NETLMM WG                                                  S. Gundavelli
Internet-Draft                                                  K. Leung
Intended status: Standards Track                                   Cisco
Expires: December 20, 2007                                V. Devarapalli
                                                         Azaire Networks
                                                            K. Chowdhury
                                                        Starent Networks
                                                                B. Patil
                                                  Nokia Siemens Networks
                                                           June 18, 2007


                           Proxy Mobile IPv6
                   draft-ietf-netlmm-proxymip6-01.txt

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   This Internet-Draft will expire on December 20, 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 & Terminology  . . . . . . . . . . . . . . . . . .  5
     2.1.  Conventions used in this document  . . . . . . . . . . . .  5
     2.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Proxy Mobile IPv6 Protocol Overview  . . . . . . . . . . . . .  7
   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 . . . . . . . . . . . . . 14
     5.3.  Routing Considerations . . . . . . . . . . . . . . . . . . 15
     5.4.  Local Mobility Anchor Address Discovery  . . . . . . . . . 16
     5.5.  Sequence Number and Time-Stamps for Message Ordering . . . 16
     5.6.  Route Optimizations Considerations . . . . . . . . . . . . 17
     5.7.  Mobile Prefix Discovery Considerations . . . . . . . . . . 18
     5.8.  Signaling Considerations . . . . . . . . . . . . . . . . . 18
       5.8.1.  Initial Proxy Binding Registration . . . . . . . . . . 18
       5.8.2.  Extending the binding lifetime . . . . . . . . . . . . 20
       5.8.3.  De-registration of the binding . . . . . . . . . . . . 20
     5.9.  Local Mobility Anchor Operational Summary  . . . . . . . . 20
   6.  Mobile Access Gateway Operation  . . . . . . . . . . . . . . . 21
     6.1.  Supported Access Link Types  . . . . . . . . . . . . . . . 21
     6.2.  Supported Home Network Prefix Models . . . . . . . . . . . 22
     6.3.  Supported Address Configuration Models . . . . . . . . . . 22
     6.4.  Access Authentication & Mobile Node Identification . . . . 23
     6.5.  Mobile Node's Policy Profile . . . . . . . . . . . . . . . 23
     6.6.  Conceptual Data Structures . . . . . . . . . . . . . . . . 24
     6.7.  Home Network Emulation . . . . . . . . . . . . . . . . . . 24
       6.7.1.  Home Network Prefix Renumbering  . . . . . . . . . . . 25
     6.8.  Link-Local and Global Address Uniqueness . . . . . . . . . 26
     6.9.  Signaling Considerations . . . . . . . . . . . . . . . . . 27
       6.9.1.  Initial Attachment and binding registration  . . . . . 27



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       6.9.2.  Extending the binding lifetime . . . . . . . . . . . . 28
       6.9.3.  De-registration of the binding . . . . . . . . . . . . 28
     6.10. Routing Considerations . . . . . . . . . . . . . . . . . . 28
       6.10.1. Transport Network  . . . . . . . . . . . . . . . . . . 29
       6.10.2. Tunneling & Encapsulation Modes  . . . . . . . . . . . 29
       6.10.3. Routing State  . . . . . . . . . . . . . . . . . . . . 30
       6.10.4. Local Routing  . . . . . . . . . . . . . . . . . . . . 31
       6.10.5. Tunnel Management  . . . . . . . . . . . . . . . . . . 31
       6.10.6. Forwarding Rules . . . . . . . . . . . . . . . . . . . 31
     6.11. Interaction with DHCP Relay Agent  . . . . . . . . . . . . 32
     6.12. Mobile Node Detachment Detection and Resource Cleanup  . . 32
     6.13. Allowing network access to other IPv6 nodes  . . . . . . . 33
   7.  Mobile Node Operation  . . . . . . . . . . . . . . . . . . . . 34
     7.1.  Booting up in a Proxy Mobile IPv6 Domain . . . . . . . . . 34
     7.2.  Roaming in the Proxy Mobile IPv6 Network . . . . . . . . . 35
     7.3.  IPv6 Host Protocol Parameters  . . . . . . . . . . . . . . 36
   8.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . . 37
     8.1.  Proxy Binding Update . . . . . . . . . . . . . . . . . . . 37
     8.2.  Proxy Binding Acknowledgment . . . . . . . . . . . . . . . 38
     8.3.  Home Network Prefix Option . . . . . . . . . . . . . . . . 39
     8.4.  Time Stamp Option  . . . . . . . . . . . . . . . . . . . . 40
     8.5.  Status Codes . . . . . . . . . . . . . . . . . . . . . . . 41
   9.  Protocol Configuration Variables . . . . . . . . . . . . . . . 42
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 42
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 42
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 44
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 44
     13.2. Informative References . . . . . . . . . . . . . . . . . . 45
   Appendix A.  Proxy Mobile IPv6 interactions with AAA
                Infrastructure  . . . . . . . . . . . . . . . . . . . 46
   Appendix B.  Supporting Shared-Prefix Model using DHCPv6 . . . . . 46
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 47
   Intellectual Property and Copyright Statements . . . . . . . . . . 49

















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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 mobile node and home agent enables the creation
   and maintenance of a binding between the mobile node's 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 Mobile IPv6 client 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 mobility 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 Proxy Mobile IPv6 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 [RFC-4830].  Proxy Mobile
   IPv6 is a solution that addresses these issues and requirements.







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2.  Conventions & Terminology

2.1.  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.


2.2.  Terminology

   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 [RFC-
   4831].  This document also provides the following context specific
   explanation to the following terms used in this document.


