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Versions: (draft-soliman-v4v6-mipv6) 00 01 02 03 04 05 06 draft-ietf-mext-nemo-v4traversal

MIP6 Working Group                                  Hesham Soliman (Ed.)
INTERNET-DRAFT                                           George Tsirtsis
Expires: December 2006                                          Qualcomm
                                                       Vijay Deverapalli
                                                         Azaire Networks
                                                             James Kempf
                                                             Docomo Labs
                                                        Henrik Levkowetz

                                                                Ericsson
                                                          Pascal Thubert
                                                                   Cisco
                                                          Ryuji Wakikawa

                                                         Keio University
                                                              June, 2006



                          Mobile IPv6 support for dual stack
                              Hosts and Routers (DSMIPv6)
                     draft-ietf-mip6-nemo-v4traversal-02.txt

Status of this memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
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   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 cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/lid-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This document is a submission of the IETF MIP6 WG. Comments should be
   directed to the MIP6 WG mailing list, mip6@ietf.org.


Abstract

   The current Mobile IPv6 and NEMO specification support only IPv6.



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   Hence, this specification extends those standards to allow the
   registration of IPv4 addresses and prefixes, respectively, and the
   transport of both IPv4 and IPv6 packets over the tunnel to the HA.
   This specification allows also the Mobile Node to roam over both IPv6
   and IPv4, including the case where Network Address Translation is
   present on the path.

   Table of Contents

  1. Introduction.....................................................2
  1.1 Motivation for using Mobile IPv6 only...........................3
     1.2 Scenarios considered by this specification...................4
  2. Solution overview................................................5
  2.1. Home Agent Address Discovery...................................5
     2.2. Mobile Prefix Solicitations and Advertisements..............6
  2.3. Binding management.............................................6
  2.3.1 Foreign network supports IPv6.................................7
  2.3.2 Foreign network supports IPv4 only............................8
  2.3.2.1 Visited network supports IPv4 only (private addresses)......9
  2.4. Route optimization.............................................9
  2.5. Dynamic IPv4 home address allocation..........................10
  3. Extensions and modifications to Mobile IPv6.....................10
  3.1. Binding update extensions.....................................10
  3.1.1 IPv4 home address option.....................................10
  3.2. Binding acknowledgement extensions............................11
  3.2.1 IPv4 address acknowledgement option..........................11
        3.2.2 The NAT detection option...............................12
  4. Protocol operation..............................................13
     4.1. NAT detection and traversal................................13
     4.2. NAT Keepalives.............................................15
  4.3. Mobile node operation.........................................15
        4.3.1 Sending packets from a visited network.................17
        4.3.2 Movement detection in IPv4-only networks...............17
  4.4. Home agent operations.........................................17
        4.4.1 Sending packets to the mobile node.....................19
  4.5. Correspondent node operations.................................20
  5. Security considerations.........................................20
  6. Protocol constants..............................................20
  7. Acknowledgements................................................20
  8. IANA considerations.............................................20
  9. References......................................................21
  Authors' Addresses.................................................21

1. Introduction

   Mobile IPv6 [MIPv6] and [NEMO] allow mobile nodes to move within the
   Internet while maintaining reachability and ongoing sessions, using
   an IPv6 home address or prefix. However, since IPv6 is not widely
   deployed, it is unlikely that mobile nodes will use IPv6 addresses
   only for their connections. It is reasonable to assume that mobile
   nodes will, for a long time, need an IPv4 home address that can be



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   used by upper layers. It is also reasonable to assume that mobile
   nodes will move to networks that might not support IPv6 and would
   therefore need the capability to support an IPv4 Care-of Address.
   Hence, this specification extends Mobile IPv6 capabilities to allow
   dual stack mobile nodes to request that their home agent (also dual
   stacked) tunnel IPv4/IPv6 packets addressed to their home addresses,
   to their IPv4/IPv6 care-of address(es).

   Using this specification, mobile nodes would only need Mobile IPv6
   and [NEMO] to manage mobility while moving within the Internet; hence
   eliminating the need to run two mobility management protocols
   simultaneously. This specification provides the extensions needed in
   order to allow Mobile IPv6 only to be used by dual sack mobile nodes.

   This specification will also consider cases where a mobile node moves
   into a private IPv4 network and gets configured with a private IPv4
   Care-of Address. In those scenarios, the mobile node needs to be able
   to traverse the IPv4 NAT in order to communicate with the Home Agent.
   IPv4 NAT traversal for Mobile IPv6 is presented in this
   specification.

   In this specification, the term mobile node refers to both a mobile
   host and mobile router unless the discussion is specific to either
   hosts or routers. Similarly, we use the term home address to reflect
   an address/prefix format.

   In this specification, extensions are defined for the binding update
   and binding acknowledgement. It should be noted that all these
   extensions apply to cases where the mobile node communicates with a
   Mobility Anchor Point (MAP) as defined in [HMIPv6]. The requirements
   on the MAP are identical to those stated for the home agent, although
   it is unlikely that NAT traversal would be needed with a MAP as it is
   expected to be in the same address domain.

1.1 Motivation for using Mobile IPv6 only

   IPv6 offers a number of improvements over today's IPv4, primarily due
   to its large address space. Mobile IPv6 offers a number of
   improvements over Mobile IPv4, mainly due to capabilities inherited
   from IPv6. For instance, route optimization and Dynamic home agent
   discovery can only be achieved with Mobile IPv6.

