INTERNET-DRAFT
July 14, 2000
Expires in six month
K. Tsuchiya, Hitachi
H. Higuchi, Hitachi
S. Sawada, Hitachi
S. Nozaki, Hitachi
An IPv6/IPv4 Multicast Translator based on IGMP/MLD Proxying (MTP)
<draft-tsuchiya-mtp-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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gress."
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Abstract
In the stage of the transition from IPv4 to IPv6 it is necessary
that IPv4 nodes and IPv6 nodes can communicate directly. This memo
proposes a mechanism which enables such direct communication for
multicast, in addition to that for unicast defined in [SIIT] and
[NAT-PT].
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1. Introduction
It is expected that many IPv4 nodes will remain, for its success,
for a long time after the transition to IPv6 starts. On the other
hand IPv6-only nodes will appear, for cost reasons or as a result
of exhaustion of the IPv4 address space, before IPv4 nodes disap-
pear. Therefore, it is highly desirable to develop a mechanism
which enables direct communication between IPv4 nodes and IPv6
nodes, in order to advance the transition smoothly. [SIIT] and
[NAT-PT] have already proposed such mechanisms, but they are
applied only to unicast communication, not to multicast. So it is
necessary to provide another mechanism for multicast.
This memo describes an entire scheme of multicast communication
between IPv4 nodes and IPv6 nodes. The scheme is composed by a mul-
ticast translator and an address mapper who are located at the site
boundary between IPv4 and IPv6. It is not necessary to modify IPv4
nodes and IPv6 nodes.
This memo uses the words defined in [IPV4], [IPV6], and [TRANS-
MECH].
2. Components
This section describes components needed for the mechanism.
The system consists of a multicast translator, and an address
mapper. In order to allow IPv4 nodes and IPv6 nodes to directly
communicate using multicast, they need to be installed on the site
boundary between IPv4 and IPv6. Figure 1 illustrates the network
system interconnected by them.
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+-----------+ +-----------+
| IPv4 | | IPv6 |
| Multicast | | Multicast |
| Sender | | Sender |
| Node | | Node |
+-----+-----+ +-----+-----+
| |
+-----+-----+ +-----+-----+
| | +------------------+ | |
| IPv4 land | | Address Mapper | | IPv6 land |
| | +--------+---------+ | |
| | | | |
| | +------------+------------+ | |
| | | Multicast Translator | | |
| | | +----------+ | | |
| +--+ |Translator| +--+ |
| | | +----------+ | | |
| | | +---------+ +---------+ | | |
| | | |IPv4 | |IPv6 | | | |
| | | |Multicast| |Multicast| | | |
| | | |Proxy | |Proxy | | | |
| | | +---------+ +---------+ | | |
| | +-------------------------+ | |
+-----+-----+ +-----+-----+
| |
+-----+-----+ +-----+-----+
| IPv4 | | IPv6 |
| Multicast | | Multicast |
| Receiver | | Receiver |
| Node | | Node |
+-----------+ +-----------+
Figure. 1 Network system
2.1 Multicast Translator
It locates between an IPv4 land and an IPv6 land, and translates
IPv4 multicast packets into IPv6 multicast packets and vice versa.
It consists of the following three sub-components.
(1) Translator
It is a component which translates IPv4 multicast packets into
IPv6 multicast packets and vice versa. There are several trans-
lation types.
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o Gateway
It terminates data bound for an IPv4 multicast group at
application layer, and relays the data to an IPv6 multicast
group and vice versa.
o Header conversion router
When receiving an IPv4 multicast packet, it converts the IPv4
header into an IPv6 header, fragments the IPv6 packet if
necessary, and then forwards the packet. Likewise, when
receiving an IPv6 multicast packet, it converts the IPv6
header into an IPv4 header, and then forwards the IPv4
packet.
(2) IPv4 Multicast Proxy
It joins IPv4 multicast groups as a proxy of IPv6 receiver
nodes. Thereby it receives packets bound for the IPv4 multicast
groups, and then hands the packets to the translator.
(3) IPv6 Multicast Proxy
It joins IPv6 multicast groups as a proxy of IPv4 receiver
nodes. Thereby it receives packets bound for the IPv6 multicast
groups, and then hands the packets to the translator.
2.2 Address mapper
It maintains each unicast address spool for IPv4 and IPv6. The IPv4
spool, for example, consists of private addresses [PRIVATE] bound
for the multicast translator. An example of the IPv6 spool is IPv6
address space assigned to virtual IPv6 organization on the IPv4
land.
