MIP4                                                            K. Leung
Internet-Draft                                                G. Dommety
Intended status: Standards Track                               P. Yegani
Expires: July 14, 2007                                     Cisco Systems
                                                            K. Chowdhury
                                                        Starent Networks
                                                            Jan 10, 2007

              Mobility Management using Proxy Mobile IPv4

Status of this Memo

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Copyright Notice

   Copyright (C) The Internet Society (2007).


   Mobile IPv4 is a standard mobility protocol that enables IPv4 device
   to roam between networks.  The mobile device has the Mobile IP
   function to signal its location to the routing anchor, known as the
   Home Agent.  However, there are many IPv4 devices without such
   capability due to various reasons.  This document describes a
   solution based on Proxy Mobile IPv4, which enables some other entity

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   to provide mobility support on behalf of an unaltered and mobility-
   unaware IPv4 device.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document  . . . . . . . . . . . . . .  3
   3.  Solution Benefits  . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Overview of Proxy Mobile IPv4  . . . . . . . . . . . . . . . .  5
     4.1.  Mobility Signaling for Mobile Station  . . . . . . . . . .  5
       4.1.1.  Proxy Registration . . . . . . . . . . . . . . . . . .  6
       4.1.2.  Resource Cleanup . . . . . . . . . . . . . . . . . . .  8
     4.2.  Establishment of Bi-Directional Tunnel . . . . . . . . . .  9
   5.  Appearance of Being at Home Network  . . . . . . . . . . . . .  9
     5.1.  ARP Considerations . . . . . . . . . . . . . . . . . . . .  9
     5.2.  ICMP Considerations  . . . . . . . . . . . . . . . . . . . 10
     5.3.  DHCP Considerations  . . . . . . . . . . . . . . . . . . . 10
     5.4.  PPP IPCP Considerations  . . . . . . . . . . . . . . . . . 11
     5.5.  Link-Local Multicast and Broadcast Considerations  . . . . 11
   6.  Mobility Proxy Agent Operation . . . . . . . . . . . . . . . . 11
   7.  Home Agent Operation . . . . . . . . . . . . . . . . . . . . . 12
     7.1.  Processing Registration Requests . . . . . . . . . . . . . 12
   8.  Mobile Station Operation . . . . . . . . . . . . . . . . . . . 12
     8.1.  Initial Network Access . . . . . . . . . . . . . . . . . . 12
     8.2.  Moving to a New MPA  . . . . . . . . . . . . . . . . . . . 12
     8.3.  Packet forwarding  . . . . . . . . . . . . . . . . . . . . 13
     8.4.  Moving to a Different Domain . . . . . . . . . . . . . . . 13
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
   Intellectual Property and Copyright Statements . . . . . . . . . . 16

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1.  Introduction

   There are many IPv4 devices which don't have or can't be enabled with
   Mobile IP [5] functionality.  For them, Proxy Mobile IPv4 provides
   mobility support without being "touched".  The scheme is based on an
   external node acting as a proxy Mobile Node that registers the
   location of the device and maintains reachability while the device is
   on the network.  The Foreign Agent and Home Agent perform their
   normal roles.  The following examples depict possible scenarios:

   1.  An Access Point or Base Station performs registration when a
       mobile station is associated on the airlink.

   2.  An Access Router or Foreign Agent performs registration when a
       mobile station is detected.

   3.  A wireless mobile termination device performs registration for an
       attached host.

   In the first two cases, the proxy node is a network element and the
   signaling can be considered part of the mobility management function
   of the domain.  The third case is when the proxy node moves along
   with the mobile device and may be considered as a part of the mobile
   device.  Some could argue that this is not a proxy mode of operation
   because the Mobile Node is the wireless mobile termination device.
   But the Home Address is "owned" by the host, meaning that packets to
   and from this IP address is received and sent by this host,
   respectively.  The wireless mobile termination device is providing
   mobility for this IP address unbeknownst to the host.  An example of
   this is cdma2000's Network Mode on the mobile termination unit.  For
   cdma2000, the true Mobile IP mode would be the Relay Mode, which is
   when the host operates as the Mobile Node.  Anyways, this mode of
   operation is well understood and commonly deployed.  The aim of this
   document is to describe how the network elements can provide mobility
   management for the mobile devices.