   Proxy Mobile IPv6 Domain (PMIPv6-Domain)

      Proxy Mobile IPv6 domain refers to the network where the mobility
      management of a mobile node is handled using Proxy Mobile IPv6
      protocol as defined in this specification.  The Proxy Mobile IPv6
      domain includes local mobility anchors and mobile access gateways
      between which security associations can be setup and authorization
      for sending Proxy Binding Updates on behalf of the mobile nodes
      can be ensured.

   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 network prefix and is the entity that
      manages the mobile node's reachability state.  It is important to
      understand that the local mobility anchor 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 protocol as defined
      in this specification.

   Mobile Access Gateway (MAG)







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      Mobile Access Gateway is a function that manages the mobility
      related signaling for a mobile node that is attached to its access
      link.  It is responsible for tracking the mobile node's attachment
      to the link and for signaling the mobile node's local mobility
      anchor.

   Mobile Node (MN)

      Through out this document, the term mobile node is used to refer
      to an IP node whose mobility is managed 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].

   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, as specified in
      [ID-IPV4-PMIP6].

   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
      mobility anchor is an IPv4 address, the term, IPv4-Proxy-CoA is
      used, as defined in [ID-IPV4-PMIP6].

   Mobile Node's Home Address (MN-HoA)







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      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.

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

      This is the on-link IPv6 prefix that the mobile node always sees
      in the Proxy Mobile IPv6 domain.  The home network prefix is
      topologically anchored at the mobile node's local mobility anchor.
      The mobile node configures its interface with an address from this
      prefix.

   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 Identifier (MN-Identifier)

      The identity of the mobile node that is presented to the network
      as part of the access authentication.  This is typically an
      identifier such as Mobile Node NAI [RFC-4283], or any other type
      of identifier which may be specific to the access technology.

   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 and is based on Mobile IPv6
   [RFC-3775].  This protocol is for providing network-based mobility



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   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, 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 characteristics and other
   related parameters such as the mobile node's Identifier, local
   mobility anchor address, permitted address configuration modes,
   roaming policy and other parameters that are essential for providing
   the network based mobility service.

   Once a mobile node enters its Proxy Mobile IPv6 domain and performs
   access authentication, the network will ensure that the mobile node
   is always on its home network and can obtain its home address on any
   access link using any of the address configuration procedures.  In
   other words, there is a home network prefix that is assigned to 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 //          \\   )
                +------\\--------//------------\\-+
                        \\      //              \\
                         \\    //                \\
                          \\  //                  \\
              Proxy-CoA1--> |                      | <-- Proxy-CoA2
                         +----+                 +----+
                         |MAG1|-----[MN2]       |MAG2|
                         +----+    |            +----+
                           |       |               |
              MN-HoA1 -->  |     MN-HoA2           | <-- MN-HoA3
                         [MN1]                   [MN3]




                    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 node is anchored and does the mobility related signaling
   on its behalf.  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 other
   mobile nodes.

   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 authentication procedure.  After a
   successful access authentication, the mobile access gateway obtains
   the mobile node's profile from the policy store.  The mobile access
   gateway would have all the required information for it to emulate the
   mobile node's home network on the access link.  It sends Router
   Advertisement messages to the mobile node on the access link
   advertising the mobile node's home network prefix as the hosted on-
   link-prefix.



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   The mobile node on receiving these Router Advertisement messages on
   the access link will attempt to configure its interface either using
   stateful 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 or a private IPv4 with NAT translation devices.

   For updating the local mobility anchor about the current location of
   the mobile node, 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 other
   required options.  Upon accepting the Proxy Binding Update message,
   the local mobility anchor sends a Proxy Binding Acknowledgment
   message including the mobile node's home network prefix option.  It
   also sets up a route for the mobile node's home network prefix over
   the tunnel to the mobile access gateway.

   The mobile access gateway on receiving this Proxy Binding
   Acknowledgment message sets up a bi-directional 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 its
   local mobility anchor through the bi-directional tunnel.

   At this point, the mobile node has a valid 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 using an address from its home network prefix.

   The local mobility anchor, being the topological anchor point for the
   mobile node's home network prefix, receives any packet that is sent
   by any corresponding node to the mobile node.  Local mobility anchor
   forwards the received packet to the mobile access gateway through the
   bi-directional tunnel.  The mobile access gateway on other end of the
   tunnel, after receiving the packet, removes the outer 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
   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 its local mobility anchor through the bi-



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   directional tunnel.  The local mobility anchor on the other end of
   the tunnel, after receiving the packet removes the outer 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
   infrastructure.

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
   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



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   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
          Then use SA ESP transport mode





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5.  Local Mobility Anchor Operation

   For supporting the Proxy Mobile IPv6 scheme specified in this
   document, the Mobile IPv6 home agent entity, defined in Mobile IPv6
   specification [RFC-3775], needs some enhancements.  The local
   mobility anchor is an entity that has the functional capabilities of
   a home agent and with the additional required capabilities for
   supporting Proxy Mobile IPv6 protocol as defined in this
   specification.  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.  The
   local mobility anchor in this model is just a topological anchor
   point for that prefix 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 home address 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



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   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 [RFC-3775].  For supporting
   this specification, the conceptual Binding Cache entry needs to be
   extended with the following additional 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  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 node 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 interface id of the bi-directional tunnel between the local
      mobility anchor and the mobile access gateway used for sending and
      receiving the mobile node's traffic.

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.



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   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 message
   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.  The other end point of
   the tunnel is the address configured on the interface of the mobile
   access gateway, Proxy-CoA.  The details related to the supported
   encapsulation modes and transport protocols is covered in detail in
   Section 6.10.2.

   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.

   When a local mobility anchor is serving a mobile node, it MUST
   attempt to intercept packets that are sent to any address that is in
   the mobile node's home network prefix address range.  The local
   mobility anchor MUST advertise a connected route in to the Routing
   Infrastructure for that mobile node's home network prefix or for an
   aggregated prefix with a larger scope.  This essentially enables
   routers in the IPv6 network to detect the local mobility anchor as
   the last-hop router for that prefix.

