path: root/doc/rfc/rfc5949.txt

Internet Engineering Task Force (IETF)                         H. Yokota
Request for Comments: 5949                                      KDDI Lab
Category: Standards Track                                   K. Chowdhury
ISSN: 2070-1721                                                R. Koodli
                                                           Cisco Systems
                                                                B. Patil
                                                                   Nokia
                                                                  F. Xia
                                                              Huawei USA
                                                          September 2010


                  Fast Handovers for Proxy Mobile IPv6

Abstract

   Mobile IPv6 (MIPv6; RFC 3775) provides a mobile node with IP mobility
   when it performs a handover from one access router to another, and
   fast handovers for Mobile IPv6 (FMIPv6) are specified to enhance the
   handover performance in terms of latency and packet loss.  While
   MIPv6 (and FMIPv6 as well) requires the participation of the mobile
   node in the mobility-related signaling, Proxy Mobile IPv6 (PMIPv6;
   RFC 5213) provides IP mobility to nodes that either have or do not
   have MIPv6 functionality without such involvement.  Nevertheless, the
   basic performance of PMIPv6 in terms of handover latency and packet
   loss is considered no different from that of MIPv6.

   When the fast handover is considered in such an environment, several
   modifications are needed to FMIPv6 to adapt to the network-based
   mobility management.  This document specifies the usage of fast
   handovers for Mobile IPv6 (FMIPv6; RFC 5568) when Proxy Mobile IPv6
   is used as the mobility management protocol.  Necessary extensions
   are specified for FMIPv6 to support the scenario when the mobile node
   does not have IP mobility functionality and hence is not involved
   with either MIPv6 or FMIPv6 operations.
















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Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5949.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.  This document is subject to
   BCP 78 and the IETF Trust's Legal Provisions Relating to IETF
   Documents (http://trustee.ietf.org/license-info) in effect on the
   date of publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.













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Table of Contents

   1. Introduction ....................................................3
   2. Requirements Notation ...........................................4
   3. Terminology .....................................................4
   4. Proxy-Based FMIPv6 Protocol Overview ............................5
      4.1. Protocol Operation .........................................7
      4.2. Inter-AR Tunneling Operation ..............................14
      4.3. IPv4 Support Considerations ...............................16
   5. PMIPv6-Related Fast Handover Issues ............................16
      5.1. Manageability Considerations ..............................16
      5.2. Expedited Packet Transmission .............................17
   6. Message Formats ................................................18
      6.1. Mobility Header ...........................................18
           6.1.1. Handover Initiate (HI) .............................18
           6.1.2. Handover Acknowledge (HAck) ........................20
      6.2. Mobility Options ..........................................22
           6.2.1. Context Request Option .............................22
           6.2.2. Local Mobility Anchor Address (LMAA) Option ........23
           6.2.3. Mobile Node Link-Local Address Interface
                  Identifier (MN LLA-IID) Option .....................24
           6.2.4. Home Network Prefix Option .........................25
           6.2.5. Link-Local Address Option ..........................25
           6.2.6. GRE Key Option .....................................25
           6.2.7. IPv4 Address Option ................................25
           6.2.8. Vendor-Specific Mobility Option ....................25
   7. Security Considerations ........................................26
   8. IANA Considerations ............................................26
   9. Acknowledgments ................................................28
   10. References ....................................................28
      10.1. Normative References .....................................28
      10.2. Informative References ...................................29
   Appendix A. Applicable Use Cases ..................................30
      A.1. PMIPv6 Handoff Indication .................................30
      A.2. Local Routing .............................................31

1.  Introduction

   Proxy Mobile IPv6 (PMIPv6) [RFC5213] provides IP mobility to a mobile
   node that does not support Mobile IPv6 (MIPv6) [RFC3775] mobile node
   functionality.  A proxy agent in the network performs the mobility
   management signaling on behalf of the mobile node.  This model
   transparently provides mobility for nodes within a PMIPv6 domain.
   Nevertheless, the basic performance of PMIPv6 in terms of handover
   latency and packet loss is considered no different from that of
   Mobile IPv6.





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   Fast handovers for Mobile IPv6 (FMIPv6) [RFC5568] describes the
   protocol to reduce the handover latency for Mobile IPv6 by allowing a
   mobile node to send packets as soon as it detects a new subnet link
   and by delivering packets to the mobile node as soon as its
   attachment is detected by the new access router.  This document
   extends FMIPv6 for Proxy MIPv6 operation to minimize handover delay
   and packet loss as well as to transfer network-resident context for a
   PMIPv6 handover.  [RFC5568] is normative for this document, except
   where this document specifies new or revised functions and messages.

2.  Requirements Notation

   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].

3.  Terminology

   This document reuses terminology from [RFC5213], [RFC5568], and
   [RFC3775].  The following terms and abbreviations are additionally
   used in this document.

   Access Network (AN):
      A network composed of link-layer access devices such as access
      points or base stations providing access to a Mobile Access
      Gateway (MAG) connected to it.

   Previous Access Network (P-AN):
      The access network to which the Mobile Node (MN) is attached
      before handover.

   New Access Network (N-AN):
      The access network to which the Mobile Node (MN) is attached after
      handover.

   Previous Mobile Access Gateway (PMAG):
      The MAG that manages mobility-related signaling for the mobile
      node before handover.  In this document, the MAG and the Access
      Router are co-located.

   New Mobile Access Gateway (NMAG):
      The MAG that manages mobility-related signaling for the mobile
      node after handover.  In this document, the MAG and the Access
      Router (AR) are co-located.







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   Local Mobility Anchor (LMA):
      The topological anchor point for the mobile node's home network
      prefix(es) and the entity that manages the mobile node's binding
      state.  This specification does not alter any capability or
      functionality defined in [RFC5213].

   Handover indication:
      A generic signaling message, sent from the P-AN to the PMAG, that
      indicates a mobile node's handover.  While this signaling is
      dependent on the access technology, it is assumed that Handover
      indication can carry the information to identify the mobile node
      and to assist the PMAG in resolving the NMAG (and the new access
      point or base station) to which the mobile node is moving.  The
      details of this message are outside the scope of this document.

4.  Proxy-Based FMIPv6 Protocol Overview

   This specification describes fast handover protocols for the network-
   based mobility management protocol called Proxy Mobile IPv6 (PMIPv6)
   [RFC5213].  The core functional entities defined in PMIPv6 are the
   Local Mobility Anchor (LMA) and the Mobile Access Gateway (MAG).  The
   LMA is the topological anchor point for the mobile node's home
   network prefix(es).  The MAG acts as an access router (AR) for the
   mobile node and performs the mobility management procedures on its
   behalf.  The MAG is responsible for detecting the mobile node's
   movements to and from the access link and for initiating binding
   registrations to the mobile node's local mobility anchor.  If the
   MAGs can be informed of the detachment and/or attachment of the
   mobile node in a timely manner via, e.g., lower-layer signaling, it
   will become possible to optimize the handover procedure, which
   involves establishing a connection on the new link and signaling
   between mobility agents, compared to the baseline specification of
   PMIPv6.

