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Versions: (draft-bernardos-dmm-pmipv6-dlif) 00 01 02 03 04 05 06

DMM Working Group                                          CJ. Bernardos
Internet-Draft                                            A. de la Oliva
Intended status: Experimental                                       UC3M
Expires: September 9, 2020                                      F. Giust
                                                                 Athonet
                                                              JC. Zuniga
                                                                  SIGFOX
                                                               A. Mourad
                                                            InterDigital
                                                           March 8, 2020


    Proxy Mobile IPv6 extensions for Distributed Mobility Management
                     draft-ietf-dmm-pmipv6-dlif-06

Abstract

   Distributed Mobility Management solutions allow for setting up
   networks so that traffic is distributed in an optimal way and does
   not rely on centrally deployed anchors to provide IP mobility
   support.

   There are many different approaches to address Distributed Mobility
   Management, as for example extending network-based mobility protocols
   (like Proxy Mobile IPv6), or client-based mobility protocols (like
   Mobile IPv6), among others.  This document follows the former
   approach and proposes a solution based on Proxy Mobile IPv6 in which
   mobility sessions are anchored at the last IP hop router (called
   mobility anchor and access router).  The mobility anchor and access
   router is an enhanced access router which is also able to operate as
   a local mobility anchor or mobility access gateway, on a per prefix
   basis.  The document focuses on the required extensions to
   effectively support simultaneously anchoring several flows at
   different distributed gateways.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

Status of This Memo

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




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Copyright Notice

   Copyright (c) 2020 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
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   publication of this document.  Please review these documents
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  PMIPv6 DMM extensions . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Initial registration  . . . . . . . . . . . . . . . . . .   7
     3.2.  The CMD as PBU/PBA relay  . . . . . . . . . . . . . . . .   8
     3.3.  The CMD as MAAR locator . . . . . . . . . . . . . . . . .  11
     3.4.  The CMD as MAAR proxy . . . . . . . . . . . . . . . . . .  12
     3.5.  De-registration . . . . . . . . . . . . . . . . . . . . .  13
     3.6.  Retransmissions and Rate Limiting . . . . . . . . . . . .  14
     3.7.  The Distributed Logical Interface (DLIF) concept  . . . .  14
   4.  Message Format  . . . . . . . . . . . . . . . . . . . . . . .  18
     4.1.  Proxy Binding Update  . . . . . . . . . . . . . . . . . .  18
     4.2.  Proxy Binding Acknowledgment  . . . . . . . . . . . . . .  19
     4.3.  Anchored Prefix Option  . . . . . . . . . . . . . . . . .  19
     4.4.  Local Prefix Option . . . . . . . . . . . . . . . . . . .  21
     4.5.  Previous MAAR Option  . . . . . . . . . . . . . . . . . .  22
     4.6.  Serving MAAR Option . . . . . . . . . . . . . . . . . . .  23
     4.7.  DLIF Link-local Address Option  . . . . . . . . . . . . .  24
     4.8.  DLIF Link-layer Address Option  . . . . . . . . . . . . .  25



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   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  26
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  27
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  27
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28

1.  Introduction

   The Distributed Mobility Management (DMM) paradigm aims at minimizing
   the impact of currently standardized mobility management solutions
   which are centralized (at least to a considerable extent) [RFC7333].

   Current IP mobility solutions, standardized with the names of Mobile
   IPv6 [RFC6275], or Proxy Mobile IPv6 (PMIPv6) [RFC5213], just to cite
   the two most relevant examples, offer mobility support at the cost of
   handling operations at a cardinal point, the mobility anchor (i.e.,
   the home agent for Mobile IPv6, and the local mobility anchor for
   Proxy Mobile IPv6), and burdening it with data forwarding and control
   mechanisms for a great amount of users.  As stated in [RFC7333],
   centralized mobility solutions are prone to several problems and
   limitations: longer (sub-optimal) routing paths, scalability
   problems, signaling overhead (and most likely a longer associated
   handover latency), more complex network deployment, higher
   vulnerability due to the existence of a potential single point of
   failure, and lack of granularity of the mobility management service
   (i.e., mobility is offered on a per-node basis, not being possible to
   define finer granularity policies, as for example per-application).

