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Versions: 00 01 02 draft-ietf-netlmm-proxymip6

NETLMM WG                                                  S. Gundavelli
Internet-Draft                                                  K. Leung
Intended status: Standards Track                           Cisco Systems
Expires: September 6, 2007                                V. Devarapalli
                                                         Azaire Networks
                                                            K. Chowdhury
                                                        Starent Networks
                                                                B. Patil
                                                                   Nokia
                                                          March 05, 2007


                           Proxy Mobile IPv6
                  draft-sgundave-mip6-proxymip6-02.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
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   This Internet-Draft will expire on September 6, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   Host based IPv6 mobility is specified in Mobile IPv6 base
   specification [RFC3775].  In that model, the mobile node is



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   responsible for doing the signaling to its home agent to enable
   session continuity as it moves between subnets.  The design principle
   in the case of host-based mobility relies on the mobile node being in
   control of the mobility management.  Network based mobility allows IP
   session continuity for a mobile node without its involvement in
   mobility management.  This specification describes a protocol
   solution for network based mobility management that relies on Mobile
   IPv6 signaling and reuse of home agent functionality.  A proxy
   mobility agent in the network which manages the mobility for a mobile
   node is the reason for referring to this protocol as Proxy Mobile
   IPv6.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Conventions used in this document  . . . . . . . . . . . . . .  5
   3.  Proxy Mobile IPv6 Protocol Overview  . . . . . . . . . . . . .  8
   4.  Proxy Mobile IPv6 Protocol Security  . . . . . . . . . . . . . 11
     4.1.  Peer Authorization Database Entries  . . . . . . . . . . . 11
     4.2.  Security Policy Database Entries . . . . . . . . . . . . . 12
   5.  Local Mobility Anchor Operation  . . . . . . . . . . . . . . . 13
     5.1.  Extensions to Binding Cache Conceptual Data Structure  . . 14
     5.2.  Bi-Directional Tunnel Management . . . . . . . . . . . . . 15
     5.3.  Routing Considerations . . . . . . . . . . . . . . . . . . 16
     5.4.  Local Mobility Anchor Address Discovery  . . . . . . . . . 17
     5.5.  Sequence Number and Time-Stamps for Message Ordering . . . 18
     5.6.  IPv4 Home Address Mobility Support . . . . . . . . . . . . 19
     5.7.  IPv4 Transport Support . . . . . . . . . . . . . . . . . . 20
     5.8.  Route Optimizations Considerations . . . . . . . . . . . . 20
     5.9.  Mobile Prefix Discovery Considerations . . . . . . . . . . 20
     5.10. Local Mobility Anchor Operational Summary  . . . . . . . . 21
   6.  Mobile Access Gateway Operation  . . . . . . . . . . . . . . . 23
     6.1.  Address Configuration Models . . . . . . . . . . . . . . . 23
     6.2.  Conceptual Data Structures . . . . . . . . . . . . . . . . 24
     6.3.  Access Authentication  . . . . . . . . . . . . . . . . . . 25
     6.4.  Home Network Emulation . . . . . . . . . . . . . . . . . . 25
     6.5.  Link-Local and Global Address Uniqueness . . . . . . . . . 26
     6.6.  IPv4 Home Address Mobility Support . . . . . . . . . . . . 27
     6.7.  IPv4 Transport Support . . . . . . . . . . . . . . . . . . 27
     6.8.  Tunnel Management  . . . . . . . . . . . . . . . . . . . . 28
     6.9.  Routing Considerations . . . . . . . . . . . . . . . . . . 29
     6.10. Interaction with DHCP Relay Agent  . . . . . . . . . . . . 30
     6.11. Mobile Node Detachment Detection and Resource Cleanup  . . 30
     6.12. Coexistence with Mobile Nodes using Host-based Mobility  . 31
     6.13. Mobile Access Gateway Operation Summary  . . . . . . . . . 32
   7.  Mobile Node Operation  . . . . . . . . . . . . . . . . . . . . 34
     7.1.  Booting up in a Proxy Mobile IPv6 Domain . . . . . . . . . 35



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     7.2.  Roaming in the Proxy Mobile IPv6 Network . . . . . . . . . 36
     7.3.  IPv6 Host Protocol Parameters  . . . . . . . . . . . . . . 36
   8.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . . 38
     8.1.  Proxy Binding Update . . . . . . . . . . . . . . . . . . . 38
     8.2.  Proxy Binding Acknowledgment . . . . . . . . . . . . . . . 39
     8.3.  Home Network Prefix Option . . . . . . . . . . . . . . . . 39
     8.4.  Time Stamp Option  . . . . . . . . . . . . . . . . . . . . 41
     8.5.  Status Codes . . . . . . . . . . . . . . . . . . . . . . . 41
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 42
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 42
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
   12. Appendix-A: Proxy Mobile IPv6 Deployment Models  . . . . . . . 44
     12.1. Case-1# Avoiding Global Mobility at home (MIPv6-HoA ==
           MN-HoA)  . . . . . . . . . . . . . . . . . . . . . . . . . 45
     12.2. Case-2# Requiring Global Mobility at home (MIPv6-CoA
           == MN-HoA) . . . . . . . . . . . . . . . . . . . . . . . . 46
   13. Appendix-B: Proxy Mobile IPv6 interactions with AAA
       Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . 47
   14. Appendix-C: Supporting Shared-Prefix Model using DHCPv6  . . . 47
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 48
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 48
     15.2. Informative References . . . . . . . . . . . . . . . . . . 49
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 50
   Intellectual Property and Copyright Statements . . . . . . . . . . 52



























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1.  Introduction

   Mobile IPv6 [RFC-3775] is the enabler for IPv6 mobility.  It requires
   Mobile IPv6 client functionality in the IPv6 stack of a mobile node.
   Signaling between the MN and HA enables the creation and maintenance
   of a binding between the MNs home address and care-of-address.
   Mobile IPv6 has been designed to be an integral part of the IPv6
   stack in a host.  However there exist IPv6 stacks today that do not
   have Mobile IPv6 functionality and there would likely be IPv6 stacks
   without MIPv6 functionality in the future as well.  It is desirable
   to support IP mobility for all hosts irrespective of the presence or
   absence of mobile IPv6 functionality in the IPv6 stack.

   It is possible to support mobility for IPv6 nodes by extending Mobile
   IPv6 [RFC-3775] signaling and reusing the home agent via a proxy
   mobility agent in the network.  This approach to supporting mobility
   does not require the mobile node to be involved in the signaling
   required for mobility management.  The proxy agent in the network
   performs the signaling and does the mobility management on behalf of
   the mobile node.  Because of the use and extension of Mobile IPv6
   signaling and home agent functionality, it is referred to as Proxy
   Mobile IPv6 (PMIP6) in the context of this document.

   Network deployments which are designed to support mobility would be
   agnostic to the capability in the IPv6 stack of the nodes which it
   serves.  IP mobility for nodes which have mobile IP client
   functionality in the IPv6 stack as well as those hosts which do not,
   would be supported by enabling PMIP6 protocol functionality in the
   network.  The advantages of developing a network based mobility
   protocol based on Mobile IPv6 are:

   o  Reuse of home agent functionality and the messages/format used in
      mobility signaling.  Mobile IPv6 is a mature protocol with several
      implementations that have been through interoperability testing.

   o  A common home agent would serve as the mobility agent for all
      types of IPv6 nodes.

   o  Addresses a real deployment need.

   The problem statement and the need for a network based mobility
   protocol solution has been documented in
   [draft-ietf-netlmm-nohost-ps-05.txt].  PMIP6 is a solution that
   addresses these issues and requirements.

   The IP Mobility protocols designed in the IETF so far involve the
   host in mobility management.  There are some deployment scenarios
   where a network-based mobility management protocol is considered



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   appropriate.  The advantages to using a network-based mobility
   protocol include avoiding tunneling overhead over the air and support
   for hosts that do not implement any mobility management protocol.

   The document describes a network-based mobility management protocol
   based on Mobile IPv6. it is called Proxy Mobile IPv6 (PMIPv6).  One
   of the most important design considerations behind PMIPv6 has been to
   re-use as much as possible from the existing mobility protocols.

   There are many advantages to develop a protocol based on Mobile IPv6.
   Mobile IPv6 is a very mature mobility protocol for IPv6.  There have
   been many implementations and inter-operability events where Mobile
   IPv6 has been tested.  There also numerous specifications enhancing
   Mobile IPv6 that can be re-used.  Further, the Proxy MIPv6 solution
   described in this document allows the same Home Agent to provide
   mobility to hosts that use Mobile IPv6 and hosts that do not use any
   mobility management protocol.  Proxy Mobile IPv6 provides solution to
   a real deployment problem.



2.  Conventions used in this document

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" used in
   this document are to be interpreted as described in RFC 2119.

   All the general mobility related terms used in this document are to
   be interpreted as defined in the Mobile IPv6 base specification [RFC-
   3775].

   This document adopts the terms, Local Mobility Anchor (LMA) and
   Mobile Access Gateway (MAG) from the NETLMM Goals document
   [draft-ietf-netlmm-nohost-req-05.txt].  It further provides the
   following context specific explanation to these terms, specific to
   this solution document.


   Local Mobility Anchor (LMA)

      Local Mobility Anchor is the home agent for the mobile node in the
      Proxy Mobile IPv6 domain.  It is the topological anchor point for
      the mobile node's home prefix and is the entity that manages the
      mobile node's reachability state.  It is important to understand
      that the LMA has the functional capabilities of a home agent as
      defined in Mobile IPv6 base specification [RFC-3775] and with the
      additional required capabilities for supporting Proxy Mobile IPv6
      as defined in this specification.



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   Mobile Access Gateway (MAG)

      Mobile Access Gateway (MAG) is the proxy mobility agent in the
      network which manages the mobility related signaling for a mobile
      node that is attached to its access link.  It is the entity
      responsible for tracking the mobile node's attachment to the link
      and for signaling the mobile node's local mobility anchor.


   The following new terminology and abbreviations are introduced in
   this document.

   Mobile Node (MN)

      Through out this document, the term mobile node is used to refer
      to an IP node whose mobility is provided by the network.  The
      mobile node may be operating in IPv6 mode, IPv4 mode or in IPv4/
      IPv6 dual mode.  The mobile node is not required to participate in
      any mobility related signaling for achieving mobility for an IP
      address that is obtained in that local domain.  This document
      further uses explicit text when referring to a mobile node that is
      involved in mobility related signaling as per Mobile IPv6
      specification [RFC-3775].  The mobile node's capability or its
      involvement in any mobility related signaling for obtaining
      mobility for an address that is obtained outside the current proxy
      mobile IPv6 domain, is not relevant in the context of this
      document and this definition of the Mobile Node shall survive.

   Mobile Node's Home Address (MN-HoA)

      MN-HoA is the home address of a mobile node in a Proxy Mobile IPv6
      domain.  It is an address obtained by the mobile node in that
      domain.  The mobile node can continue to use this address as long
      as it is attached to the network that is in the scope of that
      Proxy Mobile IPv6 domain.  When supporting IPv4 address mobility
      for a mobile node, the term, IPv4 MN-HoA is used to refer to the
      IPv4 address of the mobile node.

   Proxy Care-of Address (Proxy-CoA)

      Proxy-CoA is the address configured on the interface of the mobile
      access gateway and is the transport endpoint of the tunnel between
      the local mobility anchor and the mobile access gateway.  The
      local mobility anchor views this address as the Care-of Address of
      the mobile node and registers it in the Binding Cache entry for
      that mobile node.  When the transport network between the mobile
      access gateway and the local mobility anchor is an IPv4 network
      and if the care-of address that is registered at the local



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      mobility anchor is an IPv4 address, the term, IPv4 Proxy-CoA is
      used.