   One of the advantages of the large address space provided by IPv6 is
   that it allows mobile nodes to obtain a globally unique care-of
   address wherever they are. Hence, there is no need for Network
   Address Translator (NAT) traversal techniques designed for Mobile
   IPv4. This allows Mobile IPv6 to be a significantly simpler and more
   bandwidth efficient mobility management protocol. At the same time,
   during the transition towards IPv6, NAT traversal for existing
   private IPv4 networks needs to be considered. This specification
   introduces NAT traversal for this purpose.



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   The above benefits make the case for using Mobile IPv6 only for dual
   stack mobile nodes in order to allow for a long lasting mobility
   solution and minimize the need to changing the mobility stack due to
   the introduction of IPv6 within a deployed network.

1.2 Scenarios considered by this specification

   In [SNRIO] several scenarios that illustrate potential
   incompatibilities for mobile nodes using Mobile IPv6 were discussed.
   Some of the problems associated with mobility and transition issues
   were presented in [MIP-PB]. This specification considers a subset of
   the scenarios in [SNRIO], which address all the problems discussed in
   [MIP-PB]. The scenarios considered in this specification are listed
   below.

   All of the following scenarios assume that both the mobile node and
   the Home Agent are IPv4 and IPv6-enabled and that only Mobile IPv6 is
   used between the mobile node and the Home Agent. We also assume that
   the Home Agent is always reachable through a globally unique IPv4
   address. Finally, it's important to note that the following scenarios
   are not mutually exclusive.

   Scenario 1: IPv4-only foreign network

   In this scenario, a mobile node is connected to an IPv4-only foreign
   network. The mobile node can only configure an IPv4 Care-of Address.

   Scenario 2: Mobile node behind a NAT:

   In this scenario, the mobile node is in a private IPv4 foreign
   network that has a NAT device connecting it to the Internet. If the
   Home Agent is located outside the NAT device, the mobile node will
   need a NAT traversal mechanism to communicate with the Home Agent.

   Scenario 3: Home Agent behind a NAT:

   In this scenario, the communication between the mobile node and the
   Home Agent is further complicated by the fact that the Home Agent is
   located within a private IPv4 network. However, in this scenario, we
   assume that the Home Agent is allocated a globally unique IPv4
   address. Such address might not be physically configured on the Home
   Agent interface. Instead, it is associated with the Home Agent on the
   NAT device, which allows the Home Agent to be reachable through
   address or port mapping.

   Scenario 4: Use Of IPv4-only applications

   In this scenario, the mobile node may be located in an IPv4, IPv6 or
   a dual network. However, the mobile node might be communicating with
   an IPv4-only node. In this case, the mobile node would need a stable



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   IPv4 address for its application. The alternative to using an IPv4
   address is the use of protocol translators; however, end-to-end
   communication with IPv4 is preferred to the use of protocol
   translators.

   The mobile node may also be communicating with an IPv4-only
   application that requires an IPv4 address.

   The cases above illustrate the need for a stable IPv4 home address to
   be allocated to the mobile node. This is done using an IPv4 home
   address. Since running Mobile IPv4 and Mobile IPv6 simultaneously is
   problematic (as illustrated in [MIP-PB]), this scenario adds a
   requirement on Mobile IPv6 to support IPv4 home addresses.

2. Solution overview

   In order to allow Mobile IPv6 to be used by dual stack mobile nodes,
   the following needs to be done:

   - Mobile nodes should be able to use an IPv4 and IPv6 home or care-of
   address simultaneously and update their home agents accordingly.

   - Mobile nodes need to be able to know the IPv4 address of the home
   agent as well as its IPv6 address. There is no need for IPv4 prefix
   discovery however.

   - Mobile nodes need to be able to detect the presence of a NAT device
   and traverse such device in order to communicate with the Home Agent
   in a secure manner.

   This section presents an overview of the extensions required in order
   to allow mobile nodes to use Mobile IPv6 only for IP mobility
   management.

2.1. Home Agent Address Discovery

   Dynamic Home Agent Address Discovery (DHAAD) was defined in [MIPv6]
   to allow mobile nodes to discover their home agents by appending a
   well-known anycast interface identifier to their home link's prefix.
   However, this mechanism is based on IPv6-anycast routing. If a mobile
   node is located in an IPv4-only foreign network, it cannot rely on
   native IPv6 routing. The preferred solution for discovering the home
   agent's IPv4 address is through the Domain Name System (DNS).

   For DNS lookup by name, the mobile node should be configured with the
   name of the home agent.  When the mobile node needs to discover a
   home agent, it sends a DNS request with QNAME set to the configured
   name.  An example is "ha1.example.com".  If a home agent has an IPv4
   and IPv6 address, the corresponding DNS record should be configured
   with both 'AAAA' and 'A' records. Accordingly the DNS reply will
   contain 'AAAA' and 'A' records.



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   For DNS lookup by service, the SRV record defined in [BOOT] is
   reused.  For instance, if the service name is "_mip6ha" and the
   protocol name is "_ipv6" for the SRV record, the mobile node SHOULD
   send a DNS request with the QNAME set to "mip6ha.ipv6.example.com".
   The response should contain the home agent's FQDN(s) and may have the
   corresponding 'AAAA' and 'A' records enclosed as well.

   If multiple home agents reside on the home link, each configured with
   a public IPv4 addresses, then the operation above applies. In case
   the home agents are behind a NAT box, there are two options, 1)
   configure a public IPv4 address for each home agent on the NAT box,
   2) configure one public address and make the home agents share the
   public address.  In either case, the correct DNS entries can be
   configured.  Another possible solution is to designate one home agent
   on the home link for v4 traversal. The NAT device should associate
   that home agent with the public IPv4 address configured on it for v4
   traversal. In all cases above, both the 'AAAA' and 'A' records
   returned for a particular name MUST correspond to the same physical
   home agent; otherwise the mobile node will not be able to bind its
   addresses correctly.

