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draft-ietf-softwire-map.xml
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draft-ietf-softwire-map.xml
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<?xml version="1.0" encoding="US-ASCII"?>
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
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<!ENTITY I-D.mdt-softwire-map-dhcp-option SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.mdt-softwire-map-dhcp-option.xml">
<!ENTITY I-D.ietf-softwire-stateless-4v6-motivation SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-softwire-stateless-4v6-motivation.xml">
<!ENTITY I-D.ietf-tsvwg-iana-ports SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-tsvwg-iana-ports.xml">
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<!ENTITY I-D.dec-stateless-4v6 SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.dec-stateless-4v6.xml">
]>
<?rfc toc="yes" ?>
<?rfc tocompact="yes" ?>
<?rfc compact="yes" ?>
<?rfc subcompact="no" ?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes" ?>
<?rfc comments="yes" ?>
<?rfc inline="yes" ?>
<rfc category="std" docName="draft-ietf-softwire-map-01" ipr="trust200902">
<front>
<title abbrev="MAP">Mapping of Address and Port (MAP)</title>
<author fullname="Ole Troan" initials="O" surname="Troan">
<organization>Cisco Systems</organization>
<address>
<postal>
<street></street>
<city>Oslo</city>
<country>Norway</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Wojciech Dec" initials="W" surname="Dec">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>Haarlerbergpark Haarlerbergweg 13-19</street>
<city>Amsterdam, NOORD-HOLLAND</city>
<code>1101 CH</code>
<country>Netherlands</country>
</postal>
<phone></phone>
<email>[email protected]</email>
</address>
</author>
<author fullname="Xing Li" initials="X" surname="Li">
<organization abbrev="">CERNET Center/Tsinghua University</organization>
<address>
<postal>
<street>Room 225, Main Building, Tsinghua University</street>
<city>Beijing 100084</city>
<country>CN</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Congxiao Bao" initials="C" surname="Bao">
<organization abbrev="">CERNET Center/Tsinghua University</organization>
<address>
<postal>
<street>Room 225, Main Building, Tsinghua University</street>
<city>Beijing 100084</city>
<country>CN</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Yu Zhai" initials="Y." surname="Zhai">
<organization>CERNET Center/Tsinghua University</organization>
<address>
<postal>
<street>Room 225, Main Building, Tsinghua University</street>
<city>Beijing 100084</city>
<country>CN</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Satoru Matsushima" initials="S" surname="Matsushima">
<organization abbrev="">SoftBank Telecom</organization>
<address>
<postal>
<street>1-9-1 Higashi-Shinbashi, Munato-ku</street>
<city>Tokyo</city>
<country>Japan</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Tetsuya Murakami" initials="T" surname="Murakami">
<organization abbrev="">IP Infusion</organization>
<address>
<postal>
<street>1188 East Arques Avenue</street>
<city>Sunnyvale</city>
<country>USA</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<date day="27" month="June" year="2012" />
<area>Internet</area>
<workgroup>Network Working Group</workgroup>
<!-- SECTION 0: Abstract -->
<abstract>
<t>This document describes a mechanism for transporting IPv4 packets
across an IPv6 network, and a generic mechanism for mapping between IPv6
addresses and IPv4 addresses and transport layer ports.</t>
</abstract>
</front>
<middle>
<!-- SECTION 1: Introduction -->
<section title="Introduction">
<t>Mapping IPv4 addresses in IPv6 addresses has been described in
numerous mechanisms dating back to 1996 <xref target="RFC1933"></xref>.
