Network Working Group M. Xu
Internet-Draft Y. Cui
Expires: April 21, 2011 Shu. Yang
Tsinghua University
Chris. Metz
greg. Shepherd
Cisco Systems
October 18, 2010
Softwire Mesh Multicast
draft-xu-softwire-mesh-multicast-00
Abstract
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.
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.
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
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 21, 2011.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Scenarios of Interest . . . . . . . . . . . . . . . . . . . . 8
3.1. IPv6-over-IPv4 . . . . . . . . . . . . . . . . . . . . . . 8
3.2. IPv4-over-IPv6 . . . . . . . . . . . . . . . . . . . . . . 9
4. IPv4-over-IPv6 . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Group Address Mapping . . . . . . . . . . . . . . . . . . 11
4.3. Actions performed by AFBR . . . . . . . . . . . . . . . . 12
5. IPv6-over-IPv4 . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2. I-IP IPv4 Address Limitations . . . . . . . . . . . . . . 13
5.3. E-IP IPv6 Addressing . . . . . . . . . . . . . . . . . . . 13
5.4. Aggregation or Compression . . . . . . . . . . . . . . . . 13
5.5. AFBR Signaling . . . . . . . . . . . . . . . . . . . . . . 14
6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
9.1. Normative References . . . . . . . . . . . . . . . . . . . 18
9.2. Informative References . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
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).
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 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.
A framework on how to support such methods discribed 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
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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
interconnecting two or more networks using different IP address
families. In the context of softwires mesh multicast, the AFBR runs
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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.
o Upstream AFBR: The AFBR routers that are located at the upstream of
multicast data flow.
o Downstream AFBR: The AFBR routers that are located at the
downstream of 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 transit (or backbone) network.
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 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.
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.
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3. Scenarios of Interest
This section describes the two different scenarios where softwires
mesh multicast will apply.
3.1. 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 2: 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 2.
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
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IPv6 group address is scoped.
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.
3.2. 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 3: 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 3.
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.
The IPv4-over-IPv6 scenario is an emerging requirement as network
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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.
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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
separate from E-IP multicast state.
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.
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.
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 [7] is appended to
the PIMv6 message on its ways to the AFBR.
4.2. Group Address Mapping
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.
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0 8 16 96 127
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|FF XX| ISP Assigned Prefix | v4 address|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 8: Mapping IPv4 to IPv6 group address
The first two octets identify the the IPv6 multicast address format
described in [3]. The following 10 octets are assigned by the
network operator and the last 4 octets are the IPv4 address.
Additional group address mapping options will be provided in the next
version of this draft.
4.3. Actions performed by AFBR
The following actions are performed by the AFBR
o Process E-IPv4 PIM messages
o Perform E-IPv4 PIM to I-IP PIMv6 message conversion
o Transmit and receive I-IP PIMv6 messages
Details of these procedures will be outlined in the next version of
this document.
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5. IPv6-over-IPv4
5.1. Discussion
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.
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.
5.2. I-IP IPv4 Address Limitations
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.
5.3. E-IP IPv6 Addressing
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.
5.4. Aggregation or Compression
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
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AFBR signaling mechanism to communicate the mapping function and the
group of interest between E-IP sites.
5.5. AFBR Signaling
Specific signaling procedures and examples will be included in the
next version of this document.
]
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6. Summary
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.
The latter scenario introduces several challenges relatd to group
address constraints, AFBR signaling and the potential need for
aggregation at the edge.
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7. 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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8. IANA Considerations
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.
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9. References
9.1. 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.
9.2. Informative References
[9] Wijnands, I., Boers, A., and E. Rosen, "The RPF Vector TLV",
draft-ietf-pim-rpf-vector-08 (work in progress), January 2009.
[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] Metz, C., Cui, Y., and M. Xu, "Softwires Mesh Multicast Problem
Statement", draft-metz-softwires-multicast-problem-statement-00
(work in progress), February 2008.
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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: yangshu1988@gmail.com
Chris Metz
Cisco Systems
170 West Tasman Drive
San Jose, California 95134-1706
USA
Phone: +1-408-525-3275
Email: chmetz@cisco.com
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Greg Shepherd
Cisco Systems
170 West Tasman Drive
San Jose, California 95134
USA
Phone: +1-541-912-9758
Email: shep@cisco.com
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