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Network Working Group                                           O. Troan
Internet-Draft                                                    W. Dec
Intended status: Standards Track                           Cisco Systems
Expires: December 29, 2012                                         X. Li
                                                                  C. Bao
                                                                 Y. Zhai
                                                  CERNET Center/Tsinghua
                                                              University
                                                           S. Matsushima
                                                        SoftBank Telecom
                                                             T. Murakami
                                                             IP Infusion
                                                           June 27, 2012


                   Mapping of Address and Port (MAP)
                       draft-ietf-softwire-map-01

Abstract

   This document describes a mechanism for transporting IPv4 packets
   across an IPv6 network, and a generic mechanism for mapping between
   IPv6 addresses and IPv4 addresses and transport layer ports.

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 December 29, 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



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   (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
   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.












































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Architecture . . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Mapping Algorithm  . . . . . . . . . . . . . . . . . . . . . .  8
     5.1.  Port mapping algorithm . . . . . . . . . . . . . . . . . . 10
       5.1.1.  Bit Representation of the Algorithm  . . . . . . . . . 11
       5.1.2.  GMA examples . . . . . . . . . . . . . . . . . . . . . 11
       5.1.3.  Algorithm Provisioning Considerations  . . . . . . . . 12
     5.2.  Basic mapping rule (BMR) . . . . . . . . . . . . . . . . . 12
     5.3.  Forwarding mapping rule (FMR)  . . . . . . . . . . . . . . 15
     5.4.  Default mapping rule (DMR) . . . . . . . . . . . . . . . . 16
   6.  The IPv6 Interface Identifier  . . . . . . . . . . . . . . . . 17
   7.  MAP Configuration  . . . . . . . . . . . . . . . . . . . . . . 18
     7.1.  MAP CE . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     7.2.  MAP BR . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     7.3.  Backwards compatibility  . . . . . . . . . . . . . . . . . 19
   8.  Forwarding Considerations  . . . . . . . . . . . . . . . . . . 19
     8.1.  Receiving rules  . . . . . . . . . . . . . . . . . . . . . 20
     8.2.  MAP BR . . . . . . . . . . . . . . . . . . . . . . . . . . 20
       8.2.1.  IPv6 to IPv4 . . . . . . . . . . . . . . . . . . . . . 20
       8.2.2.  IPv4 to IPv6 . . . . . . . . . . . . . . . . . . . . . 20
   9.  ICMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     9.1.  Translating ICMP/ICMPv6 Headers  . . . . . . . . . . . . . 21
   10. Fragmentation and Path MTU Discovery . . . . . . . . . . . . . 22
     10.1. Fragmentation in the MAP domain  . . . . . . . . . . . . . 22
     10.2. Receiving IPv4 Fragments on the MAP domain borders . . . . 23
     10.3. Sending IPv4 fragments to the outside  . . . . . . . . . . 23
   11. NAT44 Considerations . . . . . . . . . . . . . . . . . . . . . 23
   12. Deployment Considerations  . . . . . . . . . . . . . . . . . . 23
     12.1. Use cases  . . . . . . . . . . . . . . . . . . . . . . . . 23
       12.1.1. Mesh Model . . . . . . . . . . . . . . . . . . . . . . 23
       12.1.2. Hub & Spoke Model  . . . . . . . . . . . . . . . . . . 24
       12.1.3. Communication with IPv6 servers in the MAP-T domain  . 24
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 24
   14. Security Considerations  . . . . . . . . . . . . . . . . . . . 24
   15. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 25
   16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26
   17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     17.1. Normative References . . . . . . . . . . . . . . . . . . . 26
     17.2. Informative References . . . . . . . . . . . . . . . . . . 27
   Appendix A.  Example of MAP-T translation  . . . . . . . . . . . . 30
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32






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1.  Introduction

   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 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
      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 generic mapping of IPv4 to
   IPv6, and mechanisms for encapsulation (IPv4 over IPv6) and
   translation between the two protocols that use this mapping.

   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



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   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 the 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].  Other means of provisioning is
   possible.  Deployment considerations are described in [I-D.mdt-
   softwire-map-deployment].

   MAP relies on IPv6 and is designed to deliver production-quality
   dual-stack service while allowing IPv4 to be phased out within the SP
   network.  The phasing out of IPv4 within the SP network is
   independent of whether the end user disables IPv4 service or not.
   Further, "Greenfield"; IPv6-only networks may use MAP in order to
   deliver IPv4 to sites via the IPv6 network.


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

   MAP domain:             One or more MAP CEs and BRs connected to the
                           same virtual link.  A service provider may
                           deploy a single MAP domain, or may utilize
                           multiple MAP domains.

