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MULTIMOB Group                                              T C. Schmidt
Internet-Draft                                               HAW Hamburg
Intended status: Standards Track                            M. Waehlisch
Expires: April 23, 2013                             link-lab & FU Berlin
                                                               R. Koodli
                                                           Cisco Systems
                                                            G. Fairhurst
                                                  University of Aberdeen
                                                        October 20, 2012


   Multicast Listener Extensions for MIPv6 and PMIPv6 Fast Handovers
           draft-schmidt-multimob-fmipv6-pfmipv6-multicast-07

Abstract

   Fast handover protocols for MIPv6 and PMIPv6 define mobility
   management procedures that support unicast communication at reduced
   handover latency.  Fast handover base operations do not affect
   multicast communication, and hence do not accelerate handover
   management for native multicast listeners.  Many multicast
   applications like IPTV or conferencing, though, are comprised of
   delay-sensitive real-time traffic and will benefit from fast handover
   execution.  This document specifies extension of the Mobile IPv6 Fast
   Handovers (FMIPv6) and the Fast Handovers for Proxy Mobile IPv6
   (PFMIPv6) protocols to include multicast traffic management in fast
   handover operations.  This multicast support is provided first at the
   control plane by a management of rapid context transfer between
   access routers, second at the data plane by an optional fast traffic
   forwarding that MAY include buffering.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 23, 2013.




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Copyright Notice

   Copyright (c) 2012 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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Multicast Context Transfer between Access Routers  . . . .  6
     3.2.  Protocol Operations Specific to FMIPv6 . . . . . . . . . .  8
     3.3.  Protocol Operations Specific to PFMIPv6  . . . . . . . . . 10
   4.  Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 13
     4.1.  Protocol Operations Specific to FMIPv6 . . . . . . . . . . 13
       4.1.1.  Operations of the Mobile Node  . . . . . . . . . . . . 13
       4.1.2.  Operations of the Previous Access Router . . . . . . . 14
       4.1.3.  Operations of the New Access Router  . . . . . . . . . 15
     4.2.  Protocol Operations Specific to PFMIPv6  . . . . . . . . . 15
       4.2.1.  Operations of the Mobile Node  . . . . . . . . . . . . 15
       4.2.2.  Operations of the Previous MAG . . . . . . . . . . . . 15
       4.2.3.  Operations of the New MAG  . . . . . . . . . . . . . . 16
       4.2.4.  IPv4 Support Considerations  . . . . . . . . . . . . . 17
   5.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . . 18
     5.1.  Multicast Indicator for Proxy Router Advertisement
           (PrRtAdv)  . . . . . . . . . . . . . . . . . . . . . . . . 18
     5.2.  Extensions to Existing Mobility Header Messages  . . . . . 18
     5.3.  New Multicast Mobility Option  . . . . . . . . . . . . . . 18
     5.4.  New Multicast Acknowledgement Option . . . . . . . . . . . 20
     5.5.  Length Considerations: Number of Records and Addresses . . 22
     5.6.  MLD (IGMP) Compatibility Aspects . . . . . . . . . . . . . 22
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 23
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 23
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 24



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   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 25
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26

















































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1.  Introduction

   Mobile IPv6 [RFC3775] defines a network layer mobility protocol
   involving mobile nodes participation, while Proxy Mobile IPv6
   [RFC5213] provides a mechanism without requiring mobility protocol
   operations at a Mobile Node (MN).  Both protocols introduce traffic
   disruptions on handovers that may be intolerable in many application
   scenarios.  Mobile IPv6 Fast Handovers (FMIPv6) [RFC5568], and Fast
   Handovers for Proxy Mobile IPv6 (PFMIPv6) [RFC5949] improve these
   handover delays for unicast communication to the order of the maximum
   delay needed for link switching and signaling between Access Routers
   (ARs) or Mobile Access Gateways (MAGs) [FMIPv6-Analysis].

   No dedicated treatment of seamless multicast data reception has been
   proposed by any of the above protocols.  MIPv6 only roughly defines
   multicast for Mobile Nodes using a remote subscription approach or a
   home subscription through bi-directional tunneling via the Home Agent
   (HA).  Multicast forwarding services have not been specified at all
   in [RFC5213], but are subject to current specification [RFC6224].  It
   is assumed throughout this document that mechanisms and protocol
   operations are in place to transport multicast traffic to ARs.  These
   operations are referred to as 'JOIN/LEAVE' of an AR, while the
   explicit techniques to manage multicast transmission are beyond the
   scope of this document.

   Mobile multicast protocols need to serve applications such as IPTV
   with high-volume content streams to be distributed to potentially
   large numbers of receivers, and therefore should preserve the
   multicast nature of packet distribution and approximate optimal
   routing [RFC5757].  It is undesirable to rely on home tunneling for
   optimizing multicast.  Unencapsulated, native multicast transmission
   requires establishing forwarding state, which will not be transferred
   between access routers by the unicast fast handover protocols.  Thus
   multicast traffic will not experience expedited handover performance,
   but an MN - or its corresponding MAG in PMIPv6 - can perform remote
   subscriptions in each visited network.