2.2. Mobile Prefix Solicitations and Advertisements

   According to [MIPv6], the mobile node can send a Mobile Prefix
   Solicitation and receive a Mobile Prefix Advertisement containing all
   prefixes advertised on the home link.

   A dual stack mobile node MAY send a Mobile Prefix Solicitation
   message encapsulated in IPv4 (i.e. IPv6 in IPv4) in the case where
   the mobile node has no access to IPv6 within the local network.
   Securing such messages would require the mobile node to have security
   association with the home agent, using IPsec (AH or ESP) and based on
   the mobile node's IPv4 care-of address as described in [MIPv6]. Since
   the mobile node needs to encapsulate all IPv6 traffic sent to the
   home agent into IPv4 while located in an IPv4-only visited network,
   such SA would affect all packets if the selectors were based on the
   information in the outer header. That is, the SA selectors being the
   protocol number (protocol is always IP in IP), as well as, source and
   destination addresses are all common to all packets. If this effect
   is not desired, the mobile node can base the SA on the information in
   the inner header (i.e. using the home agent's IPv6 address, the
   mobile node's home address and the ICMP protocol number). Such
   security association would use transport mode ESP protection.

2.3. Binding management

   A dual stack mobile node will need to update its home agent with its
   care-of address. If a mobile node has an IPv4 and an IPv6 home
   address it will need to create a binding cache entry for each
   address. The format of the IP packet carrying the binding update and



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   acknowledgement messages will vary depending on whether the mobile
   node has access to IPv6 in the visited network. There are three
   different scenarios to consider with respect to the visited network:

   A. The visited network has IPv6 connectivity and provides the mobile
      node with a care-of address (in a stateful or stateless manner).

   B. The mobile node can only configure a globally unique IPv4 address
      in the visited network.
   C. The mobile node can only configure a private IPv4 address in the
      visited network.

2.3.1 Foreign network supports IPv6

   In this case, the mobile node is able to configure a globally unique
   IPv6 address. The mobile node will send a binding update to the IPv6
   address of its home agent, as defined in [MIPv6]. The binding update
   MAY include the IPv4 home address option introduced in this document.
   After receiving the binding update, the home agent creates two
   binding cache entries, one for the mobile node's IPv4 home address,
   and another for the mobile node's IPv6 home address. Both entries
   will point to the mobile node's IPv6 care-of address. Hence, whenever
   a packet is addressed to the mobile node's IPv4 or IPv6 home
   addresses, it will be tunneled in IPv6 to the mobile node's IPv6
   care-of address included in the binding update. Effectively, the
   mobile node establishes two different tunnels, one for its IPv4
   traffic (IPv4 in IPv6) and one for its IPv6 traffic (IPv6 in IPv6)
   with a single binding update. The security implications of this
   mechanism are discussed in the security considerations section.

   In this scenario, the only addition to [MIPv6] is the inclusion of
   the IPv4 home address option in the binding update message.

   After accepting the binding update and creating the corresponding
   binding cache entries, the home agent MUST send a binding
   acknowledgement to the mobile node as defined in [MIPv6]. In
   addition, if the binding update included an IPv4 home address option,
   the binding acknowledgement MUST include the IPv4 address
   acknowledgment option as described later in this specification. This
   option informs the mobile node whether the binding was accepted for
   the IPv4 home address. If this option is not included in the binding
   acknowledgement and the IPv4 home address option was included in the
   binding update, the mobile node MUST assume that the home agent does
   not support the IPv4 home address option and therefore SHOULD NOT
   include the option in future binding updates to that home agent
   address.

   The routing header in the binding update MUST include the mobile
   node's IPv6 home address as specified in [MIPv6].





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   When a mobile node acquires both IPv4 and IPv6 care-of addresses at
   foreign network, it SHOULD prioritize IPv6 care-of address for MIP6
   binding registration. The mobile node MUST NOT register both IPv4 and
   IPv6 care-of addresses to its home agent.

2.3.2 Foreign network supports IPv4 only

   If the mobile node is in a foreign network that only supports IPv4,
   it needs to detect whether a NAT is in its communication path to the
   home agent. This is done while exchanging the binding update and
   acknowledgement messages as shown later in this document. If no NAT
   is detected between the mobile node and the home agent, the mobile
   node assumes that it is in a foreign network that supports IPv4
   public addresses. Otherwise, the mobile node assumes that private
   addresses are used in the foreign network. Note that this assumption
   is only valid for the purposes of the signaling presented in this
   specification. A mobile node SHOULD NOT assume that its IPv4 address
   is globally unique if a NAT device was not detected. The operations
   of both cases are discussed below.

2.3.2.2 Foreign network supports IPv4 only (public addresses)

   In this scenario the mobile node will need to tunnel IPv6 packets
   containing the binding update to the home agent's IPv4 address. The
   mobile node uses the IPv4 address it gets from the foreign network as
   a source address in the outer header. The binding update will contain
   the mobile node's IPv6 home address in the home address option.
   However, since the care-of address in this scenario is the mobile
   node's IPv4 address, the mobile node MUST include its IPv4 care-of
   address in the IPv6 packet. The IPv4 address is represented in an
   IPv4-mapped IPv6 address and is included in the source address field
   of the IPv6 header.

   If the mobile node had an IPv4 home address, it MUST also include the
   IPv4 home address option described in this specification.

