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Versions: 00 01 02 draft-ietf-softwire-mesh-multicast
Network Working Group M. Xu
Internet-Draft Y. Cui
Expires: January 10, 2012 S. Yang
Tsinghua University
C. Metz
G. Shepherd
Cisco Systems
July 9, 2011
Softwire Mesh Multicast
draft-xu-softwire-mesh-multicast-02
Abstract
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.
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.
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 January 10, 2012.
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Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Contributions published or made publicly available before November
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Without obtaining an adequate license from the person(s) controlling
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not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Scenarios of Interest . . . . . . . . . . . . . . . . . . . . 7
3.1. IPv4-over-IPv6 . . . . . . . . . . . . . . . . . . . . . . 7
3.2. IPv6-over-IPv4 . . . . . . . . . . . . . . . . . . . . . . 8
4. IPv4-over-IPv6 . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Source Address Mapping . . . . . . . . . . . . . . . . . . 10
4.3. Group Address Mapping . . . . . . . . . . . . . . . . . . 12
4.4. Actions performed by AFBR . . . . . . . . . . . . . . . . 12
5. IPv6-over-IPv4 . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . 14
5.2. Source Address Mapping . . . . . . . . . . . . . . . . . . 14
5.3. Group Address Mapping . . . . . . . . . . . . . . . . . . 16
5.4. Actions performed by AFBR . . . . . . . . . . . . . . . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 17
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1. Normative References . . . . . . . . . . . . . . . . . . . 19
8.2. Informative References . . . . . . . . . . . . . . . . . . 19
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
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).
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.
[6] 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.
One method to accomplish this is to re-use the multicast VPN approach
outlined in [10]. 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.
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.
A framework on how to support such methods is described in [8]. 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.
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2. Terminology
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.
._._._._. ._._._._.
| | | | --------
| 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 | --------
._._._._ ._._._._
Figure 1: Softwire Mesh Multicast Framework
Terminology used in this document:
o Address Family Border Router (AFBR) - A dual-stack router
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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.
o Upstream AFBR: The AFBR router that is located at the upstream of a
multicast data flow.
o Downstream AFBR: The AFBR router that is located at the downstream
of a multicast data flow.
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.
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.
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.
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.
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3. Scenarios of Interest
This section describes the two different scenarios where softwires
mesh multicast will apply.
3.1. IPv4-over-IPv6
._._._._. ._._._._.
| 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| --------
._._._._ ._._._._
Figure 2: IPv4-over-IPv6 Scenario
In this scenario, the E-IP client networks run IPv4 and I-IP core
runs IPv6. This scenario is illustrated in Figure 2.
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.
The IPv4-over-IPv6 scenario is an emerging requirement as network
operators build out native IPv6 backbone networks. These networks
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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.
3.2. IPv6-over-IPv4
._._._._. ._._._._.
| 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| --------
._._._._ ._._._._
Figure 3: IPv6-over-IPv4 Scenario
In this scenario, the E-IP Client Networks run IPv6 while the I-IP
core runs IPv4 and is illustrated in Figure 3.
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
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and IPv4 group addresses unless the IPv6 group address is scoped.
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.
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4. IPv4-over-IPv6
4.1. Mechanism
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.
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.
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.
4.2. Source Address Mapping
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:
o E-IP network supports SSM, I-IP network supports SSM
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 [9]:
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0-------------32--40--48--56--64--72--80--88--96--104---------|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| prefix |v4(32) | u | suffix |source address |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 4: IPv4-Embedded IPv6 Virtual Source Address Format
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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 [9]; "v4" field is the IP address
of one of upstream AFBR's E-IPv4 interface; "u" field is defined
in [4], 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.
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).
o E-IP network supports SSM, I-IP network supports ASM
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.
o E-IP network supports ASM, I-IP network supports SSM
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.
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.
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o E-IP network supports ASM, I-IP network supports ASM
To keep it as simple as possible, we treat I-IP network as SSM and
the solution is the same as the third scenario.
4.3. Group Address Mapping
For IPv4-over-IPv6 scenario, a simple algorithmic mapping between
IPv4 multicast group addresses and IPv6 group addresses is supported.
