NETLMM Working Group                                         R. Wakikawa
Internet-Draft                                                Toyota ITC
Intended status: Standards Track                           S. Gundavelli
Expires: January 15, 2009                                          Cisco
                                                           July 14, 2008


                   IPv4 Support for Proxy Mobile IPv6
              draft-ietf-netlmm-pmip6-ipv4-support-04.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
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   This Internet-Draft will expire on January 15, 2009.

Copyright Notice

   Copyright (C) The IETF Trust (2008).













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Abstract

   This document specifies extensions to Proxy Mobile IPv6 protocol for
   adding IPv4 protocol support.  The scope of IPv4 protocol support is
   two-fold: 1) For extending IPv4 home address mobility support to the
   mobile node. 2) For allowing the mobility entities in the Proxy
   Mobile IPv6 domain to exchange signaling messages over an IPv4
   transport network.











































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Table of Contents

   1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.  Stated Assumptions . . . . . . . . . . . . . . . . . . . .  6

   2.  Conventions & Terminology  . . . . . . . . . . . . . . . . . .  8
     2.1.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  8
     2.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  8

   3.  IPv4 Home Address Mobility Support . . . . . . . . . . . . . . 10
     3.1.  Local Mobility Anchor Considerations . . . . . . . . . . . 11
       3.1.1.  Extensions to Binding Cache Entry  . . . . . . . . . . 11
       3.1.2.  Signaling Considerations . . . . . . . . . . . . . . . 11
       3.1.3.  Routing Considerations for the Local Mobility
               Anchor . . . . . . . . . . . . . . . . . . . . . . . . 15
     3.2.  Mobile Access Gateway Considerations . . . . . . . . . . . 16
       3.2.1.  Extensions to Binding Update List Entry  . . . . . . . 16
       3.2.2.  Extensions to Mobile Node's Policy Profile . . . . . . 16
       3.2.3.  Signaling Considerations . . . . . . . . . . . . . . . 17
       3.2.4.  Routing Considerations for the Mobile Access
               Gateway  . . . . . . . . . . . . . . . . . . . . . . . 19
     3.3.  Mobility Options and Status Codes  . . . . . . . . . . . . 19
       3.3.1.  IPv4 Default-Router Address Option . . . . . . . . . . 19
       3.3.2.  Status Codes . . . . . . . . . . . . . . . . . . . . . 20
     3.4.  Supporting DHCP Based Address Configuration  . . . . . . . 21
       3.4.1.  DHCP Server co-located with the Mobile Access
               Gateway  . . . . . . . . . . . . . . . . . . . . . . . 22
       3.4.2.  DHCP Relay Agent co-located with the Mobile Access
               Gateway  . . . . . . . . . . . . . . . . . . . . . . . 25

   4.  IPv4 Transport Support . . . . . . . . . . . . . . . . . . . . 28
     4.1.  Local Mobility Anchor Considerations . . . . . . . . . . . 29
       4.1.1.  Extensions to Binding Cache Entry  . . . . . . . . . . 29
       4.1.2.  Extensions to Mobile Node's Policy Profile . . . . . . 30
       4.1.3.  Signaling Considerations . . . . . . . . . . . . . . . 30
       4.1.4.  Routing Considerations . . . . . . . . . . . . . . . . 32
     4.2.  Mobile Access Gateway Considerations . . . . . . . . . . . 34
       4.2.1.  Extensions to Binding Update List Entry  . . . . . . . 34
       4.2.2.  Signaling Considerations . . . . . . . . . . . . . . . 34

   5.  Protocol Configuration Variables . . . . . . . . . . . . . . . 38
     5.1.  Local Mobility Anchor - Configuration Variables  . . . . . 38
     5.2.  Mobile Access Gateway - Configuration Variables  . . . . . 38
     5.3.  Proxy Mobile IPv6 Domain - Configuration Variables . . . . 39

   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 40

   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 41



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   8.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 42

   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 42

   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 42
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 42
     10.2. Informative References . . . . . . . . . . . . . . . . . . 43

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 44
   Intellectual Property and Copyright Statements . . . . . . . . . . 45









































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1.  Overview

   The transition from IPv4 to IPv6 is a long process and during this
   period of transition, both the protocols will be enabled over the
   same network infrastructure.  Thus, it is reasonable to assume that a
   mobile node in a Proxy Mobile IPv6 domain may operate in an IPv4-only
   IPv6-only or in dual-stack mode and additionally the network between
   the mobile access gateway and a local mobility anchor may be an IPv4
   or an IPv6 network.  It is also reasonable to expect the same
   mobility infrastructure in the Proxy Mobile IPv6 domain to provide
   mobility to the mobile nodes operating in IPv4, IPv6 or in dual mode
   and when the network between the local mobility anchor and the mobile
   access gateway is an IPv4 or an IPv6 network.  The motivation and
   scope of IPv4 support in Mobile IPv6 is summarized in [RFC-4977] and
   all those requirements apply to Proxy Mobile IPv6 protocol as well.

   The Proxy Mobile IPv6 protocol [RFC-5213] specifies a mechanism for
   providing IPv6 home address mobility support to a mobile node in a
   Proxy Mobile IPv6 domain.  The protocol requires IPv6 transport
   network between the mobility entities.  The extensions defined in
   this document extends IPv4 support to the Proxy Mobile IPv6 protocol
   [RFC-5213].

   The scope of IPv4 support in Proxy Mobile IPv6 includes the support
   for the following two features:

   o  IPv4 Home Address Mobility Support: A mobile node that has an IPv4
      stack enabled will be able to obtain an IPv4 address and be able
      to use that address from any of the access networks in that Proxy
      Mobile IPv6 domain.  The mobile node is not required to be
      allocated or assigned an IPv6 address for enabling IPv4 home
      address support.

   o  IPv4 Transport Network Support: The mobility entities in the Proxy
      Mobile IPv6 domain will be able to exchange Proxy Mobile IPv6
      signaling messages over an IPv4 transport and further the mobile
      access gateway may be using an IPv4 private address and with NAT
      [RFC-3022] translation devices on the path to the local mobility
      anchor.

   These two features, the IPv4 Home Address Mobility support and the
   IPv4 transport support features, are independent of each other and
   deployments may choose to enable any one or both of these features as
   required.







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               +----+                +----+
               |LMA1|                |LMA2|
               +----+                +----+
   IPv4-LMAA1 -> |                      | <-- LMAA2
                 |                      |
                 \\                    //\\
                [NAT]                 //  \\
                   \\                //    \\
                +---\\------------- //------\\----+
               (     \\  IPv4/IPv6 //        \\    )
               (      \\  Network //          \\   )
                +------\\--------//------------\\-+
                        \\      //              \\
                         \\    //                \\
                          \\  //                  \\
         IPv4-Proxy-CoA1--> |                      | <-- Proxy-CoA2
                         +----+                 +----+
                         |MAG1|-----{MN2}       |MAG2|
                         +----+    |            +----+
        (IPv6 MN-HoA1)     |       |               | <-- (IPv6 MN-HoA2)
        (IPv4-MN-HoA1) --> |   (IPv4-MN-HoA2)      | <-- (IPv4-MN-HoA3)
                         {MN1}                   {MN3}



               Figure 1: IPv4 support for Proxy Mobile IPv6

1.1.  Stated Assumptions

   Following are the configuration requirements from the mobility
   entities in the Proxy Mobile IPv6 domain for supporting the
   extensions defined in this document.

   o  The local mobility anchor and the mobile access gateway are both
      IPv4 and IPv6 enabled.  Irrespective of the type of transport
      network (IPv4 or IPv6) separating these two entities, the mobility
      signaling is always based on Proxy Mobile IPv6 [RFC-5213].

   o  The mobile node can be operating in IPv4-only, IPv6-only or in
      dual mode.  Based on what is enabled for a mobile node, it should
      be able to obtain IPv4-only, IPv6-only or both IPv4 and IPv6
      address(es) for its interface and further achieve mobility support
      for those addresses.

   o  For enabling IPv4 home address mobility support to a mobile node,
      it is not required that the IPv6 home address mobility support
      needs to enabled.  However, the respective protocol(s) support
      must be enabled on the access link between the mobile node and the



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      mobile access gateway.

   o  The mobile node can obtain one or more IPv4 addresses for its
      attached interface.  Based on the type of link, it may be able to
      acquire its IPv4 address configuration using DHCP [RFC-2131], IPCP
      [RFC-1332], IKEv2 [RFC-4306], static configuration or through
      other standard IPv4 address configuration mechanisms.

   o  The mobile node's IPv4 home subnet is typically a shared address
      space.  Its is not for the exclusive use of any one mobile node.
      There can be more than one mobile node sharing different addresses
      from the same IPv4 subnet.

   o  The mobile access gateway is the IPv4 default-router for the
      mobile node on its access link.  It will be in the forwarding path
      for the mobile node's data traffic.



































