Subject: [Mipshop] AD review of draft-ietf-mipshop-pfmipv6

From: Jari Arkko <[email-masked]>
Date: Tue, 25 Aug 2009 17:37:45 +0300

I have reviewed this document. It was generally in good shape and easy 
to read. I did find a number of issues though. Please discuss them with 
me on this thread and/or revise the draft accordingly.

Technical:

I do not understand the IP host aspects of the handover. For an 
unmodified host, what kind of interfaces exist on the host, what 
addresses they have, and at what time are interfaces removed or added? 
Is this exactly the same as in RFC 5213, or does PFMIPv6 introduce some 
change here?

I would like to see a new section on manageability considerations. For 
instance, Section 5 talks about some configuration issues. These should 
be mentioned, and there should be a description of what the operator 
needs to configure in order to set up a PFMIPv6 network.

> If the new router's interface is configured to
> respond to queries sent to link-layer addresses than its own (e.g.,
> set to promiscuous mode), then it can respond to the NUD probe,
> providing its link-layer address in the solicited Neighbor
> Advertisement. 

Is this according to RFC 5213? I seem to recall that RFC 5213 operated 
on the same link layer addresses.

> At least one mobility option MUST
> uniquely identify the target MN (e.g., the Mobile Node Identifier
> Option defined in RFC4283 <http://tools.ietf.org/html/rfc4283>) and the transferred context MUST be for
> one MN per message.
>   

I would like the required options to be specified in more detail. Which 
identity options are sufficient to satisfy the MUST?

> If a default set of context information is defined and
> always sufficient, this option is not mandatory.  This option is more
> useful to retrieve additional or dynamically selected context
> information.
>
> Context Request Option is typically used for the reactive (NAR-
> initiated) fast handover mode to retrieve the context information
> from the PAR.  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-IID mobility options).
>   

Please specify what the default set of context information is, by 
listing the required options when the CRO is not present.

Editorial:

>    HO-Initiate:
>         A generic signaling message, sent from the P-AN to the PMAG that
>         indicates a MN handover.  While this signaling is dependent on
>         the access technology, it is assumed that HO-Initiate can carry
>         the information to identify the MN and to assist the PMAG
>         resolve the NMAG and the new access point or the base station to
>         which the MN is moving to.  The details of this message are
>         outside the scope of this document.
>
> 4. Proxy-based FMIPv6 Protocol Overview

Section 4 would probably benefit from an additional paragraph at the 
beginning to explain what assumptions there exist about lower layer 
functionality.

> A new flag 'P' is defined for the HI and
> HAck messages to distinguish from those in [RFC5268bis <http://tools.ietf.org/html/draft-ietf-mipshop-pfmipv6-08#ref-RFC5268bis>] and thus MUST
> be set in the entire document.
>   

This would be more readable as " ... those in [RFC5268bis]. This flag 
MUST be ..."

>    and the NAR creates a proxy NCE to receive those packets for the NCoA

The term NCE has not been introduced at this stage yet.

>    address that is used by the MN is MN-HoA.  Hence the PAR forwards

The term MN-HOA has not been introduced before.

>         The access network to which the MN is attached after handover.

New term MN, not introduced before.

> specifies forwarding when the MN uses HoA as its on-link address

New term HoA...

>    as MN's NAI, Home Network Prefix (HNP), IPv4 Home Address, are

New term NAI...

>         flag set and include the MN ID, the MN-HNP, the MN-IID and the

New terms MN-HNP and MN-IID (or at least they do not appear in their MN-XXX form before this point).

>         Inner destination address: HNP or IPv4-MN-HoA

IPv4-MN-HoA not defined earlier...

>    between the PCoA and NCoA to forward packets for the MN to the NAR,
New terms PCoA and NCoA... there's probably more undefined terms in the 
document, please check!

>    In (i),
In Step (i),

>           |(MN ID, Old AP ID) |     (MN ID, Old AP ID)     |        |

Old AP ID? AN ID? AR ID?

Jari

---

From: Hidetoshi Yokota <[email-masked]>
Date: Fri, 28 Aug 2009 23:50:19 +0900

Hi Jari,

Appreciate your detailed review. The editorial corrections are mostly
done and the revised version is attached to this mail. Regarding the
technical comments, only the policies for the correction are listed for
now. The complete correction will be posted as soon as possible. Please
see inline for the responses to your questions and comments:

> Is this exactly the same as in RFC 5213, or does PFMIPv6 introduce some 

The basic principle would be that this specification does not require
any additional IP-level function to the MN running in the PMIPv6 domain.
This MN should therefore be the same as defined in RFC5213.

