Internet DRAFT - draft-sarikaya-softwire-4rdmulticast
draft-sarikaya-softwire-4rdmulticast
Network Working Group B. Sarikaya
Internet-Draft Huawei USA
Intended status: Standards Track February 19, 2013
Expires: August 23, 2013
Multicast Support for MAP-E
draft-sarikaya-softwire-4rdmulticast-06.txt
Abstract
This memo specifies MAP-E (together with MAP-T and 4rd)'s multicast
component so that IPv4 hosts can receive multicast data from IPv4
servers over an IPv6 network. In the encapsulation solution for
encapsulation variant of Mapping of Address and Port (MAP), MAP-E,
IGMP Proxy at the MAP-E Customer Edge router uses IPv4-in-IPv6 tunnel
established by MAP-E to exchange IGMP messages to establish multicast
state at MAP-E Border Relay so that MAP-E Border Relay can tunnel
IPv4 multicast data to IPv4 hosts connected to MAP-E Customer Edge
device. In the Translation Multicast solution for the translation
variant of MAP, MAP-T and 4rd, IGMP messages are translated into MLD
messages at the CE router which is IGMP/MLD Proxy and sent to the
network in IPv6. MAP-T/4rd Border Relay does the reverse translation
and joins IPv4 multicast group for MAP-T/4rd hosts. Border Relay as
multicast router receives IPv4 multicast data and translates the
packet into IPv6 multicast data and sends downstream on the multicast
tree. Member CEs receive multicast data, translate it back to IPv4
and transmit to the hosts.
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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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 August 23, 2013.
Copyright Notice
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Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Encapsulation Multicast Architecture . . . . . . . . . . . 5
4.2. MAP-T and 4rd Translation Architecture . . . . . . . . . . 6
5. Encapsulation Multicast Operation . . . . . . . . . . . . . . 7
5.1. Encapsulation Interface Considerations . . . . . . . . . . 9
5.2. Avalanche Problem Considerations . . . . . . . . . . . . . 10
6. MAP-T and 4rd Translation Multicast Operation . . . . . . . . 10
6.1. Address Translation . . . . . . . . . . . . . . . . . . . 11
6.2. Protocol Translation . . . . . . . . . . . . . . . . . . . 12
6.3. Supporting IPv6 Multicast in MAP-T and 4rd Translation
Multicast . . . . . . . . . . . . . . . . . . . . . . . . 13
6.4. Learning Multicast Prefixes for IPv4-embedded IPv6
Multicast Addresses . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
10.2. Informative references . . . . . . . . . . . . . . . . . . 17
Appendix A. Group Membership Message Translation Details . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
With IPv4 address depletion on the horizon, many techniques are being
standardized for IPv6 migration including Mapping of Address and Port
(MAP) - Encapsulation, - Translation and 4rd [I-D.ietf-softwire-map],
[I-D.ietf-softwire-map-t], [I-D.ietf-softwire-4rd]. MAP/4rd enables
IPv4 hosts to communicate with external hosts using IPv6 only ISP
network. MAP/4rd Customer Edge (CE) device's LAN side is dual stack
and WAN side is IPv6 only. CE tunnels/translates IPv4 packets
received from the LAN side to 4rd Border Relays (BR). BRs have
anycast IPv6 addresses and receive encapsulated/translated packets
from CEs over a virtual interface. MAP/4rd operation is stateless.
Packets are received/ sent independent of each other and no state
needs to be maintained except for NAT44 operation on IPv4 packets
received from the user.
It should be noted that there is no depletion problem for IPv4
address space allocated for any source multicast and source specific
multicast [RFC3171]. This document is not motivated by the depletion
of IPv4 multicast addresses.
MAP-E, MAP-T and 4rd are unicast only. They do not support
multicast. In this document we specify how multicast from home IPv4
users can be supported in MAP-E (as well as MAP-T and 4rd).
In case of MAP-E we integrate the multicast solution into the MAP-E
tunnel resulting in a multicast tunneling protocol. Multicast
tunneling protocol has the advantage of not requiring multicast
enabled IPv6 network between CE routers and MAP-E BRs.
When MAP-E CE router receives an IGMP join message to an Any-Source
Multicast (ASM) [RFC1112] or Source-Specific Multicast (SSM) group
[RFC4607], it sends an aggregated IGMP membership report message in
the IPv4-in-IPv6 tunnel to the border relay. MAP-E BR joins the
source in the multicast infrastructure and sends multicast data
downstream to all member CEs in the IPv4-in-IPv6 tunnel. When a CE
has no membership state, i.e. after all member hosts leave the
group(s), its state with the BR expires and the CE can send the next
join message in anycast. IPv4 multicast data received at the BR is
tunneled to the member CE in IPv6 and CE decapsulates the packet and
sends IPv4 multicast data packet to the member hosts.