   LMA Address (LMAA)

      The address that is configured on the interface of the local
      mobility anchor and is the transport endpoint of the tunnel
      between the local mobility anchor and the mobile access gateway.
      This is the address to where the mobile access gateway sends the
      Proxy Binding Update messages.  When supporting IPv4 traversal,
      i.e. when the network between the local mobility anchor and the
      mobile access gateway is an IPv4 network, this address will be an
      IPv4 address and will be referred to as IPv4 LMAA.

   Proxy Mobile IPv6 Domain (PMIPv6-Domain)

      It is a localized mobility management domain.  It is a portion of
      the access network where the mobility management of a mobile node
      is handled using Proxy Mobile IPv6 protocol as defined in this
      specification.

   Mobile Node's Home Link

      This is the link on which the mobile node obtained its initial
      address configuration after it moved into that Proxy Mobile IPv6
      domain.  This is the link that conceptually follows the mobile
      node.  The network will ensure the mobile node always sees this
      link with respect to the layer-3 network configuration, on any
      access link that it attaches to in that proxy mobile IPv6 domain.

   Mobile Node's Home Network Prefix (MN-HNP)

      This is the on-link prefix that the mobile always sees in the
      Proxy Mobile IPv6 domain.  The home network prefix is
      topologically anchored at the mobile's local mobility anchor.  The
      mobile node configures its interface with an address from this
      prefix.  When supporting IPv4 home address mobility, the term,
      IPv4 Home Network refers to the mobile node's IPv4 home prefix and
      the term, Home Network always refers to the IPv6 home network
      prefix.

   Mobile Node Identifier (MN-Identifier)

      The identity of the mobile node that was presented to the network
      as part of the access authentication.  This is typically an
      identifier such as Mobile Node NAI [RFC-4283] or in other format
      specific to the access technology.




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   Proxy Binding Update (PBU)

      A signaling message sent by the mobile access gateway to a mobile
      node's local mobility anchor for establishing a binding between
      the mobile node's MN-HoA and the Proxy-CoA.

   Proxy Binding Acknowledgement (PBA)

      A response message sent by a local mobility anchor in response to
      a Proxy Binding Update message that it received from a mobile
      access gateway.



3.  Proxy Mobile IPv6 Protocol Overview

   This specification describes a network-based mobility management
   protocol.  It is called Proxy Mobile IPv6 (PMIPv6) and is based on
   Mobile IPv6 [RFC-3775].  This protocol is for providing network-based
   mobility management support to a mobile node, within a restricted and
   topologically localized portion of the network and with out requiring
   the participation of the mobile node in any mobility related
   signaling.

   Every mobile node that roams in a Proxy Mobile IPv6 domain, would
   typically be identified by an identifier, such as MN-Identifier, and
   using that identifier the mobile node's policy profile can be
   obtained from the policy store.  The policy profile typically
   contains the provisioned network-based mobility service
   characterstics and other related parameters such as the mobile node's
   home network prefix, permitted address configuration modes, roaming
   policy and other parameters that are essential for providing network
   based mobility service.

   Once a mobile node enters its Proxy Mobile IPv6 domain and performs
   access authentication, the network will ensure the mobile node is
   always on its home network and further ensures the mobile node can
   always obtain its home address on the access link and using any of
   the address configuration procedures.  In other words, there is home
   network prefix that is assigned for a mobile node and conceptually
   that address always follows the mobile node, where ever it roams
   within that proxy mobile IPv6 domain.  From the perspective of the
   mobile node, the entire Proxy Mobile IPv6 domain appears as its home
   link or a single link.







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           +----+              +----+
           |LMA1|              |LMA2|
           +----+              +----+
   LMAA1----  |                   | ---- LMAA2
              |                   |
              \\                // \\
            +--\\------------- //---\\----+
           (    \\  IPv4/IPv6 //     \\    )
           (     \\  Network //       \\   )
            +-----\\--------//---------\\-+
                   \\      //           \\
                    \\    //             \\  <--- Tunnel2
                     \\  //               \\
                       |-- Proxy-CoA1      |-- Proxy-CoA2
                    +----+              +----+
           [MN1].__.|MAG1|.__.[MN2]     |MAG2|
                    +----+              +----+
                       |                   |
                       |                   |
            -------------------           [MN5]
              |            |
            [MN3]        [MN4]


                    Figure 1: Proxy Mobile IPv6 Domain



   The Proxy Mobile IPv6 scheme introduces a new function, the mobile
   access gateway.  It is a function that is on the access link where
   the mobile is anchored and does the mobility related signaling on
   behalf of the mobile node.  From the perspective of the local
   mobility anchor, the mobile access gateway is a special element in
   the network that is authorized to send Mobile IPv6 signaling messages
   on behalf of a mobile node.

   When the mobile node attaches to an access link connected to the
   mobile access gateway, the mobile node presents its identity, MN-
   Identifier, as part of the access access authentication procedure.
   After a successful access authentication, the mobile access gateway
   obtains the mobile node's profile from the policy store, such as from
   a AAA infrastructure.  The mobile access gatway would have all the
   information for it to emulate the mobile node's home network on the
   access link.  The mobile access gateway also starts sending periodic
   Router Advertisements to the mobile node advertising its home network
   prefix.

   The mobile node on receiving these Router Advertisement messages on



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   the access link will attempt to configure its interface either using
   statefull or stateless address configuration modes, based on modes
   that are permitted on that access link.  At the end of a successful
   address configuration procedure, the mobile node would have obtained
   an address from its home network prefix.  If the mobile node is IPv4
   capable and if network offers IPv4 network mobility for the mobile
   node, the mobile node would have obtained an IPv4 address as well.
   The mobile node can be operating in IPv4-only mode, IPv6-only or in
   dual-mode and based on the services enabled for that mobile, the
   mobility is enabled only for those address types.  Also, the network
   between the local mobility anchor and the mobile access gateway can
   be either IPv4, IPv6, IPv4 with NAT translation devices in the access
   network.

   For updating the local mobility anchor about the current location of
   the mobile mode, the mobile access gateway sends a Proxy Binding
   Update message to the mobile node's local mobility anchor.  The
   message will have the mobile node's NAI identifier option and Home
   Network Prefix Option and/or IPv4 Home Address option.  The source
   address of that message will be the address of the mobile access
   gateway on its egress interface.  Upon accepting the Proxy Binding
   Update request, the mobile access gateway sends a Proxy Binding
   Acknowledgment message to the mobile access gateway.  It also sets up
   a route to the mobile node's home network prefix over the tunnel and
   sends Proxy Binding Acknowledgment message to the mobile access
   gateway.

   The mobile access gateway on receiving this Proxy Binding
   Acknowledgment message sets up a tunnel to the local mobility anchor
   and adds a default route over the tunnel to the local mobility
   anchor.  All traffic from the mobile node gets routed to the mobile
   node's local mobility anchor over the tunnel.

   At this point, the mobile node has a valid home address from its home
   network prefix, at the current point of attachment.  The serving
   mobile access gateway and the local mobility anchor also have proper
   routing states for handling the traffic sent to and from the mobile
   node.

   The local mobility anchor, being the topological anchor point for the
   mobile node's home network prefix, it receives any packet sent by any
   corresponding node to the mobile node.  Local mobility anchor
   forwards the received packet to the mobile access gateway through the
   tunnel.  The mobile access gateway on other end of the tunnel, after
   receiving the packet removes the tunnel header and forwards the
   packet on the access link to the mobile node.

   The mobile access gateway typically acts as a default router on the



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   access link and any packet that the mobile node sends to any
   corresponding node is received by the mobile access gateway and it
   forwards the packet to the local mobility anchor through the tunnel.
   The local mobility anchor on the other end of the tunnel, after
   receiving the packet removes the tunnel header and routes the packet
   to the destination.



4.  Proxy Mobile IPv6 Protocol Security

   The signaling messages, Proxy Binding Update and Proxy Binding
   Acknowledgement, exchanged between the mobile access gateway and the
   local mobility anchor are protected using IPsec and using the
   established security association between them.  The security
   association of the specific mobile node for which the signaling
   message is initiated is not required for protecting these messages.

   ESP in transport mode with mandatory integrity protection is used for
   protecting the signaling messages.  Confidentiality protection is not
   required.

   IKEv2 is used to setup security associations between the mobile
   access gateway and the local mobility anchor to protect the Proxy
   Binding Update and Proxy Binding Acknowledgment messages.  The mobile
   access gateway and the local mobility anchor can use any of the
   authentication mechanisms, as specified in IKEv2, for mutual
   authentication.

   Mobile IPv6 specification requires the home agent to prevent a mobile
   node from creating security associations or creating binding cache
   entries for another mobile node's home address.  In the protocol
   described in this document, the mobile node is not involved in
   creating security associations for protecting the signaling messages
   or sending binding updates.  Therefore, this is not a concern.
   However, the local mobility anchor MUST allow only authorized mobile
   access gateways to create binding cache entries on behalf of the
   mobile nodes.  The actual mechanism by which the local mobility
   anchor verifies if a specific mobile access gateway is authorized to
   send Proxy Binding Updates on behalf of a mobile node is outside the
   scope of this document.  One possible way this could be achieved is
   sending a query to the policy store such as by using AAA
   infrastrucure.

4.1.  Peer Authorization Database Entries

   The following describes PAD entries on the mobile access gateway and
   the local mobility anchor.  The PAD entries are only example



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   configurations.  Note that the PAD is a logical concept and a
   particular mobile access gateway or a local mobility anchor
   implementation can implement the PAD in an implementation specific
   manner.  The PAD state may also be distributed across various
   databases in a specific implementation.


       mobile access gateway PAD:
         - IF remote_identity = lma_identity_1
              Then authenticate (shared secret/certificate/EAP)
              and authorize CHILD_SA for remote address lma_addres_1

       local mobility anchor PAD:
         - IF remote_identity = mag_identity_1
              Then authenticate (shared secret/certificate/EAP)
              and authorize CHILD_SAs for remote address mag_address_1


   The list of authentication mechanisms in the above examples is not
   exhaustive.  There could be other credentials used for authentication
   stored in the PAD.

4.2.  Security Policy Database Entries

   The following describes the security policy entries on the mobile
   access gateway and the local mobility anchor required to protect the
   Proxy Mobile IPv6 signaling messages.  The SPD entries are only
   example configurations.  A particular mobile access gateway or a
   local mobility anchor implementation could configure different SPD
   entries as long as they provide the required security.

   In the examples shown below, the identity of the mobile access
   gateway is assumed to be mag_1, the address of the mobile access
   gateway is assumed to be mag_address_1, and the address of the local
   mobility anchor is assumed to be lma_address_1.


      mobile access gateway SPD-S:
        - IF local_address = mag_address_1 &
             remote_address = lma_address_1 &
             proto = MH & local_mh_type = BU & remote_mh_type = BAck
          Then use SA ESP transport mode
          Initiate using IDi = mag_1 to address lma_1

      local mobility anchor SPD-S:
        - IF local_address = lma_address_1 &
             remote_address = mag_address_1 &
             proto = MH & local_mh_type = BAck & remote_mh_type = BU



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          Then use SA ESP transport mode



5.  Local Mobility Anchor Operation

   For supporting the Proxy Mobile IPv6 scheme defined in this document,
   the Mobile IPv6 home agent entity, defined in Mobile IPv6
   specification [RFC-3775], needs some protocol enhancements.  The
   local mobility anchor is the functional entity with these
   capabilities for supporting Proxy Mobile IPv6.  This section
   describes the operational details of the local mobility anchor.