   MAP Rule                A set of parameters describing the mapping
                           between an IPv4 prefix, IPv4 address or
                           shared IPv4 address and an IPv6 prefix or
                           address.  Each domain uses a different
                           mapping rule set.

   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



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                           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.

   MAP IPv6 address:       The IPv6 address used to reach the MAP
                           function of a CE from other CEs and from BRs.

   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.

   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 data
                           structure, supporting longest match lookups.
                           The MRT is used by the MAP forwarding
                           function.



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   MAP-T:                  Mapping of Address and Port - Translation
                           mode.  MAP-T utilizes IPv4/IPv6 translation
                           as per [RFC6145].

   MAP-E:                  Mapping of Address and Port - Encapsulation
                           mode.  MAP-E utilizes a simple IPv4-in-IPv6
                           tunneling [RFC2473].


4.  Architecture

   The MAP mechanism is largely built up using existing standard
   building blocks.  The existing NAT44 on the CE is used with
   additional support for restricting transport protocol ports, ICMP
   identifiers and fragment identifiers to the configured port set.  MAP
   supports two forwarding modes, one using stateless NAT64 as specified
   in [RFC6145] and one encapsulation mode specified in [RFC2473].  In
   addition MAP specifies an algorithm to do "address resolution" from
   an IPv4 address and port to an IPv6 address.  This algorithmic
   mapping is specified in section 5.

   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.

   When MAP is used to provision a full IPv4 address or an IPv4 prefix
   to the CE, these restrictions do not apply.

   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 Mapping Rule Table (MRT) to make
   forwarding decisions.  The table consist of the mapping rules.  An
   entry in the table consists of an IPv4 prefix and PSID.  The normal
   best matching prefix algorithm is used.  With a maximum key length of
   48 (Length of IPv4 address (32) + Length of Transport layer port
   field (16)).  E.g. with a sharing ratio of 64 (6 bit PSID length) a
   "host route" for this CE would be a /38 (32 + 6).



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         User N
       Private IPv4
      |  Network
      |
   O--+---------------O
   |  |  MAP CE       |
   | +-----+--------+ |
   | NAPT44|  MAP   | |
   | +-----+      | | |\     ,-------.                     .------.
   |       +--------+ | \ ,-'         `-.                ,-'       `-.
   O------------------O  /              \   O---------O /   Public   \
                         /   IPv6 only   \  |  MAP    |/     IPv4     \
                        (    Network      --+  Border +-   Network     )
                         \  (MAP Domain) /  |  Relay  |\              /
   O------------------O  \              /   O---------O \             /
   |    MAP   CE      |  /".         ,-'                `-.       ,-'
   | +-----+--------+ | /   `----+--'                      ------'
   | NAPT44|  MAP   | |/
   | +-----+        | |
   |   |   +--------+ |
   O---.--------------O
       |
         User M
       Private IPv4
         Network


                        Figure 1: Network Topology

   The MAP BR is responsible for connecting external IPv4 networks to
   all devices in one or more MAP domains.

   The translation mode allows communication between both IPv4-only and
   any IPv6 enabled end hosts, with native IPv6-only servers which are
   using IPv4-mapped IPv6 address based on DMR in the MAP-T domain.  In
   this mode, the IPv6-only servers SHOULD have both A and AAAA records
   in the authorities DNS server [RFC6219].  DNS64 [RFC6147] become
   required only when IPv6 servers in the MAP-T domain are expected
   themselves to initiate communication to external IPv4-only hosts.


5.  Mapping Algorithm

   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 its IPv4 address, IPv4 prefix or



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   shared IPv4 address.  This same basic rule can also be used for
   forwarding, where an IPv4 destination address and optionally a
   destination port is mapped into an IPv6 address or prefix.
   Additional mapping rules are specified to allow for e.g. multiple
   different IPv4 subnets to exist within the domain and optimize
   forwarding between them.

   Traffic outside of the domain (i.e. when the destination IPv4 address
   does not match (using longest matching prefix) any Rule IPv4 prefix
   in the Rules database) will be forward using the Default mapping
   rule.  The Default mapping rule maps outside destinations to the BR's
   IPv6 address or prefix.

   Note: The forwarding mode is intended to apply uniformly for rules in
   a domain - subject to further WG feedback in this area.

   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)

       *  Forwarding mode

   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.
       The FMR consists of the same parameters as the BMR.

   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.

       *  IPv6 prefix of address of BR

       *  Forwarding mode

   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,



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   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

   The port mapping algorithm is used in domains whose rules allow IPv4
   address sharing.  Different Port-Set Identifiers (PSID) MUST have
   non-overlapping port-sets.  The two extreme cases are: (1) the port
   numbers are not contiguous for each PSID, but uniformly distributed
   across the port range (0-65535); (2) the port numbers are contiguous
   in a single range for each PSID.  The port mapping algorithm proposed
   here is called the Generalized Modulus Algorithm (GMA) and supports
   both these cases.

