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Versions: (draft-koodli-mip4-fmipv4) 00 01 02 03 04 05 06 07 RFC 4988

MIP4 Working Group                                        Rajeev. Koodli
Internet-Draft                                          Charles. Perkins
Intended status: Experimental                      Nokia Research Center
Expires: August 27, 2007                               February 23, 2007


                       Mobile IPv4 Fast Handovers
                     draft-ietf-mip4-fmipv4-04.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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   This Internet-Draft will expire on August 27, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document adapts the Mobile IPv6 Fast Handovers to improve delay
   and packet loss resulting from Mobile IPv4 handover operations.
   Specifically, this document addresses movement detection, IP address
   configuration and location update latencies during a handover.  For
   reducing the IP address configuration latency, the document proposes
   that the new Care-of Address is always made to be the new access
   router's IP address.  Additional mechanisms may be defined in the
   future versions of this document.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Factors Affecting Handover . . . . . . . . . . . . . . . . . .  4
   4.  Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  5
     4.2.  Operation  . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Using Previous FA Notification Extension . . . . . . . . . . .  9
   6.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  Fast Binding Update (FBU)  . . . . . . . . . . . . . . . .  9
     6.2.  Fast Binding Acknowledgment (FBAck)  . . . . . . . . . . . 10
     6.3.  Router Solicitation for Proxy Advertisement (RtSolPr)  . . 12
     6.4.  Proxy Router Advertisement (PrRtAdv) . . . . . . . . . . . 13
     6.5.  Inter-Access Router Messages . . . . . . . . . . . . . . . 16
       6.5.1.  Handover Initiate (HI) . . . . . . . . . . . . . . . . 16
       6.5.2.  Handover Acknowledge (HAck)  . . . . . . . . . . . . . 17
   7.  Option Formats . . . . . . . . . . . . . . . . . . . . . . . . 19
     7.1.  Link-Layer Address Option Format . . . . . . . . . . . . . 19
     7.2.  New IPv4 Address Option Format . . . . . . . . . . . . . . 20
     7.3.  New Router Prefix Information Option . . . . . . . . . . . 21
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
   10. Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 23
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 23
     11.2. Informative References . . . . . . . . . . . . . . . . . . 23
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
   Intellectual Property and Copyright Statements . . . . . . . . . . 26





















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1.  Introduction

   This document adapts the fast handover specification [rfc4068] to
   IPv4 networks.  The fast handover protocol specified in this document
   is particularly interesting for operation over links such as IEEE 802
   wireless links.  Fast handovers are not typically needed for wired
   media due to the relatively large delays attributable to establishing
   new connections in today's wired networks.  Mobile IPv4 [rfc3344]
   registration messages are re-used (with new type numbers) in this
   document to enable faster implementation using existing Mobile IPv4
   software.  This draft does not rely on link-layer triggers for
   protocol operation, but performance will typically be enhanced by
   using the appropriate triggers when they are available.  This
   document assumes that the reader is familiar with the basic operation
   and terminology of Mobile IPv4 [rfc3344] and Fast Handovers for
   Mobile IPv6 [rfc4068].

   The active agents that enable continued packet delivery to a mobile
   node (MN) are the access routers on the networks that the mobile node
   connects to.  Handover means that the mobile node changes its network
   connection, and we consider the scenario in which this change means
   change in access routers.  The mobile node utilizes the access
   routers as default routers in the normal sense, but also as partners
   in mobility management.  Thus, when the mobile node moves to a new
   network, it processes handover-related signaling in order to identify
   and develop a relationship with a new access router.  In this
   document, we call the previous access router PAR and the new access
   router NAR, consistent with the terminology in [rfc4068].  Unless
   otherwise mentioned, a PAR is also a Previous Foreign Agent (PFA) and
   a NAR is also a New Foreign Agent (NFA).

   On a particular network, a mobile node may obtain its IP address via
   DHCP [rfc2131] (i.e., Co-located Care-of Address) or use the Foreign
   Agent CoA.  During a handover, the new CoA (NCoA) is always made to
   be that of NAR.  This allows a mobile node to receive and send
   packets using its previous CoA (PCoA), so that delays resulting from
   IP configuration (such as DHCP address acquisition delay) subsequent
   to attaching to the new link are disengaged from affecting the
   existing sessions.

   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 [RFC2119].