A typical network interface would be one with the cellular network,
where the network basically controls the movement of the MN. Different
types of interfaces could be involved such as different generations (3G
and 3.9G) or different radio access systems. Any type of IP address
could be assigned (IPv4/v6 or global/private), but the assigned address
must be preserved before and after the handover. PFMIPv6 should be able
to handle the single radio situation, where only one interface is active
at any given time. This is a tougher situation in terms of packet loss
and delay.

> needs to configure in order to set up a PFMIPv6 network.

We will add a new section for manageability considerations to clarify
the above and to reflect your suggestion.

> on the same link layer addresses.

I think your observation is correct... I'll check with the other authors
to see if it is ok to rewrite it.

> identity options are sufficient to satisfy the MUST?

The required option should be the MN Identifier in the Mobile Node
Identifier Option.

> listing the required options when the CRO is not present.

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. With these two
options and the MN identifier, the NMAG can construct the PBU.

> beginning to explain what assumptions there exist about lower layer 

Yes, the predictive fast handover relies on the lower layer
functionality to trigger to send the HI. A new paragraph will be added
to clarify it.

>> HAck messages to distinguish from those in [RFC5268bis 
>> <http://tools.ietf.org/html/draft-ietf-mipshop-pfmipv6-08#ref-RFC5268bis>] 
>> and thus MUST

Revised.

> The term NCE has not been introduced at this stage yet.

Spelled out as "Neighbor Cache Entry".

> The term MN-HOA has not been introduced before.

Added the unabbreviated form "Mobile Node's Home Address" before it.

> New term MN, not introduced before.

Added "Mobile Node" before it.

>> specifies forwarding when the MN uses HoA as its on-link address

Changed to "Home Address".

>>    as MN's NAI, Home Network Prefix (HNP), IPv4 Home Address, are

Added "Network Access Identifier" before it.

> MN-XXX form before this point).

Modified "MN-HNP" to "HNP" for consistency.

> IPv4-MN-HoA not defined earlier...

Added "Mobile Node's IPv4 Home" before it.

> New terms PCoA and NCoA... there's probably more undefined terms in the 

Added "Previous Care-of Address" and "New Care-of Address". Will read
through it to see if there is any other undefined acronym.

> In Step (i),

Revised including other parts.

>>           |(MN ID, Old AP ID) |     (MN ID, Old AP ID)     |        |

AP ID stands for "Access Point Identifier", which is defined in RFC5568.
Added the unabbreviated form and citation.

The rest of the part will be revised soon.

Regards,
-- 
Hidetoshi

> Jari
> 
> _______________________________________________
> Mipshop mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/mipshop
> 
> 
> 

Network Working Group                                          H. Yokota
Internet-Draft                                                  KDDI Lab
Intended status: Standards Track                            K. Chowdhury
Expires: March 1, 2010                                         R. Koodli
                                                        Starent Networks
                                                                B. Patil
                                                                   Nokia
                                                                  F. Xia
                                                              Huawei USA
                                                         August 28, 2009

                  Fast Handovers for Proxy Mobile IPv6
                   draft-ietf-mipshop-pfmipv6-09.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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Copyright Notice

   Copyright (c) 2009 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
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   Please review these documents carefully, as they describe your rights
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Abstract

   Mobile IPv6 (MIPv6) [RFC3775] 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) [RFC5568] 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) [RFC5213] provides IP mobility to mobile 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 not any 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
   Mobile IPv6 (FMIPv6) 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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Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  5
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Proxy-based FMIPv6 Protocol Overview . . . . . . . . . . . . .  8
     4.1.  Protocol Operation . . . . . . . . . . . . . . . . . . . .  9
     4.2.  Inter-AR Tunneling Operation . . . . . . . . . . . . . . . 15
     4.3.  IPv4 Support Considerations  . . . . . . . . . . . . . . . 16
   5.  PMIPv6-related Fast Handover Issues  . . . . . . . . . . . . . 17
   6.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . . 18
     6.1.  Mobility Header  . . . . . . . . . . . . . . . . . . . . . 18
       6.1.1.  Handover Initiate (HI) . . . . . . . . . . . . . . . . 18
       6.1.2.  Handover Acknowledge (HAck)  . . . . . . . . . . . . . 19
     6.2.  Mobility Options . . . . . . . . . . . . . . . . . . . . . 21
       6.2.1.  Context Request Option . . . . . . . . . . . . . . . . 21
       6.2.2.  Local Mobility Anchor Address (LMAA) Option  . . . . . 23
       6.2.3.  Mobile Node Interface Identifier (MN IID) Option . . . 23
       6.2.4.  Home Network Prefix Option . . . . . . . . . . . . . . 24
       6.2.5.  Link-local Address Option  . . . . . . . . . . . . . . 24
       6.2.6.  GRE Key Option . . . . . . . . . . . . . . . . . . . . 24
       6.2.7.  IPv4 Address Option  . . . . . . . . . . . . . . . . . 24
       6.2.8.  Vendor-Specific Mobility Option  . . . . . . . . . . . 25
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 26
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 27
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 28
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 29
     10.2. Informative References . . . . . . . . . . . . . . . . . . 29
   Appendix A.  Applicable Use Cases  . . . . . . . . . . . . . . . . 30
     A.1.  PMIPv6 Handoff Indication  . . . . . . . . . . . . . . . . 30
     A.2.  Local Routing  . . . . . . . . . . . . . . . . . . . . . . 30
   Appendix B.  Change Log  . . . . . . . . . . . . . . . . . . . . . 32
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36

