One document matched: draft-ietf-mboned-64-multicast-address-format-01.xml
<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc category="std" docName="draft-ietf-mboned-64-multicast-address-format-01"
ipr="trust200902" updates="4291">
<front>
<title abbrev="64 Multicast Address Format">IPv4-Embedded IPv6 Multicast
Address Format</title>
<author fullname="Mohamed Boucadair" initials="M." role="editor"
surname="Boucadair">
<organization>France Telecom</organization>
<address>
<postal>
<street></street>
<city>Rennes</city>
<region></region>
<code>35000</code>
<country>France</country>
</postal>
<email>mohamed.boucadair@orange.com</email>
</address>
</author>
<author fullname="Jacni Qin" initials="J." surname="Qin">
<organization>ZTE</organization>
<address>
<postal>
<street></street>
<city>Shanghai</city>
<country>China</country>
</postal>
<email>jacniq@gmail.com</email>
</address>
</author>
<author fullname="Yiu L. Lee" initials="Y." surname="Lee">
<organization>Comcast</organization>
<address>
<postal>
<street></street>
<city></city>
<country>U.S.A</country>
</postal>
<email>yiu_lee@cable.comcast.com</email>
</address>
</author>
<author fullname="Stig Venaas" initials="S." surname="Venaas">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>Tasman Drive</street>
<city>San Jose</city>
<region>CA</region>
<code>95134</code>
<country>USA</country>
</postal>
<email>stig@cisco.com</email>
</address>
</author>
<author fullname="Xing Li" initials="X." surname="Li">
<organization>CERNET Center/Tsinghua University</organization>
<address>
<postal>
<street>Room 225, Main Building, Tsinghua University</street>
<city>Beijing</city>
<region></region>
<code>100084</code>
<country>P.R. China</country>
</postal>
<phone>+86 10-62785983</phone>
<email>xing@cernet.edu.cn</email>
</address>
</author>
<author fullname="Mingwei Xu" initials="M." surname="Xu">
<organization>Tsinghua University</organization>
<address>
<postal>
<street>Department of Computer Science, Tsinghua University</street>
<city>Beijing</city>
<region></region>
<code>100084</code>
<country>P.R.China</country>
</postal>
<phone>+86-10-6278-5822</phone>
<email>xmw@cernet.edu.cn</email>
</address>
</author>
<date day="29" month="February" year="2012" />
<workgroup>MBONED Working Group</workgroup>
<keyword>IPv4-IPv6 Interconnection, Multicast64, IPv4-Embedded IPv6
Address, IPv4 Address Shortage</keyword>
<abstract>
<t>This document specifies an extension to the IPv6 multicast addressing
architecture to be used in the context of IPv4-IPv6 interconnection. In
particular, this document defines an address format for IPv4-embedded
IPv6 multicast addresses. This address format can be used for IPv4-IPv6
translation or encapsulation schemes.</t>
<t>This document updates RFC4291.</t>
</abstract>
<note title="Requirements Language">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <xref
target="RFC2119">RFC 2119</xref>.</t>
</note>
</front>
<middle>
<section title="Introduction">
<t>This document specifies an extension to the IPv6 multicast addressing
architecture to be used in the context of IPv4-IPv6 interconnection. In
particular, this document defines an address format for IPv4-embedded
IPv6 multicast addresses. This address format can be used for IPv4-IPv6
translation or encapsulation schemes.</t>
<t>This document updates <xref target="RFC4291"></xref>.</t>
<t>This specification can be used in conjunction with other extensions
such as building unicast prefix-based multicast IPv6 address <xref
target="RFC3306"></xref> or embedding the rendezvous point <xref
target="RFC3956"></xref>.</t>
<t>This document is a companion document to <xref
target="RFC6052"></xref> which focuses exclusively on IPv4-embedded IPv6
unicast addresses.</t>
<t>Details about design choices are documented in <xref
target="design"></xref>.</t>
</section>
<section title="Terminology">
<t>This document makes use of the following terms:<?rfc subcompact="no" ?><list
style="symbols">
<t>IPv4-embedded IPv6 multicast address: denotes a multicast IPv6
address which includes in 32 bits an IPv4 address. Two types of IPv6
addresses are defined that carry an IPv4 address in the low-order 32
