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Network Working Group                                           O. Troan
Internet-Draft                                                     cisco
Intended status: Standards Track                           S. Matsushima
Expires: August 2, 2012                                 SoftBank Telecom
                                                             T. Murakami
                                                             IP Infusion
                                                                   X. Li
                                                                  C. Bao
                                                  CERNET Center/Tsinghua
                                                              University
                                                        January 30, 2012


                   Mapping of Address and Port (MAP)
             draft-mdt-softwire-mapping-address-and-port-03

Abstract

   This document describes a generic mechanism for mapping between IPv4
   addresses and IPv6 addresses and transport layer ports.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 2, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Architecture . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Mapping Rules  . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.1.  Port mapping algorithm . . . . . . . . . . . . . . . . . .  8
       5.1.1.  Bit Representation of the Algorithm  . . . . . . . . .  9
       5.1.2.  GMA examples . . . . . . . . . . . . . . . . . . . . .  9
       5.1.3.  GMA Provisioning Considerations  . . . . . . . . . . . 10
     5.2.  Basic mapping rule (BMR) . . . . . . . . . . . . . . . . . 10
     5.3.  Forwarding mapping rule (FMR)  . . . . . . . . . . . . . . 13
     5.4.  Default mapping rule (DMR) . . . . . . . . . . . . . . . . 14
   6.  The IPv6 Interface Identifier  . . . . . . . . . . . . . . . . 15
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     11.2. Informative References . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19






















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1.  Introduction

   The mechanism of mapping IPv4 addresses in IPv6 addresses has been
   described in numerous mechanisms dating back to 1996 [RFC1933].  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.

   There are numerous variations of this idea, described in 6over4
   [RFC2529], 6to4 [RFC3056], ISATAP [RFC5214], and 6rd [RFC5969].  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 [RFC4380] 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.

   NAT-PT [RFC2766](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
   [RFC6146] and DNS64 [RFC6147] which rely on an address format defined
   in [RFC6052].  [RFC6052] specifies the algorithmic translation of an
   IPv6 address to IPv4 address.  In particular, [RFC6052] 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]):

   "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."

   The commonalities of all these IPv6 over IPv4 mechanisms are:

   o  Automatically provisions an IPv6 address for a host or an IPv6
      prefix for a site

   o  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



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      IPv4 address can be calculated from an IPv6 destination address
      and vice versa.

   o  Embedding of an IPv4 address or part thereof and optionally
      transport layer ports into an IPv6 address.

   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.

   Just as the IPv6 over IPv4 mechanisms referred to above, the residual
   IPv4 over IPv6 mechanisms must be capable of:

   o  Provisioning an IPv4 prefix, an IPv4 address or a shared IPv4
      address.

   o  Algorithmically map between an IPv4 prefix, IPv4 address or a
      shared IPv4 address and an IPv6 address.

   The unified mapping scheme described here supports translation mode,
   encapsulation mode, in both mesh and hub and spoke topologies.

   This document describes delivery of IPv4 unicast service across an
   IPv6 infrastructure.  IPv4 multicast is not considered further in
   this document.

   The A+P (Address and Port) architecture of sharing an IPv4 address by
   distributing the port space is described in [RFC6346].  Specifically
   section 4 of [RFC6346] covers stateless mapping.  The corresponding
   stateful solution DS-lite is described in [RFC6333].  The motivation
   for work is described in
   [I-D.ietf-softwire-stateless-4v6-motivation].

   A companion document defines a DHCPv6 option for provisioning of MAP
   [I-D.mdt-softwire-map-dhcp-option].  Deployment considerations are
   described in [I-D.mdt-softwire-map-deployment].


2.  Conventions

   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 [RFC2119].






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3.  Terminology

   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.

   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.

   MAP node              A device that implements MAP.

   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.

   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.

   Port-set:             Each node has a separate part of the transport
                         layer port space; denoted as a port-set.

   Port-set ID (PSID):   Algorithmically identifies a set of ports
                         exclusively assigned to the CE.

   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.

   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 [RFC3633] or configured
                         manually.  It is unique for each CE.





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   MAP IPv6 address:     The IPv6 address used to reach the MAP function
                         of a CE from other CE's and from BR's.

   Rule IPv6 prefix:     An IPv6 prefix assigned by a Service Provider
                         for a mapping rule.

   Rule IPv4 prefix:     An IPv4 prefix assigned by a Service Provider
                         for a mapping rule.

   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.

   MRT:                  MAP Rule table.  Address and Port aware
                         datastructure, supporting longest match
                         lookups.  The MRT is used by the MAP forwarding
                         function.


4.  Architecture

   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
   [RFC6250].

   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 [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.

   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.

   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).






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5.  Mapping Rules

   A MAP node is provisioned with one or more mapping rules.