Also, it maintains a mapping table which consists of pairs of an
IPv4 address and an IPv6 address. When the translator (or the IPv4
Proxy or the IPv6 Proxy) requests it to assign an IPv6 address
corresponding to an IPv4 address, it selects a proper IPv6 address
out of the table, and returns the address to the translator. When
there is not a proper entry for an IPv4 unicast address, it selects
and returns an IPv6 unicast address out of the spool, and registers
a new entry into the table. When there is not a proper entry for an
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IPv4 multicast group address, it registers a new entry, which con-
sists of the IPv4 multicast group address and that of IPv6
corresponding to the IPv4 address, into the table. The IPv6 address
is a special type of one proposed in this memo. See section 4.
When the translator (or the IPv4 Proxy or the IPv6 Proxy) requests
it to assign an IPv4 address corresponding to an IPv6 address, it
works like the above.
3. Interaction Examples
This section explains communication from one IPv4 multicast sender
node to one or more IPv6 multicast receiver nodes, and communica-
tion from one IPv6 multicast sender node to one or more IPv4 multi-
cast receiver nodes, respectively.
3.1 Communication from IPv4 to IPv6
The following subsection explains communication from one IPv4 mul-
ticast sender node, called "sender4", to one or more IPv6 multicast
receiver nodes, called "receiver6."
Preceding the communication, the administrator of the multicast
translator carries out the setup to translate IPv4 multicast pack-
ets, which are sent by "sender4", into IPv6. According to the
direction of the administrator, the IPv4 multicast proxy joins the
IPv4 multicast group as a proxy of "receiver6", and then registers
a new entry, which consists of the IPv4 multicast group address and
that of IPv6 corresponding to the IPv4 address, into the mapping
table. The IPv6 address is a special type of one proposed in this
memo, and takes the structure which is identified by a prefix of
ffxx::/96 and holds the IPv4 address in the low-order 32-bits. See
section 4.
The communication is triggered by "sender4." "sender4" sends an
IPv4 multicast packet.
When the packet arrives at the multicast translator, the IPv4 mul-
ticast proxy receives it and hands it to the translator. The trans-
lator tries to translate it into an IPv6 packet but does not know
how to translate the IPv4 source address and the IPv4 destination
address. So the translator requests the mapper to tell mapping
entries for them.
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The mapper checks its mapping table with each of them and finds
only a mapping entry for the IPv4 destination address.
But there is not a mapping entry for the IPv4 source address, so
the mapper selects an IPv6 address out of the IPv6 spool and regis-
ters a new entry, which consists of the IPv4 address and the IPv6
address, into the mapping table. And then the mapper returns the
IPv6 destination address and the IPv6 source address to the trans-
lator.
After that the translator translates the packet to IPv6, fragments
it if necessary, and forwards it. Note: The translation from the
IPv4 source address to the IPv6 source address is unicast one.
Finally it arrives at "receiver6."
Figure 2 illustrates the interaction communicating from IPv4 to
IPv6.
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"sender4" "multicast translator" "address "receiver6"
mapper"
IPv4 translator IPv6
multicast multicast
proxy proxy
| | | | | |
| <------| Sends an "IGMP Membership Report" for joining the
| | IPv4 multicast group. | | |
| | | | | |
| |----------------------------------->| |
| | Registers a entry for the group into the mapping
| | table. | | | |
| | | | | |
| | | | | |
|=========>| Sends an IPv4 multicast packet. | |
| | | | | |
| |===========>| Hands it. | | |
| | | | | |
| | | Request IPv6 addresses corresponding
| | | to the IPv4 addresses.| |
| | |---------------------->| |
| | |<----------------------| |
| | | Reply with the IPv6 addresses. |
| | | | | |
| | | <<Translate IPv4 into IPv6.>> |
| | | | | |
| | | Forwards an IPv6 multicast packet.
| | |=================================>|
| | | | | |
Figure. 2 The interaction communicating from IPv4 to IPv6.
3.2 Communication from IPv6 to IPv4
The following subsection explains communication from one IPv6 mul-
ticast sender node, called "sender6", to one or more IPv4 multicast
receiver nodes, called "receiver4."
Preceding the communication, the administrator of the multicast
translator carries out the setup to translate IPv6 multicast pack-
ets, which are sent by "sender6" to a special type of IPv6 address
proposed in this memo, into IPv4. In the case, the IPv6 multicast
proxy joins the IPv6 multicast group as a proxy of "receiver4", and
then registers a new entry, which consists of the IPv6 multicast
group address and that of IPv4 corresponding to the IPv6 address,
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into the mapping table. The IPv4 address is the low-order 32-bits
of the IPv6 address.
Subsequent interaction is symmetric to the case described in Sec-
tion 3.1.
Figure 3 illustrates the interaction communicating from IPv6 to
IPv4.