The Automatic tunneling mechanism described in RFC1933, assigned a
globally unique IPv6 address to a host by combining the host's IPv4
address with a well-known IPv6 prefix. Given an IPv6 packet with a
destination address with an embedded IPv4 address, a node could
automatically tunnel this packet by extracting the IPv4 tunnel end-point
address from the IPv6 destination address.</t>
<t>There are numerous variations of this idea, described in 6over4 <xref
target="RFC2529"></xref>, 6to4 <xref target="RFC3056"></xref>, ISATAP
<xref target="RFC5214"></xref>, and 6rd <xref
target="RFC5969"></xref>.</t>
<!--
The differences between
these are the use of well-known IPv6 prefixes, or Service
Provider assigned IPv6 prefixes, and the position of the
embedded IPv4 bits in the IPv6 address. Teredo <xref
target="RFC4380"></xref> added a twist to this to achieve NAT
traversal by also encoding transport layer ports into the IPv6
address. 6rd, to achieve more efficient encoding, allowed for
only the suffix of an IPv4 address to be embedded, with the IPv4
prefix being deduced from other provisioning mechanisms.</t>
<t>NAT-PT <xref target="RFC2766"></xref>(deprecated) combined
with a DNS ALG used address mapping to put NAT state, namely the
IPv6 to IPv4 binding encoded in an IPv6 address. This
characteristic has been inherited by NAT64 <xref
target="RFC6146"></xref> and DNS64 <xref
target="RFC6147"></xref> which rely on an address format defined
in <xref target="RFC6052"></xref>. <xref
target="RFC6052"></xref> specifies the algorithmic translation
of an IPv6 address to IPv4 address. In particular, <xref
target="RFC6052"></xref> specifies the address format to build
IPv4-converted and IPv4-translatable IPv6 addresses. RFC6052
discusses the transport of the port-set information in an
IPv4-embedded IPv6 address but the conclusion was the following
(excerpt from [RFC6052]):</t>
<t>"There have been proposals to complement stateless
translation with a port range feature. Instead of mapping an
IPv4 address to exactly one IPv6 prefix, the options would allow
several IPv6 nodes to share an IPv4 address, with each node
managing a different set of ports. If a port-set extension is
needed, it could be defined later, using bits currently reserved
as null in the suffix."</t>
-->
<t>The commonalities of all these IPv6 over IPv4 mechanisms are: <list
style="symbols">
<t>Automatically provisions an IPv6 address for a host or an IPv6
prefix for a site</t>
<t>Algorithmic or implicit address resolution for tunneling or
encapsulation. Given an IPv6 destination address, an IPv4 tunnel
endpoint address can be calculated. Likewise for translation, an
IPv4 address can be calculated from an IPv6 destination address and
vice versa.</t>
<t>Embedding of an IPv4 address or part thereof and optionally
transport layer ports into an IPv6 address.</t>
</list></t>
<t>In phases of IPv4 to IPv6 migration, IPv6 only networks will be
common, while there will still be a need for residual IPv4 deployment.
This document describes a generic mapping of IPv4 to IPv6, and
mechanisms for encapsulation (IPv4 over IPv6) and translation between
the two protocols that use this mapping.</t>
<t>Just as the IPv6 over IPv4 mechanisms referred to above, the residual
IPv4 over IPv6 mechanisms must be capable of:</t>
<t><list style="symbols">
<t>Provisioning an IPv4 prefix, an IPv4 address or a shared IPv4
address.</t>
<t>Algorithmically map between an IPv4 prefix, IPv4 address or a
shared IPv4 address and an IPv6 address.</t>
</list></t>
<t>The unified mapping scheme described here supports translation mode,
encapsulation mode, in both mesh and hub and spoke topologies.</t>
<t>This document describes delivery of IPv4 unicast service across an
IPv6 infrastructure. IPv4 multicast is not considered further in this
document.</t>
<t>The A+P (Address and Port) architecture of sharing an IPv4 address by
distributing the port space is described in <xref
target="RFC6346"></xref>. Specifically section 4 of <xref
target="RFC6346"></xref> covers stateless mapping. The corresponding
stateful solution DS-lite is described in <xref
target="RFC6333"></xref>. The motivation for the work is described in
<xref target="I-D.ietf-softwire-stateless-4v6-motivation"></xref>.</t>
<t>A companion document defines a DHCPv6 option for provisioning of MAP
<xref target="I-D.mdt-softwire-map-dhcp-option"></xref>. Other means of
provisioning is possible. Deployment considerations are described in
[I-D.mdt-softwire-map-deployment].</t>
<t>MAP relies on IPv6 and is designed to deliver production-quality
dual-stack service while allowing IPv4 to be phased out within the SP
network. The phasing out of IPv4 within the SP network is independent of
whether the end user disables IPv4 service or not. Further,
"Greenfield"; IPv6-only networks may use MAP in order to deliver IPv4 to
sites via the IPv6 network.</t>
</section>
<!-- SECTION 2: REQUIREMENTS LANGUAGE -->
<section anchor="conventions" title="Conventions">
<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 RFC 2119 <xref
target="RFC2119"></xref>.</t>
</section>
<!-- conventions -->
<section title="Terminology">
<t><list hangIndent="24" style="hanging">