   In order to further improve the performance during the handover, this
   document specifies a bidirectional tunnel between the Previous MAG
   (PMAG) and the New MAG (NMAG) to tunnel packets meant for the mobile
   node.  In order to enable the NMAG to send the Proxy Binding Update
   (PBU), the Handover Initiate (HI) and Handover Acknowledge (HAck)
   messages in [RFC5568] are extended for context transfer, in which
   parameters such as the mobile node's Network Access Identifier (NAI),
   Home Network Prefix (HNP), and IPv4 Home Address are transferred from
   the PMAG.  New flags, 'P' and 'F', are defined for the HI and HAck
   messages to distinguish from those in [RFC5568] and to request packet
   forwarding, respectively.






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   In this document, the Previous Access Router (PAR) and New Access
   Router (NAR) are interchangeable with the PMAG and NMAG,
   respectively.  The reference network is illustrated in Figure 1.  The
   access networks in the figure (i.e., P-AN and N-AN) are composed of
   Access Points (APs) defined in [RFC5568], which are often referred to
   as base stations in cellular networks.

   Since a mobile node is not directly involved with IP mobility
   protocol operations, it follows that the mobile node is not directly
   involved with fast handover procedures either.  Hence, the messages
   involving the mobile node in [RFC5568] are not used when PMIPv6 is in
   use.  More specifically, the Router Solicitation for Proxy
   Advertisement (RtSolPr), the Proxy Router Advertisement (PrRtAdv),
   Fast Binding Update (FBU), Fast Binding Acknowledgment (FBack), and
   the Unsolicited Neighbor Advertisement (UNA) messages are not
   applicable in the PMIPv6 context.  A MAG that receives a RtSolPr or
   FBU message from a mobile node SHOULD behave as if they do not
   implement FMIPv6 as defined in [RFC5568] at all -- continuing to
   operate according to this specification within the network -- or
   alternatively, start serving that particular mobile node as specified
   in [RFC5568].

                                +----------+
                                |   LMA    |
                                |          |
                                +----------+
                                  /      \
                                 /        \
                                /          \
                    +........../..+      +..\..........+
                    . +-------+-+ .______. +-+-------+ .
                    . |  PMAG   |()_______)|  NMAG   | .
                    . |  (PAR)  | .      . |  (NAR)  | .
                    . +----+----+ .      . +----+----+ .
                    .      |      .      .      |      .
                    .   ___|___   .      .   ___|___   .
                    .  /       \  .      .  /       \  .
                    . (  P-AN   ) .      . (  N-AN   ) .
                    .  \_______/  .      .  \_______/  .
                    .      |      .      .      |      .
                    .   +----+    .      .   +----+    .
                    .   | MN |  ---------->  | MN |    .
                    .   +----+    .      .   +----+    .
                    +.............+      +.............+

               Figure 1: Reference Network for Fast Handover





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4.1.  Protocol Operation

   There are two modes of operation in FMIPv6 [RFC5568].  In the
   predictive mode of fast handover, a bidirectional tunnel between the
   PMAG (PAR) and NMAG (NAR) is established prior to the mobile node's
   attachment to the NMAG.  In the reactive mode, this tunnel
   establishment takes place after the mobile node attaches to the NMAG.
   In order to alleviate the packet loss during a mobile node's handover
   (especially when the mobile node is detached from both links), the
   downlink packets for the mobile node need to be buffered either at
   the PMAG or NMAG, depending on when the packet forwarding is
   performed.  It is hence REQUIRED that all MAGs have the capability
   and enough resources to buffer packets for the mobile nodes
   accommodated by them.  The buffer size to be prepared and the rate at
   which buffered packets are drained are addressed in Section 5.4 of
   [RFC5568].  Note that the protocol operation specified in the
   document is transparent to the local mobility anchor (LMA); hence
   there is no new functional requirement or change on the LMA.

   Unlike MIPv6, the mobile node in the PMIPv6 domain is not involved
   with IP mobility signaling; therefore, in order for the predictive
   fast handover to work effectively, it is REQUIRED that the mobile
   node is capable of reporting lower-layer information to the AN at a
   short enough interval, and that the AN is capable of sending the
   Handover indication to the PMAG at an appropriate timing.  The
   sequence of events for the predictive fast handover is illustrated in
   Figure 2.
























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                                            PMAG        NMAG
          MN         P-AN       N-AN        (PAR)       (NAR)     LMA
          |           |          |            |           |        |
     (a)  |--Report-->|          |            |           |        |
          |           |          |            |           |        |
          |           |       Handover        |           |        |
     (b)  |           |------indication------>|           |        |
          |           |          |            |           |        |
          |           |          |            |           |        |
     (c)  |           |          |            |----HI---->|        |
          |           |          |            |           |        |
          |           |          |            |           |        |
     (d)  |           |          |            |<---HAck---|        |
          |           |          |            |           |        |
          |           |          |            |           |        |
          |           |          |            |HI/HAck(optional)   |
     (e)  |           |          |            |<- - - - ->|        |
          |           |          |          #=|<===================|
     (f)  |           |          |          #====DL data=>|        |
          |  Handover |       Handover        |           |        |
     (g)  |<-command--|<------command---------|           |        |
         ~~~          |          |            |           |        |
         ~~~          |          |            |           |        |
          |   MN-AN connection   |    AN-MAG connection   |        |
     (h)  |<---establishment---->|<----establishment----->|        |
          |           |          |  (substitute for UNA)  |        |
          |           |          |            |           |        |
     (i)  |<==================DL data=====================|        |
          |           |          |            |           |        |
     (j)  |===================UL data====================>|=#      |
          |           |          |          #=|<============#      |
          |           |          |          #=====================>|
     /    |           |          |            |           |        | \
     |(k) |           |          |            |           |--PBU-->| |
     |    |           |          |            |           |        | |
     |(l) |           |          |            |           |<--PBA--| |
     |    |<==================DL data=====================|<=======| |
     |    |           |          |            |           |        | |
     \    |===================UL data====================>|=======>| /

          UL        Uplink
          DL        Downlink
          PBA       Proxy Binding Acknowledgment

     Figure 2: Predictive Fast Handover for PMIPv6 (Initiated by PMAG)






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   The detailed descriptions are as follows:

   (a)  The mobile node detects that a handover is imminent and reports
        its identifier (MN ID) and the New Access Point Identifier (New
        AP ID) [RFC5568] to which the mobile node is most likely to
        move.  The MN ID could be the NAI, link-layer address, or any
        other suitable identifier, but the MAG SHOULD be able to map any
        access-specific identifier to the NAI as the MN ID.  In some
        cases, the previous access network (P-AN) will determine the New
        AP ID for the mobile node.  This step is access technology
        specific, and details are outside the scope of this document.