2.  Conventions used in this document

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [1].

      The following new terminology and abbreviations are introduced in
      this document and all other general mobility related terms as
      defined in Mobile IPv4 specification [5].

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      Mobility Station (MS)

         Any IPv4 node that has the ability to physically access or roam
         across different networks.  The Mobile Station does not have
         the Mobile IPv4 protocol stack.

      Mobility Proxy Agent (MPA)

         The Mobile IPv4 entity that offers proxy mobility service for a
         Mobile Station by performing registration function on the
         host's behalf.  As mentioned before, this may be the Access
         Point, Base Station, Mobile Terminal, Access Router, or Access

3.  Solution Benefits

   Proxy Mobile IPv4 is designed to satisfy the requirements listed
   below.  In addition, the solution leverages well-studied
   specification and highly available implementations.  Only incremental
   enhancements are added to Mobile IPv4 protocol to enrich its breadth
   to support both client-based and network-based mobility.  For
   example, a Home Agent can anchor Mobile Stations that have Mobile IP
   as well as the hosts without such capability.

   The network-based Mobility Management solution defined in this
   document provides the following benefits:

   1.  Support for Unmodified Hosts

          An overwhelming majority of IPv4 hosts do not have Mobile IP
          capability.  Providing mobility for them is achievable using
          Proxy Mobile IPv4.  This is accomplished without "touching"
          the user's devices running on a myriad of operating systems
          and networking stacks.

   2.  Airlink Consumption

          Mobility-related signaling over the air-link is eliminated.
          Considering that Network Address Translation (NAT) is
          ubiquitous in IPv4 networks, a mobile node needs to send
          keepalives at short intervals to properly maintain the NAT
          states [6].  This can be performed by the MPA in the network
          which doesn't consume any air-link bandwidth.

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   3.  Reduction of Signaling Overhead in the Network

          The MPA can aggregate multiple MSes on the same tunnel.  Thus
          the frequent keepalives needed to maintain the NAT states can
          be reduced significantly.  The signaling load on the network
          diminishes which increases the overall capacity.

   4.  Support for Heterogeneous Wireless Link Technologies

          One aspect is how to adopt the scheme to an access technology.
          Since Proxy Mobile IPv4 is based on a heterogeneous mobility
          protocol, it can be used for any type of access network.

          The other aspect is how to support roaming across different
          access technologies.  As long as the MPA can use the same NAI
          to identify the MS for various access networks, roaming
          between them is possible.

   5.  Support for IPv4 and IPv6 Host

          As IPv6 increases in popularity, the host will likely be dual
          stack.  Adding IPv6 support to the host for Proxy Mobile IPv4
          involves the methods defined in [10].

4.  Overview of Proxy Mobile IPv4

4.1.  Mobility Signaling for Mobile Station

   After network access authentication, MPA exchange registration
   messages with the Home Agent to set up proper routing and tunneling
   of packets from/to the Mobile Station.  As specified in RFC 3344 [5],
   a Foreign Agent may be used in the registration procedure.  However,
   for the remainder of this document, MPA is described to use direct
   registration to the Home Agent.  The difference is covered in RFC
   3344 [5] and can be presumed to be adaquately understood (e.g. the
   tunnel is between FA and HA instead of MPA and HA for FA registration
   and direct registration, respectively).

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4.1.1.  Proxy Registration

      +----+        +-------+      +-------+   +-----+
      |    |        |  AR/  |      |       |   |     |
      | MN |        |  MPA  |      | AAA   |   | HA  |
      |    |        |       |      |       |   |     |
      +----+        +-------+      +-------+   +-----+
        |               |             |          |
        |     1a        |     1b      |          |
        |<------------->|<----------->|          |
        |               |             |          |
        |     2         |             |          |
        |-------------->|             |          |
        |               |       3     |          |
        |               |----------------------->|
        |               |             |          |
        |               |       4     |          |
        |               |<-----------------------|
        |     5         |             |          |
        |<--------------|             |          |
        |               |             |          |
        |     6         |             |          |
        |               |             |          |

                    Figure 1: Network Connection Setup

   Description of the steps:

   1a.  MN performs L2 establishment with the base station (not shown)
   and performs access authentication/authorization with the AR.  During
   this phase, the MN may run CHAP or PAP if PPP is used or EAP over foo
   (foo being the specific access technology or PANA).  The AR acts as
   the NAS in this phase.