bits of the address. The format to build such addresses is defined
in <xref target="format_asm"></xref> for ASM mode and <xref
target="format_ssm"></xref> for SSM mode.</t>
<t>Multicast Prefix64 (or MPREFIX64 for short) refers to an IPv6
multicast prefix to be used to construct IPv4-embedded IPv6
multicast addresses.</t>
<t>ASM_MPREFIX64: denotes a multicast Prefix64 used in ASM mode. It
follows the format described in <xref
target="format_asm"></xref>.</t>
<t>SSM_MPREFIX64: denotes a multicast Prefix64 used in SSM mode. It
follows the format described in <xref
target="format_ssm"></xref>.</t>
</list></t>
</section>
<section anchor="format_asm"
title="IPv4-Embedded IPv6 Multicast Address Format: ASM Mode">
<t>To meet the requirements listed in <xref target="m-bit"></xref>, the
following address format is defined to enclose an IPv4 multicast address
when ASM mode is used:</t>
<figure align="center" anchor="address_format"
title="IPv4-Embedded IPv6 Multicast Address Format: ASM Mode">
<preamble></preamble>
<artwork><![CDATA[| 8 | 4 | 4 | 4 | 76 | 32 |
+--------+----+----+----+------------------------------+----------+
|11111111|flgs|scop|64IX| sub-group-id |v4 address|
+--------+----+----+----+-----------------------------------------+
+-+-+-+-+
IPv4-IPv6 Interconnection bits (64IX): |M|r|r|r|
+-+-+-+-+]]></artwork>
<postamble></postamble>
</figure>
<t>The description of the fields is as follows:<?rfc subcompact="yes" ?><list
style="symbols">
<t>"flgs" and "scop" fields are defined in <xref
target="RFC4291"></xref>.</t>
<t>64IX field (IPv4-IPv6 interconnection bits): The first bit is the
M-bit. When "M-bit" is set to 1, it indicates that a multicast IPv4
address is embedded in the low-order 32 bits of the multicast IPv6
address. All the remaining bits are reserved and MUST be set to
0.</t>
<t>sub-group-id: This field is configurable according to local
policies of the entity managing the IPv4-IPv6 Interconnection
Function. This field must follow the recommendations specified in
<xref target="RFC3306"></xref> if unicast-based prefix is used or
the recommendations specified in <xref target="RFC3956"></xref> if
embedded-RP is used. The default value is all zeros.</t>
<t>The low-order 32 bits MUST include an IPv4 multicast address when
the M-bit is set to 1. The enclosed IPv4 multicast address SHOULD
NOT be in 232/8 range.</t>
</list></t>
</section>
<section anchor="format_ssm"
title="IPv4-Embedded IPv6 Multicast Address Format: SSM Mode">
<t>As mentioned above, any IPv4-embedded IPv6 address used in SSM mode
MUST be part of ff3x::/32 <xref target="RFC4607"></xref>. <xref
target="address_format_ssm"></xref> describes the format of the IPv6
multicast address to be used to enclose an IPv4 multicast address.</t>
<t><figure align="center" anchor="address_format_ssm"
title="IPv4-Embedded IPv6 Multicast Address Format: SSM Mode">
<preamble></preamble>
<artwork><![CDATA[| 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|
+-+-+-+-+]]></artwork>
<postamble></postamble>
</figure>The description of the fields is as follows:<?rfc subcompact="yes" ?></t>
<t><list style="symbols">
<t>Flags must be set to 0011.</t>
<t>"scop" is defined in <xref target="RFC4291"></xref>.</t>
<t>64IX field (IPv4-IPv6 interconnection bits): Same meaning as
<xref target="format_asm"></xref>.</t>
<t>sub-group-id: The default value is all zeros.</t>
<t>The low-order 32 bits MUST include an IPv4 multicast address when
the M-bit is set to 1. The embedded IPv4 address SHOULD be in the
232/8 range <xref target="RFC4607"></xref>. 232.0.0.1-232.0.0.255
range is being reserved to IANA.</t>
</list></t>
</section>
<section title="Textual Representation">
<t>The embedded IPv4 address in an IPv6 multicast address is included in
the last 32 bits; therefore dotted decimal notation can be used.</t>
</section>
<section anchor="mprefix" title="Multicast PREFIX64">
<t>For the delivery of the IPv4-IPv6 multicast interconnection services,
a dedicated multicast prefix denoted as MPREFIX64 should be provisioned
to any function requiring to build an IPv4-embedded IPv6 multicast
address based on an IPv4 multicast address. MPREFIX64 can be of ASM or