   After accepting the binding update, the home agent MUST create a new
   binding cache entry for the mobile node's IPv6 home address. If an
   IPv4 home address option were included, the home agent MUST create
   another entry for that address. All entries MUST point to the mobile
   node's IPv4 care-of address. Hence, all packets addressed to the
   mobile node's home address(es) (IPv4 or IPv6) will be encapsulated in
   an IPv4 header that includes the home agent's IPv4 address in the
   source address field and the mobile node's IPv4 care-of address in
   the destination address field.

   After accepting the binding updates and creating the corresponding
   entries, the home agent MUST send a binding acknowledgement as
   specified in [MIPv6]. In addition, if the binding update included an
   IPv4 home address option, the binding acknowledgement MUST include
   the IPv4 address acknowledgment option as described later in this



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   specification. The binding update is encapsulated to the IPv4 care-of
   address (represented as an IPv4-mapped IPv6 address in the binding
   update).

2.3.2.1 Visited network supports IPv4 only (private addresses)

   In this scenario the mobile node will need to tunnel IPv6 packets
   containing the binding update to the home agent's IPv4 address. In
   order to traverse the NAT device, IPv6 packets are tunneled UDP and
   IPv4. The UDP port used to send the IPv6 packet is TBD.

   The mobile node uses the IPv4 address it gets from the visited
   network as a source address in the IPv4 header. The binding update
   will contain the mobile node's IPv6 home address in the home address
   option. The content of the IPv6 packet is identical to the public
   address scenario described above.

   After accepting the binding update, the home agent MUST create a new
   binding cache entry for the mobile node's IPv6 home address. If an
   IPv4 home address option were included, the home agent MUST create
   another entry for that address. All entries MUST point to the mobile
   node's IPv4 care-of address included in the source address of the
   IPv6 packet and represented as an IPv4-mapped IPv6 address. In
   addition, the tunnel used MUST indicate UDP encapsulation for NAT
   traversal. Hence, all packets addressed to the mobile node's home
   address(es) (IPv4 or IPv6) will be encapsulated in UDP then
   encapsulated in an IPv4 header that includes the home agent's IPv4
   address in the source address field and the mobile node's IPv4 care-
   of address in the destination address field.

   After accepting the binding updates and creating the corresponding
   entries, the home agent MUST send a binding acknowledgement as
   specified in [MIPv6]. In addition, if the binding update included an
   IPv4 home address option, the binding acknowledgement MUST include
   the IPv4 address acknowledgment option as described later in this
   specification. The binding acknowledgement is encapsulated in UDP
   then IPv4 with the home agent's IPv4 address in the source address
   field and the mobile node's IPv4 care-of address in the destination
   field. The inner IPv6 packet will contain the home agent's IPv6
   address as a source address and the mobile node's IPv4 care-of
   address in the destination address field. The latter is represented
   as an IPv4-mapped IPv6 address.

   The mobile node needs to maintain the NAT bindings for its current
   IPv4 care-of address. This is done through sending the binding update
   regularly to the home agent.

2.4. Route optimization

   Route optimization, as specified in [MIPv6] will operate in an
   identical manner for dual stack mobile nodes when they are located in



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   a visited network that provides IPv6 addresses to the mobile node.
   However, when located in an IPv4-only network, route optimization
   will not be possible due to the difficulty of performing the care-of
   address test. Therefore, mobile nodes will need to communicate
   through the home agent.

   Route optimization will not be possible for IPv4 traffic. That is,
   traffic addressed to the mobile node's IPv4 home address. This is
   similar to using Mobile IPv4, therefore there is no reduction of
   features resulting from using this specification.

2.5. Dynamic IPv4 home address allocation

   It is possible to allow for the mobile node's IPv4 home address to be
   allocated dynamically. This is done by including 0.0.0.0 in the IPv4
   home address option included in the binding update. The home agent
   SHOULD allocate an IPv4 address to the mobile node and include it in
   the IPv4 address acknowledgement option sent to the mobile node. In
   this case, the lifetime of the binding is bound to the minimum of the
   lifetimes of the IPv6 binding and the lease time of the IPv4 home
   address.

3. Extensions and modifications to Mobile IPv6

   This section highlights the protocol and implementation additions
   required to support this specification.

3.1. Binding update extensions

3.1.1 IPv4 home address option

   This option is included in the Mobility Header including the binding
   update message sent from the mobile node to a home agent or Mobility
   Anchor Point.


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      |   Type        |   Length      |Pref     |P|Res|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     IPv4 home address                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type                 TBD

   Length               1

   Pref                 The length of the prefix allocated to the mobile
                        node. If only a single address is allocated,



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                        this field MUST be set to 32. In the first

                        binding update requesting a prefix, the field
                        contains the prefix length requested. However,
                        in the following binding updates, this field
                        must contain the length of the prefix allocated.

   P                    A flag indicating, when set, that the mobile
                        node requests a mobile network prefix. This flag
                        is only relevant for new requests, and must be
                        ignored for binding refreshes.

   Reserved             This field is reserved for future use. It MUST
                        be set to zero by the sender and ignored by the
                        receiver.

   IPv4 home address    The mobile node's IPv4 home address that should
                        be defended by the home agent. This field could
                        contain any unicast IPv4 address (public or
                        private) that was assigned to the mobile node.
                        The value 0.0.0.0 is used to request an IPv4
                        home address from the home agent. A mobile node
                        may choose to use this option to request a
                        prefix by setting the address to the All Zeroes
                        and setting the P flag. The mobile node could
                        then form an IPv4 home address based on the
                        allocated prefix. Alternatively, the mobile node
                        may use two different options, one for
                        requesting an address (Static or Dynamic) and
                        another for requesting a prefix.