   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.

   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.

   There are three types of mapping rules:

   1.  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.

       *  Rule IPv6 prefix (including prefix length)

       *  Rule IPv4 prefix (including prefix length)

       *  Rule EA-bits length (in bits)

       *  Rule Port Parameters (optional)

   2.  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.

       *  Rule IPv6 prefix (including prefix length)

       *  Rule IPv4 prefix (including prefix length)

       *  Rule EA-bits length (in bits)

       *  Rule Port Parameters (optional)





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   3.  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.

       *  Rule IPv6 prefix (including prefix length)

       *  Rule BR IPv4 address

   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.

   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.

   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.

   In hub and spoke mode, all traffic MUST be forwarded using the
   Default Mapping Rule.

5.1.  Port mapping algorithm

   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.

   For a given sharing ratio (R) and the maximum number of contiguous
   ports (M), the GMA algorithm is defined as:

   1.  The port number (P) of a given PSID (K) is composed of:

   P = R * M * j + M * K + i

       Where:

       *  PSID: K = 0 to R - 1

       *  Port range index: j = (4096 / M) / R to ((65536 / M) / R) - 1,
          if the port numbers (0 - 4095) are excluded.




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       *  Contiguous Port index: i = 0 to M - 1

   2.  The PSID (K) of a given port number (P) is determined by:

   K = (floor(P/M)) % R

       Where:

       *  % is the modulus operator

       *  floor(arg) is a function that returns the largest integer not
          greater than arg.

5.1.1.  Bit Representation of the Algorithm

   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:


   0                          8                         15
   +---------------+----------+------+-------------------+
   |                     P                               |
   ----------------+-----------------+-------------------+
   |        A (j)  |   PSID (K)      |        M  (i)     |
   +---------------+----------+------+-------------------+
   |<----a bits--->|<-----k bits---->|<------m bits----->|


                       Figure 1: Bit representation

   Where j and i are the same indexes defined in the port mapping
   algorithm.

   For any port number, the PSID can be obtained by bit mask operation.

   For a > 0, j MUST be larger than 0.  This ensures that the algorithm
   excludes the system ports ([I-D.ietf-tsvwg-iana-ports]).  For a = 0,
   j MAY be 0 to allow for the provisioning of the system ports.

5.1.2.  GMA examples










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   For example, for R = 1024, PSID offset: a = 4 and PSID length: k = 10
   bits

             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,| ...


                    Example 1: with offset = 4 (a = 4)

   For example, for R = 64, a = 0 (PSID offset = 0 and PSID length = 6
   bits):

             Port-set
   PSID=0   | [   0 - 1023]
   PSID=1   | [1024 - 2047]
   PSID=2   | [2048 - 3071]
   PSID=3   | [3072 - 4095]
   ...
   PSID=63  | [64512 - 65535]


                    Example 2: with offset = 0 (a = 0)

5.1.3.  GMA Provisioning Considerations

   The number of offset bits (a) and excluded ports are optionally
   provisioned via the "Rule Port Mapping Parameters" in the Basic
   Mapping Rule.

   The defaults are:

   o  Excluded ports : 0-4095

   o  Offset bits (a) : 4

   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.

5.2.  Basic mapping rule (BMR)






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    |     n bits         |  o bits   | m bits  |   128-n-o-m bits      |
    +--------------------+-----------+---------+------------+----------+
    |  Rule IPv6 prefix  |  EA bits  |subnet ID|     interface ID      |
    +--------------------+-----------+---------+-----------------------+
    |<---  End-user IPv6 prefix  --->|


                       Figure 2: IPv6 address format

   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).

   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
   Section 6.

   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.

                           Shared IPv4 address:


        |   r bits    |        p bits       |         |   q bits   |
        +-------------+---------------------+         +------------+
        |  Rule IPv4  | IPv4 Address suffix |         |Port-Set ID |
        +-------------+---------------------+         +------------+
        |            32 bits                |


                       Figure 3: Shared IPv4 address

                          Complete IPv4 address:


                   |   r bits    |        p bits       |
                   +-------------+---------------------+
                   |  Rule IPv4  | IPv4 Address suffix |
                   +-------------+---------------------+
                   |            32 bits                |


                      Figure 4: Complete IPv4 address



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                               IPv4 prefix:


                   |   r bits    |        p bits       |
                   +-------------+---------------------+
                   |  Rule IPv4  | IPv4 Address suffix |
                   +-------------+---------------------+
                   |           < 32 bits               |

                           Figure 5: IPv4 prefix

   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).

   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.

   If o + r < 32 (length of the IPv4 address in bits), then an IPv4
   prefix is assigned.

   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.

   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.

   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.











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   Example:

  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,

5.3.  Forwarding mapping rule (FMR)

   On adding an FMR rule, an IPv4 route is installed in the AP RIB for
   the Rule IPv4 prefix.