   1b.  The AR exchanges AAA messages with the AAA infrastructure to
   perform authentication and authorization of the MN.  As part of this
   step, the AAA server may download some information about the MN (e.g.
   user's profile, handset type, assigned home agent address, and other
   capabilities of the MN).

   2.  The MN sends an IPCP config request to the AR in case of PPP to
   request for an IPv4 address.  If DHCP is uses, the DHCP client in the
   MN sends a DHCPDISCOVER message.  It is assumed in this document that

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   the AR has a DHCP proxy/server function.

   3.  Triggered by step 2 the MPA in the AR sends an Mobile IPv4
   registration request (RRQ) to the Home Agent.  The Home Agent's
   address if either received at step 1b from the Home AAA or it is
   discovered in an out of band way by the AR.  The RRQ contains the
   Care-of Address (CoA) of the AR (collocated FA in this case).  The
   HoA field is set to ALL-ZERO-ONES-ADDRESS.  The RRQ may be protected
   by MN-HA authorization enabling extension.  The derivation and
   distribution of the MN-HA or FA-HA key is outside the scope of this

   4.  The home agent registers the MN's session and assigns an HoA.
   The home agent returns the HoA in the RRP.

   5.  The AR responds back to the MN with an IPCP config-NAK to suggest
   the IPv4 address which is the HoA from the HA.  This happens in
   response to step 2.  If DHCP was used at step 2, the AR/DHCP-proxy/
   server sends back a DHCPOFFER with the IPv4 address set to the
   received HoA.

   6.  At this step, regular IPCP/NCP procedures get completed and the
   MN's IP stack is ready to receive or send IP packets.  If DHCP is
   used, the regular DHCPREQUEST and DHCPACK messages are exchanged and
   the MN's IP stack is configured with the assigned IPv4 address.

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4.1.2.  Resource Cleanup

        MS         New MPA     HA       Previous MPA

        |           | Proxy     |           |
        |           | Reg       |           |
        |           | Request   |           |
      1)|           o---------->|           |
        |           |           |           |
        |           |           | Update    |
        |           |           | existing  |
      2)|           |           o MBE for MS|
        |           |           |           |
        |           |           | Reg       |
        |           |           | Revocation|
      3)|           |           o---------->|
        |           |           |           |
      4)|           |           |           o Remove visitor
        |           |           |           | entry for MS
        |           |           |           |
        |           |           |           | Reg
        |           |           |           | Revoc Ack
      5)|           |           |<----------o
        |           |           |           |
        |           | Proxy     |           |
        |           | Reg       |           |
        |           | Reply     |           |
      6)|           o<----------o           |

            Figure 2: Registration Revocation for Previous MPA

   MPA which no longer serve the Mobile Station needs to remove any
   associated mobility states and relinquish resources which are no
   longer needed.

   When the Home Agent receives a Proxy Registration Request for a
   Mobile Station with an existing MBE, a Registration Revocation [3543]
   is sent to the previous MPA (in steps #1 through #3).  The previous
   MPA removes the visitor entry for the Mobile Station before sending
   acknowledgement to the Home Agent (in steps #4 and #5).  In parallel,
   the Home Agent sends the Proxy Registration Reply to the new MPA (in
   step #6).  At the end of sequence of events, only states for the MS
   are in the new MPA and the Home Agent.

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4.2.  Establishment of Bi-Directional Tunnel

   After receiving a successful Registration Reply for the Proxy
   Registration Request, the MPA sets up a tunnel to the Mobile
   Station's Home Agent.

   The bi-directional tunnel between the MPA and the Home Agent allows
   packets to flow in both directions, while the mobile station is
   connected to its visited link.  The tunnel endpoints are the LMAP and
   the Home Agent.  All traffic to and from the Mobile Station is sent
   through this bi-directional tunnel.

   While the MPA is serving a Mobile Station, it MUST be able to
   intercept all packets sent from the Mobile Station and forward them
   out the MPA-Home Agent tunnel created for supporting that Mobile
   Station.  Typically, forwarding is based on Layer 2 information such
   as the source MAC address or ingress PPP interface.  This allows MSes
   with overlapping IP addresses to be supported.