2.  Terminology

   The terminology used in this document in based on [rfc4068] and



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   [rfc3344].  We provide some definitions below for convenience.

      Mobile Node (MN): A Mobile IPv6 host.

      Access Point (AP): A Layer 2 device connected to an IP subnet that
      offers wireless connectivity to an MN.  An Access Point Identifier
      (AP-ID) refers to the AP's L2 address.  Sometimes, AP-ID is also
      referred to as a Base Station Subsystem ID (BSSID).

      Access Router (AR): The MN's default router.

      Previous Access Router (PAR): The MN's default router prior to its
      handover.

      New Access Router (NAR): The MN's default router subsequent to its
      handover.

      Previous CoA (PCoA): The MN's Care of Address valid on PAR's
      subnet.

      New CoA (NCoA): The MN's Care of Address valid on NAR's subnet.

      Handover: A process of terminating existing connectivity and
      obtaining new IP connectivity.

      (AP-ID, AR-Info) tuple: Contains an access router's L2 and IP
      addresses, and the prefix valid on the interface to which the
      Access Point (identified by AP-ID) is attached.  The triplet
      [Router's L2 address, Router's IP address, Prefix] is called "AR-
      Info".



3.  Factors Affecting Handover

   Both the link-layer operations and IP layer procedures affect the
   perceived handover performance.  However, the overall performance is
   also (always) a function of specific implementation of the technology
   as well as the system configuration.  This document only specifies IP
   layer protocol operations.  The purpose of this section is to provide
   an illustration of events that affect handover performance, but it is
   purely informative.

   The IP layer handover delay and packet loss are influenced by
   latencies due to movement detection, IP address configuration and
   Mobile IP registration procedure.  Movement detection latency comes
   from the need to reliably detect movement to a new subnet.  This is a
   function of frequency of router advertisements as well as default



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   agent reachability.  IP address configuration latency depends on the
   particular IP CoA being used.  If co-located mode with DHCP is used,
   the latency is quite likely going to be higher and unacceptable for
   real-time applications such as Voice over IP.  Finally, the Mobile IP
   registration procedure needs a round-trip of delay between the Mobile
   Node and its Home Agent over the Internet.  This delay is incurred
   after the mobile node performs movement detection and IP
   configuration.

   Underlying the IP operations are link-layer procedures.  These are
   clearly technology-specific.  For instance in IEEE 802.11, the
   handover operation typically involves scanning access points over all
   available channels, selecting a suitable access point, and
   associating with it.  It may also involve performing access control
   operations such as those specified in IEEE 802.1X [ieee-802.1x].
   These delays contribute to the handover performance.  Optimizations
   are being proposed for standardization in IEEE, for instance see
   [ieee-802.11r] and [ieee-802.21].  Together with appropriate
   implementation techniques, these optimizations can provide the
   required level of delay support at the link-layer for real-time
   applications.


4.  Protocol

4.1.  Overview

   The design of the protocol is the same as for Mobile IPv6 [rfc4068].
   Readers should consult [rfc4068] for details, and here we provide a
   summary.

   The protocol avoids the delay due to movement detection and IP
   configuration and disengages Mobile IP registration delay from the
   time-critical path.  The protocol provides the surrounding network
   neighborhood information so that a mobile node can determine whether
   it is moving to a new subnet even before the handover.  The
   information provided and the signaling exchanged between the local
   mobility agents allows the mobile node to send and receive packets
   immediately after handover.  In order to disengage the Mobile IP
   registration latency, the protocol provides routing support for the
   continued use of a mobile node's previous CoA.

   After a mobile node obtains its IPv4 care-of address, it builds a
   neighborhood access point and subnet map using the Router
   Solicitation for Proxy Advertisement (RtSolPr) and Proxy Router
   Advertisement (PrRtAdv) messages.  The mobile node may scan for
   access points (APs) based on the configuration policy in operation
   for its wireless network interface.  If a scan results in a new AP



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   discovery, the mobile node resolves the corresponding AP Identifier
   to subnet information using the RtSolPr and PrRtAdv messages
   mentioned above.

   At some point, the mobile node decides to undergo handover.  It sends
   an FBU message to PAR from the previous link or from the new link.
   FBU message enables creation of a binding between the mobile node's
   previous CoA and the new CoA.