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1.  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].

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2.  Introduction

   Proxy Mobile IPv6 [RFC5213] provides IP mobility to a mobile node
   that does not possess Mobile IPv6 [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 mobile nodes within a PMIPv6
   domain.  Nevertheless, the basic performance of PMIPv6 in terms of
   handover latency and packet loss is considered not any different from
   that of Mobile IPv6.

   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
   describes necessary extensions to FMIPv6 to minimize handover delay
   and packet loss as well as to transfer network-resident context for a
   PMIPv6 handover.

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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 the Access Router
        (AR) 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 MN
        before handover.  In this document, the MAG and the Access
        Router are collocated.

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

   HO-Initiate:

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   In order to improve the performance during handover (when operations
   such as attachment to a new network and signaling between mobility
   agents are involved), the PFMIPv6 protocol in this document specifies
   a bi-directional 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 MN's
   Network Access Identifier (NAI), Home Network Prefix (HNP), IPv4 Home
   Address, are transferred from the PMAG.  A new flag 'P' is defined
   for the HI and HAck messages to distinguish from those in [RFC5568].
   This flag MUST be set in the entire document.

   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.

   Since a MN is not directly involved with IP mobility protocol
   operations, it follows that the MN is not directly involved with fast
   handover procedures either.  Hence, the messages involving the MN 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.

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

               Figure 1: Reference network for fast handover

4.1.  Protocol Operation

   There are two modes of operation in FMIPv6 [RFC5568].  In the
   predictive mode of fast handover, a bi-directional tunnel between the
   PAR and NAR is established prior to the MN's attachment to the NAR.
   In the reactive mode, this tunnel establishment takes place after the
   MN attaches to the NAR.  In order to alleviate the packet loss during
   a MN's handover (especially when the MN is detached from both links),
   the downlink packets for the MN need to be buffered either at the PAR
   (PMAG) or NAR (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 MNs accommodated by
   them.  Note that the protocol operation specified in the document is
   transparent to the LMA, hence there is no new functional requirement
   or change on the LMA.

   Since the MN is not involved in IP mobility signaling in PMIPv6, the
   sequence of events illustrating the predictive fast handover are
   shown in Figure 2.

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

       Figure 2: Predictive fast handover for PMIPv6 (PAR initiated)

   The detailed descriptions are as follows:

   (a)  The MN detects that a handover is imminent and reports the
        identifications of itself (MN ID) and the New Access Point
        Identifier (New AP ID) [RFC5568] to which the MN is most likely
        to move.  The MN ID could be the NAI or a Link Layer Address
        (LLA), or any other suitable identifier.  This step is access
        technology specific.  In some cases, the P-AN will determine

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        which AP ID the MN is moving to.

   (b)  The previous access network (P-AN), to which the MN is currently
        attached, indicates the handover of the MN to the PAR (PMAG).
        Detailed definition and specification of this message are
        outside the scope of this document.

   (c)  The PAR sends the HI to the NAR.  The HI message MUST have the P
        flag set and include the MN ID, the HNP, the MN IID and the
        address of the LMA that is currently serving the MN.

   (d)  The NAR sends the HAck back to the PAR with the P flag set.

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

   (f)  If the F flag is set in the previous step, a bi-directional
        tunnel is established between the PAR and NAR and packets
        destined for the MN are forwarded from the PAR to the NAR over
        this tunnel.  After decapsulation, those packets may be buffered
        at the NAR.  If the connection between the N-AN and NAR has
        already been established, those packets may be forwarded towards
        the N-AN, which then becomes responsible for them (e.g.,
        buffering or delivering depending on the condition of the MN's
        attachment); this is access technology specific.