   The base Mobile IPv6 specification [RFC-3775], defines home agent and
   the mobile node as the two functional entities.  The Proxy Mobile
   IPv6 scheme introduces a new entity, the mobile access gateway.  This
   is the entity that will participate in the mobility related
   signaling.  From the perspective of the local mobility anchor, the
   mobile access gateway is a special element in the network that has
   the privileges to send mobility related signaling messages on behalf
   of the mobile node.  Typically, the local mobility anchor is
   provisioned with the list of mobile access gateways authorized to
   send proxy registrations.

   When the local mobility anchor receives a Proxy Binding Update
   message from a mobile access gateway, the message is protected using
   the IPSec Security Association established between the local mobility
   anchor and the mobile access gateway.  The local mobility anchor can
   distinguish between a Proxy Binding Update message received from a
   mobile access gateway from a Binding Update message received directly
   from a mobile node.  This distinction is important for using the
   right security association for validating the Binding Update and this
   is achieved by relaxing the MUST requirement for having the Home
   Address Option presence in Destination Options header and by
   introducing a new flag in the Binding Update message.  The local
   mobility anchor as a traditional IPSec peer can use the SPI in the
   IPSec header [RFC-4306] of the received packet for locating the
   correct security association and for processing the Proxy Binding
   Update message in the context of the Proxy Mobile IPv6 scheme.

   For protocol simplicity, the current specification supports the Per-
   MN-Prefix addressing model.  In this addressing model, each mobile
   node is allocated an exclusively unique home network prefix and the
   prefix is not hosted on the home link.  The local mobility anchor in
   this addressing model is just a topological anchor point and the
   prefix is physically hosted on the access link where the mobile node
   is attached.  The local mobility anchor is not required to perform
   any proxy ND operations [RFC-2461] for defending the mobile node's



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   home address, MN-HoA, on the home link.  However, the local mobility
   anchor is required to manage the binding cache entry of the mobile
   node for managing the mobility session and also the routing state for
   creating a proper route path for traffic to/from the mobile node.


5.1.  Extensions to Binding Cache Conceptual Data Structure

   The local mobility anchor maintains a Binding Cache entry for each
   currently registered mobile node.  Binding Cache is a conceptual data
   structure, described in Section 9.1 of [RFC3775].  For supporting
   this specification, the conceptual Binding Cache entry needs to be
   extended with the following new fields.


   o  A flag indicating whether or not this Binding Cache entry is
      created due to a proxy registration.  This flag is enabled for
      Binding Cache entries that are proxy registrations and is turned
      off for all other entries that are direct registrations from the
      mobile node.

   o  A flag indicating if IPv4 HoA mobility binding is accepted.  If
      this flag is set, the relevant IPv4 fields in this data structure
      have to be set to the configured values.

   o  A flag indicating if IPv6 HoA mobility is accepted.  If this flag
      is set, the relevant IPv4 HoA fields in this data structure have
      to be set to the configured values.  If this flag.

   o  The identifier of the mobile node, MN-Identifier.  This MN-
      Identifier is obtained from the NAI Option present in the Proxy
      Binding Update request [RFC-4285].

   o  A flag indicating whether or not the Binding Cache entry has a
      home address that is on virtual interface.  This flag is enabled,
      if the home prefix of the mobile is configured on a virtual
      interface.  When the configured home prefix of a mobile is on a
      virtual interface, the home agent is not required to function as a
      Neighbor Discovery proxy for the mobile node.

   o  The IPv6 home network prefix of the mobile node.

   o  The IPv6 home network prefix length of the mobile node.

   o  The IPv4 home address of the mobile node, if IPv4 home address
      mobility is enabled and if the mobile has obtained an address.





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   o  The IPv4 home network prefix length of the mobile node, if IPv4
      home address mobility is enabled.

   o  The IPv4 default-router address of the mobile node, if IPv4 home
      address mobility is enabled.  This is the IPv4 LMAA.

   o  The interface id of the tunnel between the local mobility anchor
      and the mobile access gateway used for sending and receiving the
      mobile node's traffic.

   o  Tentative binding cache entry with all the above fields.  This
      entry is populated upon tentatively accepting a proxy binding
      update request for a mobile node whose direct registration still
      exists, i.e. the mobile has not deregistered and it received a
      proxy binding update request.


5.2.  Bi-Directional Tunnel Management

   The bi-directional tunnel between the local mobility anchor and the
   mobile access gateway is used for routing the traffic to and from the
   mobile node.  The tunnel hides the topology and enables a mobile node
   to use an IP address that is topologically anchored at the local
   mobility anchor, from any attached access link in that proxy mobile
   IPv6 domain.  The base Mobile IPv6 specification [RFC-3775], does use
   the tunneling scheme for routing traffic to and from the mobile that
   is using its home address.  However, there are subtle differences in
   the way Proxy Mobile IPv6 uses the tunneling scheme.

   As in Mobile IPv4 [RFC-3344], the tunnel between the local mobility
   anchor and the mobile access gateway is typically a shared tunnel and
   can be used for routing traffic streams for different mobile nodes
   attached to the same mobile access gateway.  This specification
   extends that 1:1 relation between a tunnel and a binding cache entry
   to 1:m relation, reflecting the shared nature of the tunnel.

   The tunnel is creating after accepting a Proxy Binding Update request
   for a mobile node from a mobile access gateway.  The created tunnel
   may be shared with other mobile nodes attached to the same mobile
   access gateway and with the local mobility anchor having a binding
   cache entry for those mobile nodes.  Some implementations may prefer
   to use static tunnels as supposed to creating and tearing them down
   on a need basis.

   The one end point of the tunnel is the address configured on the
   interface of the local mobility anchor, LMAA or IPv4 LMAA.  The other
   end point of the tunnel is the address configured on the interface of
   the mobile access gateway, Proxy-CoA or IPv4 Proxy-CoA.  The tunnel



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   encapsulation mode can be either IPv6/IPv6, IPv6/IPv4, IPv6/IPv4-UDP,
   IPv4/IPv6, IPv4/IPv4-UDP, based on the transport mode and the
   presence of NAT translation devices on the path.

   Implementations typically use a software timer for managing the
   tunnel lifetime and a counter for keeping a count of all the mobiles
   that are sharing the tunnel.  The timer value will be set to the
   accepted binding life-time and will be updated after each periodic
   registrations for extending the lifetime.  If the tunnel is shared
   for multiple mobile node's traffic, the tunnel lifetime will be set
   to the highest binding life time across all the binding life time
   that is granted for all the mobiles sharing that tunnel.


5.3.  Routing Considerations

   This section describes how the data traffic to/from the mobile node
   is handled at the local mobility anchor.  The following entries
   explains the routing state that is created for the mobile node home
   network prefix.


   IPv6 traffic for the Mobile Node's home address:
   ================================================
      MN-HoA::/64 via tunnel0, next-hop Proxy-CoA


   IPv4 traffic for the Mobile Node's Home Address:
   ================================================
      IPv4-MN-HoA/32 via tunnel0, next-hop IPv4-Proxy-CoA


   tunnel0:
   ========
      Source:      LMAA        or    IPv4 LMAA
      Destination: Proxy-CoA   or    IPv4 Proxy-CoA
      Tunnel Transport: IPv6 or IPv4
      Tunnel Payload: IPv6, IPv4 or IPv4-UDP


   The local mobility anchor functions as a topological anchor point for
   the mobile node's home network prefix.  When the local mobility
   anchor receives a data packet from a corresponding node, destined for
   the mobile node's home network prefix, the created routing state will
   enable the packets to be forwarded to the mobile node through the bi-
   directional tunnel established between itself and the serving mobile
   access gateway.




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   If the tunnel between the local mobility anchor and the mobile access
   gateway is an IPv6 tunnel, i.e. if the registered care-of address is
   the IPv6 Proxy-CoA, any IPv6 packets received from any corresponding
   node for the mobile node's home network prefix, MN-HNP, will be
   encapsulated in an IPv6 packet, IPv6/IPv6 mode, and will be carried
   as an IPv6 packet.  And any IPv4 packets for the mobile node's IPv4-
   MN-HoA, will be encapsulated in an IPv6 packet, IPv4/IPv6 mode, and
   will be carried as an IPv6 packet.

   If the tunnel between the local mobility anchor and the mobile access
   gateway is an IPv4 tunnel, i.e. if the registered care-of address is
   the IPv4 Proxy-CoA, any IPv6 packets received from any corresponding
   node for the mobile node's home network prefix, MN-HNP, will be
   encapsulated in an UDP header of an IPv4 packet, IPv6/IPv4-UDP mode,
   and will be carried as an IPv4 packet.  And any IPv4 packet from any
   corresponding node, will be encapsulated in an UDP header of an IPv4
   packet, IPv4/IPv4-UDP mode, and will be carried as an IPv4 packet.
   In both these cases, the UDP header will not be there, if there is no
   presence of NAT devices detected on the path.

   All the reverse tunneled packets that the local mobility anchor
   receives from the tunnel, after removing the packet encapsulation
   will get 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.



5.4.  Local Mobility Anchor Address Discovery

   Dynamic Home Agent Address Discovery, as explained in Section 10.5 of
   [RFC-3775], allows a mobile node to discover all the home agents on
   its home link by sending an ICMP Home Agent Address Discovery Request
   message to the Mobile IPv6 Home-Agents anycast address, derived from
   its home network prefix.

   The Proxy Mobile IPv6 model assumes that the mobile access gateway
   will be able to obtain the address of the local mobility anchor in
   one or more ways.  This MAY be a configured entry in the mobile
   node's policy profile, or it MAY be obtained through mechanisms
   outside the scope of this document.  It is important to note that
   there is little value in using DHAAD for discovering the local
   mobility anchor address dynamically.  As a mobile moves from one
   mobile access gateway to the another, the serving mobile access
   gateway will not predictably be able to locate the serving local
   mobility anchor for that mobile that has its binding cache entry for
   the mobile node.  However, if there is only one local mobility anchor
   configured to serve a mobile node, the mobile access gateway can use



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   Dynamic Home Agent Address Discovery scheme for discovering the
   address of the local mobility anchor.

   With the currently supported Per-MN-Prefix addressing model, every
   mobile node is assigned a unique home network prefix, the local
   mobility anchor is a topological anchor point for that prefix and
   with the prefix being hosted on the access link attached to the
   mobile access gateway.  For the discovery scheme to work, the local
   mobility anchor MUST be able to receive the ICMP discovery packets
   sent to the anycast address derived from the mobile node's home
   network prefix.



5.5.  Sequence Number and Time-Stamps for Message Ordering

   Mobile IPv6 [RFC-3775] uses the Sequence Number field in registration
   messages as a way to ensure the correct packet ordering.  The local
   mobility anchor and the mobile node are required to manage this
   counter over the lifetime of a binding.

   In Proxy Mobile IPv6, the Proxy Binding Update messages that the
   local mobility anchor receives on behalf of a specific mobile node
   may not be from the same mobile access gateway as the previously
   received message.  It creates certain ambiguity and the local
   mobility anchor will not be predictably order the messages.  This
   could lead to the local mobility anchor processing an older message
   from a mobile access gateway where the mobile node was previously
   attached, while ignoring the latest binding update message.

   In the Proxy Mobile IPv6, the ordering of packets has to be
   established accross packets received from multiple senders.  The
   sequence number scheme as specified in [RFC-3775] will not be
   sufficient.  A global scale, such as a time stamp, can be used to
   ensure the correct ordering of the packets.  This document proposes
   the use of a Time Stamp Option, specified in Section 8.4, in all
   Proxy Binding Update messages sent by mobile access gateways.  By
   leveraging the NTP [RFC-1305] service, all the entities in Proxy
   Mobile IPv6 domain will be able to synchronize their respective
   clocks.  Having a time stamp option in Proxy Binding Update messages
   will enable the local mobility anchor to predictably identify the
   latest message from a list of messages delivered in an out-of-order
   fashion.