   This document specifies extensions of FMIPv6 and PFMIPv6 for
   including multicast traffic management in fast handover operations.
   The solution common to both underlying protocols defines the per-
   group transfer of multicast contexts between ARs or MAGs.  The
   protocol defines corresponding message extensions necessary for
   carrying group context information independent of the particular
   handover protocol.  ARs or MAGs are then enabled to treat multicast
   traffic according to fast unicast handovers and with similar
   performance.  No protocol changes are introduced that prevent a
   multicast unaware node from performing fast handovers with multicast
   aware ARs or MAGs.



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   This specification is applicable when a mobile node has joined and
   maintains one or several multicast group subscriptions prior to
   undergoing a fast handover.  It does not introduce any requirements
   on the multicast routing protocols in use, nor are the ARs or MAGs
   assumed to be multicast routers.  It assumes network conditions,
   though, that allow native multicast reception in both, the previous
   and new access network.  Methods to bridge regions without native
   multicast connectivity are beyond the scope of this document.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].
   The use of the term, "silently ignore" is not defined in RFC 2119.
   However, the term is used in this document and can be similarly
   construed.

   This document uses the terminology of [RFC5568], [RFC5949],
   [RFC3775], and [RFC5213].  In addition, the following terms are
   introduced:


3.  Protocol Overview

   The reference scenario for multicast fast handover is illustrated in
   Figure 1.























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

               Figure 1: Reference Network for Fast Handover

3.1.  Multicast Context Transfer between Access Routers

   In a fast handover scenario (cf. Figure 1), ARs/MAGs establish a
   mutual binding and provide the capability to exchange context
   information concerning the MN.  This context transfer will be
   triggered by detecting MN's forthcoming move to a new AR and assist
   the MN to immediately resume communication on the new subnet link
   using its previous IP address.  In contrast to unicast, multicast
   stream reception does not primarily depend on address and binding
   cache management, but requires distribution trees to adapt so that
   traffic follows the movement of the MN.  This process may be
   significantly slower than fast handover management [RFC5757].
   Multicast listeners at handover may take the twofold advantage of
   including the multicast groups under subscription in context
   transfer.  First, the NAR can proactively join the desired groups as
   soon as it gains knowledge of them.  Second, multicast streams MAY be
   included in traffic forwarding via the tunnel established from PAR to
   NAR.

   There are two modes of operation in FMIPv6 and in PFMIPv6.  The



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   predictive mode allows for AR-binding and context transfer prior to
   an MN handover, while in the reactive mode, these steps are executed
   after detection that the MN has re-attached to NAR.  Details of the
   signaling schemes differ between FMIPv6 and PFMIPv6 and are outlined
   in Section 3.2 and Section 3.3.

   In a predictive fast handover, the access router (i.e., PAR (PMAG) in
   Figure 1) learns about the impending movement of the MN and
   simultaneously about the multicast group context as specified in
   Section 3.2 and Section 3.3.  Thereafter, PAR will initiate an AR-
   binding and context transfer by transmitting a HI message to NAR
   (NMAG).  HI is extended by multicast group states carried in mobility
   header options as defined in Section 5.3.  On reception of the HI
   message, NAR returns a multicast acknowledgement in its HACK answer
   that indicates its ability to support each requested group (see
   Section 5.4).  NAR (NMAG) expresses its willingness to receive
   multicast traffic from forwarding by PAR using standard MLD
   signaling.  There are several reasons to waive forwarding, e.g., the
   group could already be under native subscription or capacity
   constraints can hinder decapsulation of additional streams at the
   NAR.  On the previous network side, forwarding of multicast traffic
   can be in conflict with capacity or policy constraints of PAR.

   For the groups requested, PAR MAY add the tunnel interface to its
   multicast forwarding database, so that multicast streams can be
   forwarded in parallel to unicast traffic.  NAR, taking the role of an
   MLD proxy [RFC4605] with upstream router PAR, will submit an MLD
   report on this upstream tunnel interface to request the desired
   groups, but will terminate multicast forwarding [RFC3810] from PAR,
   as soon as group traffic natively arrives.  In addition, NAR
   immediately joins all groups that are not already under subscription
   using its native multicast upstream interface and loopback as
   downstream.  It starts to downstream multicast forwarding after the
   MN has arrived.

   In a reactive fast handover, PAR will learn about the movement of the
   MN, after the latter has re-associated with the new access network.
   Also from the new link, it will be informed about the multicast
   context of the MN.  As group membership information are present at
   the new access network prior to context transfer, MLD join signaling
   can proceed in parallel to HI/HACK exchange.  Following the context
   transfer, multicast data can be forwarded to the new access network
   using the PAR-NAR tunnel of the fast handover protocol.  Depending on
   the specific network topology though, multicast traffic for some
   groups may natively arrive before it is forwarded from PAR.

   In both modes of operation, it is the responsibility of the PAR
   (PMAG) to properly react on the departure of the MN in the context of



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   local group management.  Depending on the multicast state management,
   link type and MLD parameters deployed (cf., [RFC5757]), it is
   requested to take appropriate actions to adjust multicast service to
   requirements of the remaining nodes.

   In this way, the MN will be able to participate in multicast group
   communication with a handover performance comparable to that for
   unicast, while network resource consumption is minimized.