3.2. Binding acknowledgement extensions

3.2.1 IPv4 address acknowledgement option

   This option is included in the Mobility Header including the binding
   acknowledgement message sent from the home agent or Mobility Anchor
   Point to the mobile node. This option indicates whether a binding
   cache entry was created for the mobile node's IPv4 address.
   Additionally, this option can include an IPv4 home address in the
   case of Dynamic IPv4 home address configuration (i.e. if the
   unspecified IPv4 address was included in the binding update).

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |    Length     |   Status      | Pref    | Res |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      IPv4 home address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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   Type                 TBD

   Length               1

   Status               Indicates success or failure for the IPv4 home
                        address binding. Values from 0 to 127 indicate
                        success. Higher values indicate failure. The
                        following values are reserved:
                                0   Success
                                128 Failure, reason unspecified
                                129 Administratively prohibited
                                130 Incorrect IPv4 home address
                                131 Invalid IPv4 address
                                132 Dynamic IPv4 home address
                                    assignment not available
                                133 Prefix allocation unauthorized


   Pref                 The prefix length of the address allocated. This
                        field is only valid in case of success and MUST
                        be set to zero and ignored in case of failure.
                        This field overrides what the mobile node
                        requested (if not equal to the requested
                        length).

   Res                  This field is reserved for future use. It MUST
                        be set to zero by the sender and ignored by the
                        receiver.

   IPv4 home address    The IPv4 home address that the home agent will
                        use in the binding cache entry. This could be a
                        public or private address. This field MUST
                        contain the mobile node's IPv4 home address.
                        If the address were dynamically allocated the
                        home agent will add the address to inform the
                        mobile node. Otherwise, if the address were
                        statically allocated to the mobile node, the
                        home agent will copy it from the binding update
                        message.

3.2.2 The NAT detection option

   This option is sent from the home agent to the mobile node to
   indicate whether a NAT was in the path. This option MAY also include
   a suggested NAT binding refresh time for the mobile node.









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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |    Length     |F|          Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Refresh time                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type                 TBD

   Length               1

   F                    This flag indicates to the mobile node that UDP
                        encapsulation is required. When set, this flag
                        indicates that the mobile node MUST use UDP
                        encapsulation even if a NAT is not located
                        between the mobile node and home agent.

   Reserved             This field is reserved for future use. It MUST
                        be set to zero by the sender and ignored by the
                        receiver.

   Refresh time         A suggested time (in seconds) for the mobile
                        node to refresh the NAT binding. If set to zero,
                        it is ignored. If this field is set to the all
                        1s it means that keepalives are not needed, i.e.
                        no NAT was detected.

4. Protocol operation

   This section presents the protocol operation and processing for the
   messages presented above. In addition, this section introduces the
   NAT detection and traversal mechanism used by this specification.

4.1. NAT detection and traversal

   NAT detection is done when the initial binding update message is sent
   from the mobile node to the home agent. When located in an IPv4-only
   foreign link, the mobile node sends the binding update message
   encapsulated in UDP and IPv4. The source address of the IPv6 packet
   is the mobile node's IPv4 care-of address represented in IPv4-mapped
   IPv6 format. The destination address is the IPv6 address of the home
   agent. The IPv4 header contains the IPv4 care-of address in the
   source address field and the IPv4 address of the home agent in the
   destination address field.

   When the home agent receives the encapsulated binding update it
   compares the IPv4 address of the source address field in the IPv4
   header with the IPv4 address in the source address of the IPv6
   header. If the two addresses match, no NAT device was in the path.



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   Otherwise, a NAT device was in the path and the NAT detection option
   is included in the binding acknowledgement. The binding
   acknowledgement, and all future packets, are then encapsulated in UDP
   and IPv4. The source address in the IPv4 header is the IPv4 address
   of the home agent. The destination address is the IPv4 address
   received in the IPv4 header encapsulating the binding update (this
   address will be different from the IPv4 care-of address when a NAT is
   in the path).

   Upon receiving the binding acknowledgement with the NAT detection
   option, the mobile node sets the tunnel to the home agent to UDP
   encapsulation. Hence, all future packets to the home agent are
   tunneled in UDP and IPv4. For all tunneled IPv6 packets, the source
   address in the IPv6 header is the mobile node's IPv6 home address and
   the destination address is the correspondent node's IPv6 address. All
   tunneled IPv4 packets will contain the mobile node's IPv4 home
   address in the source address field of the inner IPv4 packet and the
   correspondent node's IPv4 address in the destination address field.
   The outer IPv4 header is the same whether the inner packet is IPv4 or
   IPv6.

   If no NAT device was detected in the path between the mobile node and
   the home agent then IPv6 packets are tunneled in an IPv4 header,
   unless the home agent forces UDP encapsulation using the F flag. The
   content of the inner and outer headers are identical to the UDP
   encapsulation case.

   A mobile node MUST always tunnel binding updates in UDP when located
   in an IPv4-only network. Essentially, this process allows for
   perpetual NAT detection. Similarly, the home agent MUST encapsulate
   binding acknowledgements in a UDP header whenever the binding update
   is encapsulated in UDP.

   In conclusion, the packet formats for the binding update and
   acknowledgement messages are shown below:

   A. Binding update received by the home agent:

              IPv4 header (src=V4ADDR, dst=HA_V4ADDR)
                 UDP header
                   IPv6 header (src=V4CoA, dst=HAADDR)
                      DST-OPT
                          HAO (IPv6 home address)
                      Mobility header
                          BU [IPv4 HAO]

   Where V4ADDR is either the IPv4 care-of address or the address
   provided by the NAT device. V4COA is the IPv4 care-of address of the
   mobile node. HAO is the home address option and BU is the binding
   update, which MAY contain the IPv4 home address option.