In case IPv6 network is multicast enabled, MAP-T/4rd can provide
multicast service to the hosts using MAP-T/4rd Multicast Translation
based solution. A Multicast Translator can be used that receives
IPv4 multicast group management messages in IGMP and generates
corresponding IPv6 group management messages in MLD and sends them to
IPv6 network towards MAP-T/4rd Border Relay. We use
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[I-D.ietf-softwire-map-t] or [I-D.ietf-softwire-4rd] for sending IPv4
multicast data in IPv6 to the CE routers. At MAP-T/4rd CE router
another translator is needed to translate IPv6 multicast data into
IPv4 multicast data.
It should be noted that if IPv6 network is multicast enabled the
translation multicast solution presented in Section 6 can also be
used for MAP-E.
In this document we address MAP-E (and MAP-T/4rd) multicast problem
and propose two architectures: Multicast Tunneling and Multicast
Translation based solutions. Section 2 is on terminology, Section 3
is on requirements, Section 4 is on architecture, Section 5 is on
multicast tunneling protocol Section 6 is on multicast translation
protocol, and Section 7 states security considerations.
2. Terminology
This document uses the terminology defined in
[I-D.ietf-softwire-map], [I-D.ietf-softwire-map-t],
[I-D.ietf-softwire-4rd], [RFC3810] and [RFC3376].
3. Requirements
This section states requirements on MAP-E, MAP-T and 4rd multicast
support protocol.
IPv4 hosts connected to MAP-E, MAP-T and 4rd CE router MUST be able
to join multicast groups in IPv4 and receive multicast data.
Any source multicast (ASM) SHOULD be supported and source specific
multicast (SSM) MUST be supported.
In case of encapsulation solution, MAP-E CE MUST support IGMP Proxy
as defined in [RFC4605]. MAP-E BR MUST support IGMP querier
downstream and MAP-E BR may support PIM protocol or IGMP router
upstream.
In case of translation solution, MAP-T and 4rd CE MUST support IGMP
to MLD translation. MAP-T and 4rd CE MUST be MLD Proxy as defined in
[RFC4605]. MAP-T and 4rd BR MUST support MLD Querier. MAP-T and 4rd
BR MUST support join/leave operations in IPv4 multicast upstream.
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4. Architecture
In MAP-E, MAP-T and 4rd, there are hosts (possibly IPv4/ IPv6 dual
stack) served by MAP-E, MAP-T and 4rd Customer Edge device. CE is
dual stack facing the hosts and IPv6 only facing the network or WAN
side. MAP-E, MAP-T and 4rd CE may be local IPv4 Network Address and
Port Translation (NAPT) box [RFC3022] by assigning private IPv4
addresses to the hosts. MAP-E, MAP-T and 4rd CEs in the same domain
may use shared public IPv4 addresses on their WAN side and if they do
they should avoid ports outside of the allocated port set for NAPT
operation. At the boundary of the network there is MAP-E, MAP-T and
4rd Border Relay. BR receives IPv4 packets tunneled in IPv6 from CE
and decapsulates them and sends them out to IPv4 network.
Unicast MAP-E, MAP-T and 4rd are stateless except for the local NAPT
at the CE. Each IPv4 packet sent by CE treated separately and
different packets from the same CE may go to different BRs or CEs.
CE encapsulates IPv4 packet in IPv6 with destination address set to
BR address (usually anycast IPv6 address). BR receives the
encapsulated packet and decapsulates and send it to IPv4 network.
CEs are configured with Rule IPv4 Prefixes, Rule IPv6 Prefixes and
with an BR IPv6 anycast address. BR receives IPv4 packets addressed
to this ISP and from the destination address it extracts the
destination host's IPv4 address and uses this address as destination
address and encapsulates the IPv4 packet in IPv6 and sends it to
IPv6-only network.
4.1. Encapsulation Multicast Architecture
Encapsulation variant of MAP called MAP-E network lends itself easily
to the Multicast Tunneling architecture. Dual stack hosts are
connected to the Customer Edge router and it is multicast enabled.
It is assumed that IPv6 only network is the unicast only network and
that IPv6 multicast is not enabled or IPv6 multicast is partially
enabled. At the boundary of the network MAP-E Border Relay is
connected to the native multicast backbone infrastructure.