3.2.  Protocol Operations Specific to FMIPv6

   ARs that provide multicast support in FMIPv6 will advertise this
   general service by setting an indicator bit (M-bit) in its PrRtAdv
   message as defined in Section 5.1.  Additional details about the
   multicast service support, e.g., flavors and groups, will be
   exchanged within HI/HACK dialogs later at handovers.

   An MN operating FMIPv6 will actively initiate the handover management
   by submitting a fast binding update (FBU).  The MN, which is aware of
   the multicast groups it wishes to maintain, will attach mobility
   options containing its group states (see Section 5.3) to the FBU, and
   thereby inform ARs about its multicast context.  ARs will use these
   multicast context options for inter-AR context transfer.

   In predictive mode, FBU is issued on the previous link and received
   by PAR as displayed in Figure 2.  PAR will extract the multicast
   context options and append them to its HI message.  From the HACK
   message, PAR will redistribute the multicast acknowledgement by
   adding the corresponding mobility options to its FBACK message.  From
   receiving FBACK, the MN will learn about a per group multicast
   support in the new access network.  If some groups or a multicast
   flavour are not supported, it MAY decide on taking actions to
   compensate the missing service.  Note that the proactive multicast
   context transfer may proceed successfully, even if the MN misses the
   FBACK message on the previous link.
















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                  MN                    PAR                    NAR
                   |                     |                      |
                   |------RtSolPr------->|                      |
                   |<-----PrRtAdv--------|                      |
                   |                     |                      |
                   |                     |                      |
                   |---------FBU-------->|----------HI--------->|
                   | (Multicast MobOpt)  | (Multicast MobOpt)   |
                   |                     |                      |
                   |                     |<--------HAck---------|
                   |                     | (Multicast AckOpt)   |
                   |                     |                   Join to
                   |                     |                  Multicast
                   |                     |                   Groups
                   |                     |                      |
                   |       <-----FBack---|--FBack------>        |
                   |  (Multicast AckOpt) | (Multicast AckOpt)   |
                   |                     |                      |
                disconnect            optional                  |
                   |                   packet  ================>|
                   |                 forwarding                 |
                   |                     |                      |
                connect                  |                      |
                   |                     |                      |
                   |------------UNA --------------------------->|
                   |<=================================== deliver packets
                   |                                            |

            Figure 2: Predictive Multicast Handover for FMIPv6

   The call flow for reactive mode is visualized in Figure 3.  After
   attaching to the new access link and performing an unsolicited
   neighbor advertisement (UNA), the MN issues an FBU which NAR forwards
   to PAR without processing.  At this time, the MN is able to re-join
   all desired multicast groups without relying on AR assistance.
   Nevertheless, multicast context options are exchanged in the HI/HACK
   dialog to facilitate intermediate forwarding of requested streams.
   Note that group traffic possibly already arrives from a MN's
   subscription at the time NAR receives the HI message.  Such streams
   may be transparently excluded from forwarding by setting an
   appropriate multicast acknowledge option.  In any case, NAR MUST
   ensure that not more than one stream of the same group is forwarded
   to the MN.








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                  MN                    PAR                    NAR
                   |                     |                      |
                   |------RtSolPr------->|                      |
                   |<-----PrRtAdv--------|                      |
                   |                     |                      |
                disconnect               |                      |
                   |                     |                      |
                   |                     |                      |
                connect                  |                      |
                   |-------UNA-----------|--------------------->|
                   |-------FBU-----------|---------------------)|
                   | (Multicast MobOpt)  |<-------FBU----------)|
                   |                     |                      |
                Join to                  |                      |
               Multicast                 |                      |
                Groups                   |                      |
                   |                     |----------HI--------->|
                   |                     |  (Multicast MobOpt)  |
                   |                     |<-------HAck----------|
                   |                     |  (Multicast AckOpt)  |
                   |                     |                      |
                   |                     |(HI/HAck if necessary)|
                   |                     |                      |
                   |              FBack, optional               |
                   |              packet forwarding  ==========>|
                   |                     |                      |
                   |<=================================== deliver packets
                   |                                            |

             Figure 3: Reactive Multicast Handover for FMIPv6

3.3.  Protocol Operations Specific to PFMIPv6

   In a proxy mobile IPv6 environment, the MN remains agnostic of
   network layer changes, and fast handover procedures are operated by
   the access routers or MAGs.  The handover initiation, or the re-
   association respectively are managed by the access networks.
   Consequently, access routers need to be aware of multicast membership
   state at the mobile node.  There are two ways to obtain record of
   MN's multicast membership.  First, MAGs MAY perform an explicit
   tracking (cf., [RFC4605], [RFC6224]) or extract membership status
   from forwarding states at node-specific point-to-point links.
   Second, routers can perform general queries at handovers.  Both
   methods are equally applicable.  However, a router that does not
   operate explicit tracking MUST query its downstream links subsequent
   to handovers.  In either case, the PAR will become knowledgeable
   about multicast group subscriptions of the MN.




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   In predictive mode, the PMAG (PAR) will learn about the upcoming
   movement of the mobile node.  Without explicit tracking, it will
   immediately submit a general MLD query and learn about the multicast
   groups under subscription.  As displayed in Figure 4, it will
   initiate binding and context transfer with the NMAG (NAR) by issuing
   a HI message that is augmented by multicast contexts in the mobility
   options defined in Section 5.3.  NAR will extract multicast context
   information and act as described in Section 3.1.