   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.

       *  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:





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       *  % 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 2: 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

   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)




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   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.  Algorithm 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 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)




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


                       Figure 3: 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



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   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.

   The MAP IPv6 is created by combining the End-User IPv6 prefix with
   the all zeros subnet-id and the MAP IPv6 interface identifier.

                           Shared IPv4 address:


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


                       Figure 4: Shared IPv4 address

                          Complete IPv4 address:


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


                      Figure 5: Complete IPv4 address













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                               IPv4 prefix:


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

                           Figure 6: 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 (default value as per section 5.1.3)

     We get IPv4 address and port-set:
      EA bits offset:       40
      IPv4 suffix bits (p): Length of IPv4 address (32) -
                            IPv4 prefix length (24) = 8
      IPv4 address:         192.0.2.18 (0x12)

      PSID start:           40 + p = 40 + 8 = 48
      PSID length:          o - p = 16 (56 - 40) - 8 = 8
      PSID:                 0x34
      Port-set-1:        4928, 4929, 4930, 4931, 4932, 4933, 4934, 4935,
                         4936, 4937, 4938, 4939, 4940, 4941, 4942, 4943
      Port-set-2:        9024, 9025, 9026, 9027, 9028, 9029, 9030, 9031,
                         9032, 9033, 9034, 9035, 9036, 9037, 9038, 9039
      ...
      Port-set-15:          62272, 62273, 62274, 62275,
                            62276, 62277, 62278, 62279,
                            62280, 62281, 62282, 62283,
                            62284, 62285, 62286, 62287,

5.3.  Forwarding mapping rule (FMR)

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

   On forwarding an IPv4 packet, a best matching prefix lookup is done
   in the MRT 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   | s bits  |   128-n-o-s bits      |
   +--------------------+-----------+---------+------------+----------+
   |  Rule IPv6 prefix  |  EA bits  |subnet ID|     interface ID      |
   +--------------------+-----------+---------+-----------------------+
   |<---  End-user IPv6 prefix  --->|


                  Figure 7: 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 (default value as per section 5.1.3)

     We get IPv6 address:
      IPv4 suffix bits (p): 32 - 24 = 8 (18 (0x12))
      PSID length:          8
      PSID:                 0x34 (9030 (0x2346))
      EA bits:              0x1234
      MAP IPv6 address:     2001:db8:0012:3400:00c0:0002:1200:3400

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 DMR consist of the IPv6 address or IPv6 prefix of the BR.  Which
   is used, is dependent on the forwarding mode used.  Translation mode
   requires that the IPv4 destination address is encoded in the BR IPv6
   address, so only a prefix is used in the DMR to allow for a generated



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   interface identifier.  For the encapsulation mode the complete IPv6
   address of the BR is used.


6.  The IPv6 Interface Identifier

   The Interface identifier format of a MAP node is based on the format
   specified in section 2.2 of [RFC6052], with the added PSID field if
   present, as shown in figure Figure 8.



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


                                 Figure 8

   For traffic destined outside of a MAP domain (i.e. for traffic
   following the default mapping rule), the destination IPv4 address is
   mapped to the IPv6 address or prefix of the BR.  For MAP-E this is
   the IPv6 tunnel end point address of the BR, while for MAP-T this is
   the IPv6 converted representation of the IPv6 address per RFC6052,
   shown in the form of an example in figure Figure 9 below.  Note that
   the BR prefix-length is variable and can be both shorter or longer
   than 64 bits, up to 96 bits.


   <---------- 64 ------------>< 8 ><----- 32 -----><--- 24 --->
   +--------------------------+----+---------------+-----------+
   |        BR prefix         | u  | IPv4 address  |     0     |
   +--------------------------+----+---------------+-----------+


                                 Figure 9

   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.

   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.




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   If the End-user IPv6 prefix length is larger than 64, the most
   significant parts of the interface identifier is overwritten by the
   prefix.


7.  MAP Configuration

   For a given MAP domain, the BR and CE MUST be configured with the
   following MAP elements.  The configured values for these elements are
   identical for all CEs and BRs within a given MAP domain.

   o  The End-User IPv6 prefix (Part of the normal IPv6 provisioning).

   o  The Basic Mapping Rule and optionally the Forwarding Mapping
      Rules, including the Rule IPv6 prefix, Rule IPv4 prefix, Length of
      EA bits, and Forwarding mode

   o  The Default Mapping Rule with the BR IPv6 prefix or address

   o  The domain's MAP-E or MAP-T forwarding mode.