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   B. Binding acknowledgement sent by the home agent:
              IPv4 header (src=V4ADDR, dst=HA_V4ADDR)
                  UDP header
                   IPv6 header (src=V4CoA, dst=HAADDR)
                      Route HDR Type 2
                          HOA (IPv6 home address)
                      Mobility header
                          BA ([IPv4 ACK], NAT DET)

   Where HOA is IPv6 home address of the mobile node. The IPv4 ACK is
   the IPv4 address acknowledgement option, which is only included if
   the IPv4 home address option were present in the BU. The NAT DET is
   the NAT detection option, which MUST be present in the binding
   acknowledgement message if the binding update was encapsulated in
   UDP.

4.2. NAT Keepalives

   If a NAT is detected, the mobile node will need to refresh the NAT
   bindings in order to be reachable from the home agent. NAT bindings
   can be refreshed through sending and receiving traffic encapsulated
   in UDP. However, if the mobile node is not active, it will need to
   periodically send a message to the home agent in order to refresh the
   NAT binding. This can be done using the binding update message. The
   binding update/acknowledgement pair will ensure that the NAT bindings
   are refreshed in a reliable manner.
   There is no way for the mobile node to know the exact time of the NAT
   binding. The default time suggested in this specification is
   NATKATIMEOUT. If the home agent suggests a different refresh period
   in the binding acknowledgement, the mobile node SHOULD use the value
   suggested by the home agent.

   If the refresh time in the NAT detection option in the binding
   acknowledgement is set to the all 1s, the mobile node need not send
   messages to refresh the NAT binding. However, the mobile node may
   still be required to encapsulate traffic in UDP. This scenario may
   take place when a NAT is not detected, but the home agent still
   requires the mobile node to use UDP encapsulation.

   It should be noted that a mobile node that does not need to be
   reachable (i.e. only cares about the session continuity aspect of
   Mobile IP) does not need to refresh NAT binding. In this case, the
   mobile node would only be able to initiate communication with other
   nodes.

4.3. Mobile node operation

   In addition to the operations specified in [MIPv6] and [NEMO], this
   specification requires mobile nodes to be able to support an IPv4
   home address. The IPv4 home address is never sent in the IPv4-mapped
   IPv6 address format. This is primarily done to save bandwidth.



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   However, to simplify the mobile node's implementation, they may store
   the IPv4 home address in the binding update list, using the IPv4-
   mapped IPv6 format.

   When sending an IPv6 packet containing a binding update while
   connected to an IPv4-only access network, mobile nodes MUST ensure
   the following:

   - The IPv6 packet is encapsulated in UDP and an IPv4 packet.
   - The source address in the IPv4 header is the mobile node's IPv4
     care-of address
   - The destination address in the IPv4 header is the home agent's
     IPv4 address.
   - The source address in the IPv6 header is the mobile node's IPv4-
     mapped IPv6 address. That is, the same IPv4 address in the outer
     header is placed in the IPv6 header using the mapped address
     format.
   - The home address option contains the IPv6 home address as
     specified in [MIPv6].
   - The IPv4 home address option MAY be included in the mobility
     header. This option contains the IPv4 home address. If the mobile
     node did not have a static home address it MAY include the
     unspecified IPv4 address, which acts as a request for a dynamic
     IPv4 home address. Alternatively, one or more IPv4 home address
     options may be included with requests for IPv4 prefixes (i.e. with
     the P flag set.).
   - The IPv6 packet MUST be authenticated as per [MIPv6], based on the
     mobile node's IPv6 home address.

   When sending a binding update from a visited network that supports
   IPv6, the mobile node MUST follow the rules specified in [MIPv6]. In
   addition, if the mobile node has an IPv4 home address or needs one,
   it should include the IPv4 home address option in the mobility
   header. If the mobile node already has a static IPv4 home address,
   such address MUST be included in the IPv4 home address option.
   Otherwise, if the mobile node needs a dynamic IPv4 address, it should
   include the IPv4 unspecified address in the IPv4 home address option.

   When the mobile node receives a binding acknowledgement from the home
   agent, it should follow the rules in [MIPv6] and [NEMO]. In addition,
   the following actions MUST be made:

   - If the mobility header includes an IPv4 address acknowledgement
     option indicating success, the mobile node should create two
     entries in its binding update list, one for the IPv6 home address
     and another for the IPv4 home address.
   - If the NAT detection option were present, the mobile node
     MUST tunnel future packets in UDP and IPv4. This MUST be indicated
     in the binding update list.
   - If no IPv4 address acknowledgement option were present, and an
     IPv4 home address option was present in the binding update, the



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     mobile node MUST only create one binding update list entry for its
     IPv6 home address. The mobile node MAY include the IPv4 home
     address option in future binding updates.
   - If an IPv4 address acknowledgement option were present and it
     indicates failure for the IPv4 home address binding, the mobile
     node MUST NOT create an entry for that address in its binding
     update list. The mobile node MAY include the IPv4 home address
     option in future binding updates.

4.3.1 Sending packets from a visited network.

   When the mobile node is located in an IPv6-enabled network it sends
   and receives IPv6 packets as described in [MIPv6]. IPv4 traffic is
   encapsulated in IPv6 packets to the home agent.