                                             PMAG          NMAG
           MN           P-AN       N-AN        (PAR)         (NAR)
           |             |          |            |             |
           |    Report   |          |            |             |
           |---(MN ID,-->|          |            |             |
           |  New AP ID) |          |            |             |
           |             |    HO Indication      |             |
           |             |--(MN ID, New AP ID)-->|             |
           |             |          |            |             |
           |             |          |         Optional:        |
           |             |          |         MLD Query        |
           |             |          |            |             |
           |             |          |            |------HI---->|
           |             |          |            |(Multicast MobOpt)
           |             |          |            |             |
           |             |          |            |<---HAck-----|
           |             |          |            |(Multicast AckOpt)
           |             |          |            |             |
           |             |          |            |          Join to
           |             |          |            |         Multicast
           |             |          |            |          Groups
           |             |          |            |             |
           |             |          |            |HI/HAck(optional)
           |             |          |            |<- - - - - ->|
           |             |          |            |             |
           |             |          |     optional packet      |
           |             |          |       forwarding =======>|
       disconnect        |          |            |             |
           |             |          |            |             |
        connect          |          |            |             |
           |    MN-AN connection    |    AN-MAG connection     |
           |<----establishment----->|<----establishment------->|
           |             |          |  (substitute for UNA)    |
           |             |          |            |             |
           |<========================================== deliver packets
           |             |          |            |             |





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            Figure 4: Predictive Multicast Handover for PFMIPv6

   In reactive mode, the NMAG (NAR) will learn about MN's attachment to
   the N-AN and establish connectivity by means of PMIPv6 protocol
   operations.  However, it will have no knowledge about multicast state
   at the MN.  Triggered by a MN attachment, the NMAG will send a
   general MLD query and thereafter join the requested groups.  In the
   case of a reactive handover, the binding is initiated by NMAG, and
   the HI/HACK message semantic is inverted (see [RFC5949]).  For
   multicast context transfer, the NMAG attaches to its HI message those
   group identifiers it requests to be forwarded from PMAG.  Using the
   identical syntax in its multicast mobility option headers as defined
   in Section 5.4, PMAG acknowledges those requested groups in its HACK
   answer that it is willing to forward .  The corresponding call flow
   is displayed in Figure 5.




































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                                             PMAG          NMAG
           MN         P-AN       N-AN        (PAR)         (NAR)
           |           |          |            |             |
       disconnect      |          |            |             |
           |           |          |            |             |
        connect        |          |            |             |
           |           |          |            |             |
           |   MN-AN connection   |    AN-MAG connection     |
           |<---establishment---->|<----establishment------->|
           |           |          |(substitute for UNA & FBU)|
           |           |          |            |             |
           |           |          |            |         MLD Query
           |           |          |            |             |
           |           |          |            |          Join to
           |           |          |            |         Multicast
           |           |          |            |          Groups
           |           |          |                          |
           |           |          |            |<------HI----|
           |           |          |            |(Multicast MobOpt)
           |           |          |            |             |
           |           |          |            |---HAck----->|
           |           |          |            |(Multicast AckOpt)
           |           |          |            |             |
           |           |          |            |             |
           |           |          |            |HI/HAck(optional)
           |           |          |            |<- - - - - ->|
           |           |          |            |             |
           |           |          |    optional packet       |
           |           |          |       forwarding =======>|
           |           |          |            |             |
           |<======================================== deliver packets
           |           |          |            |             |


             Figure 5: Reactive Multicast Handover for PFMIPv6


4.  Protocol Details

4.1.  Protocol Operations Specific to FMIPv6

4.1.1.  Operations of the Mobile Node

   A Mobile Node willing to manage multicast traffic within fast
   handover operations will inform about its MLD listener state records
   within handover signaling.

   When sensing a handover in predictive mode, an MN will build a



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   Multicast Mobility Option as described in Section 5.3 that contains
   the MLD (IGMP) multicast listener state and append it to the Fast
   Binding Update (FBU) prior to signaling with PAR.  It will receive
   the Multicast Acknowledgement Option(s) as part of Fast Binding
   Acknowledge (FBack) (see Section 5.4) and learn about unsupported or
   prohibited groups at the NAR.  The MN MAY take appropriate actions
   like home tunneling to bridge missing multicast services in the new
   access network.  No multicast-specific operation is required by the
   MN when re-attaching in the new network besides standard FMIPv6
   signaling.

   In reactive mode, the MN appends an identical Multicast Mobility
   Option to FBU sent after its reconnect.  In response, it will learn
   about the Multicast Acknowledgement Option(s) from FBACK and expect
   corresponding multicast data.  Concurrently it joins all desired
   multicast groups (channels) directly on its newly established access
   link.

4.1.2.  Operations of the Previous Access Router

   A PAR will advertise its multicast support by setting the M-bit in
   PrRtAdv.