   (b)  The previous access network, to which the mobile node is
        currently attached, indicates the handover of the mobile node to
        the previous mobile access gateway (PMAG), with the MN ID and
        New AP ID.  Detailed definition and specification of this
        message are outside the scope of this document.

   (c)  The previous MAG derives the new mobile access gateway (NMAG)
        from the New AP ID, which is a similar process to that of
        constructing an [AP ID, AR-Info] tuple in [RFC5568].  The
        previous MAG then sends the Handover Initiate (HI) message to
        the new MAG.  The HI message MUST have the 'P' flag set and
        include the MN ID, the HNP(s), and the address of the local
        mobility anchor that is currently serving the mobile node.  If
        there is a valid (non-zero) MN Link-layer Identifier (MN LL-ID),
        that information MUST also be included.  With some link layers,
        the MN Link-local Address Interface Identifier (MN LLA-IID) can
        also be included (see Section 6.2.3).

   (d)  The new MAG sends the Handover Acknowledge (HAck) message back
        to the previous MAG with the 'P' flag set.

   (e)  If it is preferred that the timing of buffering or forwarding
        should be later than step (c), the new MAG MAY optionally
        request that the previous MAG buffer or forward packets at a
        later and appropriate time, by setting the 'U' flag [RFC5568] or
        the 'F' flag in the HI message, respectively.

   (f)  If the 'F' flag is set in the previous step, a bidirectional
        tunnel is established between the previous MAG and new MAG, and
        packets destined for the mobile node are forwarded from the
        previous MAG to the new MAG over this tunnel.  After
        decapsulation, those packets MAY be buffered at the new MAG.  If
        the connection between the new access network and new MAG has
        already been established, those packets MAY be forwarded towards





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        the new access network, which then becomes responsible for them
        (e.g., buffering or delivering, depending on the condition of
        the mobile node's attachment); this is access technology
        specific.

   (g)  When handover is ready on the network side, the mobile node is
        triggered to perform handover to the new access network.  This
        step is access technology specific, and details are outside the
        scope of this document.

   (h)  The mobile node establishes a physical-layer connection with the
        new access network (e.g., radio channel assignment), which in
        turn triggers the establishment of a link-layer connection
        between the new access network and new MAG if not yet
        established.  An IP-layer connection setup may be performed at
        this time (e.g., PPP IPv6 Control Protocol) or at a later time
        (e.g., stateful or stateless address autoconfiguration).  This
        step can be a substitute for the Unsolicited Neighbor
        Advertisement (UNA) in [RFC5568].  If the new MAG acquires a
        valid new MN LL-ID via the new access network and a valid old MN
        LL-ID from the previous MAG at step (c), these IDs SHOULD be
        compared to determine whether the same interface is used before
        and after handover.  When the connection between the mobile node
        and new MAG is PPP and the same interface is used for the
        handover, the new MAG SHOULD confirm that the same interface
        identifier is used for the mobile node's link-local address
        (this is transferred from the previous MAG using the MN LLA-IID
        option at step (c), and sent to the mobile node during the
        Configure-Request/Ack exchange).

   (i)  The new MAG starts to forward packets destined for the mobile
        node via the new access network.

   (j)  The uplink packets from the mobile node are sent to the new MAG
        via the new access network, and the new MAG forwards them to the
        previous MAG.  The previous MAG then sends the packets to the
        local mobility anchor that is currently serving the mobile node.

   (k)  The new MAG sends the Proxy Binding Update (PBU) to the local
        mobility anchor, whose address is provided in step (c).  Steps
        (k) and (l) are not part of the fast handover procedure but are
        shown for reference.

   (l)  The local mobility anchor sends back the Proxy Binding
        Acknowledgment (PBA) to the new MAG.  From this time on, the
        packets to/from the mobile node go through the new MAG instead
        of the previous MAG.




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   According to Section 4 of [RFC5568], the previous MAG establishes a
   binding between the Previous Care-of Address (PCoA) and New Care-of
   Address (NCoA) to forward packets for the mobile node to the new MAG,
   and the new MAG creates a proxy neighbor cache entry to receive those
   packets for the NCoA before the mobile node arrives.  In the case of
   PMIPv6, however, the only address that is used by the mobile node is
   the Mobile Node's Home Address (MN-HoA), so the PMAG forwards the
   mobile node's packets to the NMAG instead of the NCoA.  The NMAG then
   simply decapsulates those packets and delivers them to the mobile
   node.  FMIPv4 [RFC4988] specifies forwarding when the mobile node
   uses the home address as its on-link address rather than the care-of
   address.  The usage in PMIPv6 is similar to that in FMIPv4, where the
   address(es) used by the mobile node is/are based on its HNP(s).
   Since the NMAG can obtain the link-layer address (MN LL-ID) and
   HNP(s) via the HI message (also the interface identifier of the
   mobile node's link-local address (MN LLA-ID), if available), it can
   create a neighbor cache entry for the link-local address and the
   routes for the whole HNP(s), even before the mobile node performs
   Neighbor Discovery.  For the uplink packets from the mobile node
   after handover in step (j), the NMAG forwards the packets to the PMAG
   through the tunnel established in step (f).  The PMAG then
   decapsulates and sends them to the local mobility anchor.

   The timing of the context transfer and that of packet forwarding may
   be different.  Thus, a new flag 'F' and Option Code values for it in
   the HI and HAck messages are defined to request forwarding.  To
   request buffering, the 'U' flag has already been defined in
   [RFC5568].  If the PMAG receives the HI message with the 'F' flag
   set, it starts forwarding packets for the mobile node.  The HI
   message with the 'U' flag set MAY be sent earlier if the timing of
   buffering is different from that of forwarding.  If packet forwarding
   is completed, the PMAG MAY send the HI message with the 'F' flag set
   and the Option Code value set to 2.  Via this message, the ARs on
   both ends can tear down the forwarding tunnel synchronously.