   (g)  The MN undergoes handover to the New Access Network (N-AN).

   (h)  The MN establishes a physical link connection with the N-AN
        (e.g., radio channel assignment), which in turn triggers the
        establishment of a link-layer connection between the N-AN and
        NAR if not yet established.  An IP layer connection setup may be
        performed at this time (e.g., PPP IPv6CP) or at a later time
        (e.g., stateful or stateless auto address configuration).  This
        step can be a substitute for the UNA in [RFC5568], but since
        they are all access technology specific, details are outside the
        scope of this document.

   (i)  The NAR starts to forward packets destined for the MN via the
        N-AN.

   (j)  The uplink packets from the MN are sent to the NAR via the N-AN
        and the NAR forwards them to the PAR.  The PAR then sends the
        packets to the LMA that is currently serving the MN.

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   (k)  The NAR (NMAG) sends the Proxy Binding Update (PBU) to the LMA,
        whose address is provided in (c).  Steps (k) and (l) are not
        part of the fast handover procedure, but shown for reference.

   (l)  The LMA sends back the Proxy Binding Acknowledgment (PBA) to the
        NAR (NMAG).  From this time on, the packets to/from the MN go
        through the NAR instead of the PAR.

   According to Section 4 of [RFC5568], the PAR establishes a binding
   between the Previous Care-of Address (PCoA) and New Care-of Address
   (NCoA) to forward packets for the MN to the NAR, and the NAR creates
   a proxy neighbor cache entry to receive those packets for the NCoA
   before the MN arrives.  In the case of PMIPv6, however, the only
   address that is used by the MN is MN-HoA (Mobile Node's Home
   Address).  Hence the PAR forwards MN's packets to the NAR instead of
   the NCoA.  FMIPv4 [RFC4988] specifies forwarding when the MN 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
   is used by the MN is based on Home Network Prefix.  Hence the PAR
   forwards MN's packets to the NAR instead of the NCoA.  The NAR then
   simply decapsulates those packets and delivers them to the MN.  Since
   the NAR obtains the LLA (MN IID) and HNP by the HI, it can create the
   Neighbor Cache Entry for the MN and deliver packets to it even before
   the MN can perform Neighbor Discovery.  For the uplink packets from
   the MN after handover in (j), the NAR forwards the packets to the PAR
   through the tunnel established in step (f).  The PAR then
   decapsulates and sends them to the LMA.

   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, 'U' flag has already been defined in [RFC5568].
   If the PAR receives the HI message with the F flag set, it starts
   forwarding packets for the MN.  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 PAR MAY send
   the HI message with the F flag set and the Option Code value being 2.
   By 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),

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        Inner source address: IP address of the CN

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

        Outer source address: IP address of the PAR (PMAG)

        Outer destination address: IP address of the NAR (NMAG)

   In Step (i),

        Source address: IP address of the CN

        Destination address: HNP or IPv4-MN-HoA

   In Step (j),

   - from the MN to the NMAG,

        Source address: HNP or IPv4-MN-HoA

        Destination address: IP address of the CN

   - from the NMAG to the PMAG,

        Inner source address: HNP or IPv4-MN-HoA

        Inner destination address: IP address of the CN

        Outer source address: IP address of the NAR (NMAG)

        Outer destination address: IP address of the PAR (PMAG)

   - from the PMAG to the LMA,

        Inner source address: HNP or IPv4-MN-HoA

        Inner destination address: IP address of the CN

        Outer source address: IP address of the PAR (PMAG)

        Outer destination address: IP address of the LMA

   The encapsulation type for these user packets SHOULD follow that used
   in the tunnel between the LMA and MAG (IPv6-in-IPv6 as specified in
   [RFC2473], IPv6-in-IPv4, IPv6-in-IPv4-UDP as specified in
   [IPv4PMIPv6], TLV-header UDP tunneling as specified in [GREKEY] or
   any new method defined in the future).

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   In the case of the reactive handover for PMIPv6, since the MN does
   not send either the FBU or UNA, it would be more natural that the NAR
   sends the HI to the PAR after the MN has moved to the new link.  The
   NAR then needs to obtain the information of the PAR beforehand.  Such
   information could be provided, for example, by the MN 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 bi-directional tunnel establishment is
   initiated by the NAR.