7.1.  MAP CE

   The MAP elements are set to values that are the same across all CEs
   within a MAP domain.  The values may be configured in a variety of
   manners, including provisioning methods such as the Broadband Forum's
   "TR-69" Residential Gateway management interface, an XML-based object
   retrieved after IPv6 connectivity is established, or manual
   configuration by an administrator.  This document describes how to
   configure the necessary parameters via a single DHCPv6 option.  A CE
   that allows IPv6 configuration by DHCP SHOULD implement this option.
   Other configuration and management methods may use the format
   described by this option for consistency and convenience of
   implementation on CEs that support multiple configuration methods.

   The only remaining provisioning information the CE requires in order
   to calculate the MAP IPv4 address and enable IPv4 connectivity is the
   IPv6 prefix for the CE.  The End-user IPv6 prefix is configured as
   part of obtaining IPv6 Internet access.

   A single MAP CE MAY be connected to more than one MAP domain, just as
   any router may have more than one IPv4-enabled service provider
   facing interface and more than one set of associated addresses
   assigned by DHCP.  Each domain a given CE operates within would
   require its own set of MAP configuration elements and would generate
   its own IPv4 address.

   The MAP DHCP option is specified in



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   [I-D.mdt-softwire-map-dhcp-option].

7.2.  MAP BR

   The MAP BR MUST be configured with the same MAP elements as the MAP
   CEs operating within the same domain.

   For increased reliability and load balancing, the BR IPv6 address may
   be an anycast address shared across a given MAP domain.  As MAP is
   stateless, any BR may be used at any time.  If the BR IPv6 address is
   anycast the relay MUST use this anycast IPv6 address as the source
   address in packets relayed to CEs.

   Since MAP uses provider address space, no specific routes need to be
   advertised externally for MAP to operate, neither in IPv6 nor IPv4
   BGP.  However, if anycast is used for the MAP IPv6 relays, the
   anycast addresses must be advertised in the service provider's IGP.

7.3.  Backwards compatibility

   A MAP-E CE provisioned with only a Default Mapping Rule makes a MAP-E
   CE compatible for use with DS-Lite [RFC6333] AFTRs, whose addresses
   are configured as the MAP BR.

   A MAP-T CE, in all configuration modes, is by default compatible with
   stateful NAT64 gateways, whose prefixes are passed as the BR
   prefixes.  Furthermore, when a MAP-T CE configured to operate without
   address sharing (no PSID), is compatible with stateless NAT64
   elements acting as BRs.


8.  Forwarding Considerations

   Figure 1 depicts the overall MAP architecture with IPv4 users (N and
   M) networks connected to a routed IPv6 network.

   MAP supports two forwarding modes.  Translation mode as specified in
   [RFC6145] and Encapsulation mode as specified in [RFC2473].

   A MAP CE forwarding IPv4 packets from the LAN SHOULD perform NAT44
   functions first and create appropriate NAT44 bindings.  The resulting
   IPv4 packets MUST contain the source IPv4 address and source
   transport number defined by MAP.  The resulting IPv4 packet is
   forwarded to the CE's MAP forwarding function.  The IPv6 source and
   destination addresses MUST then be derived as per Section 5 of this
   draft.

   A MAP CE receiving an IPv6 packet to its MAP IPv6 address are



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   forwarded to the CE's MAP function.  All other IPv6 traffic is
   forwarded as per the CE's IPv6 routing rules.  In other cases, the
   MAP-T function MUST derive the IPv4 source and destination addresses
   as per Section 6 of this draft and MUST replace the IPv6 header with
   an IPv4 header in accordance with [RFC6145].  The resulting IPv4
   packet is then forwarded to the CE's NAT44 function where the
   destination port number MUST be checked against the stateful port
   mapping session table and the destination port number MUST be mapped
   to its original value.

8.1.  Receiving rules

   The CE SHOULD check that MAP received packets' transport-layer
   destination port number is in the range configured by MAP for the CE
   and the CE SHOULD drop any non conforming packet and respond with an
   ICMPv6 "Address Unreachable" (Type 1, Code 3).

8.2.  MAP BR

8.2.1.  IPv6 to IPv4

   A MAP BR receiving IPv6 packets selects a best matching MAP domain
   rule based on a longest address match of the packets' source address
   against the BR's configured MAP BMR prefix(es), as well as a match of
   the packet destination address against the configured BR prefixes or
   FMR prefix(es).  The selected MAP rule allows the BR to determine the
   EA-bits from the source IPv6 address.  The BR MUST perform a
   validation of the consistency of the source IPv6 address and source
   port number for the packet using BMR.  If the packets source port
   number is found to be outside the range allowed for this CE and the
   BMR, the BR MUST drop the packet and respond with an ICMPv6
   "Destination Unreachable, Source address failed ingress/egress
   policy" (Type 1, Code 5).