We place IGMP Proxy at the CE router. CE router serves all the
connected hosts. For multicast traffic, CE Router uses MAP-E
tunneling interface with MAP-E BR to send/receive IGMP messages using
IPv4-in-IPv6 tunnel [RFC2473].
MAP-E BR is IGMP Router towards the CEs and it could be IGMP Router
or PIM router upstream. A given relay and all CEs connected to it
can be considered to be on a separate logical link. On this link,
gateways and relay communicate using IPv4-in-IPv6 tunneling to
transmit and receive multicast control messages for membership
management and multicast data from the relay to the gateways.
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All the elements of MAP-E multicast support system with tunneling are
shown in Figure 1.
Dual Stack Hosts IPv4
+----+ Network
| H1 | IPv6
+----+ +-------+ only +--------------+ +
+----+ | CE | network | BR |
| H2 | ---| IGMP |--- -- |IGMP | IGMP | IPv6
+----+ | Proxy | |Router| PIM | Network
+----+ +-------+ +--------------+
| H3 |
+----+
Figure 1: Architecture of MAP-E Multicast Tunneling
4.2. MAP-T and 4rd Translation Architecture
In case IPv6 only network is multicast enabled, translation multicast
architecture can be used. CE implements IGMP Proxy function
[RFC4605] towards the LAN side and MLD Proxy on its WAN interface.
IPv4 hosts send their join requests (IGMP Membership Report messages)
to CE. CE as a MLD proxy sends aggregated MLD Report messages
upstream towards BR. CE replies MLD membership query messages with
MLD membership report messages based on IGMP membership state in the
IGMP/MLD proxy.
BR is MLD querier on its WAN side. On its interface to IPv4 network
BR may either have IGMP client or PIM. PIM being able to support
both IPv4 and IPv6 multicast should be preferred. BR receives MLD
join requests, extracts IPv4 multicast group address and then joins
the group upstream, possibly by issuing a PIM join message.
IPv4 multicast data received by the BR as a leaf node in IPv4
multicast distribution tree is translated into IPv6 multicast data by
the translator using [I-D.ietf-softwire-map-t],
[I-D.ietf-softwire-4rd] and then sent downstream to the IPv6 part of
the multicast tree to all downstream routers that are members. IPv6
data packet eventually gets to the CE. At the CE, a reverse
[I-D.ietf-softwire-map-t], [I-D.ietf-softwire-4rd] operation takes
place by the translator and then IPv4 multicast data packet is sent
to the member hosts on the LAN interface. [I-D.ietf-softwire-map-t],
[I-D.ietf-softwire-4rd] are modified to handle multicast addresses.
In order to support SSM, IGMPv3 MUST be supported by the host, CE and
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BR. For ASM, BR MUST be the Rendezvous Point (RP).
MAP-T and 4rd Translation Multicast solution uses the multicast 46
translator in not one but two places in the architecture: at the CE
router and at the Border Relay. IPv4 multicast data received at 4rd
BR goes through a [I-D.ietf-softwire-4rd] header-mapping into IPv6
multicast data at the BR and another [I-D.ietf-softwire-4rd] header-
mapping back to IPv4 multicast data at the CE router. Encapsulation
variant of [I-D.ietf-softwire-4rd] is not used. In case of MAP-T,
IPv4 data packet is translated using v4 to v6 header translation
using multicast addresses instead of the mapping algorithm used in
[I-D.ietf-softwire-map-t].
All the elements of MAP-T and 4rd translation-based multicast support
system are shown in Figure 2.
Dual Stack Hosts IPv4
+----+ Network
| H1 | +----------+ IPv6 +-------------+
| | | CE | | BR |
+----+ |Translator| only | Translator |
|MAP-T/4rd | | MAP-T/4rd |
+----+ | | network | |IGMP| +
| H2 | ---|IGMP-MLD |--------- -- |MLD | or | IPv6
+----+ | Proxy | |Querier |PIM | Network
+----+ +----------+ +-------------+
| H3 |
+----+
Figure 2: Architecture of MAP-T and 4rd Translation Multicast
5. Encapsulation Multicast Operation
When a host (H1, H2 or H3 in Figure 1) wants to join an IPv4
multicast group G or (S,G), it sends an IGMP report (IGMPv3 report
for a source-specific group) to CE router.
CE encapsulates IGMP report messages in IPv6 and sends it over the
tunnel to BR in anycast. CE router uses BR's anycast address this CE
router is configured with. After CE receives unicast address of BR,
it sends all subsequent IGMP messages for G or (S,G) in unicast.