[11] has already defined an applicable format. Figure 5 is a
reminder of the format:
| 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|
+-+-+-+-+
Figure 5: IPv4-Embedded IPv6 Multicast Address Format: SSM Mode
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.
4.4. Actions performed by AFBR
The following actions are performed by AFBRs:
o Receive E-IPv4 PIM messages
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.
o Translate E-IPv4 PIM messages into I-IPv6 PIM messages
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.
o Transmit I-IPv6 PIM messages
The downstream AFBR sends the I-IPv6 PIM message to the upstream
AFBR. When the upstream AFBR receives this I-IPv6 PIM message, it
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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.
o Process and forward multicast data
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.
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5. IPv6-over-IPv4
5.1. Mechanism
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.
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.
5.2. Source Address Mapping
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:
o E-IP network supports SSM, I-IP network supports SSM
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.
We apply a fixed IPv6 prefix and static mapping to solve this
problem. A recommended source address format is defined in [9].
Figure 6 is a reminder of the format:
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0-------------32--40--48--56--64--72--80--88--96--104---------|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| prefix(96) | v4(32) |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 6: IPv4-Embedded IPv6 Source Address Format
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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 [9]; "v4" field is the
corresponding I-IPv4 source address.
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'.
o E-IP network supports SSM, I-IP network supports ASM
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.
o E-IP network supports ASM, I-IP network supports SSM
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.
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.
o E-IP network supports ASM, I-IP network supports ASM
To keep it as simple as possible, we treat I-IP network as SSM and
the solution is the same as the third scenario.
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5.3. Group Address Mapping
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.
A recommended multicast address format is defined in [11]. 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.
5.4. Actions performed by AFBR
The following actions are performed by AFBRs
o Receive E-IPv6 PIM messages
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.
o Translate E-IPv6 PIM messages into I-IPv4 PIM messages
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.
o Transmit I-IPv4 PIM messages
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.
o Process and forward multicast data
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.
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6. Security Considerations
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.
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7. IANA Considerations
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.
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8. References
8.1. Normative References
[1] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina,
"Generic Routing Encapsulation (GRE)", RFC 2784, March 2000.
[2] Foster, B. and F. Andreasen, "Media Gateway Control Protocol
(MGCP) Redirect and Reset Package", RFC 3991, February 2005.
[3] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[4] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[5] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[6] Li, X., Dawkins, S., Ward, D., and A. Durand, "Softwire Problem
Statement", RFC 4925, July 2007.
[7] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path
Forwarding (RPF) Vector TLV", RFC 5496, March 2009.
[8] Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh
Framework", RFC 5565, June 2009.
[9] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. Li,
"IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
8.2. Informative References
[10] Aggarwal, R., Bandi, S., Cai, Y., Morin, T., Rekhter, Y.,
Rosen, E., Wijnands, I., and S. Yasukawa, "Multicast in MPLS/
BGP IP VPNs", draft-ietf-l3vpn-2547bis-mcast-10 (work in
progress), January 2010.
[11] Boucadair, M., Qin, J., Lee, Y., Venaas, S., Li, X., and M. Xu,
"IPv4-Embedded IPv6 Multicast Address Format",
draft-boucadair-behave-64-multicast-address-format-02 (work in
progress), June 2011.
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Appendix A. Acknowledgements
Wenlong Chen, Xuan Chen, Alain Durand, Yiu Lee, Jacni Qin and Stig
Venaas provided useful input into this document.
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Authors' Addresses
Mingwei Xu
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R. China
Phone: +86-10-6278-5822
Email: xmw@cernet.edu.cn
Yong Cui
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R. China
Phone: +86-10-6278-5822
Email: cuiyong@tsinghua.edu.cn
Shu Yang
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R. China
Phone: +86-10-6278-5822
Email: yangshu@csnet1.cs.tsinghua.edu.cn
Chris Metz
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
USA
Phone: +1-408-525-3275
Email: chmetz@cisco.com
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Greg Shepherd
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
USA
Phone: +1-541-912-9758
Email: shep@cisco.com
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