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Versions: (draft-sgundave-mip6-proxymip6) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 RFC 5213

NETLMM WG                                         S. Gundavelli (Editor)
Internet-Draft                                                  K. Leung
Intended status: Standards Track                                   Cisco
Expires: May 7, 2008                                      V. Devarapalli
                                                         Azaire Networks
                                                            K. Chowdhury
                                                        Starent Networks
                                                                B. Patil
                                                  Nokia Siemens Networks
                                                       November 04, 2007


                           Proxy Mobile IPv6
                   draft-ietf-netlmm-proxymip6-07.txt

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on May 7, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   Network-based mobility management enables IP mobility for a host
   without requiring its participation in any mobility related



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   signaling.  The Network is responsible for managing mobility on
   behalf of the host.  The design principle in the case of a network-
   based mobility management protocol relies on the network being in
   control of the mobility management.  The mobility entities in the
   network are responsible for tracking the movements of the host and
   initiating the required mobility signaling on its behalf.  This
   specification describes a network-based mobility management protocol
   and is referred to 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  . . . . . . . . . . . . .  8
   4.  Proxy Mobile IPv6 Protocol Security  . . . . . . . . . . . . . 14
     4.1.  Peer Authorization Database Entries  . . . . . . . . . . . 14
     4.2.  Security Policy Database Entries . . . . . . . . . . . . . 15
   5.  Local Mobility Anchor Operation  . . . . . . . . . . . . . . . 16
     5.1.  Extensions to Binding Cache Entry Data Structure . . . . . 16
     5.2.  Supported Home Network Prefix Models . . . . . . . . . . . 18
     5.3.  Signaling Considerations . . . . . . . . . . . . . . . . . 18
     5.4.  Multihoming Support  . . . . . . . . . . . . . . . . . . . 24
     5.5.  Timestamp Option for Message Ordering  . . . . . . . . . . 27
     5.6.  Routing Considerations . . . . . . . . . . . . . . . . . . 30
       5.6.1.  Bi-Directional Tunnel Management . . . . . . . . . . . 30
       5.6.2.  Forwarding Considerations  . . . . . . . . . . . . . . 31
     5.7.  Local Mobility Anchor Address Discovery  . . . . . . . . . 31
     5.8.  Mobile Prefix Discovery Considerations . . . . . . . . . . 32
     5.9.  Route Optimizations Considerations . . . . . . . . . . . . 32
   6.  Mobile Access Gateway Operation  . . . . . . . . . . . . . . . 33
     6.1.  Extensions to Binding Update List Entry Data Structure . . 33
     6.2.  Mobile Node's Policy Profile . . . . . . . . . . . . . . . 34
     6.3.  Supported Access Link Types  . . . . . . . . . . . . . . . 35
     6.4.  Supported Address Configuration Models . . . . . . . . . . 35
     6.5.  Access Authentication & Mobile Node Identification . . . . 36
     6.6.  Acquiring Mobile Node's Identifier . . . . . . . . . . . . 36
     6.7.  Home Network Emulation . . . . . . . . . . . . . . . . . . 37
     6.8.  Link-Local and Global Address Uniqueness . . . . . . . . . 37
     6.9.  Signaling Considerations . . . . . . . . . . . . . . . . . 39
       6.9.1.  Binding Registrations  . . . . . . . . . . . . . . . . 39
       6.9.2.  Router Solicitation Messages . . . . . . . . . . . . . 44
       6.9.3.  Retransmissions and Rate Limiting  . . . . . . . . . . 44
     6.10. Routing Considerations . . . . . . . . . . . . . . . . . . 45
       6.10.1. Transport Network  . . . . . . . . . . . . . . . . . . 45
       6.10.2. Tunneling & Encapsulation Modes  . . . . . . . . . . . 45



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       6.10.3. Routing State  . . . . . . . . . . . . . . . . . . . . 46
       6.10.4. Local Routing  . . . . . . . . . . . . . . . . . . . . 47
       6.10.5. Tunnel Management  . . . . . . . . . . . . . . . . . . 48
       6.10.6. Forwarding Rules . . . . . . . . . . . . . . . . . . . 48
     6.11. Supporting DHCPv6 based Address Configuration on the
           Access Link  . . . . . . . . . . . . . . . . . . . . . . . 49
     6.12. Home Network Prefix Renumbering  . . . . . . . . . . . . . 50
     6.13. Mobile Node Detachment Detection and Resource Cleanup  . . 50
     6.14. Allowing network access to other IPv6 nodes  . . . . . . . 51
   7.  Mobile Node Operation  . . . . . . . . . . . . . . . . . . . . 52
     7.1.  Moving into a Proxy Mobile IPv6 Domain . . . . . . . . . . 52
     7.2.  Roaming in the Proxy Mobile IPv6 Domain  . . . . . . . . . 53
     7.3.  IPv6 Host Protocol Parameters  . . . . . . . . . . . . . . 53
   8.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . . 54
     8.1.  Proxy Binding Update Message . . . . . . . . . . . . . . . 55
     8.2.  Proxy Binding Acknowledgement Message  . . . . . . . . . . 56
     8.3.  Home Network Prefix Option . . . . . . . . . . . . . . . . 57
     8.4.  Access Technology Type Option  . . . . . . . . . . . . . . 59
     8.5.  Mobile Node Interface Identifier Option  . . . . . . . . . 60
     8.6.  Link-local Address Option  . . . . . . . . . . . . . . . . 61
     8.7.  Timestamp Option . . . . . . . . . . . . . . . . . . . . . 62
     8.8.  Status Values  . . . . . . . . . . . . . . . . . . . . . . 63
   9.  Protocol Configuration Variables . . . . . . . . . . . . . . . 65
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 66
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 66
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 67
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 68
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 68
     13.2. Informative References . . . . . . . . . . . . . . . . . . 68
   Appendix A.  Proxy Mobile IPv6 interactions with AAA
                Infrastructure  . . . . . . . . . . . . . . . . . . . 69
   Appendix B.  Supporting Shared-Prefix Model using DHCPv6 . . . . . 70
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 71
   Intellectual Property and Copyright Statements . . . . . . . . . . 72

















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1.  Introduction

   IP mobility for IPv6 hosts is specified in Mobile IPv6 [RFC-3775].
   Mobile IPv6 requires client functionality in the IPv6 stack of a
   mobile node.  Exchange of signaling messages between the mobile node
   and home agent enables the creation and maintenance of a binding
   between the mobile node's home address and its care-of-address.
   Mobility as specified in [RFC-3775] is host centric as it requires
   the IP host to manage its own mobility by signaling the Home Agent,
   which is located in the network.

   Network-based mobility is another approach to solving the IP mobility
   challenge.  It is possible to support mobility for IPv6 nodes without
   host involvement by extending Mobile IPv6 [RFC-3775] signaling
   messages and reusing the home agent.  This approach to supporting
   mobility does not require the mobile node to be involved in the
   exchange of signaling messages between itself and the Home Agent.  A
   proxy mobility agent in the network performs the signaling with the
   home agent and does the mobility management on behalf of the mobile
   node attached to the network.  Because of the use and extension of
   Mobile IPv6 signaling and home agent functionality, this protocol is
   referred to as Proxy Mobile IPv6 (PMIPv6).

   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 undergone interoperability testing.

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

   o  Addresses a deployment need.

   o  May be better suited on certain types of resource-constrained
      links or because of service provider specific policies.

   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.
   This document builds on Mobile IPv6 [RFC-3775] in specifying a
   network-based mobility management protocol.



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2.  Conventions & Terminology

2.1.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC-2119].


2.2.  Terminology

   All the 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 the 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 binding 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] with the additional capabilities required
      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 movements
      on the access link and for signaling the mobile node's local
      mobility anchor.

   Mobile Node (MN)

      Throughout this document, the term mobile node is used to refer to
      an IP host 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 Proxy Mobile IPv6 domain.  This
      document further uses explicit text when referring to a mobile
      node that is involved in mobility related signaling as per the
      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 bi-
      directional tunnel established 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 specified 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 from its home network prefix obtained by
      a mobile node in a Proxy Mobile IPv6 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 is always present in the
      Router Advertisements that the mobile node receives when it is
      attached to any of the access links in that Proxy Mobile IPv6
      domain.  This 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.  If the mobile
      node connects to the Proxy Mobile IPv6 domain through multiple
      interfaces, simultaneously, there will be multiple and unique home
      network prefixes assigned for that mobile node.

   Mobile Node's Home Link

      This is the link on which the mobile node obtained its initial
      Layer-3 address configuration for one of its interfaces 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.

   Multihomed Mobile Node

      A mobile node that connects to the Proxy Mobile IPv6 domain
      through more than one interface and uses the interfaces
      simultaneously is referred to as a multihomed mobile node.

   Mobile Node Identifier (MN-Identifier)

      The identity of a mobile node in the Proxy Mobile IPv6 domain.
      This is the stable identifier of a mobile node that the mobility
      entities in a Proxy Mobile IPv6 domain can always acquire and
      using which a mobile node can predictably be identified.  This is
      typically an identifier such as NAI or other identifier such as a
      MAC address.

   Mobile Node Interface Identifier (MN-Interface-Identifier)







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      The interface identifier that identifies a given interface of a
      mobile node.  For those interfaces that have a layer-2 identifier,
      the interface identifier can be based on that layer-2 identifier.
      The interface identifier in some cases is generated by the mobile
      node and conveyed to the access router or the mobile access
      gateway.  In some cases, there might not be any interface
      identifier associated with the mobile node's interface.

   Proxy Binding Update (PBU)

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

   Proxy Binding Acknowledgement (PBA)

      A binding registration reply message sent by a local mobility
      anchor in response to a Proxy Binding Update request 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].

   Proxy Mobile IPv6 protocol is intended for providing network-based
   mobility management support to a mobile node, without requiring the
   participation of the mobile node in any mobility related signaling.
   The mobility entities in the network will track the mobile node's
   movements and will initiate the mobility signaling and setup the
   required routing state.

   The core functional entities in the NETLMM infrastructure are the
   Local Mobility Anchor (LMA) and the Mobile Access Gateway (MAG).  The
   local mobility anchor is responsible for maintaining the mobile
   node's reachability state and is the topological anchor point for the
   mobile node's home network prefix.  The mobile access gateway is the
   entity that performs the mobility management on behalf of a mobile
   node and it resides on the access link where the mobile node is
   anchored.  The mobile access gateway is responsible for detecting the
   mobile node's movements on its access link and for sending binding
   registrations to the mobile node's local mobility anchor.  The
   architecture of a Proxy Mobile IPv6 domain is shown in Figure 1.






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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



   Once a mobile node enters a Proxy Mobile IPv6 domain and attaches to
   an access link, the mobile access gateway on that access link, after
   identifying the mobile node and acquiring its identity, will
   determine if the mobile node is authorized for the network-based
   mobility management service.

   If the network determines that the network-based mobility management
   service needs to be offered to that mobile node, the network will
   ensure that the mobile node using any of the address configuration
   mechanisms permitted by the network will be able to obtain the
   address configuration on the connected interface and move anywhere in
   that Proxy Mobile IPv6 domain.  The obtained address configuration
   includes the address(es) from its home network prefix, the default-
   router address on the link and other related configuration
   parameters.  From the perspective of the mobile node, the entire
   Proxy Mobile IPv6 domain appears as a single link, the network
   ensures that the mobile node believes it is always on the same link
   where it obtained its initial address configuration, even after



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   changing its point of attachment in that network.

   The mobile node may be operating in an IPv4-only mode, IPv6-only mode
   or in dual IPv4/IPv6 mode.  Based on what is enabled in the network
   for that mobile node, the mobile node will be able to obtain an IPv4,
   IPv6 or dual IPv4/IPv6 addresses and move anywhere in that Proxy
   Mobile IPv6 domain.  However, the specific details related to the
   IPv4 addressing or IPv4 transport support are specified in the
   companion document [ID-IPV4-PMIP6].