   The coordination between the access routers is done by way of the
   Handover Initiate (HI) and Handover Acknowledge (HAck) messages
   defined in [rfc4068].  After these signals have been exchanged
   between the previous and new access routers (PAR and NAR), data
   arriving at PAR will be tunneled to NAR for delivery to the newly
   arrived mobile node.  The purpose of HI is to securely deliver the
   routing parameters for establishing this tunnel.  The tunnel is
   created by the access routers in response to the delivery of the FBU
   from the mobile node.

4.2.  Operation

   In response to a handover trigger or indication, the mobile node
   sends a Fast Binding Update message to Previous Access Router (PAR)
   (see Section Section 6.1).  Depending on the Mobile IP mode of
   operation, the PCoA is either the Home Address (in FA CoA mode) or
   co-located CoA (in CCoA mode).  The FBU message SHOULD be sent when
   the mobile node is still connected to PAR.  When sent in this
   "predictive" mode, the fields in the FBU are used as follows:

      "Home Address" field must be the PCoA (which can be either the
      Home Address or the co-located CoA)

      Home Agent field, even though redundant, must be set to PAR's IP
      address

      Care-of Address field must be the NAR's IP address discovered via
      PrRtAdv message

      Destination IP address must be PAR's IP address

      Source IP address must be the PCoA (which can be either the Home
      Address or the co-located CoA)


   As a result of processing the FBU, PAR creates a binding between PCoA
   and NAR's IP address in its routing table.  The PAR sends an FBack
   message (see Section Section 6.2) as a response to the mobile node.




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   The timeline for the predictive mode of operation (adapted from
   [rfc4068]) is shown in Figure Figure 1.



                 MN                    PAR                  NAR
                  |                     |                    |
                  |------RtSolPr------->|                    |
                  |<-----PrRtAdv--------|                    |
                  |                     |                    |
                  |------FBU----------->|--------HI--------->|
                  |                     |<------HAck---------|
                  |          <--FBack---|--FBack--->         |
                  |                     |                    |
               disconnect             forward                |
                  |                   packets===============>|
                  |                     |                    |
                  |                     |                    |
              connect                   |                    |
                  |                     |                    |
                  |--------- FBU --------------------------->|
                  |<=================================== deliver packets
                  |                     |<-----FBU-----------|



                    Figure 1: Predictive Fast Handover

   The mobile node sends the FBU regardless of its previous transmission
   when attachment to a new link is detected.  This minimally allows NAR
   to detect mobile node's attachment, but also the retransmission of
   FBU when an FBack has not been received yet.  When sent in this
   "reactive" mode, the following fields in FBU are set differently
   compared to the predictive mode:

      Destination IP address must be NAR's IP address

      Source IP address must be PCoA (either the Home Address or the co-
      located CoA)

   When NAR receives FBU, it may already have processed the HI message
   and created a host route entry for the PCoA.  In that case, NAR
   should immediately forward arriving and buffered packets including
   the FBAck message.  In any case, NAR MUST forward the contents of
   this message, starting from the Type field, to PAR, which means the
   Source and Destination IP addresses in the new packet now contain the
   IP addresses of NAR and PAR respectively.




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   The reactive mode of operation (adapted from [rfc4068]) is
   illustrated in Figure Figure 2.



                 MN                    PAR                  NAR
                  |                     |                    |
                  |------RtSolPr------->|                    |
                  |<-----PrRtAdv--------|                    |
                  |                     |                    |
               disconnect               |                    |
                  |                     |                    |
                  |                     |                    |
               connect                  |                    |
                  |-----------FBU-------|------------------->|
                  |                     |<-----FBU-----------|
                  |                     |------FBack-------->|
                  |                   forward                |
                  |                   packets===============>|
                  |                     |                    |
                  |<=================================== deliver packets
                  |                                          |



                     Figure 2: Reactive Fast Handover

   The Handover Initiate (HI) and Handover Acknowledge (HAck) messages
   serve to establish a bidirectional tunnel between the routers to
   support packet forwarding for PCoA.  The tunnel itself is established
   as a response to the FBU message.  The PAR sends HI message with Code
   = 0 when it receives FBU with source IP address set to PCoA.  The PAR
   sends HI with Code = 1 when it receives FBU with source IP address
   not set to PCoA (i.e., when received from NAR).  This allows NAR to
   disambiguate HI message processing sent as a response to predictive
   and reactive modes of operation.  If NAR receives a HI message with
   Code = 1, and it has already set up a host route entry and a reverse
   tunnel for PCoA, it should silently discard the HI message.

