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rfc:rfc4068

Network Working Group R. Koodli, Ed. Request for Comments: 4068 Nokia Research Center Category: Experimental July 2005

                   Fast Handovers for Mobile IPv6

Status of This Memo

 This memo defines an Experimental Protocol for the Internet
 community.  It does not specify an Internet standard of any kind.
 Discussion and suggestions for improvement are requested.
 Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2005).

Abstract

 Mobile IPv6 enables a Mobile Node to maintain its connectivity to the
 Internet when moving from one Access Router to another, a process
 referred to as handover.  During handover, there is a period during
 which the Mobile Node is unable to send or receive packets because of
 link switching delay and IP protocol operations.  This "handover
 latency" resulting from standard Mobile IPv6 procedures, namely
 movement detection, new Care of Address configuration, and Binding
 Update, is often unacceptable to real-time traffic such as Voice over
 IP.  Reducing the handover latency could be beneficial to non-real-
 time, throughput-sensitive applications as well.  This document
 specifies a protocol to improve handover latency due to Mobile IPv6
 procedures.  This document does not address improving the link
 switching latency.

Koodli, Ed. Experimental [Page 1] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
 2.  Terminology. . . . . . . . . . . . . . . . . . . . . . . . . .  3
 3.  Protocol Overview. . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Addressing the Handover Latency. . . . . . . . . . . . .  5
     3.2.  Protocol Operation . . . . . . . . . . . . . . . . . . .  7
     3.3.  Protocol Operation of Network-initiated Handover . . . .  9
 4.  Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 10
 5.  Miscellaneous. . . . . . . . . . . . . . . . . . . . . . . . . 15
     5.1.  Handover Capability Exchange . . . . . . . . . . . . . . 15
     5.2.  Determining New Care of Address. . . . . . . . . . . . . 15
     5.3.  Packet Loss. . . . . . . . . . . . . . . . . . . . . . . 15
     5.4.  DAD Handling . . . . . . . . . . . . . . . . . . . . . . 16
     5.5.  Fast or Erroneous Movement . . . . . . . . . . . . . . . 16
 6.  Message Formats. . . . . . . . . . . . . . . . . . . . . . . . 17
     6.1.  New Neighborhood Discovery Messages. . . . . . . . . . . 17
           6.1.1. Router Solicitation for Proxy Advertisement
                  (RtSolPr) . . . . . . . . . . . . . . . . . . . . 17
           6.1.2. Proxy Router Advertisement (PrRtAdv). . . . . . . 20
     6.2.  Inter-Access Router Messages . . . . . . . . . . . . . . 23
           6.2.1. Handover Initiate (HI). . . . . . . . . . . . . . 23
           6.2.2. Handover Acknowledge (HAck) . . . . . . . . . . . 25
     6.3.  New Mobility Header Messages . . . . . . . . . . . . . . 27
           6.3.1. Fast Binding Update (FBU) . . . . . . . . . . . . 27
           6.3.2. Fast Binding Acknowledgment (FBack) . . . . . . . 28
           6.3.3. Fast Neighbor Advertisement (FNA) . . . . . . . . 30
     6.4.  New Options. . . . . . . . . . . . . . . . . . . . . . . 31
           6.4.1. IP Address Option . . . . . . . . . . . . . . . . 32
           6.4.2. New Router Prefix Information Option. . . . . . . 33
           6.4.3. Link-Layer Address (LLA) Option . . . . . . . . . 34
           6.4.4. Mobility Header Link-Layer Address (MH-LLA)
                  Option. . . . . . . . . . . . . . . . . . . . . . 35
           6.4.5. Neighbor Advertisement Acknowledgment (NAACK) . . 35
 7.  Configurable Parameters. . . . . . . . . . . . . . . . . . . . 36
 8.  Security Considerations. . . . . . . . . . . . . . . . . . . . 37
 9.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 38
 10. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 39
 11. Normative References . . . . . . . . . . . . . . . . . . . . . 39
 12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 39

Koodli, Ed. Experimental [Page 2] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

1. Introduction

 Mobile IPv6 [3] describes the protocol operations for a mobile node
 to maintain connectivity to the Internet during its handover from one
 access router to another.  These operations involve movement
 detection, IP address configuration, and location update.  The
 combined handover latency is often sufficient to affect real-time
 applications.  Throughput-sensitive applications can also benefit
 from reducing this latency.  This document describes a protocol to
 reduce the handover latency.
 This specification addresses the following problem: how to allow a
 mobile node to send packets as soon as it detects a new subnet link,
 and how to deliver packets to a mobile node as soon as its attachment
 is detected by the new access router.  The protocol defines IP
 protocol messages necessary for its operation regardless of link
 technology.  It does this without depending on specific link-layer
 features while allowing link-specific customizations.  By definition,
 this specification considers handovers that interwork with Mobile IP:
 once attached to its new access router, an MN engages in Mobile IP
 operations including Return Routability [3].  There are no special
 requirements for a mobile node to behave differently with respect to
 its standard Mobile IP operations.

2. Terminology

 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 [1].  The use
 of the term, "silently ignore" is not defined in RFC 2119.  However,
 the term is used in this document and can be similarly construed.
 The following terminology and abbreviations are used in this
 document.  The reference handover scenario is illustrated in
 Figure 1.
    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.

Koodli, Ed. Experimental [Page 3] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

    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.
    Router Solicitation for Proxy Advertisement (RtSolPr)
          A message from the MN to the PAR requesting information for
          a potential handover.
    Proxy Router Advertisement (PrRtAdv)
          A message from the PAR to the MN that provides information
          about neighboring links facilitating expedited movement
          detection.  The message also acts as a trigger for network-
          initiated handover.
    (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".
    Assigned Addressing
          A particular type of NCoA configuration in which the NAR
          assigns an IPv6 address for the MN.  The method by which NAR
          manages its address pool is not specified in this document.
    Fast Binding Update (FBU)
          A message from the MN instructing its PAR to redirect its
          traffic (toward NAR).
    Fast Binding Acknowledgment (FBack)
          A message from the PAR in response to an FBU.

Koodli, Ed. Experimental [Page 4] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

    Fast Neighbor Advertisement (FNA)
          A message from the MN to the NAR to announce attachment, and
          to confirm the use of NCoA when the MN has not received an
          FBACK.
    Handover Initiate (HI)
          A message from the PAR to the NAR regarding an MN's
          handover.
    Handover Acknowledge (HAck)
          A message from the NAR to the PAR as a response to HI.
           v            +------------+
         +-+            |  Previous  |        <
         | | ---------- |   Access   | ------ > ----\
         +-+            |   Router   |        <      \
             MN         |   (PAR)    |                \
          |             +------------+            +---------------+
          |                   ^            IP     | Correspondent |
          |                   |         Network   |  Node         |
          V                   |                   +---------------+
                              v                        /
           v            +------------+                /
         +-+            |    New     |        <      /
         | | ---------- |   Access   | ------ > ----/
         +-+            |   Router   |        <
            MN          |   (NAR)    |
                        +------------+
             Figure 1: Reference Scenario for Handover

3. Protocol Overview

3.1. Addressing the Handover Latency

 The ability to immediately send packets from a new subnet link
 depends on the "IP connectivity" latency, which in turn depends on
 the movement detection latency and new CoA configuration latency.
 Once an MN is IP-capable on the new subnet link, it can send a
 Binding Update to its Home Agent and one or more correspondents.
 Once its correspondents successfully process the Binding Update,
 which typically involves the Return Routability procedure, the MN can
 receive packets at the new CoA.  So, the ability to receive packets
 from correspondents directly at its new CoA depends on the Binding
 Update latency as well as the IP connectivity latency.