   If the mobile node connects to the Proxy Mobile IPv6 domain, through
   multiple interfaces and over multiple access networks, the network
   will allocate an unique home network prefix for each of the connected
   interfaces and the mobile node will be able to configure an
   address(es) on those interfaces from the respective home network
   prefixes.  If the mobile node performs a handover from one interface
   to another in the same Proxy Mobile IPv6 domain, then the local
   mobility anchor will assign the same prefix to the new interface.

































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    +-----+                +-----+                +-----+
    | MN  |                | MAG |                | LMA |
    +-----+                +-----+                +-----+
       |                      |                      |
   MN Attached                |                      |
       |                      |                      |
       |               MN Attached Event             |
       |        (Acquire MN-Id and Profile)          |
       |                      |                      |
       |                      |----- PBU ----------->|
       |                      |                      |
       |                      |                  Accept PBU
       |                      |  (Allocate MN-HNP, Setup BCE and Tunnel)
       |                      |                      |
       |                      |<--------- PBA -------|
       |                      |                      |
       |                 Accept PBA                  |
       |          (Setup Tunnel and Routing)         |
       |                      |                      |
       |                      |==== Bi-Dir Tunnel ===|
       |                      |                      |
       |--- Rtr Sol --------->|                      |
       |                      |                      |
       |<------- Rtr Adv -----|                      |
       |                      |                      |
    IP Address                |                      |
   Configuration              |                      |
       |                      |                      |




          Figure 2: Mobile Node Attachment - Signaling Call Flow



   Figure 2 shows the signaling call flow when the mobile node enters
   the Proxy Mobile IPv6 domain.

   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.  Upon
   accepting this Proxy Binding Update message, the local mobility
   anchor sends a Proxy Binding Acknowledgement message including the
   mobile node's home network prefix.  It also creates the Binding Cache
   entry and establishes a bi-directional tunnel to the mobile access
   gateway.




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   The mobile access gateway on receiving the Proxy Binding
   Acknowledgement message sets up a bi-directional tunnel to the local
   mobility anchor and sets up the data path for the mobile node's
   traffic.  At this point the mobile access gateway will have all the
   required information for emulating the mobile node's home 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.

   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 the modes
   that are permitted on that access link.  At the end of a successful
   address configuration procedure, the mobile node will end up with an
   address from its home network prefix.

   Once the address configuration is complete, 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 packets that are sent
   by any correspondent node to the mobile node.  The local mobility
   anchor forwards these received packets 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.  Any packet that the mobile node sends to any
   correspondent node will be received by the mobile access gateway and
   will be sent to its local mobility anchor through the bi-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.












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    +-----+          +-----+          +-----+          +-----+
    | MN  |          |p-MAG|          | LMA |          |n-MAG|
    +-----+          +-----+          +-----+          +-----+
       |                |                |                |
       |                |==Bi-Dir Tunnel=|                |
   MN Detached          |                |                |
       |         MN Detached Event       |                |
       |                |                |                |
       |                |-- DeReg PBU -->|                |
       |                |                |                |
       |                |            Accept PBU           |
       |                |   (Start MinDelayBeforeBCEDelete Timer)
       |                |                |                |
       |                |<-------- PBA --|                |
       |                |                |                |
   MN Attached          |                |                |
       |                |                |       MN Attached Event
       |                |                |   (Acquire MN-Id and Profile)
                               ....
                                    Registration steps as in fig 2.
                               ....
       |                |                |==Bi-Dir Tunnel=|
       |--- Rtr Sol ------------------------------------->|
       |                |                |                |
       |<------------------------------------ Rtr Adv ----|
       |                |                |                |
   MN retains HoA/HNP
       |                |                |                |


            Figure 3: Mobile Node Handoff - Signaling Call Flow



   Figure 3 shows the signaling call flow for the mobile node's handoff
   from previously attached mobile access gateway (p-MAG) to the newly
   attached mobile access gateway (n-MAG).

   After obtaining the initial address configuration in the Proxy Mobile
   IPv6 domain, if the mobile node changes its point of attachment, the
   mobile access gateway on the new access link will signal the local
   mobility anchor for updating the binding and routing state.  The
   mobile node will continue to receive the Router Advertisements
   containing its home network prefix, making it believe it is still on
   the same link and can use the same address configuration on the new
   access link.





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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 MUST be protected using end-to-end security
   association(s) offering integrity and data origin authentication.  A
   security association with the mobile node for which the signaling
   message is issued is not required for protection of these messages.

   The mobile access gateway and the local mobility anchor MUST
   implement IPsec for protecting the Proxy Mobile IPv6 signaling
   messages [RFC-4301].  IPsec is the default security mechanism for
   securing the signaling messages.  However in certain deployments of
   this protocol, other security mechanisms MAY be applied and the
   signaling messages must be protected using the semantics provided by
   that respective mechanism.

   IPsec ESP [RFC-4303] in transport mode with mandatory integrity
   protection SHOULD be used for protecting the signaling messages.
   Confidentiality protection of these messages is not required.

   IKEv2 [RFC-4306] SHOULD be used to setup security associations
   between the mobile access gateway and the local mobility anchor to
   protect the Proxy Binding Update and Proxy Binding Acknowledgement
   messages.  The mobile access gateway and the local mobility anchor
   can use any of the authentication mechanisms, as specified in IKEv2,
   for mutual authentication.

   The Mobile IPv6 specification [RFC-3775] 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 by sending a query to the policy store, such as AAA.

4.1.  Peer Authorization Database Entries

   This section 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



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   implementation can implement the PAD in any implementation specific
   manner.  The PAD state may also be distributed across various
   databases in a specific implementation.


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

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


                           Figure 4: PAD Entries

   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

   This section 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.
















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      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 = BA
          Then use SA ESP transport mode
          Initiate using IDi = mag_1 to address lma_address_1

      local mobility anchor SPD-S:
        - IF local_address = lma_address_1 &
             remote_address = mag_address_1 &
             proto = MH & local_mh_type = BA & remote_mh_type = BU
          Then use SA ESP transport mode


                           Figure 5: SPD Entries


5.  Local Mobility Anchor Operation

   For supporting the Proxy Mobile IPv6 protocol specified in this
   document, the home agent function, specified in [RFC-3775] requires
   certain functional modifications and enhancements.  The home agent
   with these modifications and enhanced capabilities for supporting
   Proxy Mobile IPv6 protocol is referred to as the local mobility
   anchor.

   This section describes the operational details of the local mobility
   anchor.

5.1.  Extensions to Binding Cache Entry Data Structure

   Every local mobility anchor MUST maintain a Binding Cache entry for
   each currently registered mobile node.  Binding Cache entry is a
   conceptual data structure, described in Section 9.1 [RFC-3775].

   For supporting this specification, the Binding Cache Entry data
   structure 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 created due to the
      registrations directly sent by the mobile node.

   o  The identifier of the registered mobile node, MN-Identifier.  This
      identifier is obtained from the Mobile Node Identifier Option
      [RFC-4283] present in the received Proxy Binding Update request.



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   o  The interface identifier of the mobile node's connected interface
      on the access link.  This identifier can be acquired from the
      Mobile Node Interface Identifier option (with P Flag set to 0),
      present in the received Proxy Binding Update request.  If the
      option was not present in the request, this value MUST be set to
      ALL_ZERO.

   o  The Link-local address of the mobile node on the interface
      attached to the access link.  This is obtained from the Link-local
      Address option, present in the Proxy Binding Update request.

   o  The IPv6 home network prefix of the registered mobile node.  The
      home network prefix of the mobile node may have been statically
      configured in the mobile node's policy profile, or, it may have
      been dynamically allocated by the local mobility anchor.  The IPv6
      home network prefix also includes the corresponding prefix length.

   o  The interface identifier of the bi-directional tunnel established
      between the local mobility anchor and the mobile access gateway
      where the mobile node is currently anchored.  The tunnel interface
      identifier is acquired during the tunnel creation.

   o  The access technology through which the mobile node is currently
      connected.  This is obtained from the Access Technology Type
      option, present in the Proxy Binding Update message.

   o  The 64-bit timestamp value of the most recently accepted Proxy
      Binding Update request sent for this mobile node.  This is
      obtained from the Timestamp option, present in the request.


   Typically, the MN-Identifier is the key for locating a Binding Cache
   entry.  However, when supporting multihoming there MAY be more than
   one Binding Cache entry with the same MN-Identifier and in such cases
   the entry can be located using any of the following key combinations:

   o  MN-Identifier, MN-HNP

   o  MN-Identifier, Proxy-CoA

   o  MN-Identifier, MN-Interface-Identifier

   o  MN-Identifier, Access Technology Type (When MN-Interface-
      Identifier is not present)







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5.2.  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
   an unique home network prefix assigned to each mobile node and no
   other node shares an address from that prefix.

   The mobile node's home network prefix is always hosted on the access
   link where the mobile node is anchored.  Conceptually, the entire
   home network prefix follows the mobile node as it moves within the
   Proxy Mobile IPv6 domain.  The local mobility anchor is not required
   to perform any proxy ND operations [RFC-4861] for defending the
   mobile node's home address on the home link.  However, from the
   routing perspective, the home network prefix is topologically
   anchored on the local mobility anchor.

5.3.  Signaling Considerations


   Processing Binding Registrations

   Upon receiving a Proxy Binding Update request (a Binding Update
   Request with the 'P' flag set) from a mobile access gateway on behalf
   of a mobile node, the local mobility anchor MUST process the request
   as defined in Section 10.3 [RFC-3775], with one exception that this
   request is a Proxy Binding Update request and hence the following
   additional considerations must be applied.


   o  The local mobility anchor MUST observe the rules described in
      Section 9.2 [RFC-3775] when processing Mobility Headers in the
      received Proxy Binding Update request.

   o  The local mobility anchor MUST identify the mobile node from the
      identifier present in the Mobile Node Identifier option [RFC-4283]
      of the Proxy Binding Update request.  If the Mobile Node
      Identifier option is not present in the Proxy Binding Update
      request, the local mobility anchor MUST reject the request and
      send a Proxy Binding Acknowledgement message with Status field set
      to MISSING_MN_IDENTIFIER_OPTION (Missing mobile node identifier).

   o  If the local mobility anchor cannot identify the mobile node, from
      the Mobile Node Identifier option [RFC-4283] present in the
      request, it MUST reject the Proxy Binding Update request and send
      a Proxy Binding Acknowledgement message with Status field set to
      133 (Not home agent for this mobile node).