<t hangText="MAP domain:">One or more MAP CEs and BRs connected to
the same virtual link. A service provider may deploy a single MAP
domain, or may utilize multiple MAP domains.</t>
<t hangText="MAP Rule">A set of parameters describing the mapping
between an IPv4 prefix, IPv4 address or shared IPv4 address and an
IPv6 prefix or address. Each domain uses a different mapping rule
set.</t>
<t hangText="MAP node">A device that implements MAP.</t>
<t hangText="MAP Border Relay (BR):">A MAP enabled router managed by
the service provider at the edge of a MAP domain. A Border Relay
router has at least an IPv6-enabled interface and an IPv4 interface
connected to the native IPv4 network. A MAP BR may also be referred
to simply as a "BR" within the context of MAP.</t>
<t hangText="MAP Customer Edge (CE):">A device functioning as a
Customer Edge router in a MAP deployment. A typical MAP CE adopting
MAP rules will serve a residential site with one WAN side interface,
and one or more LAN side interfaces. A MAP CE may also be referred
to simply as a "CE" within the context of MAP.</t>
<t hangText="Port-set:">Each node has a separate part of the
transport layer port space; denoted as a port-set.</t>
<t hangText="Port-set ID (PSID):">Algorithmically identifies a set
of ports exclusively assigned to the CE.</t>
<t hangText="Shared IPv4 address:">An IPv4 address that is shared
among multiple CEs. Only ports that belong to the assigned port-set
can be used for communication. Also known as a Port-Restricted IPv4
address.</t>
<t hangText="End-user IPv6 prefix:">The IPv6 prefix assigned to an
End-user CE by other means than MAP itself. E.g. Provisioned using
DHCPv6 PD <xref target="RFC3633"></xref> or configured manually. It
is unique for each CE.</t>
<t hangText="MAP IPv6 address:">The IPv6 address used to reach the
MAP function of a CE from other CEs and from BRs.</t>
<t hangText="Rule IPv6 prefix:">An IPv6 prefix assigned by a Service
Provider for a mapping rule.</t>
<t hangText="Rule IPv4 prefix:">An IPv4 prefix assigned by a Service
Provider for a mapping rule.</t>
<t hangText="Embedded Address (EA) bits:">The IPv4 EA-bits in the
IPv6 address identify an IPv4 prefix/address (or part thereof) or a
shared IPv4 address (or part thereof) and a port-set identifier.</t>
<t hangText="MRT:">MAP Rule table. Address and Port aware data
structure, supporting longest match lookups. The MRT is used by the
MAP forwarding function.</t>
<t hangText="MAP-T:">Mapping of Address and Port – Translation
mode. MAP-T utilizes IPv4/IPv6 translation as per <xref
target="RFC6145"></xref>.</t>
<t hangText="MAP-E:">Mapping of Address and Port –
Encapsulation mode. MAP-E utilizes a simple IPv4-in-IPv6 tunneling
<xref target="RFC2473"></xref>.</t>
</list></t>
</section>
<!-- SECTION 3: DESCRIPTION -->
<section title="Architecture">
<t>The MAP mechanism is largely built up using existing standard
building blocks. The existing NAT44 on the CE is used with additional
support for restricting transport protocol ports, ICMP identifiers and
fragment identifiers to the configured port set. MAP supports two
forwarding modes, one using stateless NAT64 as specified in <xref
target="RFC6145"></xref> and one encapsulation mode specified in <xref
target="RFC2473"></xref>. In addition MAP specifies an algorithm to do
"address resolution" from an IPv4 address and port to an IPv6 address.
This algorithmic mapping is specified in section 5.</t>
<t>A full IPv4 address or IPv4 prefix can be used like today, e.g. for
identifying an interface or as a DHCP pool. A shared IPv4 address on the
other hand, MUST NOT be used to identify an interface. While it is
theoretically possible to make host stacks and applications port-aware,
that is considered a too drastic change to the IP model <xref
target="RFC6250"></xref>.</t>
<t>The MAP architecture described here, restricts the use of the shared
IPv4 address to only be used as the global address (outside) of the NAPT
<xref target="RFC2663"></xref> running on the CE. The NAPT MUST in turn
be connected to a MAP aware forwarding function, that does
encapsulation/decapsulation or translation to IPv6.</t>
<t>When MAP is used to provision a full IPv4 address or an IPv4 prefix
to the CE, these restrictions do not apply.</t>
<t>For packets outbound from the private IPv4 network, the CE NAPT MUST
translate transport identifiers (e.g. TCP and UDP port numbers) so that
they fall within the assigned CE's port-range.</t>
<t>The forwarding function uses the Mapping Rule Table (MRT) to make
forwarding decisions. The table consist of the mapping rules. An entry
in the table consists of an IPv4 prefix and PSID. The normal best
matching prefix algorithm is used. With a maximum key length of 48
(Length of IPv4 address (32) + Length of Transport layer port field
(16)). E.g. with a sharing ratio of 64 (6 bit PSID length) a "host
route" for this CE would be a /38 (32 + 6).</t>
<figure align="center" anchor="topology" title="Network Topology">
<preamble></preamble>
<artwork align="center"><![CDATA[
User N
Private IPv4
| Network
|
O--+---------------O
| | MAP CE |
| +-----+--------+ |
| NAPT44| MAP | |
| +-----+ | | |\ ,-------. .------.
| +--------+ | \ ,-' `-. ,-' `-.