   The purpose of Distributed Mobility Management is to overcome the
   limitations of the traditional centralized mobility management
   [RFC7333] [RFC7429]; the main concept behind DMM solutions is indeed
   bringing the mobility anchor closer to the Mobile Node (MN).
   Following this idea, the central anchor is moved to the edge of the
   network, being deployed in the default gateway of the mobile node.
   That is, the first elements that provide IP connectivity to a set of
   MNs are also the mobility managers for those MNs.  In this document,
   we call these entities Mobility Anchors and Access Routers (MAARs).

   This document focuses on network-based DMM, hence the starting point
   is making PMIPv6 work in a distributed manner [RFC7429].  Mobility is
   handled by the network without the MNs involvement, but, differently
   from PMIPv6, when the MN moves from one access network to another, it
   may also change anchor router, hence requiring signaling between the
   anchors to retrieve the MN's previous location(s).  Also, a key-
   aspect of network-based DMM, is that a prefix pool belongs
   exclusively to each MAAR, in the sense that those prefixes are



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   assigned by the MAAR to the MNs attached to it, and they are routable
   at that MAAR.  Prefixes are assigned to MNs attached a MAAR at that
   time, but remain with those MNs as mobility occurs, remaining always
   routable at that MAAR as well as towards the MN itself.

   We consider partially distributed schemes, where only the data plane
   is distributed among access routers similar to MAGs, whereas the
   control plane is kept centralized towards a cardinal node used as
   information store, but relieved from any route management and MN's
   data forwarding task.

2.  Terminology

   The following terms used in this document are defined in the Proxy
   Mobile IPv6 specification [RFC5213]:

      Local Mobility Anchor (LMA)

      Mobile Access Gateway (MAG)

      Mobile Node (MN)

      Binding Cache Entry (BCE)

      Proxy Care-of Address (P-CoA)

      Proxy Binding Update (PBU)

      Proxy Binding Acknowledgement (PBA)

   The following terms are used in this document:

   Home Control-Plane Anchor (Home-CPA or H-CPA):  The Home-CPA function
      hosts the mobile node (MN)'s mobility session.  There can be more
      than one mobility session for a mobile node and those sessions may
      be anchored on the same or different Home-CPA's.  The home-CPA
      will interface with the home-DPA for managing the forwarding
      state.



   Home Data Plane Anchor (Home-DPA or H-DPA):  The Home-DPA is the
      topological anchor for the MN's IP address/ prefix(es).  The Home-
      DPA is chosen by the Home-CPA on a session- basis.  The Home-DPA
      is in the forwarding path for all the mobile node's IP traffic.






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   Access Control Plane Node (Access-CPN or A-CPN):  The Access-CPN is
      responsible for interfacing with the mobile node's Home-CPA and
      with the Access-DPN.  The Access-CPN has a protocol interface to
      the Home-CPA.



   Access Data Plane Node (Access-DPN or A-DPN):  The Access-DPN
      function is hosted on the first-hop router where the mobile node
      is attached.  This function is not hosted on a layer-2 bridging
      device such as a eNode(B) or Access Point.



   The following terms are defined and used in this document:

   MAAR (Mobility Anchor and Access Router).  First hop router where the
      mobile nodes attach to.  It also plays the role of mobility
      manager for the IPv6 prefixes it anchors, running the
      functionalities of PMIP's MAG and LMA.  Depending on the prefix,
      it plays the role of Access-DPN, Home-DPA and Access-CPN.

   CMD (Central Mobility Database).  The node that stores the BCEs
      allocated for the MNs in the mobility domain.  It plays the role
      of Home-CPA.

   P-MAAR (Previous MAAR).  When a MN moves to a new point of attachment
      a new MAAR might be allocated as its anchor point for future IPv6
      prefixes.  The MAAR that served the MN prior to new attachment
      becomes the P-MAAR.  It is still the anchor point for the IPv6
      prefixes it had allocated to the MN in the past and serves as the
      Home-DPA for flows using these prefixes.  There might be several
      P-MAARs serving a MN when the MN is frequently switching points of
      attachment while maintaining long-lasting flows.

   S-MAAR (Serving MAAR).  The MAAR which the MN is currently attached
      to.  Depending on the prefix, it plays the role of Access-DPN,
      Home-DPA and Access-CPN.

   Anchoring MAAR.  A MAAR anchoring an IPv6 prefix used by an MN.