   On forwarding an IPv4 packet, a best matching prefix lookup is done
   in the IPv4 routing table and the correct FMR is chosen.















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   |        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  --->|


                  Figure 6: Deriving of MAP IPv6 address

   Example:

     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

5.4.  Default mapping rule (DMR)

   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.

   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



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   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.

   There MUST be only one Default Mapping Rule within a MAP domain.


    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)}

                      Example 3: Default Mapping Rule

   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:


      0.0.0.0 -> 192.0.2.1, MAP-Interface0


6.  The IPv6 Interface Identifier

   The Interface identifier format is based on the format specified in
   section 2.2 of [RFC6052], with the added PSID format field.

   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.

   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.

   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.




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   +--+---+---+---+---+---+---+---+---+
   |PL|   8  16  24  32  40  48  56   |
   +--+---+---+---+---+---+---+---+---+
   |64| u | IPv4 address  |  PSID | 0 |
   +--+---+---+---+---+---+---+---+---+


                                 Figure 7

   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.

   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.


7.  IANA Considerations

   This specification does not require any IANA actions.


8.  Security Considerations

   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].

   [RFC6269] outlines general issues with IPv4 address sharing.


9.  Contributors

   Mohamed Boucadair, Gang Chen, Maoke Chen, Wojciech Dec, Xiaohong
   Deng, Jouni Korhonen, Tomasz Mrugalski, Jacni Qin, Chunfa Sun, Qiong
   Sun, Leaf Yeh.


10.  Acknowledgements

   This document is based on the ideas of many.  In particular Remi
   Despres, who has tirelessly worked on generalized mechanisms for
   stateless address mapping.

   The authors would like to thank Guillaume Gottard, Dan Wing, Jan



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   Zorz, Necj Scoberne, Tina Tsou for their thorough review and
   comments.


11.  References

11.1.  Normative References

   [I-D.mdt-softwire-map-dhcp-option]
              Mrugalski, T., Boucadair, M., Deng, X., Troan, O., and C.
              Bao, "DHCPv6 Options for Mapping of Address and Port",
              draft-mdt-softwire-map-dhcp-option-02 (work in progress),
              January 2012.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6346]  Bush, R., "The Address plus Port (A+P) Approach to the
              IPv4 Address Shortage", RFC 6346, August 2011.

11.2.  Informative References

   [I-D.ietf-softwire-stateless-4v6-motivation]
              Boucadair, M., Matsushima, S., Lee, Y., Bonness, O.,
              Borges, I., and G. Chen, "Motivations for Stateless IPv4
              over IPv6 Migration Solutions",
              draft-ietf-softwire-stateless-4v6-motivation-00 (work in
              progress), September 2011.

   [I-D.ietf-tsvwg-iana-ports]
              Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry",
              draft-ietf-tsvwg-iana-ports-10 (work in progress),
              February 2011.

   [RFC1933]  Gilligan, R. and E. Nordmark, "Transition Mechanisms for
              IPv6 Hosts and Routers", RFC 1933, April 1996.

   [RFC2529]  Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
              Domains without Explicit Tunnels", RFC 2529, March 1999.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, August 1999.

   [RFC2766]  Tsirtsis, G. and P. Srisuresh, "Network Address



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              Translation - Protocol Translation (NAT-PT)", RFC 2766,
              February 2000.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

   [RFC4380]  Huitema, C., "Teredo: Tunneling IPv6 over UDP through
              Network Address Translations (NATs)", RFC 4380,
              February 2006.

   [RFC5214]  Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
              Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
              March 2008.

   [RFC5969]  Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
              Infrastructures (6rd) -- Protocol Specification",
              RFC 5969, August 2010.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

   [RFC6147]  Bagnulo, M., Sullivan, A., Matthews, P., and I. van
              Beijnum, "DNS64: DNS Extensions for Network Address
              Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
              April 2011.

   [RFC6250]  Thaler, D., "Evolution of the IP Model", RFC 6250,
              May 2011.

   [RFC6269]  Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
              Roberts, "Issues with IP Address Sharing", RFC 6269,
              June 2011.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.






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Authors' Addresses

   Ole Troan
   cisco
   Oslo
   Norway

   Email: ot@cisco.com


   Satoru Matsushima
   SoftBank Telecom
   1-9-1 Higashi-Shinbashi, Munato-ku
   Tokyo
   Japan

   Email: satoru.matsushima@tm.softbank.co.jp


   Tetsuya Murakami
   IP Infusion
   1188 East Arques Avenue
   Sunnyvale
   USA

   Email: tetsuya@ipinfusion.com


   Xing Li
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Email: xing@cernet.edu.cn


   Congxiao Bao
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Email: congxiao@cernet.edu.cn







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