Koodli, Ed. Experimental [Page 5] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 The protocol enables an MN to quickly detect that it has moved to a
 new subnet by providing the new access point and the associated
 subnet prefix information when the MN is still connected to its
 current subnet (i.e., PAR in Figure 1).  For instance, an MN may
 discover available access points using link-layer specific mechanisms
 (i.e., a "scan" in WLAN) and then request subnet information
 corresponding to one or more of those discovered access points.  The
 MN may do this after performing router discovery or at any time while
 connected to its current router.  The result of resolving an
 identifier associated with an access point is a [AP-ID, AR-Info]
 tuple, which an MN can use in readily detecting movement:  when
 attachment to an access point with AP-ID takes place, the MN knows
 the corresponding new router's coordinates including its prefix, IP
 address, and L2 address.  The "Router Solicitation for Proxy
 Advertisement (RtSolPr)" and "Proxy Router Advertisement (PrRtAdv)"
 messages (see Section 6.1) are used for aiding movement detection.
 Through the RtSolPr and PrRtAdv messages, the MN also formulates a
 prospective new CoA (NCoA) when it is still present on the PAR's
 link.  Hence, the latency due to new prefix discovery subsequent to
 handover is eliminated.  Furthermore, this prospective address can be
 used immediately after attaching to the new subnet link (i.e., NAR's
 link) when the MN has received a "Fast Binding Acknowledgment
 (FBack)" message prior to its movement.  If it moves without
 receiving an FBack, the MN can still start using NCoA after
 announcing its attachment through a "Fast Neighbor Advertisement
 (FNA)" message.  NAR responds to FNA if the tentative address is
 already in use thereby reducing NCoA configuration latency.  Under
 some limited conditions in which the probability of address collision
 is considered insignificant, it may be possible to use NCoA
 immediately after attaching to the new link.  Even so, all
 implementations MUST support and SHOULD use the mechanism specified
 in this document to avoid potential address conflicts.
 To reduce the Binding Update latency, the protocol specifies a tunnel
 between the Previous CoA (PCoA) and the NCoA.  An MN sends a "Fast
 Binding Update" message to its Previous Access Router to establish
 this tunnel.  When feasible, the MN SHOULD send an FBU from PAR's
 link.  Otherwise, it should be sent immediately after attachment to
 NAR has been detected.  Subsequent sections describe the protocol
 mechanics.  As a result, PAR begins tunneling packets arriving for
 PCoA to NCoA.  Such a tunnel remains active until the MN completes
 the Binding Update with its correspondents.  In the opposite
 direction, the MN SHOULD reverse tunnel packets to PAR until it
 completes the Binding Update.  PAR SHOULD forward the inner packet in
 the tunnel to its destination (i.e., to the MN's correspondent).
 Such a reverse tunnel ensures that packets containing PCoA as a
 source IP address are not dropped due to ingress filtering.  Readers

Koodli, Ed. Experimental [Page 6] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 may observe that even though the MN is IP-capable on the new link, it
 cannot use NCoA directly with its correspondents without the
 correspondents first establishing a binding cache entry (for NCoA).
 Forwarding support for PCoA is provided through a reverse tunnel
 between the MN and the PAR.
 Setting up a tunnel alone does not ensure that the MN receives
 packets as soon as it is attached to a new subnet link, unless the
 NAR can detect the MN's presence.  A neighbor discovery operation
 involving a neighbor's address resolution (i.e., Neighbor
 Solicitation and Neighbor Advertisement) typically results in
 considerable delay, sometimes lasting multiple seconds.  For
 instance, when arriving packets trigger NAR to send Neighbor
 Solicitation before the MN attaches, subsequent retransmissions of
 address resolution are separated by a default period of one second
 each.  To circumvent this delay, an MN announces its attachment
 through the FNA message that allows the NAR to consider MN to be
 reachable.  If there is no existing entry, FNA allows NAR to create
 one.  If NAR already has an entry, FNA updates the entry while taking
 potential address conflicts into consideration.  Through tunnel
 establishment for PCoA and fast advertisement, the protocol provides
 expedited forwarding of packets to the MN.
 The protocol also provides the following important functionalities.
 The access routers can exchange messages to confirm that a proposed
 NCoA is acceptable.  For instance, when an MN sends an FBU from PAR's
 link, FBack can be delivered after the NAR considers the NCoA
 acceptable for use.  This is especially useful when addresses are
 assigned by the access router.  The NAR can also rely on its trust
 relationship with PAR before providing forwarding support for the MN.
 That is, it may create a forwarding entry for the NCoA subject to
 "approval" from PAR which it trusts.  Finally, the access routers
 could transfer network-resident contexts, such as access control,
 QoS, and header compression, in conjunction with handover.  For these
 operations, the protocol provides "Handover Initiate (HI)" and
 "Handover Acknowledge (HAck)" messages.  Both of these messages MUST
 be supported and SHOULD be used.  The access routers MUST have
 necessary security association established by means outside the scope
 of this document.

3.2. Protocol Operation

 The protocol begins when an MN sends an RtSolPr to its access router
 to resolve one or more Access Point Identifiers to subnet-specific
 information.  In response, the access router (e.g., PAR in Figure 1)
 sends a PrRtAdv message containing one or more [AP-ID, AR-Info]
 tuples.  The MN may send a RtSolPr at any convenient time, for
 instance as a response to some link-specific event (a "trigger") or

Koodli, Ed. Experimental [Page 7] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 simply after performing router discovery.  However, the expectation
 is that prior to sending RtSolPr, the MN will have discovered the
 available APs by link-specific methods.  The RtSolPr and PrRtAdv
 messages do not establish any state at the access router; their
 packet formats are defined in Section 6.1.
 With the information provided in the PrRtAdv message, the MN
 formulates a prospective NCoA and sends an FBU message when a link-
 specific handover event occurs.  The purpose of the FBU is to
 authorize PAR to bind PCoA to NCoA, so that arriving packets can be
 tunneled to the new location of the MN.  Whenever feasible, the FBU
 SHOULD be sent from PAR's link.  For instance, an internal link-
 specific trigger could enable FBU transmission from the previous
 link.  When it is not feasible, the FBU is sent from the new link.
 Care must be taken to ensure that the NCoA used in FBU does not
 conflict with an address already in use by some other node on the
 link.  For this, FBU encapsulation within FNA MUST be implemented and
 SHOULD be used (see below) when the FBU is sent from NAR's link.
 The format and semantics of FBU processing are specified in Section
 6.3.1.
 Depending on whether an FBack is received on the previous link (which
 clearly depends on whether the FBU was sent in the first place),
 there are two modes of operation.
 1. The MN receives an FBack on the previous link.  This means that
    packet tunneling is already in progress by the time the MN
    handovers to NAR.  The MN SHOULD send FNA immediately after
    attaching to NAR, so that arriving and buffered packets can be
    forwarded to the MN right away.
    Before sending an FBack to an MN, PAR can determine whether the
    NCoA is acceptable to the NAR through the exchange of HI and HAck
    messages.  When assigned addressing (i.e., addresses are assigned
    by the router) is used, the proposed NCoA in the FBU is carried in
    HI, and the NAR MAY assign the proposed NCoA.  Such an assigned
    NCoA MUST be returned in HAck, and the PAR MUST in turn provide
    the assigned NCoA in the FBack.  If there is an assigned NCoA
    returned in the FBack, the MN MUST use the assigned address (and
    not the proposed address in the FBU) upon attaching to NAR.
 2. The MN does not receive the FBack on the previous link because the
    MN has not sent the FBU or the MN has left the link after sending
    the FBU (which itself may be lost), but before receiving an FBack.
    Without receiving an FBack in the latter case, the MN cannot
    ascertain whether PAR has successfully processed the FBU.  Hence,
    it (re)sends an FBU as soon as it attaches to NAR.  To enable NAR