   DLIF (Distributed Logical Interface).  It is a logical interface at
      the IP stack of the MAAR.  For each active prefix used by the MN,
      the S-MAAR has a DLIF configured (associated to each MAAR still
      anchoring flows).  In this way, an S-MAAR exposes itself towards
      each MN as multiple routers, one as itself and one per P-MAAR.





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3.  PMIPv6 DMM extensions

   The solution consists of de-coupling the entities that participate in
   the data and the control planes: the data plane becomes distributed
   and managed by the MAARs near the edge of the network, while the
   control plane, besides those on the MAARs, relies on a central entity
   called Central Mobility Database (CMD).  In the proposed
   architecture, the hierarchy present in PMIPv6 between LMA and MAG is
   preserved, but with the following substantial variations:

   o  The LMA is relieved from the data forwarding role, only the
      Binding Cache and its management operations are maintained.  Hence
      the LMA is renamed into CMD, which is therefore a Home-CPA.  Also,
      the CMD is able to send and parse both PBU and PBA messages.

   o  The MAG is enriched with the LMA functionalities, hence the name
      Mobility Anchor and Access Router (MAAR).  It maintains a local
      Binding Cache for the MNs that are attached to it and it is able
      to send and parse PBU and PBA messages.

   o  The binding cache will be extended to include information
      regarding P-MAARs where the mobile node was anchored and still
      retains active data sessions.

   o  Each MAAR has a unique set of global prefixes (which are
      configurable), that can be allocated by the MAAR to the MNs, but
      must be exclusive to that MAAR, i.e. no other MAAR can allocate
      the same prefixes.

   The MAARs leverage the CMD to access and update information related
   to the MNs, stored as mobility sessions; hence, a centralized node
   maintains a global view of the network status.  The CMD is queried
   whenever a MN is detected to join/leave the mobility domain.  It
   might be a fresh attachment, a detachment or a handover, but as MAARs
   are not aware of past information related to a mobility session, they
   contact the CMD to retrieve the data of interest and eventually take
   the appropriate action.  The procedure adopted for the query and the
   message exchange sequence might vary to optimize the update latency
   and/or the signaling overhead.  Here is presented one method for the
   initial registration, and three different approaches for updating the
   mobility sessions using PBUs and PBAs.  Each approach assigns a
   different role to the CMD:

   o  The CMD is a PBU/PBA relay;

   o  The CMD is only a MAAR locator;

   o  The CMD is a PBU/PBA proxy.



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   The solution described in this document allows performing per-prefix
   anchoring decisions, to support e.g., some flows to be anchored at a
   central Home-DPA (like a traditional LMA) or to enable an application
   to switch to the locally anchored prefix to gain route optimization,
   as indicated in [RFC8563].  This type of per-prefix treatment would
   potentially require additional extensions to the MAARs and signaling
   between the MAARs and the MNs to convey the per-flow anchor
   preference (central, distributed), which are not covered in this
   document.

   Note that a MN may move across different MAARs, which might result in
   several P-MAARs existing at a given moment of time, each of them
   anchoring a different prefix used by the MN.

3.1.  Initial registration

   Initial registration is performed when an MN attaches to a network
   for the first time (rather than attaching to a new network after
   moving from a previous one).

   In this description (shown in Figure 1), it is assumed that:

   1.  The MN is attaching to MAAR1.

   2.  The MN is authorized to attach to the network.

   Upon MN attachment, the following operations take place:

   1.  MAAR1 assigns a global IPv6 prefix from its own prefix pool to
       the MN (Pref1).  It also stores this prefix (Pref1) in the
       locally allocated temporary Binding Cache Entry (BCE).

   2.  MAAR1 sends a PBU [RFC5213] with Pref1 and the MN's MN-ID to the
       CMD.

   3.  Since this is an initial registration, the CMD stores a BCE
       containing as primary fields the MN-ID, Pref1 and MAAR1's address
       as a Proxy-CoA.

   4.  The CMD replies with a PBA with the usual options defined in
       PMIPv6 [RFC5213], meaning that the MN's registration is fresh and
       no past status is available.

   5.  MAAR1 stores the BCE described in (1) and unicasts a Router
       Advertisement (RA) to the MN with Pref1.

   6.  The MN uses Pref1 to configure an IPv6 address (IP1) (e.g., with
       stateless auto-configuration, SLAAC).



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   Note that:

   1.  Alternative IPv6 auto-configuration mechanisms can also be used,
       though this document describes the SLAAC-based one.