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2.  Conventions & Terminology


2.1.  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 [RFC-2119].

2.2.  Terminology

   All the mobility related terms used in this document are to be
   interpreted as defined in the Mobile IPv6 specification [RFC-3775]
   and Proxy Mobile IPv6 specification [RFC-5213].  In addition this
   document introduces the following terms.

   IPv4 Proxy Care-of Address (IPv4-Proxy-CoA)

      The IPv4 address that is configured on the egress-interface of the
      mobile access gateway.  When using IPv4 transport, this address
      will be the registered care-of address in the mobile node's
      Binding Cache entry and will also be the transport-endpoint of the
      tunnel between the local mobility anchor and a mobile access
      gateway.  However, if the configured address is a private IPv4
      address and with a NAT device in the path to the local mobility
      anchor, the care-of address as seen by the local mobility anchor
      will be the address allocated by the NAT device for that flow.

   IPv4 Local Mobility Anchor Address (IPv4-LMAA)

      The IPv4 address that is configured on the egress-interface of the
      local mobility anchor.  When using IPv4 transport, the mobile
      access gateway sends the Proxy Binding Update messages to this
      address and will be the transport-endpoint of the tunnel between
      the local mobility anchor and the mobile access gateway.

   Mobile Node's IPv4 Home Address (IPv4-MN-HoA)

      This is the IPv4 home address assigned to the mobile node's
      attached interface.  This IPv4 home address is topologically
      anchored at the local mobility anchor.  The mobile node configures
      this address on its attached interface.  There can be more than
      one IPv4 home addresses assigned to the mobile node's attached
      interface.  Further, if the mobile node connects to the Proxy
      Mobile IPv6 domain through multiple interfaces and for
      simultaneous access, each of the attached interfaces will be
      assigned a unique set of IPv4 home addresses and all the IPv4
      addresses that are assigned to a given interface of a mobile node



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      will be managed under one mobility session.

   Encapsulation Modes

      This document uses the following terms when referring to the
      different encapsulation modes.

      IPv4-over-IPv6

         IPv4 packet carried as a payload of an IPv6 packet

      IPv4-over-IPv4

         IPv4 packet carried as a payload of an IPv4 packet

      IPv4-over-IPv4-UDP

         IPv4 packet carried as a payload in an UDP header of an IPv4
         packet

      IPv4-over-IPv4-UDP-TLV

         IPv4 packet carried as a payload in an IPv4 packet with UDP and
         TLV headers



























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3.  IPv4 Home Address Mobility Support

   The IPv4 home address mobility support essentially enables a mobile
   node in a Proxy Mobile IPv6 domain to obtain IPv4 home address
   configuration for its attached interface and be able to retain that
   address configuration even after changing its point of attachment in
   that Proxy Mobile IPv6 domain.  This section describes the protocol
   operation and the required extensions to Proxy Mobile IPv6 protocol
   for supporting IPv4 home address mobility support.

   When an IPv4-enabled or a dual-stack enabled mobile node attaches to
   the Proxy Mobile IPv6 domain, the mobile access gateway on the access
   network where the mobile node is attached will identify the mobile
   node and will initiate the Proxy Mobile IPv6 signaling with the
   mobile node's local mobility anchor.  The mobile access gateway will
   follow the signaling considerations specified in Section 3.2 for
   requesting IPv4 home address support.  Upon the completion of the
   signaling the local mobility anchor and the mobile access gateway
   will have the required states for allowing the mobile node to use its
   IPv4 home address(es) from the current point of attachment.

   The mobile node on the access link using any of the standard IPv4
   address configuration mechanisms supported on that access link, such
   as IPCP [RFC-1332], IKEv2 [RFC-4306] or using DHCP [RFC-2131], will
   be able to obtain one or more IPv4 home addresses (IPv4-MN-HoA) for
   the attached interface.  Although the address configuration protocol
   mechanisms for delivering the address configuration to the mobile
   node is independent of the Proxy Mobile IPv6 protocol operation,
   however there needs to be some interactions between these two
   protocol flows.  Section 3.4 identifies these interactions for
   supporting DHCP based address configuration.

   The support for IPv4 home address mobility is not dependent on the
   IPv6 home address support.  The mobile node is not required to have
   an IPv6 home address for obtaining IPv4 home address mobility.  A
   mobile node will be able to obtain just IPv4 address configuration or
   both IPv4 and IPv6 address configuration on its attached interface.
   The mobile node's policy profile will determine if the mobile node is
   entitled for both the protocols or a single protocol and based on
   what is enabled, only those protocols will be enabled on the access
   link.  Further, if the mobile node after obtaining the address
   configuration on its interface performs an handoff, either by
   changing its point of attachment over the same interface or to a
   different interface, the network will ensure the mobile node will be
   able to use the same IPv4 address configuration after the handoff.

   Additionally, If the mobile node connects to the Proxy Mobile IPv6
   domain, through multiple interfaces and simultaneously through



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   different access networks, each of the connected interfaces will
   obtain one or more IPv4 home addresses from different subnets.  In
   such scenario, there will be multiple Binding Cache entries for the
   mobile node on the local mobility anchor.  All the address (IPv4/
   IPv6) assigned to a given interface will be managed as part of one
   mobility session, as specified in Section 5.4 of [RFC-5213].

3.1.  Local Mobility Anchor Considerations


3.1.1.  Extensions to Binding Cache Entry

   For supporting this feature, the conceptual Binding Cache entry data
   structure maintained by the local mobility anchor needs to be
   extended with the following additional parameters.

   o  List of IPv4 home addresses assigned to the mobile node's
      interface registered by the mobile access gateway.  Each of these
      IPv4 home address entries also include the corresponding prefix
      length.

   o  The IPv4 default-router address assigned to the mobile node.

3.1.2.  Signaling Considerations


3.1.2.1.  Processing Proxy Binding Updates

   The processing rules specified in Section 5.3 of [RFC-5213] are
   applied for processing the received Proxy Binding Update message.
   However, if the received Proxy Binding Update message has one or more
   IPv4 Home Address options, the following additional considerations
   MUST be applied.

   o  If there is an IPv4 Home Address option present in the received
      Proxy Binding Update message, but if there is no Home Network
      Prefix option present in the request, the local mobility anchor
      MUST NOT reject the request as specified in Section 5.3.1 of [RFC-
      5213].  At least one instance of any of these two options MUST be
      present.  However, if not a single instance of any of these
      options are not present, the local mobility anchor MUST reject the
      request and send a Proxy Binding Acknowledgement message with
      Status field set to MISSING_HOME_NETWORK_PREFIX_OPTION (Missing
      mobile node's home network prefix option).

   o  For performing the Binding Cache entry existence test, the
      following considerations MUST be applied:




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      *  If there is at least one Home Network Prefix option with a
         NON_ZERO prefix value, or, if there is no IPv4 Home Address
         option with a NON_ZERO IPv4 address, considerations from
         Section 5.4 of [RFC-5213] MUST be applied.

      *  If there is at least one IPv4 Home Address option present in
         the request with a NON_ZERO IPv4 address value, considerations
         from Section 3.2.2.7 MUST be applied.

   o  If there is no existing Binding Cache entry that can be associated
      with the request, the local mobility anchor MUST consider this
      request as an initial binding registration request and
      considerations from Section 3.2.2.2 MUST be applied.

   o  If there exists a Binding Cache entry that can be associated with
      the request, the local mobility anchor MUST apply considerations
      from Section 5.3.1 of [RFC-5213], (point 13), to determine if the
      request is re-registration request or a de-registration request
      and the respective considerations from below MUST be applied.

3.1.2.2.  Initial Binding Registration (New Mobility Session)


   o  If there is at least one IPv4 Home Address option present in the
      Proxy Binding Update message with the IPv4 address value set to
      ALL_ZERO, the local mobility anchor MUST allocate one or more IPv4
      home addresses to the mobile node and associate them to the new
      mobility session created for that mobile node.  The decision on
      how many IPv4 home addresses to be allocated can be based on a
      domain-wide policy or a policy specific to that mobile node.

   o  If there are one or more IPv4 Home Address options present in the
      received Proxy Binding Update message (with the IPv4 address field
      in the option set to a NON_ZERO value), the local mobility anchor
      before accepting the request, MUST ensure the address is owned by
      the local mobility anchor and further the mobile node is
      authorized to use that address.  If the mobile node is not
      authorized for a specific address, the local mobility anchor MUST
      reject the request and send a Proxy Binding Acknowledgement
      message with Status field set to
      NOT_AUTHORIZED_FOR_IPV4_HOME_ADDRESS (mobile node not authorized
      for the requesting IPv4 Home Address).  It MUST also set the
      status field value in the corresponding IPv4 Address
      Acknowledgement option [ID-DSMIP6] to 129 (Administratively
      prohibited).

   o  If the local mobility anchor is unable to allocate an IPv4 address
      due to lack of resources, it MUST reject the request and send a



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      Proxy Binding Acknowledgement message with Status field set to 130
      (Insufficient resources).  It MUST also set the status field value
      in the corresponding IPv4 Address Acknowledgement option [ID-
      DSMIP6], to 128 (Failure, reason unspecified).

   o  Upon accepting the request, the local mobility anchor MUST create
      a Binding Cache entry for this mobility session.  However, if the
      request also contains one or more Home Network Prefix options,
      there should still be only one Binding Cache entry that should be
      created for this mobility session.  The created Binding Cache
      entry MUST be used for managing both IPv4 and IPv6 home address
      bindings.  The fields in the Binding Cache entry MUST be updated
      with the accepted values for that binding.

   o  The local mobility anchor MUST establish a bi-directional tunnel
      to the mobile access gateway and with the encapsulation mode as
      negotiated.  When using IPv6 transport, the encapsulation mode is
      IPv4 over IPv6.

   o  The local mobility anchor MUST create IPv4 host route(s) for
      tunneling the packets received for any of the mobile node's home
      address(es) associated with this mobility session.

   o  The local mobility anchor MUST send the Proxy Binding
      Acknowledgement message with the Status field set to 0 (Proxy
      Binding Update Accepted).  The message MUST be constructed as
      specified in Section 3.1.2.6.