Koodli, Ed. Experimental [Page 8] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

    to forward packets immediately (when FBU has been processed) and
    to allow NAR to verify whether NCoA is acceptable, the MN SHOULD
    encapsulate the FBU in the FNA.  If NAR detects that NCoA is in
    use when processing the FNA, for instance while creating a
    neighbor entry, it MUST discard the inner FBU packet and send a
    Router Advertisement with the "Neighbor Advertisement Acknowledge
    (NAACK)" option in which NAR MAY include an alternate IP address
    for the MN to use.  This discarding avoids the rare and
    undesirable outcome that results from address collision.  Detailed
    FNA processing rules are specified in Section 6.3.3.
 The scenario in which an MN sends an FBU and receives an FBack on
 PAR's link is illustrated in Figure 2.  For convenience, this
 scenario is characterized as "predictive" mode of operation.  The
 scenario in which the MN sends an FBU from NAR's link is illustrated
 in Figure 3.  For convenience, this scenario is characterized as a
 "reactive" mode of operation.  Note that the reactive mode also
 includes the case in which an FBU has been sent from PAR's link but
 an FBack has not been received yet.
 Finally, the PrRtAdv message may be sent unsolicited (i.e., without
 the MN first sending a RtSolPr).  This mode is described in Section
 3.3.

3.3. Protocol Operation of Network-initiated Handover

 In some wireless technologies, the handover control may reside in the
 network even though the decision to undergo handover may be mutually
 arrived at between the MN and the network.  In these networks, the
 PAR can send an unsolicited PrRtAdv containing the link layer
 address, IP address, and subnet prefixes of the NAR when the network
 decides that a handover is imminent.  The MN MUST process this
 PrRtAdv to configure a new care of address on the new subnet, and
 MUST send an FBU to PAR prior to switching to the new link.  After
 transmitting PrRtAdv, the PAR MUST continue to forward packets to the
 MN on its current link until the FBU is received.  The rest of the
 operation is the same as that described in Section 3.2.
 The unsolicited PrRtAdv also allows the network to inform the MN
 about geographically adjacent subnets without the MN having to
 explicitly request that information.  This can reduce the amount of
 wireless traffic required for the MN to obtain a neighborhood
 topology map of links and subnets.  Such usage of PrRtAdv is
 decoupled from the actual handover; see Section 6.1.2.

Koodli, Ed. Experimental [Page 9] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

            MN                    PAR                  NAR
             |                     |                    |
             |------RtSolPr------->|                    |
             |<-----PrRtAdv--------|                    |
             |                     |                    |
             |------FBU----------->|--------HI--------->|
             |                     |<------HAck---------|
             |          <--FBack---|--FBack--->         |
             |                     |                    |
          disconnect             forward                |
             |                   packets===============>|
             |                     |                    |
             |                     |                    |
         connect                   |                    |
             |                     |                    |
             |--------- FNA --------------------------->|
             |<=================================== deliver packets
             |                                          |
                Figure 2: "Predictive" Fast Handover

4. Protocol Details

 All descriptions refer to Figure 1.
 After discovering one or more nearby access points, the MN sends
 RtSolPr to resolve access point identifiers to subnet router
 information.  This is convenient to do after performing router
 discovery.  However, the MN can send RtSolPr at any time, e.g., when
 one or more new access points are discovered.  The MN can also send
 RtSolPr more than once during its attachment to PAR.  The trigger for
 sending RtSolPr can originate from a link-specific event, such as the
 promise of a better signal strength from another access point coupled
 with fading signal quality with the current access point.  Such
 events, often broadly referred to as "L2 triggers", are outside the
 scope of this document.  Nevertheless, they serve as events that
 invoke this protocol.  For instance, when a "link up" indication is
 obtained on the new link, protocol messages (e.g., FNA) can be
 immediately transmitted.  Implementations SHOULD make use of such
 triggers whenever possible.

Koodli, Ed. Experimental [Page 10] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

            MN                    PAR                  NAR
             |                     |                    |
             |------RtSolPr------->|                    |
             |<-----PrRtAdv--------|                    |
             |                     |                    |
          disconnect               |                    |
             |                     |                    |
             |                     |                    |
          connect                  |                    |
             |------FNA[FBU]-------|------------------->|
             |                     |<-----FBU-----------|
             |                     |------FBack-------->|
             |                   forward                |
             |                   packets===============>|
             |                     |                    |
             |<=================================== deliver packets
             |                                          |
                 Figure 3: "Reactive" Fast Handover
 The RtSolPr message contains one or more AP-IDs.  A wildcard requests
 all available tuples.
 As a response to RtSolPr, PAR sends a PrRtAdv message that indicates
 one of the following possible conditions.
 1. If the PAR does not have an entry corresponding to the new access
    point, it MUST respond indicating that the new access point is
    unknown.  The MN MUST stop fast handover protocol operations on
    the current link.  The MN MAY send an FBU from its new link.
 2. If the new access point is connected to the PAR's current
    interface (to which MN is attached), the PAR MUST respond with a
    Code value indicating that the new access point is connected to
    the current interface, but not send any prefix information.  This
    scenario could arise, for example, when several wireless access
    points are bridged into a wired network.  No further protocol
    action is necessary.
 3. If the new access point is known and the PAR has information about
    it, then PAR MUST respond indicating that the new access point is
    known and supply the [AP-ID, AR-Info] tuple.  If the new access
    point is known, but does not support fast handover, the PAR MUST
    indicate this with Code 3 (See Section 6.1.2).

Koodli, Ed. Experimental [Page 11] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 4. If a wildcard is supplied as an identifier for the new access
    point, the PAR SHOULD supply neighborhood [AP-ID, AR-Info] tuples
    that are subject to path MTU restrictions (i.e., provide any `n'
    tuples without exceeding the link MTU).
 When further protocol action is necessary, some implementations MAY
 choose to begin buffering copies of incoming packets at the PAR.  If
 such FIFO buffering is used, the PAR MUST continue forwarding the
 packets to PCoA (i.e., buffer and forward).  Such buffering can be
 useful when the MN leaves without sending the FBU message from the
 PAR's link.  The PAR SHOULD stop buffering after processing the FBU
 message.  The size of the buffer is an implementation-specific
 consideration.
 The method by which Access Routers exchange information about their
 neighbors, and thereby allow construction of Proxy Router
 Advertisements with information about neighboring subnets is outside
 the scope of this document.
 The RtSolPr and PrRtAdv messages MUST be implemented by an MN and an
 access router that supports fast handovers.  However, when the
 parameters necessary for the MN to send packets immediately upon
 attaching to the NAR are supplied by the link layer handover
 mechanism itself, use of above messages is optional on such links.
 After a PrRtAdv message is processed, the MN sends an FBU at a time
 determined by link-specific events, and includes the proposed NCoA.
 The MN SHOULD send the FBU from PAR's link whenever "anticipation" of
 handover is feasible.  When anticipation is not feasible or when it
 has not received an FBack, the MN sends an FBU immediately after
 attaching to NAR's link.  This FBU SHOULD be encapsulated in an FNA
 message.  The encapsulation allows the NAR to discard the (inner) FBU
 packet if an address conflict is detected as a result of (outer) FNA
 packet processing (see FNA processing below).  In response to the
 FBU, the PAR establishes a binding between PCoA ("Home Address") and
 NCoA, and sends the FBack to the MN.  Prior to establishing this
 binding, PAR SHOULD send an HI message to NAR, and receive HAck in
 response.  To determine the NAR's address for the HI message, the PAR
 can perform the longest prefix match of NCoA (in FBU) with the prefix
 list of neighboring access routers.  When the source IP address of
 the FBU is PCoA, i.e., the FBU is sent from the PAR's link, and the
 HI message MUST have a Code value set to 0; see Section 6.2.1.  When
 the source IP address of the FBU is not PCoA, i.e., the FBU is sent
 from the NAR's link, the HI message MUST have a Code value of 1; see
 Section 6.2.1.