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   o  If the local mobility anchor determines that the mobile node is
      not authorized for the network-based mobility management service,
      it MUST reject the request and send a Proxy Binding
      Acknowledgement message with Status field set to
      PROXY_REG_NOT_ENABLED (Proxy Registration not enabled).

   o  The local mobility anchor MUST ignore the check, specified in
      Section 10.3.1 [RFC-3775], related to the presence of Home Address
      destination option in the Proxy Binding Update request.

   o  The local mobility anchor MUST authenticate the Proxy Binding
      Update request as described in Section 4.0.  When IPsec is used
      for message authentication, the SPI in the IPsec header [RFC-4306]
      of the received packet for locating the security association
      needed for authenticating the Proxy Binding Update request.

   o  The local mobility anchor MUST apply the required policy checks,
      as explained in Section 4.0, to verify the sender is a trusted
      mobile access gateway, authorized to send Proxy Binding Update
      requests on behalf of this mobile node.

   o  If the local mobility anchor determines that the requesting node
      is not authorized to send Proxy Binding Update requests, it MUST
      reject the request and send a Proxy Binding Acknowledgement
      message with Status field set to MAG_NOT_AUTHORIZED_FOR_PROXY_REG
      (Not authorized to send proxy registrations).

   o  If the Home Network Prefix option is not present in the Proxy
      Binding Update request, the local mobility anchor MUST reject the
      request and send a Proxy Binding Acknowledgement message with
      Status field set to MISSING_HOME_NETWORK_PREFIX_OPTION (Missing
      mobile node's home network prefix option).

   o  If the Access Technology Type option is not present in the Proxy
      Binding Update request, the local mobility anchor MUST reject the
      request and send a Proxy Binding Acknowledgement message with
      Status field set to MISSING_ACCESS_TECH_TYPE_OPTION (Missing
      mobile node's access technology type).

   o  The local mobility anchor MUST apply the considerations specified
      in Section 5.5, for processing the Sequence Number field and the
      Timestamp option, in the Proxy Binding Update request.

   o  The local mobility anchor MUST use the identifier from the Mobile
      Node Identifier Option [RFC-4283] present in the Proxy Binding
      Update request and MUST apply multihoming considerations specified
      in Section 5.4 for performing the Binding Cache entry existence
      test or for identifying the mobility session.  If the entry does



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      not exist, the local mobility anchor MUST consider this request as
      an initial binding registration request.  If the entry exists, the
      local mobility anchor MUST consider this request as an binding re-
      registration request.  However, from the perspective of the mobile
      access gateway that sent the request, this binding re-registration
      request may be an initial Binding Update request after the mobile
      node's attachment to that mobile access gateway.


   Initial Binding Registration:

   o  If the Home Network Prefix option present in the Proxy Binding
      Update request has the value 0::/0, the local mobility anchor MUST
      allocate a prefix for the mobile node and send a Proxy Binding
      Acknowledgement message including the Home Network Prefix option
      containing the allocated prefix value.  The specific details on
      how the local mobility anchor allocates the home network prefix is
      outside the scope of this document.  The local mobility anchor
      MUST ensure the allocated prefix is not in use by any other mobile
      node.

   o  If the local mobility anchor is unable to allocate a home network
      prefix for the mobile node, it MUST reject the request and send a
      Proxy Binding Acknowledgement message with Status field set to 130
      (Insufficient resources).

   o  If the Home Network Prefix option present in the request has a
      specific prefix hint, the local mobility anchor before accepting
      that request, MUST ensure the prefix is owned by the local
      mobility anchor and further the mobile node is authorized to use
      that prefix.  If the mobile node is not authorized to use that
      prefix, the local mobility anchor MUST reject the request and send
      a Proxy Binding Acknowledgement message with Status field set to
      NOT_AUTHORIZED_FOR_HOME_NETWORK_PREFIX (Mobile node not authorized
      to use that prefix).

   o  Upon accepting the request, the local mobility anchor MUST create
      a Binding Cache entry for the mobile node.  It must set the fields
      in the Binding Cache entry to the accepted values for that
      binding.  If there is a Link-local Address option present in the
      request, the address must be copied to the link-local address
      field in the Binding Cache entry.

   o  Upon accepting the Proxy Binding Update request, the local
      mobility anchor MUST establish a bi-directional tunnel to the
      mobile access gateway, as described in [RFC-2473].  Considerations
      from Section 5.6 must be applied.




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   Binding Re-Registration:

   o  If the requesting prefix in the Home Network Prefix option is a
      non 0::/0 value and is different from what is present in the
      currently active Binding Cache entry for that mobile node, the
      local mobility anchor MUST reject the request and send a Proxy
      Binding Acknowledgement message with Status field set to 129
      (Administratively Prohibited).

   o  If there is a Link-local Address option present in the request
      with a value other than ALL_ZERO (not set), and upon accepting the
      binding re-registration request, the local mobility anchor MUST
      update the link-local address field in the Binding Cache entry to
      the address value received in the request.

   o  Upon accepting a Proxy Binding Update request for extending the
      lifetime of a currently active binding for a mobile node, the
      local mobility anchor MUST update the existing Binding Cache entry
      for this mobile node.  Unless there exists an established bi-
      directional tunnel to the mobile access gateway with the same
      transport and encapsulation mode, the local mobility anchor MUST
      create a tunnel to the mobile access gateway, as described in
      [RFC-2473] and also delete the existing tunnel route to the
      previous mobile access gateway.  It MUST also send a Proxy Binding
      Acknowledgement message to the mobile access gateway with the
      Status field set to 0 (Proxy Binding Update Accepted).


   Binding De-Registration:

   o  If the prefix in the Home Network Prefix option is a non 0::/0
      value and is different from what is present in the currently
      active Binding Cache entry for that mobile node, the local
      mobility anchor MUST reject the request and send a Proxy Binding
      Acknowledgement message with Status field set to 129
      (Administratively Prohibited).

   o  If the received Proxy Binding Update request with the lifetime
      value of zero, has a Source Address in the IPv6 header different
      from what is present in the Proxy-CoA address field in the Binding
      Cache entry existing for that mobile node, the local mobility
      anchor MUST ignore the request.

   o  Upon accepting the Proxy Binding Update request for a mobile node,
      with the lifetime value of zero, the local mobility anchor MUST
      wait for MinDelayBeforeBCEDelete amount of time, before it deletes
      the mobile node's Binding Cache entry.  Within this wait period,
      if the local mobility anchor receives a Proxy Binding Update



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      request message for the same mobile node with the lifetime value
      of greater than zero, and if that request is accepted, then the
      Binding Cache entry MUST NOT be deleted, but must be updated with
      the newly accepted registration values.  The local mobility anchor
      MUST send the Proxy Binding Acknowledgement message, immediately
      upon accepting the request.  However, within this wait period, if
      the local mobility anchor does not receive any valid binding
      registration request for that mobile node, then at the end of this
      wait period, it MUST delete the mobile node's Binding Cache entry
      and remove the routing state created for that mobile node.  In
      addition, during this MinDelayBeforeBCEDelete wait period, the
      local mobility anchor MUST continue to route the mobile node's
      data traffic.


   Constructing the Proxy Binding Acknowledgement Message:

   o  The local mobility anchor when sending the Proxy Binding
      Acknowledgement message to the mobile access gateway MUST
      construct the message as specified below.



               IPv6 header (src=LMAA, dst=Proxy-CoA)
                    Mobility header
                        -BA /*P flag is set*/
                       Mobility Options
                          - Home Network Prefix Option
                          - Link-local Address Option (optional)
                          - Timestamp Option (optional)
                          - Mobile Node Identifier Option
                          - Access Technology Type option (Mandatory)
                          - Mobile Node Interface Identifier option
                            (Optional)


            Figure 6: Proxy Binding Acknowledgement message format

   o  The Source Address field in the IPv6 header of the message SHOULD
      be set to the destination address of the received Proxy Binding
      Update request.

   o  The Destination Address field in the IPv6 header of the message
      SHOULD be set to the source address of the received Proxy Binding
      Update request.

   o  The Home Network Prefix option MUST be present in the Proxy
      Binding Acknowledgement message.  If the option was not present in



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      the request and if the Status field value is set to
      MISSING_HOME_NETWORK_PREFIX_OPTION, the value MUST be set to
      ALL_ZERO.

   o  The Access Technology Type option MUST be present.  The access
      technology type value in the option MUST be copied from the Access
      Technology Type option in the received Proxy Binding Update
      request.  If the option was not present in the request and if the
      Status field value is set to MISSING_ACCESS_TECH_TYPE_OPTION, the
      value MUST be set to 0.

   o  The Mobile Node Interface Identifier option MAY be present, if the
      same option was present in the corresponding Proxy Binding Update
      request message.

   o  If the Status field is set to a value greater than or equal to
      128, i.e., if the binding request was rejected, then the prefix
      value in the Home Network Prefix option MUST be set to the prefix
      value from the received Home Network Prefix option.  For all other
      cases, the prefix value MUST be set to the allocated prefix value
      for that mobile node.

   o  The Link-local Address option MUST be present in the Proxy Binding
      Acknowledgement message if and only if the same option was present
      in the corresponding Proxy Binding Update request message.

   o  If the Status field is set to a value greater than or equal to
      128, i.e., if the binding request was rejected, then the link-
      local address value in the Link-local Address option MUST be set
      to the value from the received Link-local Address option.

   o  If there is an existing Binding Cache entry for the mobile node
      with the link-local address value of ALL_ZERO (value not set), or
      if there was no existing Binding Cache entry, then the link-local
      address MUST be copied from the Link-local Address option in the
      received Proxy Binding Update request.  For all other cases, it
      MUST be copied from the mobile node's Binding Cache entry.

   o  Considerations from Section 5.5 must be applied for constructing
      the Timestamp option.

   o  The identifier in the Mobile Node Identifier option [RFC-4283]
      MUST be copied from the received Proxy Binding Update request.  If
      the Status field value is set to MISSING_MN_IDENTIFIER_OPTION, the
      Mobile Node Identifier Option MUST NOT be present in the Proxy
      Binding Acknowledgement message.





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   o  The message MUST be protected by using IPsec, using the security
      association existing between the local mobility anchor and the
      mobile access gateway.

   o  The Type 2 Routing header MUST NOT be present in the IPv6 header
      of the packet.

5.4.  Multihoming Support

   When a mobile node connects to a Proxy Mobile IPv6 domain through
   multiple interfaces simultaneously, the local mobility anchor MUST
   allocate a unique home network prefix for each of the connected
   interfaces.

   The local mobility anchor MUST manage each of the allocated home
   network prefixes as part of a separate mobility session, each with a
   separate Binding Cache entry.

   The local mobility anchor MUST allow for an handover between two
   different interfaces of the mobile node.  In such a case, the home
   network prefix that is associated with a specific interface
   identifier of a mobile node will be updated with the new interface
   identifier.


   The local mobility anchor MUST apply the following multihoming
   considerations when processing a received Proxy Binding Update
   request message.


   Processing De-Registration Message:

   o  If the received Proxy Binding Update message has lifetime value of
      zero, the local mobility anchor MUST verify if there is an
      existing Binding Cache entry for the mobile node, identified by
      the MN-Identifier and with the Proxy-CoA address matching the
      source address in the IPv6 header of the received packet.  If
      there exists a Binding Cache entry, the local mobility anchor MUST
      consider the message as a request for de-registering that specific
      mobility session.  If there does not exist a Binding Cache entry,
      the message MUST be ignored.


   Mobile Node Interface Identifier Option not present in the request:

   o  The local mobility anchor MUST verify if there is an existing
      Binding Cache entry for the mobile node, identified by the MN-
      Identifier and with the interface identifier value set to ALL_ZERO



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      .

   o  If there does not exist a Binding Cache entry, the local mobility
      anchor upon accepting the request MUST assign a new home network
      prefix and create a new Binding Cache entry.

   o  If there exists a Binding Cache entry and if the Handoff Indicator
      flag in the Access Technology Type option present in the received
      Proxy Binding Update message is set to value 1 (Attachment over a
      new interface), the local mobility anchor upon accepting the
      request MUST assign a new home network prefix and create a new
      Binding Cache entry.

   o  If there exists a Binding Cache entry and if the Handoff Indicator
      flag in the Access Technology Type option present in the received
      Proxy Binding Update message is set to either value 2 (Handoff
      between interfaces) or 3 (Handoff between mobile access gateways
      for the same mobile node's interface), the local mobility anchor
      upon accepting the request MUST update the existing Binding Cache
      entry and assign the home network prefix present in the Binding
      Cache entry.

   o  If there exists a Binding Cache entry and if the Handoff Indicator
      flag in the Access Technology Type option present in the received
      Proxy Binding Update message is set to value 4 (Handoff state
      unknown), the local mobility anchor SHOULD wait till the existing
      Binding Cache entry is de-registered by the previously serving
      mobile access gateway, before it assigns the same home network
      prefix or updates the existing Binding Cache entry.  However, if
      there is no de-registration message that is received within a
      given amount of time, the local mobility anchor upon accepting the
      request MUST assign a new home network prefix and create a new
      Binding Cache entry.  The local mobility anchor MAY also choose to
      assign a new home network prefix and without waiting for a de-
      registration message.

   o  Either upon creating a new Binding Cache entry or from matching an
      existing Binding Cache entry, after applying the above
      considerations, the interface identifier field in the Binding
      Cache entry MUST be set to the value present in the received
      Mobile Node Interface Identifier Option and the access technology
      type MUST be copied from the Access Technology type option present
      in the received Proxy Binding Update message.  If the Mobile Node
      Interface Identifier Option is not present, the interface
      identifier field in the Binding Cache entry MUST be set to
      ALL_ZERO.





