draft-mdt-softwire-mapping-address-and-port.xml

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<rfc category="std" docName="draft-mdt-softwire-mapping-address-and-port-03"
     ipr="trust200902">
  <front>
    <title abbrev="MAP">Mapping of Address and Port (MAP)</title>

    <author fullname="Ole Troan" initials="O" surname="Troan">
      <organization abbrev="">cisco</organization>
      <address>
	<postal>
          <street></street>
          <city>Oslo</city>
          <country>Norway</country>
        </postal>
        <email>ot@cisco.com</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>satoru.matsushima@tm.softbank.co.jp</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>tetsuya@ipinfusion.com</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>xing@cernet.edu.cn</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>congxiao@cernet.edu.cn</email>
      </address>
    </author>

    <date year="2012" />

    <area>Internet</area>

    <workgroup>Network Working Group</workgroup>

    <!--  SECTION 0:  Abstract                      -->

    <abstract>
      <t>This document describes a generic mechanism for mapping
      between IPv4 addresses and IPv6 addresses and transport layer
      ports.</t>
    </abstract>
  </front>

  <middle>
    <!--  SECTION 1:  Introduction                  -->

    <section title="Introduction">
      <t>The mechanism of 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>. 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 more generic mapping of
      IPv4 to IPv6 that can be used both for encapsulation (IPv4 over
      IPv6) and for translation between the two protocols.</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"/> covers stateless mapping. The corresponding
      stateful solution DS-lite is described in <xref
      target="RFC6333"></xref>. The motivation for 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>. Deployment
      considerations are described in
      [I-D.mdt-softwire-map-deployment].</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="22" style="hanging">

	<t hangText="MAP domain:">A set of 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 MAP node in the
	domain has the same set of rules.</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"/> 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 CE's and from BR's.</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="IPv4 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
	datastructure, supporting longest match lookups. The MRT is
	used by the MAP forwarding function.</t>

      </list></t>

    </section>

    <!--  SECTION 3: DESCRIPTION                   -->

    <section title="Architecture">
      <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"/>.</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"/> 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>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 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 (32 + 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>
    </section>

    <section title="Mapping Rules">
      <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 itself with
      an IPv4 address, IPv4 prefix or shared IPv4 address from an
      End-user IPv6 prefix. 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 can be specified to allow for
      e.g. multiple different IPv4 subnets to exist within the
      domain. Additional mapping rules are recognized by having a Rule
      IPv6 prefix different from the base End-user IPv6 prefix.</t>

      <t>Traffic outside of the domain (IPv4 address not matching
      (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.</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.

	<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>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>Rule IPv6 prefix (including prefix length)</t>
	  <t>Rule BR IPv4 address</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>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>
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>
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" title="Bit representation" anchor="bitrepresentation-fig">
	  <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"/>). 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">
          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">
          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="GMA 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 GMA 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" title="IPv6 address format"
		   anchor="addressallocation-fig">
	  <preamble></preamble>
	  <artwork align="center"><![CDATA[


|     n bits         |  o bits   | m bits  |   128-n-o-m 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"/>.</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><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 &lt; 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

  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

   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 AP
	RIB for the Rule IPv4 prefix.</t>

	<t>On forwarding an IPv4 packet, a best matching prefix lookup
	is done in the IPv4 routing table 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   | m bits  |   128-n-o-m 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

  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 Rule IPv4 prefix in the DMR is: 0.0.0.0/0. The Rule
	IPv6 prefix is the IPv6 address or prefix of the BR. Which is
	used, is dependent on the mode used. For example translation
	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 Rule IPv6 prefix can be the full IPv6 address of the
	BR.</t>

	<t>There MUST be only one Default Mapping Rule within a MAP domain.</t>

	<t><figure title="Example 3: Default Mapping Rule">
	  <artwork align="left"><![CDATA[
 Default Mapping Rule:     
      {2001:db8:0001:0000:&lt;interface-id>:/128 (Rule IPv6 prefix),
       0.0.0.0/0 (Rule IPv4 prefix),
       192.0.2.1 (BR IPv4 address)}
       ]]></artwork>
	</figure></t>