BR (topologically closest to this CE router) receives the message,
decapsulates it and then lets IGMP router to process it. On the
upstream, an IGMP Join message is sent to subscribe group G or (S,G)
or a PIMv4 Join message is sent if PIM is supported. BR establishes
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membership state for group G or (S,G). BR sends all related IGMP
messages to this CE in unicast using IPv4-in-IPv6 tunneling.
CE now has BR's unicast address which it uses to send all IGMP
packets for group G for any source multicast or (S,G) for source
specific multicast. If CE receives multiple join messages for the
same group G, CE sends an aggregated join message to BR.
If CE receives another join message for a different group G', (S',G')
CE encapsulates it and sends it in anycast to the BR. This enables
the use of multiple BRs that may be deployed as anchor points and
makes downstream multicast data delivery more efficient.
A CE is required to assist in IGMP signaling and data forwarding
between the hosts that it serves and the corresponding BRs that are
handling the multicast group G or (S,G). CE must have IGMP Proxy for
each upstream tunnel interface that has been established with the BR.
The CE decides on the mapping of downstream links to a proxy instance
connected to an upstream link to a BR based on the unicast source
IPv6 address in the packets received from BR. Because of this BRs
MUST use the unicast source IPv6 address in packets sent to CEs.
Encapsulation at the CE is according to [RFC2473] with an IPv4
payload carrying IGMP messages.
On the reception of IGMP reports from the hosts, the CE must identify
the corresponding proxy instance from the incoming interface and
perform regular IGMP proxy operations of inserting, updating or
removing multicast forwarding state on the incoming interface and
will merge state updates into the IGMP proxy membership database. It
will then send an aggregated Report via the upstream tunnel to the BR
when the membership database changes.
On the reception of IGMP queries, the CE proxy instance will answer
the Queries on behalf of all active downstream receivers maintained
in its membership database. Queries sent by the BR do not force the
CE to trigger corresponding messages immediately towards hosts.
BR acts as the default multicast querier for the corresponding CE.
It implements the function of the designated multicast router or a
further IGMP proxy. After BR receives IGMP Join message it adds the
tunnel to the CE in its outgoing interface list for the group (G) or
the source, group (S,G) that the host wants to join. BR establishes
group-/source-specific multicast forwarding states at its
corresponding downstream tunnel interfaces. Afterwards, BR
maintains/removes these group-/source-specific multicast forwarding
states. BR treats its tunnel interfaces as multicast-enabled
downstream links, serving zero to many listening nodes. BR will send
a join message upstream towards the source of the multicast group to
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build a multicast tree in the native multicast infrastructure and
becomes a leaf node in the multicast tree.
BR will send any group management messages (IGMP Report or Query
messages) downstream to specific CEs on the tunnel interface by
encapsulating these IGMP messages in IPv6 using [RFC2473].
As for multicast data, the data packets from the source received at
the BR will be replicated to all interfaces in it's outgoing
interface list as well as the tunnel outgoing interface for all
member CEs. BR sends multicast data in IPv4-in-IPv6 tunnel to the CE
with the data packet encapsulated. Encapsulation is according to
[RFC2473] with an IPv4 payload.
CE receives Multicast Data message over the tunnel interface
associated with the tunnel to BR. After decapsulation, multicast
traffic arriving at the CE on an upstream interface will be forwarded
according to the group-specific or source-specific forwarding states
as acquired for each downstream interface within the IGMP proxy
instance.
5.1. Encapsulation Interface Considerations
Legacy IPv4 in IPv6 tunneling is performed as in [RFC2473]. Packets
upstream from CE carry only IGMP signaling messages and they are not
expected to be subject to fragmentation. However packets downstream,
i.e. multicast data to CE may be subject to fragmentation.
Source and destination addresses of IGMP messages in IPv4-in-IPv6
softwire from CE is as follows:
Source address of IPv6 header is CE IPv6 address, e.g.
2001:db8:0:1::1, destination address is BR anycast address, possibly
shared of the MAP domain.
Source address of IGMP messages is CE's IPv4 interface address, e.g.
192.0.0.2, destination address is the all-systems multicast address
of 224.0.0.1 for IGMP Query, all IGMPv3-capable multicast routers of
224.0.0.22 for IGMPv3 Report, the multicast group specified in the
Group Address field of the Report for IGMPv1 or IGMPv2 Report.
Source and destination addresses of IGMP messages in IPv4-in-IPv6
softwire from BR is as follows:
Source address of IPv6 header is BR's unicast IPv6 address, e.g.
2001:db8:0:2::1, destination address is CE IPv6 address, e.g. 2001:
db8:0:1::1.