   In predictive mode, a PAR will receive the multicast listener state
   of a MN prior to handover from the Multicast Mobility Option appended
   to the FBU.  It will forward these records to NAR within HI messages
   and will expect Multicast Acknowledgement Option(s) in HACK, which
   itself is returned to the MN as an appendix to FBACK.  In performing
   multicast context exchange, the AR is instructed to include the PAR-
   to-NAR tunnel obtained from unicast handover management in its
   multicast downstream interfaces and await MLD listener reports from
   NAR.  In response to receiving multicast subscriptions, PAR will
   normally forward group data acting as a normal multicast router or
   proxy.  However, NAR MAY refuse to forward some or all of the
   multicast streams.

   In reactive mode, PAR will receive the FBU augmented by the Multicast
   Mobility Option from the new network, but will continue with an
   identical multicast record exchange in the HI/HACk dialog.  As in the
   predictive case, it will configure the PAR-to-NAR tunnel for
   multicast downstream and forward data according to MLD reports
   obtained from NAR, if capable of forwarding.

   In both modes, PAR will interpret the first of the two events, the
   departure of the MN or the reception of the Multicast Acknowledgement
   Option(s) as a multicast LEAVE message of the MN and react according
   to the signaling scheme deployed in the access network (i.e., MLD
   querying, explicit tracking).



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4.1.3.  Operations of the New Access Router

   NAR will advertise its multicast support by setting the M-bit in
   PrRtAdv.

   In predictive mode, a NAR will receive the multicast listener state
   of an expected MN from the Multicast Mobility Option appended to the
   HI message.  It will extract the MLD/IGMP records from the message
   and intersect the request subscription with its multicast service
   offer.  Further on it will adjoin the supported groups (channels) to
   the MLD listener state using loopback as downstream interface.  This
   will lead to suitable regular subscriptions on its native multicast
   upstream interface without additional forwarding.  Concurrently, NAR
   builds a Multicast Acknowledgement Option(s) (see Section 5.4)
   listing those groups (channels) unsupported on the new access link
   and returns them within HACK.  As soon as the bidirectional tunnel
   from PAR to NAR is operational, NAR joins the groups desired for
   forwarding on the tunnel link.

   In reactive mode, NAR will learn about the multicast listener state
   of a new MN from the Multicast Mobility Option appended to HI at a
   time, when the MN has already performed local subscriptions of the
   multicast service.  Thus NAR solely determines the intersection of
   requested and supported groups (channels) and issues the join
   requests for group forwarding on the PAR-NAR tunnel interface.

   In both modes, NAR MUST send a LEAVE message to the tunnel
   immediately after forwarding of a group (channel) becomes unneeded,
   e.g., after native multicast traffic arrives or group membership of
   the MN terminates.

4.2.  Protocol Operations Specific to PFMIPv6

4.2.1.  Operations of the Mobile Node

   A Mobile Node willing to participate in multicast traffic will join,
   maintain and leave groups as if located in the fixed Internet.  It
   will cooperate in handover indication as specified in [RFC5949] and
   required by its access link-layer technology.  No multicast-specific
   mobility actions nor implementations are required at the MN in a
   PMIPv6 domain.

4.2.2.  Operations of the Previous MAG

   A MAG receiving a handover indication for one of its MNs follows the
   predictive fast handover mode as a PMAG.  It MUST issue an MLD
   General Query immediately on its corresponding link unless it
   performs an explicit tracking on that link.  After gaining knowledge



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   of the multicast subscriptions of the MN, the PMAG builds a Multicast
   Mobility Option as described in Section 5.3 that contains the MLD
   (IGMP) multicast listener state.  If not empty, this Mobility Option
   is appended to the regular fast handover HI messages, or - in the
   case of unicast HI message being submitted prior to multicast state
   detection - sent in an additional HI message to the NMAG.  PMAG then
   waits for receiving the Multicast Acknowledgement Option(s) with HACK
   (see Section 5.4) and the creation of the bidirectional tunnel with
   NMAG.  Thereafter PMAG will add the tunnel to its downstream
   interfaces in the multicast forwarding database.  For those groups
   (channels) reported in the Multicast Acknowledgement Option(s), i.e.,
   not supported in the new access network, PMAG normally takes
   appropriate actions (e.g., forwarding, termination) in concordance
   with the network policy.  It SHOULD start forwarding traffic down the
   tunnel interface for those groups it receives an MLD listener report
   message from NMAG.  However, it MAY deny forwarding service.  After
   the departure of the MN and on the reception of LEAVE messages for
   groups/channels, PMAG MUST terminate forwarding of the specific
   groups and update its multicast forwarding database.  Correspondingly
   it issues a group/channel LEAVE to its upstream link, if no more
   listeners are present on its downstream links.

   A MAG receiving a HI message with Multicast Mobility Option for a
   currently attached node follows the reactive fast handover mode as a
   PMAG.  It will return Multicast Acknowledgement Option(s) (see
   Section 5.4) within HACK listing those groups/channels unsupported at
   NMAG.  It will add the bidirectional tunnel with NMAG to its
   downstream interfaces and will start forwarding multicast traffic for
   those groups it receives an MLD listener report message from NMAG.
   At the reception of LEAVE messages for groups (channels), PMAG MUST
   terminate forwarding of the specific groups and update its multicast
   forwarding database.  According to its multicast forwarding states,
   it MAY need to issue a group/channel LEAVE to its upstream link, if
   no more listeners are present on its downstream links.

   In both modes, PMAG will interpret the departure of the MN as a
   multicast LEAVE message of the MN and react according to the
   signaling scheme deployed in the access network (i.e., MLD querying,
   explicit tracking).