   The protocol provides an option for NAR to return NCoA for use by the
   mobile node.  When NAR can provide an NCoA for exclusive use of the
   mobile node, the address is supplied in the HAck message.  The PAR
   includes this NCoA in FBack.  Exactly how NAR manages the address
   pool from which it supplies NCoA is not specified in this document.
   Nevertheless, the MN should be prepared to use this address instead
   of performing DHCP or similar operations to obtain an IPv4 address.

   Even though the mobile node can obtain this NCoA from the NAR, it is



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   unaware of the address at the time it sends an FBU.  Hence, it binds
   PCoA to NAR's IP address as before.


5.  Using Previous FA Notification Extension

   Sending FBU from the new link (i.e., reactive mode) is similar to
   using the extension defined in [draft-mip4-ro].  However, with the
   neighborhood information gathered using the proxy router messages
   (see Section Section 6.3, Section Section 6.4), movement detection
   and router discovery delays are avoided even in the reactive case.
   The FBU and FBAck messages defined in this document can be naturally
   used even when no neighborhood information is available.


6.  Message Formats

6.1.  Fast Binding Update (FBU)

   The FBU format is bitwise identical to the Registration Request
   format in [rfc3344].  The same destination port number, 434, is used,
   but the FBU and FBAck messages in this specification have new message
   type numbers.


       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      |x|x|D|M|G|r|T|x| reserved  |     Lifetime      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Home Address                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Home Agent                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Care-of Address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                         Identification                        +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Extensions ...
      +-+-+-+-+-+-+-+-


                Figure 3: Fast Binding Update (FBU) Message






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      Source address: The interface address from which the message is
      sent.  Either PCoA (co-located or Home Address), or NAR's IP
      address (when forwarded from NAR to PAR).

      Destination Address: The IP address of the Previous Access Router
      or the New Access Router.

      Source Port: variable

      Destination port: 434


         Type: To be assigned by IANA

         Flags: See [rfc3344].  The 'S' and 'B' flags in [rfc3344] are
         sent as zero, and ignored on reception.

         reserved: Sent as zero, ignored on input

         Lifetime: The number of seconds remaining before binding
         expires.  MUST NOT exceed 10 seconds.

         Home Address: MUST be PCoA, which can either be the co-located
         CoA or the Home Address

         Home Agent: The Previous Access Router's global IP address

         Care-of Address: The New Access Router's global IP address

         Identification: a 64-bit number used for matching an FBU with
         FBack.  Identical to usage in [rfc3344]

         Extensions: MUST contain the MN - PAR Authentication Extension


6.2.  Fast Binding Acknowledgment (FBAck)

   The FBAck format is bitwise identical to the Registration Reply
   format in [rfc3344].












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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      |     Code      | reserved  |     Lifetime      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Home Address                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Home Agent                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                         Identification                        +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Extensions ...
      +-+-+-+-+-+-+-+-



          Figure 4: Fast Binding Acknowledgement (FBAck) Message

      Source address: Typically copied from the destination address of
      the FBU message

      Destination Address: Copied from the Source IP address in FBU
      message

      Source Port: variable

      Destination port: copied from the source port in FBU message


         Type: To be assigned by IANA

         Code: Indicates the result of processing FBU message.  Code = 0
         means Fast Binding Update accepted.  Code = 1 means Fast
         Binding Update accepted but NCoA is supplied as an extension.

         reserved: Sent as zero, ignored on input

         Lifetime: The granted number of seconds remaining before
         binding expires.

         Home Address: PCoA (i.e., either co-located CoA or Home
         Address)

         Home Agent: The Previous Access Router's global IP address





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         Identification: a 64-bit number used for matching FBU.  Copied
         from the field in FBU for which this FBack is a reply.

         Extensions: The PAR - MN Authentication extension MUST be
         present.  In addition, an NCoA option MUST be present when NAR
         supplies the NCoA.


   If the FBAck message indicates that the new care-of address is a
   Foreign Agent care-of address [rfc3344], then the mobile node MUST
   set the 'D' bit in its Registration Request message that it uses to
   register the NCoA with its home agent.