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Source address of IGMP messages is CE's IPv4 interface address, e.g.
192.0.2.1, destination address is the all-systems multicast address
of 224.0.0.1 for IGMP Query, all IGMPv3-capable multicast routers of
224.0.0.22 for IGMPv3 Report, the multicast group specified in the
Group Address field of the Report for IGMPv1 or IGMPv2 Report.
Source and destination addresses of multicast data messages in IPv4-
in-IPv6 softwire is as follows:
Source address of IPv6 header is BR IPv6 unicast address, e.g. 2001:
db8:0:2::1, destination address is CE IPv6 address, e.g.
2001:db8:0:1::1.
Source address of IPv4 multicast data is unicast IPv4 address of the
multicast source, e.g. the content provider, destination address is
IPv4 multicast group address.
BR decapsulates datagrams carrying IGMP messages from CE's and then
IGMP/PIM router processing takes over. Network Address Translation
(NAT) is not applied on IGMP messages.
5.2. Avalanche Problem Considerations
In Section 5 BR replicates the data packets from the source received
to all outgoing interfaces for all member CEs. This replication
(often called avalanche problem) can be very costly if there are very
large number of downstream member CEs such as in IPTV application.
Note that the avalanche problem is faced by all multicast solutions
that use tunneling to bypass non-multicast enabled access network.
In multicast MAP-E, one approach that can be used is to deploy MAP-E
BRs close to the user. BRs colocated at the access network gateway
such as at the Border Network Gateway (BNG) could reduce the packet
duplication bottleneck considerably.
In multicast MAP-E, another approach is to exploit multiple BRs that
can be deployed in the network. MAP-E CE can use BR anycast address
when sending an encapsulated upstream IGMP join request and then use
the unicast source address of this BR in subsequent IGMP messages.
6. MAP-T and 4rd Translation Multicast Operation
In this section we specify how the host can subscribe and receive
IPv4 multicast data from IPv4 content providers based on the
architecture defined in Figure 2 in two parts: address translation
and protocol translation. Translation details are given in
Appendix A.
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6.1. Address Translation
IPv4-only host, H1 will join IPv4 multicast group by sending IGMP
Membership Report message upstream towards the IGMP Proxy in
Figure 2. MLD Proxy first creates a synthesized IPv6 address of IPv4
multicast group address using IPv4-embedded IPv6 multicast address
format [I-D.ietf-mboned-64-multicast-address-format]. ASM_MPREFIX64
for any source multicast groups and SSM_MPREFIX64 for source specific
multicast groups are used. Both are /96 prefixes.
SSM_MPREFIX64 is set to ff3x:0:8000::/96, with 'x' set to any valid
scope. ASM_MPREFIX64 values are formed as shown in Figure 3. M bit
MUST BE set to 1. "flgs" and "scop" fields are defined in [RFC3956].
The usage of the "rsv" bits is the same as defined in [RFC3306].
"sub-group-id" field MUST follow the recommendations specified in
[RFC3306] if unicast-based prefix is used or the recommendations
specified in [RFC3956] if embedded-RP is used. The default value is
all zeros.
| 8 | 4 | 4 | 4 | 76 | 32 |
+--------+----+----+----+------------------------------+----------+
|11111111|flgs|scop|rsvM| sub-group-id |v4 address|
+--------+----+----+----+-----------------------------------------+
Figure 3: ASM_MPREFIX64 Formation
Each translator in the upstream BR is assigned a unique ASM_MPREFIX64
prefix. CE (MLD Proxy in CE) can learn this value by means out of
scope with this document. With this, CE can easily create an IPv6
multicast address from the IPv4 group address a.b.c.d that the host
wants to join.
Source-Specific Multicast (SSM) can also be supported similar to the
Any Source Multicast (ASM) described above. In case of SSM, IPv4
multicast addresses use 232.0.0.0/8 prefix. IPv6 SSM_MPREFIX64 is
set to FF3x:0:8000::/96.
Since SSM translation requires a unique address for each IPv4
multicast source, an IPv6 unicast prefix must be configured to the
translator in the upstream BR to represent IPv4 sources. This prefix
is prepended to IPv4 source addresses in translated packets.
The join message from the host for the group ASM_MPREFIX64:a.b.c.d or
SSM_MPREFIX64:a.b.c.d or an aggregate join message will be received
by MLD querier at the BR. BR as multicast anchor checks the group
address and recognizes ASM_MPREFIX64 or SSM_MPREFIX64 prefix. It
next checks the last 32 bits is an IPv4 multicast address in range
224/8 - 239/8. If all checks succeed, IGMPv4 Client joins a.b.c.d
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using IGMP on its IPv4 interface.