O------------------O / \ O---------O / Public \
/ IPv6 only \ | MAP |/ IPv4 \
( Network --+ Border +- Network )
\ (MAP Domain) / | Relay |\ /
O------------------O \ / O---------O \ /
| MAP CE | /". ,-' `-. ,-'
| +-----+--------+ | / `----+--' ------'
| NAPT44| MAP | |/
| +-----+ | |
| | +--------+ |
O---.--------------O
|
User M
Private IPv4
Network
]]></artwork>
</figure>
<t>The MAP BR is responsible for connecting external IPv4 networks to
all devices in one or more MAP domains.</t>
<t>The translation mode allows communication between both IPv4-only and
any IPv6 enabled end hosts, with native IPv6-only servers which are
using IPv4-mapped IPv6 address based on DMR in the MAP-T domain. In this
mode, the IPv6-only servers SHOULD have both A and AAAA records in the
authorities DNS server <xref target="RFC6219"></xref>. DNS64 <xref
target="RFC6147"></xref> become required only when IPv6 servers in the
MAP-T domain are expected themselves to initiate communication to
external IPv4-only hosts.</t>
</section>
<section title="Mapping Algorithm">
<t>A MAP node is provisioned with one or more mapping rules.</t>
<t>Mapping rules are used differently depending on their function. Every
MAP node must be provisioned with a Basic mapping rule. This is used by
the node to configure its IPv4 address, IPv4 prefix or shared IPv4
address. This same basic rule can also be used for forwarding, where an
IPv4 destination address and optionally a destination port is mapped
into an IPv6 address or prefix. Additional mapping rules are specified
to allow for e.g. multiple different IPv4 subnets to exist within the
domain and optimize forwarding between them.</t>
<t>Traffic outside of the domain (i.e. when the destination IPv4 address
does not match (using longest matching prefix) any Rule IPv4 prefix in
the Rules database) will be forward using the Default mapping rule. The
Default mapping rule maps outside destinations to the BR's IPv6 address
or prefix. A forwarding mode is defined on a per domain basis.</t>
<t>There are three types of mapping rules: <list style="numbers">
<t>Basic Mapping Rule - used for IPv4 prefix, address or port set
assignment. There can only be one Basic Mapping Rule per End-user
IPv6 prefix. The Basic Mapping Rule is used to configure the MAP
IPv6 address or prefix. <list style="symbols">
<t>Rule IPv6 prefix (including prefix length)</t>
<t>Rule IPv4 prefix (including prefix length)</t>
<t>Rule EA-bits length (in bits)</t>
<t>Rule Port Parameters (optional)</t>
</list></t>
<t>Forwarding Mapping Rule - used for forwarding. The Basic Mapping
Rule is also a Forwarding Mapping Rule. Each Forwarding Mapping Rule
will result in an entry in the MRT for the Rule IPv4 prefix. The FMR
consists of the same parameters as the BMR.</t>
<t>Default Mapping Rule - used for destinations outside the MAP
domain. A 0.0.0.0/0 entry is installed in the MRT for this rule.