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   Mobile Node Interface Identifier Option present in the request:

   o  The local mobility anchor MUST verify if there is an existing
      Binding Cache entry for the mobile node, identified by the MN-
      Identifier and with the interface identifier value matching the
      identifier value present in the received Mobile Node Interface
      Identifier Option.

   o  If there exists a Binding Cache entry, the local mobility anchor
      upon accepting the request MUST update the existing Binding Cache
      entry and assign the home network prefix present in the Binding
      Cache entry.

   o  If there does not exist a Binding Cache entry and if the Handoff
      Indicator flag in the Access Technology Type option present in the
      received Proxy Binding Update message is set to value 1
      (Attachment over a new interface), the local mobility anchor upon
      accepting the request MUST assign a new home network prefix and
      create a new Binding Cache entry.

   o  If there does not exist a Binding Cache entry and if the Handoff
      Indicator flag in the Access Technology Type option present in the
      received Proxy Binding Update message is set to value 2 (Handoff
      between interfaces), the local mobility anchor MUST verify if
      there exists one and only one Binding Cache entry for the mobile
      node, identified by the MN-Identifier and with any interface
      identifier value.  If there exists such an entry, the local
      mobility anchor upon accepting the request MUST update the
      existing Binding Cache entry and assign the home network prefix
      present in the Binding Cache entry.

   o  If there does not exist a Binding Cache entry and if the Handoff
      Indicator flag in the Access Technology Type option present in the
      received Proxy Binding Update message is set to value 2 (Handoff
      between interfaces), the local mobility anchor MUST verify if
      there exists a Binding Cache entry for the mobile node, identified
      by the MN-Identifier and with the home network prefix value
      matching the prefix value in the received Home Network Prefix
      option.  If there exists a Binding Cache entry, the local mobility
      anchor upon accepting the request MUST assign the same prefix,
      else it MUST assign a new home network prefix and create a new
      Binding Cache entry.

   o  If there does not exist a Binding Cache entry and if the Handoff
      Indicator flag in the Access Technology Type option present in the
      received Proxy Binding Update message is set to value 4 (Handoff
      state unknown), the local mobility anchor SHOULD wait till the
      existing Binding Cache entry is de-registered by the previously



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      serving mobile access gateway.  However, if there is no de-
      registration message that is received within a given time, the
      local mobility anchor upon accepting the request MUST assign a new
      home network prefix and create a new Binding Cache entry.  The
      local mobility anchor MAY also choose to assign a new home network
      prefix and without waiting for a de-registration message.

   o  Either upon creating a new Binding Cache entry or from matching an
      existing Binding Cache entry, after applying the above
      considerations, the interface identifier field in the Binding
      Cache entry MUST be set to the value present in the received
      Mobile Node Interface Identifier Option and the access technology
      type MUST be copied from the Access Technology type option present
      in the received Proxy Binding Update message.  If the Mobile Node
      Interface Identifier Option is not present, the interface
      identifier field in the Binding Cache entry MUST be set to
      ALL_ZERO.


5.5.  Timestamp Option for Message Ordering

   Mobile IPv6 [RFC-3775] uses the Sequence Number field in binding
   registration messages as a way for the home agent to process the
   binding updates in the order they were sent by a mobile node.  The
   home agent and the mobile node are required to manage this counter
   over the lifetime of a binding.  However, in Proxy Mobile IPv6, as
   the mobile node moves from one mobile access gateway to another and
   in the absence of mechanisms such as context transfer between the
   mobile access gateways, the serving mobile access gateway will be
   unable to determine the sequence number that it needs to use in the
   signaling messages.  Hence, the sequence number scheme, as specified
   in [RFC-3775], will be insufficient for Proxy Mobile IPv6.

   If the local mobility anchor cannot determine the sending order of
   the received binding registration messages, it may potentially
   process an older message sent by a mobile access gateway where the
   mobile node was previously anchored, resulting in an incorrect
   Binding Cache entry.

   For solving this problem, this specification adopts two alternative
   solutions.  One is based on timestamps and the other based on
   sequence numbers, as defined in [RFC-3775].

   The basic principle behind the use of timestamps in binding
   registration messages is that the node generating the message inserts
   the current time-of-day, and the node receiving the message checks
   that this timestamp is greater than all previously accepted
   timestamps.  The timestamp based solution may be used, when the



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   serving mobile access gateways in a Proxy Mobile IPv6 domain do not
   have the ability to obtain the last sequence number that was sent in
   a binding registration message for updating a given mobile node's
   binding.

   As an alternative to the Timestamp based approach, the specification
   also allows the use of Sequence Number based scheme, as per [RFC-
   3775].  However, for this scheme to work, the serving mobile access
   gateways in a Proxy Mobile IPv6 domain MUST have the ability to
   obtain the last sequence number that was sent in a binding
   registration message for updating a given mobile node's binding.  The
   sequence number MUST be maintained on a per mobile node basis and
   MUST be synchronized between the serving mobile access gateways.
   This may be achieved by using context transfer schemes or by
   maintaining the sequence number in a policy store.  However, the
   specific details on how the mobile node's sequence number is
   synchronized between different mobile access gateways is outside the
   scope of this document.


   Using Timestamps based approach:

   o  A local mobility anchor implementation MUST support Timestamp
      option.  If the Timestamp option is present in the received Proxy
      Binding Update request message, then the local mobility anchor
      MUST include a valid Timestamp option in the Proxy Binding
      Acknowledgement message that it sends to the mobile access
      gateway.

   o  All the mobility entities in a Proxy Mobile IPv6 domain that are
      exchanging binding registration messages using the Timestamp
      option must have adequately synchronized time-of-day clocks.  This
      is the essential requirement for this solution to work.  If this
      requirement is not met, the solution will not predictably work in
      all cases.

   o  The mobility entities in a Proxy Mobile IPv6 domain SHOULD
      synchronize their clocks to a common time source.  For
      synchronizing the clocks, the nodes may use Network Time Protocol
      [RFC-4330].  Deployments may also adopt other approaches suitable
      for that specific deployment.  Alternatively, if there is mobile
      node generated timestamp that is increasing at every attachment to
      the access link and if that timestamp is available to the mobile
      access gateway (Ex: The timestamp option in the SEND messages that
      the mobile node sends), the mobile access gateway can use this
      timestamp or sequence number in the Proxy Binding Update messages
      and does not have to depend on any external clock source.
      However, the specific details on how this is achieved is outside



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      the scope of this document.

   o  When generating the timestamp value for building the Timestamp
      option, the mobility entities MUST ensure that the generated
      timestamp is the elapsed time past the same reference epoch, as
      specified in the format for the Timestamp option [Section 8.7].

   o  If the Timestamp option is present in the received Proxy Binding
      Update message, the local mobility anchor MUST ignore the sequence
      number field in the message.  However, it MUST copy the sequence
      number from the received Proxy Binding Update message to the Proxy
      Binding Acknowledgement message.

   o  Upon receipt of a Proxy Binding Update message with the Timestamp
      option, the local mobility anchor MUST check the timestamp field
      for validity.  In order for it to be considered valid, the
      timestamp value contained in the Timestamp option MUST be close
      enough to the local mobility anchor's time-of-day clock and the
      timestamp MUST be greater than all previously accepted timestamps
      in the Proxy Binding Update messages sent for that mobile node.

   o  If the timestamp value in the received Proxy Binding Update is
      valid (validity as specified in the above considerations), the
      local mobility anchor MUST return the same timestamp value in the
      Timestamp option included in the Proxy Binding Acknowledgement
      message that it sends to the mobile access gateway.

   o  If the timestamp value in the received Proxy Binding Update is
      lower than the previously accepted timestamp in the Proxy Binding
      Update messages sent for that mobility binding, the local mobility
      anchor MUST reject the Proxy Binding Update request and send a
      Proxy Binding Acknowledgement message with Status field set to
      TIMESTAMP_LOWER_THAN_PREV_ACCEPTED (Timestamp lower than
      previously accepted timestamp).  The message MUST also include the
      Timestamp option with the value set to the current time-of-day on
      the local mobility anchor.

   o  If the timestamp value in the received Proxy Binding Update is not
      valid (validity as specified in the above considerations), the
      local mobility anchor MUST reject the Proxy Binding Update and
      send a Proxy Binding Acknowledgement message with Status field set
      to TIMESTAMP_MISMATCH (Timestamp mismatch).  The message MUST also
      include the Timestamp option with the value set to the current
      time-of-day on the local mobility anchor.


   Using Sequence Number based approach:




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   o  If the Timestamp option is not present in the received Proxy
      Binding Update request, the local mobility anchor MUST fallback to
      the Sequence Number based scheme.  It MUST process the sequence
      number field as specified in [RFC-3775].  Also, it MUST NOT
      include the Timestamp option in the Proxy Binding Acknowledgement
      messages that it sends to the mobile access gateway.

   o  An implementation MUST support Sequence Number based scheme, as
      per [RFC-3775].

5.6.  Routing Considerations

5.6.1.  Bi-Directional Tunnel Management


   o  A bi-directional tunnel is established between the local mobility
      anchor and the mobile access gateway with IP-in-IP encapsulation,
      as described in [RFC-2473].  The tunnel end points are the Proxy-
      CoA and LMAA.  When using IPv4 transport with a specific
      encapsulation mode, the end points of the tunnel are the IPv4-LMAA
      and IPv4-Proxy-CoA, as specified in [ID-IPV4-PMIP6].

   o  The bi-directional tunnel is used for routing the mobile node's
      data traffic between the mobile access gateway and the local
      mobility anchor.  The tunnel hides the topology and enables a
      mobile node to use an address from its home network prefix from
      any access link attached to the mobile access gateway.

   o  The bi-directional tunnel is established after accepting the Proxy
      Binding Update request message.  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.  Implementations MAY choose to use static
      tunnels instead of dynamically creating and tearing them down on a
      need basis.

   o  Implementations typically use a software timer for managing the
      tunnel lifetime and a counter for keeping a count of all the
      mobile nodes that are sharing the tunnel.  The timer value will be
      set to the accepted binding lifetime and will be updated after
      each periodic re-registration for extending the lifetime.  If the
      tunnel is shared for multiple mobile nodes, the tunnel lifetime
      will be set to the highest binding lifetime that is granted to any
      one of those mobile nodes sharing that tunnel.







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5.6.2.  Forwarding Considerations

   Intercepting Packets Sent to the Mobile Node's Home Network:

   o  When the local mobility anchor is serving a mobile node, it MUST
      be able to receive packets that are sent to the mobile node's home
      network.  In order for it to receive those packets, it MUST
      advertise a connected route in to the Routing Infrastructure for
      the mobile node's home network prefix or for an aggregated prefix
      with a larger scope.  This essentially enables IPv6 routers in
      that network to detect the local mobility anchor as the last-hop
      router for that prefix.


   Forwarding Packets to the Mobile Node:

   o  On receiving a packet from a correspondent node with the
      destination address matching a mobile node's home network prefix,
      the local mobility anchor MUST forward the packet through the bi-
      directional tunnel setup for that mobile node.  The format of the
      tunneled packet is shown below.  However, when using IPv4
      transport, the format of the packet is as described in [ID-IPV4-
      PMIP6].