   When forwarding any packets that have the destination address
   matching the mobile node's home network prefix, the local mobility
   anchor MUST encapsulate the packet with the outer IPv6 header, as



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   specified in Generic Packet Tunneling in IPv6 specification [RFC-
   2473].  If the negotiated encapsulation header is either IPv6-over-
   IPv4 or IPv6-over-IPv4-UDP, as specified in the companion document,
   IPv4 support for Proxy Mobile IP6 [ID-Pv4-PMIP6], the packet must be
   encapsulated and routed as specified in that specification.

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

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.

   In Proxy Mobile IPv6, the address of the local mobility anchor
   configured to serve a mobile node can be discovered by the mobility
   entities 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 message in the current
   form for discovering the local mobility anchor address dynamically.
   As a mobile node 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.  Hence, this specification
   does not support Dynamic Home Agent Address Discovery protocol.

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.



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   In the Proxy Mobile IPv6, the ordering of packets has to be
   established across 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 IPv6 model, defined in this document requires the
   Proxy 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 MUST the
   value from the Time Stamp option to establish ordering of the
   received Binding Update messages.  If the local mobility anchor
   receives a Proxy Binding Update message with an invalid Time Stamp
   Option, the Proxy Binding Update MUST be rejected and a Proxy 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 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.  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-



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   address mode.  Hence, the return routability procedure as defined in
   RFC-3775 is not applicable for the proxy model.

5.7.  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, the mobile node's home network prefix is hosted
   on the access link connected to the mobile access gateway. 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 message for Proxy Mobile IPv6.
   This specification does not use Mobile Prefix Discovery.

5.8.  Signaling Considerations

5.8.1.  Initial Proxy Binding Registration

   Upon receiving a Proxy Binding Update message 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.

   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
   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 messages.

   The local mobility anchor MUST use the MN-Identifier from the NAI
   option of the Proxy Binding Update message for identifying the mobile
   node.

   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 that are required as per the Mobile IPv6
   specification [RFC-3775].  However, the received sequence number MUST



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   be copied and returned in the Proxy Binding Acknowledgement message
   sent to the mobile access gateway.

   The local mobility anchor before accepting a Proxy Binding Update
   request containing the Home Network Prefix Option with a specific
   prefix, MUST ensure the prefix is owned by the local mobility anchor
   and further the mobile node is authorized to use that prefix.  If the
   Home Network Prefix Option has the value 0::/0, the local mobility
   anchor MUST allocate a prefix for the mobile node and send a Proxy
   Binding Acknowledgement message with the Home Network Prefix Option
   containing the allocated value.  The specific details on how the
   local mobility anchor allocates the home network prefix is outside
   the scope of this document.

   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
   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.

   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 network prefix through the proxy mobile IPv6 tunnel.

   Upon accepting this Proxy Binding Update message, the local mobility
   anchor must create a Binding Cache entry and must set up a tunnel to
   the mobile access gateway serving the mobile node.  This bi-
   directional tunnel between the local mobility anchor and the mobile
   access gateway is used for routing the mobile node's traffic.

   The Proxy Binding Acknowledgment message must be constructed as shown
   below.


               IPv6 header (src=LMAA, dst=Proxy-CoA)
                    Mobility header
                        -BA /*P flag is set*/
                       Mobility Options
                          - Home Network Prefix Option



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                          - TimeStamp Option (optional)
                          - NAI Option


               Proxy Binding Acknowledgment message contents

5.8.2.  Extending the binding lifetime

   Upon accepting the Proxy Binding Update request for extending the
   lifetime of a currently active binding, the local mobility anchor
   MUST update the lifetime for that binding and send a Proxy Binding
   Acknowledgment message to the mobile access gateway.  The Proxy
   Binding Acknowledgment message MUST be constructed as specified in
   Section 5.8.1.

5.8.3.  De-registration of the binding

   Upon accepting the Proxy Binding Update request sent with the
   lifetime value of zero, the local mobility anchor MUST delete the
   binding from its Binding Cache and MUST send a Proxy Binding
   Acknowledgment message to the mobile access gateway.  The message
   MUST be constructed as specified in Section 6.9.1.

   The local mobility anchor MUST also remove the prefix route over the
   tunnel for that mobile node's home network prefix.

5.9.  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.

   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



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      document.


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 performs mobility management 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 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  Responsible for detecting the mobile node's attachment or
      detachment on the connected access link and for initiating the
      mobility signaling with the mobile node's local mobility anchor.

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

   o  Registering the binding state at the mobile node's local mobility
      anchor.

   o  Responsible for setting up the data path for enabling the mobile
      node to use an address from its home network prefix and use it
      from the access link.

   The mobile access gateway is a function that typically runs on an
   access router.  However, implementations MAY choose to split this
   function and run it across multiple systems.  The specifics on how
   that is achieved is beyond the scope of this document.

6.1.  Supported Access Link Types

   This specification supports only point-to-point access link types and
   thus it assumes that the link between the mobile node and the mobile
   access gateway is a dedicated link and that the mobile node and the
   mobile access gateway are the only two nodes present on that link.
   The assumed properties for the point-to-point link type are just as
   assumed by the Neighbor Discovery specification [RFC-2461] for that
   link type.  The link is assumed to have multicast capability and the



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   interfaces connecting to the link can be configured with a link-local
   address.

   Support for shared links or other link types is left for the future
   work.

6.2.  Supported Home Network Prefix Models

   This specification supports Per-MN-Prefix model and does not support
   Shared-Prefix model.  As per the Per-MN-Prefix model, there will be a
   unique home network prefix assigned for each mobile node and no other
   host shares an address from that prefix.  The prefix is always hosted
   on the access link where the mobile node is anchored.  Conceptually,
   the prefix follows the mobile node as it moves within the proxy
   mobile IPv6 domain.  However, from the routing perspective, the home
   network prefix is topologically anchored on the local mobility
   anchor.