<list style="symbols">
<t>IPv6 prefix of address of BR</t>
</list></t>
</list></t>
<t>A MAP node finds its Basic Mapping Rule by doing a longest match
between the End-user IPv6 prefix and the Rule IPv6 prefix in the Mapping
Rule database. The rule is then used for IPv4 prefix, address or shared
address assignment.</t>
<t>A MAP IPv6 address (or prefix) is formed from the BMR Rule IPv6
prefix. This address MUST be assigned to an interface of the MAP node
and is used to terminate all MAP traffic being sent or received to the
node.</t>
<t>Port-aware IPv4 entries in the MRT are installed for all the
Forwarding Mapping Rules and an IPv4 default route for the Default
Mapping Rule.</t>
<t>In hub and spoke mode, all traffic MUST be forwarded using the
Default Mapping Rule.</t>
<section title="Port mapping algorithm">
<t>The port mapping algorithm is used in domains whose rules allow
IPv4 address sharing. Different Port-Set Identifiers (PSID) MUST have
non-overlapping port-sets. The two extreme cases are: (1) the port
numbers are not contiguous for each PSID, but uniformly distributed
across the port range (0-65535); (2) the port numbers are contiguous
in a single range for each PSID. The port mapping algorithm proposed
here is called the Generalized Modulus Algorithm (GMA) and supports
both these cases.</t>
<t>For a given sharing ratio (R) and the maximum number of contiguous
ports (M), the GMA algorithm is defined as:</t>
<t><list style="numbers">
<t>The port number (P) of a given PSID (K) is composed of: <figure>
<artwork><![CDATA[
P = R * M * j + M * K + i
]]></artwork>
</figure> Where:<list style="symbols">
<t>PSID: K = 0 to R - 1</t>
<t>Port range index: j = (4096 / M) / R to ((65536 / M) / R) -
1, if the port numbers (0 - 4095) are excluded.</t>
<t>Contiguous Port index: i = 0 to M - 1</t>
</list></t>
<t>The PSID (K) of a given port number (P) is determined by:
<figure>
<artwork><![CDATA[
K = (floor(P/M)) % R
]]></artwork>
</figure> Where:<list style="symbols">
<t>% is the modulus operator</t>
<t>floor(arg) is a function that returns the largest integer
not greater than arg.</t>
</list></t>
</list></t>
<section title="Bit Representation of the Algorithm">
<t>Given a sharing ratio (R=2^k), the maximum number of contiguous
ports (M=2^m), for any PSID (K) and available ports (P) can be
represented as:</t>
<t><figure align="left" anchor="bitrepresentation-fig"
title="Bit representation">
<preamble></preamble>
<artwork align="left"><![CDATA[
0 8 15
+---------------+----------+------+-------------------+
| P |
----------------+-----------------+-------------------+
| A (j) | PSID (K) | M (i) |
+---------------+----------+------+-------------------+
|<----a bits--->|<-----k bits---->|<------m bits----->|
]]></artwork>
</figure></t>
<t>Where j and i are the same indexes defined in the port mapping
algorithm.</t>
<t>For any port number, the PSID can be obtained by bit mask
operation.</t>
<t>For a > 0, j MUST be larger than 0. This ensures that the
algorithm excludes the system ports (<xref
target="I-D.ietf-tsvwg-iana-ports"></xref>). For a = 0, j MAY be 0
to allow for the provisioning of the system ports.</t>
</section>
<section title="GMA examples">
<t><figure align="left" title="Example 1: with offset = 4 (a = 4)">
<preamble>For example, for R = 1024, PSID offset: a = 4 and PSID
length: k = 10 bits</preamble>
<artwork align="left"><![CDATA[
Port-set-1 Port-set-2
PSID=0 | 4096, 4097, 4098, 4099, | 8192, 8193, 8194, 8195, | ...
PSID=1 | 4100, 4101, 4102, 4103, | 8196, 8197, 8198, 8199, | ...
PSID=2 | 4104, 4105, 4106, 4107, | 8200, 8201, 8202, 8203, | ...
PSID=3 | 4108, 4109, 4110, 4111, | 8204, 8205, 8206, 8207, | ...
...
PSID=1023| 8188, 8189, 8190, 8191, | 12284, 12285, 12286, 12287,| ...
]]></artwork>
</figure></t>
<t><figure align="left" title="Example 2: with offset = 0 (a = 0)">
<preamble>For example, for R = 64, a = 0 (PSID offset = 0 and
PSID length = 6 bits):</preamble>
<artwork align="left"><![CDATA[
Port-set
PSID=0 | [ 0 - 1023]
PSID=1 | [1024 - 2047]
PSID=2 | [2048 - 3071]
PSID=3 | [3072 - 4095]
...
