draft-mdt-softwire-mapping-address-and-port-02.txt

Network Working Group                                      O. Troan, Ed.
Internet-Draft                                                     cisco
Intended status: Standards Track                       November 25, 2011
Expires: May 28, 2012


                   Mapping of Address and Port (MAP)
             draft-mdt-softwire-mapping-address-and-port-02

Abstract

   This document describes a generic mechanism for mapping between an
   IPv4 prefix, address or parts thereof, and transport layer ports and
   an IPv6 prefix or address.

Status of this Memo

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   This Internet-Draft will expire on May 28, 2012.

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   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Mapping Rules  . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Port mapping algorithm . . . . . . . . . . . . . . . . . .  7
       4.1.1.  Bit Representation of the Algorithm  . . . . . . . . .  8
       4.1.2.  GMA examples . . . . . . . . . . . . . . . . . . . . .  9
       4.1.3.  GMA Provisioning Considerations  . . . . . . . . . . .  9
       4.1.4.  Features of the Algorithm  . . . . . . . . . . . . . . 10
     4.2.  Basic mapping rule (BMR) . . . . . . . . . . . . . . . . . 10
     4.3.  Forwarding mapping rule (FMR)  . . . . . . . . . . . . . . 12
     4.4.  Default mapping rule (DMR) . . . . . . . . . . . . . . . . 13
   5.  The IPv6 Interface Identifier  . . . . . . . . . . . . . . . . 14
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   8.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     10.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17




























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1.  Introduction

   The mechanism of mapping IPv4 addresses in IPv6 address 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 an
   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 are the use of well known IPv6 prefixes, or Service
   Provider assigned IPv6 prefixes, and the exact position of the IPv4
   bits embedded 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 deducted 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, could be defined later, using bits
   currently reserved as null in the suffix."

   The commonalities of all these mechanisms are:

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



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   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 refereed 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.

   In particular the architecture of a shared IPv4 address by
   distributing the port space is described in [RFC6346].  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].


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].


3.  Terminology








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   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 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.

   Shared IPv4 address:  An IPv4 address that is shared among multiple
                         CEs.  Each node has a separate part of the
                         transport layer port space; denoted as a port
                         set.  Only ports that belong to the assigned
                         port set can be used for communication.

   End-user IPv6 prefix: The IPv6 prefix assigned to an End-user CE by
                         other means than MAP itself.

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

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

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







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   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.


4.  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 Rule.  The Default 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 a route in a conceptual routing table for the
       Rule IPv4 prefix.



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       *  Rule IPv6 prefix (including prefix length)

       *  Rule IPv4 prefix (including prefix length)

       *  Rule EA-bits length (in bits)

       *  Rule Port Parameters (optional)

   3.  Default Mapping Rule - used for destinations outside the MAP
       domain.  A 0.0.0.0/0 route is installed in the conceptual routing
       table 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 as to terminate all MAP traffic being sent or
   received to the node.

   Routes in the conceptual routing table are installed for all the
   Forwarding Mapping Rules and an IPv4 default route for the Default
   Mapping Rule.

   In the hub and spoke mode, all traffic should be forwarded using the
   Default Mapping Rule.  Hub and spoke mode is achieved with a BMR IPv4
   rule prefix length of 32 and no further Forwarding Mapping Rules.

4.1.  Port mapping algorithm

   Different Port Set Identificators (PSID) MUST have non-overlapping
   port sets.  The two extreme cases are: (1) the port number is not
   contiguous for each PSID, but uniformly distributed across the whole
   port range (0-65535); (2) the port number is 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:





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   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 well-known port numbers (0 - 4096) are excluded.

       *  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.

4.1.1.  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----->|
                          |k-c |<--c 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.




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   For a > 0, A MUST be larger than 0.  This ensures that the algorithm
   excludes the well known ports.  For a = 0, A MAY be 0 to allow for
   the provisioning of the well known ports.

   When m = 0, GMA becomes a modulo operation.  When a = 0, GMA becomes
   division operation.

4.1.2.  GMA examples

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

              Port set-1                Port set-2
    PSID=0   | 4096, 4097, 4098, 4099, | 8192, 8193, 8194, 8195, | 12288
    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=127 | 4604, 4605, 4606, 4607, | 8700, 8701, 8702, 8703, | ....


                             Figure 2: Example

    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]


                 Figure 3: Example with offset = 0 (a = 0)

4.1.3.  GMA Provisioning Considerations

   The sharing ratio (R), the PSID (K) and the PSID length are derived
   from existing information.

   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:




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   o  Excluded ports : 0-4095

   o  Offset bits (A) : 4

4.1.4.  Features of the Algorithm

   The GMA algorithm has the following features:

   1.  There is no waste of the port numbers, except the well-known
       ports.

   2.  The algorithm is flexible, the control parameters are PSID offset
       (a) and PSID length (c) / Sharing ratio.

   3.  The algorithm is simple to perform effectively.

   4.  It allows Service Providers to define their own address sharing
       ratio, the theoretical value is from 1:1 to 1:65536 and a more
       practical value is from 1:1 to 1:4096.