   For packets that are to be forwarded outside of a MAP domain, the BR
   MUST derive the source and destination IPv4 addresses as per Section
   7 of this draft and translate the IPv6 to IPv4 headers following
   [RFC6145].  The resulting IPv4 packets are then passed to regular
   IPv4 forwarding.

8.2.2.  IPv4 to IPv6

   A MAP BR receiving IPv4 packets uses a longest match IPv4 lookup to
   select the target MAP domain and rule.  The BR MUST then derive the
   IPv6 source and destination addresses from the IPv4 source and
   destination address and port as per Section 7 of this draft.
   Following this, the BR MUST translate the IPv4 to IPv6 headers
   following [RFC6145].  The resulting IPv6 packets are then passed to



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   regular IPv6 forwarding.

   Note that the operation of a BR when forwarding to MAP domains that
   do not utilize IPv4 address sharing, is the same as stateless IPv4/
   IPv6 translation.


9.  ICMP

   ICMP message should be supported in MAP domain.  Hence, the NAT44 in
   MAP CE must implement the behavior for ICMP message conforming to the
   best current practice documented in [RFC5508].

   If a MAP CE receives an ICMP message having ICMP identifier field in
   ICMP header, NAT44 in the MAP CE must rewrite this field to a
   specific value assigned from the port-set.  BR and other CEs must
   handle this field similar to the port number in the TCP/UDP header
   upon receiving the ICMP message with ICMP identifier field.

   If a MAP node receives an ICMP error message without the ICMP
   identifier field for some errors that is detected inside a IPv6
   tunnel, a MAP BR and CE should replay the ICMP error message to the
   original source.  This behavior should be implemented conforming to
   the section 8 of [RFC2473].  The MAP-E BR and CE obtain the original
   IPv6 tunnel packet storing in ICMP payload and then decapsulate IPv4
   packet.  Finally the MAP-E BR and CE generate a new ICMP error
   message from the decapsulated IPv4 packet and then forward it.

9.1.  Translating ICMP/ICMPv6 Headers

   MAP-T CEs and BRs MUST follow ICMP/ICMPv6 translation as per
   [RFC6145], with the following extension to cover the address sharing/
   port-range feature.

   Unlike TCP and UDP, which each provide two port fields to represent
   both source and destination, the ICMP/ICMPv6 Query message header has
   only one ID field [RFC0792], [RFC4443].  Thus, if the ICMP Query
   message is originated from an IPv4 host behind a MAP-T CE, the ICMP
   ID field SHOULD be used to exclusively identify that IPv4 host.  This
   means that the MAP-T CE SHOULD rewrite the ID field to a port-set
   value obtained via the BMR during the IPv4 to IPv6 ICMPv6 translation
   operation.  A BR can translate the resulting ICMPv6 packets back to
   ICMP preserving the ID field on its way to an IPv4 destination.  In
   the return path, when MAP-T BR receives an ICMP packet containing an
   ID field which is bound for a shared address in the MAP-T domain, the
   MAP-T BR SHOULD use the ID value as a substitute for the destination
   port in determining the IPv6 destination address according to Section
   5.1.  In all other cases, the MAP-T BR MUST derive the destination



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   IPv6 address by simply mapping the destination IPv4 address without
   additional port info.

   If a MAP BR receives an ICMP error message on its IPv4 interface, the
   MAP BR should replay the ICMP message to an appropriate MAP CE.  If
   IPv4 address is not shared, the MAP BR generates a CE IPv6 address
   from the IPv4 destination address in the ICMP error message and
   encapsulates the ICMP message in IPv6.  If IPv4 address is shared,
   the MAP BR derives an original IPv4 packet from the ICMP payload and
   generates a CE IPv6 address from the source address and the source
   port in the original IPv4 packet.  If the MAP BR can generate the CE
   IPv6 address, the MAP BR encapsulates the ICMP error message in IPv6
   and then forward it to its IPv6 interface.


10.  Fragmentation and Path MTU Discovery

   Due to the different sizes of the IPv4 and IPv6 header, handling the
   maximum packet size is relevant for the operation of any system
   connecting the two address families.  There are three mechanisms to
   handle this issue: Path MTU discovery (PMTUD), fragmentation, and
   transport-layer negotiation such as the TCP Maximum Segment Size
   (MSS) option [RFC0897].  MAP uses all three mechanisms to deal with
   different cases.