   The Proxy Mobile IP model, defined in this document requires the
   Binding Update messages sent by the mobile access gateway to have the
   time stamp option.  The local mobility anchor processing a proxy
   registration MUST ignore the sequence number field and SHOULD use the



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   value from the Time Stamp option to establish ordering of the
   received Binding Update messages.  If the local mobility anchor
   receives a Binding Update message with an invalid Time Stamp Option,
   the Binding Update MUST be rejected and a Binding Acknowledgement
   MUST be returned in which the Status field is set to 148 (invalid
   time stamp option).

   In the absence of Time Stamp option in the Proxy Binding Update, the
   entities can fall back to Sequence Number scheme for message
   ordering, as defined in RFC-3775.  However, the specifics on how
   different mobile access gateways synchronize the sequence number is
   outside the scope of this document.

   When using the Time Stamp Option, the local mobility anchor or the
   mobile access gateway MUST set the the timestamp field to a 64-bit
   value formatted as specified by the Network Time Protocol [RFC-1305].
   The low-order 32 bits of the NTP format represent fractional seconds,
   and those bits which are not available from a time source SHOULD be
   generated from a good source of randomness.


5.6.  IPv4 Home Address Mobility Support

   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 infrastructure.  It is reasonable to assume that the mobile node
   and the local mobility anchor are IPv4 and IPv6 enabled and further
   it is also reasonable to expect the same mobility infrastructure to
   provide IPv4 and IPv6 address mobility.  The Proxy Mobile IPv6 scheme
   defined in this document allows the mobile node to obtain an IPv4
   address and to roam in the network using the same address.

   When a mobile node attached to a mobile access gateway sends a DHCP
   request, the network will ensure it gets an IP address from its home
   address prefix.  The mobile access on the access link where mobile
   node is attached, will register this address with the local mobility
   anchor using the IPv4 Home Address option, defined in Section 3.1.1,
   DSMIP6 draft [draft-ietf-mip6-nemo-v4traversal-03.txt].  Upon
   receiving the Proxy Binding Update Message with this IPv4 Home
   Address option, the local mobility anchor is required to apply the
   processing rules as specified in DSMIP6 draft.  Further, if the
   received option has a value set to 0.0.0.0, the local mobility anchor
   needs to consider this as a request for an IPv4 Home Address
   allocation and must return the allocated value in the IPv4 Home
   Address option carried in the Proxy Binding Acknowledgement.

   Upon accepting the registration for the mobile node's IPv4 home
   address, the local mobility anchor will add an IPv4 host route over



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   the tunnel to the mobile access gateway.  Any IPv4 packets that the
   local mobility anchor receives from a correspondent node will be
   tunneled to the mobile access gateway over the IPv4/IPv6 tunnel, and
   then routed accordingly after removing the tunnel header.


5.7.  IPv4 Transport Support

   It is possible the transport network between the local mobility
   anchor and the mobile access gateway is an IPv4 network.  Further, it
   is possible the access network is behind a NAT translation device
   with the mobile access gateway using an IPv4 private address.

   For supporting the mobile node's mobility of the MN-HoA and IPv4 MN-
   HoA, the IPv4 tunnel established between the local mobility anchor
   and the mobile access gateway will be used routing the mobile node's
   IPv4 and IPv6 traffic.

   The DSMIP6 specification provides the semantics on how the IPv4
   tunnel needs to be negotiated and the detection logic of the NAT
   devices.  This specification leverages the DSMIP6 work and extends
   the use of the NAT Detection Option defined for Binding
   Acknowledgement to Proxy Binding Acknowledgement messages.


5.8.  Route Optimizations Considerations

   Mobile IPv6 route optimization, as defined in [RFC-3775], enables a
   mobile node to communicate with a corresponding node directly using
   its care-of address and further the Return Routability procedure
   enables the corresponding node to have reasonable trust that the
   mobile node owns both the home address and care-of address.

   In the Proxy Mobile IPv6 model, the mobile is not involved in any
   mobility related signaling and also it does not operate in the dual-
   address mode.  Hence, the return routability procedure as defined in
   RFC-3775 is not applicable for the proxy model.  This document does
   not address the Route Optimization problem and leaves this work item
   for future enhancements.


5.9.  Mobile Prefix Discovery Considerations

   The ICMP Mobile Prefix Advertisement message, described in Section
   6.8 and Section 11.4.3 of [RFC-3775], allows a home agent to send a
   Mobile Prefix Advertisement to the mobile node.

   In Proxy Mobile IPv6 deployments, the mobile node's home network



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   prefix is hosted on the access link shared between the mobile access
   gateway and the mobile node, but topologically anchored on the local
   mobility anchor.  Since, there is no physical home-link for the
   mobile node's home network prefix on the local mobility anchor and as
   the mobile is always on the link where the prefix is hosted, any
   prefix change messages can just be advertised by the mobile access
   gateway on the access link and thus there is no applicability of this
   messaging for Proxy Mobile IPv6.  This specification does not support
   Mobile Prefix Discovery.


5.10.  Local Mobility Anchor Operational Summary

   o  For supporting this scheme, the local mobility anchor MUST satisfy
      all the requirements listed in Section 8.4 of Mobile IPv6
      specification [RFC-3775] with the following considerations.

   o  For supporting the per-MN-Prefix addressing model as defined in
      this specification, the local mobility anchor service MUST NOT be
      tied to a specific interface.  It SHOULD be able to accept Proxy
      Binding Update requests sent to any of the addresses configured on
      any of its interfaces.

   o  The requirement for a home agent to maintain a list of home agents
      for a mobile node's home link is not applicable for the local
      mobility anchor, when supporting Per-MN-Prefix addressing model as
      there is no link specific relation between the two.

   o  After receiving a Proxy Binding Update request from a mobile
      access gateway on behalf of mobile node, the local mobility anchor
      MUST process the request as defined in Section 10, of the base
      Mobile IPv6 specification [RFC-3775], with one exception that this
      request is a proxy request, the sender is not the mobile node and
      so the message has to be processed with the considerations
      explained in this section.

   o  The local mobility anchor MUST apply the required policy checks,
      as explained in Section 4.0 of this document to verify the sender
      is a a trusted mobile access gateway, authorized to send proxy
      binding updates requests on behalf of that mobile nodes, using its
      own identity.  The local mobility anchor must check the local/
      remote policy store to ensure the requesting node is authorized to
      send proxy binding update requests.

   o  Upon accepting a proxy binding update request from a mobile access
      gateway, the local mobility anchor must check if there exists a
      binding cache entry for that mobile node, identified using the MN-
      Identifier, that was created due to a direct registration from the



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      mobile node.  If there exists a binding cache entry with the proxy
      registration flag turned off, the local mobility anchor MUST NOT
      modify that binding state, instead it must create a tentative
      binding cache entry and update the tentative binding cache entry
      fields of that binding cache entry.

   o  Upon receiving a Binding Update request from a mobile node with
      lifetime value set to 0, from a tunnel between itself and a
      trusted mobile access gateway, the local mobility anchor upon
      accepting that de-registration message, MUST forward the Binding
      Acknowledgement message in the tunnel from where it received the
      Binding Update request.  It must also replace the binding cache
      entry with the tentative binding cache entry and enable routing
      for the mobile node's home prefix through the proxy mobile IPv6
      tunnel.

   o  The local mobility anchor MUST use the MN-Identifier present in
      the NAI option of the Proxy Binding Update request for identifying
      the mobile node.

   o  The local mobility anchor MUST ensure the prefix presented in the
      Home Network Prefix option of the received Proxy Binding Update
      request is owned by itself and further the mobile node identified
      by MN-Identifier is authorized to use this prefix.

   o  The local mobility anchor MUST ignore the sequence number field in
      the Proxy Binding Updates requests, if the Time-Stamp Option is
      present in the message.  It must also skip all the checks related
      to sequence number as suggested in the Mobile IPv6 specification
      [RFC-3775].  However, the received sequence number MUST be copied
      and returned in the Proxy Binding Acknowledgement sent to the
      mobile access gateway.

   o  Upon accepting this request, the local mobility anchor must create
      a Binding Cache entry with the home address from the Home Network
      Prefix Option in the Binding Update and must set up a tunnel to
      the proxy mobile agent serving the mobile node.  This bi-
      directional tunnel between the local mobility anchor and the
      mobile access gateway is used for routing the mobile traffic.

   o  The local mobility anchors SHOULD drop all HoTI messages received
      for a home address that has corresponding Binding Cache entry with
      the proxy registration flag set.

   o  The local mobility anchor must handle the mobile node's data
      traffic as explained in the Routing Considerations section of this
      document.




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6.  Mobile Access Gateway Operation

   The Proxy Mobile IPv6 scheme specified in this document, introduces a
   new functional entity, the Mobile Access Gateway (MAG).  It is the
   entity that detects the mobile node's movements and initiates the
   signaling with the mobile node's local mobility anchor for updating
   the route to the mobile node's home address.  In essence, the mobile
   access gateway does the mobility management of the mobile node.

   From the perspective of the local mobility anchor, the mobile access
   gateway is a special element in the network that sends Mobile IPv6
   signaling messages on behalf of a mobile node, but using its own
   identity.  It is the entity that binds the mobile node's home address
   to an address on its own access interface.

   The mobile access gateway has the following functional roles.

   o  It is responsible for detecting the mobile node's attachment or
      detachment on the connected access link and for initiating the
      mobility signaling to the mobile node's local mobility anchor.

   o  Emulation of the mobile node's home link on the access link.

   o  It is responsible for setting up the data path for enabling the
      mobile node to use its home address for communication from the
      access link.

   This Proxy Mobile IPv6 scheme is independent of the underlying access
   technology or the link model.  The interface between the mobile node
   and the mobile access gateway can be either:


   o  Point-to-Point Link

   o  Shared Link

   This specification does not support split links.


6.1.  Address Configuration Models

   Currently, this specification only supports Per-MN-Prefix model In
   the Per-MN-Prefix model, there is a unique home network prefix
   assigned for each mobile node and that prefix is hosted on the access
   link.  Conceptually, the prefix just follows the mobile node as it
   moves within the proxy mobile IPv6 domain.  In this addressing model,
   based on the administrative policy, the mobile node can use either
   Stateless Address Autoconfiguration or Statefull Address



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   Configuration using DHCP for obtaining the IPv6 address configuration
   for its interface on the access link.  Further, the mobile node can
   also generate interface identifiers with privacy considerations, as
   specified in Privacy Extensions specification [RFC-3041] and as per
   CGA specification [RFC-3042].  For IPv4 home address configuration,
   the mobile node can obtain the address configuration using DHCP or
   optionally by using IPCP.  In addition to this, Other address
   configuration mechanisms specific to the access link between the
   mobile node and the mobile access gateway may also be used by the
   mobile node.

   The configured administrative policy for the mobile dictates the type
   of addressing model that is supported for a mobile on the access
   link.  The mobile access gateway on the access router will control
   this by setting the relevant flags in the Router Advertisement that
   it sends on the access link.