   5.  It supports differentiated port ranges per mapping rule.

   6.  It support exclusion of the well-known ports.

   7.  It supports assigning the well-known ports to a CE.

   8.  It supports legacy RTP/RTCP compatibility.

4.2.  Basic mapping rule (BMR)




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


                       Figure 4: IPv6 address format

   The Embedded Address bits (EA bits) are unique per end user within a
   Domain IPv6 prefix.  The Domain 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.  There MUST be a Basic Mapping
   Rule with a Rule IPv6 prefix equal to the Domain IPv6 prefix.  The EA
   bits encode the CE specific IPv4 address and port information.  The



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   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 ~0 and the interface-id as specified in
   the Interface-id section.

                           Shared IPv4 address:


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


                                 Figure 5

                          Complete IPv4 address:


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


                                 Figure 6

                               IPv4 prefix:


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

                                 Figure 7

   If only a part of the IPv4 address/prefix is encoded in the EA bits,
   the Domain 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 from the EA bits, are concatenated with the
   Domain IPv4 prefix (r bits).



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   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 in the Rule EA-bits length parameter.

   If o + r < 32, then an IPv4 prefix is assigned.  The IPv4 prefix
   length is equal to r bits + Rule EA-bits length.

   If o + r is equal to 32, then a full IPv4 address is to be assigned.
   The address is created by concatenating the Domain 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 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.

   Example:

     Given:
      End-user IPv6 prefix: 2001:db8:0012:34::/56
      Domain IPv6 prefix:   2001:db8:00::/40
      IPv4 prefix:          192.0.2.0/24
      Basic Mapping Rule:   {2001:db8:00::/40, 192.0.2.0/24, 256, 6}

     We get IPv4 address and port set:
      EA bits offset:       40
      IPv4 suffix bits (p): 32 - 24 = 8
      IPv4 address:         192.0.2.18

      PSID start:           40 + p = 40 + 8 = 48
      PSID length:          o - p = log2(256) - 8 = 8.
      PSID:                 0x34.

4.3.  Forwarding mapping rule (FMR)

   On adding a FMR rule an IPv4 route is installed the conceptual
   routing table for the Rule IPv4 prefix.

   On forwarding an IPv4 packet a lookup is done in the routing table
   and the correct FMR is used.











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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      |
    +--------------------+-----------+---------+------------+----------+
    | Domain IPv6 prefix |  EA bits  |subnet ID|     interface ID      |
    +--------------------+-----------+---------+-----------------------+
    |<---  End-user IPv6 prefix  --->|


                                 Figure 8

   The subnet ID for MAP is defined to be ~0.  I.e. the last subnet in
   an End-user IPv6 prefix allocation is used for MAP.  A MAP node MUST
   reserve the topmost IPv6 prefix in a End-user IPv6 prefix for the
   purpose of MAP.  This prefix MUST NOT be used for native IPv6
   traffic.

   Example:

     Given:
      IPv4 destination address: 192.0.2.18
      IPv4 destination port:    1232
      Forwarding Mapping Rule:  {2001:db8:00::/40, 192.0.2.0/24,
                                 Sharing ratio: 256, PSID offset: 4}

     We get IPv6 address:
      IPv4 suffix bits (p): 32 - 24 = 8 (18)
      PSID length:          8 (sharing ratio)
      PSID:                 0x17 (1232)
      EA bits:              0x1217
      IPv6 address:         2001:db8:0012:17FF:<interface-identifier>

4.4.  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.




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   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.

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

   An example of a DMR is:

   Default Mapping Rule: {2001:db8:0001:0000:<interface-id>:/128,
   0.0.0.0/0, BR IPv4 address: 192.0.2.1, }

   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 routing table:


      0.0.0.0 -> 192.0.2.1, MAP-Interface0


5.  The IPv6 Interface Identifier

   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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                  <-8-><-------- L>=32 -------><48-L><8->
                  +---+----------------+------+-----+---+
                  | u |  IPv4 address  | PSID |  0  | L |
                  +---+----------------+------+-----+---+


                                 Figure 9

   The L field denotes the length of the IPv4 address, IPv4 prefix or
   shared IPv4 address.  In the case of an full IPv4 address L = 32, in
   case of an IPv4 prefix L < 32, in the case of an shared IPv4 address
   32 < L <= 48.

   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.


6.  IANA Considerations

   This specification does not require any IANA actions.


7.  Security Considerations

   There are no new security considerations pertaining to this document.


8.  Contributors

   The members of the MAP design team are:

      Congxiao Bao, Mohamed Boucadair, Gang Chen, Maoke Chen, Wojciech
      Dec, Xiaohong Deng, Jouni Korhonen, Xing Li, Satoru Matsushima,
      Tomasz Mrugalski, Tetsuya Murakami, Jacni Qin, Necj Scoberne,
      Qiong Sun, Tina Tsou, Dan Wing, Leaf Yeh and Jan Zorz.


9.  Acknowledgements

   The authors would like to thank Guillaume Gottard.


10.  References






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10.1.  Normative References

   [I-D.mdt-softwire-map-dhcp-option]
              Mrugalski, T., Boucadair, M., Troan, O., Deng, X., and C.
              Bao, "DHCPv6 Options for Mapping of Address and Port",
              draft-mdt-softwire-map-dhcp-option-01 (work in progress),
              October 2011.

   [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.

10.2.  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.

   [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.

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

   [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.




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   [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.

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


Author's Address

   Ole Troan (editor)
   cisco
   Oslo
   Norway

   Email: ot@cisco.com

























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