10.1.  Fragmentation in the MAP domain

   Encapsulating or translating an IPv4 packet to carry it across the
   MAP domain will increase its size (40 bytes and 20 bytes
   respectively).  It is strongly recommended that the MTU in the MAP
   domain is well managed and that the IPv6 MTU on the CE WAN side
   interface is set so that no fragmentation occurs within the boundary
   of the MAP domain.

   Fragmentation on MAP domain entry is described for encapsulation in
   section 7.2 of [RFC2473] and in section 4 and 5 of of [RFC6145] for
   translation mode.

   The use of an anycast source address could lead to any ICMP error
   message generated on the path being sent to a different BR.
   Therefore, using dynamic tunnel MTU Section 6.7 of [RFC2473] is
   subject to IPv6 Path MTU blackholes.

   Multiple BRs using the same anycast source address could send
   fragmented packets to the same CE at the same time.  If the
   fragmented packets from different BRs happen to use the same fragment
   ID, incorrect reassembly might occur.




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10.2.  Receiving IPv4 Fragments on the MAP domain borders

   Forwarding of an IPv4 packet received from the outside of the MAP
   domain requires the IPv4 destination address and the transport
   protocol destination port.  The transport protocol information is
   only available in the first fragment received.  As described in
   section 5.3.3 of [RFC6346] a MAP node receiving an IPv4 fragmented
   packet from outside has to reassemble the packet before sending the
   packet onto the MAP link.  If the first packet received contains the
   transport protocol information, it is possible to optimize this
   behaviour by using a cache and forwarding the fragments unchanged.  A
   description of this algorithm is outside the scope of this document.

10.3.  Sending IPv4 fragments to the outside

   If two IPv4 host behind two different MAP CE's with the same IPv4
   address sends fragments to an IPv4 destination host outside the
   domain.  Those hosts may use the same IPv4 fragmentation identifier,
   resulting in incorrect reassembly of the fragments at the destination
   host.  Given that the IPv4 fragmentation identifier is a 16 bit
   field, it could be used similarly to port ranges.  A MAP CE SHOULD
   rewrite the IPv4 fragmentation identifier to be within its allocated
   port set.


11.  NAT44 Considerations

   The NAT44 implemented in the MAP CE SHOULD conform with the behavior
   and best current practice documented in [RFC4787], [RFC5508],
   [RFC5382] and [RFC5383].  In MAP address sharing mode (determined by
   the MAP domain/rule configuration parameters) the operation of the
   NAT44 MUST be restricted to the available port numbers derived via
   the basic mapping rule.


12.  Deployment Considerations

12.1.  Use cases

   Editorial Note: Carried over from Use-cases/forwarding considerations
   in previous drafts.

12.1.1.  Mesh Model

   MAP allows the mesh model in order for all CEs to communicate each
   others directly.  If one mapping rules is applied to a given MAP
   domain, all CEs can communicate each others directly.  If multiple
   mapping rules are applied to a given MAP domain, or if multiple MAP



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   domains exist, CE can communicate with each other directly when the
   CEs know the respective mapping rules.  When a CE receives an IPv4
   packet from its LAN side, the CE looks up a mapping rule
   corresponding to an IPv4 destination address in the received IPv4
   packet.  If the corresponding mapping rule is found, CE can
   communicate to another CE directly based on the Forwarding mapping
   rule (FMR).  If the corresponding mapping rule is not found, CE must
   forward the packet to a given BR using the Default Mapping rule
   (DMR).

12.1.2.  Hub & Spoke Model

   In order to achieve the hub & spoke mode fully, Forwarding mapping
   rule (FMR) should be disabled.  In this case, all CEs do not look up
   the mapping rules upon receiving an IPv4 packet from its LAN side and
   then CE must encapsulate the IPv4 packet with IPv6 whose destination
   must be a given BR using the Default Mapping Rule (DMR).

12.1.3.  Communication with IPv6 servers in the MAP-T domain

   MAP-T allows communication between both IPv4-only and any IPv6
   enabled end hosts, with native IPv6-only servers which are using
   IPv4-mapped IPv6 address based on DMR in the MAP-T domain.  In this
   mode, the IPv6-only servers SHOULD have both A and AAAA records in
   DNS [RFC6219].  DNS64 [RFC6147] become required only when IPv6
   servers in the MAP-T domain are expected themselves to initiate
   communication to external IPv4-only hosts.


13.  IANA Considerations

   This specification does not require any IANA actions.


14.  Security Considerations

   Spoofing attacks:  With consistency checks between IPv4 and IPv6
      sources that are performed on IPv4/IPv6 packets received by MAP
      nodes, MAP does not introduce any new opportunity for spoofing
      attacks that would not already exist in IPv6.