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



                  Figure 7: Tunneled Packets from LMA to MAG


   Forwarding Packets Sent by the Mobile Node:

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

5.7.  Local Mobility Anchor Address Discovery

   Dynamic Home Agent Address Discovery, as explained in Section 10.5
   [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



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   its home network prefix.

   The DHAAD message in the current form cannot be used in Proxy Mobile
   IPv6 for discovering the address of the mobile node's local mobility
   anchor.  In Proxy Mobile IPv6, the local mobility anchor will not be
   able to receive any messages sent to the Mobile IPv6 Home-Agents
   anycast address corresponding to the mobile node's home network
   prefix, as the prefix is not hosted on any of its interfaces.
   Further, the mobile access gateway will not predictably be able to
   locate the serving local mobility anchor that has the mobile node's
   binding cache entry.  Hence, this specification does not support
   Dynamic Home Agent Address Discovery protocol.

   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 other 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.

5.8.  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 it is
   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 node 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.
   Hence, this specification does not support Mobile Prefix Discovery.

5.9.  Route Optimizations Considerations

   The Route Optimization in Mobile IPv6, as defined in [RFC-3775],
   enables a mobile node to communicate with a correspondent node
   directly using its care-of address and further the Return Routability
   procedure enables the correspondent node to have reasonable trust
   that the mobile node is reachable at both its home address and
   care-of address.

   In Proxy Mobile IPv6, the mobile node is not involved in any mobility
   related signaling.  The mobile node uses only its home address for
   all its communication and the Care-of address (Proxy-CoA) is not
   visible to the mobile node.  Hence, the Return Routability procedure



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   as defined in Mobile IPv6 cannot be used in Proxy Mobile IPv6.


6.  Mobile Access Gateway Operation

   The Proxy Mobile IPv6 protocol described in this document introduces
   a new functional entity, the Mobile Access Gateway (MAG).  The mobile
   access gateway is the entity that is responsible for detecting the
   mobile node's movements on its access link and sending the binding
   registration requests to the local mobility anchor.  In essence, the
   mobile access gateway performs mobility management on behalf of a
   mobile node.

   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 or the signaling interactions between those
   functional entities are beyond the scope of this document.

   The mobile access gateway has the following key functional roles:

   o  It is responsible for detecting the mobile node's movements on the
      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 by
      sending Router Advertisements with the mobile node's home network
      prefix information.

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

6.1.  Extensions to Binding Update List Entry Data Structure

   Every mobile access gateway MUST maintain a Binding Update List.
   Each entry in the Binding Update List represents a mobile node's
   mobility binding with its local mobility anchor.  The Binding Update
   List is a conceptual data structure, described in Section 11.1 [RFC-
   3775].

   For supporting this specification, the conceptual Binding Update List
   entry data structure needs be extended with the following additional
   fields.


   o  The Identifier of the attached mobile node, MN-Identifier.  This
      identifier is acquired during the mobile node's attachment to the



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      access link through mechanisms outside the scope of this document.

   o  The interface identifier of the mobile node's connected interface.
      This address can be acquired from the received Router Solicitation
      messages from the mobile node or during the mobile node's
      attachment to the access network.  This is typically a L2
      identifier conveyed by the mobile node

   o  The IPv6 home network prefix of the attached mobile node.  The
      home network prefix of the mobile node is acquired from the mobile
      node's local mobility anchor through the received Proxy Binding
      Acknowledgement messages.  The IPv6 home network prefix also
      includes the corresponding prefix length.

   o  The Link-local address of the mobile node on the interface
      attached to the access link.

   o  The IPv6 address of the local mobility anchor serving the attached
      mobile node.  This address is acquired from the mobile node's
      policy profile or from other means.

   o  The Interface identifier (If-Id) of the access link where the
      mobile node is currently attached.  This is internal to the mobile
      access gateway and is used to associate the Proxy Mobile IPv6
      tunnel to the right access link where the mobile node is attached.

   o  The interface identifier (If-Id) of the bi-directional tunnel
      between the mobile node's local mobility anchor and the mobile
      access gateway.  This is internal to the mobile access gateway.
      The tunnel interface identifier is acquired during the tunnel
      creation.

6.2.  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.  The policy profile MAY also be handed over to a serving
   mobile access gateway as part of a context transfer procedure during
   a handoff or the serving mobile access gateway MAY be able to
   dynamically generate this profile.  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:



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


   The following are the optional fields of the policy profile:

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

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

   o  Supported address configuration procedures (Stateful, Stateless or
      both) on the access links in the Proxy Mobile IPv6 domain


6.3.  Supported Access Link Types

   This specification supports only point-to-point access link types and
   thus it assumes that the mobile node and the mobile access gateway
   are the only two nodes on the access link.  The link is assumed to
   have multicast capability.  This protocol may also be used on other
   link types, as long as the link is configured in such a way that it
   guarantees a point-to-point delivery between the mobile node and the
   mobile access gateway for all the protocol traffic.

6.4.  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.  However,
   the advertised flags with respect to 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.

   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-4862] or as per Privacy
   extension specification [RFC-4941].

   When stateful address autoconfiguration is supported on the link, the
   mobile node can obtain the address configuration from the DHCPv6
   server using DHCPv6 client protocol, as specified in DHCPv6
   specification [RFC-3315].




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   Additionally, 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.

6.5.  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
   SHOULD 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 between the mobile node and mobile access gateway,
   before the protocol operation begins.

6.6.  Acquiring Mobile Node's Identifier

   All the network entities in a Proxy Mobile IPv6 domain MUST be able
   to identify a mobile node, using its MN-Identifier.  This identifier
   MUST be stable across the Proxy Mobile IPv6 domain and the entities
   must be able to use this identifier in the signaling messages.
   Typically, this identifier is obtained as part of the access
   authentication or through other means as specified below.

   o  The identifier of the mobile node that the mobile access gateway
      obtains typically as part of the access authentication or from the
      notified network attachment event, can be a temporary identifier
      and this identifier may also change at each re-authentication.
      However, the mobile access gateway MUST be able to use this
      identifier and obtain the mobile node's MN-Identifier from the
      policy store, such as from the RADIUS attribute, Chargeable-User-
      Identifier [RFC-4372].

   o  The MN-Identifier that the policy store delivers to the mobile
      access gateway may not be the true identifier of the mobile node.
      However, the mobility access gateway MUST be able to use this
      identifier in the signaling messages exchanged with the local
      mobility anchor.

   o  The mobile access gateway MUST be able identify the mobile node by
      its MN-Identifier and it MUST be able to associate this identity
      to the sender of any IPv4 or IPv6 packets on the access link.






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6.7.  Home Network Emulation

   One of the key functions of a mobile access gateway is to emulate the
   mobile node's home network 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 initial address configuration after it
   moved into that Proxy Mobile IPv6 domain.

   For emulating the mobile node's home link on the access link, the
   mobile access gateway must be able to send Router Advertisements
   advertising the mobile node's home network prefix and other address
   configuration parameters consistent with its home link properties.
   Typically, these configuration settings will be based on the domain
   wide policy or based on a policy specific to each mobile node.

   Typically, the mobile access gateway learns the mobile node's home
   network prefix information from the received Proxy Binding
   Acknowledgement message or it may be obtained from the mobile node's
   policy profile.  However, the mobile access gateway SHOULD send the
   Router Advertisements advertising the mobile node's home network
   prefix only after successfully completing the binding registration
   with the mobile node's local mobility anchor.

   When advertising the home network prefix in the Router Advertisement
   messages, the mobile access gateway MAY set the prefix lifetime value
   for the advertised prefix to any chosen value at its own discretion.
   An implementation MAY choose to tie the prefix lifetime to the mobile
   node's binding lifetime.  The prefix lifetime can also be an optional
   configuration parameter in the mobile node's policy profile.

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, will continue to detect its home
   network and thus making it 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 mobile node is DNAv6 enabled, as specified in [ID-DNAV6], it may
   not detect the link change due to DNAv6 optimizations and may 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-4862], there is a very low
   possibility of a link-local address collision between the two
   neighbors on that access link.




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   For solving this problem, this specification allows the mobile access
   gateway to upload the mobile node's link-local address to the local
   mobility anchor using the Link-local Address option, exchanged in the
   binding registration messages.  The mobile access gateway can learn
   the mobile node's link-local address, by snooping the DAD messages
   sent by the mobile node for establishing the link-local address
   uniqueness on the access link.  Subsequently, at each handoff, the
   mobile access gateway can obtain this address from the local mobility
   anchor to ensure link-local address uniqueness and may change its own
   link-local address, if it detects a collision.

   Alternatively, 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 on the global and
   link-local addresses every time the interface detects a handover,
   even when DNAv6 does not detect a link change.

   However, this issue will not impact point-to-point links based on a
   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, IPV6CP [RFC-5072] 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 whenever 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 mobile
   access gateway and there will not be any need for establishing link-
   local address uniqueness on that link.

   The issue of address collision is not relevant to the mobile node's
   global address.  Since there is an unique home network prefix
   assigned for each mobile node, the uniqueness for the mobile node's
   global address is assured on the access link.



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6.9.  Signaling Considerations

6.9.1.  Binding Registrations

   Mobile Node Attachment and Initial Binding Registration:

   o  After detecting a new mobile node on its access link, the mobile
      access gateway must identify the mobile node and acquire its MN-
      Identifier.  If it determines that the network-based mobility
      management service needs to be offered to the mobile node, it MUST
      send a Proxy Binding Update message to the local mobility anchor.

   o  The Proxy Binding Update message MUST have the Mobile Node
      Identifier option [RFC-4283], identifying the mobile node, the
      Home Network Prefix option, either the Timestamp option or a valid
      sequence number and optionally the Link-local Address option.
      When Timestamp option is added to the message, the mobile access
      gateway MAY set the Sequence Number field to a value of a
      monotonically increasing counter and the local mobility anchor
      will ignore this field, but will return the same value in the
      Proxy Binding Acknowledgement message.  This will be useful for
      matching the reply to the request message.

   o  The Home Address option MUST NOT be present in the Destination
      Option extension header of the Proxy Binding Update message.

   o  The Access Technology Type option MUST be present in the Proxy
      Binding Update message.  The access technology Type field in the
      option MUST be set to the access technology using which the mobile
      node is currently attached to the mobile access gateway.

   o  The Handoff Indicator flag in the Access Technology Type option
      MUST be set to value 1 (Attachment over a new interface), if the
      mobile access gateway predictably knows that the mobile node's
      attachment to the network using the current interface is due to
      neither a handover between two interfaces of the mobile node nor a
      handover of the mobility session for the same interface of the
      mobile node between two mobile access gateways.  This essentially
      serves as a request to the local mobility anchor to allocate a new
      home network prefix for this mobility session and not update any
      existing Binding Cache entry created for the same mobile node
      connected to the Proxy Mobile IPv6 domain through a different
      interface.

   o  The Handoff Indicator flag in the Access Technology Type option
      MUST be set to value 2 (Handoff between interfaces), if the mobile
      access gateway definitively knows the mobile node's current
      attachment is due to a handoff of the mobility session between two



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      interfaces of the mobile node.

   o  The Handoff Indicator flag in the Access Technology Type option
      MUST be set to value 3 (Handoff between mobile access gateways for
      the same interface), if the mobile access gateway definitively
      knows the mobile node's current attachment is due to a handoff of
      the mobility session between two interfaces of the mobile node.

   o  The Handoff Indicator flag in the Access Technology Type option
      MUST be set to value 4 (Handoff State Unknown), if the mobile
      access gateway cannot predictably know if the mobile node's
      session is due to a handoff.

   o  The Mobile Node Interface Identifier option carrying the
      identifier of the currently attached interface MUST be present in
      the Proxy Binding Update message, if the mobile access gateway
      knows the interface identifier of the mobile node's currently
      attached interface.  The "P" Flag in the option MUST be set to 0,
      indicating that the carried identifier is the currently attached
      interface identifier.  If the interface identifier is now known,
      this identifier MUST NOT be present.

   o  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
      allocate that prefix.  If the specified value is 0::/0, then the
      local mobility anchor will consider this as a request for prefix
      allocation.