PSID=63 | [64512 - 65535]
]]></artwork>
</figure></t>
</section>
<section title="Algorithm Provisioning Considerations">
<t>The number of offset bits (a) and excluded ports are optionally
provisioned via the "Rule Port Mapping Parameters" in the Basic
Mapping Rule.</t>
<t>The defaults are: <list style="symbols">
<t>Excluded ports : 0-4095</t>
<t>Offset bits (a) : 4</t>
</list></t>
<t>To simplify the port mapping algorithm the defaults are chosen so
that the PSID field starts on a nibble boundary and the excluded
port range (0-1023) is extended to 0-4095.</t>
</section>
</section>
<section title="Basic mapping rule (BMR)">
<t><figure align="center" anchor="addressallocation-fig"
title="IPv6 address format">
<preamble></preamble>
<artwork align="center"><![CDATA[
| n bits | o bits | s bits | 128-n-o-s bits |
+--------------------+-----------+---------+------------+----------+
| Rule IPv6 prefix | EA bits |subnet ID| interface ID |
+--------------------+-----------+---------+-----------------------+
|<--- End-user IPv6 prefix --->|
]]></artwork>
</figure></t>
<t>The Embedded Address bits (EA bits) are unique per end user within
a Rule IPv6 prefix. The Rule IPv6 prefix is the part of the End-user
IPv6 prefix that is common among all CEs using the same Basic Mapping
Rule within the MAP domain. The EA bits encode the CE specific IPv4
address and port information. The EA bits can contain a full or part
of an IPv4 prefix or address, and in the shared IPv4 address case
contains a Port-Set Identifier (PSID).</t>
<t>The MAP IPv6 address is created by concatenating the End-user IPv6
prefix with the MAP subnet-id and the interface-id as specified in
<xref target="interface-id"></xref>.</t>
<t>The MAP subnet ID is defined to be the first subnet (all bits set
to zero). A MAP node MUST reserve the first IPv6 prefix in a End-user
IPv6 prefix for the purpose of MAP.</t>
<t>The MAP IPv6 is created by combining the End-User IPv6 prefix with
the all zeros subnet-id and the MAP IPv6 interface identifier.</t>
<t><figure align="center" anchor="addressallocation2-fig"
title="Shared IPv4 address">
<preamble>Shared IPv4 address:</preamble>
<artwork align="center"><![CDATA[
| r bits | p bits | | q bits |
+-------------+---------------------+ +------------+
| Rule IPv4 | IPv4 Address suffix | |Port-Set ID |
+-------------+---------------------+ +------------+
| 32 bits |
]]></artwork>
</figure></t>
<t><figure align="center" anchor="addressallocation3-fig"
title="Complete IPv4 address">
<preamble>Complete IPv4 address:</preamble>
<artwork align="center"><![CDATA[
| r bits | p bits |
+-------------+---------------------+
| Rule IPv4 | IPv4 Address suffix |
+-------------+---------------------+
| 32 bits |
]]></artwork>
</figure></t>
<t><figure align="center" anchor="addressallocation4-fig"
title="IPv4 prefix">
<preamble>IPv4 prefix:</preamble>
<artwork align="center"><![CDATA[
| r bits | p bits |
+-------------+---------------------+
| Rule IPv4 | IPv4 Address suffix |
+-------------+---------------------+
| < 32 bits |
]]></artwork>
</figure></t>
<t>The length of r MAY be zero, in which case the complete IPv4
address or prefix is encoded in the EA bits. If only a part of the
IPv4 address/prefix is encoded in the EA bits, the Rule IPv4 prefix is
provisioned to the CE by other means (e.g. a DHCPv6 option). To create
a complete IPv4 address (or prefix), the IPv4 address suffix (p) from
the EA bits, are concatenated with the Rule IPv4 prefix (r bits).</t>
<t>The offset of the EA bits field in the IPv6 address is equal to the
BMR Rule IPv6 prefix length. The length of the EA bits field (o) is
given by the BMR Rule EA-bits length. The sum of the Rule IPv6 Prefix
length and the Rule EA-bits length MUST be less or equal than the
End-user IPv6 prefix length.</t>
<t>If o + r < 32 (length of the IPv4 address in bits), then an IPv4
prefix is assigned.</t>
<t>If o + r is equal to 32, then a full IPv4 address is to be
assigned. The address is created by concatenating the Rule IPv4 prefix
and the EA-bits.</t>
<t>If o + r is > 32, then a shared IPv4 address is to be assigned.
The number of IPv4 address suffix bits (p) in the EA bits is given by
32 - r bits. The PSID bits are used to create a port-set. The length
of the PSID bit field within EA bits is: o - p.</t>
<t>In the following examples, only the suffix (last 8 bits) of the
IPv4 address is embedded in the EA bits (r = 24), while the IPv4
prefix (first 24 bits) is given in the BMR Rule IPv4 prefix.</t>
<t><figure>
<preamble>Example:</preamble>
<artwork align="left"><![CDATA[
Given:
End-user IPv6 prefix: 2001:db8:0012:3400::/56
Basic Mapping Rule: {2001:db8:0000::/40 (Rule IPv6 prefix),
192.0.2.0/24 (Rule IPv4 prefix),
16 (Rule EA-bits length)}
Sharing ratio: 256 (16 - (32 - 24) = 8. 2^8 = 256)
PSID offset: 4 (default value as per section 5.1.3)
We get IPv4 address and port-set:
EA bits offset: 40
IPv4 suffix bits (p): Length of IPv4 address (32) -
IPv4 prefix length (24) = 8
IPv4 address: 192.0.2.18 (0x12)
PSID start: 40 + p = 40 + 8 = 48
PSID length: o - p = 16 (56 - 40) - 8 = 8
PSID: 0x34
Port-set-1: 4928, 4929, 4930, 4931, 4932, 4933, 4934, 4935,
4936, 4937, 4938, 4939, 4940, 4941, 4942, 4943
Port-set-2: 9024, 9025, 9026, 9027, 9028, 9029, 9030, 9031,
9032, 9033, 9034, 9035, 9036, 9037, 9038, 9039
...