4.2.3.  Operations of the New MAG

   A MAG receiving a HI message with Multicast Mobility Option for a
   currently unattached node follows the predictive fast handover mode
   as NMAG.  It will decide on those multicast groups/channels it wants
   forwarded from the PMAG and builds a Multicast Acknowledgement Option
   (see Section 5.4) that enumerates only unwanted groups/channels.
   This Mobility Option is appended to the regular fast handover HACK



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   messages, or - in the case of unicast HACK message being submitted
   prior to multicast state acknowledgement - sent in an additional HACK
   message to the PMAG.  Immediately thereafter, NMAG SHOULD update its
   MLD listener state by the new groups/channels obtained from the
   Multicast Mobility Option.  Until the MN re-attaches, NMAG uses its
   loopback interface for downstream and does not forward traffic to the
   potential link of the MN.  NMAG SHOULD issue JOIN messages for those
   newly adopted groups to its regular multicast upstream interface.  As
   soon as the bidirectional tunnel with PMAG is established, NMAG
   additionally joins those groups/channels on the tunnel interface that
   it wants to receive by forwarding from PMAG.  NMAG MUST send a LEAVE
   message to the tunnel immediately after forwarding of a group/channel
   becomes unneeded, e.g., after native multicast traffic arrives or
   group membership of the MN terminates.

   A MAG experiencing a connection request for a MN without prior
   reception of a corresponding Multicast Mobility Option is operating
   in the reactive fast handover mode as NMAG.  Following the re-
   attachment, it immediately issues an MLD General Query to learn about
   multicast subscriptions of the newly arrived MN.  Using standard
   multicast operations, NMAG joins the missing groups (channels) on its
   regular multicast upstream interface.  Concurrently, it selects
   groups (channels) for forwarding from PMAG and builds a Multicast
   Mobility Option as described in Section 5.3 that contains the MLD
   (IGMP) multicast listener state.  If not empty, this Mobility Option
   is appended to the regular fast handover HI messages with the F flag
   set, or - in the case of unicast HI message being submitted prior to
   multicast state detection - sent in an additional HI message to the
   PMAG.  Upon reception of the Multicast Acknowledgement Option and
   upcoming of the bidirectional tunnel, NMAG additionally joins those
   groups/channels on the tunnel interface that it wants to receive by
   forwarding from PMAG.  When multicast streams arrive, the NMAG
   forwards data to the appropriate downlink(s).  NMAG MUST send a LEAVE
   message to the tunnel immediately after forwarding of a group/channel
   becomes unneeded, e.g., after native multicast traffic arrives or
   group membership of the MN terminates.

4.2.4.  IPv4 Support Considerations

   An MN in a PMIPv6 domain may use an IPv4 address transparently for
   communication as specified in [RFC5844].  For this purpose, LMAs can
   register IPv4-Proxy-CoAs in its Binding Caches and MAGs can provide
   IPv4 support in access networks.  Correspondingly, multicast
   membership management will be performed by the MN using IGMP.  For
   multiprotocol multicast support on the network side, IGMPv3 router
   functions are required at both MAGs (see Section 5.6 for
   compatibility considerations with previous IGMP versions).  Context
   transfer between MAGs can transparently proceed in HI/HACK message



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   exchanges by encapsulating IGMP multicast state records within
   Multicast Mobility Options (see Section 5.3 and Section 5.4 for
   details on message formats.

   It is worth mentioning the scenarios of a dual-stack IPv4/IPv6 access
   network, and the use of GRE tunneling as specified in[RFC5845].
   Corresponding implications and operations are discussed in the PMIP
   Multicast Base Deployment document, cf., [RFC6224].


5.  Message Formats

5.1.  Multicast Indicator for Proxy Router Advertisement (PrRtAdv)

   An FMIPv6 AR will indicate its multicast support by activating the
   M-bit in its Proxy Router Advertisements (PrRtAdv).  The message
   extension has the following format.
        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Type     |      Code     |           Checksum            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Subtype    |M|  Reserved   |           Identifier          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Options ...
       +-+-+-+-+-+-+-+-+-+-+-+-

     Figure 6: Multicast Indicator Bit for Proxy Router Advertisement
                             (PrRtAdv) Message

5.2.  Extensions to Existing Mobility Header Messages

   The fast handover protocols use a new IPv6 header type called
   Mobility Header as defined in [RFC3775].  Mobility headers can carry
   variable Mobility Options.

   Multicast listener context of an MN is transferred in fast handover
   operations from PAR/PMAG to NAR/NMAG within a new Multicast Mobility
   Option, and acknowledged by a corresponding Acknowledgement Option.
   Depending on the specific handover scenario and protocol in use, the
   corresponding option is included within the mobility option list of
   HI/HAck only (PFMIPv6), or of FBU/FBAck/HI/HAck (FMIPv6).

5.3.  New Multicast Mobility Option

   The Multicast Mobility Option contains the current listener state
   record of the MN obtained from the MLD Report message, and has the
   format displayed in Figure 7.



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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |   Length      | Option-Code   |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                    MLD (IGMP) Report Payload                  +
       ~                                                               ~
       ~                                                               ~
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 7: Mobility Header Multicast Option

   Type: TBD

   Length: 8-bit unsigned integer.  The size of this option in 8 octets
   including the Type, Option-Code, and Length fields.