   Receiving Binding Registration Reply:

   o  The mobile access gateway MUST observe the rules described in
      Section 9.2 [RFC-3775] when processing Mobility Headers in the
      received Proxy Binding Acknowledgement message (a Binding
      Acknowledgement message with the 'P' flag set).

   o  The message MUST be authenticated as described in Section 4.0.
      When IPsec is used for message authentication, the SPI in the
      IPsec header [RFC-4306] of the received packet MUST be used for
      locating the security association needed for authenticating the
      message.

   o  The mobile access gateway MUST apply the considerations specified
      in Section 5.5 for processing the Sequence Number field and the
      Timestamp option, in the message.




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   o  The mobile access gateway MUST ignore any checks, specified in
      [RFC-3775] related to the presence of Type 2 Routing header in the
      Proxy Binding Acknowledgement message.

   o  If the Timestamp option is present in the received Proxy Binding
      Acknowledgement message and with the Status field value set to any
      value other than TIMESTAMP_MISMATCH (Invalid Timestamp), the
      mobile access gateway MAY use the timestamp value for matching the
      response to the request message that it sent recently.  For all
      other cases, it MAY use the sequence number in combination with
      the identifier present in the Mobile Node Identifier option for
      matching the response to the request.

   o  If the received Proxy Binding Acknowledgement message has the
      Status field value set to PROXY_REG_NOT_ENABLED (Proxy
      registration not enabled for the mobile node), the mobile access
      gateway SHOULD NOT send binding registration requests again for
      that mobile node.  It must also deny the mobility service to that
      mobile node.

   o  If the received Proxy Binding Acknowledgement message has the
      Status field value set to TIMESTAMP_LOWER_THAN_PREV_ACCEPTED
      (Timestamp lower than previously accepted timestamp), the mobile
      access gateway SHOULD try to register again to reassert the mobile
      node's presence to the mobility anchor.  The mobile access gateway
      is not specifically required to synchronize its clock upon
      receiving this error code.

   o  If the received Proxy Binding Acknowledgement message has the
      Status field value set to TIMESTAMP_MISMATCH (Invalid Timestamp),
      the mobile access gateway SHOULD try to register again only after
      it has synchronized its clock to a common time source that is used
      by all the mobility entities in that domain for their clock
      synchronization.  The mobile access gateway SHOULD NOT synchronize
      its clock to the local mobility anchor's system clock, based on
      the timestamp present in the received message.

   o  If the received Proxy Binding Acknowledgement message has the
      Status field value set to NOT_AUTHORIZED_FOR_HOME_NETWORK_PREFIX
      (Not authorized for that prefix), the mobile access gateway SHOULD
      try to request for that prefix in the binding registration
      request, only after it learned the validity of that prefix.

   o  If the received Proxy Binding Acknowledgement message has the
      Status field value set to any value greater than or equal to 128
      (i.e., if the binding is rejected), the mobile access gateway MUST
      NOT advertise the mobile node's home network prefix in the Router
      Advertisements sent on that access link and there by denying



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      mobility service to the mobile node.

   o  If the received Proxy Binding Acknowledgement message has the
      Status field value set to 0 (Proxy Binding Update accepted) and if
      there is no existing Binding Update List entry for that mobile
      node, the mobile access gateway MUST create a Binding Update List
      entry and must setup the routing state, as explained in section
      6.10.  But, if there is an existing Binding Update List entry for
      that mobile node, the entry MUST be updated reflecting the
      accepted binding registration.

   o  If the received Proxy Binding Acknowledgement message has the
      address in the Link-local Address option set to a value that
      matches its own link-local address on that access interface where
      the mobile node is anchored, the mobile access gateway MUST change
      its link-local address on that interface.


   Extending Binding Lifetime:

   o  For extending the lifetime of a currently registered mobile node
      (i.e., if there exists a Binding Update List entry for that mobile
      node), the mobile access gateway MUST send a Proxy Binding Update
      message to the local mobility anchor.  The prefix value in the
      Home Network Prefix option present in the request SHOULD be set to
      the currently registered home network prefix and the value in the
      Link-local Address option MAY be set to ALL_ZERO or to the link-
      local address of the mobile node.


   Mobile Node Detachment and Binding De-Registration:

   o  At any point, if the mobile access gateway detects that the mobile
      node has moved away from its access link, it SHOULD send a Proxy
      Binding Update message to the local mobility anchor with the
      lifetime value set to zero.

   o  Either upon receipt of a Proxy Binding Acknowledgement message
      from the local mobility anchor or after a certain timeout waiting
      for the reply, the mobile access gateway MUST remove the Binding
      Cache entry for that mobile node from its Binding Update List and
      withdraw the mobile node's home network prefix as the hosted on-
      link prefix on that access link.


   Constructing the Proxy Binding Update Message:





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   o  The mobile access gateway when sending the Proxy Binding Update
      request to the local mobility anchor MUST construct the message as
      specified below.


               IPv6 header (src=Proxy-CoA, dst=LMAA)
                    Mobility header
                        -BU /*P & A flags are set*/
                       Mobility Options
                          - Home Network Prefix option
                          - Link-local Address option (Optional)
                          - Timestamp Option (optional)
                          - Mobile Node Identifier option
                          - Access Technology Type option (Mandatory)
                          - Mobile Node Interface Identifier option
                            (Optional)


                Figure 8: Proxy Binding Update message format

   o  The Source Address field in the IPv6 header of the message SHOULD
      be set to the address of the mobile access gateway.

   o  The Destination Address field in the IPv6 header of the message
      SHOULD be set to the local mobility anchor address.

   o  The Home Network Prefix option MUST be present.  The prefix value
      MAY be set 0::/0 or to a specific prefix value.

   o  The Link-local Address option MAY be present.  The value MAY be
      set to ALL_ZERO or the mobile node's link-local address.

   o  The Access Technology Type option MUST be present.  The value MUST
      be set to the type of the access technology using which the mobile
      node is currently attached to the mobile access gateway.

   o  The Mobile Node Interface Identifier option MAY be present.

   o  Considerations from Section 5.5 must be applied for constructing
      the Timestamp option.

   o  The Mobile Node Identifier option [RFC-4283] MUST be present, the
      identifier field in the option MUST be set to mobile node's
      identifier, MN-Identifier.

   o  The message MUST be protected by using IPsec, using the security
      association existing between the local mobility anchor and the
      mobile access gateway.



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6.9.2.  Router Solicitation Messages

   The mobile node may send a Router Solicitation message on the access
   link whenever the link-layer detects a media change.  The Source
   Address in the IPv6 header of the Router Solicitation message may
   either be the link-local address of the mobile node or an unspecified
   address (::).


   o  The mobile access gateway on receiving the Router Solicitation
      message SHOULD send a Router Advertisement containing the mobile
      node's home network prefix as the on-link prefix.  However, before
      sending the Router Advertisement message containing the mobile
      node's home network prefix, it SHOULD complete the binding
      registration process with the mobile node's local mobility anchor.

   o  If the local mobility anchor rejects the binding registration
      request, or, if the mobile access gateway failed to complete the
      binding registration process for whatever reasons, the mobile
      access gateway MUST NOT advertise the mobile node's home network
      prefix in the Router Advertisement messages that it sends on the
      access link.  However, it MAY choose to advertise a local visited
      network prefix to enable the mobile node for regular IPv6 access.

6.9.3.  Retransmissions and Rate Limiting

   The mobile access gateway is responsible for retransmissions and rate
   limiting the binding registration requests that it sends for updating
   a mobile node's binding.  Implementations MUST follow the below
   guidelines.


   o  When the mobile access gateway sends a Proxy Binding Update
      request, it should use the constant, INITIAL_BINDINGACK_TIMEOUT
      [RFC-3775], for configuring the retransmission timer.

   o  If the mobile access gateway fails to receive a valid matching
      response within the retransmission interval, it SHOULD retransmit
      the message until a response is received.  However, the mobile
      access gateway MUST ensure the mobile node is still attached to
      the connected link before retransmitting the message.

   o  As specified in Section 11.8 [RFC-3775], the mobile access gateway
      MUST use an exponential back-off process in which the timeout
      period is doubled upon each retransmission, until either the node
      receives a response or the timeout period reaches the value
      MAX_BINDACK_TIMEOUT [RFC-3775].  The mobile access gateway MAY
      continue to send these messages at this slower rate indefinitely.



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   o  If Timestamp based scheme is in use, the retransmitted Proxy
      Binding Update messages MUST use the latest timestamp.  If
      Sequence number scheme is in use, the retransmitted Proxy Binding
      Update messages MUST use a Sequence Number value greater than that
      used for the previous transmission of this Proxy Binding Update
      message, just as specified in [RFC-3775].

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|
    +--+          +---+                      +---+          +--+
                            IPv6 Tunnel


                    Figure 9: Proxy Mobile IPv6 Tunnel

6.10.1.  Transport Network

   The transport network between the local mobility anchor and the
   mobile access gateway can be either an IPv6 or IPv4 network.
   However, this specification only deals with the IPv6 transport and
   the companion document [ID-IPV4-PMIP6] specifies the required
   extensions for negotiating IPv4 transport and the corresponding
   encapsulation mode for supporting this protocol operation.

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 to 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.




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   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 gets 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.

   o  IPv6-In-IPv6 - IPv6 datagram encapsulated in an IPv6 packet [RFC-
      2473].

   o  IPv6-In-IPv4 - IPv6 datagram encapsulation in an IPv4 packet.  The
      details on how this mode is negotiated is specified in [ID-IPV4-
      PMIP6].

   o  IPv6-In-IPv4-UDP - IPv6 datagram encapsulation in an IPv4 UDP
      packet.  This mode is specified in [ID-IPV4-PMIP6].

6.10.3.  Routing State

   The following section explains 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.








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   +==================================================================+
   |  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           |
   + (IPv6 Prefix or   -----------------------------------------------|
   |  Input Interface  | Locally Connected    |     direct            |
   +------------------------------------------------------------------+


               Figure 10: Example - Policy based Route Table



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


                Figure 11: Example - Tunnel Interface Table

6.10.4.  Local Routing

   If there is data traffic between a visiting mobile node and a
   correspondent 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.  The configuration variable, EnableMAGLocalRouting MAY be
   used for controlling this aspect.  However, in some systems, this may
   have 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 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 are beyond of the scope of this document.





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6.10.5.  Tunnel Management

   All the considerations mentioned in Section 5.6.1 for the tunnel
   management on the local mobility anchor apply for the mobile access
   gateway as well.

6.10.6.  Forwarding Rules

   Forwarding Packets sent to the Mobile Node's Home Network:

   o  On receiving a packet from the bi-directional tunnel established
      with the mobile node's local mobility anchor, the mobile access
      gateway MUST use the destination address of the inner packet for
      forwarding it on the interface where the destination network
      prefix is hosted.  The mobile access gateway MUST remove the outer
      header 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
      a scenario, in the form of ICMP control message, the
      considerations from Generic Packet Tunneling specification [RFC-
      2473] must be applied.

   o  On receiving a packet from a correspondent node that is locally
      connected and which is destined to a mobile node that is on
      another locally connected access link, 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 mobile node.  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 node's local mobility anchor.  Otherwise, it can route
      the packet directly to the mobile node.