6.2.  Conceptual Data Structures

   Every mobile access gateway maintains a Binding Update List for each
   currently attached mobile node.  The Binding Update List is a
   conceptual data structure, described in Section 11.1 of Mobile IPv6
   base specification [RFC-3775].  For supporting this specification,
   the conceptual Binding Update List data structure must be extended
   with the following new additional fields.


   o  The Identifier of the mobile node, MN-Identifier.  The format of
      the MN-Identifier is specific to the access technology.  This MN
      identifier is obtained as part of the Access Authentication
      procedure and is used for downloading the mobile node's profile
      from the policy store.

   o  The physical address or the MAC address of the mobile node's
      connected interface.

   o  The IPv6 home network prefix of the mobile node.

   o  The IPv6 home network prefix length of the mobile node.

   o  The link-local address of the mobile node on the link.  This
      address MAY be learnt from the source address of the Router
      Solicitation message received from the mobile node.

   o  The IPv4 home address of the mobile node, if IPv4 home address
      mobility is supported.




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   o  The IPv4 home network prefix length of the mobile node, if IPv4
      home address mobility is supported.

   o  The IPv4 default-router address of the mobile node, if IPv4 home
      address mobility is supported.  This is the IPv4 LMAA.

   o  The tunnel identifier of the tunnel between the mobile access
      gateway and the local mobility anchor used for reverse tunneling
      the mobile node's traffic.  On a given implementation, if a tunnel
      appears like a virtual interface, that applies the proper
      encapsulation on every packet that is routed through that
      interface, then the interface identifier is stored in the binding
      update list. entry.


6.3.  Access Authentication

   When a mobile node attaches to the access link connected to the
   mobile access gateway, the deployed access security protocols will
   ensure that only authorized mobile nodes will be able to access the
   link and further the mobile access gateway will be able to identify
   the mobile node by its MN-Identifier and optionally will be able to
   detect the mobile node's attachment or detachment to the link.  The
   exact specifics on how this is achieved is outside the scope of this
   document.  This document goes with the stated assumption of having an
   established trust between the mobile node and mobile access gateway
   on the access link before the protocol operation begins.  The mobile
   access gateway will be able to use the mobile node's MN-Identity and
   will be obtain its policy profile from the network policy store or
   from the local policy store.


6.4.  Home Network Emulation

   One of the key functions of the mobile access gateway is to emulate
   the mobile node's home network on the access link.  It has to ensure,
   the mobile node believes it is connected to its home link or the link
   where it obtained its address configuration after it moved into that
   proxy mobile IPv6 domain.  After the access authentication is
   complete, the mobile access gateway will have access to the mobile
   node's profile, obtained from querying a local/network policy store
   or provided to it as part of some context transfer procedure.  After
   this point, the mobile access gateway will have enough information to
   emulate the mobile node's home link.  It must send the Router
   Advertisement messages advertising the mobile node's home network
   prefix and other parameters.

   If the access link connecting the mobile access gateway and the



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   mobile node is a point-to-point link, the Router Advertisements
   advertising a specific home network prefix is received only by the
   respective mobile node and hence there is clearly a unique link for
   each mobile node that is attached to that mobile access gateway.

   If the access link connecting the mobile access gateway and the
   mobile node is a shared-link, the mobile access gateway MUST ensure
   that each of the mobile node that is attached to that link receives
   Router Advertisements with its respective home network prefix as the
   on-link prefix.  For this to happen, the mobile access gateway MUST
   unicast the Router Advertisement to the mobile node.  The destination
   field of the link-layer header in the Router Advertisement MUST be
   the mobile's node's interface physical/MAC address and however, the
   destination field in the IPv6 header set to the all-nodes-multicast
   address.


6.5.  Link-Local and Global Address Uniqueness

   A mobile node in a proxy mobile IPv6 domain, as it moves from one
   access link to the other, will continue to detect its home network
   and hence the issue of link-local address uniqueness arises.  The
   link-local that the mobile node attempts to use on the new link must
   be unique.

   On a point-to-point link, such as in a PPP session, when the mobile
   node tries to establish a PPP session [RFC-1661] with the mobile
   access gateway, the PPP goes through the Network layer Protocol phase
   and the IPv6 Control Protocol, IPCP6 [RFC-2472] gets triggered.  Both
   the PPP peers negotiate a unique identifier using Interface-
   Identifier option in IPV6CP and the negotiated identifier is used for
   generating a unique link-local address on that link.  Now, if the
   mobile node moves to a new access router, the PPP session gets torn
   down and new PPP session with the new mobile access gateway will be
   established and the mobile obtains a new link-local address.  Now,
   even if the mobile is DNAv6 capable, as specified in the DNAv6
   specification [draft-ietf-dna-protocol-03], the mobile node always
   configures a new link-local address when ever it moves to a new link.

   However, if the link between the mobile node and the mobile access
   gateway is a shared link and if a DNAv6 capable mobile node moves
   from one access link to the other, the mobile node may not detect a
   link change due to the optimizations from DNAv6 and hence there is a
   possibility of the link-local address collision on the connected
   access link, One of the work around for this issue to the set
   following flag on the mobile node, DNASameLinkDADFlag to TRUE and
   that will force the mobile node to redo DAD operation even when DNAv6
   detects no link change.



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   The global address or the MN-HoA uniqueness is assured as the
   uniqueness is established by the local mobility anchor before
   accepting a proxy binding update for a mobile node.  This is further
   assured with the currently supported per-mn-prefix model, as there
   are two mobile nodes that share the same home network prefix.
   Further, if the address configuration is based on statefull address
   configuration using DHCP, the DHCP server will ensure the uniqueness.


6.6.  IPv4 Home Address Mobility Support

   If the mobile node is permitted to roam using an IPv4 home address
   and if the mobile node has an IPv4 stack, the mobile node will be
   able to obtain an IPv4 MN-HoA by using DHCP address configuration
   procedures.  As part of this address configuration, the mobile node
   will also be able to obtain its IPv4 home network prefix length and
   default-router address.  The DHCP relay agent function on the access
   router will ensure the mobile node is assigned an address from its
   home network prefix, by marking the DHCP request with the mobile
   node's IPv4 home network prefix hint.

   However, the default-router address that is obtained from the DHCP
   will be that of the IPv4 address of its local mobility anchor and it
   is on a different link and not on the access link.  In order for the
   mobile node to be able use the default-router for routing all IPv4
   packets, the mobile access gateway on the access link must respond to
   the ARP requests from the mobile node for the default-router's IPv4
   address.  Now, if the mobile node roams to a new access link, the
   mobile access gateway on that link must send a gratuitous ARP for the
   mobile router's default-router address.

   In IPv6, the nodes on the link use the link-local address of the
   default-router for routing packets and it is not required that the
   default-router needs to have a configured address from the prefix
   that the node uses.  However, in IPv4, the default-router address on
   the link must be from the same subnet as of the IP address of the
   node.  Since, the mobile access gateway will not have an address on
   the mobile node's home prefix, it must act as a proxy for the mobile
   router's IPv4 gateway address.


6.7.  IPv4 Transport Support

   The network between the mobile access gateway and local mobility
   anchor can be an IPv4 or an IPv6 network.  If the network is an IPv4
   network, the mobile access gateway can potentially register its IPv4
   care-of address for a mobility binding and thus creating an IPv4
   transport for carrying the mobile node's MN-HoA and IPv4 MN-HoA



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   traffic over that tunnel.  The signaling messages will always be IPv6
   messages encapsulated in an IPv4 packet and carried as an IPv4
   packet.  The data traffic to and from the mobile node will also be
   encapulsulated in an IPv4 packet, as explained below in the Routing
   Considerations section.

   The DSMIPv6 draft [draft-ietf-mip6-nemo-v4traversal] defines a
   solution for allowing a mobile node to roam over an IPv4 and IPv6
   network.  The options defined in the DSMIP6 spec, IPv4 home address
   option, IPv4 address acknowledgement option and the NAT detection
   option can all be carried in the Proxy Binding Update and
   Acknowledgement messages exchanged between the mobile access gateway
   and the local mobility anchor.  As explained in Section 4.1, of the
   DSMIP6 spec, the mobile access gateway can encapsulate a Proxy
   Binding Update message and carry it in an IPv4 packet.  The
   processing logic for handling the NAT detection at the mobile node is
   applicable to the mobile access gateway.


6.8.  Tunnel Management

   In the traditional Mobile IPv6 model, there is a separate tunnel from
   the local mobility anchor to every mobile node that has a binding
   cache entry.  The one end-point of these tunnels is the respective
   mobile node's care-of address and that is unique to that mobile node.
   In the case of Proxy Mobile IPv6, the care-of address or the tunnel
   end-point is the address of the mobile access gateway and there could
   be multiple mobile nodes attached to the same mobile access gateway
   and hence the tunnel is a shared tunnel serving multiple mobile
   nodes.  This is identical to the Mobile IPv4 model [RFC-3344], where
   a tunnel between the foreign agent and the home agent is shared by
   many visiting mobile nodes and hence the tunnel management needs to
   be on a global basis and not be dependent on a specific mobile node's
   binding.

   The life of the Proxy Mobile IPv6 tunnel should not be based on a
   single binding cache entry.  The tunnel may get created as part of
   creating a mobility state for a mobile node and later the same tunnel
   may be associated with other mobile nodes.  So, the tearing down
   logic of the tunnel must be based on the number of visitors over that
   tunnel.  Implementations are free to pre-establish tunnels between
   every local mobility anchor and every mobile access gateway in a
   proxy mobile IPv6 domain and with out having to create and destroy
   the tunnels on a need basis.







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6.9.  Routing Considerations

   This section describes how the data traffic to/from the mobile node
   is handled at the mobile access gateway.  The following entries
   explains the routing state for the mobile node on the mobile access
   gateway.



   Mobile Node's IPv6 traffic:
   ===========================
   For all traffic from the source address MN-HoA to destination 0::/0
   route via tunnel0, next-hop LMAA.

   MN-HoA::/64 is reachable via the directly connected interface.


   Mobile Node's IPv4 traffic:
   ===========================
   For all IPv4 traffic from the source address IPv4 MN-HoA to
   destination 0.0.0.0/0.0.0.0 route via tunnel0, next-hop LMAA.

   IPv4-MN-HoA/32 is on the interface locally connected


   tunnel0:
   ========
      Source: Proxy-CoA  or  IPv4 Proxy-CoA
      Destination: LMAA  or  IPv4 LMAA
      Tunnel Payload: IPv6  or  IPv4
      Tunnel Transport: IPv6, IPv4 or IPv4-UDP


   When the mobile access gateway receives any packets from the mobile
   node to any destination, the packet will be forwarded to the local
   mobility anchor through the bi-directional tunnel established between
   itself and the mobile's local mobility anchor.  However, the packets
   that are sent with link-local source address are not forwarded.

   If the tunnel between the mobile access gateway and local mobility
   anchor is an IPv6 tunnel i.e. if the registered care-of address is an
   IPv6 Proxy-CoA, any IPv6 packet from the mobile node with the source
   MN-HoA, will be encapsulated in an IPv6 packet, IPv6/IPv6 mode and
   will be carried as an IPv6 packet.  And any IPv4 packet from the
   mobile node with the source IPv4 Mobile-HoA, will be encapsulated in
   an IPv6 packet, IPv4/IPv6 mode, and will be carried as an IPv6
   packet.




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   If the tunnel between the mobile access gateway and local mobility
   anchor is an IPv4 tunnel i.e. if the registered care-of address is
   the IPv4 Proxy-CoA, any IPv6 packet from the mobile node with the
   source MN-HoA, will be encapsulated in an UDP header of an IPv4
   packet, IPv6/IP-UDP mode, and will be carried as an IPv4 packet.  And
   any IPv4 packet from the mobile node with the source IPv4 MN-HoA,
   will be encapsulated in an UDP header of an IPv4 packet, IPv4/
   IPv4-UDP, and will be carried as an IPv4 packet.  In both these
   cases, the UDP header will not be there, if there is no presence of
   NAT devices detected on the path.