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

        Figure 3: Reactive fast handover for PMIPv6 (NAR initiated)

   The detailed descriptions are as follows:

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   (a)  The MN undergoes handover from the P-AN to the N-AN.  The AP-ID
        on the old link may be provided by the MN to help identify the
        PMAG on the new link.

   (b)  The MN establishes a connection (e.g., radio channel) with the
        N-AN, which triggers the establishment of the connection between
        the N-AN and NAR.  The MN ID is transferred to the NAR for the
        subsequent procedures.  The AP-ID on the old link may also be
        provided by the MN to help identify the PMAG on the new link.
        This can be regarded as a substitute for the UNA and FBU.

   (c)  The NAR sends the HI to the PAR.  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 MN
        to the PAR.

   (d)  The PAR sends the HAck back to the NAR with the P flag set.  The
        HAck message MUST include the HNP and/or IPv4-MN-HoA that is
        corresponding to the MN ID in the HI message and SHOULD include
        the MN IID and the LMA address that is currently serving the MN.
        The context information requested by the NAR MUST be included.
        If the requested context is not available for some reason, the
        PAR MUST return the HAck with the Code value 131.  If the F flag
        is set in the HI at step (c) and forwarding is nevertheless not
        executable for some reason, the PAR MUST return the HAck with
        the Code value 132.

   (e)  If the F flag in the HI is set at step (c), a bi-directional
        tunnel is established between the PAR and NAR and packets
        destined for the MN are forwarded from the PAR to the NAR over
        this tunnel.  After decapsulation, those packets are delivered
        to the MN via the N-AN.

   (f)  The uplink packets from the MN are sent to the NAR via the N-AN
        and the NAR forwards them to the PAR.  The PAR then sends the
        packets to the LMA that is currently serving the MN.

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

   In step (c), The IP address of the PAR needs to be resolved by the
   NAR to send the HI to the PAR.  This information may come from the
   N-AN or some database that the NAR 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

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   send/receive the MN's packets to/from the other MAG and returns the
   HAck message with the same sequence number.  The necessary
   information MUST be transferred in the HI message to distinguish MN's
   packets for forwarding in advance or at this time.  Such information
   includes the HoA of the MN and/or GRE key(s).  For the downlink
   packets, the PMAG redirects MN's packets from the LMA towards the
   NMAG and if the MN is ready to receive those packets or the N-AN can
   handle them regardless of the state of the MN, the NAR should
   immediately send them towards the N-AN; otherwise it should buffer
   them until the MN is ready.  For the uplink packets, the NMAG SHOULD
   reverse-tunnel them from the MN towards the PMAG and the PMAG sends
   them to the LMA.

   When the PMAG or NMAG receives the HI message with the U flag set, it
   prepares to buffer the MN'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 operation.

4.3.  IPv4 Support Considerations

   The motivation and usage scenarios of IPv4 protocol support by PMIPv6
   are described in [IPv4PMIPv6].  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 MN acquires 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,
   a new option called IPv4 Address Option is defined in this document.
   In order to provide IPv4 Transport Support, the NMAG needs to know
   the IPv4 address of the LMA (IPv4-LMAA) to send PMIPv6 signaling
   messages to the LMA in the IPv4 transport network.  In this case, a
   new option called LMA Address (LMAA) option is used so as to convey
   IPv4-LMAA from the PMAG to NMAG.  The supported encapsulation type
   follows Section 6.10.2 in [RFC5213], that is, IPv4, IPv4-UDP and
   IPv4-UDP-TLV.

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5.  PMIPv6-related Fast Handover Issues

   The protocol specified in this document enables the NMAG to obtain
   parameters which would otherwise be available only by communicating
   with the LMA.  For instance, the HNP and/or IPv4-MN-HoA of a MN are
   made available to the NMAG through context transfer.  This allows the
   NMAG to perform some procedures that may be beneficial.  For
   instance, the NMAG could send a Router Advertisement (RA) with the
   HNP option to the MN 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 MN uses a new radio
   interface while attaching to the NMAG; since the MN does not have
   information regarding the new interface, it will not be able to
   immediately send packets without first receiving an RA with HNP.
   Especially, in the reactive fast handover, the NMAG gets to know the
   HNP assigned to the MN on the previous link at step (d) in Figure 3.
   In order to reduce the communication disruption time, the NMAG SHOULD
   expect the MN to keep using the same HNP and to send uplink packets
   before that step upon the MN's request.  However, if the HAck 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
   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 MN and its access
   router.  A MN should be able to continue sending packets on the
   uplink even when it changes link.  When link-layer addresses are
   used, the MN performs Neighbor Unreachability Detection (NUD)
   [RFC4861], after attaching to a new link, probing the reachability of
   its default router.  If the new router's interface is configured to
   respond to queries sent to link-layer addresses than its own (e.g.,
   set to promiscuous mode), then it can respond to the NUD probe,
   providing its link-layer address in the solicited Neighbor
   Advertisement.  Implementations should allow the MN 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                        .
     .                                                               .
     |                                                               |
     +---------------------------------------------------------------+

   IP Fields:

   Source Address

                       The IP address of 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.