6.3.  Supported Address Configuration Models

   A mobile node in the proxy mobile IPv6 domain can configure one or
   more IPv6 addresses on its interface using Stateless or Stateful
   address autoconfiguration procedures.  The Router Advertisement
   messages sent on the access link, specify the address configuration
   methods permitted on that access link for that mobile node.  The
   exact semantics of the flags that are enabled, the options that are
   carried in these advertisement messages is as per the Neighbor
   Discovery specification [RFC-2461].  However, the advertised flags
   with respect the address configuration will be consistent for a
   mobile node, on any of the access links in that proxy mobile IPv6
   domain.  Typically, these configuration settings will be based on the
   domain wide policy or based on a policy specific to each mobile node.
   This specification requires that all the mobile access gateways in a
   given proxy mobile IPv6 domain MUST ensure that the permitted address
   configuration procedures or the address configuration parameters that
   are sent in the Router Advertisements are consistent for a mobile
   node when attached to on any of the access links in the proxy mobile
   IPv6 domain.

   When stateless address autoconfiguration is supported on the link,
   the mobile node can generate one or more IPv6 addresses by combining
   the network prefix advertised on the access link with an interface
   identifier, using the techniques described in Stateless
   Autoconfiguration specification [RFC-2462] or in Privacy extension
   specification [RFC-3041].

   When stateful address autoconfiguration is supported on the link, the
   mobile node obtains the address configuration from the DHCPv6 server



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   using DHCPv6 client protocol, as specified in DHCPv6 specification
   [RFC-3315].

   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 for pushing the address configuration to the
   mobile node.

6.4.  Access Authentication & Mobile Node Identification

   When a mobile node attaches to an access link connected to the mobile
   access gateway, the deployed access security protocols on that link
   will ensure that the network-based mobility management service is
   offered only after authenticating and authorizing the mobile node for
   that service.  The exact specifics on how this is achieved or the
   interactions between the mobile access gateway and the access
   security service is outside the scope of this document.  This
   specification goes with the stated assumption of having an
   established trust and a secured communication link between the mobile
   node and mobile access gateway, before the protocol operation begins.
   The specification also requires that the mobile access gateway MUST
   be able to identify the mobile node by its MN-Identifier and it must
   also be able to associate this identity to the sender of any IPv4 or
   IPv6 packets on the access link.  The mobile access gateway MUST also
   be able to obtain the mobile node's policy profile using the MN-
   Identifier.

6.5.  Mobile Node's Policy Profile

   A mobile node's policy profile contains the essential operational
   parameters that are required by the network entities for managing the
   mobile node's mobility service.  These policy profiles are stored in
   a local or a remote policy store, the mobile access gateway and the
   local mobility anchor MUST be able to obtain a mobile node's policy
   profile using its MN-Identifier.  The policy profile may also be
   handed over to a serving mobile access gateway as part of a context
   transfer procedure during a handoff.  The exact details on how this
   achieved is outside the scope of this document.  However, this
   specification requires that a mobile access gateway serving a mobile
   node MUST have access to its policy profile.

   The following are the mandatory fields of the policy profile:

   o  The mobile node's identifier (MN-Identifier)

   o  The IPv6 address of the local mobility anchor (LMAA)





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   o  Supported address configuration procedures on the link (Stateful,
      Stateless or both)


   The following are the optional fields of the policy profile:

   o  The mobile node's IPv6 home network prefix (MN-HoA)

   o  The mobile node's IPv6 home network prefix length

6.6.  Conceptual Data Structures

   Every mobile access gateway MUST maintain 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.

   o  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 interface identifier of the point-to-point link to the mobile
      node.

   o  The interface identifier of the tunnel between the mobile access
      gateway and the mobile node's local mobility anchor.

6.7.  Home Network Emulation

   One of the key functions of a mobile access gateway is to emulate the
   mobile node's home network prefix on the access link.  It must
   ensure, the mobile node believes it is still connected to its home
   link or on the link where it obtained its address configuration after
   it moved into that proxy mobile IPv6 domain.

   After detecting new mobile node on its access link and after a
   successful access authentication and authorization of the mobile node
   for network-based mobility service, the mobile access gateway MUST to
   emulate the mobile node's home link by sending the Router
   Advertisements with the mobile node's home network prefix as the
   hosted on-link prefix.  The Router Advertisement MUST be sent in



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   response to a Router Solicitation message that it received from the
   mobile node.  The Router Advertisement messages MAY also be sent
   periodically, based on the interface configuration on the mobile
   access gateway.

   For emulating the mobile node's home link on the access link, the
   mobile access gateway must know the home network prefix of the mobile
   node for constructing the Router Advertisement.  Typically and as a
   default method, the mobile access gateway learns the mobile node's
   home network prefix information from the Proxy Binding
   Acknowledgement message, it received in response to the Proxy Binding
   Update message that it sent to the mobile node's local mobility
   anchor for that mobile node.

   However, it is also possible, the mobile node's home network prefix
   information may be statically configured in the mobile node's policy
   profile or it may be handed over to the mobile access gateway as part
   of a context transfer procedure.  If the mobile access gateway can
   predictably know the mobile node's home network prefix information,
   it MAY choose to send the Router Advertisement prior to receiving the
   Proxy Binding Acknowledgement message from the local mobility anchor.
   However, in the event, the local mobility anchor rejects the Proxy
   Binding Update message, or if the prefix that is received from the
   local mobility anchor for that mobile node is a different prefix than
   what the mobile access gateway previously advertised, the mobile
   access gateway MUST withdraw the prefix by sending a Router
   Advertisement message with zero lifetime for the prior advertised
   prefix.