   The IP addresses in the headers of those user packets are summarized
   below:

   In step (f),

      Inner source address: IP address of the correspondent node

      Inner destination address: HNP or Mobile Node's IPv4 Home Address
      (IPv4-MN-HoA)

      Outer source address: IP address of the PMAG

      Outer destination address: IP address of the NMAG



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   In step (i),

      Source address: IP address of the correspondent node

      Destination address: HNP or IPv4-MN-HoA

   In step (j),

      - from the mobile node to the NMAG,

        Source address: HNP or IPv4-MN-HoA

        Destination address: IP address of the correspondent node

      - from the NMAG to the PMAG,

        Inner source address: HNP or IPv4-MN-HoA

        Inner destination address: IP address of the correspondent node

        Outer source address: IP address of the NMAG

        Outer destination address: IP address of the PMAG

      - from the PMAG to the LMA,

        Inner source address: HNP or IPv4-MN-HoA

        Inner destination address: IP address of the correspondent node

        Outer source address: IP address of the PMAG

        Outer destination address: IP address of the LMA

   In the case of the reactive handover for PMIPv6, since the mobile
   node does not send either the FBU or UNA, it would be more natural
   that the NMAG send the HI message to the PMAG after the mobile node
   has moved to the new link.  The NMAG then needs to obtain the
   information of the PMAG beforehand.  Such information could be
   provided, for example, by the mobile node sending the AP-ID on the
   old link and/or by the lower-layer procedures between the P-AN and
   N-AN.  The exact method is not specified in this document.  Figure 3
   illustrates the reactive fast handover procedures for PMIPv6, where
   the bidirectional tunnel establishment is initiated by the NMAG.







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                                         PMAG            NMAG
          MN       P-AN      N-AN        (PAR)           (NAR)     LMA
          |         |         |            |               |        |
     (a) ~~~        |         |            |               |        |
         ~~~        |         |            |               |        |
          |  MN-AN connection |       AN-MAG connection    |        |
     (b)  |<--establishment-->|<-------establishment------>|        |
          |         |         |(substitute for UNA and FBU)|        |
          |         |         |            |               |        |
          |         |         |            |               |        |
     (c)  |         |         |            |<-----HI-------|        |
          |         |         |            |               |        |
          |         |         |            |               |        |
     (d)  |         |         |            |-----HAck----->|        |
          |         |         |            |               |        |
          |         |         |            |               |        |
     (e)  |         |         |          #=|<=======================|
          |         |         |          #================>|=#      |
          |<====================DL data======================#      |
          |         |         |            |               |        |
     (f)  |=====================UL data===================>|=#      |
          |         |         |          #=|<================#      |
          |         |         |          #=========================>|
          |         |         |            |               |        |
     /    |         |         |            |               |        | \
     |(g) |         |         |            |               |--PBU-->| |
     |    |         |         |            |               |        | |
     |(h) |         |         |            |               |<--PBA--| |
     |    |<====================DL data====================|<=======| |
     |    |         |         |            |               |        | |
     \    |=====================UL data===================>|=======>| /

      Figure 3: Reactive Fast Handover for PMIPv6 (Initiated by NMAG)

   The detailed descriptions are as follows:

   (a)  The mobile node undergoes handover from the previous access
        network to the new access network.

   (b)  The mobile node establishes a connection (e.g., radio channel)
        with the new access network, which triggers the establishment of
        the connection between the new access network and new MAG.  The
        MN ID is transferred to the new MAG at this step for the
        subsequent procedures.  The AP-ID on the old link (Old AP ID),
        which will be provided by either the mobile node or the new
        access network, is also transferred to the new MAG to help
        identify the previous MAG on the new link.  This can be regarded
        as a substitute for the UNA and FBU.



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   (c)  The new MAG sends the HI message to the previous MAG.  The HI
        message MUST have the 'P' flag set and include the MN ID.  The
        Context Request option MAY be included to request additional
        context information on the mobile node to the previous MAG.

   (d)  The previous MAG sends the HAck message back to the new MAG with
        the 'P' flag set.  The HAck message MUST include the HNP(s)
        and/or IPv4-MN-HoA that corresponds to the MN ID in the HI
        message and SHOULD include the MN LL-ID, only if it is valid
        (non-zero), and the local mobility anchor address that is
        currently serving the mobile node.  The context information
        requested by the new MAG MUST be included.  If the requested
        context is not available for some reason, the previous MAG MUST
        return the HAck message with the Code value 131.  If the 'F'
        flag is set in the HI message at step (c) and forwarding is
        nevertheless not executable for some reason, the previous MAG
        MUST return the HAck message with the Code value 132.

   (e)  If the 'F' flag in the HI message is set at step (c), a
        bidirectional tunnel is established between the previous MAG and
        new MAG, and packets destined for the mobile node are forwarded
        from the previous MAG to the new MAG over this tunnel.  After
        decapsulation, those packets are delivered to the mobile node
        via the new access network.

   (f)  The uplink packets from the mobile node are sent to the new MAG
        via the new access network, and the new MAG forwards them to the
        previous MAG.  The previous MAG then sends the packets to the
        local mobility anchor that is currently serving the mobile node.

   Steps (g)-(h) are the same as steps (k)-(l) in the predictive fast
   handover procedures.

   In step (c), the IP address of the PMAG needs to be resolved by the
   NMAG to send the HI message to the PMAG.  This information may come
   from the N-AN or some database that the NMAG can access.

4.2.  Inter-AR Tunneling Operation

   When the PMAG (PAR) or NMAG (NAR), depending on the fast handover
   mode, receives the HI message with the 'F' flag set, it prepares to
   send/receive the mobile node's packets to/from the other MAG and
   returns the HAck message with the same sequence number.  Both MAGs
   SHOULD support the following encapsulation modes for the user
   packets, which are also defined for the tunnel between the local
   mobility anchor and MAG:





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   o  IPv4-or-IPv6-over-IPv6 [RFC5844]

   o  IPv4-or-IPv6-over-IPv4 [RFC5844]

   o  IPv4-or-IPv6-over-IPv4-UDP [RFC5844]

   o  TLV-header UDP tunneling [RFC5845]

   o  Generic Routing Encapsulation (GRE) tunneling with or without GRE
      key(s) [RFC5845]

   The PMAG and the NMAG MUST use the same tunneling mechanism for the
   data traffic tunneled between them.  The encapsulation mode to be
   employed SHOULD be configurable.  It is RECOMMENDED that:

   1.  As the default behavior, the inter-MAG tunnel uses the same
       encapsulation mechanism as that for the PMIPv6 tunnel between the
       local mobility anchor and the MAGs.  The PMAG and NMAG
       automatically start using the same encapsulation mechanism
       without a need for a special configuration on the MAGs or a
       dynamic tunneling mechanism negotiation between them.