3.1.2.3.  Binding Lifetime Extension (No handoff)

   All the consideration from Section 5.3.2 of [RFC-5213] MUST be
   applied.


3.1.2.4.  Binding Lifetime Extension (After handoff)

   o  The local mobility anchor MUST remove the previously created host
      route(s), towards the mobile access gateway where the mobile node
      was anchored prior to the handoff.

   o  The local mobility anchor MUST create a host route(s) for
      tunneling the packets received for any of the mobile node's home
      address(es) associated with this mobility session.

   o  The required forwarding state identified in Section 5.3.6 of [RFC-
      5213] is for IPv6 payload traffic.  Those considerations apply for
      IPv4 payload traffic as well.  However, if IPv4 transport is in
      use, considerations from Section 4.0 MUST be applied.



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3.1.2.5.  Binding De-Registration

   All the consideration from Section 5.3.5 of [RFC-5213] MUST be
   applied.  Additionally, for removing the routing state as part of the
   Binding Cache entry deletion, any IPv4 host route(s) added for this
   mobility session MUST be removed.

3.1.2.6.  Constructing the Proxy Binding Acknowledgement Message

   The local mobility anchor when sending the Proxy Binding
   Acknowledgement message to the mobile access gateway MUST construct
   the message as specified in Section 5.3.6 of [RFC-5213].
   Additionally, the following considerations MUST be applied.

   o  Section 5.3.6 of [RFC-5213] requires the local mobility anchor to
      include at least one instance of Home Network Prefix option in the
      Proxy Binding Acknowledgement message that it sends to the mobile
      access gateway.  However, if the received Proxy Binding Update
      message has only the IPv4 Home Address option and did not contain
      the Home Network Prefix option(s), then the local mobility anchor
      MUST NOT include the Home Network Prefix option in the reply.

   o  The IPv4 Address Acknowledgement option(s) MUST be present in the
      Proxy Binding Acknowledgement message.

      1.  If the Status field is set to a value greater than or equal to
          128, i.e., if the Proxy Binding Update is rejected, then there
          MUST be an IPv4 Address Acknowledgement option for each of the
          IPv4 Home Address options present in the request and with the
          address value and the prefix length in the option set to the
          values present in the corresponding request option.  The
          status field value in the option must be set to the specific
          error code.

      2.  For all other cases, there MUST be an IPv4 Address
          Acknowledgement option for each of the assigned IPv4 home
          addresses assigned for that mobility session and with the
          value in the option set to the allocated address value.  The
          prefix length in the option MUST be set to the prefix length
          of the allocated address.  The status field value in the
          option must be set to 0 (Success).

   o  The IPv4 Default-Router Address option MUST be present, if the
      Status field value in the Proxy Binding Acknowledgement message is
      set to 0 (Proxy Binding Update Accepted).  Otherwise, the option
      MUST NOT be present.  If the option is present, the default-router
      address in the option MUST be set to the mobile node's default-
      router address.



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3.1.2.7.  Binding Cache Entry Lookup Considerations

   The Binding Cache entry lookup considerations specified in Section
   5.4.1.1 of [RFC-5213] is for using the Home Network Prefix as the key
   parameter for identifying the Binding Cache entry.  When using an
   IPv4 address with a NON_ZERO value, the exact same considerations
   specified in Section 5.4.1.1 of [RFC-5213] MUST be applied, with the
   exception of using an IPv4 home address in place of an IPv6 home
   network prefix.

3.1.3.  Routing Considerations for the Local Mobility Anchor


   Intercepting Packets Sent to the Mobile Node's IPv4 home address:

   o  When the local mobility anchor is serving a mobile node, it MUST
      be able to receive packets that are sent to any of the mobile
      node's IPv4 addresses.  In order for it to receive those packets,
      it MUST advertise a connected route in to the Routing
      Infrastructure for the mobile node's IPv4 home address or for its
      home subnet.  This essentially enables IPv4 routers in that
      network to detect the local mobility anchor as the last-hop router
      for that subnet.


   Forwarding Packets to the Mobile Node:

   o  On receiving a packet from a correspondent node with the
      destination address matching a mobile node's IPv4 home address,
      the local mobility anchor MUST forward the packet through the bi-
      directional tunnel setup for that mobile node.

   o  The format of the tunneled packet when payload protection is not
      enabled:


        IPv6 header (src= LMAA, dst= Proxy-CoA       /* Tunnel Header */
           IPv4 header (src= CN, dst= IPv4-MN-HOA )  /* Packet Header */
              Upper layer protocols                  /* Packet Content*/



                   Figure 2: Tunneled Packets from LMA to MAG


   Forwarding Packets Sent by the Mobile Node:





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   o  All the reverse tunneled packets that the local mobility anchor
      receives from the mobile access gateway, after removing the tunnel
      header MUST be routed to the destination specified in the inner
      IPv4 packet header.  These routed packets will have the source
      address field set to the mobile node's IPv4 home address.

3.2.  Mobile Access Gateway Considerations


3.2.1.  Extensions to Binding Update List Entry

   For supporting the IPv4 home address mobility feature, the conceptual
   Binding Update List entry data structure needs to be extended with
   the following additional fields.

   o  List of IPv4 home addresses assigned to the mobile node's attached
      interface.  These IPv4 home addresses may have been statically
      configured in the mobile node's policy profile, or, may have been
      dynamically allocated by the local mobility anchor through the
      received Proxy Binding Acknowledgement message.  Each of these
      IPv4 home address entries also includes the corresponding subnet-
      mask.

   o  The IPv4 default-router address of the mobile node.  This is
      acquired from the mobile node's local mobility anchor through the
      received Proxy Binding Acknowledgment message.

3.2.2.  Extensions to Mobile Node's Policy Profile

   For supporting this feature the mobile node's policy profile,
   specified in Section 6.2 of [RFC-5213] MUST be extended with the
   following additional fields.


   Extensions to the mandatory section of the policy profile:

   o  This field indicates the scope of IP address mobility support that
      needs to be extended for the mobile node.  If the mobile access
      gateway should enable support for IPv4, IPv6 or IPv4/IPv6 home
      address mobility support.


   Extensions to the optional section of the policy profile:

   o  The IPv4 home addresses assigned to the mobile node's attached
      interface.  These addresses have to be maintained on a per-
      interface basis.  The specific details on how the network
      maintains the association between the addresses and the interfaces



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      is outside the scope of this document.  These address entries also
      include the corresponding prefix length.

3.2.3.  Signaling Considerations


3.2.3.1.  Mobile Node Attachment and Initial Binding Registration

   After detecting a new mobile node on its access link, the mobile
   access gateway on the access link MUST determine if IPv4 home address
   mobility support needs to be enabled for that mobile node.  The
   mobile node's policy profile specifies if IPv4-only, IPv6-only or
   IPv4/IPv6 home address mobility service needs to be enabled for that
   mobile node.  Based on those policy considerations, if it is
   determined that IPv4 home address mobility support is required to be
   enabled for the mobile node, the considerations from section 6.9.1.1
   of [RFC-5213] MUST be applied with the following exceptions.

   o  The IPv4 Home Address option(s) MUST be present in the Proxy
      Binding Update request.

      *  If the mobile access gateway learns the mobile node's IPv4 home
         address(es) either from its policy profile, or from other means
         the mobile access gateway MAY choose to request the local
         mobility anchor to allocate the requested addresses by
         including an IPv4 Home Address option for each of those
         addresses.  The IPv4 address and the prefix length fields in
         the option MUST be set to that specific address and its prefix
         length.  The (P) flag in the option MUST be set to 0.