Port-set-15: 62272, 62273, 62274, 62275,
62276, 62277, 62278, 62279,
62280, 62281, 62282, 62283,
62284, 62285, 62286, 62287,
]]></artwork>
</figure></t>
</section>
<section title="Forwarding mapping rule (FMR)">
<t>On adding an FMR rule, an IPv4 route is installed in the MRT for
the Rule IPv4 prefix.</t>
<t>On forwarding an IPv4 packet, a best matching prefix lookup is done
in the MRT and the correct FMR is chosen.</t>
<t><figure align="left" anchor="aplusptoipv6-fig"
title="Deriving of MAP IPv6 address">
<preamble></preamble>
<artwork align="left"><![CDATA[
| 32 bits | | 16 bits |
+--------------------------+ +-------------------+
| IPv4 destination address | | IPv4 dest port |
+--------------------------+ +-------------------+
: : ___/ :
| p bits | / q bits :
+----------+ +------------+
|IPv4 sufx| |Port-Set ID |
+----------+ +------------+
\ / ____/ ________/
\ : __/ _____/
\ : / /
| n bits | o bits | s bits | 128-n-o-s bits |
+--------------------+-----------+---------+------------+----------+
| Rule IPv6 prefix | EA bits |subnet ID| interface ID |
+--------------------+-----------+---------+-----------------------+
|<--- End-user IPv6 prefix --->|
]]></artwork>
</figure></t>
<t><figure>
<preamble>Example:</preamble>
<artwork align="left"><![CDATA[
Given:
IPv4 destination address: 192.0.2.18
IPv4 destination port: 9030
Forwarding Mapping Rule: {2001:db8:0000::/40 (Rule IPv6 prefix),
192.0.2.0/24 (Rule IPv4 prefix),
16 (Rule EA-bits length)}
PSID offset: 4 (default value as per section 5.1.3)
We get IPv6 address:
IPv4 suffix bits (p): 32 - 24 = 8 (18 (0x12))
PSID length: 8
PSID: 0x34 (9030 (0x2346))
EA bits: 0x1234
MAP IPv6 address: 2001:db8:0012:3400:00c0:0002:1200:3400
]]></artwork>
</figure></t>
</section>
<section title="Default mapping rule (DMR)">
<t>The Default Mapping rule is used to reach IPv4 destinations outside
of the MAP domain. Traffic using this rule will be sent from a CE to a
BR.</t>
<t>The DMR consist of the IPv6 address or IPv6 prefix of the BR. Which
is used, is dependent on the forwarding mode used. Translation mode
requires that the IPv4 destination address is encoded in the BR IPv6
address, so only a prefix is used in the DMR to allow for a generated
interface identifier. For the encapsulation mode the complete IPv6
address of the BR is used.</t>
</section>
</section>
<section anchor="interface-id" title="The IPv6 Interface Identifier">
<t>The Interface identifier format of a MAP node is based on the format
specified in section 2.2 of <xref target="RFC6052"></xref>, with the
added PSID field if present, as shown in figure <xref
target="interfaceid2-fig"></xref>.</t>
<t><figure align="left" anchor="interfaceid2-fig" title="">
<preamble></preamble>
<artwork align="left"><![CDATA[
+--+---+---+---+---+---+---+---+---+
|PL| 8 16 24 32 40 48 56 |
+--+---+---+---+---+---+---+---+---+
|64| u | IPv4 address | PSID | 0 |
+--+---+---+---+---+---+---+---+---+
]]></artwork>
</figure></t>
<t>For traffic destined outside of a MAP domain (i.e. for traffic
following the default mapping rule), the destination IPv4 address is
mapped to the IPv6 address or prefix of the BR. For MAP-E this is the
IPv6 tunnel end point address of the BR, while for MAP-T this is the
IPv6 converted representation of the IPv6 address per RFC6052, shown in
the form of an example in figure <xref target="interfaceid3-fig"></xref>
below. Note that the BR prefix-length is variable and can be both
shorter or longer than 64 bits, up to 96 bits.</t>
<t><figure anchor="interfaceid3-fig" title="">
<preamble></preamble>
<artwork><![CDATA[
<---------- 64 ------------>< 8 ><----- 32 -----><--- 24 --->
+--------------------------+----+---------------+-----------+
| BR prefix | u | IPv4 address | 0 |
+--------------------------+----+---------------+-----------+
]]></artwork>
</figure></t>
<t>The encoding of the full IPv4 address into the interface identifier,
both for the source and destination IPv6 addresses have been shown to be
useful for troubleshooting.</t>