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   U flag      Buffer flag.  Same as [RFC5568].

   P flag      Proxy flag.  Used to distinguish the message from that
               defined in [RFC5568] and to indicate that it follows the
               specification in this document.

   F flag      Forwarding flag.  Used to request to forward the packets
               for the MN.

   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 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 in both 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].  At least one mobility option MUST
   uniquely identify the target MN (e.g., the Mobile Node Identifier
   Option defined in RFC4283) and the transferred context MUST be for
   one MN per message.  In addition, the NAR can request necessary
   mobility options by the Context Request Option defined in this
   document.

   Context Request Option

            This option MAY be present to request context information
            typically by the NAR to the PAR in the NAR-initiated fast
            handover.

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:

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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
                                     +-------------------------------+
                                     |           Sequence #          |
     +-+-+-+---------+---------------+-------------------------------+
     |U|P|F|Reserved |      Code     |                               |
     +-+-+-+---------+---------------+                               |
     |                                                               |
     .                                                               .
     .                       Mobility options                        .
     .                                                               .
     |                                                               |
     +---------------------------------------------------------------+

   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      Used to distinguish the message from that defined in
               [RFC5568] and to indicate that it follows the
               specification in this document.

   F flag      Same as defined in Section 6.1.1.

   Code
               Code values 0 through 4 and 128 through 130 are defined
               in [RFC5568].  In this specification, the meaning of Code
               value 0 is modified, 128 through 130 are reused, and 5,
               6, 131 and 132 are newly defined.

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                       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 MN MUST be copied from the corresponding HI
   message and the transferred context MUST be for one MN per message.

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

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   MN IID mobility options).

      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  |
     +---------------------------------------------------------------+
     |                              ...                              |

   Option-Type    TBD1

   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 n'th requested option.

   Req-length-n   The length of the n'th requested option excluding the
                  Req-type-n and Req-length-n fields.

   In the case where there are only Req-type-n and Req-length-n fields,
   the value of the Req-length-n is set to zero.  If additional
   information besides the Req-type-n is necessary to uniquely specify
   the requested context, such information follows after the
   Req-length-n.  For example, when the requested context is the Vendor-
   Specific Option described in Section 6.2.8, the requested option
   format looks as follows:

     |                              ...                              |
     +---------------+---------------+-------------------------------+
     | Req-type-N=19 | Req-length-N=5|           Vendor-ID           |
     +-------------------------------+---------------+---------------+
     |           Vendor-ID           |   Sub-Type    |               |
     +-----------------------------------------------+               |
     |                              ...                              |

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   The exact values in the Vendor-ID and Sub-Type are outside the scope
   of this document.

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 MN is
   currently registered.  The detailed definition of the LMAA is
   described in [RFC5213].

      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    TBD2

   Option-Length  18 or 6

   Option-Code

                  0  Reserved

                  1  IPv6 address of the LMA (LMAA)

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

6.2.3.  Mobile Node Interface Identifier (MN IID) Option

   This option is used to transfer the interface identifier of the MN
   that is used in the P-AN.

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

   Option-Type    TBD3

   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 of the MN that is used
                  in the P-AN.

6.2.4.  Home Network Prefix Option

   This option is used to transfer the home network prefix that is
   assigned to the MN in the P-AN.  The Home Network Prefix Option
   defined in [RFC5213] is used for this.

6.2.5.  Link-local Address Option

   This option is used to transfer the link-local address of the PAR
   (PMAG).  The Link-local Address Option defined in [RFC5213] is used
   for this.

6.2.6.  GRE Key Option

   This option is used to transfer the GRE Key for the MN's data flow
   over the bi-directional tunnel between the PAR and NAR.  The message
   format of this option follows the GRE Key Option defined in [GREKEY].
   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 MN runs in IPv4-only mode or
   dual-stack mode, it requires 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 the IPv4 Home

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   Address Request Option defined in [IPv4PMIPv6].

6.2.8.  Vendor-Specific Mobility Option

   This option is used to transfer any other information defined in this
   document.  The format of this option follows the Vendor-Specific
   Mobility Option defined in [RFC5094].  The exact values in the Vendor
   ID, Sub-Type and Data fields are outside the scope of this document.