      *  The mobile access gateway MAY also choose to request the local
         mobility anchor for dynamic home address allocation.  It can
         include exactly one instance of the IPv4 home address option
         with the IPv4 address value, prefix length fields and (P) flag
         in the option set to a ALL_ZERO value.  This essentially serves
         as a request to the local mobility anchor for the IPv4 home
         address allocation.

   o  The Proxy Binding Update message MUST be constructed as specified
      in Section 6.9.1.5.  However, the Home Network Prefix option(s)
      MUST be present in the Proxy Binding Update only if IPv6 home
      address mobility support also needs to be enabled for the mobile
      node.  Otherwise, the Home Network Prefix option(s) MUST NOT be
      present.

   o  When using IPv4 transport for carrying the signaling messages, the
      related considerations from section 4.0 MUST be applied.




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3.2.3.2.  Receiving Proxy Binding Acknowledgement

   All the considerations from section 6.9.1.2 of [RFC-5213] MUST be
   applied with the following exceptions.

   o  If the received Proxy Binding Acknowledgement message has the
      Status field value set to
      NOT_AUTHORIZED_FOR_IPV4_HOME_ADDRESS_SUPPORT (The mobile node is
      not authorized for IPv4 home address support), the mobile access
      gateway SHOULD NOT send a Proxy Binding Update message including
      the IPv4 Home Address option(s) till an administrative action is
      taken.

   o  If the received Proxy Binding Acknowledgement message has the
      Status field value set to NOT_AUTHORIZED_FOR_REQ_IPV4_HOME_ADDRESS
      (The mobile node is not authorized for the requesting IPv4 home
      address), the mobile access gateway SHOULD NOT request for the
      same address again, but MAY request the local mobility anchor to
      do the assignment of address by including exactly one instance if
      IPv4 Home Address option with the address value set to ALL_ZERO.

   o  If there is no IPv4 Address Acknowledgement option present in the
      received Proxy Binding Acknowledgement message, the mobile access
      gateway MUST NOT enable IPv4 support for the mobile node and the
      rest of the considerations from this section can be skipped.

   o  If the received Proxy Binding Acknowledgement message has the
      Status field value in the IPv4 Address Acknowledgement Option set
      to a value that indicates that the request was rejected by the
      local mobility anchor, the mobile access gateway MUST NOT enable
      forwarding for that specific IPv4 home address.

   o  If the received Proxy Binding Acknowledgement message has the
      Status field value set to 0 (Proxy Binding Update accepted), the
      mobile access gateway MUST update a Binding Update List entry for
      that mobile node.  The entry MUST be updated with the assigned
      IPv4 home address(es).

   o  The bi-directional established with the local mobility anchor with
      IPv4 or IPv6 transport and using any of the supported
      encapsulation mode, as per [RFC-5213] or as per this specification
      when using IPv4 transport, MUST be enabled to carry IPv4 traffic.

   o  The mobile access gateway MUST set up the route for forwarding the
      IPv4 packets received from the mobile node through the bi-
      directional tunnel set up for that mobile node.





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3.2.3.3.  Binding Re-Registration and De-Registrations

   When sending a Proxy Binding Update either for extending the lifetime
   of a mobility session or for de-registering the mobility session, the
   respective considerations from [RFC-5213] MUST be applied.  However,
   the following additional considerations MUST be applied.

   o  There MUST be an IPv4 Home Address option for each of the assigned
      IPv4 home address(es) for that mobility session.  The IPv4 address
      and the prefix length fields in the option MUST be set to that
      specific address and its prefix length.  The (P) flag in the
      option MUST be set to 0.

   o  The Home Network Prefix option(s) MUST NOT be present if the same
      option(s) was not present in the initial Proxy Binding Update
      message.  Otherwise considerations from [RFC-5213] with respect to
      this option MUST be applied.

3.2.4.  Routing Considerations for the Mobile Access Gateway


   o  On receiving a packet from the bi-directional tunnel established
      with the mobile node's local mobility anchor, the mobile access
      gateway MUST remove the outer header before forwarding the packet
      to the mobile node.

   o  Considerations from Section 6.10.3 of [RFC-5213] MUST be applied
      with respect the local routing and on the use of
      EnableMAGLocalRouting flag.

   o  On receiving a packet from a mobile node connected to its access
      link, the packet MUST be forwarded to the local mobility anchor
      through the bi-directional tunnel established with the local
      mobility anchor.  The encapsulation considerations specified in
      section 3.1.3 MUST be applied.

3.3.  Mobility Options and Status Codes

   For supporting IPv4 home address mobility feature, this specification
   defines the following new options and Status Codes.


3.3.1.  IPv4 Default-Router Address Option

   A new option, IPv4 Default-Router Address Option is defined for using
   it in the Proxy Binding Acknowledgment message sent by the local
   mobility anchor to the mobile access gateway.  This option can be
   used for sending the mobile node's IPv4 default-router address.



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   The IPv4 Default-Router Address option has an alignment requirement
   of 4n.  Its format is as follows:


       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      |         Reserved (R)          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  IPv4 Default Router Address                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Type
           <IANA>

       Length

           8-bit unsigned integer indicating the length of the option in
           octets, excluding the type and length fields. This field MUST
           be set to 6.

       Reserved (R)

           This 8-bit field is unused for now.  The value MUST be
           initialized to 0 by the sender and MUST be ignored by the
           receiver.

       IPv4 Default-Router Address

           A four-byte field containing the mobile node's default router
           address.


               Figure 3: IPv4 Default-Router Address Option

3.3.2.  Status Codes

   This document defines the following new Status values for use in the
   Proxy Binding Acknowledgement message.  These values are to be
   allocated from the same numbering space, as defined in Section 6.1.8
   of [RFC-3775].


   NOT_AUTHORIZED_FOR_IPV4_HOME_ADDRESS: IANA







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      Mobile node not authorized for the requesting IPv4 home address

3.4.  Supporting DHCP Based Address Configuration


   This section explains how DHCP based address configuration support
   can be enabled for a mobile node in a Proxy Mobile IPv6 domain.  It
   explains the protocol operation, supported DHCP server deployment
   configurations and the protocol interactions between DHCP agents and
   mobility entities in each of the supported configurations.


   This specification supports the following two DHCP deployment
   configurations.

   o  DHCP relay agent co-located with the mobile access gateway.

   o  DHCP server co-located in the mobile access gateway.


   The following are the configuration requirements:

   o  The DHCP server or the DHCP relay agent configured on the mobile
      access gateway is required to have an IPv4 address for exchanging
      the DHCP messages with the mobile node.  This address can either
      the IPv4 Proxy Care-of Address or the mobile node's default-router
      address provided by the local mobility anchor.  Optionally, all
      the DHCP servers co-located with the mobile access gateways in the
      Proxy Mobile IPv6 domain can be configured with a fixed IPv4
      address.  This can be a virtual address used only for the DHCP
      protocol communication on any of the access links.  This address
      will be the server identifier in the DHCP messages.

   o  The DHCP server identifies the a DHCP client either from the
      client identifier or the client hardware address (chaddr).  A
      mobile node in a Proxy Mobile IPv6 domain may present any of these
      identifiers to the DHCP server as long as the identifier remains
      the same through out the mobile node's attachment in that Proxy
      Mobile IPv6 domain.  If the client hardware address is used as the
      identifier and if the mobile node performs an handoff between two
      interfaces, this hardware identifier will change and the DHCP
      server will not be able to identify the mobile node.  Thus, it is
      recommended that the DHCP client in the mobile node is configured
      to use a stable client identifier that does not change during the
      active life of that DHCP session.

   o  All the DHCP servers co-located with the mobile access gateways in
      a Proxy Mobile IPv6 domain SHOULD be configured with the same set



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      of DHCP option values (Ex: DNS Server, SIP Server ..etc.).

3.4.1.  DHCP Server co-located with the Mobile Access Gateway

   Figure 4 shows the operational sequence of the home address
   assignment when a DHCP server is co-located with the mobile access
   gateways.



     MN   MAG(DHCP-S)  LMA
      |------>|        |    1. DHCPDISCOVERY
      |       |------->|    2. Proxy Binding Update *
      |       |<-------|    3. Proxy Binding Acknowledgement (IPv4HoA)
      |       |========|    4. Tunnel/Route Setup*
      |<------|        |    5. DHCPOFFER  (IPv4 HoA)
      |------>|        |    6. DHCPREQUEST (IPv4 HoA)
      |<------|        |    7. DHCPACK
      |       |        |
      * DHCP discovery (no.1) and PBU (no.2) are operated in parallel.
      * Tunnel/Route setup(no.4) and DHCPOFFER/REQUEST/ACK(no.5-7)
        are processed in parallel.