   If the access link connecting the mobile access gateway and the
   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.

6.7.1.  Home Network Prefix Renumbering

   If the mobile node's home network prefix gets renumbered or becomes
   invalid during the middle of a mobility session, the mobile access
   gateway MUST withdraw the prefix by sending a Router Advertisement on
   the access link with zero prefix lifetime for the mobile node's home
   network prefix.  Also, the local mobility anchor and the mobile
   access gateway MUST delete the routing state for that prefix.
   However, the specific details on how the local mobility anchor
   notifies the mobile access gateway is outside the scope of this
   document.





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6.8.  Link-Local and Global Address Uniqueness

   A mobile node in the proxy mobile IPv6 domain, as it moves from one
   mobile access gateway to the other, it will continue to detect its
   home network and thus making the node believe it is still on the same
   link.  Every time the mobile node attaches to a new link, the event
   related to the interface state change, will trigger the mobile node
   to perform DAD operation on the link-local and global addresses.
   However, if the node is DNAv6 enabled, as specified in [ID-DNAV6], it
   may not detect the link change due to DNAv6 optimizations and hence
   it will not trigger the duplicate address detection (DAD) procedure
   for establishing the link-local address uniqueness on that new link.
   Further, if the mobile node uses an interface identifier that is not
   based on EUI-64 identifier, such as specified in IPv6 Stateless
   Autoconfiguration specification [RFC-2462], there is a possibility,
   with the odds of 1 to billion, of a link-local address collision
   between the two neighbors, the mobile node and the mobile access
   gateway.

   One of the workarounds for this issue is to set the DNAv6
   configuration parameter, DNASameLinkDADFlag to TRUE and that will
   force the mobile node to redo DAD operation every time the interface
   comes up, even when DNAv6 does detect a link change .

   However, this issues will not impact point-to-point links based on
   PPP session.  Each time the mobile node moves and attaches to a new
   mobile access gateway, either the PPP session [RFC-1661] is
   reestablished or the PPP session may be moved as part of context
   transfer procedures between the old and the new mobile access
   gateway.

   When the mobile node tries to establish a PPP session 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 mobile access gateway, the PPP session
   gets torn down with the old mobile access gateway and a new PPP
   session gets established with the new mobile access gateway, and the
   mobile node obtains a new link-local address.  So, even if the mobile
   node is DNAv6 capable, the mobile node always configures a new link-
   local address when ever it moves to a new link.

   If the PPP session state is moved to the new mobile access gateway,
   as part of context transfer procedures that are in place, there will
   not be any change to the interface identifiers of the two nodes on
   that point-to-point change.  The whole link is moved to the new



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   mobile access gateway and there will not be any need for establishing
   link-local address uniqueness on that link.

   This issue is not relevant to the mobile node's global address.
   Since, there is a unique home network prefix for each mobile node,
   the uniqueness for the mobile node's global address is ensured on the
   access link.

6.9.  Signaling Considerations

6.9.1.  Initial Attachment and binding registration

   After detecting a new mobile node on its access link after a
   successful access authentication and authorization, the mobile access
   gateway MUST send a Proxy Binding Update message to the mobile node's
   local mobility anchor.

   The Proxy Binding Update message must be constructed as shown below.


               IPv6 header (src=Proxy-CoA, dst=LMAA)
                    Mobility header
                        -BU /*P flag is set*/
                       Mobility Options
                          - Home Network Prefix Option*
                          - TimeStamp Option (optional)
                          - NAI Option

   *Home Network Prefix option may contain 0::/0 or a specific prefix.


                   Proxy Binding Update message contents

   The Proxy Binding Update message that the mobile access gateway sends
   to the mobile node's local mobility anchor MUST have the NAI option,
   identifying the mobile node, the Home Network Prefix option and
   optionally the Time Stamp option SHOULD be present.  The Time Stamp
   option is not required if the mobile access gateway can send a valid
   sequence number that matches the sequence number maintained by the
   local mobility anchor for that mobile node in its binding cache
   entry.  The message MUST be protected by using IPsec ESP, using the
   security association existing between the local mobility anchor and
   the mobile access gateway, created either dynamically or statically.

   If the mobile access gateway learns the mobile node's home network
   prefix either from its policy store or from other means, the mobile
   access gateway MAY choose to specify the same in the Home Network
   Prefix option for requesting the local mobility anchor to register



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   that prefix.  If the specified value is 0::/0, then the local
   mobility anchor will allocate a prefix to the mobile node.

   After receiving a Proxy Binding Acknowledgment with the status code
   indicating the acceptance of the Proxy Binding Update, the mobile
   access gateway MUST setup a tunnel to the mobile node's local
   mobility anchor, as explained in section 6.10.  The mobile access
   gateway MUST also add a policy route for tunneling all the packets
   that it receives from the mobile node to its local mobility anchor.

   If the local mobility anchor rejects the Proxy Binding Update
   message, 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.

6.9.2.  Extending the binding lifetime

   For extending the lifetime of a currently existing binding at the
   local mobility, the mobile access gateway MUST send a Proxy Binding
   Update message with a specific lifetime.  The message MUST be
   constructed as specified in Section 6.9.1.

6.9.3.  De-registration of the binding

   At any point, the mobile access gateway detects that the mobile node
   has moved away from its access link, it MUST send a Proxy Binding
   Update message to the mobile node's local mobility anchor with the
   lifetime value set to zero.  The message MUST be constructed as
   specified in Section 6.9.1.

   The mobile access gateway MUST also remove the default route over the
   tunnel for that mobile node and delete the Binding Update List for
   that mobile node, either upon receiving an Proxy Binding
   Acknowledgment message from the local mobility anchor or after a
   certain timeout waiting for the acknowledgment message.