SSM type. When both modes are used, two prefixes are required to be
provisioned.</t>
<t>The structure of the MPREFIX64 follows the guidelines specified in
<xref target="format_asm"></xref> for the ASM mode and <xref
target="format_ssm"></xref> when SSM mode is used.</t>
<t>The RECOMMENDED MPREFIX64 length is /96 (as shown in <xref
target="mprefix64"></xref>).</t>
<t>The format of the MPREFIX64 should follow what is specified in <xref
target="RFC3306"></xref> and <xref target="RFC3956"></xref> if
corresponding mechanisms are used. <?rfc subcompact="no" ?></t>
<t><list style="empty">
<t>The format specified in <xref target="format_asm"></xref> uses
some reserved bits defined in <xref target="RFC3306"></xref> and
<xref target="RFC3956"></xref>: the first of the reserved bits now
has a meaning, while the remaining bits MUST be set to 0.</t>
</list> <?rfc subcompact="yes" ?></t>
<t><figure align="center" anchor="mprefix64" title="MPREFIX64">
<preamble></preamble>
<artwork><![CDATA[ASM Mode:
| 8 | 4 | 4 | 4 | 76 | 32 |
+--------+----+----+----+------------------------------+----------+
|11111111|flgs|scop|64IX| sub-group-id |v4 address|
+--------+----+----+----+------------------------------+----------+
| | |
v v v
+------------------------------------------------------+----------+
| ASM_MPREFIX64 |v4 address|
+------------------------------------------------------+----------+
SSM Mode:
| 8 | 4 | 4 | 16 | 4 | 60 | 32 |
+--------+----+----+-----------+----+------------------+----------+
|11111111|0011|scop|00.......00|64IX| sub-group-id |v4 address|
+--------+----+----+-----------+----+------------------+----------+
| | |
v v v
+------------------------------------------------------+----------+
| SSM_MPREFIX64 |v4 address|
+------------------------------------------------------+----------+
]]></artwork>
<postamble></postamble>
</figure></t>
</section>
<section title="Source IPv4 Address in the IPv6 Realm">
<t>An IPv4 source is represented in the IPv6 realm with its
IPv4-converted IPv6 address <xref target="RFC6052"></xref>.</t>
</section>
<section title="Examples">
<t><xref target="asm_ex"></xref> provides an example of ASM
IPv4-Embedded IPv6 Address while <xref target="ssm_ex"></xref> provides
an example of SSM IPv4-Embedded IPv6 Address.</t>
<t><figure align="center" anchor="asm_ex"
title="Example of ASM IPv4-embedded IPv6 address">
<artwork><![CDATA[ +---------------------+--------------+----------------------------+
| MPREFIX64 | IPv4 address | IPv4-embedded IPv6 address |
+---------------------+--------------+----------------------------+
| ffxx:8000:abc::/96 | 224.1.2.3 | ffxx:8000:abc::224.1.2.3 |
+---------------------+--------------+----------------------------+]]></artwork>
</figure></t>
<t><figure align="center" anchor="ssm_ex"
title="Example of SSM IPv4-embedded IPv6 address">
<artwork><![CDATA[ +---------------------+--------------+----------------------------+
| MPREFIX64 | IPv4 address | IPv4-embedded IPv6 address |
+---------------------+--------------+----------------------------+
| ff3x:0:8000::/96 | 232.1.2.3 | ff3x:0:8000::232.1.2.3 |
+---------------------+--------------+----------------------------+]]></artwork>
</figure></t>
<t></t>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>Authors of this document request to reserve:<list style="symbols">
<t>ff3x:0:8000/33 SSM block to embed an IPv4 multicast address in
the last 32 bits.</t>
<t>ffxx:8000/17 ASM block to embed an IPv4 multicast address in the
last 32 bits.</t>
</list></t>
</section>
<section anchor="Security" title="Security Considerations">
<t>This document defined an address format to embed an IPv4 multicast
address in an IPv6 multicast address. The same security considerations
as those discussed in <xref target="RFC6052"></xref> are to be taken
into consideration.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>Many thanks to R. Bonica, B. Sarikaya, P. Savola and T. Tsou for
their comments and review.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"
?>
<?rfc include='reference.RFC.3956'?>
<?rfc include='reference.RFC.3306'?>
<?rfc include='reference.RFC.4291'?>
<?rfc include='reference.RFC.6052'?>