Koodli, Ed. Experimental [Page 12] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 The HI message contains the PCoA, Link-Layer Address, and the NCoA of
 the MN.  In response to processing an HI message with Code 0, the NAR
 1. determines whether NCoA supplied in the HI message is a valid
    address for use.  If it is, the NAR starts proxying [6] the
    address for PROXY_ND_LIFETIME during which the MN is expected to
    connect to the NAR.  The NAR MAY use the Link-Layer Address to
    verify whether a corresponding IP address exists in its forwarding
    tables.
 2. allocates NCoA for the MN when assigned addressing is used,
    creates a proxy neighbor cache entry, and begins defending it.
    The NAR MAY allocate the NCoA proposed in HI.
 3. MAY create a host route entry for PCoA in case NCoA cannot be
    accepted or assigned.  This host route entry SHOULD be implemented
    such that until the MN's presence is detected, either through
    explicit announcement by the MN or by other means, arriving
    packets do not invoke neighbor discovery.  The NAR MAY also set up
    a reverse tunnel to the PAR in this case.
 4. provides the status of the handover request in the Handover
    Acknowledge (HAck) message.
 When the Code value in HI is 1, NAR MUST skip the above operations
 since it would have performed those operations during FNA processing.
 However, it SHOULD be prepared to process any other options that may
 be defined in the future.  Sending an HI message with Code 1 allows
 NAR to validate the neighbor cache entry it creates for the MN during
 FNA processing.  That is, NAR can make use of the knowledge that its
 trusted peer (i.e., PAR) has a trust relationship with the MN.
 If HAck contains an assigned NCoA, the FBack MUST include it, and the
 MN MUST use the address provided in the FBack.  The PAR MAY send the
 FBack to the previous link to facilitate faster reception in the
 event that the MN is still present.  The result of the FBU and FBack
 processing is that PAR begins tunneling the MN's packets to NCoA.  If
 the MN does not receive an FBack message even after retransmitting
 the FBU for FBU_RETRIES, it must assume that fast handover support is
 not available and stop the protocol operation.
 When the MN establishes link connectivity with the NAR, it SHOULD
 send a Fast Neighbor Advertisement (FNA) message (see 6.3.3).  If the
 MN has not received an FBack by the time the FNA is being sent, it
 SHOULD encapsulate the FBU in the FNA and send them together.

Koodli, Ed. Experimental [Page 13] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 When the NCoA corresponding to the FNA message is acceptable, the NAR
 MUST
 1. delete its proxy neighbor cache entry, if any is present.
 2. create a neighbor cache entry and set its state to REACHABLE
    without overwriting an existing entry for a different layer 2
    address.
 3. forward any buffered packets.
 4. enable the host route entry for PCoA, if any is present.
 When the NCoA corresponding to the FNA message is not acceptable, the
 NAR MUST
 1. discard the inner (FBU) packet.
 2. send a Router Advertisement with the NAACK option in which it MAY
    include an alternate NCoA for use.  This message MUST be sent to
    the source IP address present in the FNA using the same Layer 2
    address present in the FNA.
 If the MN receives a Router Advertisement with a NAACK option, it
 MUST use the IP address, if any, provided in the NAACK option.
 Otherwise, the MN should configure another NCoA.  Subsequently, the
 MN SHOULD send an FBU using the new CoA.  As a special case, the
 address supplied in NAACK could be PCoA itself, in which case the MN
 MUST NOT send any more FBUs.
 Once the MN has confirmed its NCoA, it SHOULD send a Neighbor
 Advertisement message.  This message allows MN's neighbors to update
 their neighbor cache entries with the MN's addresses.
 Just as in Mobile IPv6, the PAR sets the 'R' bit in the Prefix
 Information option, and includes its 128 bit global address in the
 router advertisements.  This allows the mobile nodes to learn the
 PAR's global IPv6 address.  The MN reverse tunnels its packets to the
 same global address of PAR.  The tunnel end-point addresses must be
 configured accordingly.  When PAR receives a reverse tunneled packet,
 it must verify if a secure binding exists for the MN identified by
 PCoA in the tunneled packet, before forwarding the packet.

Koodli, Ed. Experimental [Page 14] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

5. Miscellaneous

5.1. Handover Capability Exchange

 The MN expects a PrRtAdv in response to its RtSolPr message.  If the
 MN does not receive a PrRtAdv message even after RTSOLPR_RETRIES, it
 must assume that PAR does not support the fast handover protocol and
 stop sending RtSolPr messages.
 Even if an MN's current access router is capable of fast handover,
 the new access router to which the MN attaches may be incapable of
 fast handover.  This is indicated to the MN during "runtime", through
 the PrRtAdv message with a Code value of 3 (see Section 6.1.2).

5.2. Determining New Care of Address

 Typically, the MN formulates its prospective NCoA using the
 information provided in a PrRtAdv message and sends the FBU.  The PAR
 MUST use the NCoA present in the FBU in its HI message.  The NAR MUST
 verify if the NCoA present in HI is already in use.  In any case, NAR
 MUST respond to HI using a HAck, in which it may include another NCoA
 to use, especially when assigned address configuration is used.  If
 there is a CoA present in HAck, the PAR MUST include it in the FBack
 message.
 If a PrRtAdv message carries an NCoA, the MN MUST use it as its
 prospective NCoA.

5.3. Packet Loss

 Handover involves link switching, which may not be exactly
 coordinated with fast handover signaling.  Furthermore, the arrival
 pattern of packets is dependent on many factors, including
 application characteristics, network queuing behaviors, etc.  Hence,
 packets may arrive at the NAR before the MN is able to establish its
 link there.  These packets will be lost unless they are buffered by
 the NAR.  Similarly, if the MN attaches to the NAR and then sends an
 FBU message, packets arriving at the PAR will be lost unless they are
 buffered.  This protocol provides an option to indicate a request for
 buffering at the NAR in the HI message.  When the PAR requests this
 feature (for the MN), it SHOULD also provide its own support for
 buffering.

Koodli, Ed. Experimental [Page 15] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

5.4. DAD Handling

 Duplicate Address Detection (DAD) was defined in [7] to avoid address
 duplication on links when stateless address auto-configuration is
 used.  The use of DAD to verify the uniqueness of an IPv6 address
 configured through stateless auto-configuration adds delays to a
 handover.
 The probability of an interface identifier duplication on the same
 subnet is very low, however it cannot be ignored.  In this document,
 certain precautions are proposed to minimize the effects of a
 duplicate address occurrence.
 In some cases, the NAR may already have the knowledge required to
 assess whether the MN's address is a duplicate before the MN moves to
 the new subnet.  For example, the NAR can have a list of all nodes on
 its subnet, perhaps for access control, and by searching this list,
 it can confirm whether the MN's address is a duplicate.  The result
 of this search is sent back to the PAR in the HAck message.  If such
 knowledge is not available at the NAR, it may indicate this by not
 confirming the NCoA in the HAck message.  The NAR may also indicate
 this in the NAACK option in response to the FNA message.  In such
 cases, the MN would have to follow the address configuration
 procedure according to [6] after attaching to the NAR.