   2.  Configuration on the MAGs can override the default mechanism
       specified in scenario #1 above.  The PMAG and NMAG MUST be
       configured with the same mechanism, and this configuration is
       most likely to be uniform throughout the PMIPv6 domain.  If the
       packets on the PMIPv6 tunnel cannot be uniquely mapped on to the
       configured inter-MAG tunnel, this scenario is not applicable, and
       scenario #3 below SHOULD directly be applied.

   3.  An implicit or explicit tunnel negotiation mechanism between the
       MAGs can override the default mechanism specified in scenario #1
       above.  The employed tunnel negotiation mechanism is outside the
       scope of this document.

   The necessary information MUST be transferred in the HI/HAck messages
   to determine whether a mobile node's packets should be forwarded
   immediately or at a later time.  Such information includes the HNP(s)
   (or IPv4-MN-HoA) and/or GRE key(s).  In the case of GRE tunneling
   with GRE keys being used, for each mobility session, the NMAG selects
   the GRE key for the downlink packets, and the PMAG selects the GRE
   key for the uplink packets.  These GRE keys are exchanged between the
   PMAG and the NMAG using the GRE Key option as described in [RFC5845];
   e.g., in the case of the reactive mode as shown in Figure 3, the DL
   GRE key is communicated in the HI message while the UL GRE key is
   sent in the HAck message.  In the case of downlink packets, the PMAG
   redirects the mobile node's packets from the local mobility anchor
   towards the NMAG, and if the mobile node is ready to receive those



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   packets or the N-AN can handle them regardless of the state of the
   mobile node, the NMAG SHOULD immediately send them towards the N-AN;
   otherwise, it SHOULD buffer them until the mobile node is ready.  In
   the case of uplink packets, the NMAG SHOULD reverse-tunnel them from
   the mobile node towards the PMAG, and the PMAG will then send them to
   the local mobility anchor.

   When the PMAG or NMAG receives the HI message with the 'U' flag set,
   it prepares to buffer the mobile node's packets and returns the HAck
   message with the same sequence number.  It MUST be followed by
   another HI message with the 'F' flag set at an appropriate time to
   forward the buffered packets.

   If the MAG that received the HI message encounters an erroneous
   situation (e.g., insufficient buffer space), it SHOULD immediately
   send the HAck message with the cause of the error and cancel all
   tunneling operations.

4.3.  IPv4 Support Considerations

   The motivation and usage scenarios of IPv4 protocol support by PMIPv6
   are described in [RFC5844].  The scope of IPv4 support covers the
   following two features:

   o  IPv4 Home Address Mobility Support, and

   o  IPv4 Transport Support.

   As for IPv4 Home Address Mobility Support, the mobile node acquires
   the IPv4 Home Address (IPv4-MN-HoA), and in the case of handover, the
   PMAG needs to transfer IPv4-MN-HoA to the NMAG, which is the inner
   destination address of the packets forwarded on the downlink.  For
   this purpose, the IPv4 Address option described in Section 6.2.7 is
   used.  In order to provide IPv4 Transport Support, the NMAG needs to
   know the IPv4 address of the local mobility anchor (IPv4-LMAA) to
   send PMIPv6 signaling messages to the local mobility anchor in the
   IPv4 transport network.  For this purpose, a new option called the
   LMA Address (LMAA) option is defined in Section 6.2.2 so as to convey
   IPv4-LMAA from the PMAG to the NMAG.

5.  PMIPv6-Related Fast Handover Issues

5.1.  Manageability Considerations

   This specification does not require any additional IP-level
   functionality on the local mobility anchor and the mobile node
   running in the PMIPv6 domain.  A typical network interface that the
   mobile node could be assumed to have is one with the cellular



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   network, where the network controls the movement of the mobile node.
   Different types of interfaces could be involved, such as different
   generations (3G and 3.9G) or different radio access systems.  This
   specification supports a mobile node with the single radio mode,
   where only one interface is active at any given time.  The assigned
   IP address is preserved whether the physical interface changes or
   not, and the mobile node can identify which interface should be used
   if there are multiple ones.

5.2.  Expedited Packet Transmission

   The protocol specified in this document enables the NMAG to obtain
   parameters that would otherwise be available only by communicating
   with the local mobility anchor.  For instance, the HNP(s) and/or
   IPv4-MN-HoA of a mobile node are made available to the NMAG through
   context transfer.  This allows the NMAG to perform some procedures
   that may be beneficial.  The NMAG, for example, SHOULD send a Router
   Advertisement (RA) with prefix information to the mobile node as soon
   as its link attachment is detected (e.g., via receipt of a Router
   Solicitation message).  Such an RA is recommended, for example, in
   scenarios where the mobile node uses a new radio interface while
   attaching to the NMAG; since the mobile node does not have
   information regarding the new interface, it will not be able to
   immediately send packets without first receiving an RA with HNP(s).
   Especially in the reactive fast handover, the NMAG gets to know the
   HNP(s) assigned to the mobile node on the previous link at step (d)
   in Figure 3.  In order to reduce the communication disruption time,
   the NMAG SHOULD expect the mobile node to keep using the same HNP and
   to send uplink packets before that step upon the mobile node's
   request.  However, if the HAck message from the PMAG returns a
   different HNP or the subsequent PMIPv6 binding registration for the
   HNP fails for some reason, then the NMAG MUST withdraw the advertised
   HNP by sending another RA with zero prefix lifetime for the HNP in
   question.  This operation is the same as that described in
   Section 6.12 of [RFC5213].

   The protocol specified in this document is applicable regardless of
   whether link-layer addresses are used between a mobile node and its
   MAG.  A mobile node should be able to continue sending packets on the
   uplink even when it changes link.  When link-layer addresses are
   used, the mobile node performs Neighbor Unreachability Detection
   (NUD) [RFC4861], after attaching to a new link, probing the
   reachability of its default router.  The new router should respond to
   the NUD probe, providing its link-layer address in the solicited
   Neighbor Advertisement, which is common in the PMIPv6 domain.
   Implementations should allow the mobile node to continue to send
   uplink packets while it is performing NUD.




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6.  Message Formats

   This document defines new Mobility Header messages for the extended
   HI and HAck, and new mobility options for conveying context
   information.

6.1.  Mobility Header

6.1.1.  Handover Initiate (HI)

   This section defines extensions to the HI message in [RFC5568].  The
   format of the Message Data field in the Mobility Header is as
   follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                     +-------------------------------+
                                     |           Sequence #          |
     +-+-+-+-+-------+---------------+-------------------------------+
     |S|U|P|F|Resv'd |      Code     |                               |
     +-+-+-+-+-------+---------------+                               |
     |                                                               |
     .                                                               .
     .                       Mobility options                        .
     .                                                               .
     |                                                               |
     +---------------------------------------------------------------+
     (Note: P=1)

   IP Fields:

   Source Address

               The IP address of the PMAG or NMAG

   Destination Address

               The IP address of the peer MAG

   Message Data:

   Sequence #  Same as [RFC5568].