<?rfc include='reference.RFC.4607'?>
</references>
<section anchor="design" title="Design Choices">
<t></t>
<section title="Location of the IPv4 Address">
<t>There is no strong argument to allow for flexible options to encode
the IPv4 address inside the multicast IPv6 address. The option
retained by the authors is to encode the multicast IPv4 address in the
low-order 32 bits of the IPv6 address.</t>
<t>This choice is also motivated by the need to be compliant with
<xref target="RFC3306"></xref> and <xref target="RFC3956"></xref>.</t>
</section>
<section anchor="m-bit" title="Location of the M-bit">
<t><xref target="af_4291"></xref> is a reminder of the IPv6 multicast
address format as defined in <xref target="RFC4291"></xref>:</t>
<t><figure anchor="af_4291"
title="IPv6 Multicast address format as defined in RFC4291">
<preamble></preamble>
<artwork><![CDATA[ | 8 | 4 | 4 | 112 bits |
+------ -+----+----+---------------------------------------------+
|11111111|flgs|scop| group ID |
+--------+----+----+---------------------------------------------+
+-+-+-+-+
flgs is a set of 4 flags: |0|R|P|T|
+-+-+-+-+
* "T-bit" is defined in [RFC4291];
* "P-bit" is defined in [RFC3306]
* "R-bit" is defined in [RFC3956]
]]></artwork>
<postamble></postamble>
</figure></t>
<t>It was tempting to use the remaining flag to indicate whether an
IPv6 address embeds an IPv4 address or not. This choice has been
abandoned by the authors for various reasons: <?rfc subcompact="yes" ?><list
style="symbols">
<t>ff3x::/32 is defined as SSM. Defining a new flag would require
standards and implementations to also treat ffbx::/32 as SSM.</t>
<t>Prefixes starting with ff7x are defined as embedded-RP, but not
prefixes starting with fffx. Below is provided an excerpt from
<xref target="RFC3956"></xref>: <list style="empty">
<t>" ...the encoding and the protocol mode used when the two
high-order bits in "flgs" are set to 11 ("fff0::/12") is
intentionally unspecified until such time that the
highest-order bit is defined. Without further IETF
specification, implementations SHOULD NOT treat the fff0::/12
range as Embedded-RP."</t>
<t>as such defining a new flag would require implementations
to also treat ff7x::/12 as embedded-RP prefix.</t>
</list></t>
<t>This is the last remaining flag and at this stage we are not
sure whether there is other usage scenarios of the flag.</t>
</list></t>
<t>As a conclusion, the remaining flag is not used to indicate an IPv6
multicast address embeds an IPv4 multicast address. However the
following constraints should be met:<?rfc subcompact="yes" ?></t>
<t><list style="empty">
<t>(1) Belong to ff3x::/32 and be compatible with unicast-based
prefix <xref target="RFC3306"></xref> for SSM. Note that <xref
target="RFC3306"></xref> suggests to set "plen" to 0 and
"network-prefix" to 0.</t>
<t>(2) Be compatible with embedded-RP <xref
target="RFC3956"></xref> and unicast-based prefix <xref
target="RFC3306"></xref> for ASM;</t>
<t>(3) Avoid ff3x::4000:0001-ff3x::7fff:ffff which is reserved for
IANA.</t>
</list>Meeting (1) and (2) with the same location of the M-bit is
not feasible without modifying embedded-RP and unicast-based prefix
specifications; this option is avoided.</t>
<t>As a consequence, two multicast blocks are proposed to be used when
embedding IPv4 address: one block for ASM (<xref
target="format_asm"></xref> ) and another one for the SSM (<xref
target="format_ssm"></xref>).</t>
</section>
<section anchor="why_s_bit" title="Encapsulation vs. Translation">
<t>IPv4-IPv6 encapsulator and translator may be embedded in the same
device or even implemented with the same software module. In order to
help the function whether an encapsulated IPv6 multicast packets or
translated IPv6 ones are to be transferred. It was tempting to define
an S-bit for that purpose but this choice has been abandoned in favor
of the recommendation to use distinct MPREFIX64 for each scheme.</t>
<t>As such, there is no need to reserve a bit in the IPv6 multicast
address to separate between the translation and the encapsulation
schemes.</t>
</section>
</section>
</back>
</rfc>
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