   Denial-of-service attacks:  In MAP domains where IPv4 addresses are
      shared, the fact that IPv4 datagram reassembly may be necessary
      introduces an opportunity for DOS attacks.  This is inherent to
      address sharing, and is common with other address sharing
      approaches such as DS-Lite and NAT64/DNS64.  The best protection
      against such attacks is to accelerate IPv6 enablement in both
      clients and servers so that, where MAP is supported, it is less



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      and less used.

   Routing-loop attacks:  This attack may exist in some automatic
      tunneling scenarios are documented in [RFC6324].  They cannot
      exist with MAP because each BRs checks that the IPv6 source
      address of a received IPv6 packet is a CE address based on
      Forwarding Mapping Rule.

   Attacks facilitated by restricted port set:  From hosts that are not
      subject to ingress filtering of [RFC2827], some attacks are
      possible by an attacker injecting spoofed packets during ongoing
      transport connections ([RFC4953], [RFC5961], [RFC6056].  The
      attacks depend on guessing which ports are currently used by
      target hosts, and using an unrestricted port set is preferable,
      i.e. using native IPv6 connections that are not subject to MAP
      port range restrictions.  To minimize this type of attacks when
      using a restricted port set, the MAP CE's NAT44 filtering behavior
      SHOULD be "Address-Dependent Filtering".  Furthermore, the MAP CEs
      SHOULD use a DNS transport proxy function to handle DNS traffic,
      and source such traffic from IPv6 interfaces not assigned to
      MAP-T.  Practicalities of these methods are discussed in Section
      5.9 of [I-D.dec-stateless-4v6].

   [RFC6269] outlines general issues with IPv4 address sharing.


15.  Contributors

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

   This document is the result of the IETF Softwire MAP design team
   effort and numerous previous individual contributions in this area
   initiated by dIVI [I-D.xli-behave-divi] along with a similar idea
   proposed by [I-D.murakami-softwire-4v6-translation].  The following
   are the authors who contributed in a major way to this document:

      Chongfeng Xie (China Telecom)

      Room 708, No.118, Xizhimennei Street Beijing 100035 CN

      Phone: +86-10-58552116

      Email: xiechf@ctbri.com.cn

      Qiong Sun (China Telecom)




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      Room 708, No.118, Xizhimennei Street Beijing 100035 CN

      Phone: +86-10-58552936

      Email: sunqiong@ctbri.com.cn

      Gang Chen (China Mobile)

      53A,Xibianmennei Ave. Beijing 100053 P.R.China

      Email: chengang@chinamobile.com

      Wentao Shang (CERNET Center/Tsinghua University)

      Room 225, Main Building, Tsinghua University Beijing 100084 CN

      Email: wentaoshang@gmail.com

      Guoliang Han (CERNET Center/Tsinghua University)

      Room 225, Main Building, Tsinghua University Beijing 100084 CN

      Email: bupthgl@gmail.com

      Rajiv Asati (Cisco Systems)

      7025-6 Kit Creek Road Research Triangle Park NC 27709 USA

      Email: rajiva@cisco.com


16.  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
   Zorz, Necj Scoberne, Tina Tsou for their thorough review and
   comments.


17.  References

17.1.  Normative References

   [I-D.mdt-softwire-map-dhcp-option]
              Mrugalski, T., Boucadair, M., Deng, X., Troan, O., and C.



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              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.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.

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

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, April 2011.

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

17.2.  Informative References

   [I-D.dec-stateless-4v6]
              Dec, W., Asati, R., and H. Deng, "Stateless 4Via6 Address
              Sharing", draft-dec-stateless-4v6-04 (work in progress),
              October 2011.

   [I-D.ietf-softwire-stateless-4v6-motivation]
              Boucadair, M., Matsushima, S., Lee, Y., Bonness, O.,
              Borges, I., and G. Chen, "Motivations for Carrier-side
              Stateless IPv4 over IPv6 Migration Solutions",
              draft-ietf-softwire-stateless-4v6-motivation-03 (work in
              progress), June 2012.

   [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.

   [I-D.murakami-softwire-4v6-translation]
              Murakami, T., Chen, G., Deng, H., Dec, W., and S.
              Matsushima, "4via6 Stateless Translation",
              draft-murakami-softwire-4v6-translation-00 (work in
              progress), July 2011.




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   [I-D.xli-behave-divi]
              Shang, W., Li, X., Zhai, Y., and C. Bao, "dIVI: Dual-
              Stateless IPv4/IPv6 Translation", draft-xli-behave-divi-04
              (work in progress), October 2011.

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, September 1981.

   [RFC0897]  Postel, J., "Domain name system implementation schedule",
              RFC 897, February 1984.

   [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.