   When the mobile node is located in an IPv4 only network, it will send
   IPv6 packets to its home agent according to the following format:

                IPv4 header (src=V4ADDR, dst=HA_V4ADDR)
                 [UDP header]
                   IPv6 header (src=V6HoA, dst=CN)
                    Upper layer protocols

   Where the UDP header is only used if a NAT were detected between the
   mobile node and the home agent, or if the home agent forced UDP
   encapsulation.

   Similarly, IPv4 packets are sent according to the following format:

                IPv4 header (src=V4ADDR, dst=HA_V4ADDR)
                 [UDP header]
                   IPv4 header (src=V4HoA, dst=V4CN)
                    Upper layer protocols

   Where the UDP header is only used if a NAT were detected between the
   mobile node and the home agent, or if the home agent forced UDP
   encapsulation.

4.3.2 Movement detection in IPv4-only networks

   [MIPv6] describes movement detection mostly based on IPv6-specific
   triggers. Such triggers would not be available in an IPv4-only
   network. Hence, a mobile node located in an IPv4-only network SHOULD
   use [DNAv4] for guidance on movement detection mechanisms in IPv4-
   only networks.

4.4. Home agent operations

   In addition to the home agent specification in [MIPv6] and [NEMO],
   the home agent needs to be able to process the IPv4 home address
   option and generate the IPv4 address acknowledgement option. Both



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   options are included in the mobility header. Furthermore, the home
   agent MUST be able to detect the presence of a NAT device and
   indicate that in the NAT detection option included in the binding
   acknowledgement.

   A home agent must also act as a proxy for address resolution in IPv4
   for the registered IPv4 home addresses of mobile nodes it is serving.
   Moreover, the administrative domain of the home agent is responsible
   for advertising the routing information of registered IPv4 mobile
   network prefixes of the mobile nodes.

   In order to comply with this specification, the home agent MUST be
   able to find the IPv4 home address of a mobile node when given the
   IPv6 home address. That is, given an IPv6 home address, the home
   agent MUST store the corresponding IPv4 home address if a static one
   is present. If a dynamic address were requested by the mobile node,
   the home agent MUST store that address (associated with the IPv6 home
   address) after it's allocated to the mobile node.

   When the home agent receives a binding update encapsulated in UDP and
   containing the IPv4 home address option, it needs to follow all the
   steps in [MIPv6] and [NEMO]. In addition, the following checks MUST
   be done:

   - If the IPv4 care-of address in the IPv6 header is not the same as
     the IPv4 address in the source address in the IPv4 header then a
     NAT was in the path. This information should be flagged for the
     binding acknowledgement.

   - If the IPv4 home address option contains a valid unicast IPv4
     address, the home agent MUST check that this address is allocated
     to the mobile node that has the IPv6 home address included in the
     home address option. The same MUST be done for an IPv4 prefix.

   - If the IPv4 home address option contained the unspecified IPv4
     address, the home agent SHOULD dynamically allocate an IPv4 home
     address to the mobile node. If none is available, the home agent
     MUST return an appropriate error code in the status field of the
     IPv4 address acknowledgement option. If a prefix were requested,
     the home agent MUST allocate a prefix with the requested length;
     otherwise the home agent MUST indicate failure of the operation
     with the appropriate error code.

   - If the binding update is accepted for the IPv4 home address, the
     home agent MUST create a binding cache entry for the IPv4 home
     address/prefix. If a single IPv4 home address were requested, it
     MAY be stored in the IPv4-mapped IPv6 address format. The home
     agent MUST include an IPv4 acknowledgement option in the mobility
     header containing the binding acknowledgement.





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   If the binding update is accepted for both IPv4 and IPv6 home
   addresses, the home agent MUST create two separate binding cache
   entries, one for each home address. The care-of address is the one
   included in the binding update. If the care-of address is an IPv4-
   mapped IPv6 address, the home agent MUST setup a tunnel to the IPv4
   care-of address of the mobile node.

   When sending a binding acknowledgement to the mobile node, the home
   agent would construct the message according to [MIPv6] and [NEMO].
   Note that the routing header MUST always contain the IPv6 home
   address as specified in [MIPv6].

   If the care-of address of the mobile node were an IPv4 address, the
   home agent MUST include this address in the destination address in
   the IPv6 header using the IPv4-mapped IPv6 format. If a NAT were
   detected, the home agent MUST then encapsulate the packet in UDP and
   an IPv4 header. The source address is set to the home agent's IPv4
   address and the destination address is set to the address received in
   the source address of the IPv4 header encapsulating the binding
   update.

   After creating a binding cache entry for the mobile node's home
   addresses, all packets sent to the mobile node's home addresses are
   tunneled by the home agent to the mobile node's care-of address. If a
   NAT were detected, packets are encapsulated in UDP and IPv4.
   Otherwise, if the care-of address is an IPv4 address, and no NAT were
   detected, packets are encapsulated in an IPv4 header.

4.4.1 Sending packets to the mobile node

   The home agent follows the rules specified in [MIPv6] for sending
   IPv6 packets to mobile nodes located in IPv6 networks. When sending
   IPv4 packets to When mobile nodes in an IPv6 network, the home agent
   must encapsulate the IPv4 packets in IPv6.

   When sending IPv6 packets to a mobile node located in an IPv4
   network, the home agent must follow the following format:

                IPv4 header (src= HA_V4ADDR, dst= V4CoA)
                 [UDP header]
                   IPv6 header (src=CN, dst= V6HoA)
                    Upper layer protocols

   Where the UDP header is only included if a NAT were detected between
   the mobile node and the home agent, or if the home agent forced UDP
   encapsulation.