   Option-Code:

      1: IGMPv3 Payload Type

      2: MLDv2 Payload Type

      3: IGMPv3 Payload Type from IGMPv2 Compatibility Mode

      4: MLDv2 Payload Type from MLDv1 Compatibility Mode

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

   MLD (IGMP) Report Payload: this field is composed of the MLD (IGMP)
   Report message after stripping its ICMP header.  Corresponding
   message formats are defined for MLDv2 in [RFC3810], and for IGMPv3 in
   [RFC3376].

   Figure 8 shows the Report Payload for MLDv2, while the payload format
   for IGMPv3 is defined corresponding to the IGMPv3 payload format (see
   Section 5.2. of [RFC3810], or Section 4.2 of [RFC3376]) for the
   definition of Multicast Address Records).






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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Reserved            |No of Mcast Address Records (M)|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |     .                                                               .
    .                  Multicast Address Record [1]                 .
    .                                                               .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                                                               .
    .                  Multicast Address Record [2]                 .
    .                                                               .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               .                               |
    .                               .                               .
    |                               .                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                                                               .
    .                  Multicast Address Record [M]                 .
    .                                                               .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 8: MLDv2 Report Payload

5.4.  New Multicast Acknowledgement Option

   The Multicast Acknowledgement Option reports the status of the
   context transfer and contains the list of state records that could
   not be successfully transferred to the next access network.  It has
   the format displayed in Figure 9.
















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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |   Length      | Option-Code   |    Status     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +           MLD (IGMP) Unsupported Report Payload               +
       ~                                                               ~
       ~                                                               ~
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 9: Mobility Header Multicast Acknowledgement Option

   Type: TBD

   Length: 8-bit unsigned integer.  The size of this option in 8 octets.
   The length is 1 when the MLD (IGMP) Unsupported Report Payload field
   contains no Mcast Address Record.

   Option-Code: 0

   Status:

      1: Report Payload type unsupported

      2: Requested group service unsupported

      3: Requested group service administratively prohibited

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

   MLD (IGMP) Unsupported Report Payload: this field is syntactically
   identical to the MLD (IGMP) Report Payload field described in
   Section 5.3, but is only composed of those multicast address records
   that are not supported or prohibited in the new access network.  This
   field MUST always contain the first header line (reserved field and
   No of Mcast Address Records), but MUST NOT contain any Mcast Address
   Records, if the status code equals 1.

   Note that group subscriptions to specific sources may be rejected at
   the destination network, and thus the composition of multicast
   address records may differ from initial requests within an MLD (IGMP)



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   Report Payload option.

5.5.  Length Considerations: Number of Records and Addresses

   Mobility Header Messages exchanged in HI/HACK and FBU/FBACK dialogs
   impose length restrictions on multicast context records.  The maximal
   payload length available in FBU/FBACK messages is the PATH-MTU - 40
   octets (IPv6 Header) - 6 octets (Mobility Header) - 6 octets (FBU/
   FBACK Header).  For example, on an Ethernet link with an MTU of 1500
   octets, not more than 72 Multicast Address Records of minimal length
   (without source states) may be exchanged in one message pair.  In
   typical handover scenarios, this number reduces further according to
   unicast context and Binding Authorization data.  A larger number of
   MLD Report Payloads MAY be sent within multiple HI/HACK or FBU/FBACK
   message pairs.  In PFMIPv6, context information can be fragmented
   over several HI/HACK messages.  However, a single MLDv2 Report
   Payload MUST NOT be fragmented.  Hence, for a single Multicast
   Address Record on an Ethernet link, the number of source addresses is
   limited to 89.

5.6.  MLD (IGMP) Compatibility Aspects

   Access routers (MAGs) MUST support MLDv2 (IGMPv3).  To enable
   multicast service for MLDv1 (IGMPv2) listeners, the routers MUST
   follow the interoperability rules defined in [RFC3810] ([RFC3376])
   and appropriately set the Multicast Address Compatibility Mode.  When
   the Multicast Address Compatibility Mode is MLDv1 (IGMPv2), a router
   internally translates the following MLDv1 (IGMPv2) messages for that
   multicast address to their MLDv2 (IGMPv2) equivalents and uses these
   messages in the context transfer.  The current state of Compatibility
   Mode is translated into the code of the Multicast Mobility Option as
   defined in Section 5.3.  A NAR (nMAG) receiving a Multicast Mobility
   Option during handover will switch to the minimum obtained from its
   previous and newly learned value of MLD (IGMP) Compatibility Mode for
   continued operation.


6.  Security Considerations

   Security vulnerabilities that exceed issues discussed in the base
   protocols of this document ([RFC5568], [RFC5949], [RFC3810],
   [RFC3376]) are identified as follows.

   Multicast context transfer at predictive handovers implements group
   states at remote access routers and may lead to group subscriptions
   without further validation of the multicast service requests.
   Thereby a NAR (nMAG) is requested to cooperate in potentially complex
   multicast re-routing and may receive large volumes of traffic.