    Figure 4: Overview of DHCP Server located at Mobile Access Gateway


   Initial IPv4 Home Address Assignment:

   o  If the mobile node attached to the access link sends a
      DHCPDISCOVERY message, the DHCP server co-located with the mobile
      access gateway will trigger the mobile access gateway to complete
      the Proxy Mobile IPv6 signaling.  This is the required interaction
      between these two protocols.  If the mobile access gateway is
      unable to complete the Proxy Mobile IPv6 signaling or if the local
      mobility anchor does not assign an IPv4 address for the mobile
      node, the mobile access gateway MUST tear down the point-to-point
      link shared with the mobile node.

   o  After a successful completion of the Proxy Mobile IPv6 signaling
      and acquiring the mobile node's IPv4 home address assigned by the
      local mobility anchor, the DHCP server on the mobile access
      gateway will send a DHCP offer message to the mobile node.  The
      offered address will the mobile node's IPv4 home address, assigned
      by the local mobility anchor.  The 'siaddr' field of the DHCPOFFER
      message will be set to the mobile node's default-router address or
      to the globally fixed address used for all DHCP servers.  The
      DHCPOFFER message will be unicasted to the mobile node.



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   o  If the mobile node sends the DHCPREQUEST message, the DHCP server
      will send DHCPACK message, as per [RFC-2131].


   IPv4 Home Address Renewal with the DHCP server (No Handoff):

   o  When the DHCP client goes into the DHCP-RENEWING-STATE [RFC-2131],
      it simply unicasts DHCPREQUEST message including the assigned IPv4
      home address in the 'requested IPv4 address' option.  The
      DHCPREQUEST is sent to the address specified in 'server
      identifier' field of the previously received DHCPOFFER and DHCPACK
      messages.

   o  The DHCP server will send a DHCPACK to the mobile node.


   IPv4 Home Address Renewal with the different DHCP server (After
   Handoff):



   1. The use of Virtual DHCP server address
     MN   oMAG(DHCP-S) nMAG(DHCP-S)
      |       :        |
    RENEW------------->|    1. DHCPREQUEST (IPv4 HoA)
    BOUND<-------------|    2. DHCPACK or DHCPNACK
      |       :        |

   2. The use of FORCERENEW [RFC3-203]
     MN   oMAG(DHCP-S) nMAG(DHCP-S)
      |       :        |
    RENEW------------->|    1. DHCPREQUEST*a (IPv4 HoA)
      |<---------------|    2. FORCERENEW
      |--------------->|    3. DHCPREQUEST*b (IPv4 HoA)
    BOUND<-------------|    4. DHCPACK or DHCPNACK
      |       :        |
                            *a DHCPREQUEST sent to oMAG
                            *b DHCPREQUEST sent to nMAG

   3. The use of Individual DHCP server address
     MN   oMAG(DHCP-S) nMAG(DHCP-S)
      |       :        |
    RENEW------------->|    1. DHCPREQUEST (IPv4 HoA)
      |       :        |     (discarding & timeout)
    REBINDING--------->|    2. DHCPDISCOVERY
      |<---------------|    3. DHCPOFFER  (IPv4 HoA)
      |--------------->|    4. DHCPREQUEST(IPv4 HoA)
    BOUND<-------------|    5. DHCPACK    (IPv4 HoA)



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      |       :        |


            Figure 5: Renewing Address to different DHCP server

   o  When the DHCP client goes into the DHCP-RENEWING-STATE [RFC-2131],
      it directly unicasts DHCPREQUEST message to the DHCP server.  If
      the mobile node moves and attaches to a new mobile access gateway,
      it needs to update the DHCP server address to the new one (i.e.
      the address of the currently attached mobile access gateway).
      Thus, one of following operations is required.

   o  If the IPv4 virtual DHCP address is used, the DHCPREQUEST for
      renewing address is received by the mobile access gateway to which
      the mobile node is currently attached.  The mobile access gateway
      SHOULD reply DHCPACK or DHCPNACK depending on the correctness of
      the requesting IPv4 home address in the DHCPREQUEST as shown in
      Figure 5-1).

   o  If the IPv4 virtual DHCP address is not used, the mobile node
      reconfigures the DHCP server address whenever it changes the
      attached mobile access gateway.

      *  If a mobile access gateway receives any DHCP messages unicasted
         to a different mobile access gateway from the mobile node, it
         SHOULD unicast FORCERENEW message [RFC-3203] to the mobile node
         as shown in Figure 5-2).  In the FORCERENEW, the 'server
         identifier' field MUST be overwritten by the IPv4 address of
         the current mobile access gateway so that the client can update
         the DHCP server address.

      *  If the IPv4 virtual DHCP address is not used and the FORCERENEW
         [RFC-3203] is not supported at the mobile access gateway, the
         mobile access gateway SHOULD discard any DHCPREQUEST message
         sent not to the mobile access gateway itself, so that the
         mobile node should go into the DHCP-REBINDING-STATE and
         broadcast DHCPDISCOVERY without server identifier as shown in
         Figure 5-3).


   Additional Operation:

   o  At an point the mobile access gateway fails to extend the binding
      lifetime with the local mobility anchor, it MUST send an
      unsolicited DHCPNACK to the mobile node.  It MUST also tear down
      the point-to-point link shared with the mobile node.





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3.4.2.  DHCP Relay Agent co-located with the Mobile Access Gateway

   A DHCP relay is co-located with each mobile access gateway.  A DHCP
   server is located somewhere in the Proxy Mobile IPv6 domain or is co-
   located with the local mobility anchor.  Figure 6 are the sequence of
   IPv4 home address assignment using DHCP Relay.


   MN   MAG(DHCP-R)  LMA DHCP-S
    |       |------->|      | 1. Proxy Binding Update *
    |       |<-------|      | 2. Proxy Binding Acknowledgement (IPv4HoA)
    |       |========|      | 3. Tunnel/Route Setup*
    |------>|-------------->| 4. DHCPDISCOVERY (IPv4HoA) via DHCP-R
    |<------|<--------------| 5. DHCPOFFER (IPv4 HoA) via DHCP-R
    |------>|-------------->| 6. DHCPREQUEST (IPv4 HoA) via DHCP-R
    |<------|<--------------| 7. DHCPACK via DHCP-R
    |       |        |
    * Tunnel/Route setup(no.3) and DHCPOFFER/REQUEST/ACK (no.4-7)
      are processed in parallel.


   Figure 6: Overview of the DHCP relay located at mobile access gateway


   Initial IPv4 Home Address Assignment:

   o  When the mobile access gateway receives a DHCPDISCOVERY message
      from a mobile node, it MUST check whether it has already obtained
      the IPv4 home address for the mobile node from the local mobility
      anchor.

   o  If the IPv4 home address is not yet assigned by the local mobility
      anchor, the mobile access gateway MUST send a Proxy Binding Update
      for that.

   o  If the IPv4 home address is not assigned to the mobile node by the
      local mobility anchor due to administrative policy or resource
      limitation, it MUST discard the DHCPDISCOVERY messages from the
      mobile node.

   o  Otherwise, it MUST add the DHCP relay agent information option
      [RFC-3046] to the DHCPDISCOVERY message.  The assigned IPv4 home
      address (32-bit full address) is included in the Agent Remote ID
      Sub-option of the DHCP relay agent information option.  This sub-
      option is used as a hint of address assignment of the DHCP server.

   o  When the mobile access gateway receives the DHCPOFFER from the
      DHCP server, it MUST verify whether the DHCP server offers the



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      correct IPv4 home address which is indicated in the Agent Remote
      ID Sub-option of the DHCPDISOCVERY.  If the DHCP server offers the
      different address from the expected address, the mobile access
      gateway MUST drop the DHCPOFFER.

   o  After the successful relaying the DHCPOFFER, the mobile access
      gateway acts as a regular DHCP relay agent as [RFC-2131].

   o  As shown in Figure 6, the DHCP messages MAY be sent across an
      administrative boundaries.  The operators MUST ensure to secure
      these messages.  All the DHCP messages relayed by the mobile
      access gateway can be tunneled over the local mobility anchor if
      needed.  Alternatively, if the networks in the Proxy Mobile IPv6
      domain are secured enough, the mobile access gateway just relays
      the DHCP messages to the server without the tunnel.  For doing
      this, all the mobile access gateway MUST have the route toward the
      DHCP server.  More remarks can be found in Section 7.


   IPv4 Home Address Renewal to the same DHCP server: (No Hanover)

   o  When the DHCP client goes into the DHCP-RENEWING-STATE [RFC-2131],
      it directly unicasts DHCPREQUEST message to the DHCP server.  The
      DHCP relay agent cannot receive the DHCPREQUEST for renewing
      addresses.  Thus, one of following operations is required.

      *  The DHCP relay agent SHOULD intercept all the DHCP packets
         regardless of the destination address.  Since the link between
         a mobile node and a mobile access gateway is the point-to-point
         link, it is possible to check the DHCP packets at the interface
         by enabling the promiscuous mode.