	<t>In most implementations of a routing table, the next-hop
	address must be of the same address family as the prefix. To
	satisfy this requirement a BR IPv4 address is included in the
	rule. Giving a default route in the IPv4 routing table:</t>

	<t><figure>
	  <artwork align="left"><![CDATA[
   0.0.0.0 -> 192.0.2.1, MAP-Interface0
  ]]></artwork>
	</figure></t>

      </section>
    </section>

    <section title="The IPv6 Interface Identifier" anchor="interface-id">
      <t>The Interface identifier format is based on the format
      specified in section 2.2 of <xref target="RFC6052"/>, with the
      added PSID format field.</t>

      <t>In an encapsulation solution, an IPv4 address and port is
      mapped to an IPv6 address. This is the address of the tunnel end
      point of the receiving MAP CE. For traffic outside the MAP
      domain, the IPv6 tunnel end point address is the IPv6 address of
      the BR. The interface-id used for all MAP nodes in the domain
      MUST be deterministic.</t>

      <t>When translating, the destination IPv4 address is translated
      into a corresponding IPv6 address. In the case of traffic
      outside of the MAP domain, it is translated to the BR's IPv6
      prefix. For the BR to be able to reverse the translation, the
      full destination IPv4 address must be encoded in the IPv6
      address. The same thing applies if an IPv4 prefix is encoded in
      the IPv6 address, then the reverse translator needs to know the
      full destination IPv4 address, which has to be encoded in the
      interface-id.</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><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>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. For translation mode the End-user IPv6
      prefix MUST be 64 or shorter.</t>

    </section>
	
    <!--  SECTION 4:  IANA Considerations           -->

    <section title="IANA Considerations">
      <t>This specification does not require any IANA actions.</t>
    </section>

    <!--  SECTION 5:  Security Considerations      	-->

    <section title="Security Considerations">
      <t>Specific security considerations with the MAP mechanism are
      detailed in the encapsulation and translation documents
      [I-D.mdt-map-t/I-D.mdt-map-e].</t>

      <t><xref target="RFC6269"/> outlines general issues with IPv4 address sharing.</t>
    </section>



    <!--  SECTION 6:  Contributors     			-->

    <section title="Contributors">
      <t>Mohamed Boucadair, Gang Chen, Maoke Chen, Wojciech Dec,
      Xiaohong Deng, Jouni Korhonen, Tomasz Mrugalski, Jacni Qin,
      Chunfa Sun, Qiong Sun, Leaf Yeh.</t>
    </section>

    <!--  SECTION 7:  Acknowledgements     			-->

    <section title="Acknowledgements">
      <t>This document is based on the ideas of many. In particular
      Remi Despres, who has tirelessly worked on generalized
      mechanisms for stateless address mapping.</t>

      <t>The authors would like to thank Guillaume Gottard, Dan Wing,
      Jan Zorz, Necj Scoberne, Tina Tsou for their thorough review and
      comments.</t>
    </section>

  </middle>

  <back>

    <!--  SECTION 8.1:  Normative References		-->

    <references title="Normative References">
      &rfc2119;
      &rfc6346;
      &I-D.mdt-softwire-map-dhcp-option;
    </references>

    <!--  SECTION 8.2:  Informative References		-->
    <references title="Informative References">
      &I-D.ietf-softwire-stateless-4v6-motivation;
      &I-D.ietf-tsvwg-iana-ports;
      &rfc6333;
      &rfc6052;
      &rfc1933;
      &rfc5969;
      &rfc3056;
      &rfc2529;
      &rfc5214;
      &rfc4380;
      &rfc2766;
      &rfc6146;
      &rfc6147;
      &rfc3633;
      &rfc6269;
      &rfc6250;
      &rfc2663;
    </references>
  </back>
</rfc>