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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 LMA 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 Acknowledgement (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 MAY be used to protect the MN's
   packets at the time of forwarding if protection of data traffic is
   required.

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8.  IANA Considerations

   This document defines three new mobility options, which are described
   in Section 6.2.  The Type value for these options are assigned from
   the same numbering space as allocated for the other mobility options,
   as defined in [RFC3775].

    Mobility Options
    Value  Description                              Reference
    -----  -------------------------------------    -------------
    TBD1   Context Request Option                   Section 6.2.1
    TBD2   Local Mobility Anchor Address Option     Section 6.2.2
    TBD3   Mobile Node Interface Identifier Option  Section 6.2.3

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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 working group mailing list.

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10.  References

10.1.  Normative References

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

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

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

   [RFC3775]  Johnson, D., "Mobility Support in IPv6", RFC 3775,
              June 2004.

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

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.

   [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.

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.

   [IPv4PMIPv6]
              Wakikawa, R., Ed. and S. Gundavelli, "IPv4 Support for
              Proxy Mobile IPv6",
               draft-ietf-netlmm-pmip6-ipv4-support-14.txt, July 2009.

   [GREKEY]   Muhanna, A., Ed., "GRE Key Option for Proxy Mobile IPv6",
               draft-ietf-netlmm-grekey-option-09.txt, May 2009.

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Appendix A.  Applicable Use Cases

A.1.  PMIPv6 Handoff Indication

   PMIPv6 [RFC5213] defines the Handoff Indicator Option and describes
   the type of the handoff and the values to set to the option.  This
   document proposes one approach to determining the handoff type by the
   NMAG when the handoff of the MN 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)

   By using the MN Interface Identifier (MN IID) option, which is
   defined in this document, the following solution can be considered.
   When the NMAG receives the MN IID used in the P-AN from the PMAG via
   the HI or HAck messages, the NMAG compares it with the new MN IID
   that is obtained from the MN in the N-AN.  If these two MN IIDs are
   the same, the handover type falls into 3) and the Handoff Indicator
   value is set to 3.  If these two MN IIDs are different, the handover
   is likely to be 2) since the HI/HAck message exchange implies that
   this is a handover not a multi-homing, 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 MN in the new
   network, 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 MN 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 none of them can be assumed, the NMAG
   may set the value to 4.

A.2.  Local Routing

   Section 6.10.3 in [RFC5213] describes that if 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 MN's detachment, it will continue to forward packets

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   locally forever.  This situation is more likely to happen in the
   reactive fast handover with WLAN access, which does not have the
   capability to detect the detachment of the MN in a timely manner.
   PFMIPv6 can be applied to handle this case.  When the MN attaches to
   the NMAG, it sends the HI message to the PMAG, which makes it realize
   the detachment of the MN.  The PMAG immediately stops the local
   routing and sends the packets for the MN towards the LMA, which in
   turn forwards them to the NMAG over the PMIPv6 tunnel.

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Appendix B.  Change Log

   Changes at -00

      *  Added separate sections for MH and ICMP.

      *  Clarified usage of HNP and IPv4-MN-HoA throughout the document.

      *  Added IANA Considerations.

      *  Added section on Other Considerations, including operation of
         uplink packets when using link-layer addresses, multiple
         interface usage and transmission of RA to withdraw HNP in the
         event of failure of PMIP6 registration.

      *  Revised Security Considerations.

   Changes from -00 to -01

      *  Removed ICMPv6-based message format.

      *  Clarified HI/HAck exchange in the predictive mode (step (e) in
         Figure 2).

      *  Clarified information retrieval about the PMAG in the reactive
         mode.

      *  Removed the extension to the GRE Key Option.

      *  Clarified the handoff type considerations in Appendix A.

      *  Home Network Prefix Option, Link-local Address Option and
         Vendor-Specific Mobility Option are added.

   Changes from -01 to -02

      *  Aligned HI/HAck message formats with
         draft-ietf-mipshop-rfc5268bis-00.txt.

      *  Revised Section 8 removing the request for the type assignment
         of HI/HAck Mobility Headers.

   Changes from -02 to -03

      *  Updated HI/HAck message formats according to
         draft-ietf-mipshop-rfc5268bis-01.txt.

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      *  Cleaned up Figure 2 and Figure 3.

      *  Moved PMIP domain boundary crossing situation in Section 4.1 to
         Appendix A.3.

      *  Removed the alternative protocol operation with an unsolicited
         HAck from Section 4.1.