Joining IPv4 groups can also be done using PIM since PIM supports
both IPv4 and IPv6. The advantage of using PIM is that there is no
need to enable IGMP support in neighboring IPv4 routers. The
advantage of using IGMP is that IGMP is a simpler protocol and it is
supported by a wider range of routers. The use of PIM or IGMP is
left as an implementation choice.
6.2. Protocol Translation
The hosts will send their subscription requests for IPv4 multicast
groups upstream to the default router, i.e. Costumer Edge device.
After subscribing the group, the host can receive multicast data from
the CE. The host implements IGMP protocol's host part.
Customer Edge device is IGMP Proxy facing the LAN interface. After
receiving the first IGMP Report message requesting subscription to an
IPv4 multicast group, a.b.c.d, MLD Proxy in the CE's WAN interface
synthesizes an IPv6 multicast group address corresponding to a.b.c.d
and sends an MLD Report message upstream to join the group.
When CE is a NAT or NAPT box assigning private IPv4 addresses to the
hosts, IP Multicast requirements for a Network Address Translator
(NAT) and a Network Address Port Translator (NAPT) stated in
[RFC5135] apply to IGMP messages and IPv4 multicast data packets.
When MAP-T or 4rd BR receives IPv4 multicast data for an IPv4 group
a.b.c.d it [I-D.ietf-softwire-4rd] translates/encapsulates IPv4
packet into IPv6 multicast packet and sends it to IPv6 synthesized
address corresponding to a.b.c.d using ASM_MPREFIX64 or
SSM_MPREFIX64. The header mapping described in
[I-D.ietf-softwire-4rd] Section 4.2 (using Table 1) is used except
for mapping the source and destination addresses. In this document
we use the multicast address translation described in Section 6.1 and
propose it as a complementary enhancement to the translation
algorithm in [I-D.ietf-softwire-4rd].
The IP/ICMP translation translates IPv4 packets into IPv6 using
minimum MTU size of 1280 bytes (Section 4.3 in
[I-D.ietf-softwire-4rd]) but this can be changed for multicast. Path
MTU discovery for multicast is possible in IPv6 so 4rd BR can perform
path MTU discovery for each ASM group and use these values instead of
1280. For SSM, a different MTU value MUST be kept for each SSM
channel. Because of this 8 bytes added by IPv6 fragment header in
each data packet can be tolerated.
Since multicast address translation does not preserve checksum
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neutrality, [I-D.ietf-softwire-4rd] translator/encapsulator at 4rd BR
must however modify the UDP checksum to replace the IPv4 addresses
with the IPv6 source and destination addresses in the pseudo-header
which consists of source address, destination address, protocol and
UDP length fields before calculating the new checksum.
IPv6 multicast data must be translated back to IPv4 at the 4rd CE
(e.g. using Table 2 in Section 4.3 of [I-D.ietf-softwire-4rd]). Such
a task is much simpler than the translation at 4rd BR because IPv6
header is much simpler than IPv4 header and IPv4 link on the LAN side
of 4rd CE is a local link. The packet is sent on the local link to
IPv4 group address a.b.c.d for IPv6 group address of ASM_MPREFIX64:
a.b.c.d or SSM_MPREFIX64:a.b.c.d.
In case an IPv4 multicast source sends multicast data with the don't
fragment (DF) flag set to 1, [I-D.ietf-softwire-4rd] header mapping
sets the D bit in IPv6 fragment header before sending the packet
downstream as in Fig. 3 in Section 4.3 of [I-D.ietf-softwire-4rd].
This feature of [I-D.ietf-softwire-4rd] preserves the semantics of DF
flag at the BR and CE.
Because MAP-T/4rd is stateless, Multicast MAP-T/4rd should stay
faithful to this as much as possible. Border Relay acts as the
default multicast querier for all CEs that have established multicast
communication with it. In order to keep a consistent multicast state
between a CE and BR, CE MUST use the same IPv6 multicast prefixes
(ASM_MPREFIX64/SSM_REFIX64) until the state becomes empty. After
that point, the CE may obtain different values for these prefixes,
effectively changing to a different 4rd BR.
6.3. Supporting IPv6 Multicast in MAP-T and 4rd Translation Multicast
IPv6 multicast can be supported natively since IPv6-only network is
assumed to be multicast enabled. MAP-T or 4rd Customer Edge device
has MLD Proxy function. Proxy operation for MLD [RFC3810] is
described in [RFC4605].
