Chris Metz" initials="Chris" surname="Metz">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<city>San Jose, California</city>
<code>95134-1706</code>
<country>USA</country>
</postal>
<phone>+1-408-525-3275</phone>
<email>chmetz@cisco.com</email>
</address>
</author>
<author fullname="Greg Shepherd" initials="greg" surname="Shepherd">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<city>San Jose, California</city>
<code>95134</code>
<country>USA</country>
</postal>
<phone>+1-541-912-9758</phone>
<email>shep@cisco.com</email>
</address>
</author>
<date month="October" year="2010" />
<abstract>
<t>The Internet will need to support IPv4 and IPv6 packets. Both address
families and their attendent 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 suppporting 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 will need to support IPv4 and IPv6 packets. Both address
families and their attendent 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 a 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 discribed 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 softwires mesh multicast, the AFBR runs E-IP
and I-IP control planes to maintain E-IP and I-IP multicast state
respectively and performs the appropriate encapsulation/decapsulation
client E-IP multicast packets for transport across the I-IP core. An
AFBR will can act as a source and/or receiver in an I-IP multicast
tree.</t>
<t>o Upstream AFBR: The AFBR routers that are located at the upstream of
multicast data flow.</t>
<t>o Downstream AFBR: The AFBR routers that are located at the
downstream of 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 transit (or backbone)
network.</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 branching 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. An I-IPv6 core network
runs IPv6 and an I-IPv4 core network runs IPv4.</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 branching 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="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 2: 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 2.</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 effort in the
form of inter-AFBR signaling will be required to ensure client E-IPv6
multicast packets are 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 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 softwires mesh multicast scenario will be a
necessary feature supported by networks operators. </t>
</section>
<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 3: 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 3.</t>
<t>Because of the much larger IPv6 group address space, it will not be
a problem to map individual client E-IPv4 trees 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 will 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 accomodated. </t>
<t></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
separate from E-IP multicast state.</t>
<t>Suppose a downstream AFBR D 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 D router can translate the E-IPv4 PIMv4 message into an
I-IPv6 PIMv6 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 A, it should translate the message back into an
E-IPv4 PIM message. The result of these actions is the construction
of E-IPv4 tree with (S,G) or (*,G) state deposited in the E-IP
networks and an I-IP trees with (S',G') or (*,G') contained in the I-IP
network.</t>
<t>In this case it is incumbent upon the AFBR routers to perform PIM
signaling message conversions in the control plane and IP group
address conversions or mappings in the data plane. It becomes possible to
devise an algorithmic IPv4-to-IPv6 group mapping at AFBR. AFBR A can
translate the IPv4 source address S into the corresponding IPv4-mapped
IPv6 address, and then B can translate it back. A proposed group
address mapping is described in the next section.</t>
<t>Note that the I-IPv6 core routers do not contain E-IPv4 routes. To
ensure that PIMv6 join messages can reach the correct AFBR router
leading to E-IPv4 source network, the RPF Vector <xref
target="RFC5496"></xref> is appended to the PIMv6 message on its ways
to the AFBR.</t>
</section>
<section title="Group Address Mapping">
<t></t>
<t>For IPv4-over-IPv6 scenario, an simple algorithmic mapping between
IPv4 multicast group addresses and IPv6 group addresses is supported.
One possibility is to prepend the operator's IPv6 prefix to the IPv4
address when mapping an E-IP address to an I-IP address, just like
figure 8 shows.</t>
<figure>
<artwork><![CDATA[
0 8 16 96 127
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|FF XX| ISP Assigned Prefix | v4 address|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
]]></artwork>
<postamble>Figure 8: Mapping IPv4 to IPv6 group address</postamble>
</figure>
<t></t>
<t>The first two octets identify the the IPv6 multicast address format
described in <xref target="RFC2373"></xref>. The following 10 octets
are assigned by the network operator and the last 4 octets are the
IPv4 address.</t>
<t>Additional group address mapping options will be provided in the
next version of this draft. </t>
</section>
<section title="Actions performed by AFBR">
<t>The following actions are performed by the AFBR</t>
<t><list style="symbols">
<t>Process E-IPv4 PIM messages</t>
<t>Perform E-IPv4 PIM to I-IP PIMv6 message conversion</t>
<t>Transmit and receive I-IP PIMv6 messages</t>
</list></t>
<t>Details of these procedures will be outlined in the next version of
this document.</t>
</section>
</section>
<section title="IPv6-over-IPv4">
<section title="Discussion">
<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
separate 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. There are however a number
of approaches to either reduce the scope of the one-to-one requirement
or to provide minimal aggregation as a compromise. These can be
explored in greater detail and articulated in future drafts for
consideration of the Softwire Multicast solution by the working group.
Simple examples of these follow as discussion items for this work in
progress.</t>
</section>
<section title="I-IP IPv4 Address Limitations">
<t>We must first consider what range of I-IP IPv4 multicast addresses
are available for the IPv6-over-IPv4 mapping. If the I-IP provider is
also using IPv4 multicast for other services then the entire 224/4
address range will not be available. Additionally, the 239/8 scoped
range may also be used for other services limiting the available
addresses for Softwire Multicast even further. These limitations need
to be addressed in any Softwire Mesh Multicast IPv6-over-IPv4
solution.</t>
</section>
<section title="E-IP IPv6 Addressing">
<t>The multicast 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. The high order bits of the IPv6 address range may
be discarded for mapping purposes. Additional bit may also be reduced
if the agreed solution limits the E-IP IPv6 multicast addresses
available for Softwire Multicast.</t>
</section>
<section title="Aggregation or Compression ">
<t>It will be necessary in this use-case to support a non -
"one-to-one" mapping of E-IPv6 to I-IPv4 trees. This could take the
form of address aggregation or address compression using an agreed
upon hashing mechanism. In both cases there may be a requirement for
an AFBR signaling mechanism to communicate the mapping function and
the group of interest between E-IP sites. </t>
</section>
<section title="AFBR Signaling">
<t>Specific signaling procedures and examples will be included in the
next version of this document.</t>
<t>]</t>
</section>
</section>
<section title="Summary">
<t>There are two scenarios applicable to softwires mesh multicast:
IPv4-over-IPv6 and IPv6-over-IPv4. In the former senario, one-to-one
group address mapping and PIM signaling conversion can be realized. </t>
<t>The latter scenario introduces several challenges relatd to group
address constraints, AFBR signaling and the potential need for
aggregation at the edge. </t>
</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>For Inter-AFBR signaling, address mapping is applied, and it should
follow some predefined rule, especially the format of IPv6 prefix for
address mapping should be predefined, so that ingress AFBR and egress
AFBR can finish the mapping procedure correctly. The format of IPv6
prefix for translation can be unified within only the transit core, or
within global area. In the later condition, the format 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" ?>
</references>
<references title="Informative References">
<?rfc include="reference.I-D.ietf-pim-rpf-vector" ?>
<?rfc include="reference.I-D.ietf-l3vpn-2547bis-mcast" ?>
<?rfc include="reference.I-D.draft-metz-softwires-multicast-problem-statement-00" ?>
</references>
</back>
</rfc>
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