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   Malicious or inadvertent multicast context transfers may result in a
   significant burden of route establishment and traffic management onto
   the backbone infrastructure and the access router itself.  Rapid re-
   routing or traffic overload can be mitigated by a rate control at the
   AR that restricts the frequency of traffic redirects and the total
   number of subscriptions.  In addition, the wireless access network
   remains protected from multicast data injection until the requesting
   MN attaches to the new location.


7.  IANA Considerations

   This document defines new flags and status codes in the HI and HAck
   messages as well as two new mobility options.  The Type values for
   these mobility options are assigned from the same numbering space as
   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], or [RFC5949] and requested to
   be 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].


8.  Acknowledgments

   Protocol extensions to support multicast in Fast Mobile IPv6 have
   been loosely discussed since several years.  Repeated attempts have
   been taken to define corresponding protocol extensions.  The first
   draft [fmcast-mip6] was presented by Suh, Kwon, Suh, and Park already
   in 2004.

   This work was stimulated by many fruitful discussions in the MobOpts
   research group.  We would like to thank all active members for
   constructive thoughts and contributions on the subject of multicast
   mobility.  Comments, discussions and reviewing remarks have been
   contributed by (in alphabetical order) Carlos J. Bernardos, Luis M.
   Contreras, Dirk von Hugo, Marco Liebsch, Behcet Sarikaya, Stig Venaas
   and Juan Carlos Zuniga.


9.  References

9.1.  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



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              in IPv6", RFC 3775, June 2004.

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

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

   [RFC5949]  Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F.
              Xia, "Fast Handovers for Proxy Mobile IPv6", RFC 5949,
              September 2010.

   [RFC1112]  Deering, S., "Host extensions for IP multicasting", STD 5,
              RFC 1112, August 1989.

   [RFC4605]  Fenner, B., He, H., Haberman, B., and H. Sandick,
              "Internet Group Management Protocol (IGMP) / Multicast
              Listener Discovery (MLD)-Based Multicast Forwarding
              ("IGMP/MLD Proxying")", RFC 4605, August 2006.

   [RFC3810]  Vida, R. and L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, October 2002.

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

9.2.  Informative References

   [RFC5757]  Schmidt, T., Waehlisch, M., and G. Fairhurst, "Multicast
              Mobility in Mobile IP Version 6 (MIPv6): Problem Statement
              and Brief Survey", RFC 5757, February 2010.

   [fmcast-mip6]
              Suh, K., Kwon, D., Suh, Y., and Y. Park, "Fast Multicast
              Protocol for Mobile IPv6 in the fast handovers
              environments", draft-suh-mipshop-fmcast-mip6-00 (work in
              progress), July 2004.

   [FMIPv6-Analysis]
              Schmidt, TC. and M. Waehlisch, "Predictive versus Reactive
              - Analysis of Handover Performance and Its Implications on
              IPv6 and Multicast Mobility", Telecommunication
              Systems Vol 33, No. 1-3, pp. 131-154, November 2005.



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   [RFC6224]  Schmidt, T., Waehlisch, M., and S. Krishnan, "Base
              Deployment for Multicast Listener Support in Proxy Mobile
              IPv6 (PMIPv6) Domains", RFC 6224, April 2011.

   [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.


Appendix A.  Change Log

   The following changes have been made from
   draft-schmidt-multimob-fmipv6-pfmipv6-multicast-04.

   1.  Following working group feedback, multicast traffic forwarding is
       now a two-sided option between PAR (PMAG) and NAR (NMAG): Either
       access router can decide on its contribution to the data plane.

   2.  Several editorial improvements.

   The following changes have been made from
   draft-schmidt-multimob-fmipv6-pfmipv6-multicast-03.

   1.  References updated.

   The following changes have been made from
   draft-schmidt-multimob-fmipv6-pfmipv6-multicast-02.

   1.  Detailed operations on PFMIPv6 entities completed.

   2.  Some editorial improvements & clarifications.

   3.  References updated.

   The following changes have been made from
   draft-schmidt-multimob-fmipv6-pfmipv6-multicast-01.

   1.  First detailed operations on PFMIPv6 added.

   2.  IPv4 support considerations for PFMIPv6 added.

   3.  Section on length considerations for multicast context records
       corrected.





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   4.  Many editorial improvements & clarifications.

   5.  References updated.

   The following changes have been made from
   draft-schmidt-multimob-fmipv6-pfmipv6-multicast-00.

   1.  Editorial improvements & clarifications.

   2.  Section on length considerations for multicast context records
       added.

   3.  Section on MLD/IGMP compatibility aspects added.

   4.  Security section added.


Authors' Addresses

   Thomas C. Schmidt
   HAW Hamburg
   Dept. Informatik
   Berliner Tor 7
   Hamburg,   D-20099
   Germany

   Email: schmidt@informatik.haw-hamburg.de


   Matthias Waehlisch
   link-lab & FU Berlin
   Hoenower Str. 35
   Berlin  D-10318
   Germany

   Email: mw@link-lab.net


   Rajeev Koodli
   Cisco Systems
   30 International Place
   Xuanwu District,
   Tewksbury  MA 01876
   USA

   Email: rkoodli@cisco.com





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   Godred Fairhurst
   University of Aberdeen
   School of Engineering
   Aberdeen  AB24 3UE
   UK

   Email: gorry@erg.abdn.ac.uk












































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