   When sending IPv4 packets to a mobile node located in an IPv4
   network, the home agent must follow the following format:

                IPv4 header (src= HA_V4ADDR, dst= V4CoA)



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                 [UDP header]
                   IPv4 header (src=V4CN, dst= V4HoA)
                    Upper layer protocols

   Where the UDP header is only included if a NAT were detected between
   the mobile node and home agent, or if the home agent forced UDP
   encapsulation.

4.5. Correspondent node operations

   This specification has no impact on IPv4 or IPv6 correspondent nodes.

5. Security considerations

   This specification allows a mobile node to send one binding update
   for its IPv6 and IPv4 home addresses. This is a slight deviation from
   [MIPv6] which requires one binding update per home address. However,
   like [MIPv6], the IPsec security association needed to authenticate
   the binding update is still based on the mobile node's IPv6 home
   address. Therefore, in order to authorize the mobile node's IPv4 home
   address binding, the home agent MUST store the IPv4 address
   corresponding to the IPv6 address that is allocated to a mobile node.
   Therefore, it is sufficient for the home agent to know that the IPsec
   verification for the packet containing the binding update was valid
   provided that it knows which IPv4 home address is associated with
   which IPv6 home address. Hence, the security of the IPv4 home address
   binding is the same as the IPv6 binding.

   In effect, associating the mobile node's IPv4 home address with its
   IPv6 home address moves the authorization of the binding update for
   the IPv4 address to the Mobile IPv6 implementation, which infers it
   from the fact that mobile node has an IPv6 home address and the right
   credentials for sending an authentic binding update for such address.

6. Protocol constants

           NATKATIMEOUT      110 seconds

7. Acknowledgements

   Thanks to Keiichi Shima for his comments on the draft.

8. IANA considerations

   The specification requires the following allocations from IANA:
   - A UDP port is needed for the NAT traversal mechanism described in
     section 4.1.
   - The IPv4 home address option described in section 3.1.1 requires an
     option type. This option is included in the Mobility header
     described in [MIPv6].
   - The IPv4 address acknowledgement option described in section 3.2.1



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     requires a new option type. This option is included in the Mobility
     header described in [MIPv6].
   - The NAT detection option described in section 3.2.2 requires a new
     option type. This option is included in the Mobility header
     described in [MIPv6].

9. References

   [BOOT] Giaretta, G. (Ed.), Kempf J., and V. Devarapalli, " Mobile
          IPv6 bootstrapping in split scenario", draft-ietf-mip6-
          bootstrapping-split, June 2005, work in progress.

   [HMIPv6] Soliman, H., Castelluccia, C., ElMalki, K., and L. Bellier,
            "Hierarchical Mobile IPv6 Mobility Management (HMIPv6)",
            RFC 4140, August 2005.

   [IPv6] S. Deering and B. Hinden, "Internet Protocol version 6 (IPv6)
          specification", RFC 2460

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

   [MIP-PB]   Tsirtsis, G., and H. Soliman, "Mobility management for
              Dual stack mobile nodes, A Problem Statement",
              draft-ietf-mip6-dsmip-problem-01.txt, July 2005.

   [MIPv4] C. Perkins, "Mobility Support for IPv4", RFC3344

   [MIPv6] D. Johnson, C. Perkins and J. Arkko, "Mobility Support in
           IPv6", RFC 3775, June 2004.

   [NEMO]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
           "Network Mobility (NEMO) Basic Support protocol", RFC 3963,
           January 2005.

   [SEC]   Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to
           Protoect Mobile IPv6 Signaling between Mobile Nodes and Home
           Agents", RFC 3776, June 2004.

   [SNRIO] Larsson, T., Gustafsson, E., and H. Levkowetz, "Use of MIPv6
           in IPv4 and MIPv4 in IPv6 networks", draft-larsson-v6ops-
           mip-scenarios-01.txt, February 2004.

Authors' Addresses

   Hesham Soliman
   Qualcomm-Flarion Technologies
   E-mail: Hesham@Qualcomm.com

   George Tsirtsis
   Qualcomm-Flarion Technologies



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   Phone: +1 908 947 7059
   E-mail1: G.Tsirtsis@Qualcomm.com
   E-mail2: tsirtsisg@yahoo.com

   Vijay Devarapalli
   E-mail: vijay.devarapalli@nokia.com

   James Kempf
   DoCoMo Labs USA
   181 Metro Drive
   Suite 300
   San Jose, CA
   95110
   E-mail: kempf@docomolabs-usa.com

   Henrik Levkowetz
   Ericsson Research
   Torshamsgatan 23
   S-164 80 Stockholm
   SWEDEN
   Phone: +46 708 32 16 08
   E-mail: henrik@levkowetz.com

   Pascal Thubert
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis
   06410
   FRANCE
   Phone: +33 4 97 23 26 34
   E-mail: pthubert@cisco.com

   Wakikawa Ryuji
   Keio University
   Department of Environmental Information,
   Keio University.
   5322 Endo
   Fujisawa,
   Kanagawa 252-8520
   Japan

   Phone: +81-466-49-1100</phone>
   Fax: +81-466-49-1395</facsimile>
   E-mailryuji@sfc.wide.ad.jp
   Web: http://www.wakikawa.org/

Intellectual Property Statement





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   The IETF takes no position regarding the validity or scope of any
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   Copies of IPR disclosures made to the IETF Secretariat and any
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   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
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   ipr@ietf.org.

Full Copyright Statement

   Copyright (C) The Internet Society (2006). This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Disclaimer of Validity

   This document and the information contained herein are provided on an
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   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
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   This Internet-Draft expires December, 2006.












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