6.3.  Router Solicitation for Proxy Advertisement (RtSolPr)

   Mobile Nodes send Router Solicitation for Proxy Advertisement in
   order to prompt routers for Proxy Router Advertisements.  All the
   link-layer address options have the format defined in Section 7.1.
   The message format and processing rules are identical to those
   defined in [rfc4068].


      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      |     Code      |          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Subtype     |   Reserved    |          Identifier           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-


      Figure 5: Router Solicitation for Proxy Advertisement (RtSolPr)
                                  Message

      IP Fields:

         Source Address: An IP address assigned to the sending interface

         Destination Address: The address of the Access Router or the
         all routers multicast address.

         Time-to-Live: At least 1.  See [rfc1256].






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      ICMP Fields:

         Type: To be assigned by IANA

         Code: 0

         Checksum: The 16-bit one's complement of the one's complement
         sum of the ICMP message, start ing with the ICMP Type.  For
         computing the checksum, the Checksum and the Reserved fields
         are set to 0.  See [rfc1256].

         Subtype: To be assigned by IANA

         Reserved: MUST be set to zero by the sender and ignored by the
         receiver.

         Identifier: MUST be set by the sender so that replies can be
         matched to this Solicitation.

      Valid Options:

         New Access Point Link-layer Address: The link-layer address or
         identification of the access point for which the MN requests
         routing advertisement information.  It MUST be included in all
         RtSolPr messages.  More than one such address or identifier can
         be present.  This field can also be a wildcard address (see
         Section 7.1).


6.4.  Proxy Router Advertisement (PrRtAdv)

   Access routers send out Proxy Router Advertisement message
   gratuitously if the handover is network-initiated or as a response to
   RtSolPr message from a mobile node, providing the link-layer address,
   IP address and subnet prefixes of neighboring routers.  All the link-
   layer address options have the format defined in Section 7.1.

   The message format and processing rules are identical to those
   defined in [rfc4068].












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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      |     Code      |          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Subtype     |   Reserved    |          Identifier           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-


          Figure 6: Proxy Router Advertisement (PrRtAdv) Message

      IP Fields:

         Source Address: An IP address assigned to the sending interface

         Destination Address: The Source Address of an invoking Router
         Solicitation for Proxy Advertisement or the address of the node
         the Access Router is instructing to handover.

         Time-to-Live At least 1.  See [rfc1256].

      ICMP Fields:

         Type: To be assigned by IANA

         Code 0, 1, 2, 3 or 4.  See below.

         Checksum: The 16-bit one's complement of the one's complement
         sum of the ICMP message, start- ing with the ICMP Type.  For
         computing the checksum, the Checksum and the Reserved fields
         are set to 0.  See [rfc1256].

         Subtype: To be assigned by IANA.

         Reserved: MUST be set to zero by the sender and ignored by the
         receiver.

         Identifier: Copied from Router Solicitation for Proxy
         Advertisement or set to Zero if unsolicited.

      Valid Options in the following order:

         New Access Point Link-layer Address: The link-layer address or
         identification of the access point is copied from RtSolPr
         message.  This option MUST be present.




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         New Router's Link-layer Address: The link-layer address of the
         Access Router for which this message is proxied for.  This
         option MUST be included when Code is 0 or 1.

         New Router's IP Address: The IP address of NAR.  This option
         MUST be included when Code is 0 or 1.

         New Router Prefix Information Option: The number of leading
         bits that define the network number of the corresponding
         Router's IP Address option (see above).

         New CoA Option: MAY be present when PrRtAdv is sent
         unsolicited.  PAR MAY compute new CoA using NAR's prefix
         information and the MN's L2 address, or by any other means.  In
         any case, the MN should be prepared to use this address instead
         of performing DHCP or similar operations to obtain an IPv4
         address.


   A PrRtAdv with Code 0 means that the MN should use the [AP-ID, AR-
   Info] tuple present in the options above.  In this case, the Option-
   Code field (see Section 7.1) in the New AP LLA option is 1,
   reflecting the LLA of the access point for which the rest of the
   options are related, and the Option-Code for the New Router's LLA
   option is 3.  Multiple tuples may be present.