   'S' flag    Defined in [RFC5568], and MUST be set to zero in this
               specification.

   'U' flag    Buffer flag.  Same as [RFC5568].




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   'P' flag    Proxy flag.  Used to distinguish the message from that
               defined in [RFC5568], and MUST be set in all new message
               formats defined in this document when using this protocol
               extension.

   'F' flag    Forwarding flag.  Used to request to forward the packets
               for the mobile node.

   Reserved    Same as [RFC5568].

   Code        [RFC5568] defines this field and its values, 0 and 1.  In
               this specification, with the 'P' flag set, this field can
               be set to zero by default, or to the following values:

                  2: Indicate the completion of forwarding

                  3: All available context transferred

               Code value 3 is set when the transfer of all necessary
               context information is completed with this message.  This
               Code value is used both in cases where the context
               information is fragmented into several pieces and the
               last fragment is contained in this message, and where the
               whole information is transferred in one piece.

   Mobility options:

   This field contains one or more mobility options, whose encoding and
   formats are defined in [RFC3775].

   Required option

      In order to uniquely identify the target mobile node, the mobile
      node identifier MUST be contained in the Mobile Node Identifier
      option.

   The transferred context MUST be for one mobile node per message.  In
   addition, the NMAG can request necessary mobility options via the
   Context Request option defined in this document.

   Context Request Option

      This option MAY be present to request context information,
      typically by the NMAG to the PMAG in the NMAG-initiated fast
      handover.






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6.1.2.  Handover Acknowledge (HAck)

   This section defines extensions to the HAck message in [RFC5568].
   The format of the Message Data field in the Mobility Header is as
   follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                     +-------------------------------+
                                     |           Sequence #          |
     +-+-+-+---------+---------------+-------------------------------+
     |U|P|F|Reserved |      Code     |                               |
     +-+-+-+---------+---------------+                               |
     |                                                               |
     .                                                               .
     .                       Mobility options                        .
     .                                                               .
     |                                                               |
     +---------------------------------------------------------------+
     (Note: P=1)

   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.

   Message Data:

   The usages of Sequence # and Reserved fields are exactly the same as
   those in [RFC5568].

   'U' flag    Same as defined in Section 6.1.1.

   'P' flag    Same as defined in Section 6.1.1.  Used to distinguish
               the message from that defined in [RFC5568], and MUST be
               set in all new message formats defined in this document
               when using this protocol extension.

   'F' flag    Same as defined in Section 6.1.1.





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   Code        Code values 0 through 4 and 128 through 130 are defined
               in [RFC5568].  When the 'P' flag is set, the meaning of
               Code value 0 is as defined in this specification; 128
               through 130 are reused; and 5, 6, 131, and 132 are newly
               defined.

               0: Handover Accepted or Successful

               5: Context Transfer Accepted or Successful

               6: All available Context Transferred

               128: Handover Not Accepted, reason unspecified

               129: Administratively prohibited

               130: Insufficient resources

               131: Requested Context Not Available

               132: Forwarding Not Available

   Mobility options:

   This field contains one or more mobility options, whose encoding and
   formats are defined in [RFC3775].  The mobility option that uniquely
   identifies the target mobile node MUST be copied from the
   corresponding HI message, and the transferred context MUST be for one
   mobile node per message.

   Required option(s)

      All the context information requested by the Context Request
      option in the HI message SHOULD be present in the HAck message.
      The other cases are described below.

   In the case of the PMAG-initiated fast handover, when the PMAG sends
   the HI message to the NMAG with the context information and the NMAG
   successfully receives it, the NMAG returns the HAck message with Code
   value 5.  In the case of the NMAG-initiated fast handover, when the
   NMAG sends the HI message to the PMAG with or without the Context
   Request option, the PMAG returns the HAck message with the requested
   or default context information (if any).  If all available context
   information is transferred, the PMAG sets the Code value in the HAck
   message to 6.  If more context information is available, the PMAG






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   sets the Code value in the HAck message to 5, and the NMAG MAY send
   new HI message(s) to retrieve the rest of the available context
   information.  If none of the requested context information is
   available, the PMAG returns the HAck message with Code value 131
   without any context information.

6.2.  Mobility Options

6.2.1.  Context Request Option

   This option is sent in the HI message to request context information
   on the mobile node.  If a default set of context information is
   defined and always sufficient, this option is not used.  This option
   is more useful to retrieve additional or dynamically selected context
   information.

   The Context Request option is typically used for the reactive (NMAG-
   initiated) fast handover mode to retrieve the context information
   from the PMAG.  When this option is included in the HI message, all
   the requested context information SHOULD be included in the HAck
   message in the corresponding mobility option(s) (e.g., HNP, LMAA, or
   MN LL-ID mobility options).

   The default context information to request is the Home Network Prefix
   option.  If the Mobile Node link layer is available and used, the
   Mobile Node Link-layer Identifier option MUST also be requested.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+---------------+---------------+---------------+
     |  Option-Type  | Option-Length |           Reserved            |
     +---------------+---------------+-------------------------------+
     |  Req-type-1   | Req-length-1  |  Req-type-2   | Req-length-2  |
     +---------------------------------------------------------------+
     |  Req-type-3   | Req-length-3  |          Req-option-3         |
     +---------------------------------------------------------------+
     |                              ...                              |

   Option-Type    40

   Option-Length  The length in octets of this option, not including the
                  Option Type and Option Length fields.

   Reserved       This field is unused.  It MUST be initialized to zero
                  by the sender and MUST be ignored by the receiver.

   Req-type-n     The type value for the nth requested option.




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   Req-length-n   The length of the nth requested option, excluding the
                  Req-type-n and Req-length-n fields.

   Req-option-n   The optional data to uniquely identify the requested
                  context for the nth requested option.

   In the case where there are only Req-type-n and Req-length-n fields,
   the value of Req-length-n is set to zero.  If additional information
   besides Req-type-n is necessary to uniquely specify the requested
   context, such information follows after Req-length-n.  For example,
   when the requested contexts start with the HNP option (type=22), the
   MN Link-layer ID option (type=25), and the Vendor-Specific option
   (type=19), the required option format looks as follows:

     |                              ...                              |
     +---------------+---------------+---------------+---------------+
     |Option-Type=CRO| Option-Length |           Reserved            |
     +---------------+---------------+---------------+---------------+
     | Req-type-n=22 | Req-length-n=0| Req-type-n=25 | Req-length-n=0|
     +---------------+---------------+-------------------------------+
     | Req-type-n=19 | Req-length-n=5|           Vendor-ID           |
     +-------------------------------+---------------+---------------+
     |           Vendor-ID           |   Sub-Type    |               |
     +-----------------------------------------------+               |
     |                              ...                              |

     Note: CRO = Context Request Option

   The first two options can uniquely identify the requested contexts
   (i.e., the HNP and MN Link-layer ID) by the Req-type, so the
   Req-length is set to zero; however, the subsequent Vendor-Specific
   option further needs the Vendor-ID and Sub-Type to identify the
   requested context, so these parameters follow, and the Req-length is
   set to 5.  Note that the exact values in the Vendor-ID and Sub-Type
   follow [RFC5094].