6.10.  Routing Considerations

   This section describes how the mobile access gateway handles the
   traffic to/from the mobile node that is attached to one of its access
   interface.


                 Proxy-CoA                   LMAA
                    |                          |
    +--+          +---+                      +---+          +--+
    |MN|----------|MAG|======================|LMA|----------|CN|
    +--+          +---+                      +---+          +--+



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                            IPv6 Tunnel


6.10.1.  Transport Network

   The transport network between the local mobility anchor and the
   mobile access can be either an IPv6 or IPv4 network.  However, this
   specification only deals with the scenario where the transport
   network between the mobility entities is IPv6-only and requires
   reachability between the local mobility anchor and the mobile access
   gateway over IPv6 transport.  Just as in Mobile IPv6 specification
   [RFC-3775], the negotiated tunnel transport between the local
   mobility anchor and the mobile access gateway is IPv6, by default.
   The companion document, IPv4 support for Proxy Mobile IPv6 [IPv4-
   PMIP6-SPEC] specifies the required extensions for negotiating IPv4
   tunneling mechanism and a specific encapsulation mode for supporting
   this protocol operation over IPv4 transport network.

6.10.2.  Tunneling & Encapsulation Modes

   The IPv6 address that a mobile node uses from its home network prefix
   is topologically anchored at the local mobility anchor.  For a mobile
   node to use this address from an access network attached to a mobile
   access gateway, proper tunneling techniques have to be in place.
   Tunneling hides the network topology and allows the mobile node's
   IPv6 datagrams to be encapsulated as a payload of another IPv6 packet
   and be routed between the local mobility anchor and the mobile access
   gateway.  The Mobile IPv6 base specification [RFC-3775] defines the
   use of IPv6-over-IPv6 tunneling, between the home agent and the
   mobile node and this specification extends the use of the same
   tunneling mechanism between the local mobility anchor and the mobile
   access gateway.

   On most operating systems, tunnels are implemented as a virtual
   point-to-point interface.  The source and the destination address of
   the two end points of this virtual interface along with the
   encapsulation mode are specified for this virtual interface.  Any
   packet that is routed over this interface, get encapsulated with the
   outer header and the addresses as specified for that point to point
   tunnel interface.  For creating a point to point tunnel to any local
   mobility anchor, the mobile access gateway may implement a tunnel
   interface with the source address field set to its Proxy-CoA address
   and the destination address field set to the LMA address.

   The following are the supported packet encapsulation modes that can
   be used by the mobile access gateway and the local mobility anchor
   for routing mobile node's IPv6 datagrams.




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   o  IPv6-In-IPv6 - IPv6 datagram encapsulated in an IPv6 packet.  This
      mechanism is defined in the Generic Packet Tunneling for IPv6
      specification [RFC-2473].

   o  IPv6-In-IPv4 - IPv6 datagram encapsulation in an IPv4 packet.  The
      details related to this encapsulation mode and the specifics on
      how this mode is negotiated is specified in the companion
      document, IPv4 support for Proxy Mobile IPv6 [ID-IPv4-PMIP6].

   o  IPv6-In-IPv4-UDP - IPv6 datagram encapsulation in an IPv4 UDP
      packet.  The details related to this mode are covered in the
      companion document, IPv4 support for Proxy Mobile IPv6 [IPv4-
      PMIP6-SPEC].

6.10.3.  Routing State

   The following section explain the routing state for a mobile node on
   the mobile access gateway.  This routing state reflects only one
   specific way of implementation and one MAY choose to implement it in
   other ways.  The policy based route defined below acts as a traffic
   selection rule for routing a mobile node's traffic through a specific
   tunnel created between the mobile access gateway and that mobile
   node's local mobility anchor and with the specific encapsulation
   mode, as negotiated.

   The below example identifies the routing state for two visiting
   mobile nodes, MN1 and MN2 with their respective local mobility
   anchors LMA1 and LMA2.

   For all traffic from the mobile node, identified by the mobile node's
   MAC address, ingress interface or source prefix (MN-HNP) to
   _ANY_DESTINATION_ route via interface tunnel0, next-hop LMAA.


   +==================================================================+
   |  Packet Source    | Destination Address  | Destination Interface |
   +==================================================================+
   | MAC_Address_MN1,  | _ANY_DESTINATION_    |     Tunnel0           |
   | (IPv6 Prefix or   |----------------------------------------------|
   |  Input Interface) | Locally Connected    |     Tunnel0           |
   +------------------------------------------------------------------+
   | MAC_Address_MN2   | _ANY_DESTINATION_    |     Tunnel1           |
   +                   -----------------------------------------------|
   |                   | Locally Connected    |     direct            |
   +------------------------------------------------------------------+


                    Example - Policy based Route Table



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   +==================================================================+
   | Interface | Source Address | Destination Address | Encapsulation |
   +==================================================================+
   | Tunnel0   |   Proxy-CoA    |        LMAA1         | IPv6-in-IPv6 |
   +------------------------------------------------------------------+
   | Tunnel1   |IPv4-Proxy-CoA  |    IPv4-LMA2         | IPv6-in-IPv4 |
   +------------------------------------------------------------------+


                     Example - Tunnel Interface Table

6.10.4.  Local Routing

   If there is data traffic between a visiting mobile node and a
   corresponding node that is locally attached to an access link
   connected to the mobile access gateway, the mobile access gateway MAY
   optimize on the delivery efforts by locally routing the packets and
   by not reverse tunneling them to the mobile node's local mobility
   anchor.  However, this has an implication on the mobile node's
   accounting and policy enforcement as the local mobility anchor is not
   in the path for that traffic and it will not be able to apply any
   traffic policies or do any accounting for those flows.