"receiver4" "multicast translator" "address "sender6"
mapper"
IPv4 translator IPv6
multicast multicast
proxy proxy
| | | | | |
| | | Sends an "MLD Multicast Listener |
| | | Report" for joining the IPv6 multicast
| | | group. | | |
| | | |-----> | |
| | | | | |
| | | |---------->| |
| | | Registers a entry for the group into
| | | the mapping table. | |
| | | | | |
| | | | | |
| | | Sends an IPv6 multicast packet. |
| | | |<=====================|
| | | | | |
| | |<==========| Hands it. | |
| | | | | |
| | | Request IPv4 addresses corresponding
| | | to the IPv6 addresses.| |
| | |---------------------->| |
| | |<----------------------| |
| | | Reply with the IPv4 addresses. |
| | | | | |
| | | <<Translate IPv6 into IPv4.>> |
| | | | | |
|<======================| Forwards an IPv4 multicast packet.
| | | | | |
Figure. 3 The interaction communicating from IPv6 to IPv4.
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4. Addressing for IPv4/IPv6 multicast communication
The mechanism uses a special type of an IPv6 address which is
termed an "IPv4-compatible" IPv6 multicast group address. The
address is identified by an prefix for IPv6 multicast (ffxx::/96),
and holds an IPv4 multicast group address in the low-order 32-bits.
Its format is:
| 96-bits | 32-bits |
+--------------------------------------+---------------+
| ffxx:0:0:0:0:0 | IPv4 multicast|
| | group address |
+--------------------------------------+---------------+
5. Applicability and Limitations
This section considers applicability and limitations.
5.1 Applicability
The multicast translator based on the mechanism locates at the site
boundary between IPv4 and IPv6, and allows them to communicate
directly. Therefore, the mechanism can be useful during a long
term, until IPv4 nodes disappear after IPv6-only nodes appear.
It can be applicable to small-scale network systems, and to the
extent of division networks in intranets where its administrator
can operate the setup easily on demand by receivers.
5.2 Limitations
In common with NAT [NAT], IP conversion needs to translate IP
addresses embedded in application layer protocols. So it is hard to
translate all such applications completely.
It cannot be applicable to large-scale network systems like world-
wide Internet because it needs the setup by its administrator. In
order to apply it to large-scale network systems, it needs develop-
ing a new standard protocol between multicast translators and
receivers for carrying out the setup automatically on demand by
receivers.
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6. Security considerations
Header conversions of AH [AH] and ESP [ESP] may be cryptographi-
cally impossible in header conversion router approach. It is a big
disadvantage. On the other hand it will be possible to use both AH
and ESP in proxy gateway approach.
7. References
[SIIT] Erik Nordmark, "Stateless IP/ICMP Translation Algorithm
(SIIT)", RFC 2765, February 2000.
[NAT-PT] G. Tsirtsis, P. Srisuresh, "Network Address Translation -
Protocol Translation (NAT-PT)", RFC 2766, February 2000.
[IPV4] J. Postel, "Internet Protocol", RFC 791, September 1981.
[NAT] Kjeld Borch Egevang and Paul Francis, "The IP Network Address
Translator (NAT)", RFC1631, May 1994.
[IPV6] S. Deering and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[TRANS-MECH] R. Gilligan and E. Nordmark, "Transition Mechanisms
for IPv6 Hosts and Routers", RFC 1933, April 1996.
[PRIVATE] Y. Rekhter, B. Moskowitz, D. Karrenberg,
G. J. de Groot and E. Lear, "Address Allocation for
Private Internets", RFC1918, February 1996.
8. Acknowledgements
The authors would like to thank the WIDE project for giving the
many helpful suggestions.
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9. Authors' Addresses
Kazuaki TSUCHIYA
Enterprise Server Division, Hitachi, Ltd.
1 Horiyamashita, Hadano-shi, Kanagawa-ken, 259-1392 JAPAN
Phone: +81-463-87-6771
Fax: +81-463-87-7341
Email: tsuchiya@kanagawa.hitachi.co.jp
Hidemitsu HIGUCHI
Enterprise Server Division, Hitachi, Ltd.
1 Horiyamashita, Hadano-shi, Kanagawa-ken, 259-1392 JAPAN
Phone: +81-463-87-6771
Fax: +81-463-87-7341
Email: hhiguchi@kanagawa.hitachi.co.jp
Sunao SAWADA
Enterprise Server Division, Hitachi, Ltd.
1 Horiyamashita, Hadano-shi, Kanagawa-ken, 259-1392 JAPAN
Phone: +81-463-87-6771
Fax: +81-463-87-7341
Email: susawada@kanagawa.hitachi.co.jp
Shinji NOZAKI
Enterprise Server Division, Hitachi, Ltd.
1 Horiyamashita, Hadano-shi, Kanagawa-ken, 259-1392 JAPAN
Phone: +81-463-87-6771
Fax: +81-463-87-7341
Email: nozaki@kanagawa.hitachi.co.jp
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