   Forwarding Packets Sent by the Mobile Node:

   o  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.

   o  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,



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      it MUST route the packet through the bi-directional tunnel
      established between itself and the mobile node's local mobility
      anchor.  Otherwise, it can route the packet directly to the
      destination.

   o  On receiving a packet from the mobile node connected to its access
      link, to a destination that is not directly connected, the packet
      MUST be forwarded to the local mobility anchor through the bi-
      directional tunnel established between itself and the mobile
      node's local mobility anchor.  However, the packets that are sent
      with the link-local source address MUST NOT be forwarded.  The
      format of the tunneled packet is shown below.  However, when using
      IPv4 transport, the format of the tunneled packet is as described
      in [ID-IPV4-PMIP6].


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



                 Figure 12: Tunneled Packets from MAG to LMA

6.11.  Supporting DHCPv6 based Address Configuration on the Access Link

   This section explains how Stateful Address Configuration using DHCPv6
   can be enabled on the access link attached to a mobile access gateway
   and how a mobile node attached to that link can obtain an address
   from its home network prefix using DHCPv6.

   o  The DHCPv6 relay agent [RFC-3315] service needs to be enabled on
      each of the access links in the Proxy Mobile IPv6 domain.
      Further, as specified in Section 20 [RFC-3315], the relay agent
      should be configured to use a list of destination addresses, which
      MAY include unicast addresses, the All_DHCP_Servers multicast
      address, or other addresses selected by the network administrator.

   o  The DHCPv6 server in the Proxy Mobile IPv6 domain can be
      configured with a list of prefix pools (P1, P2, ..., Pn).  Each
      one of these prefix pools corresponds to a home network prefix
      that a local mobility anchor allocates to a mobile node in that
      domain.  However, the DHCPv6 server will not know the relation
      between a given address pool and a mobile node to which the
      corresponding prefix is allocated.  It just views these pools as
      prefixes hosted on different links in that domain.





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   o  When a mobile node sends a DHCPv6 request message, the DHCP relay
      agent function on the access link will set the link-address field
      in the DHCP message to an address in the mobile node's home
      network prefix, so as to provide a prefix hint to the DHCP Server
      for the address pool selection.  The DHCP server on receiving the
      request from the mobile node, will allocate an address from the
      prefix pool present in the link-address field of the request.

   o  Once the mobile node obtains an address and moves to a different
      link and sends a DHCP request, the DHCP relay agent on the new
      link will set the prefix hint in the DHCP messages to the mobile
      node's home network prefix.  The DHCP server will identify the
      client from the Client-DUID option and present in the request and
      will allocate the same address as before.

   o  The DHCP based address configuration is not recommended for
      deployments where the local mobility anchor and the mobile access
      gateways are located in different administrative domains.  For
      this configuration to work, all the mobile access gateways in the
      Proxy Mobile IPv6 domain should be able to ensure that the DHCP
      requests from a given mobile node anchored on any of the access
      links in that domain, will always be handled by the same DHCP
      server.

   o  The DHCP server should be configured to offer low address lease
      times.  A lease time that is too large prevents the DHCP server
      from reclaiming the address even after the local mobility anchor
      deletes the mobile node's binding cache entry.

6.12.  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 about the mobile node's home
   network prefix renumbering are outside the scope of this document.

6.13.  Mobile Node Detachment Detection and Resource Cleanup

   Before sending a Proxy Binding Update message to the local mobility
   anchor for extending the lifetime of a currently existing binding of
   a mobile node, the mobile access gateway MUST make sure the mobile
   node is still attached to the connected link by using some reliable
   method.  If the mobile access gateway cannot predictably detect the



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   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 SHOULD 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

6.14.  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 IP access to some other nodes.  This requires the network to
   have control on when to enable network-based mobility management
   service to a mobile node and when to enable regular IPv6 access.
   This specification does not disallow such configuration.

   Upon detecting a mobile node on its access link and after policy
   considerations, the mobile access gateway MUST determine if network-
   based mobility management service should be offered to that mobile
   node.  If the mobile node is entitled for network-based mobility
   management 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.

   If the mobile node is not entitled for the network-based mobility
   management service, as determined from the policy considerations, the
   mobile access gateway MAY choose to offer regular IPv6 access to the
   mobile node and in such scenario the normal IPv6 considerations



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   apply.  If IPv6 access is enabled, the mobile node SHOULD be able to
   obtain an IPv6 address using normal IPv6 address configuration
   procedures.  The obtained address must be from a local visitor
   network prefix.  This essentially ensures that the mobile access
   gateway functions as a normal access router to a mobile node attached
   to its access link and with out impacting its host-based mobility
   protocol operation.


7.  Mobile Node Operation

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

7.1.  Moving into a Proxy Mobile IPv6 Domain

   Once a mobile node enters a Proxy Mobile IPv6 domain and attaches to
   an access network, the mobile access gateway on the access link
   detects the attachment of the mobile node and completes the binding
   registration with the mobile node's local mobility anchor.  If the
   binding update operation is successfully performed, the mobile access
   gateway will create the required state and setup the data path for
   the mobile node's data traffic.

   If the mobile node is IPv6 enabled, on attaching to the access link,
   it will typically send Router Solicitation message [RFC-4861].  The
   mobile access gateway on the access 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.

   If the mobile access gateway on the access link, receives a Router
   Solicitation message from the mobile node, before it completed the
   signaling with the mobile node's local mobility anchor, the mobile
   access gateway may not know the mobile node's home network prefix and
   may not be able to emulate the mobile node's home link on the access
   link.  In such scenario, the mobile node may notice a slight delay
   before it receives a Router Advertisement message.

   If the received Router Advertisement has the Managed Address
   Configuration flag set, the mobile node, as it would normally do,
   will send a DHCPv6 Request [RFC-3315].  The DHCP relay service
   enabled on that access link will ensure the mobile node will obtain
   its IPv6 address as a lease from its home network prefix.

   If the received 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 be able to obtain



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   an IPv6 address using an interface identifier generated as per the
   Autoconf specification [RFC-4862] or as per the Privacy Extensions
   specification [RFC-4941].

   If the mobile node is IPv4 enabled and if the network permits, it
   will be able to obtain the IPv4 address configuration for the
   connected interface by using DHCP [RFC-2131].  The details related to
   IPv4 support is specified in the companion document [ID-IPV4-PMIP6].

   Once the address configuration is complete, the mobile node can
   continue to use this address configuration as long as it is attached
   to the network that is in the scope of that Proxy Mobile IPv6 domain.

7.2.  Roaming in the Proxy Mobile IPv6 Domain

   After obtaining the address configuration in the Proxy Mobile IPv6
   domain, as the mobile node moves and changes its point of attachment
   from one mobile access gateway to the other, it can still continue to
   use the same address configuration.  As long as the attached access
   network is in the scope of that Proxy Mobile IPv6 domain, the mobile
   node will always detect the same link, where it obtained its initial
   address configuration.  If the mobile node performs DHCP operation,
   it will always obtain the same address as before.

   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 does not require any changes to the mobile node's
   IP stack.  It assumes the mobile node to be a normal IPv4/IPv6 node,
   with its protocol operation consistent with the respective
   specifications.

   However, for achieving protocol efficiency and for faster hand-offs,
   implementations may choose to adjust the following IPv6 operating
   parameters on the mobile node be adjusted to the below recommended
   values.


   Lower Default-Router List Cache Time-out:

   As per the base IPv6 specification [RFC-4861], each IPv6 host is
   required to 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



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   routers on that link.  The Router Lifetime field in the received
   Router Advertisement defines the life of this entry.

   In case of Proxy Mobile IPv6, when a mobile node moves from one link
   to another, the source address of the received Router Advertisement
   messages advertising the mobile node'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
   and not the previously known 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 [RFC-4861].  This action
   will help in minimizing packet losses during a hand off switch.

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

   In access network where SEND [RFC-3971] is not deployed, the mobile
   access gateway may 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 this will force the flush of the Previous
   Default-Router entry from the mobile node's cache.  This certainly
   requires 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 fixed link-local address for all the mobility
   entities in a Proxy Mobile IPv6 domain and where SEND [RFC-3971] is
   not deployed.  In such scenario, the mobile node is not required to
   update the default-router entry.  However, 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.



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8.1.  Proxy Binding Update Message



       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           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .                        Mobility options                       .
      .                                                               .

      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




   A Binding Update message that is sent by a mobile access gateway to a
   local mobility anchor is referred to as the "Proxy Binding Update"
   message.  A new flag (P) is included in the Binding Update message.
   The rest of the Binding Update message format remains the same as
   defined in [RFC-3775] and with the additional (R) and (M) flags as
   specified in [RFC-3963] and [RFC-4140] respectively.


   Proxy Registration Flag (P)

      A new flag (P) is included in the Binding Update message to
      indicate to the local mobility anchor that the Binding Update
      message is a proxy registration.  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.

   Mobility Options

      Variable-length field of such length that the complete Mobility
      Header is an integer multiple of 8 octets long.  This field
      contains zero or more TLV-encoded mobility options.  The encoding
      and format of defined options are described in Section 6.2 [RFC-
      3775].  The local mobility anchor MUST ignore and skip any options
      which it does not understand.





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      As per this specification, the following mobility options are
      valid in a Proxy Binding Update message:

         Home Network Prefix option

         Link-local Address option

         Mobile Node Identifier Option

         Timestamp option

   For descriptions of other fields present in this message, refer to
   section 6.1.7 [RFC-3775].


8.2.  Proxy Binding Acknowledgement Message



       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .                        Mobility options                       .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



   A Binding Acknowledgement message that is sent by a local mobility
   anchor to a mobile access gateway is referred to as the "Proxy
   Binding Acknowledgement" message.  A new flag (P) is included in the
   Binding Acknowledgement message.  The rest of the Binding
   Acknowledgement message format remains the same as defined in [RFC-
   3775] and with the additional (R) and (M) flags as specified in [RFC-
   3963] and [RFC-4140] respectively.

   Proxy Registration Flag (P)







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      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.

   Mobility Options

      Variable-length field of such length that the complete Mobility
      Header is an integer multiple of 8 octets long.  This field
      contains zero or more TLV-encoded mobility options.  The encoding
      and format of defined options are described in Section 6.2 [RFC-
      3775].  The mobile access gateway MUST ignore and skip any options
      which it does not understand.

      As per this specification, the following mobility options are
      valid in a Proxy Binding Acknowledgement message:

         Home Network Prefix option

         Link-local Address option

         Mobile Node Identifier option

         Timestamp option

   Status

      8-bit unsigned integer indicating the disposition of the Proxy
      Binding Update.  Values of the Status field less than 128 indicate
      that the Proxy Binding Update was accepted by the local mobility
      anchor.  Values greater than or equal to 128 indicate that the
      binding registration was rejected by the local mobility anchor.
      Section 8.8 defines the Status values that can used in Proxy
      Binding Acknowledgement message.

   For descriptions of other fields present in this message, refer to
   the section 6.1.8 [RFC-3775].

8.3.  Home Network Prefix Option

   A new option, Home Network Prefix Option is defined for using it in
   the Proxy Binding Update and Proxy Binding Acknowledgement messages
   exchanged between a local mobility anchor and a mobile access
   gateway.  This option is used for exchanging the mobile node's home
   network prefix information.




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   The Home Network Prefix Option has an alignment requirement of 8n+4.
   Its format is as follows:



       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Type     |   Length      |   Reserved    | Prefix Length |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                    Home Network Prefix                        +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Type
           <IANA>

       Length

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

       Reserved (R)

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

       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.








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8.4.  Access Technology Type Option

   A new option, Access Technology Type Option is defined for using it
   in the Proxy Binding Update and Proxy Binding Acknowledgement
   messages exchanged between a local mobility anchor and a mobile
   access gateway.  This option is used for exchanging the type of the
   access technology using which the mobile node is currently attached
   to the mobile access gateway.

   The Access Technology Type Option has no alignment requirement.  Its
   format is as follows:



    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |   Length      |   Acc Tech    | HI| Reserved  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    Type
        <IANA>

    Length

        8-bit unsigned integer indicating the length of the option
        in octets, excluding the type and length fields. This field
        MUST be set to 2.