CE receives MLD join requests from the hosts and then sends
aggregated MLD Report messages upstream towards BR. No address or
protocol translation is needed at the CE or at the BR. IPv6 Hosts in
MAP-T or 4rd domain use any source multicast block FF0X [RFC4291] or
source specific multicast block FF3X::8000:0-FF3X::FFFF:FFFF for
dynamic allocation by a host [RFC4607], [RFC3307].
MAP-T or 4rd Border Relay is MLD querier. It serves all CEs
downstream. After receiving an MLD join message, BR sends PIM join
message upstream to join IPv6 multicast group. Multicast membership
database is maintained based on the aggregated Reports received from
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downstream interfaces in the multicast tree.
MAP-T or 4rd Border Relay is a Rendezvous Point (RP) for ASM groups.
For SSM, BR MUST support MLDv2.
IPv6 multicast data received from the Single Source Multicast or Any
Source Multicast sources are replicated according to the multicast
membership database and the data packets are sent downstream on the
multicast tree and eventually received by the CEs that have one of
more members of this multicast group.
MLD Proxy in the CE receives multicast data then forwards the packet
downstream. Each member host receives IPv6 multicast data packet
from its Layer 2 interface.
6.4. Learning Multicast Prefixes for IPv4-embedded IPv6 Multicast
Addresses
CE can be pre-configured with Multicast Prefix64 of ASM_MPREFIX64 and
SSM_MPREFIX64 that are supported in their network. However
automating this process is also desired.
A new router advertisement option, a Multicast ASM Translation Prefix
option, can be defined for this purpose. The option contains IPv6
ASM multicast translation prefix, ASM_MPREFIX64. A new router
advertisement option, a Multicast SSM Translation Prefix option, can
be defined for this purpose. The option contains IPv6 SSM multicast
prefix translation prefix SSM_MPREFIX64.
After the host gets the multicast prefixes, when an application in
the host wishes to join an IPv4 multicast group the host MUST use
ASM_MPREFIX64 or SSM_MPREFIX64 and then obtain the synthesized IPv6
group address before sending MLD join message.
Source-specific multicast (SSM) group membership message payloads in
IGMPv3 and MLDv2 contain address literals and their translation
requires another multicast translation prefix option. IPv4 source
addresses in IGMPv3 Membership Report message are unicast addresses
of IPv4 sources and they have to be translated into unicast IPv6
source addresses in MLDv2 Membership Report message. A new router
advertisement option, a Multicast Translation Unicast Prefix option
can be defined for this purpose. The option contains IPv6 unicast
Network-Specific Prefix U_PREFIX64. The host can be configured by
its default router using router advertisements containing the
prefixes [I-D.sarikaya-softwire-6man-raoptions]. 64:ff9b::/96 is the
global value called well-known prefix that is assigned to U_PREFIX64
[RFC6052]. Organization specific values called Network-Specific
Prefixes can also be used. Since multicast is potentially inter-
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domain, the use of well-known prefix for U_PREFIX64 is recommended.
Note that U_PREFIX64 is also used in multicast data packet address
translation. Source-specific multicast source address in multicast
data packets coming from SSM sources MUST be translated using
U_PREFIX64.
7. Security Considerations
4rd Encapsulation Multicast control and data message security can be
provided by the security architecture, mechanisms, and services
described in [RFC4301], [RFC4302] and [RFC4303]. 4rd Translation
Multicast control and data message security are as described in
[RFC4607] for source specific multicast.
8. IANA Considerations
TBD.
9. Acknowledgements
TBD.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, August 1989.
[RFC2113] Katz, D., "IP Router Alert Option", RFC 2113,
February 1997.
[RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, October 1999.
[RFC3171] Albanna, Z., Almeroth, K., Meyer, D., and M. Schipper,
"IANA Guidelines for IPv4 Multicast Address Assignments",
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RFC 3171, August 2001.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, August 2006.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, August 2006.
[RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast
Addresses", RFC 3307, August 2002.
[RFC2491] Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6
over Non-Broadcast Multiple Access (NBMA) networks",
RFC 2491, January 1999.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[RFC2765] Nordmark, E., "Stateless IP/ICMP Translation Algorithm
(SIIT)", RFC 2765, February 2000.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
January 2001.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC5135] Wing, D. and T. Eckert, "IP Multicast Requirements for a
Network Address Translator (NAT) and a Network Address
Port Translator (NAPT)", BCP 135, RFC 5135, February 2008.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
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Algorithm", RFC 6145, April 2011.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
[I-D.ietf-softwire-map]
Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S., and
T. Murakami, "Mapping of Address and Port with
Encapsulation (MAP)", draft-ietf-softwire-map-04 (work in
progress), February 2013.