5.5. Fast or Erroneous Movement

 Although this specification is for fast handover, the protocol is
 limited in terms of how fast an MN can move.  Ping-Pong is a special
 case of fast movement, where an MN moves between the same two access
 points rapidly.  Another instance of the same problem is erroneous
 movement, i.e., the MN receives information prior to a handover that
 it is moving to a new access point, but it is either moved to a
 different one or it aborts movement altogether.  All of the above
 behaviors are usually the result of link layer idiosyncrasies and
 thus are often resolved at the link layer itself.
 IP layer mobility, however, introduces its own limits.  IP layer
 handovers should occur at a rate suitable for the MN to update the
 binding of, at least, its HA and preferably that of every CN with
 which it is in communication.  An MN that moves faster than necessary
 for this signaling to complete, which may be a few seconds, may start
 losing packets.  The signaling cost over the air interface and in the
 network may increase significantly, especially in the case of rapid
 movement between several access routers.  To avoid the signaling
 overhead, the following measures are suggested.

Koodli, Ed. Experimental [Page 16] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 An MN returning to the PAR before updating the necessary bindings
 when present on the NAR MUST send a Fast Binding Update with the Home
 Address equal to the MN's PCoA and a lifetime of zero to the PAR.
 The MN should have a security association with the PAR since it
 performed a fast handover to the NAR.  The PAR, upon receiving this
 Fast Binding Update, will check its set of outgoing (temporary fast
 handover) tunnels.  If it finds a match, it SHOULD tear down that
 tunnel (i.e., stop forwarding packets for this MN and start
 delivering packets directly to the node instead).  The MN SHOULD NOT
 attempt to use any of the fast handover mechanisms described in this
 specification and SHOULD revert back to standard Mobile IPv6.
 Temporary tunnels for the purpose of fast handovers should use short
 lifetimes (a small number of seconds or less).  The lifetime of such
 tunnels should be enough to allow an MN to update all its active
 bindings.  The default lifetime of the tunnel should be the same as
 the lifetime value in the FBU message.
 The effect of erroneous movement is typically limited to the loss of
 packets since routing can change and the PAR may forward packets
 toward another router before the MN actually connects to that router.
 If the MN discovers itself on an unanticipated access router, a Fast
 Binding Update to the PAR SHOULD be sent.  Since Fast Binding Updates
 are authenticated, they supercede the existing binding and packets
 MUST be redirected to the newly confirmed location of the MN.

6. Message Formats

 All the ICMPv6 messages have a common Type specified in [4].  The
 messages are distinguished based on the Subtype field (see below).
 The values for the Subtypes are specified in Section 9.  For all the
 ICMPv6 messages, the checksum is defined in [2].

6.1. New Neighborhood Discovery Messages

6.1.1. 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 6.4.3.

Koodli, Ed. Experimental [Page 17] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

  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 4: Router Solicitation for Proxy (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.
    Hop Limit      255.  See RFC 2461.
    Authentication Header
                   If a Security Association for the IP Authentication
                   Header exists between the sender and the
                   destination address, then the sender SHOULD include
                   this header.  See RFC 2402 [5].
 ICMP Fields:
    Type           The Experimental Mobility Protocol Type.  See [4].
    Code           0
    Checksum       The ICMPv6 checksum.
    Subtype        2
    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.

Koodli, Ed. Experimental [Page 18] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 Valid Options:
    Source Link-Layer Address
                   When known, the Link-Layer Address of the sender
                   SHOULD be included using the Link-Layer Address
                   option.  See the LLA option format below.
    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 with all bits set to zero.
 Future versions of this protocol may define new option types.
 Receivers MUST silently ignore any options that they do not recognize
 and continue processing the rest of the message.
 Including the source LLA option allows the receiver to record the
 sender's L2 address so that neighbor discovery can be avoided when
 the receiver needs to send packets back to the sender (of the RtSolPr
 message).
 When a wildcard is used for a New Access Point LLA, no other New
 Access Point LLA options must be present.
 A Proxy Router Advertisement (PrRtAdv) message should be received by
 the MN in response to a RtSolPr.  If such a message is not received
 in a timely manner (no less than twice the typical round trip time
 (RTT) over the access link or 100 milliseconds if RTT is not known),
 it SHOULD resend the RtSolPr message.  Subsequent retransmissions can
 be up to RTSOLPR_RETRIES, but MUST use an exponential backoff in
 which the timeout period (i.e., 2xRTT or 100 milliseconds) is doubled
 prior to each instance of retransmission.  If Proxy Router
 Advertisement is not received by the time the MN disconnects from the
 PAR, the MN SHOULD send an FBU immediately after configuring a new
 CoA.
 When RtSolPr messages are sent more than once, they MUST be rate
 limited with MAX_RTSOLPR_RATE per second.  During each use of a
 RtSolPr, exponential backoff is used for retransmissions.

Koodli, Ed. Experimental [Page 19] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

6.1.2. Proxy Router Advertisement (PrRtAdv)

 Access routers send Proxy Router Advertisement messages gratuitously
 if the handover is network-initiated or as a response to a RtSolPr
 message from an MN, 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 6.4.3.
 IP Fields:
    Source Address
                   MUST be the Link-Local Address assigned to the
                   interface from which this message is sent.
    Destination Address
                   The Source Address of an invoking Router
                   Solicitation for a Proxy Advertisement or the
                   address of the node the Access Router is
                   instructing to handover.
  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: Proxy Router Advertisement (PrRtAdv) Message
    Hop Limit      255.  See RFC 2461 [6].
    Authentication Header
                   If a Security Association for the IP Authentication
                   Header exists between the sender and the
                   destination address, the sender SHOULD include this
                   header.  See RFC 2402 [5].
 ICMP Fields:
    Type           The Experimental Mobility Protocol Type.  See RFC
                   4065 [4].
    Code           0, 1, 2, 3 or 4.  See below.

Koodli, Ed. Experimental [Page 20] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

    Checksum       The ICMPv6 checksum.
    Subtype        3
    Reserved       MUST be set to zero by the sender and ignored by
                   the receiver.
    Identifier     Copied from the Router Solicitation for Proxy
                   Advertisement or set to Zero if unsolicited.
 Valid Options in the following order:
    Source Link-Layer Address
                   When known, the Link-Layer Address of the sender
                   SHOULD be included using the Link-Layer Address
                   option.  See the LLA option format below.
    New Access Point Link-Layer Address
                   The Link-Layer Address or identification of the
                   access point is copied from the RtSolPr message.
                   This option MUST be present.
    New Router's Link-Layer Address
                   The Link-Layer Address of the Access Router for
                   which this message is proxied.  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.
                   Specifies the prefix of the Access Router for which
                   the message is proxied and is used for address
                   auto-configuration.  This option MUST be included
                   when Code is 0 or 1.  However, when this prefix is
                   the same as that used in the New Router's IP
                   Address option (above), the Prefix Information
                   option need not be present.
    New CoA Option
                   MAY be present when a PrRtAdv is sent unsolicited.
                   PAR MAY compute a new CoA using NAR's prefix
                   information and the MN's L2 address, or by any
                   other means.

Koodli, Ed. Experimental [Page 21] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 Future versions of this protocol may define new option types.
 Receivers MUST silently ignore any options they do not recognize and
 continue processing the message.
 Currently, Code values 0, 1, 2, 3 and 4 are defined.
 A Proxy Router Advertisement with Code 0 means that the MN should use
 the [AP-ID, AR-Info] tuple (present in the options above) for
 movement detection and NCoA formulation.  In this case, the Option-
 Code field in the New Access Point LLA option is 1, reflecting the
 LLA of the access point for which the rest of the options are
 related.  Multiple tuples may be present.
 A Proxy Router Advertisement with Code 1 means that the message is
 sent unsolicited.  If a New CoA option is present following the New
 Router Prefix Information option, 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; see Section
 3.3.  The Option-Code field in the New Access Point LLA option (see
 below) 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.  Each New Access Point LLA option contains an
 Option-Code value (described below) that indicates a specific
 outcome.
  1. When the Option-Code field in the New Access Point LLA option

is 5, handover to that access point does not require a change

       of CoA.  No other options are required in this case.
  1. When the Option-Code field in the New Access Point LLA option

is 6, the PAR is not aware of the Prefix Information requested.