   This decision of path optimization SHOULD be based on the configured
   policy configured on the mobile access gateway, but enforced by the
   mobile node's local mobility anchor.  The specific details on how
   this is achieved is beyond of the scope of this document.

6.10.5.  Tunnel Management

   All the considerations mentioned in Section 5.2, for the tunnel
   management on the local mobility anchor apply for the mobile access
   gateway as well.

   As explained in Section 5.2, the life of the Proxy Mobile IPv6 tunnel
   should not be based on a single visiting mobile node's lifetime.  The
   tunnel may get created as part of creating a mobility state for a
   visiting 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.

6.10.6.  Forwarding Rules

   Upon receipt of an encapsulated packet sent to its configured Proxy-
   CoA address i.e. on receiving a packet from a tunnel, the mobile
   access gateway MUST use the destination address of the inner packet
   for forwarding it to the interface where the prefix for that address
   is hosted.  The mobile access gateway MUST remove the outer header



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   before forwarding the packet.  If the mobile access gateway cannot
   find the connected interface for that destination address, it MUST
   silently drop the packet.  For reporting an error in such scenario,
   in the form of ICMP control message, the considerations from Generic
   Packet Tunneling specification [RFC-2473] apply.

   On receiving a packet from a mobile node connected to its access
   link, the mobile access gateway MUST ensure that there is an
   established binding for that mobile node with its local mobility
   anchor before forwarding the packet directly to the destination or
   before tunneling the packet to the mobile node's local mobility
   anchor.

   On receiving a packet from a mobile node connected to its access
   link, to a destination that is locally connected, the mobile access
   gateway MUST check the configuration variable, EnableMAGLocalRouting,
   to ensure the mobile access gateway is allowed to route the packet
   directly to the destination.  If the mobile access gateway is not
   allowed to route the packet directly, it MUST route the packet
   through the bi-directional tunnel established between itself and the
   mobile's local mobility anchor.

   On receiving a packet from the mobile node to any destination i.e.
   not directly connected to the mobile access gateway, the packet MUST
   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 the link-local
   source address MUST not be forwarded.

6.11.  Interaction with DHCP Relay Agent

   If Stateful 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.  Since, the access link is a point-to-point
   link with the configured mobile node's prefix as the on-link prefix,
   the normal DHCP relay agent configuration on the MAG will ensure the
   prefix hint is set to the mobile node's home network prefix.

6.12.  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



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   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
   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 the
   Binding Update List 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

6.13.  Allowing network access to other IPv6 nodes

   In some proxy mobile IPv6 deployments, network operators may want to
   provision the mobile access gateway to offer network-based mobility
   management service only to some visiting mobile nodes and enable just
   regular IPv6/IPv4 access to some other nodes attached to that mobile
   access gateway.  This requires the network to have the control on
   when to enable network-based mobility management service to a mobile
   node and when to enabled a regular IPv6 access.  This specification
   does not disallow such configuration.

   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 mobile access gateway must ensure the mobile
   node believes it is on its home link, as explained in various
   sections of this specification.



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   If the mobile node is not entitled for the network-based mobility
   management service, as enforced by the policy, the mobile access
   gateway MAY choose to offer regular IPv6 access to the mobile node
   and hence the normal IPv6 considerations apply.  If IPv6 access is
   enabled, the mobile node SHOULD be able to obtain any IPv6 address
   using normal IPv6 address configuration mechanisms.  The obtained
   address must be from a local visitor network prefix.  This
   essentially ensures, the mobile access gateway functions as any other
   access router and does not impact the protocol operation of a mobile
   node attempting to use host-based mobility management service when it
   attaches to an access link connected to a mobile access gateway in a
   proxy mobile IPv6 domain.


7.  Mobile Node Operation

   This non-normative section discusses the mobile node's operation in a
   Proxy Mobile IPv6 domain.

   Once the mobile node enters a Proxy Mobile IPv6 domain and attaches
   to an access network and after the access authentication, the network
   ensures, the mobile using any of the address configuration mechanisms
   permitted by the network for that mobile node, will be able to obtain
   an address and move anywhere in that proxy mobile IPv6 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.  However, the specific details on how the
   IPv4 network-based mobility management service is offered to the
   mobile node is specified in the companion document, IPv4 Support for
   Proxy Mobile IPv6 [ID-IPV4-PMIP6].

   Typically, the configured policy in the network determines if the
   mobile node is authorized for IPv6, IPv4 or IPv6/IPv4 home address
   mobility.  If the configured policy for a mobile node is for IPv6-
   only home address mobility, the mobile node will be able to obtain
   its IPv6 home address, any where in that Proxy Mobile IPv6 domain,
   otherwise 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 after it moves to
   a new link.

7.1.  Booting up in a Proxy Mobile IPv6 Domain


   When a mobile node moves into a proxy mobile IPv6 domain and attaches



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   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
   network prefix and the permitted address configuration modes.  The
   mobile node's home network prefix may also be dynamically assigned by
   the mobile node's local mobility anchor and the same may be learnt by
   the mobile access gateway.

   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
   as Managed Address Configuration, Stateful 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 gets an address from its home network prefix
   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 can
   continue to use the obtained address configuration 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



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   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 network prefix as the on-link
   prefix and with the other configuration parameters consistent with
   its home link properties.

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
   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



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   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 withdraw the
   previous default-router entry, by sending a Router Advertisement
   using the link-local address that of the previous mobile access
   gateway and with the Router Lifetime field set to value 0, then it is
   possible to force the flush 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 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 mobile access
   gateways in a Proxy Mobile IPv6 domain.  In any 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 9: Proxy Binding Update Message



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   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
   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 registrations
   sent by a mobile node when 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 10: Proxy Binding Acknowledgment Message

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

   Proxy Registration Flag (P)

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



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   For descriptions of other fields present in this message, refer to
   the section 6.1.8 of Mobile IPv6 specification [RFC3775].