   All the packets that the mobile access gateway receives from the
   tunnel, after removing the tunnel encapsulation, will forward it to
   the mobile node on the connected interface.


6.10.  Interaction with DHCP Relay Agent

   If Statefull Address Configuration using DHCP is supported on the
   link on which the mobile node is attached, the DHCP relay agent [RFC-
   3315] needs to be configured on the access router.  When the mobile
   node sends a DHCPv6 Request message, the relay agent function on the
   access router must set the link-address field in the DHCPv6 message
   to the mobile node's home network prefix, so as to provide a prefix
   hint to the DHCP Server.  On a point-to-point link, this is just a
   normal DHCP relay agent configuration.  However, on the shared links
   supporting multiple mobile nodes with different home prefixes, there
   is some interaction required between the relay agent and the mobile
   access gateway, for setting the link-address field to the requesting
   mobile node's home network prefix.

   If the mobile is permitted to roam using IPv4 home address, the
   DHCPv4 relay agent service [RFC-2131] needs to be configured on that
   link.  Further, the giaddr field in the DHCPv4 Request message must
   be set to the mobile node's IPv4 home network prefix.



6.11.  Mobile Node Detachment Detection and Resource Cleanup

   Before sending a Proxy Binding Update message to the local mobility
   anchor for extending the lifetime of a currently existing binding of
   a mobile node, the mobile access gateway MUST make sure the mobile
   node is still attached to the connected link by using some reliable
   method.  If the mobile access gateway cannot predictably detect the
   presence of the mobile node on the connected link, it MUST NOT
   attempt to extend the registration lifetime of the mobile node.
   Further, in such scenario, the mobile access gateway MUST terminate



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   the binding of the mobile node by sending a Proxy Binding Update
   message to the mobile node's local mobility anchor with lifetime
   value set to 0.  It MUST also remove any local state such as binding
   update list entry that was created for that mobile node.

   The specific detection mechanism of the loss of a visiting mobile
   node on the connected link is specific to the access link between the
   mobile node and the mobile access gateway and is outside the scope of
   this document.  Typically, there are various link-layer specific
   events specific to each access technology that the mobile access
   gateway can depend on for detecting the node loss.  In general, the
   mobile access gateway can depend on one or more of the following
   methods for the detection presence of the mobile node on the
   connected link:

   o  Link-layer event specific to the access technology

   o  PPP Session termination event on point-to-point link types

   o  IPv6 Neighbor Unreachability Detection event from IPv6 stack

   o  Notification event from the local mobility anchor

   o  Absence of data traffic from the mobile node on the link for a
      certain duration of time


6.12.  Coexistence with Mobile Nodes using Host-based Mobility

   In some operating environments, network operators may want to
   provision the access link attached to the mobile access gateway to
   offer network-based mobility service only to some nodes and enable
   normal IP access support for some other nodes on that link.  This
   specification supports access links with such mixture of nodes.  The
   network has the control on when to enable the mobile node with the
   network mobility service.

   Upon obtaining the mobile node's profile after a successful access
   authentication and after a policy consideration, the mobile access
   gateway MUST determine if the network based mobility service should
   be offered to that mobile node.  If the mobile node is entitled for
   such service, then the network should ensure the mobile node believes
   it is on its home link, as explained in various sections of this
   document.

   If the mobile node is not entitled for the network based mobility
   service, as determined from the policy, the mobile access gateway
   MUST ensure the mobile node can obtain an IPv6 address using normal



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   IPv6 address configuration mechanisms.  The obtained address should
   be from a local visitor network prefix.  In other words the mobile
   node should be able to operate as a traditional mobile node roaming
   in a visitor network and with the ability to obtain an address from
   the local visitor network prefix hosted on that link.  This
   essentially ensures, the proxy mobile IPv6 protocol will not impact
   the behavior of a mobile node that is using host-based mobility, as
   per [RFC-3775].

   If the stateless address configuration mode is supported on that
   link, the prefix information option in the router advertisements
   should contain local visitor network prefix.  If statefull address
   configuration mode is enforced on the link and if DHCP is in used,
   the mobile node should be able to obtain the IPv6 or IPv4 care-of
   address from the local visitor network prefix.

   If the link between the mobile access gateway and the mobile node is
   a shared link, the Router Advertisement has to unicasted to the
   mobile node with the destination address in the layer-2 header set to
   the mobile's MAC address and the destination address in the IPv6
   header set to the all-nodes multicast address.


6.13.  Mobile Access Gateway Operation Summary

   o  After detecting a new mobile node on its access link and after the
      successful access authentication and authorization of the mobile
      node, the mobile access gateway MUST be able to able to access the
      mobile node's profile.  This may be downloaded from the local/
      network policy store using MN-Identity or may be obtained as part
      of a context transfer procedure.  The mobile node's profile at the
      minimum MUST have the mobile node's local mobility anchor address
      and the MN-Identity.  Optionally, it may have the mobile node's
      home network prefix and other configuration parameters.

   o  The mobile access gateway MAY use one or more ways to detect the
      attachment of a mobile node on to the link.  The techniques can be
      specific to the access technology or can be other generic events
      as mentioned in the above sections.

   o  If the network determines that the mobile node will not be offered
      the network-based mobility service, the mobile access gateway MUST
      ensure that the Router Advertisements it sends will not contain
      the mobile node's home prefix, but will be the hosted on-link
      prefix.  Also, if the mobile node attempts to obtain an IPv4/IPv6
      address, the mobile access gateway or the DHCP relay agent on the
      link MUST ensure that the prefix hint that gets added to the DHCP
      message will be of the local hosted prefix.



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   o  `The mobile access gateway on receiving a Router Solicitation
      message from a mobile node MUST send a Router Advertisement
      message containing the mobile node's home network prefix.

   o  The mobile access gateway MUST send the periodic Router
      Advertisement messages, as per the ND specification [RFC-2461],
      advertising the mobile node's home network prefix on the access
      link.

   o  If the link between the mobile node and the mobile access gateway
      is a shared-link, then the Router Advertisement MUST be unicasted
      to the mobile node by setting the destination address in the link-
      layer header to the mobile node's MAC address and with the
      destination address in the IPv6 header set to the all-nodes
      multicast address.

   o  If the mobile node uses DHCP for address configuration, the mobile
      access gateway or specifically the DHCP relay agent on the link
      MUST ensure the DHCPv4/v6 packets are properly tagged with the
      sending mobile node's MN-HoA or IPv4 MN-HoA, as the prefix hint.

   o  If IPv4 home address is supported for a given mobile node, the
      mobile access gateway must act as a proxy for the mobile node's
      IPv4 default-router and that is the address of the local mobility
      anchor.  The mobile access gateway must be able receive all the
      IPv4 packets from the mobile node.  The mobile access gateway MUST
      respond to any ARP request message from the mobile node attempting
      to resolve the MAC address of its default-router.  The ARP reply
      must contain the MAC address of the mobile access gateway.

   o  The Proxy Binding Update message that the mobile access gateway
      sends to the local mobility anchor, MUST have the configured IPv6
      address of the egress interface.  The Proxy Binding Update message
      MUST have the NAI option identifying the mobile node, home network
      prefix option, IPv4 home address option and optionally the time
      stamp option.  If the home network prefix option or the IPv4 home
      address option are set to value 0, the local mobility anchor will
      assign the home network prefix and IPv4 home address and will
      return them in the Proxy Binding Acknowledgment.  This message
      MUST be protected by using IPSec security association created
      between the mobile access gateway and local mobility anchor.

   o  After receiving a Proxy Binding Acknowledgment with the status
      code indicating the acceptance of the Binding Update, the mobile
      access gateway MUST setup a tunnel to the mobile node's local
      mobility anchor, as explained in the above sections, if there is
      exists no tunnel.  The mobile access gateway MUST also add a
      default route over the tunnel for all the traffic from the mobile



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      node.

   o  If the local mobility anchor denies the Proxy Binding Update
      request, the mobile access gateways MUST NOT advertise the mobile
      node's home prefix on the access link and there by denying
      mobility service to the mobile node.

   o  Before attempting to extend binding lifetime of a mobile node, the
      mobile access gateway MUST make sure the mobile node is still
      attached to the connected link by using some reliable method.  If
      the mobile access gateway cannot predictably detect the presence
      of the mobile node on the connected link, it MUST NOT attempt to
      extend the registration lifetime of the mobile node.  Also, it
      MUST terminate the binding of the mobile node by sending a Proxy
      Binding Update message to the mobile node's local mobility anchor
      with lifetime value set to 0.

   o  At any point, if the mobile access gateway detects that the mobile
      node has roamed away from its access link, it MUST send a Proxy
      Binding Update to the local mobility anchor with the lifetime
      value set to 0 and it must also remove the default route over the
      tunnel for that mobile and also remove the Binding Update list
      entry and any other local state created for that mobile node.




7.  Mobile Node Operation


   The Network-based mobility scheme defined in this document, allows a
   mobile node to obtain IP mobility within the proxy mobile IPv6
   domain, with out requiring the mobile node to involve in any mobility
   management.

   When a mobile node enters a proxy mobile IPv6 domain and attached to
   an access link, the network identifies the mobile node as part of the
   access authentication and establishes an identity for the mobile
   node.  This identity has a binding to a cryptographic state and
   potentially associating the mobile node's link-layer address of the
   attached interface.  The specifics on how this is achieved is beyond
   the scope of this document and is very much specific to the access
   technology and depends on the applied security protocols in place.
   For all practical purposes, this document assumes that the mobile
   node's access to the network is secure.

   Once the mobile node enters a Proxy Mobile IPv6 domain and attaches
   to an access network, the network identifies the mobile as part of



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   the access authentication procedure and ensures the mobile using any
   of the address configuration mechanisms permitted by the network for
   that mobile, will be able to obtain an address and move anywhere in
   that managed domain.  From the perspective of the mobile, the entire
   Proxy Mobile IPv6 domain appears as a single link, the network
   ensures the mobile believes it is always on the same link.

   The mobile node can be operating in an IPv4-only mode, IPv6-only mode
   or in dual IPv4/IPv6 mode.  Typically, the configured policy in the
   network determines the type of home address(es) i.e.  MN-HoA, IPv4
   MN-HoA or both, that the network mobility is supported for.  If the
   configured policy for a mobile node is for IPv6-only home address
   mobility, the mobile node will be able to obtain its MN-HoA, any
   where in that proxy mobile IPv6 domain and if policy allows only
   IPv4-only home address mobility, the mobile node will be able to
   obtain its IPv4 MN-HoA, any where in that domain.  Similarly, if the
   policy permits both the IPv4 and IPv6 home address mobility, the
   mobile node will be able to obtain its MN-HoA and IPv4 MN-HoA and
   move anywhere in the network.  However, if the mobile node is
   configured for IPv6-only mobility and if the mobile node attempts to
   obtain an IPv4 address configuration via DHCP mechanism, the obtained
   address configuration will not have any mobility properties, i.e. the
   obtained address will be from a local prefix and not from a prefix
   that is topologically anchored at the local mobility anchor and hence
   the mobile will loose that address as it moves to a different link.
   The specifics on how this is achieved is the operational logic of the
   mobile access gateway on the access link.

7.1.  Booting up in a Proxy Mobile IPv6 Domain


   When a mobile node moves into a proxy mobile IPv6 domain and attaches
   to an access link, the mobile node will present its identity, MN-
   Identity, to the network as part of the access authentication
   procedure.  Once the authentication procedure is complete and the
   mobile node is authorized to access the network, the network or
   specifically the mobile access gateway on the access link will have
   the mobile node's profile and so it would know the mobile node's home
   prefix and other address configuration details and other related
   parameters.