   A PrRtAdv with Code 1 means that the message is sent unsolicited.  If
   a New IPv4 option (see Figure 10) is present following the New Router
   Prefix Information option (see Section 7.3), the MN SHOULD use the
   supplied NCoA and send the FBU immediately or else stand to lose
   service.  This message acts as a network-initiated handover trigger.
   The Option-Code field (see Section 7.1) in the New AP LLA option in
   this case is 1 reflecting the LLA of the access point for which the
   rest of the options are related.

   A Proxy Router Advertisement with Code 2 means that no new router
   information is present.  The LLA option contains an Option-Code value
   that indicates a specific reason (see Section 7.1).

   A Proxy Router Advertisement with Code 3 means that new router
   information is only present for a subset of access points requested.
   The Option-Code values in the LLA option distinguish different
   outcomes (see Section 7.1).

   A Proxy Router Advertisement with Code 4 means that the subnet
   information regarding neighboring access points is sent unsolicited,
   but the message is not a handover trigger, unlike when the message is



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   sent with Code 1.  Multiple tuples may be present.

   When a wildcard AP identifier is supplied in the RtSolPr message, the
   PrRtAdv message should include any 'n' [Access Point Identifier,
   Link-Layer Address option, Prefix Information Option] tuples
   corresponding to the PAR's neighborhood.

6.5.  Inter-Access Router Messages

6.5.1.  Handover Initiate (HI)

   The Handover Initiate (HI) is an ICMP message sent by an Access
   Router (typically PAR) to another Access Router (typically NAR) to
   initiate the process of a mobile node's handover.

   The message format and processing rules are identical to those
   defined in [rfc4068].


      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      |     Code      |          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Subtype     |S|U| Reserved  |          Identifier           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-


                 Figure 7:  Handover Initiate (HI) Message

      IP Fields:

         Source Address: The IP address of the PAR

         Destination Address: The IP address of the NAR

         Time-to-Live: At least 1.  See [rfc1256].

      ICMP Fields:

         Type: To be assigned by IANA

         Code: 0 or 1.  See below






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         Checksum: The 16-bit one's complement of the one's complement
         sum of the ICMP message, start- ing with the ICMP Type.  For
         computing the checksum, the Checksum and the Reserved fields
         are set to 0.  See [rfc1256].

         Subtype: To be assigned by IANA

         S: Assigned address configuration flag.  When set, this message
         requests a new CoA to be returned by the destination.  May be
         set when Code = 0.  MUST be 0 when Code = 1.

         U: Buffer flag.  When set, the destination SHOULD buffer any
         packets towards the node indicated in the options of this
         message.  Used when Code = 0, SHOULD be set to 0 when Code = 1.

         Reserved: MUST be set to zero by the sender and ignored by the
         receiver.

         Identifier: MUST be set by the sender so replies can be matched
         to this message.

      Valid Options:

         Link-layer address of MN: The link-layer address of the MN that
         is undergoing handover to the destination (i.e., NAR).  This
         option MUST be included so that the destination can recognize
         the MN.

         Previous Care of Address: The IP address used by the MN while
         attached to the originating router.  This option MUST be
         included so that a host route can be established on the NAR.

         New Care of Address: This option MAY be present when the MN
         wishes to use a new IP address when connected to the
         destination.  When the 'S' bit is set, NAR MAY provide this
         address in HAck, in which case t he MN should be prepared to
         use this address instead of performing DHCP or similar
         operations to obtain an IPv4 address.


6.5.2.  Handover Acknowledge (HAck)

   The Handover Acknowledgment message is a new ICMP message that MUST
   be sent (typically by NAR to PAR) as a reply to the Handover Initiate
   (HI) (see Section Section 6.5.1) message.

   The message format and processing rules are identical to those
   defined in [rfc4068].



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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      |     Code      |          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Subtype     |    Reserved   |          Identifier           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-


              Figure 8:  Handover Acknowledge (HAck) Message

      IP Fields:

         Source Address: Copied from the destination address of the
         Handover Initiate Message to which this message is a response.

         Destination Address: Copied from the source address of the
         Handover Initiate Message to which this message is a response.

         Time-to-Live: At least 1.  See [rfc1256].