   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, May 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.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC4787]  Audet, F. and C. Jennings, "Network Address Translation
              (NAT) Behavioral Requirements for Unicast UDP", BCP 127,
              RFC 4787, January 2007.

   [RFC4953]  Touch, J., "Defending TCP Against Spoofing Attacks",
              RFC 4953, July 2007.

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

   [RFC5382]  Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.



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              Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
              RFC 5382, October 2008.

   [RFC5383]  Gellens, R., "Deployment Considerations for Lemonade-
              Compliant Mobile Email", BCP 143, RFC 5383, October 2008.

   [RFC5508]  Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
              Behavioral Requirements for ICMP", BCP 148, RFC 5508,
              April 2009.

   [RFC5961]  Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
              Robustness to Blind In-Window Attacks", RFC 5961,
              August 2010.

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

   [RFC6056]  Larsen, M. and F. Gont, "Recommendations for Transport-
              Protocol Port Randomization", BCP 156, RFC 6056,
              January 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.

   [RFC6219]  Li, X., Bao, C., Chen, M., Zhang, H., and J. Wu, "The
              China Education and Research Network (CERNET) IVI
              Translation Design and Deployment for the IPv4/IPv6
              Coexistence and Transition", RFC 6219, May 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.

   [RFC6324]  Nakibly, G. and F. Templin, "Routing Loop Attack Using
              IPv6 Automatic Tunnels: Problem Statement and Proposed
              Mitigations", RFC 6324, August 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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Appendix A.  Example of MAP-T translation

   Example 1:


      Given the MAP domain information and an IPv6 address of
      an endpoint:

      IPv6 prefix assigned to the end user:  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

      A MAP node (CE or BR) can via the BMR determine the IPv4 address
      and port-set as shown below:

      EA bits offset:  40
      IPv4 suffix bits (p)  Length of IPv4 address (32) - IPv4 prefix
         length (24) = 8
      IPv4 address  192.0.2.18 (0xc0000212)
      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

      The BMR information allows a MAP CE also to determine (complete)
      its IPv6 address within the indicated IPv6 prefix.

      IPv6 address of MAP-T CE:  2001:db8:0012:3400:00c0:0002:1200:3400














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   Example 2:


      Another example can be made of a hypothetical MAP-T BR,
      configured with the following FMR when receiving a packet
      with the following characteristics:

      IPv4 source address:  1.2.3.4 (0x01020304)
      IPv4 source port:  80
      IPv4 destination address:  192.0.2.18 (0xc0000212)
      IPv4 destination port:  9030

      Configured Forwarding Mapping Rule:  {2001:db8:0000::/40
         (Rule IPv6 prefix), 192.0.2.0/24 (Rule IPv4 prefix),
         16 (Rule EA-bits length)}

      MAP-T BR Prefix  2001:db8:ffff::/64

      The above information allows the BR to derive as follows
      the mapped destination IPv6 address for the corresponding
      MAP-T CE, and also the mapped source IPv6 address for
      the IPv4 source.

      IPv4 suffix bits (p)  32 - 24 = 8 (18 (0x12))
      PSID length:  8
      PSID:  0x34 (9030 (0x2346))

      The resulting IPv6 packet will have the following key fields:

      IPv6 source address  2001:db8:ffff:0:0001:0203:0400::
      IPv6 destination address:  2001:db8:0012:3400:00c0:0002:1200:3400
      IPv6 source Port:  80
      IPv6 destination Port:  9030


















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   Example 3:


      An IPv4 host behind the MAP-T CE (addressed as per the previous
      examples) corresponding with IPv4 host 1.2.3.4 will have its
      packets converted into IPv6 using the DMR configured on the MAP-T
      CE as follows:

      Default Mapping Rule used by MAP-T CE:  {2001:db8:ffff::/64
      (Rule IPv6 prefix), 0.0.0.0/0 (Rule IPv4 prefix), null (BR IPv4
         address)}

      IPv4 source address (post NAT44 if present)  192.0.2.18
      IPv4 destination address:  1.2.3.4
      IPv4 source port (post NAT44 if present):  9030
      IPv4 destination port:  80
      IPv6 source address of MAP-T CE:
                           2001:db8:0012:3400:00c0:0002:1200:3400
      IPv6 destination address:  2001:db8:ffff:0:0001:0203:0400::



Authors' Addresses

   Ole Troan
   Cisco Systems
   Oslo
   Norway

   Email: ot@cisco.com


   Wojciech Dec
   Cisco Systems
   Haarlerbergpark Haarlerbergweg 13-19
   Amsterdam, NOORD-HOLLAND  1101 CH
   Netherlands

   Phone:
   Email: wdec@cisco.com











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   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


   Yu Zhai
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing 100084
   CN

   Email: jacky.zhai@gmail.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








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