6.2.2.  Local Mobility Anchor Address (LMAA) Option

   This option is used to transfer the Local Mobility Anchor IPv6
   Address (LMAA) or its IPv4 Address (IPv4-LMAA) with which the mobile
   node is currently registered.  The detailed definition of the LMAA is
   described in [RFC5213].









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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Option-Type  | Option-Length |  Option-Code  |   Reserved    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Local Mobility Anchor Address ...                |

   Option-Type    41

   Option-Length  18 or 6

   Option-Code    0  Reserved

                  1  IPv6 address of the local mobility anchor (LMAA)

                  2  IPv4 address of the local mobility anchor
                  (IPv4-LMAA)

   Reserved       This field is unused.  It MUST be initialized to zero
                  by the sender and MUST be ignored by the receiver.

   Local Mobility Anchor Address

                  If the Option-Code is 1, the LMA IPv6 address (LMAA)
                  is inserted.  If the Option-Code is 2, the LMA IPv4
                  address (IPv4-LMA) is inserted.

6.2.3.  Mobile Node Link-Local Address Interface Identifier (MN LLA-IID)
        Option

   This option is used to transfer the interface identifier of the
   mobile node's IPv6 Link-local Address that is used in the P-AN.  In
   deployments where the interface identifier is assigned by the network
   or is known to the network, this option is used to transfer this
   identifier from the PMAG to the NMAG.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Option-Type   | Option-Length |            Reserved           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                      Interface Identifier                     +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






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   Option-Type    42

   Option-Length  10

   Reserved       This field is unused.  It MUST be initialized to zero
                  by the sender and MUST be ignored by the receiver.

   Interface Identifier

                  The Interface Identifier value used for the mobile
                  node's IPv6 Link-local address in the P-AN.

6.2.4.  Home Network Prefix Option

   This option, as defined in [RFC5213], is used to transfer the home
   network prefix that is assigned to the mobile node in the P-AN.

6.2.5.  Link-Local Address Option

   This option, as defined in [RFC5213], is used to transfer the link-
   local address of the PMAG.

6.2.6.  GRE Key Option

   This option is used to transfer the GRE Key for the mobile node's
   data flow over the bidirectional tunnel between the PMAG and NMAG.
   The message format of this option follows that of the GRE Key option
   defined in [RFC5845].  The GRE Key value uniquely identifies each
   flow, and the sender of this option expects to receive packets of the
   flow from the peer AR with this value.

6.2.7.  IPv4 Address Option

   As described in Section 4.3, if the mobile node runs in IPv4-only
   mode or dual-stack mode, it requires the IPv4 home address
   (IPv4-MN-HoA).  This option is used to transfer the IPv4 home address
   if assigned on the previous link.  The format of this option follows
   that of the IPv4 Home Address Request option defined in [RFC5844].

6.2.8.  Vendor-Specific Mobility Option

   This option is used to transfer any other information defined in this
   document.  The format and used values of this option follow those of
   the Vendor-Specific Mobility option defined in [RFC5094].







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7.  Security Considerations

   Security issues for this document follow those for PMIPv6 [RFC5213]
   and FMIPv6 [RFC5568].  In PMIPv6, the MAG and local mobility anchor
   are assumed to share security associations.  In FMIPv6, the access
   routers (i.e., the PMAG and NMAG in this document) are assumed to
   share security associations.

   The Handover Initiate (HI) and Handover Acknowledge (HAck) messages
   exchanged between the PMAG and NMAG MUST be protected using end-to-
   end security association(s) offering integrity and data origin
   authentication.  The PMAG and the NMAG MUST implement IPsec [RFC4301]
   for protecting the HI and HAck messages.  IPsec Encapsulating
   Security Payload (ESP) [RFC4303] in transport mode with mandatory
   integrity protection SHOULD be used for protecting the signaling
   messages.  Confidentiality protection SHOULD be used if sensitive
   context related to the mobile node is transferred.

   IPsec ESP [RFC4303] in tunnel mode SHOULD be used to protect the
   mobile node's packets at the time of forwarding if the link between
   the PMAG and NMAG exposes the mobile node's packets to more threats
   than if they had followed their normal routed path.

8.  IANA Considerations

   This document defines new flags and status codes in the HI and HAck
   messages, as well as three new mobility options.  The Type values for
   these mobility options are assigned from the same numbering space as
   that allocated for the other mobility options defined in [RFC3775].
   Those for the flags and status codes are assigned from the
   corresponding numbering space defined in [RFC5568], and have been
   created as new tables in the IANA registry (marked with asterisks).
   New values for these registries can be allocated by Standards Action
   or IESG approval [RFC5226].

    Mobility Options
    Value  Description                                Reference
    -----  -------------------------------------      -------------
    40     Context Request Option                     Section 6.2.1
    41     Local Mobility Anchor Address Option       Section 6.2.2
    42     Mobile Node Link-local Address
                    Interface Identifier Option       Section 6.2.3









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    Handover Initiate Flags (*)
    Registration Procedures: Standards Action or IESG Approval
    Flag  Value  Description                          Reference
    ----  -----  -----------------------------------  -------------
      S   0x80   Assigned Address Configuration flag  [RFC5568]
      U   0x40   Buffer flag                          [RFC5568]
      P   0x20   Proxy flag                           Section 6.1.1
      F   0x10   Forwarding flag                      Section 6.1.1

    Handover Acknowledge Flags (*)
    Registration Procedures: Standards Action or IESG Approval
    Flag  Value  Description                          Reference
    ----  -----  -------------------------------      -------------
      U   0x80   Buffer flag                          Section 6.1.2
      P   0x40   Proxy flag                           Section 6.1.2
      F   0x20   Forwarding flag                      Section 6.1.2

    Handover Initiate Status Codes (*)
    Registration Procedures: Standards Action or IESG Approval
    Code  Description                                 Reference
    ----  --------------------------------------      -------------
      0   FBU with the PCoA as source IP address      [RFC5568]
      1   FBU whose source IP address is not PCoA     [RFC5568]
      2   Indicate the completion of forwarding       Section 6.1.1
      3   All available context transferred           Section 6.1.1
    4-255 Unassigned