   If the mobile node is IPv6 enabled, on attaching to the link and
   after access authentication, the mobile node typically would send a
   Router Solicitation message.  The mobile access gateway on the
   attached link will respond to the Router Solicitation message with a
   Router Advertisement.  The Router Advertisement will have the mobile
   node's home network prefix, default-router address and other address
   configuration parameters.  The address configuration parameters such



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   as Managed Address Configuration, Statefull Configuration flag values
   will typically be consistent through out that domain for that mobile
   node.

   If the Router Advertisement has the Managed Address Configuration
   flag set, the mobile node, as it would normally do, will send a
   DHCPv6 Request and the mobile access gateway on that access link will
   ensure, the mobile node node gets the MN-HoA as a lease from the DHCP
   server.

   If the Router Advertisement does not have the Managed Address
   Configuration flag set and if the mobile node is allowed to use an
   autoconfigured address, the mobile node will generate an interface
   identifier, as per the Autoconf specification [RFC-2462] or using
   privacy extensions as specified in Privacy Extensions specification
   [RFC-3041].

   If the mobile node is IPv4 enabled or IPv4-only enabled, the mobile
   node after the access authentication, will be able to obtain the IPv4
   address configuration for the connected interface by using DHCPv4.

   Once the address configuration is complete, the mobile node will have
   the MN-HoA, IPv4 MN-HoA or both, that it can continue to use as long
   as it is with in the scope of that proxy mobile IPv6 domain.


7.2.  Roaming in the Proxy Mobile IPv6 Network


   After booting in the Proxy Mobile IPv6 domain and obtaining the
   address configuration, the mobile node as it roams in the network
   between access links, will always detect its home network prefix on
   the link, as long as the attached access network is in the scope of
   that proxy mobile IPv6 domain.  The mobile node can continue to use
   its IPv4/IPv6 MN-HoA for sending and receiving packets.  If the
   mobile node uses DHCP for address configuration, it will always be
   able to obtain its MN-HoA using DHCP.  However, the mobile node will
   always detect a new default-router on each connected link, but still
   advertising the mobile node's home prefix as the on-link prefix and
   with the other configuration parameters consistent with the link
   properties as before.


7.3.  IPv6 Host Protocol Parameters


   This specification assumes the mobile node to be a normal IPv6 node,
   with its protocol operation consistent with the base IPv6



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   specification [RFC-2460].  All aspects of Neighbor Discovery
   Protocol, including Router Discovery, Neighbor Discovery, Address
   Configuration procedures will just remain consistent with the base
   IPv6 Neighbor Discovery Specification [RFC-2461].  However, this
   specification recommends that the following IPv6 operating parameters
   on the mobile node be adjusted to the below recommended values for
   protocol efficiency and for achieving faster hand-offs.


   Lower Default-Router List Cache Time-out:

   As per the base IPv6 specification [RFC-2460], each IPv6 host will
   maintain certain host data structures including a Default-Router
   list.  This is the list of on-link routers that have sent Router
   Advertisement messages and are eligible to be default routers on that
   link.  The Router Lifetime field in the received Router Advertisement
   defines the life of this entry.

   In the Proxy Mobile IPv6 scenario, when the mobile node moves from
   one link to another, the received Router Advertisement messages
   advertising the mobile's home network prefix will be from a different
   link-local address and thus making the mobile node believe that there
   is a new default-router on the link.  It is important that the mobile
   node uses the newly learnt default-router as supposed to the
   previously learnt default-router.  The mobile node must update its
   default-router list with the new default router entry and must age
   out the previously learnt default router entry from its cache, just
   as specified in Section 6.3.5 of the base IPv6 ND specification [RFC-
   2461].  This action is critical for minimizing packet losses during a
   hand off switch

   On detecting a reachability problem, the mobile node will certainly
   detect the neighbor or the default-router unreachability by
   performing a Neighbor Unreachability Detection procedure, but it is
   important that the mobile node times out the previous default router
   entry at the earliest.  If a given IPv6 host implementation has the
   provision to adjust these flush timers, still conforming to the base
   IPv6 ND specification, it is desirable to keep the flush-timers to
   suit the above consideration.

   However, if the mobile access gateway has the ability to with draw
   the previous default-router entry, by multicasting a Router
   Advertisement using the link-local address that of the previous
   mobility proxy agent and with the Router Lifetime field set to value
   0, then it is possible to force the flush out of the Previous
   Default-Router entry from the mobile node's cache.  This certainly
   requires some context-transfer mechanisms in place for notifying the
   link-local address of the default-router on the previous link to the



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   mobile access gateway on the new link.

   There are other solutions possible for this problem, including the
   assignment of a unique link-local address for all the access routers
   in the Proxy Mobile IPv6 Network.  In either case, this is an
   implementation choice and has no bearing on the protocol
   interoperability.  Implementations are free to adopt the best
   approach that suits their target deployments.





8.  Message Formats

   This section defines extensions to the Mobile IPv6 [RFC-3775]
   protocol messages.



8.1.  Proxy 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
                                      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                      |            Sequence #         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |A|H|L|K|M|R|P|  Reserved       |            Lifetime           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                  Figure 6: Proxy Binding Update Message



   A Binding Update message that is sent by mobile access gateway is
   referred to as the Proxy Binding Update message.


   Proxy Registration Flag (P)

   The Proxy Registration Flag is set to indicate to the local mobility
   anchor that the Binding Update is from a mobile access gateway acting



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   as a proxy mobility agent.  The flag MUST be set to the value of 1
   for proxy registrations and MUST be set to 0 for direct registration
   send my a mobile node using host-base mobility.

   For descriptions of other fields present in this message, refer to
   the section 6.1.7 of Mobile IPv6 specification [RFC3775].


8.2.  Proxy Binding Acknowledgment



       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
                                      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                      |   Status      |K|R|P|Reserved |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Sequence #            |           Lifetime            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


              Figure 7: Proxy Binding Acknowledgment Message



   Proxy Registration Flag (P)

   A new flag (P) is included in the Binding Acknowledgement message to
   indicate that the local mobility anchor Agent that processed the
   corresponding Binding Update supports Proxy Registrations.  The flag
   is set only if the corresponding Proxy Binding Update had the Proxy
   Registration Flag (P) set to 1.  The rest of the Binding
   Acknowledgement format remains the same, as defined in [RFC-3775].

   For descriptions of other fields present in this message, refer to
   the Mobile IPv6 base specificatoin [RFC-3775].

   A Binding Acknowledgment message that is sent by the mobile access
   gateway is also referred to as "Proxy Binding Acknowledgement".


8.3.  Home Network Prefix Option

   A new option, Home Network Prefix Option is defined for using it in
   the Proxy Binding Update and Acknowledgment messages exchanged



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   between the local mobility anchor to the mobile access gateway.  This
   option can be used for exchanging the mobile node's home prefix and
   home address information.

   The home network prefix Option has an alignment requirement of 8n+4.
   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    | Prefix Length |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                    Home Network Prefix                        +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


       Type
           <IANA>

       Length

           8-bit unsigned integer indicating the length in octets of
           the option, excluding the type and length fields. This field
           MUST be set to 18.

       Reserved

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

       Prefix Length

           8-bit unsigned integer indicating the prefix length of the
           IPv6 prefix contained in the option. If the prefix length
           is set to the value 128, indicates the presence of the
           mobile node's 128-bit home address.

       Home Network Prefix

           A sixteen-byte field containing the Home Network Prefix




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                   Figure 8: Home Network Prefix Option



8.4.  Time Stamp Option

   A new option, Time Stamp Option is defined for use in Proxy Binding
   Update and Acknowledgement messages.  This option MUST be present in
   all Proxy Binding Update and Acknowledgement messages.



      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
                                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  |      Option Type  | Option Length |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                          Timestamp                            +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


       Type
           <IANA>

       Length

           8-bit unsigned integer indicating the length in octets of
           the option, excluding the type and length fields.  This field
           MUST be set to 18.

       Timestamp

           64-bit time stamp


                        Figure 9: Time Stamp Option




8.5.  Status Codes

   This document defines the following new Binding Acknowledgement
   status values:

   145: Proxy Registration not supported by the local mobility anchor



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   146: Proxy Registrations from this mobile access gateway not allowed

   147: No home address for this NAI is configured and the Home Network
   Prefix Option not present in the Binding Update.

   148: Invalid Time Stamp Option in the Binding Update

   Status values less than 128 indicate that the Binding Update was
   processed successfully by the receiving nodes.  Values greater than
   128 indicate that the Binding Update was rejected by the local
   mobility anchor.

   The value allocation for this usage needs to be approved by the IANA
   and must be updated in the IANA registry.




9.  IANA Considerations

   This document defines a new Mobility Header Option, the Mobile Home
   Network Prefix Option.  This option is described in Section 8.3.  The
   Type value for this option needs to be assigned from the same
   numbering space as allocated for the other mobility options defined
   in [RFC-3775].

   This document defines a new Mobility Header Option, the Time Stamp
   Option.  This option is described in Section 8.4.  The type value for
   this option needs to be assigned from the same numbering space as
   allocated for the other mobility options defined in [RFC-3775].

   This document also defines new Binding Acknowledgement status values
   as described in Section 8.5.  The status values MUST be assigned from
   the same space used for Binding Acknowledgement status values in
   [RFC-3775].



10.  Security Considerations

   The security threats against any general network-based mobility
   management protocol are covered in the document, Security Threats to
   Network-Based Localized Mobility Management
   [draft-ietf-netlmm-threats-04.txt].  This section analyses those
   vulnerabilities in the context of Proxy Mobile IPv6 protocol and
   covers all aspects around those identified vulnerabilities.

   A compromised mobile access gateway can send Proxy Binding Update



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   requests for mobile nodes that are not attached to its access link.
   This threat is similar to an attack on a typical routing protocol or
   equivalent to the compromise of a on-path router and hence this
   threat exists in the network today and this specification does not
   make this vulnerability any worse than what it is.  However, to
   eliminate this attack, the local mobility anchor can ensure that the
   mobile node is attached to the access link of the requesting mobile
   access gateway.  This can be achieved using out of band mechanisms,
   such as from the mobile node's access authentication to the network
   and the specifics of how that is achieved is beyond the scope of this
   document.

   This document does not cover the security requirements for
   authorizing the mobile node for the use of the access link.  It is
   assumed that there are proper Layer-2 based authentication
   procedures, such as EAP, in place and will ensure the mobile node is
   properly identified and authorized before permitting it to access the
   network.  It is further assumed that the same security mechanism will
   ensure the mobile session is not hijacked by malicious nodes on the
   access link.

   This specification requires that all the signaling messages exchanged
   between the mobile access gateway and the local mobility anchor MUST
   be authenticated by IPsec [RFC-4301].  The use of IPsec to protect
   Mobile IPv6 signaling messages is described in detail in the HA-MN
   IPsec specification [RFC-3776] and the extension of that security
   model to Proxy Mobile IPv6 is covered in Section 4.0 of this
   document.

   As described in the base Mobile IPv6 specification [RFC-3775],
   Section 5.1 both the mobile client (in this case, its the mobile
   access gateway) and the local mobility anchor MUST support and SHOULD
   use the Encapsulating Security Payload (ESP) header in transport mode
   and MUST use a non-NULL payload authentication algorithm to provide
   data origin authentication, data integrity and optional anti-replay
   protection.

   The proxy solution allows one device creating a routing state for
   some other device at the local mobility anchor.  It is important that
   the local mobility anchor has proper authorization services in place
   to ensure a given mobile access gateway is permitted to be a proxy
   for a specific mobile node.  If proper security checks are not in
   place, a malicious node may be able to hijack a session or may do a
   denial-of-service attacks.