   Any packets received on the tunnel from Home Agent, the MPA
   decapsulates before forwarding to the Mobile Station on its link.
   Typically, the forwarding is based on the Destination IP address and
   HA indicator such as tunnel interface identifier or HA address.  This
   allows MSes with overlapping IP addresses to be supported.

5.  Appearance of Being at Home Network

   Since the Mobile Station is not aware of mobility and does not
   participate in handover signaling, the network elements deceive the
   host to believe that it is stationary yet directing its traffic to
   the location where it has actually moved.  An unmodified host uses
   ARP [8] to learn the MAC address of other nodes on the subnet,
   obtains an IP address and other host configuration via DHCP [2], and
   sends link-local multicast/broadcasts.  The network's response to the
   host has to be equivalent to the situation when host is always on the
   home subnet.

5.1.  ARP Considerations

   For IEEE 802 type of access networks (e.g.  WLAN, WiMAX), the Mobile
   Station sends ARP request for host and default gateway on its subnet.
   The purpose of maintaining an ARP entry is to allow the delivery of
   the packet from MS to the IP node on the link.

   For Proxy Mobile IP, the objective is to get the packet from the MS
   to the Home Agent.  For CNs with the same home network but roaming
   elsewhere, the HA will tunnel the packet to them.  Otherwise, the HA

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   forwards the traffic via normal routing.

   The method to deliver the packet to the HA depends on whether the MPA
   is on the BS or AR.  If the MPA is in the Base Station, the ARP entry
   in the MS serves no purpose since the packet will be tunneled to the
   HA by the BS.  If the MPA is in the Access Router, then the Base
   Station needs to rewrite the destination MAC address properly to
   reach the AR.  Alternatively, a common MAC address - listened to by
   all participating AR - is sent to MS in response to an ARP Request.

   MPA@BS:    MS <-> BS/MPA <==============> HA

       MS has ARP entries for default gateway and hosts on subnet which
       are set to some pseudo MAC address that is never used.

   MPA@AR:    MS <-> BS     <-> AR/MPA <===> HA

       MS has ARP entries for default gateway and hosts on subnet which
       are set to some pseudo MAC address which is rewritten by BS or a
       common MAC address for ARs.

                      Figure 3: ARP Entry Management

5.2.  ICMP Considerations

   In some cases, the Mobile Station sends an ICMP Query [9] with IP TTL
   set to 1 destined to the default gateway.  This check is used to
   detect if default gateway is still reachable on the link.  The MPA
   should respond with ICMP Reply when it is providing mobility service.

5.3.  DHCP Considerations

   Proxy Mobile IP allows the Mobile Station to operate as a normal IPv4
   host using the standard IP address configuration via DHCP.

   the MS boots up and initiates DHCP.  The rest of the procedure is as
   per the description under fig 1.

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5.4.  PPP IPCP Considerations

   When MS access the network via PPP [3], LCP CHAP is used to
   authenticate the user.  After authentication, the NAS (which is the
   LMAP) sends the proxy Registration Request to the Home Agent, which
   responds with the Home Address in the Registration Reply.  The NAS
   informs the MS to use the Home Address during IPCP [4].  When MS
   moves to a new NAS, the same procedure happens and MS has the same IP
   address for communication.

   The messgae exchange is illustrated in fig 1.

5.5.  Link-Local Multicast and Broadcast Considerations

   MPA may tunnel all packets destined to Link-Local Multicast or
   Broadcast to the HA.  The HA looks up the hosts which are in the same
   subnet and send a duplicated packet to each of them.

6.  Mobility Proxy Agent Operation

   The role of the MPA is performing the functions of a Mobile Node.  It
   sends Registration Request to the Home Agent (via the Foreign Agent
   when available) to set up routing.  When there is no FA, MPA operates
   in Collocated Care-of Address mode and provides tunneling support.
   FA can provide tunneling when it is used during registration in
   accordance to RFC 3344.

   The MPA needs to know the following information for sending a

   1.  NAI

   2.  MN-HA Mobility Security Association

   3.  Home Agent Address

   This information can be downloaded from AAA server or configured by
   administrator.  One example is configuration of subnet to HA mapping.
   When an MS associates with the Base Station, the MPA registers to the
   HA base on the IP address of the MS.