      ICMP Fields:

         Type: To be assigned by IANA

         Code:

            0: Handover Accepted
            1: Handover Accepted, NCoA not valid
            2: Handover Accepted, NCoA in use
            3: Handover Accepted, NCoA assigned (used in Assigned
               addressing)
            4: Handover Accepted, NCoA not assigned
            128: Handover Not Accepted, reason unspecified
            129: Administratively prohibited
            130: Insufficient resources

         Checksum: The 16-bit one's complement of the one's complement
         sum of the ICMP message, start- ing with the ICMP Type.  For
         computing the checksum, the Checksum and the Reserved fields
         are set to 0.  See [rfc1256].

         Subtype: To be assigned by IANA.






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         Reserved: MUST be set to zero by the sender and ignored by the
         receiver.

         Identifier: Copied from the corresponding field in the Handover
         Initiate message this message is in response to.

      Valid Options:

         New Care of Address: If the 'S' flag in the HI message is set,
         this option MUST be used to provide NCoA the MN should use when
         connected to this router.  This option MAY be included even
         when 'S' bit is not set, e.g., Code 2 above.  The MN should be
         prepared to use this address instead of performing DHCP or
         similar operations to obtain an IPv4 address.


   The Code 0 is the expected average case of a handover being accepted
   and the routing support provided for the use of PCoA.  The rest of
   the Code values pertain to the use of NCoA (which is common in
   [rfc4068]).  Code values 1 and 2 are for cases when the MN proposes
   an NCoA and the NAR provides a response.  Code 3 is when the NAR
   provides NCoA (which could be the same as that proposed by the MN).
   Code 4 is when the NAR does not provide NCoA, but instead provides
   routing support for PCoA.


7.  Option Formats

   The options in this section are specified as extensions for the HI
   and HAck messages, as well as for the PrRtSol and PrRtAdv messages.

7.1.  Link-Layer Address Option Format


      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     |  Option-Code  |     LLA ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                Figure 9: Link Layer Address Option Format

      Fields:

         Type: To be assigned by IANA





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         Option-Code:

            0: wildcard requesting resolution for all nearby access
               points
            1: Link-Layer Address of the New Access Point
            2: Link-Layer Address of the MN
            3: Link-Layer Address of the NAR
            4: Link-Layer Address of the source of the RtSolPr or
               PrRtAdv message
            5: The access point identified by the LLA belongs to the
               current interface of the router
            6: No prefix information available for the access point
               identified by the LLA
            7: No fast handovers support available for the access point
               identified by the LLA

         Length: The length of the option (including the Type, Length
         and Option-Code fields) in units of 8 octets.

         Link-Layer Address: The variable length link-layer address.
         The content and format of this field (including byte and bit
         ordering) depends on the specific link-layer in use.


   Depending on the size of the individual LLA option, appropriate
   padding MUST be used to ensure that the entire option size is a
   multiple of 8 octets.

7.2.  New IPv4 Address Option Format

   This option is used to provide the new router's IPv4 address or the
   NCoA in PrRtAdv, as well as PCoA and NCoA in HI and HAck messages.


      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |    Length     |  Option-Code  |    Reserved   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      New IPv4 Address                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                 Figure 10: New IPv4 Address Option Format






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      Fields:

         Type: To be assigned by IANA

         Length: The length of the option (including the Type, Length
         and Option-Code fields) in units of 8 octets.

         Option-Code:

            1: Previous CoA
            2: New CoA
            3: NAR's IP Address

         Reserved: Set to zero.

         New IPv4 Address: NAR's IPv4 address or the NCoA assigned by
         NAR.


7.3.  New Router Prefix Information Option

   This option is used in the PrRtAdv 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |    Length     |  Option-Code  | Prefix-Length |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Reserved                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



          Figure 11: New Router Prefix Information Option Format

      Fields:

         Type: To be assigned by IANA

         Length: The length of the option (including the Type, Length
         and Option-Code fields) in units of 8 octets.

         Option-Code: 0

         Prefix-Length The number of leading bits that define the
         network number of the corresponding Router's IP Address option.




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         Reserved: Set to zero.



8.  Security Considerations

   As outlined in [rfc4068], the following vulnerabilities are
   identified and the solutions mentioned.

   Insecure FBU:

   Failure to protect the FBU message could result in packets meant for
   an address being stolen or redirected to some unsuspecting node.
   This concern is similar to that in Mobile Node and Home Agent
   relationship.