      *  The cost of packets monitoring is not negligible.  Therefore,
         The DHCP relay agent MAY use the DHCP Server Identifier
         Override Sub-option [RFC-5107] to intercept DHCPREQUESTs for
         the address renewal.  The DHCP client uses the DHCP server
         address which is overridden by the DHCP relay agent address as
         a destination address of DHCPREQUEST.  The DHCP Server
         Identifier Override Sub-option is recommended only when the
         Virtual DHCP address is configured on all the mobile access
         gateways.  Otherwise, the DHCP relay agent address is changed
         when the mobile node changes the attached mobile access
         gateway.  As a result, the DHCP relay agent MUST monitor DHCP
         packets by force as described above.

   o  Once the DHCP relay agent intercepts the DHCPREQUEST from the
      mobile node, it MUST verify the requesting IPv4 home address
      stored in the DHCPREQUEST message.  The verification is operated



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      by checking it with the binding update list for the mobile node.
      If the requesting IPv4 home address is not registered to the local
      mobility anchor, the mobile access gateway MUST NOT relay the
      DHCPREQUEST and MUST discard it.

   o  If the address verification is successfully completed, the DHCP
      relay agent SHOULD forward the DHCPREQUEST to the DHCP server.


   Additional Operations:

   o  If the mobile access gateway sends Proxy Binding Update for the
      IPv4 home address and receives the unsuccessful Proxy Binding
      Acknowledgement (by indicating the error codes), it MUST send
      unsolicited DHCPNACK for the invalid IPv4 home address to the
      mobile node.  XXXX



































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4.  IPv4 Transport Support

   The Proxy Mobile IPv6 specification [RFC-5213] requires the signaling
   messages exchanged between the local mobility anchor and the mobile
   access gateway to be over an IPv6 transport.  The extensions defined
   in this section allow the exchange of signaling messages over an IPv4
   transport when the local mobility anchor and the mobile access
   gateway are separated by an IPv4 network and are reachable using only
   IPv4 addresses.


             IPv4-Proxy-CoA                      IPv4-LMAA
                    |         + - - - - - - +        |
    +--+          +---+      /               \     +---+          +--+
    |MN|----------|MAG|=====   IPv4  Network  =====|LMA|----------|CN|
    +--+          +---+      \               /     +---+          +--+
                              + - - - - - - +



                     Figure 7: IPv4 Transport Network

   When the local mobility anchor and the mobile access gateway are
   configured and reachable using only IPv4 addresses, the mobile access
   gateway serving a mobile node can potentially send the signaling
   messages over IPv4 transport and register its IPv4 address as the
   care-of address in the mobile node's Binding Cache entry.  An IPv4
   tunnel (with any of the supported encapsulation modes) can be used
   for tunneling the mobile node's data traffic.  The following are the
   key aspects of this feature.

   o  The local mobility anchor and the mobile access gateway are both
      configured and reachable using only an IPv4 address.
      Additionally, both these entities are also IPv6 enabled and have
      configured IPv6 addresses on its interfaces, as specified in [RFC-
      5213], but are reachable only over an IPv4 transport.

   o  The mobile access gateway can be potentially in a private IPv4
      network behind a NAT [RFC-3022] device, with a private IPv4
      address configured on its egress interface.  However, the local
      mobility anchor must not be behind a NAT and must be using a
      globally routable IPv4 address.

   o  The Proxy Mobile IPv6 signaling messages exchanged between the
      local mobility anchor and the mobile access gateway for
      negotiating the IPv4 transport will be encapsulated and carried as
      IPv4 packets.  However, these signaling messages are fundamentally
      IPv6 messages using the mobility header and the related semantics



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      as specified in base Proxy Mobile IPv6 specification [RFC-5213],
      but carried as a payload in an IPv4 packet (IPv4-UDP encapsulation
      mode).

   o  The mobile node can be an IPv6, IPv4 or a dual IPv4/IPv6 node and
      the IPv4 transport support specified in this section is agnostic
      to the type of address mobility enabled for that mobile node.

   o  The IPv4 tunnel established between the local mobility anchor and
      the mobile access gateway (with any of the supported encapsulation
      modes over IPv4 transport) will be used for carrying the mobile
      node's IPv4 and IPv6 traffic.  The supported encapsulation modes
      for carrying mobile node's IPv4 or IPv6 packets when using IPv4
      transport are as shown below.

      *  IPv4

      *  IPv4-UDP (Payload packet carried in an IPv4 packet with UDP
         header)

      *  IPv4-UDP-TLV (Payload packet carried in an IPv4 packet with UDP
         and TLV header.  Refer to [ID-DSMIP6]).

      *  IPv4-UDP-ESP (Payload packet carried in an IPv4 packet with UDP
         and ESP headers.  Refer to [RFC-3948].

4.1.  Local Mobility Anchor Considerations

4.1.1.  Extensions to Binding Cache Entry

   For supporting this feature, the conceptual Binding Cache entry data
   structure maintained by the local mobility anchor [RFC-5213] MUST be
   extended with the following additional parameters.

   o  The IPv4 address of the mobile access gateway.  This is the
      address configured on the egress interface of the mobile access
      gateway that sent the Proxy Binding Update message.  This address
      can be obtained from the IPv4 Care-of Address option, present in
      the received Proxy Binding Update message.  If the option was not
      present in the request, this field MUST be set to the source
      address of the IPv4 header of the received Proxy Binding Update
      message.  However, if the received Proxy Binding Update message is
      not sent as an IPv4 packet, this field MUST be set to ALL_ZERO
      value.

   o  The IPv4 NAT translated address of the mobile access gateway.  If
      the mobile access gateway is not behind a NAT [RFC-3022], this
      address will be the same as the address configured on the egress



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      interface of the mobile access gateway.  This address can be
      obtained from the IPv4 header of the received Proxy Binding Update
      message.  However, if the received Proxy Binding Update message is
      not sent as an IPv4 packet, this field MUST be set to ALL_ZERO
      value.

4.1.2.  Extensions to Mobile Node's Policy Profile

   For supporting this feature the mobile node's policy profile,
   specified in Section 6.2 of [RFC-5213] MUST be extended with the
   following additional fields.  This are mandatory fields of the policy
   profile required for supporting this feature.

   o  A flag indicating if IPv4 transport should be used.  The value of
      this flag can be different at different mobile access gateway.
      The specific details on how this flag is maintained on a per
      mobile access gateway basis is outside the scope of this document.

   o  The IPv4 address of the local mobility anchor (IPv4-LMAA).

4.1.3.  Signaling Considerations

   This section provides the rules for processing the Proxy Mobile IPv6
   signaling messages received over IPv4 transport.  The local mobility
   anchor MUST apply these signaling rules on the IPv4 UDP encapsulated
   Proxy Binding Update messages received on DSMIP UDP port [ID-DSMIP6].

4.1.3.1.  Processing Proxy Binding Updates

   o  If the received Proxy Binding Update message (encapsulated in IPv4
      UDP packet) is protected using IPsec ESP header, then the message
      MUST be authenticated as described in Section 4 of [RFC-5213].
      However, if the IPv4 packet is not protected using IPsec ESP
      header, then the message MUST be authenticated after removing the
      outer IPv4 UDP header.

   o  All the considerations from Section 5.3.1 of [RFC-5213] MUST be
      applied on the encapsulated Proxy Binding Update message, after
      removing the outer IPv4 UDP header.

   o  If there is an IPv4 Care-of Address present in the request, the
      NAT presence detection procedure specified in Section 4.1.3.3 MUST
      be used for detecting the NAT in the path.

   o  Upon accepting the request, the local mobility anchor MUST set up
      an IPv4 bi-directional tunnel to the mobile access gateway.  The
      tunnel endpoint addresses are IPv4-LMAA and the IPv4-Proxy-CoA.
      The encapsulation mode MUST be determined from the below



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      considerations.

      *  If the NAT is detected on the path, then the encapsulation mode
         for the tunnel MUST be set to IPv4-UDP.  Otherwise the
         encapsulation mode MUST be set to IPv4.  However, if the (F)
         flag in the received Proxy Binding Update message is set to
         value of 1 and even if NAT is not detected, then the
         encapsulation mode MUST be set to IPv4-UDP.

      *  If the (T) flag in the Proxy Binding Update message is set to
         value of 1, then the encapsulation mode MUST be set to IPv4-
         UDP-TLV.

   o  The local mobility anchor MUST send the Proxy Binding
      Acknowledgement message with the Status field value set to 0
      (Proxy Binding Update Accepted).  The message MUST be constructed
      as specified in Section 4.1.3.2.