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7.  Home Agent Operation

   The Home Agent has the functionalities described in RFC 3344.  In
   addition, the following feature is introduced.

7.1.  Processing Registration Requests


8.  Mobile Station Operation

   As per this specification, a mobile station would function as a
   normal IPv4 host.  The required behavior of the node will be
   consistent with the base IPv4 specification [1].  The mobile station
   will have the ability to retain its IPv4 address as it moves from one
   point of network attachment to the other with out ever requiring it
   to participate in any mobility related signaling.

   The mobile station when boots up for the first time can obtain an
   IPv4 address using DHCP.

   As the mobile station roams, it is always able to communicate using
   the DHCP leased IP address on the home network.  The MPA on the
   currently attached network signals to the HA to ensure proper
   forwarding path for MS's traffic.

8.1.  Initial Network Access

   When the Mobile Station access the network for the first time and
   attaches to a network on the MPA, it will present its identity in the
   form of NAI to the network as part of the network access
   authentication process.

   Once the address configuration is complete, the Mobile Station will
   always be able to use that IP address anywhere in network.

8.2.  Moving to a New MPA

   When a Mobile Station moves to a new MPA from another MPA, the
   following occurs:

   The Mobile Station will perform a network access authentication with

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   the attached MPA.  If the authentication fails, the Mobile Station
   will not be able to use the link.  After a succesful authentication,
   the MPA will have the identifier and the other profile data of the
   Mobile Station.

   Once the network access authentication process is complete, the
   Mobile Station may sense a change in the Link Layer and use ARP,
   DHCP, and/or ICMP to detect if it is still on the same subnet.  These
   mechanisms are handled by the network as described in section 5
   "Appearance of Being At Home Network".

8.3.  Packet forwarding

   All packets that are be sent from the Mobile Station to the
   corresponding node will be sent as normal IPv4 packets setting the
   Source Address of the IPv4 header to the Home Address and the
   Destination Address to the corresponding node's IP address.  The
   default gateway for the Mobile Station will always be its HA.  The
   ARP Entry for HA address is a pseudo HA MAC address.

   Similarly, all packets sent to the Mobile Node's Home Address by the
   corresponding node will be received by the Mobile Station in the
   original form (without any tunneling overhead) on its link.

   No special operation is required by the Mobile Station to either send
   or receive packets.

8.4.  Moving to a Different Domain

   The scheme defined in this document, provides mobility support to the
   Mobile Station within that domain.  Once the Mobile Station obtains
   an assigned Home Address, it can continue to use the same address
   roaming between MPAs in the network with its HA providing the
   topological anchor point for that address.  However, the Mobile
   Station that roams across domains is required to have the Mobile IPv4
   stack and operate as a normal MIPv4 mobile node to achieve mobility
   across domains.

9.  IANA Considerations


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10.  Security Considerations

   The functionality in this document is protected by the Authentication
   Extensions described in RFC 3344 [5].  Each MPA needs to have the
   same MN-HA SA to register the MS.  The SA can be provisioned by the
   administrator.  The dynamic key distribution for this scheme is
   outside the scope of this document.

11.  Acknowledgements

12.  References

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

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

   [3]   Simpson, W., "The Point-to-Point Protocol (PPP) for the
         Transmission of Multi-protocol Datagrams over Point-to-Point
         Links", RFC 1331, May 1992.

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

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

   [6]   Levkowetz, H. and S. Vaarala, "Mobile IP Traversal of Network
         Address Translation (NAT) Devices", RFC 3519, May 2003.

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

   [8]   Plummer, D., "An Ethernet Address Resolution Protocol",
         RFC 826, November 1982.

   [9]   Postel, J., "Internet Control Message Protocol", RFC 792,
         September 1981.

   [10]  Navali, J. and K. Chowdhury, "IPv6 over Network based Mobile
         IPv4", draft-navali-ip6-over-netmip4-00.txt (work in progress),
         February 2006.

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Authors' Addresses

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

   Email: kleung@cisco.com

   Gopal Dommety
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134

   Email: gdommety@cisco.com

   Parviz Yegani
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134

   Email: pyegani@cisco.com

   Kuntal Chowdhury
   Starent Networks
   30 International Place
   Tewksbury, MA  01876

   Email: kchowdhury@starentnetworks.com

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