[I-D.ietf-softwire-map-t]
Li, X., Bao, C., Dec, W., Troan, O., Matsushima, S., and
T. Murakami, "Mapping of Address and Port using
Translation (MAP-T)", draft-ietf-softwire-map-t-01 (work
in progress), February 2013.
[I-D.ietf-softwire-4rd]
Jiang, S., Despres, R., Penno, R., Lee, Y., Chen, G., and
M. Chen, "IPv4 Residual Deployment via IPv6 - a Stateless
Solution (4rd)", draft-ietf-softwire-4rd-04 (work in
progress), October 2012.
[I-D.ietf-mboned-64-multicast-address-format]
Boucadair, M., Qin, J., Lee, Y., Venaas, S., Li, X., and
M. Xu, "IPv6 Multicast Address With Embedded IPv4
Multicast Address",
draft-ietf-mboned-64-multicast-address-format-04 (work in
progress), August 2012.
10.2. Informative references
[RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
Multicast Addresses", RFC 3306, August 2002.
[RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous
Point (RP) Address in an IPv6 Multicast Address",
RFC 3956, November 2004.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[I-D.sarikaya-softwire-6man-raoptions]
Sarikaya, B., "IPv6 RA Options for Translation Multicast
Prefixes", draft-sarikaya-softwire-6man-raoptions-00 (work
in progress), August 2012.
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[I-D.perreault-mboned-igmp-mld-translation]
Perreault, S. and T. Tsou, "Internet Group Management
Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based
Multicast Translation ("IGMP/MLD Translation")",
draft-perreault-mboned-igmp-mld-translation-01 (work in
progress), April 2012.
Appendix A. Group Membership Message Translation Details
IGMP Report messages (IGMP type number 0x12 and 0x16, in IGMPv1 and
IGMPv2 and 0x22 in IGMPv3) are translated into MLD Report messages
(MLDv1 ICMPv6 type number 0x83 and MLDv2 type number 0x8f). IGMP
Query message (IGMP type number 0x11) is translated into MLD Query
message (ICMPv6 type number 0x82)
[I-D.perreault-mboned-igmp-mld-translation].
Destination address in ASM, i.e. IGMPv1, IGMPv2 and MLDv1, is the
multicast group address so the destination address in IGMP message is
translated into the destination address in MLD message using
[I-D.ietf-mboned-64-multicast-address-format].
Destination address in SSM, i.e. IGMPv3 and MLDv2 is translated as
follows: it could be all nodes on link, which has the value of
224.0.0.1 (IGMPv3) and ff02::1 (MLDv2), all routers on link, which
has the value of 224.0.0.2 (IGMPv3) and ff02::2 (MLDv2), all IGMP/
MLD-capable routers on link, which has the value of 224.0.0.22
(IGMPv3) and ff02::16 (MLDv2).
Source address of MLD message that CE sends is set to link-local IPv6
address of CE's WAN side interface. Source address of MLD message
that BR sends is set to link-local IPv6 address of BR's downstream
interface.
Multicast Address or Group Address field in IGMP message payloads is
translated using [I-D.ietf-mboned-64-multicast-address-format] as
described above into the corresponding field in MLD message.
Source Address in IGMPv3 message payloads is translated using
U_PREFIX64, the IPv6 unicast prefix to be used by SSM source.
[RFC6052] defines in Section 2.3 the address translation algorithm of
embedding an IPv4 source address and obtaining an IPv6 source address
using a network specific prefix like U_PREFIX64. At the BR on its
upstream interface or at the CE on its LAN interface, IPv4 addresses
are extracted from the IPv4-embedded IPv6 addresses.
Maximum Response Time (MRT) field in IGMPv2 and IGMPv3 queries are
translated into Maximum Response Delay (MRD) in MLDv1 and MLDv2
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queries, respectively. In the corresponding MLD message, MRD is set
to 100 times the value of MRT. At the BR on its upstream interface
or at the CE on its LAN interface, MRT value is obtained by dividing
MRD into 100 and rounding it to the nearest integer.
IGMP messages are sent with a Router Alert IPv4 option [RFC2113].
The translated MLD message are sent with a Router Alert option in a
Hop-By-Hop IPv6 extension header [RFC2711]. In both cases, 2-octet
value is set to 0.
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Author's Address
Behcet Sarikaya
Huawei USA
5340 Legacy Dr. Building 175
Plano, TX 75024
Phone:
Email: sarikaya@ieee.org
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