4.1.3.2.  Constructing the Proxy Binding Acknowledgement Message

   The local mobility anchor when sending the Proxy Binding
   Acknowledgement message to the mobile access gateway MUST construct
   the message as specified in Section 5.3.6 of [RFC-5213].  However, if
   the received Proxy Binding Update message was encapsulated in an UDP
   header of an IPv4 packet, the following additional considerations
   MUST be applied.

   o  The NAT Detection option [ID-DSMIP6] MUST be present only if there
      is a IPv4 Care-of Address option present in the received Proxy
      Binding Update and if the NAT detection procedure resulted in
      detecting a NAT on path.  In all other cases, the option MUST NOT
      be present.

   o  The Proxy Binding Acknowledgement message MUST be encapsulated in
      an UDP header of an IPv4 packet.

   o  The source address in the IPv4 header of the message MUST be set
      to the destination IPv4 address of the received request.

   o  If the mobile access gateway and the local mobility anchor are
      using globally routable IPv4 addresses and if there is a security
      associated that is based of IPv4 addresses, then the encapsulated
      IPv4 packet (containing the IPv6 PBA) MUST be protected using
      IPsec ESP [RFC-4301] mode and additionally there is no need to
      apply IPsec ESP header on the IPv6 packet.  In all other cases,
      the Proxy Binding Acknowledgement message MUST be protected using
      IPsec prior to the IPv4 UDP encapsulation.




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   o  The format of the Proxy Binding Acknowledgement message
      encapsulated in an IPv4 UDP packet and protected using IPv6
      security association.


            IPv4 header (src=IPv4-LMAA, dst=pbu_src_address)
               UDP header (sport=DSMIP_PORT, dport= pbu_sport)
                   /* IPv6 PBU Packet protected with ESP header */


        Figure 8: Proxy Binding Acknowledgment Message encapsulated in
                                 IPv4 header

   o  The format of the Proxy Binding Acknowledgement message
      encapsulated in an IPv4 UDP packet and protected using IPv4
      security association.


            IPv4 header (src=IPv4-LMAA, dst=pbu_src_address)
               ESP Header
                  UDP header (sport=DSMIP_PORT, dport= pbu_sport)
                     /* IPv6 PBU Packet protected with no ESP header */


       Figure 9: Proxy Binding Acknowledgment encapsulated in IPv4 ESP
                                    header

4.1.3.3.  NAT Presence Detection

   When the transport network between the local mobility anchor and the
   mobile access gateway is an IPv4 network, the mobile access gateway
   will send the Proxy Binding Update messages encapsulated in the IPv4-
   UDP packet.  On receiving this Proxy Binding Update packet
   encapsulated in an IPv4-UDP packet, the local mobility anchor if it
   detects a NAT on the path, will send the Proxy Binding Acknowledgment
   message with the NAT Detection Option.  The presence of this option
   in the Proxy Binding Acknowledgment is an indication to the mobile
   access gateway about the presence of NAT in the path.  On detecting
   the NAT in the path, both the local mobility anchor and the mobile
   access gateway MUST set the encapsulation mode of the tunnel to IPv4-
   UDP-based encapsulation.  The specific details around the NAT
   detection and the related logic is described in DSMIPv6 specification
   [ID-DSMIP6].

4.1.4.  Routing Considerations






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4.1.4.1.  Forwarding Considerations


   Forwarding Packets to the Mobile Node:

   o  On receiving an IPv4 or an IPv6 packet from a correspondent node
      with the destination address matching any of the mobile node's
      IPv4 or IPv6 home addresses, the local mobility anchor MUST
      forward the packet through the bi-directional tunnel set up for
      that mobile node.

   o  The format of the tunneled packet is shown below.


  IPv4 Header (src= IPv4-LMAA, dst= IPv4-Proxy-CoA)] /* Tunnel Header */
    [UDP Header (src port=DSMIPv6, dst port=Z]   /* If UDP encap nego */
      [TLV Header]                               /* If TLV negotiated */
        /* IPv6 or IPv4 Payload Packet */
               IPv6 header (src= CN, dst= MN-HOA)
                          OR
               IPv4 header (src= CN, dst= IPv4 MN-HoA)


               Figure 10: Tunneled IPv4 Packet from LMA to MAG


   o  Forwarding Packets Sent by the Mobile Node:

      *  All the reverse tunneled packets (IPv4 and IPv6) that the local
         mobility anchor receives from the mobile access gateway, after
         removing the tunnel header (i.e., the outer IPv4 header along
         with the UDP and TLV header, if negotiated) MUST be routed to
         the destination specified in the inner packet header.  These
         routed packets will have the source address field set to the
         mobile node's home address.

4.1.4.2.  ECN Considerations

   The ECN considerations specified in Section 5.6.3 of [RFC-5213] apply
   for the IPv4 transport tunnels as well.  The mobility agents at the
   tunnel entry and exit points MUST handle ECN information as specified
   in that document.

4.1.4.3.  Bi-Directional Tunnel Management

   The Tunnel Management considerations specified in section 5.6.1 of
   [RFC-5213] apply for the IPv4 transport tunnels as well, with just
   one difference that the encapsulation mode is different.



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4.2.  Mobile Access Gateway Considerations

4.2.1.  Extensions to Binding Update List Entry

   For supporting this feature, the conceptual Binding Update List entry
   data structure maintained by the mobile access gateway [RFC-5213]
   MUST be extended with the following additional parameters.

   o  The IPv4 address of the local mobility anchor.  This address can
      be obtained from the mobile node's policy profile.

   o  The IPv4 address of the mobile access gateway.  This is the
      address configured on the egress interface of the mobile access
      gateway and is registered with the mobile node's local mobility
      anchor as the IPv4 Proxy-CoA.  However, if the mobile access
      gateway is in a private IPv4 network and behind a NAT, the address
      that is registered with the mobile node's local mobility anchor is
      the NAT translated public IPv4 address.

4.2.2.  Signaling Considerations

   The mobile access gateway when sending a Proxy Binding Update message
   to the local mobility anchor MUST construct the message as specified
   in Section 6.9.1.5.  However, if the mobile access gateway is in an
   IPv4-only access network, the following additional considerations
   MUST be applied.

   o  The Proxy Binding Update message MUST be encapsulated in an UDP
      header of an IPv4 packet.

   o  The IPv4 Care-of Address option [ID-DSMIP6] MUST be present.  The
      IPv4 address in the option MUST be set to the mobile access
      gateway's IPv4-Proxy-CoA.

   o  The packet MUST be constructed as specified in Section 4.2.3.

   o  When sending a Proxy Binding message for extending the lifetime of
      a currently existing mobility session or for de-registering the
      mobility session, the Proxy Binding Update message MUST be
      constructed as the initial request.


   Receiving Proxy Binding Acknowledgement

   o  If the received Proxy Binding Acknowledgement message
      (encapsulated in IPv4 UDP packet) is protected using IPsec ESP
      header, then the message MUST be authenticated as described in
      Section 4 of [RFC-5213].  However, if the IPv4 packet is not



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      protected using IPsec ESP header, then the message MUST be
      authenticated after removing the outer IPv4 UDP header.

   o  All the considerations from Section 6.9.1.2 of [RFC-5213] MUST be
      applied on the encapsulated Proxy Binding Acknowledgement message,
      after removing the outer IPv4 UDP header.

   o  If the Status field indicates Success, the mobile access gateway
      MUST setup a bi-directional tunnel to the local mobility anchor.

   o  Upon accepting the request, the local mobility anchor MUST set up
      an IPv4 bi-directional tunnel to the mobile access gateway.  The
      tunnel endpoint addresses are IPv4-LMAA and the IPv4-Proxy-CoA.
      The encapsulation mode MUST be determined from the below
      considerations.

      *  If there is a NAT Detection option [ID-DSMIP6] in the received
         Proxy Binding Acknowledgement message, then the encapsulation
         mode for the tunnel MUST be set to IPv4-UDP.  Otherwise the
         encapsulation mode MUST be set to IPv4.

      *  If the (T) flag in the Proxy Binding Acknowledgement message is
         set to value of 1, then the encapsulation mode MUST be set to
         IPv4-UDP-TLV.

4.2.2.1.  Constructing the Proxy Binding Update Message

   o  The source address in the IPv4 header MUST be set to IPv4-Proxy-
      CoA of the mobile access gateway and the destination address MUST
      be set to the local mobility anchor's IPv4-LMAA.

   o  The IPv4 Care-of Address option [ID-DSMIP6] MUST be present.  The
      address MUST be set to the mobile access gateway's IPv4-Proxy-CoA.

   o  If the configuration variable ForceIPv4UDPEncapsulationSupport is
      set to value of 1, then the (F) flag in the Proxy Binding Update
      message MUST be enabled.

   o  If the mobile access gateway and the local mobility anchor are
      using globally routable IPv4 addresses and if there is a security
      associated that is based of IPv4 addresses, then the encapsulated
      IPv4 packet (containing the IPv6 PBU) MUST be protected using
      IPsec ESP [RFC-4301] mode and additionally there is no need to
      apply ESP header on the IPv6 packet.  In all other cases, the
      Proxy Binding Update message MUST be protected on the IPv6 packet
      of the Proxy Binding Update message, prior to the IPv4
      encapsulation.