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

   The home network prefix Option has an alignment requirement of 8n+4.
   Its format is as follows:






































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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Type     |   Length      |   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.

       Home Network Prefix

           A sixteen-byte field containing the mobile node's IPv6 Home
           Network Prefix.


                   Figure 11: Home Network Prefix Option

8.4.  Time Stamp Option

   A new option, Time Stamp Option is defined for use in the Proxy
   Binding Update and Acknowledgement messages.  This option can be used
   in Proxy Binding Update and Proxy Binding Acknowledgement messages.




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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  |      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 8.

       Timestamp

           64-bit time stamp


                       Figure 12: 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

   146: Proxy Registrations from this mobile access gateway not allowed

   147: Home Network prefix for this NAI is not configured and the Home
   Network Prefix Option not present in the Proxy Binding Update.

   148: Invalid Time Stamp Option in the received Proxy Binding Update
   message.

   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



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   and must be updated in the IANA registry.


9.  Protocol Configuration Variables

   The mobile access gateway MUST allow the following variables to be
   configured by the system management.

   EnableMAGLocalrouting

   This flag indicates whether or not the mobile access gateway is
   allowed to enable local routing of the traffic exchanged between a
   visiting mobile node and a corresponding node that is locally
   connected to one of the interfaces of the mobile access gateway.  The
   corresponding node can be another visiting mobile node as well, or a
   local fixed node.

   The default value for this flag is set to "FALSE", indicating that
   the mobile access gateway MUST reverse tunnel all the traffic to the
   mobile node's local mobility anchor.

   When the value of this flag is set to "TRUE", the mobile access
   gateway MUST route the traffic locally.

   This aspect of local routing MAY be defined as policy on a per mobile
   basis and when present will take precedence over this flag.


10.  IANA Considerations

   This document defines a two new Mobility Header Options, the Home
   Network Prefix Option and the Time Stamp Option.  These options are
   described in Sections 8.3 and 8.5 respectively.  The Type value for
   these options needs to be assigned from the same numbering space as
   allocated for the other mobility options, as defined in [RFC-3775].

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


11.  Security Considerations

   The potential security threats against any general network-based
   mobility management protocol are covered in the document, Security
   Threats to Network-Based Localized Mobility Management [RFC-4832].
   This section analyses those vulnerabilities in the context of Proxy



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   Mobile IPv6 protocol solution and covers all aspects around those
   identified vulnerabilities.

   A compromised mobile access gateway can potentially send Proxy
   Binding Update messages on behalf of the 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 an on-
   path router.  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 vulnerability, the local mobility
   anchor before accepting Proxy Binding Update message received from a
   mobile access gateway, MUST ensure the mobile node is attached to the
   mobile access gateway that sent the Proxy Binding Update message.
   This can be achieved using out of band mechanisms 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/Layer-3 based authentication
   procedures, such as EAP, are 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 applicability of that security
   model to Proxy Mobile IPv6 protocol is covered in Section 4.0 of this
   document.

   As described in the base Mobile IPv6 specification [RFC-3775], both
   the mobile node (in case of Proxy Mobile IPv6, 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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12.  Acknowledgements

   The authors would like to specially thank Julien Laganier, Christian
   Vogt, Pete McCann, Brian Haley, Ahmad Muhanna, JinHyeock Choi 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, Parviz
   Yegani, Mark Grayson, Michael Hammer, Vojislav Vucetic, Jay Iyer and
   Tim Stammers for their input on this document.


13.  References

13.1.  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



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   Protect Mobile IPv6 Signaling Between Mobile Nodes and Home Agents",
   RFC 3776, June 2004.

   [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.

   [RFC-4830] Kempf, J., Leung, K., Roberts, P., Nishida, K., Giaretta,
   G., Liebsch, M., "Problem Statement for Network-based Localized
   Mobility Management", September 2006.

   [RFC-4831] Kempf, J., Leung, K., Roberts, P., Nishida, K., Giaretta,
   G., Liebsch, M., "Goals for Network-based Localized Mobility
   Management", October 2006.

   [RFC-4832] Vogt, C., Kempf, J., "Security Threats to Network-Based
   Localized Mobility Management", September 2006.

   [ID-IPV4-PMIP6] Wakikawa, R. and Gundavelli, S., "IPv4 Support for
   Proxy Mobile IPv6", draft-ietf-netlmm-pmip6-ipv4-support-00.txt, May
   2007.

   [ID-DSMIP6] Soliman, H. et al, "Mobile IPv6 support for dual stack
   Hosts and Routers (DSMIPv6)",
   draft-ietf-mip6-nemo-v4traversal-03.txt, October 2006.

13.2.  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.



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

   [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.

   [ID-DNAV6] Kempf, J., et al "Detecting Network Attachment in IPv6
   Networks (DNAv6)", draft-ietf-dna-protocol-03.txt, October 2006.

   [ID-MIP6-IKEV2] Devarapalli, V. and Dupont, F., "Mobile IPv6
   Operation with IKEv2 and the revised IPsec Architecture",
   draft-ietf-mip6-ikev2-ipsec-08.txt, December 2006.


Appendix A.  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.



Appendix B.  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 stateful 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



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   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].

   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
   _ANY_DESTINATION_, 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.



Authors' Addresses

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

   Email: sgundave@cisco.com


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

   Email: kleung@cisco.com












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

   Email: vijay.devarapalli@azairenet.com


   Kuntal Chowdhury
   Starent Networks
   30 International Place
   Tewksbury, MA


   Email: kchowdhury@starentnetworks.com


   Basavaraj Patil
   Nokia Siemens Networks
   6000 Connection Drive
   Irving, TX  75039
   USA

   Email: basavaraj.patil@nsn.com


























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Full Copyright Statement

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