    Handover Acknowledge Status Codes (*)
    Registration Procedures: Standards Action or IESG Approval
    Code    Description                                 Reference
    ----    ---------------------------------------     -------------
      0     Handover Accepted or Successful
               (when 'P' flag is set)                   Section 6.1.2
            Handover Accepted with NCoA valid           [RFC5568]
      1     Handover Accepted, NCoA not valid           [RFC5568]
      2     Handover Accepted, NCoA assigned            [RFC5568]
      3     Handover Accepted, use PCoA                 [RFC5568]
      4     Message sent unsolicited                    [RFC5568]
      5     Context Transfer Accepted or Successful     Section 6.1.2
      6     All available Context Transferred           Section 6.1.2
    7-127   Unassigned
    128     Handover Not Accepted, reason unspecified   [RFC5568]
    129     Administratively prohibited                 [RFC5568]
    130     Insufficient resources                      [RFC5568]
    131     Requested Context Not Available             Section 6.1.2
    132     Forwarding Not Available                    Section 6.1.2
   133-255  Unassigned




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9.  Acknowledgments

   The authors would like to specially thank Vijay Devarapalli and Sri
   Gundavelli for their thorough reviews of this document.

   The authors would also like to thank Charlie Perkins, Desire Oulai,
   Ahmad Muhanna, Giaretta Gerardo, Domagoj Premec, Marco Liebsch, Fan
   Zhao, Julien Laganier, and Pierrick Seite for their passionate
   discussions in the MIPSHOP working group mailing list.

10.  References

10.1.  Normative References

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

   [RFC3775]   Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
               in IPv6", RFC 3775, June 2004.

   [RFC4301]   Kent, S. and K. Seo, "Security Architecture for the
               Internet Protocol", RFC 4301, December 2005.

   [RFC4303]   Kent, S., "IP Encapsulating Security Payload (ESP)",
               RFC 4303, December 2005.

   [RFC5094]   Devarapalli, V., Patel, A., and K. Leung, "Mobile IPv6
               Vendor Specific Option", RFC 5094, December 2007.

   [RFC5213]   Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury,
               K., and B. Patil, "Proxy Mobile IPv6", RFC 5213,
               August 2008.

   [RFC5226]   Narten, T. and H. Alvestrand, "Guidelines for Writing an
               IANA Considerations Section in RFCs", BCP 26, RFC 5226,
               May 2008.

   [RFC5568]   Koodli, R., "Mobile IPv6 Fast Handovers", RFC 5568,
               July 2009.

   [RFC5844]   Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
               Mobile IPv6", RFC 5844, May 2010.

   [RFC5845]   Muhanna, A., Khalil, M., Gundavelli, S., and K. Leung,
               "Generic Routing Encapsulation (GRE) Key Option for Proxy
               Mobile IPv6", RFC 5845, June 2010.





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10.2.  Informative References

   [RFC4861]   Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
               "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
               September 2007.

   [RFC4988]   Koodli, R. and C. Perkins, "Mobile IPv4 Fast Handovers",
               RFC 4988, October 2007.











































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Appendix A.  Applicable Use Cases

A.1.  PMIPv6 Handoff Indication

   PMIPv6 [RFC5213] defines the Handoff Indicator option and also
   describes the type of handoff and values that can be set for this
   option.  This document proposes one approach to determining the
   handoff type by the NMAG when the handoff of the mobile node is
   executed.

   According to [RFC5213], the following handoff types are defined:

      0) Reserved

      1) Attachment over a new interface

      2) Handoff between two different interfaces of the mobile node

      3) Handoff between mobile access gateways for the same interface

      4) Handoff state unknown

      5) Handoff state not changed (Re-registration)

   Assuming that there is a valid MN Link-layer Identifier (MN LL-ID),
   the following solution can be considered.  When the NMAG receives the
   MN LL-ID from the PMAG in the MN LL-ID option via the HI or HAck
   message, the NMAG compares it with the new MN LL-ID that is obtained
   from the mobile node in the N-AN.  If these two MN LL-IDs are the
   same, the handoff type falls into type 3 (defined above) and the
   Handoff Indicator value is set to 3.  If these two MN LL-IDs are
   different, the handoff is likely to be type 2 (defined above) since
   the HI/HAck message exchange implies that this is a handoff rather
   than a multihoming, and therefore the Handoff Indicator value can be
   set to 2.  If there is no HI/HAck exchange performed prior to the
   network attachment of the mobile node in the N-AN, the NMAG may infer
   that this is a multi-homing case and set the Handoff Indicator value
   to 1.  In the case of re-registration, the MAG, to which the mobile
   node is attached, can determine if the handoff state is not changed,
   so the MAG can set the HI value to 5 without any additional
   information.  If no handoff type can be assumed or if there is no
   valid MN LL-ID available, the NMAG may set the value to 4.









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A.2.  Local Routing

   As described in Section 6.10.3 of [RFC5213], if the
   EnableMAGLocalRouting flag is set, when two mobile nodes are attached
   to one MAG, the traffic between them may be locally routed.  If one
   mobile node moves from this MAG (PMAG) to another MAG (NMAG) and if
   the PMAG does not detect the mobile node's detachment, it will
   continue to forward packets locally forever.  This situation is more
   likely to happen in the reactive fast handover with Wireless Local
   Area Network (WLAN) access, which does not have the capability to
   detect the detachment of the mobile node in a timely manner.  This
   specification can be applied to handle this case.  When the mobile
   node attaches to the NMAG, the NMAG sends the HI message to the PMAG
   with the 'F' flag set, which makes the PMAG realize the detachment of
   the mobile node and establish the inter-MAG tunnel.  The PMAG
   immediately stops the local routing and sends the packets for the
   mobile node to the NMAG via that tunnel; the packets are then
   delivered to the mobile node on the new link.

































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Authors' Addresses

   Hidetoshi Yokota
   KDDI Lab
   2-1-15 Ohara, Fujimino
   Saitama  356-8502
   Japan

   EMail: yokota@kddilabs.jp


   Kuntal Chowdhury
   Cisco Systems
   30 International Place
   Tewksbury, MA  01876
   USA

   EMail: kchowdhu@cisco.com


   Rajeev Koodli
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   EMail: rkoodli@cisco.com


   Basavaraj Patil
   Nokia
   6000 Connection Drive
   Irving, TX  75039
   USA

   EMail: basavaraj.patil@nokia.com


   Frank Xia
   Huawei USA
   1700 Alma Dr. Suite 500
   Plano, TX  75075
   USA

   EMail: xiayangsong@huawei.com






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