   Hence, the FBU and FBack messages MUST be protected using a security
   association shared between a mobile node and its access router.  In
   particular, the MN - PAR Authentication Extension MUST be present in
   each of these messages.  This document does not specify how the
   security association is established between a MN and the AR/FA.

   Secure FBU, malicious or inadvertent redirection:

   Even if the MN - PAR authentication extension is present in an FBU, a
   MN may indevertently or maliciously attempt to bind its PCoA to an
   unintended address on NAR's link, and cause traffic flooding to an
   unsuspecting node.

   This vulnerability is avoided by always binding the PCoA to the NAR's
   IP address, even when the NAR supplies an NCoA to use for the MN.  It
   is still possible to jam NAR's buffer with redirected traffic.
   However, the handover state corresponding to the MN's PCoA has a
   finite lifetime, and can be configured to be a few multiples of the
   anticipated handover latency.  Hence, the extent of this
   vulnerability is small.

   Communication between the access routers:

   The access routers communicate using HI and HAck messages in order to
   establish a temporary routing path for the MN undergoing handover.
   This message exchange needs to be secured to ensure routing updates
   take place as intended.

   The HI and HAck messages need to be secured using a pre-existing
   security association between the access routers to ensure at least
   message integrity and authentication, and should also include



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   encryption.


9.  IANA Considerations

   All the messages and the option formats specified in this document
   require Type assignment from IANA.  Specifically, the Types, Sub-
   types and the Codes need assignment from ICMP, Mobile IP and
   Experimental Mobility Type [rfc4065] registries.


10.  Acknowledgement

   Thanks to all those who expressed interest in having a Fast Handovers
   for Mobile IPv4 protocol along the lines of [rfc4068].  Thanks to
   Vijay Devarapalli, Keng Leung for their review and input.  Kumar
   Viswanath and Uday Mohan implemented an early version of this
   protocol.  Many thanks to Alex Petrescu for his thorough review that
   improved this document.


11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [rfc1256]  Deering, S., "ICMP Router Discovery Messages", RFC 1256,
              September 1991.

   [rfc3344]  Perkins (Editor), C., "IP Mobility Support for IPv4",
              RFC 3344, August 2002.

   [rfc4065]  Kempf, J., "Instructions for Seamoby and Experimental
              Mobility Protocol IANA Allocations", RFC 4065, July 2005.

   [rfc4068]  Koodli (Editor), R., "Fast Handovers for Mobile IPv6",
              RFC 4068, July 2005.

11.2.  Informative References

   [draft-mip4-ro]
              Perkins, C. and D. Johnson, "Route Optimization in Mobile
              IP (work in progress).   Internet Draft, Internet
              Engineering Task Force", February 2000.

   [ieee-802.11r]



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              "IEEE Standard forLocal and Metropolitan Area Networks:
              Fast Roaming/Fast BSS Transition, the IEEE Task Group TGr.
              Technical report, IEEE.".

   [ieee-802.1x]
              "IEEE Standard for Local and Metropolitan Area Networks:
              Port-Based Network Access Control. Technical report,
              IEEE.".

   [ieee-802.21]
              "The IEEE 802.21 group. http://www.ieee802.org/21.".

   [rfc2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.


Appendix A.  Change Log

   Addressed the following Last Call and subsequent reviews:

      Provided all the Code values in PrRtAdv message to cover various
      cases involving neighborhood discovery.  Harmonized the option
      formats with [rfc4068].

      Added the Terminology Section

      Added text regarding FBU message flags 'S' and 'B'

      Revised text in Security Considerations

      Clarified text in different places based on ML comments (including
      "forwarding", MN's use of assigned addresses in lieu of DHCP, and
      so on.)

      Clarified using ICMPv4 checksum for RtSolPr, PrRtAdv, HI and HAck

      Added Figures illustrating predictive and reactive handovers

      Added references to IEEE 802.21 and IEEE 802.11r

      All id nits (attempt to move from LaTex to xml turned out to be
      quite a task, sigh..)









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Authors' Addresses

   Rajeev Koodli
   Nokia Research Center
   975 Page Mill Road, 200
   Palo Alto, CA  94304
   USA

   Email: rajeev.koodli@nokia.com


   Charles Perkins
   Nokia Research Center
   975 Page Mill Road, 200
   Palo Alto, CA  94304
   USA

   Email: charles.perkins@nokia.com

































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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
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Acknowledgment

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





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