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   o  The format of the Proxy Binding Update message encapsulated in an
      IPv4 UDP packet with IPsec protection on the encapsulated packet:


            IPv4 header (src=IPv4-Proxy-CoA, dst=IPv4-LMAA)
               UDP header (sport=ANY, dport= DSMIP_PORT)
                   /* IPv6 PBU Packet protected with ESP header */


       Figure 11: Proxy Binding Update Message encapsulated in IPv4 UDP
                                    header

   o  The format of the Proxy Binding Update message encapsulated in an
      IPv4 UDP packet and with IPsec protection on the encapsulated
      packet:


            IPv4 header (src=IPv4-Proxy-CoA, dst=IPv4-LMAA)
               ESP Header
                  UDP header (sport=ANY, dport= DSMIP_PORT)
                     /* IPv6 PBU Packet protected with no ESP header */


       Figure 12: Proxy Binding Update Message Encapsulated with IPsec
                                  protection

4.2.2.2.  Forwarding Considerations


   Forwarding Packets Sent by the Mobile Node:

   o  On receiving an IPv4 or an IPv6 packet from the mobile node to any
      destination, the mobile access gateway MUST tunnel the packet to
      the local mobility anchor.  The format of the tunneled packet is
      shown below.  However, considerations from Section 6.10.3 of [RFC-
      5213] MUST be applied with respect the local routing and on the
      use of EnableMAGLocalRouting flag.


 IPv4 Header (src= IPv4-Proxy-CoA, dst= IPv4-LMAA)] /* Tunnel Header */
    [UDP Header (src port=DSMIPv6, dst port=Z]   /* If UDP encap nego */
        [TLV Header]                             /* If TLV negotiated */
              /* IPv6 or IPv4 Payload Packet */
              IPv6 header (src= CN, dst= MN-HOA)
                          OR
              IPv4 header (src= CN, dst= IPv4 MN-HoA)





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               Figure 13: Tunneled IPv4 Packet from LMA to MAG

   o  Forwarding Packets received from the bi-directional tunnel:

   o  On receiving a packet from the bi-directional tunnel established
      with the mobile node's local mobility anchor, the mobile access
      gateway MUST remove the outer header before forwarding the packet
      to the mobile node.











































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5.  Protocol Configuration Variables


5.1.  Local Mobility Anchor - Configuration Variables

   The local mobility anchor MUST allow the following variables to be
   configured by the system management.  The configured values for these
   protocol variables MUST survive server reboots and service restarts.


   AcceptIPv4UDPEncapsulationRequest

      This flag indicates whether or not the local mobility anchor
      should accept IPv4 UDP encapsulation support if there is NAT
      detected in the path.

      The default value for this flag is set to value of 1, indicating
      that the local mobility anchor MUST enable IPv4 UDP encapsulation
      support on detecting NAT in the path.

      When the value for this flag is set to value of 0, the local
      mobility anchor MUST NOT enable IPv4 UDP encapsulation support.


5.2.  Mobile Access Gateway - Configuration Variables


   The mobile access gateway MUST allow the following variables to be
   configured by the system management.  The configured values for these
   protocol variables MUST survive server reboots and service restarts.


   RequestIPv4UDPEncapsulationSupport

      This flag indicates whether or not the mobile access gateway
      should request the mobile node's local mobility anchor for IPv4
      UDP encapsulation support if NAT is detected in the path.

      The default value for this flag is set to value of 0, indicating
      that the mobile access gateway MUST NOT request the mobile node's
      local mobility anchor for IPv4 UDP encapsulation support.

      When the value for this flag is set to value of 1, the mobile
      access gateway MUST request the mobile node's local mobility
      anchor for IPv4 UDP encapsulation support if there is NAT detected
      in the path.

   ForceIPv4UDPEncapsulationSupport



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      This flag indicates whether or not the mobile access gateway
      should request the mobile node's local mobility anchor for forcing
      IPv4 UDP encapsulation support even when NAT is not detected in
      path.

      The default value for this flag is set to value of 0, indicating
      that the mobile access gateway MUST NOT request the mobile node's
      local mobility anchor for forcing IPv4 UDP encapsulation support
      even when NAT is not detected in path.

      When the value for this flag is set to value of 1, the mobile
      access gateway MUST force the mobile node's local mobility anchor
      for IPv4 UDP encapsulation support.

      This flag is applicable only when the flag
      RequestIPv4UDPEncapsulationSupport is set to a value of 1.

5.3.  Proxy Mobile IPv6 Domain - Configuration Variables


   All the mobile entities (local mobility anchors and mobile access
   gateways) in a Proxy Mobile IPv6 domain MUST allow the following
   variables to be configured by the system management.  The configured
   values for these protocol variables MUST survive server reboots and
   service restarts.  These variables MUST be globally fixed for a given
   Proxy Mobile IPv6 domain resulting in the same values being enforced
   on all the mobility entities in that domain.


   FixedDHCPServerId

      This variable indicates the DHCP server id that all the DHCP
      servers co-located with the mobile access gateways SHOULD
      configure in that Proxy Mobile IPv6 domain.  If this variable is
      initialized to ALL_ZERO value, it implies the use of fixed address
      is not enabled for that Proxy Mobile IPv6 domain.















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6.  IANA Considerations

   This document defines a new Mobility Header option, IPv4 Default
   Router Address option.  This option is described in Section 3.3.1.
   The Type value for this option needs to be assigned from the same
   numbering space as allocated for the other mobility options, as
   defined in [RFC-3775].

   This document also defines new Binding Acknowledgement status values,
   as described in Section 3.3.2.  The status values MUST be assigned
   from the same number space used for Binding Acknowledgement status
   values, as defined in [RFC3775].  The allocated values for each of
   these status values must be greater than 128.






































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7.  Security Considerations

   All the security considerations from the base Proxy Mobile IPv6
   protocol [RFC-5213] apply when using the extensions defined in this
   document.  Additionally, the following security considerations need
   to be applied.

   This document defines news mobility options for supporting the IPv4
   Home Address assignment and IPv4 Transport Support features.  It also
   uses some of the mobility options from DSMIPv6 specification [ID-
   DSMIP6].  These options are to be carried in Proxy Binding Update and
   Proxy Binding Acknowledgement messages.  The required security
   mechanisms specified in the base Proxy Mobile IPv6 protocol for
   protecting these signaling messages are sufficient when carrying
   these mobility options.

   This specification describes the use of IPv4 transport for exchanging
   the signaling messages between the local mobility anchor and the
   mobile access gateway.  These messages are protected using IPsec
   using the security associations established using the IPv4 transport
   addresses and offer the same security as when the messages are
   protected when using IPv6 transport.





























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8.  Contributors

   This document reflects discussions and contributions from several
   people (in alphabetical order):

   Kuntal Chowdhury

      kchowdhury@starentnetworks.com

   Vijay Devarapalli

      vijay.devarapalli@azairenet.com

   Sangjin Jeong

      sjjeong@etri.re.kr

   Basavaraj Patil

      basavaraj.patil@nsn.com

   Myungki Shin

      myungki.shin@gmail.com


9.  Acknowledgments

   The IPv4 support for Proxy Mobile IPv6 was initially covered in the
   internet-draft [draft-sgundave-mip6-proxymip6-02.txt].  We would like
   to thank all the authors of the document and acknowledge that initial
   work.

   Thanks to Jonne Soinnen, Julien Laganier, Zu Qiang, Premec Domagoj,
   Sammy Touati and Niklas Nuemann for their helpful review of this
   document.


10.  References


10.1.  Normative References

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

   [RFC-2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
   2131, March 1997.



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

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

   [ID-DSMIP6] Soliman, H. et al, "Mobile IPv6 support for dual stack
   Hosts and Routers (DSMIPv6)",
   draft-ietf-mip6-mext-nemo-v4traversal-05.txt,July 2008.

   [RFC-5213] Gundavelli, S., et.al, "Proxy Mobile IPv6", RFC 5213,
   November 2007.

10.2.  Informative References

   [RFC-2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
   2131, March 1997.

   [RFC-3011] G. Waters, "The IPv4 Subnet Selection Option for DHCP",
   RFC 3011, November 2000.

   [RFC-3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
   Address Translator (Traditional NAT)", RFC 3022, January 2001.

   [RFC-3203] Y. T'Joens and C. Hublet and P. De Schrijver, "DHCP
   reconfigure extension", RFC 3203, December 2001.

   [RFC-4977] Tsirtsis, G., Soliman, H., "Problem Statement: Dual Stack
   Mobility", RFC 4977, August 2007.

   [RFC-5107] R. Johnson and J. Jumarasamy and K. Kinnear and M. Stapp,
   "DHCP Server Identifier Override Suboption", RFC 5107, February 2008.



















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Authors' Addresses

   Ryuji Wakikawa
   Toyota ITC / Keio University
   6-6-20 Akasaka, Minato-ku
   Tokyo  107-0052
   Japan

   Phone: +81-3-5561-8276
   Fax:   +81-3-5561-8292
   Email: ryuji@jp.toyota-itc.com


   Sri Gundavelli
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: sgundave@cisco.com































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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   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.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
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   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





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