       The MN SHOULD attempt to send an FBU as soon as it regains
       connectivity with the NAR.  No other options are required in
       this case.
  1. When the Option-Code field in the New Access Point LLA option

is 7, it means that the NAR does not support fast handover.

       The MN MUST stop fast handover protocol operations.  No other
       options are required in this case.
 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 field values (defined above including a value of 1)
 distinguish different outcomes for individual access points.

Koodli, Ed. Experimental [Page 22] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 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
 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.

6.2. Inter-Access Router Messages

6.2.1. Handover Initiate (HI)

 The Handover Initiate (HI) is an ICMPv6 message sent by an Access
 Router (typically PAR) to another Access Router (typically NAR) to
 initiate the process of a MN's handover.
  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 6: Handover Initiate (HI) Message
 IP Fields:
    Source Address
                   The IP address of the PAR.
    Destination Address
                   The IP address of the NAR.
    Hop Limit      255.  See RFC 2461 [6].
     Authentication Header
                   The authentication header MUST be used when this
                   message is sent.  See RFC 2402 [5].

Koodli, Ed. Experimental [Page 23] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 ICMP Fields:
    Type           The Experimental Mobility Protocol Type.  See RFC
                   4065 [4].
    Code           0 or 1.  See below
    Checksum       The ICMPv6 checksum.
    Subtype        4
    S flag         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 flag         Buffer flag.  When set, the destination SHOULD
                   buffer any packets moving toward 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 SHOULD be included
                   so that a host route can be established if
                   necessary.
    New Care of Address
                   The IP address the MN wishes to use when connected
                   to the destination.  When the `S' bit is set, the
                   NAR MAY assign this address.

Koodli, Ed. Experimental [Page 24] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 The PAR uses a Code value of 0 when it processes an FBU with PCoA as
 a source IP address.  The PAR uses a Code value of 1 when it
 processes an FBU whose source IP address is not PCoA.
 If a Handover Acknowledge (HAck) message is not received as a
 response in a short time period (no less than twice the typical RTT
 between source and destination, or 100 milliseconds if RTT is not
 known), the Handover Initiate SHOULD be resent.  Subsequent
 retransmissions can be up to HI_RETRIES, but MUST use exponential
 backoff in which the timeout period (i.e., 2xRTT or 100 milliseconds)
 is doubled during each instance of retransmission.

6.2.2. Handover Acknowledge (HAck)

 The Handover Acknowledgment message is a new ICMPv6 message that MUST
 be sent (typically by NAR to PAR) as a reply to the Handover Initiate
 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      |     Code      |          Checksum             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Subtype     |    Reserved   |          Identifier           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Options ...
 +-+-+-+-+-+-+-+-+-+-+-+-
            Figure 7: 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.
    Hop Limit      255.  See RFC 2461 [6].
    Authentication Header
                   The authentication header MUST be used when this
                   message is sent.  See RFC 2402 [5].

Koodli, Ed. Experimental [Page 25] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 ICMP Fields:
    Type           The Experimental Mobility Protocol Type.  See RFC
                   4065 [4].
    Code
                     0: Handover Accepted, NCoA valid
                     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
                        (used in Assigned addressing)
                   128: Handover Not Accepted, reason unspecified
                   129: Administratively prohibited
                   130: Insufficient resources
    Checksum       The ICMPv6 checksum.
    Subtype        5
    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 to which this message is a
                   response.
 Valid Options:
    New Care of Address
                   If the S flag in the Handover Initiate 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 the `S' bit is
                   not set, e.g., Code 2 above.
 Upon receiving an HI message, the NAR MUST respond with a Handover
 Acknowledge message.  If the `S' flag is set in the HI message, the
 NAR SHOULD include the New Care of Address option and a Code 3.
 The NAR MAY provide support for PCoA (instead of accepting or
 assigning NCoA), establish a host route entry for PCoA, and set up a
 tunnel to the PAR to forward MN's packets sent with PCoA as a source
 IP address.  This host route entry SHOULD be used to forward packets
 once the NAR detects that the particular MN is attached to its link.

Koodli, Ed. Experimental [Page 26] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 When responding to an HI message containing a Code value 1, the Code
 values 1, 2, and 4 in the HAck message are not relevant.
 Finally, the new access router can always refuse handover, in which
 case it should indicate the reason in one of the available Code
 values.

6.3. New Mobility Header Messages

 Mobile IPv6 uses a new IPv6 header type called Mobility Header [3].
 The Fast Binding Update, Fast Binding Acknowledgment, and Fast
 Neighbor Advertisement messages use the Mobility Header.

6.3.1. Fast Binding Update (FBU)

 The Fast Binding Update message is identical to the Mobile IPv6
 Binding Update (BU) message.  However, the processing rules are
 slightly different.
                                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  |          Sequence #           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |A|H|L|K|        Reserved       |           Lifetime            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  .                                                               .
  .                        Mobility options                       .
  .                                                               .
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Figure 8: Fast Binding Update (FBU) Message
 IP fields:
    Source Address
                   The PCoA or NCoA
    Destination Address
                   The IP address of the Previous Access Router
    A flag       MUST be set to one to request that PAR send a Fast
                   Binding Acknowledgment message.
    H flag       MUST be set to one.  See RFC 3775 [3].
    L flag       See RFC 3775 [3].

Koodli, Ed. Experimental [Page 27] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

    K flag       See RFC 3775 [3].
    Reserved       This field is unused.  MUST be set zero.
    Sequence Number
                   See RFC 3775 [3].
    Lifetime       See RFC 3775 [3].
    Mobility Options
                   MUST contain an alternate CoA option set to the
                   NCoA when an FBU is sent from PAR's link.
 The MN sends an FBU message any time after receiving a PrRtAdv
 message.  If the MN moves prior to receiving a PrRtAdv message, it
 SHOULD send an FBU to the PAR after configuring NCoA on the NAR
 according to Neighbor Discovery and IPv6 Address Configuration
 protocols.
 The source IP address is PCoA when the FBU is sent from PAR's link,
 and the source IP address is NCoA when sent from NAR's link.  When
 the FBU is sent from NAR's link, it SHOULD be encapsulated within an
 FNA.
 The FBU MUST also include the Home Address Option, and the Home
 Address is PCoA.  An FBU message MUST be protected so that PAR is
 able to determine that the FBU message is sent by a genuine MN.

6.3.2. Fast Binding Acknowledgment (FBack)

 The Fast Binding Acknowledgment message is sent by the PAR to
 acknowledge receipt of a Fast Binding Update message in which the 'A'
 bit is set.  The Fast Binding Acknowledgment message SHOULD NOT be
 sent to the MN before the PAR receives a HAck message from the NAR.
 The Fast Binding Acknowledgment MAY also be sent to the MN on the old
 link.

Koodli, Ed. Experimental [Page 28] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

                                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  |    Status     |K|  Reserved   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Sequence #          |           Lifetime            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  .                                                               .
  .                        Mobility options                       .
  .                                                               .
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        Figure 9: Fast Binding Acknowledgment (FBack) Message
 IP fields:
    Source Address
                   The IP address of the Previous Access Router.
                   Destination Address
                   The NCoA
    Status         8-bit unsigned integer indicating the disposition
                   of the Fast Binding Update.  Values of the Status
                   field that are less than 128 indicate that the
                   Binding Update was accepted by the receiving node.
                   The following such Status values are currently
                   defined:
                   0 Fast Binding Update accepted
                   1 Fast Binding Update accepted but NCoA is
                     invalid.  Use NCoA supplied in "alternate" CoA
                   Values of the Status field that are greater than or
                   equal to 128 indicate that the Binding Update was
                   rejected by the receiving node.  The following such
                   Status values are currently defined:
                   128 Reason unspecified
                   129 Administratively prohibited
                   130 Insufficient resources
                   131 Incorrect interface identifier length
    `K' flag       See RFC 3775 [3].
    Reserved       An unused field.  MUST be set to zero.