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11.  Acknowledgements

   The authors would like to specially thank Julien Laganier, Christian
   Vogt, Pete McCann, Brian Haley and Ahmad Muhanna for their thorough
   review of this document.

   The authors would also like to thank the Gerardo Giaretta, Kilian
   Weniger, Alex Petrescu, Mohamed Khalil, Fred Templing, Nishida
   Katsutoshi, James Kempf, Vidya Narayanan, Henrik Levkowetz, Phil
   Roberts, Jari Arkko, Ashutosh Dutta, Hesham Soliman, Behcet Sarikaya,
   George Tsirtsis and many others for their passionate discussions in
   the working group mailing list on the topic of localized mobility
   management solutions.  These discussions stimulated much of the
   thinking and shaped the draft to the current form.  We acknowledge
   that !

   The authors would also like to thank Ole Troan, Akiko Hattori, Perviz
   Yegani, Mark Grayson and Tim Stammers for their input on this
   document.



12.  Appendix-A: Proxy Mobile IPv6 Deployment Models


   Localized Mobility Management and Global Mobility Management can be
   combined in many different ways.  Proxy Mobile IPv6 is typically used
   for localized mobility management and Mobile IPv6 is applied for
   global mobility management.  The following section covers some of the
   potential deployment use-cases.  However, it is to be noted that the
   protocol is not restricted for the given use cases.  Its up to the
   specific architecture as how it leverages the base protocol defined
   in this document.


















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            |<-- Global Mobility -->|

   |<- Local Mobility ->|        |<- Local Mobility ->|
         +-----+                  +-----+
        /       \                /       \
        \       /                \       /
         +-----+                  +-----+
     PMIPv6 Domain#2             PMIPv6 Domain#3
                 \              /
                  \            /
                   \__________/
                   (__________)
                     Internet
                        |
                        |
                        |
                     +-----+
                    /       \
                    \       /
                     +-----+
                 MIPv6 Home Domain
                 (PMIPv6 Domain#1)


        Figure 10: Integrated Local and Global Mobility Management


12.1.  Case-1# Avoiding Global Mobility at home (MIPv6-HoA == MN-HoA)


   In this mode, the mobile node uses Proxy Mobile IPv6 as long as it is
   in the Proxy Mobile IPv6 domain.  It has Mobile IPv6 stack active at
   the same time, but as long as it is attached to the same Proxy Mobile
   IPv6 domain, it will appear as if it is attached to the home link.
   If it attaches to an access network that is not part of the Proxy
   Mobile IPv6 domain, it acquires a care-of address from the access
   networks, treats the earlier home address in the Proxy Mobile IPv6
   domain as the Mobile IPv6 home address and performs a Mobile IPv6
   registration.  The Mobile IPv6 registration is performed with the
   same home agent that was earlier a local mobility anchor in the Proxy
   Mobile IPv6 domain.  Following are the key aspects of this ulti-layer
   mobility management scheme.

   The mobile node has a Mobile IPv6 home domain and is either
   statically configured or will be dynamically assigned with an home
   address (MIPv6-HoA).  The home agent supporting this mobile node
   based on host-based mobility management scheme, is also configured to
   function as a local mobility anchor for supporting local mobility



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   management.

   MIPv6-HoA = MN-HoA.

   When the mobile node is in its mobile IPv6 home domain, it will be
   able to roam in that domain using its MN-HoA and with out having to
   participate in any mobility related signaling.  The domain is enabled
   for network-based mobility and the obtained home address in the proxy
   mobile IPv6 context (MN-HoA) is the same as its global home address
   (MIPv6-HoA).  The mobile is not required to initiate host-based
   mobility and avoiding any IPv6 tunneling over ahead in the home
   domain.

   When the mobile moves away from its home domain and enters a domain
   where network-based mobility management is enabled, the mobile node
   can obtain an home address, MN-HoA, for that Proxy Mobile IPv6 domain
   and can establish mobility session with its home agent.  The obtained
   MN-HoA in that visitor domain is valid through out that domain and
   the mobile node is not required to update its global mobility binding
   as long as it is in that domain.  From the context of the global
   mobility session, the obtain home address in that domain is the
   mobile IPv6 Care-Off Address.

   MIPv6-CoA = MN-HoA.

   If the mobile node moves in to a domain, where network based mobility
   is not enabled, the mobile node will use the locally obtained IPv6
   address on the anchored link and establish global mobility management
   for its home address (MIPv6-HoA), using host-based mobility
   signaling.


12.2.  Case-2# Requiring Global Mobility at home (MIPv6-CoA == MN-HoA)


   In this model, PMIPv6 and MIPv6 are used in a hierarchical manner
   where proxy mobile IPv6 is used for local mobility and mobile IPv6 is
   used for global mobility.  The MN-HoA address assigned to the mobile
   node in the Proxy Mobile IPv6 domain is used as the care-of address
   for Mobile IPv6 registration.  If the mobile node moves and attaches
   to an access network that is not part of the proxy mobile IPv6
   domain, it acquires a care-of address from the access network and
   performs a regular Mobile IPv6 registration with its home agent.
   When the mobile node is outside the Proxy Mobile IPv6 domain, only
   Mobile IPv6 is used.

   The key difference between this model and the above model is the
   restriction of the home address obtained from the proxy mobile IPv6



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   domain which also happens to be its mobile IPv6 home domain, to be
   used as a care-of address for global mobility.  The mobile node
   cannot obtain its MIPv6-HoA as a MN-HoA, when at home and hence it
   always needs to establish global mobility session if sustaining
   sessions when moving between the domains is desired.

   When at home or away, where network-based mobility is enabled, the
   mobile node will use the locally obtained IPv6address (MIPv6-CoA) on
   the attached link and establish global mobility management for its
   home address (MIPv6-HoA), using host-based mobility signaling.




13.  Appendix-B: Proxy Mobile IPv6 interactions with AAA Infrastructure


   Every mobile node that roams in a proxy Mobile IPv6 domain, would
   typically be identified by an identifier, MN-Identifier, and that
   identifier will have an associated policy profile that identifies the
   mobile node's home network prefix, permitted address configuration
   modes, roaming policy and other parameters that are essential for
   providing network-based mobility service.  This information is
   typically configured in AAA.  It is possible the home network prefix
   is dynamically allocated for the mobile node when it boots up for the
   first time in the network, or it could be a statically configured
   value on per mobile node basis.  However, for all practical purposes,
   the network entities in the proxy Mobile IPv6 domain, while serving a
   mobile node will have access to this profile and these entities can
   query this information using RADIUS/DIAMETER protocols.



14.  Appendix-C: Supporting Shared-Prefix Model using DHCPv6


   For supporting shared-prefix model, i.e, if multiple mobile nodes are
   configured with a common IPv6 network prefix, as in Mobile IPv6
   specification, it is possible to support that configuration under the
   following guidelines:

   The mobile node is allowed to use statefull address configuration
   using DHCPv6 for obtaining its address configuration.  The mobile
   nodes is not allowed to use any of the stateless autoconfiguration
   techniques.  The permitted address configuration models for the
   mobile node on the access link can be enforced by the mobile access
   gateway by setting the relevant flags in the Router Advertisements,
   as per ND Specification, [RFC-2461]



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   The Home Network Prefix Option that is sent by the mobile access
   gateway in the Proxy Binding Update message, must contain the 128-bit
   host address that the mobile node obtained via DHCPv6.

   Routing state at the mobile access gateway:

   For all IPv6 traffic from the source MN-HoA::/128 to destination
   0::/0, route via tunnel0, next-hop LMAA, where tunnel0 is the MAG to
   LMA tunnel.

   Routing state at the local mobility anchor:

   For all IPv6 traffic to destination MN-HoA::/128, route via tunnel0,
   next-hop Proxy-CoA, where tunnel0 is the LMA to MAG tunnel.



15.  References


15.1.  Normative References


   [RFC-1305] Mills, D., "Network Time Protocol (Version 3)
   Specification, Implementation", RFC 1305, March 1992.

   [RFC-2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
   (IPv6) Specification", RFC 2460, December 1998.

   [RFC-2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor
   Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998.

   [RFC-2462] Thompson, S., Narten, T., "IPv6 Stateless Address
   Autoconfiguration", RFC 2462, December 1998.

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

   [RFC-3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and
   M.Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
   RFC 3315, July 2003.

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

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



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   [RFC-4283] Patel, A., Leung, K., Khalil, M., Akhtar, H., and K.
   Chowdhury, "Mobile Node Identifier Option for Mobile IPv6", RFC 4283,
   November 2005.

   [RFC-4301] Kent, S. and Atkinson, R., "Security Architecture for the
   Internet Protocol", RFC 4301, December 2005.

   [RFC-4303] Kent, S. "IP Encapsulating Security Protocol (ESP)", RFC
   4303, December 2005.

   [RFC-4306] Kaufman, C, et al, "Internet Key Exchange (IKEv2)
   Protocol", RFC 4306, December 2005.

   [draft-ietf-netlmm-nohost-req-05.txt] Kempf, J., Leung, K., Roberts,
   P., Nishida, K., Giaretta, G., Liebsch, M., "Goals for Network-based
   Localized Mobility Management", October 2006.

   [draft-ietf-netlmm-nohost-ps-05.txt] Kempf, J., Leung, K., Roberts,
   P., Nishida, K., Giaretta, G., Liebsch, M., "Problem Statement for
   Network-based Localized Mobility Management", September 2006.

   [draft-ietf-netlmm-threats-04.txt] Vogt, C., Kempf, J., "Security
   Threats to Network-Based Localized Mobility Management", September
   2006.

   [draft-ietf-mip6-nemo-v4traversal-03.txt] Soliman, H. et al, "Mobile
   IPv6 support for dual stack Hosts and Routers (DSMIPv6)", October
   2006.


15.2.  Informative References


   [RFC-1332] McGregor, G., "The PPP Internet Protocol Control Protocol
   (IPCP)", RFC 1332, May 1992.

   [RFC-1661] Simpson, W., Ed., "The Point-To-Point Protocol (PPP)", STD
   51, RFC 1661, July 1994.

   [RFC-2472] Haskin, D. and Allen, E., "IP version 6 over PPP", RFC
   2472, December 1998.

   [RFC-2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
   IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

   [RFC-3041] Narten, T. and Draves, R., "Privacy Extensions for
   Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001.




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   [RFC-3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
   August 2002.

   [RFC-3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
   Discovery (ND) Trust Models and Threats", RFC 3756, May 2004.

   [draft-iab-multilink-subnet-issues-03.txt] Thaler, D., "Multilink
   Subnet Issues", January 2006.

   [draft-ietf-dna-protocol-03] Kempf, J., et al "Detecting Network
   Attachment in IPv6 Networks (DNAv6)", draft-ietf-dna-protocol-03,
   October 2006.

   [draft-ietf-mip6-ikev2-ipsec-08] Devarapalli, V. and Dupont, F.,
   "Mobile IPv6 Operation with IKEv2 and the revised IPsec
   Architecture", December 2006.


Authors' Addresses

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

   Email: sgundave@cisco.com


   Kent Leung
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: kleung@cisco.com


   Vijay Devarapalli
   Azaire Networks
   4800 Great America Pkwy
   Santa Clara, CA  95054
   USA

   Email: vijay.devarapalli@azairenet.com






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   Kuntal Chowdhury
   Starent Networks
   30 International Place
   Tewksbury, MA


   Email: kchowdhury@starentnetworks.com


   Basavaraj Patil
   Nokia
   6000 Connection Drive
   Irving, TX  75039
   USA

   Email: basavaraj.patil@nokia.com



































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Full Copyright Statement

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