<t>In the case of an IPv4 prefix, the IPv4 address field is right-padded
with zeroes up to 32 bits. The PSID field is left-padded to create a 16
bit field. For an IPv4 prefix or a complete IPv4 address, the PSID field
is zero.</t>
<t>If the End-user IPv6 prefix length is larger than 64, the most
significant parts of the interface identifier is overwritten by the
prefix.</t>
</section>
<section title="MAP Configuration">
<t>For a given MAP domain, the BR and CE MUST be configured with the
following MAP elements. The configured values for these elements are
identical for all CEs and BRs within a given MAP domain.</t>
<t><list style="symbols">
<t>The End-User IPv6 prefix (Part of the normal IPv6
provisioning).</t>
<t>The Basic Mapping Rule and optionally the Forwarding Mapping
Rules, including the Rule IPv6 prefix, Rule IPv4 prefix, Length of
EA bits, and Forwarding mode</t>
<t>The Default Mapping Rule with the BR IPv6 prefix or address</t>
<t>The domain's MAP-E or MAP-T forwarding mode.</t>
</list></t>
<section title="MAP CE">
<t>The MAP elements are set to values that are the same across all CEs
within a MAP domain. The values may be configured in a variety of
manners, including provisioning methods such as the Broadband Forum's
"TR-69" Residential Gateway management interface, an XML-based object
retrieved after IPv6 connectivity is established, or manual
configuration by an administrator. This document describes how to
configure the necessary parameters via a single DHCPv6 option. A CE
that allows IPv6 configuration by DHCP SHOULD implement this option.
Other configuration and management methods may use the format
described by this option for consistency and convenience of
implementation on CEs that support multiple configuration methods.</t>
<t>The only remaining provisioning information the CE requires in
order to calculate the MAP IPv4 address and enable IPv4 connectivity
is the IPv6 prefix for the CE. The End-user IPv6 prefix is configured
as part of obtaining IPv6 Internet access.</t>
<t>A single MAP CE MAY be connected to more than one MAP domain, just
as any router may have more than one IPv4-enabled service provider
facing interface and more than one set of associated addresses
assigned by DHCP. Each domain a given CE operates within would require
its own set of MAP configuration elements and would generate its own
IPv4 address.</t>
<t>The MAP DHCP option is specified in <xref
target="I-D.mdt-softwire-map-dhcp-option"></xref>.</t>
</section>
<section title="MAP BR">
<t>The MAP BR MUST be configured with the same MAP elements as the MAP
CEs operating within the same domain.</t>
<t>For increased reliability and load balancing, the BR IPv6 address
may be an anycast address shared across a given MAP domain. As MAP is
stateless, any BR may be used at any time. If the BR IPv6 address is
anycast the relay MUST use this anycast IPv6 address as the source
address in packets relayed to CEs.</t>
<t>Since MAP uses provider address space, no specific routes need to
be advertised externally for MAP to operate, neither in IPv6 nor IPv4
BGP. However, if anycast is used for the MAP IPv6 relays, the anycast
addresses must be advertised in the service provider's IGP.</t>
</section>
<section title="Backwards compatibility">
<t>A MAP-E CE provisioned with only a Default Mapping Rule makes a
MAP-E CE compatible for use with DS-Lite <xref
target="RFC6333"></xref> AFTRs, whose addresses are configured as the
MAP BR.</t>
<t>A MAP-T CE, in all configuration modes, is by default compatible
with stateful NAT64 gateways, whose prefixes are passed as the BR
prefixes. Furthermore, when a MAP-T CE configured to operate without
address sharing (no PSID), is compatible with stateless NAT64 elements
acting as BRs.</t>
</section>
</section>
<section title="Forwarding Considerations">
<t>Figure 1 depicts the overall MAP architecture with IPv4 users (N and
M) networks connected to a routed IPv6 network.</t>
<t>MAP supports two forwarding modes. Translation mode as specified in