Koodli, Ed. Experimental [Page 29] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

    Sequence Number
                   Copied from the FBU message for use by the MN in
                   matching this acknowledgment with an outstanding
                   FBU.
    Lifetime       The granted lifetime in seconds for which the
                   sender of this message will retain a binding for
                   traffic redirection.
    Mobility Options
                   MUST contain an "alternate" CoA if Status is 1.

6.3.3. Fast Neighbor Advertisement (FNA)

 A MN sends a Fast Neighbor Advertisement to announce itself to the
 NAR.  When the Mobility Header Type is FNA, the Payload Proto field
 may be set to IPv6 to assist FBU encapsulation.
                                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  |            Reserved           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  .                                                               .
  .                        Mobility Options                       .
  .                                                               .
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Figure 10: Fast Neighbor Advertisement (FNA) Message
 IP fields:
    Source Address
                   NCoA
    Destination Address
                   NAR's IP Address
    Mobility Options
                   MUST contain the Mobility Header Link-Layer Address
                   of the MN in the MH-LLA option format.  See Section
                   6.4.4.
 The MN sends a Fast Neighbor Advertisement to the NAR, as soon as it
 regains connectivity on the new link.  Arriving or buffered packets
 can be immediately forwarded.  If NAR is proxying NCoA, it creates a
 neighbor cache entry in REACHABLE state.  If there is no entry, it
 creates one and sets it to REACHABLE.  If there is an entry in the
 INCOMPLETE state without a Link-Layer Address, it sets it to

Koodli, Ed. Experimental [Page 30] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 REACHABLE.  During the process of creating a neighbor cache entry,
 NAR can also detect if NCoA is in use, thus avoiding address
 collisions.  Since the FBU is encapsulated within the FNA when sent
 from NAR's link, NAR drops the FBU if it detects a collision.
 The combination of NCoA (present in source IP address) and the Link-
 Layer Address (present as a Mobility Option) SHOULD be used to
 distinguish the MN from other nodes.

6.4. New Options

 All the options are of the form shown in Figure 11.
 The Type values are defined from the Neighbor Discovery options
 space.  The Length field is in units of 8 octets, except for the
 Mobility Header Link-Layer Address option, whose Length field is in
 units of octets in accordance with Section 6.2 in [3].  Option-Code
 provides additional information for each of the options (See
 individual options below).
  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  |               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                              ...                              ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     Figure 11: Option Format

Koodli, Ed. Experimental [Page 31] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

6.4.1. IP Address Option

 This option is sent in the Proxy Router Advertisement, the Handover
 Initiate, and Handover Acknowledge 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   | Prefix Length |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          Reserved                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 +                                                               +
 |                                                               |
 +                          IPv6 Address                         +
 |                                                               |
 +                                                               +
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 12: IPv6 Address Option
    Type           17
    Length         The size of this option in 8 octets including the
                   Type, Option-Code, and Length fields.
    Option-Code    1   Old Care-of Address
                   2   New Care-of Address
                   3   NAR's IP address
    Prefix Length
                   The Length of the IPv6 Address Prefix.
    Reserved       MUST be set to zero by the sender and MUST be
                   ignored by the receiver.
    IPv6 Address   The IP address for the unit defined by the Type
                   field.

Koodli, Ed. Experimental [Page 32] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

6.4.2. New Router Prefix Information Option

 This option is sent in the PrRtAdv message to provide the prefix
 information valid on the NAR.
 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                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 +                                                               +
 |                                                               |
 +                            Prefix                             +
 |                                                               |
 +                                                               +
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Figure 13: New Router Prefix Information Option
    Type           18
    Length         The size of this option in 8 octets including the
                   Type, Option-Code, and Length fields.
    Option-Code    0
    Prefix Length
                   8-bit unsigned integer.  The number of leading bits
                   in the Prefix that are valid.  The value ranges
                   from 0 to 128.
    Reserved       MUST be set to zero by the sender and MUST be
                   ignored by the receiver.
    Prefix         An IP address or a prefix of an IP address.  The
                   Prefix Length field contains the number of valid
                   leading bits in the prefix.  The bits in the prefix
                   after the prefix length are reserved and MUST be
                   initialized to zero by the sender and ignored by
                   the receiver.

Koodli, Ed. Experimental [Page 33] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

6.4.3. Link-Layer Address (LLA) Option

  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 14: Link-Layer Address Option
    Type           19
    Length         The size of this option in 8 octets including the
                   Type, Option-Code, and Length fields.
    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 (i.e., Proxied
                      Originator)
                   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
    LLA            The variable length Link-Layer Address.
 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.
 The New Access Point Link-Layer Address contains the Link-Layer
 Address of the access point for which handover is about to be
 attempted.  This is used in the Router Solicitation for the Proxy
 Advertisement message.
 The MN Link-Layer Address option contains the Link-Layer Address of
 an MN.  It is used in the Handover Initiate message.
 The NAR (i.e., Proxied Originator) Link-Layer Address option contains
 the Link-Layer Address of the Access Router to which the Proxy Router
 Solicitation message refers.

Koodli, Ed. Experimental [Page 34] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

6.4.4. Mobility Header Link-Layer Address (MH-LLA) Option

 This option is identical to the LLA option, but is carried in the
 Mobility Header messages (i.e., FNA).  In the future, other Mobility
 Header messages may also make use of this option.  For instance,
 including this option in FBU allows PAR to obtain the MN's LLA
 readily.  The format of the option when the LLA is 6 bytes is shown
 in Figure 15.  When the LLA size is different, the option MUST be
 aligned appropriately.  See Section 6.2 in [3].
  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   |    Pad0=0     |         LLA                   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             LLA                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       Figure 15: Mobility Header Link-Layer Address Option
    Type           7
    Length         The size of this option in octets not including the
                   Type, Length, and Option-Code fields.
    Option-Code    2 Link-Layer Address of the MN
    LLA            The variable length Link-Layer Address.

6.4.5. Neighbor Advertisement Acknowledgment (NAACK)

  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   |     Status    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          Reserved                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Figure 16: Neighbor Advertisement Acknowledgment Option
    Type           20

Koodli, Ed. Experimental [Page 35] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

    Length         8-bit unsigned integer.  Length of the option, in 8
                   octets.  The length is 1 when NCoA is not supplied.
                   The length is 3 when NCoA is supplied (immediately
                   following the Reserved field).
    Option-Code    0
    Status         8-bit unsigned integer indicating the disposition
                   of the Fast Neighbor Advertisement message.  The
                   following Status values are currently defined:
                     1   The New CoA is invalid.
                     2   The New CoA is invalid; use the supplied CoA.
                         The New CoA MUST be present following the
                         Reserved field.
                   128   Link Layer Address unrecognized.
    Reserved       MUST be set to zero by the sender and MUST be
                   ignored by the receiver.
 The NAR responds to the FNA with the NAACK option to notify the MN to
 use a different NCoA if there is address collision.  If the NCoA is
 invalid, the Router Advertisement MUST use the NCoA as the
 destination address but use the L2 address present in the FNA.  The
 MN SHOULD use the NCoA if it is supplied with the NAACK option.  If
 the NAACK indicates that the Link-Layer Address is unrecognized, the
 MN MUST NOT use the NCoA or PCoA and SHOULD start the process of
 acquiring an NCoA at the NAR immediately.
 New option types may be defined in the future.