      *  Modified Code values in the HAck message in order to avoid
         collision with those in draft-ietf-mipshop-rfc5268bis-01.txt.

      *  Clarified the usage scenarios of Context Request Option.

      *  Modified the description of Code values in the HAck message.

      *  Changed the container for the IPv4-LMAA from IPv4 Address
         option to the LMAA option.

      *  Made Confidentiality protection "SHOULD" for context transfer.

   Changes from -03 to -04

      *  Added more explanations about MIPv6, FMIPv6 and PMIPv6 in
         Abstract.

      *  Moved Figure 1 to Section 4.

      *  More clearly indicated the FMIPv6 messages that are not
         applicable in the PMIPv6 context.

      *  Mandated the support of IP Sec on the PMAG and NMAG in order to
         protect signaling and user packets and the context information.

      *  Added a new section for the inter-AR tunneling operation
         (Section 4.2).

      *  Added descriptions about the encapsulation type in Sections 4.1
         and 4.3.

      *  Added a description about buffering requirements on the MAG in
         Section 4.1.

      *  Added a description about the timing of L2 and L3 connection
         establishments in Section 4.1.

      *  Added a new section for PMIPv6-related fast handover issues
         (Section 5) and a description about preferable behaviors of the
         MN and MAG to reduce packet loss.

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      *  Added Acknowledgments section (Section 9).

      *  Added a new section for local routing in Appendix (A.2).

   Changes from -04 to -05

      *  Fixed Figure 2 (step (i)).

      *  Defined the Mobile Network Interface Identifier (MN-IID)
         mobility option in Section 6.2.4 (swapped with old Section
         6.2.5), and added it to IANA considerations (Section 8).

      *  Changed from SHOULD to MUST regarding the inclusion of the
         MN-ID, MN-HNP, MN-IID and the LMAA options in the HI message
         (step (c) in Section 4.1).

      *  The optional behavior of the NMAG that allows it to send uplink
         packets directly to the LMA before the PBU/PBA exchange was
         removed from section 4.2 (as out of scope).

      *  In Section A.3, the description about the HA address assignment
         from the NAR to the MN was removed (as out of scope).

   Changes from -05 to -06

      *  Added 'P' flag in the HI and Hack messages to distinguish them
         from those in FMIPv6.

      *  Made editorial corrections in Section 2 (Introduction), Section
         3 (Terminology), Section 4 (Protocol Overview) and Section 4.2
         (Inter-AR Tunneling Operation).

      *  Added a description on how forwarded packets should be handled
         in the access network at step (f) in Section 4.1.

      *  Added all types of encapsulation methods that should be
         supported in Section 4.1.

      *  Revised the Code values for the HI message in Section 6.1.1.

      *  Revised the Code values for the HAck message in Section 6.1.2
         and added a description of its usage at step (d) of the
         reactive handover mode in Section 4.1.

      *  Removed the definition of the IP Address Option in Section
         6.2.3 and moved to Section 6.2.7, which currently refers to the
         IPv4 Home Address Option defined by RFC5555.  Revised the IANA
         Consideration section accordingly.

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      *  Removed the Option-Code from the Mobile Node Identifier (MN
         IID) Option.

      *  Removed Appendix A.3 (Handling of PMIPv6/MIPv6 switching).

   Changes from -06 to -07

      *  Added explanations about defining and setting the 'P' flag for
         the HI and Hack messages in Sections 4 and 4.1.

      *  Corrected the references for the encapsulation types in Section
         4.1.

      *  Modified the Code values for the HI message in Section 6.1.1 to
         avoid overlapping with those in
         draft-ietf-mipshop-rfc5268bis-01.txt.

      *  Modified the reference for the IPv4 Address Option from RFC5555
         to [IPv4PMIPv6] in Section 6.2.7.

   Changes from -07 to -08

      *  Corrected the reference for the TLV-header UDP encapsulation in
         Section 4.1.

      *  Updated the version number of the reference document
         [IPv4PMIPv6] and the option name defined by that document in
         Section 6.2.7.

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Authors' Addresses

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

   Email: [email-masked]

   Kuntal Chowdhury
   Starent Networks
   30 International Place
   Tewksbury, MA  01876
   US

   Email: [email-masked]

   Rajeev Koodli
   Starent Networks
   30 International Place
   Tewksbury, MA  01876
   US

   Email: [email-masked]

   Basavaraj Patil
   Nokia
   6000 Connection Drive
   Irving, TX  75039
   US

   Email: [email-masked]

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

   Email: [email-masked]

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