    Access Technology Type (Acc Tech)

        A 8-bit field that specifies the access technology through
        which the mobile node is connected to the access link on the
        mobile access gateway.

        The values 0-255 will be allocated and managed by IANA. The
        following values are currently reserved for the below specified
        access technology types.

        0: Reserved
        1: 802.3
        2: 802.11a/b/g
        3: 802.16e
        4: PPP
        5: LTE

    Handoff Indicator (HI)



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        A 2-bit field that specifies the type of handoff. The values
        (0-3) will be allocated and managed by IANA. The following
        values are currently reserved.

        0: Reserved
        1: Attachment over a new interface
        2: Handoff between interfaces
        3: Handoff between mobile access gateways for the same interface
        4: Handoff state unknown

    Reserved (R)

        This 6-bit field is unused for now.  The value MUST be
        initialized to 0 by the sender and MUST be ignored by the
        receiver.



8.5.  Mobile Node Interface Identifier Option

   A new option, Mobile Node Interface Identifier Option is defined for
   using it in the Proxy Binding Update and Proxy Binding
   Acknowledgement messages exchanged between a local mobility anchor
   and a mobile access gateway.  This option is used for exchanging the
   mobile node's interface identifier.

   The format of the Interface Identifier option when the interface
   identifier is 8 bytes is shown below.  When the size is different,
   the option MUST be aligned appropriately, as per mobility option
   alignment requirements specified in [RFC-3775].





















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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     |P|        Reserved             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                     Interface Identifier                      +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Type
         <IANA>

     Length
         8-bit unsigned integer indicating the length of the option
         in octets, excluding the type and length fields. This field
         MUST be set to 10.

     P Flag
         A 1-bit field that specifies whether the carried interface
         identifier is the currently attached interface identifier of
         the mobile node, or if it is the identifier of the interface
         from where the session is being handed off to a different
         interface of the mobile node.

         0: Interface Identifier of the currently attached interface
         1: Interface Identifier of the other interface, when the
            handoff is performed between two interfaces of the mobile
            node.

     Reserved

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

     Interface Identifier

         A variable length field containing the mobile node's interface
         identifier.


8.6.  Link-local Address Option

   A new option, Link-local Address Option is defined for using it in
   the Proxy Binding Update and Proxy Binding Acknowledgement messages
   exchanged between a local mobility anchor and a mobile access
   gateway.  This option is used for exchanging the mobile node's link-
   local address.



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   The Link-local Address option has an alignment requirement of 8n+6.
   Its format is as follows:




       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                      |   Type        |    Length     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                  Link-local Address                           +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Type
           <IANA>

       Length

           8-bit unsigned integer indicating the length of the option
           in octets, excluding the type and length fields. This field
           MUST be set to 16.

       Link-local Address

           A sixteen-byte field containing the mobile node's link-local
           address.


8.7.  Timestamp Option

   A new option, Timestamp Option is defined for use in the Proxy
   Binding Update and Proxy Binding Acknowledgement messages.

   The Timestamp option has an alignment requirement of 8n+2.  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      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                          Timestamp                            +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Type
        <IANA>

    Length

        8-bit unsigned integer indicating the length in octets of
        the option, excluding the type and length fields.  The value
        for this field MUST be set to 8.

    Timestamp

      A 64-bit unsigned integer field containing a timestamp.  The value
      indicates the number of seconds since January 1, 1970, 00:00 UTC,
      by using a fixed point format.  In this format, the integer number
      of seconds is contained in the first 48 bits of the field, and the
      remaining 16 bits indicate the number of 1/65536 fractions of a
      second.


8.8.  Status Values

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

   Status values less than 128 indicate that the Proxy Binding Update
   request was accepted by the local mobility anchor.  Status values
   greater than 128 indicate that the Proxy Binding Update was rejected
   by the local mobility anchor.


   PROXY_REG_NOT_ENABLED:

      Proxy Registration not enabled for the mobile node.


   MAG_NOT_AUTHORIZED_FOR_PROXY_REG:



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      The mobile access gateway is not authorized to send proxy binding.
      updates.


   NOT_AUTHORIZED_FOR_HOME_NETWORK_PREFIX

      The mobile node is not authorized for the requesting home network
      prefix.


   TIMESTAMP_MISMATCH:

      Invalid timestamp value in the received Proxy Binding Update
      message (the clocks are out of sync).


   TIMESTAMP_LOWER_THAN_PREV_ACCEPTED:

      The timestamp value in the received Proxy Binding Update message
      is lower than the previously accepted value.


   MISSING_HOME_NETWORK_PREFIX_OPTION

      Missing mobile node home network prefix option.

   MISSING_MN_IDENTIFIER_OPTION:

      Missing mobile node identifier in the Proxy Binding Update
      message.

   MISSING_ACCESS_TECH_TYPE_OPTION

      Missing mobile node's access technology type in the Proxy Binding
      Update message.


   Additionally, the following Status values defined in [RFC-3775] can
   also be used in Proxy Binding Acknowledgement message.

      0 Proxy Binding Update accepted

      128 Reason unspecified

      129 Administratively prohibited






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      130 Insufficient resources

      133 Not local mobility anchor for this mobile node


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 correspondent node that is locally
      connected to one of the interfaces of the mobile access gateway.
      The correspondent 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.


   The local mobility anchor MUST allow the following variables to be
   configured by the system management.


   MinDelayBeforeBCEDelete

      This variable specifies the amount of time in milliseconds the
      local mobility anchor MUST wait before it deletes a Binding Cache
      entry of a mobile node, upon receiving a Proxy Binding Update
      message from a mobile access gateway with a lifetime value of 0.
      During this wait time, if the local mobility anchor receives a
      Proxy Binding Update for the same mobility binding, with lifetime
      value greater than 0, then it must update the binding cache entry
      with the accepted binding values.  By the end of this wait-time,
      if the local mobility anchor did not receive any valid Proxy
      Binding Update message for that mobility binding, it MUST delete
      the Binding Cache entry.  This delay essentially ensures a mobile



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      node's Binding Cache entry is not deleted too quickly and allows
      some time for the new mobile access gateway to complete the
      signaling for the mobile node.

      The default value for this variable is 10000 milliseconds.


10.  IANA Considerations

   This document defines a three new Mobility Header Options, the Home
   Network Prefix option, Access Technology Type option, Interface
   Identifier option, Link-local Address option and Timestamp option.
   These options are described in Sections 8.3, 8.4, 8.5, 8.6 and 8.7
   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].

   The Mobility Header Option, Access Technology Type option defined in
   Section 8.4 of this document introduces a new Access Technology type
   numbering space, where the values from 0 to 5 have been reserved by
   this document.  Approval of new Access Technology type numbers is
   subject to IANA Approval.

   This document also defines new Binding Acknowledgement status values
   as described in Section 8.8.  The status values MUST be assigned from
   the same number space used for Binding Acknowledgement status values,
   as defined in [RFC-3775].  The allocated values for each of these
   status values MUST be greater than 128.


11.  Security Considerations

   The potential security threats against any network-based mobility
   management protocol are described in [RFC-4832].  This section
   explains how Proxy Mobile IPv6 protocol defends itself against those
   threats.

   Proxy Mobile IPv6 protocol requires the signaling messages, Proxy
   Binding Update and Proxy Binding Acknowledgement, exchanged between
   the mobile access gateway and the local mobility anchor to be
   protected using IPsec, using the established security association
   between them.  This essentially eliminates the threats related to the
   impersonation of the mobile access gateway or the local mobility
   anchor.

   This specification allows a mobile access gateway to send binding
   registration messages on behalf of a mobile node.  If proper
   authorization checks are not in place, a malicious node may be able



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   to hijack a mobile node's session or may carry out a denial-of-
   service attack.  To prevent this attack, this specification requires
   the local mobility anchor to allow only authorized mobile access
   gateways that are part of that Proxy Mobile IPv6 domain to send
   binding registration messages on behalf of a mobile node.

   To eliminate the threats on the interface between the mobile access
   gateway and the mobile node, this specification requires an
   established trust between the mobile access gateway and the mobile
   node and to authenticate and authorize the mobile node before it is
   allowed to access the network.  Further, the established
   authentication mechanisms enabled on that access link will ensure
   that there is a secure binding between the mobile node's identity and
   its link-layer address.  The mobile access gateway will definitively
   identify the mobile node from the packets that it receives on that
   access link.

   To address the threat related to a compromised mobile access gateway,
   the local mobility anchor, before accepting a Proxy Binding Update
   message for a given mobile node, may ensure that the mobile node is
   definitively attached to the mobile access gateway that sent the
   proxy binding registration request.  This may be accomplished by
   contacting a trusted entity which is able to track the mobile node's
   current point of attachment.  However, the specific details of the
   actual mechanisms for achieving this is outside the scope of this
   document.


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 Alex Petrescu, Alice Qinxia,
   Alper Yegin, Ashutosh Dutta, Behcet Sarikaya, Fred Templin, Genadi
   Velev, George Tsirtsis, Gerardo Giaretta, Henrik Levkowetz, Hesham
   Soliman, James Kempf, Jari Arkko, Jean-Michel Combes, John Zhao,
   Jong-Hyouk Lee, Jonne Soininen, Jouni Korhonen, Kilian Weniger, Marco
   Liebsch, Mohamed Khalil, Nishida Katsutoshi, Phil Roberts, Ryuji
   Wakikawa, Sangjin Jeong, Suresh Krishnan, Ved Kafle, Vidya Narayanan,
   Youn-Hee Han 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



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

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

   [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-4861] Narten, T., Nordmark, E. and W. Simpson, Soliman, H.,
   "Neighbor Discovery for IP Version 6 (IPv6)", RFC 4861, September
   2007.

13.2.  Informative References

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

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

   [RFC-3971] Arkko, J., Ed., Kempf, J., Sommerfeld, B., Zill, B., and



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   P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March
   2005.

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

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

   [RFC-4330] Mills, D., "Simple Network Time Protocol (SNTP) Version 4
   for IPv4, IPv6 and OSI", RFC 2030, October 1996.

   [RFC-4372] Adrangi, F., Lior, A., Korhonen, J., and J. Loughney,
   "Chargeable User Identity", RFC 4372, January 2006.

   [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.

   [RFC-4862] Thompson, S., Narten, T., Jinmei, T., "IPv6 Stateless
   Address Autoconfiguration", RFC 4862, September 2007.

   [RFC-4941] Narten, T., Draves, R., Krishnan, S., "Privacy Extensions
   for Stateless Address Autoconfiguration in IPv6", RFC 4941, September
   2007.

   [RFC-5072] Varada, S., Haskin, D. and Allen, E., "IP version 6 over
   PPP", RFC 5072, September 2007.

   [ID-IPV4-PMIP6] Wakikawa, R. and Gundavelli, S., "IPv4 Support for
   Proxy Mobile IPv6", draft-ietf-netlmm-pmip6-ipv4-support-01.txt, May
   2007.

   [ID-DNAV6] Kempf, J., et al "Detecting Network Attachment in IPv6
   Networks (DNAv6)", draft-ietf-dna-protocol-06.txt, October 2006.


Appendix A.  Proxy Mobile IPv6 interactions with AAA Infrastructure





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   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


   This specification supports Per-MN-Prefix model.  However, it is
   possible to support Shared-Prefix model under the following
   guidelines.

   The mobile node is allowed to use stateful address configuration
   using DHCPv6 for obtaining its address configuration.  The mobile
   node is not allowed to use any of the stateless autoconfiguration
   techniques.  The permitted address configuration models for the
   mobile node on the access link can be enforced by the mobile access
   gateway, by setting the relevant flags in the Router Advertisements,
   as per [RFC-4861].

   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.






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Authors' Addresses

   Sri Gundavelli (Editor)
   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


   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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