7. Configurable Parameters

    Parameter Name       Default Value            Definition
    -------------------  ----------------------   -------
    RTSOLPR_RETRIES      3                        Section 6.1.1
    MAX_RTSOLPR_RATE     3                        Section 6.1.1
    FBU_RETRIES          3                        Section 4
    PROXY_ND_LIFETIME    1.5 seconds              Section 6.2.2
    HI_RETRIES           3                        Section 6.2.1

Koodli, Ed. Experimental [Page 36] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

8. Security Considerations

 The following security vulnerabilities are identified, and suggested
 solutions are mentioned.
 1. Insecure FBU: In this case, packets meant for one address could be
    stolen, or redirected to some unsuspecting node.  This concern is
    the same as that in an MN and Home Agent relationship.
    Hence, the PAR MUST ensure that the FBU packet arrived from a node
    that legitimately owns the PCoA.  The access router and its hosts
    may use any available mechanism to establish a security
    association that MUST be used to secure FBU.  The current version
    of this protocol does not specify how this security association is
    established.  However, future work may specify this security
    association establishment.
    If an access router can ensure that the source IP address in an
    arriving packet could only have originated from the node whose
    Link-Layer Address is in the router's neighbor cache, then a bogus
    node cannot use a victim's IP address for malicious redirection of
    traffic.  Such an operation is recommended at least on neighbor
    discovery messages including the RtSolPr message.
 2. Secure FBU, malicious or inadvertent redirection: In this case,
    the FBU is secured, but the target of binding happens to be an
    unsuspecting node due to inadvertent operation or malicious
    intent.  This vulnerability can lead to an MN with a genuine
    security association with its access router redirecting traffic to
    an incorrect address.
    However, the target of malicious traffic redirection is limited to
    an interface on an access router with which the PAR has a security
    association.  The PAR MUST verify that the NCoA to which PCoA is
    being bound actually belongs to NAR's prefix.  To do this, HI and
    HAck message exchanges are to be used.  When NAR accepts NCoA in
    HI (with Code = 0), it proxies NCoA so that any arriving packets
    are not sent on the link until the MN attaches and announces
    itself through FNA.  Therefore, any inadvertent or malicious
    redirection to a host is avoided.  It is still possible to jam
    NAR's buffer with redirected traffic.  However, since NAR's
    handover state corresponding to NCoA has a finite (and short)
    lifetime corresponding to a small multiple of anticipated handover
    latency, the extent of this vulnerability is arguably small.
 3. Sending an FBU from NAR's link: A malicious node may send an FBU
    from NAR's link providing an unsuspecting node's address as NCoA.
    Since the FBU is encapsulated in the FNA, NAR should detect the

Koodli, Ed. Experimental [Page 37] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

    collision with an address in use when processing the FNA, and then
    drop the FBU.  When NAR is unable to detect address collisions,
    there is a vulnerability that redirection can affect an
    unsuspecting node.

9. IANA Considerations

 This document defines four new experimental ICMPv6 messages that use
 the Experimental Mobility Protocol ICMPv6 format [4].  These four new
 Subtype value assignments out of the Experimental Mobility Protocol
 Subtype Registry [4] have been assigned as follows:
    Subtype    Description              Reference
    -------    -----------              ---------
    2          RtSolPr                  Section 6.1.1
    3          PrRtAdv                  Section 6.1.2
    4          HI                       Section 6.2.1
    5          HAck                     Section 6.2.2
 This document defines four new Neighbor Discovery [6] options that
 have received Type assignments from IANA.
    Option-Type     Description              Reference
    -----------     -----------              ---------
    17              IP Address Option        Section 6.4.1
    18              New Router Prefix
                    Information Option       Section 6.4.2
    19              Link-Layer Address
                    Option                   Section 6.4.3
    20              Neighbor Advertisement
                    Acknowledgment Option    Section 6.4.5
 This document defines three new Mobility Header messages that have
 received type allocations from the Mobility Header Types registry at
 http://www.iana.org/assignments/mobility-parameters:
 1. Fast Binding Update, described in Section 6.3.1
 2. Fast Binding Acknowledgment, described in Section 6.3.2, and
 3. Fast Neighbor Advertisement, described in Section 6.3.3.
 This document defines a new Mobility Option which has received type
 assignments from the Mobility Options Type registry at
 http://www.iana.org/assignments/mobility-parameters:
 1. Mobility Header Link-Layer Address option, described in Section
    6.4.4.

Koodli, Ed. Experimental [Page 38] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

10. Acknowledgments

 The editor would like to thank all those who have provided feedback
 on this specification, but can only mention a few here:  Martin
 Andre, Vijay Devarapalli, Youn-Hee Han, Emil Ivov, Suvidh Mathur,
 Koshiro Mitsuya, Gabriel Montenegro, Takeshi Ogawa, Sun Peng, YC
 Peng, Domagoj Premec, and Jonathan Wood.  The editor would like to
 acknowledge a contribution from James Kempf to improve this
 specification.  The editor would also like to thank the [mipshop]
 working group chair Gabriel Montenegro and the erstwhile [mobile ip]
 working group chairs Basavaraj Patil and Phil Roberts for providing
 much support for this work.

11. Normative References

 [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [2]  Conta, A. and S. Deering, "Internet Control Message Protocol
      (ICMPv6) for the Internet Protocol Version 6 (IPv6)
      Specification", RFC 2463, December 1998.
 [3]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
      IPv6", RFC 3775, June 2004.
 [4]  Kempf, J., "Instructions for Seamoby and Experimental Mobility
      Protocol IANA Allocations", RFC 4065, July 2005.
 [5]  Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
      November 1998.
 [6]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
      for IP Version 6 (IPv6)", RFC 2461, December 1998.
 [7]  Thomson, S. and T. Narten, "IPv6 Stateless Address
      Autoconfiguration", RFC 2462, December 1998.

12. Contributors

 This document originated in the fast handover design team effort.
 The members of this design team in alphabetical order were:  Gopal
 Dommety, Karim El-Malki, Mohammed Khalil, Charles Perkins, Hesham
 Soliman, George Tsirtsis, and Alper Yegin.

Koodli, Ed. Experimental [Page 39] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 The design team member's contact information:
 Gopal Dommety
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, CA 95134
 Phone:+1 408 525 1404
 EMail: gdommety@cisco.com
 Karim El Malki
 Ericsson Radio Systems AB
 LM Ericssons Vag. 8
 126 25 Stockholm
 SWEDEN
 Phone:  +46 8 7195803
 Fax:    +46 8 7190170
 EMail: Karim.El-Malki@era.ericsson.se
 Mohamed Khalil
 Nortel Networks
 EMail: mkhalil@nortelnetworks.com
 Charles E. Perkins
 Communications Systems Lab
 Nokia Research Center
 313 Fairchild Drive
 Mountain View, California 94043
 USA
 Phone:  +1-650 625-2986
 Fax:  +1 650 625-2502
 EMail:  charliep@iprg.nokia.com
 Hesham Soliman
 Flarion Technologies
 EMail: H.Soliman@flarion.com

Koodli, Ed. Experimental [Page 40] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

 George Tsirtsis
 Flarion Technologies
 EMail: G.Tsirtsis@flarion.com
 Alper E. Yegin
 Samsung Advanced Institute of Technology
 75 West Plumeria Drive
 San Jose, CA 95134
 USA
 Phone: +1 408 544 5656
 EMail: alper.yegin@samsung.com

Author's Address

 Rajeev Koodli, Editor
 Nokia Research Center
 313 Fairchild Drive
 Mountain View, CA 94043 USA
 Phone: +1 650 625 2359
 Fax: +1 650 625 2502
 EMail: Rajeev.Koodli@nokia.com

Koodli, Ed. Experimental [Page 41] RFC 4068 Fast Handovers for Mobile IPv6 July 2005

Full Copyright Statement

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 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
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 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Koodli, Ed. Experimental [Page 42]

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