   2.  IP1 is routable at MAAR1, in the sense that it is on the path of
       packets addressed to the MN.

   3.  MAAR1 acts as a plain router for packets destined to the MN, as
       no encapsulation nor special handling takes place.

   In the diagram shown in Figure 1 (and subsequent diagrams), the flow
   of packets is presented using '*'.

     +-----+      +---+                +--+
     |MAAR1|      |CMD|                |CN|
     +-----+      +---+                +*-+
        |           |                   *
       MN           |                   *     +---+
     attach.        |               *****    _|CMD|_
   detection        |         flow1 *       / +-+-+ \
        |           |               *      /    |    \
    local BCE       |               *     /     |     \
    allocation      |               *    /      |      \
        |--- PBU -->|           +---*-+-'    +--+--+    `+-----+
        |          BCE          |   * |      |     |     |     |
        |        creation       |MAAR1+------+MAAR2+-----+MAAR3|
        |<-- PBA ---|           |   * |      |     |     |     |
    local BCE       |           +---*-+      +-----+     +-----+
    finalized       |               *
        |           |         Pref1 *
        |           |              +*-+
        |           |              |MN|
        |           |              +--+

     Operations sequence                  Packets flow

                 Figure 1: First attachment to the network

   Note that the registration process does not change regardless of the
   CMD's modes (relay, locator or proxy) described next.  The procedure
   is depicted in Figure 1.

3.2.  The CMD as PBU/PBA relay

   Upon MN mobility, if the CMD behaves as PBU/PBA relay, the following
   operations take place:




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   1.  When the MN moves from its current point of attachment and
       attaches to MAAR2 (now the S-MAAR), MAAR2 reserves an IPv6 prefix
       (Pref2), it stores a temporary BCE, and it sends a PBU to the CMD
       for registration.

   2.  Upon PBU reception and BC lookup, the CMD retrieves an already
       existing entry for the MN, binding the MN-ID to its former
       location; thus, the CMD forwards the PBU to the MAAR indicated as
       Proxy CoA (MAAR1), including a new mobility option to communicate
       the S-MAAR's global address to MAAR1, defined as Serving MAAR
       Option in Section 4.6.  The CMD updates the P-CoA field in the
       BCE related to the MN with the S-MAAR's address.

   3.  Upon PBU reception, MAAR1 can install a tunnel on its side
       towards MAAR2 and the related routes for Pref1.  Then MAAR1
       replies to the CMD with a PBA (including the option mentioned
       before) to ensure that the new location has successfully changed,
       containing the prefix anchored at MAAR1 in the Home Network
       Prefix option.

   4.  The CMD, after receiving the PBA, updates the BCE populating an
       instance of the P-MAAR list.  The P-MAAR list is an additional
       field on the BCE that contains an element for each P-MAAR
       involved in the MN's mobility session.  The list element contains
       the P-MAAR's global address and the prefix it has delegated.
       Also, the CMD sends a PBA to the new S-MAAR, containing the
       previous Proxy-CoA and the prefix anchored to it embedded into a
       new mobility option called Previous MAAR Option (defined in
       Section 4.5), so that, upon PBA arrival, a bi-directional tunnel
       can be established between the two MAARs and new routes are set
       appropriately to recover the IP flow(s) carrying Pref1.

   5.  Now packets destined to Pref1 are first received by MAAR1,
       encapsulated into the tunnel and forwarded to MAAR2, which
       finally delivers them to their destination.  In uplink, when the
       MN transmits packets using Pref1 as source address, they are sent
       to MAAR2, as it is MN's new default gateway, then tunneled to
       MAAR1 which routes them towards the next hop to destination.
       Conversely, packets carrying Pref2 are routed by MAAR2 without
       any special packet handling both for uplink and downlink.











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   +-----+      +---+      +-----+           +--+            +--+
   |MAAR1|      |CMD|      |MAAR2|           |CN|            |CN|
   +-----+      +---+      +-----+           +*-+            +*-+
      |           |           |               *               *
      |           |          MN               *     +---+     *
      |           |        attach.        *****    _|CMD|_    *
      |           |          det.   flow1 *       / +-+-+ \   *flow2
      |           |<-- PBU ---|           *      /    |    \  *
      |          BCE          |           *     /     | *******
      |        check+         |           *    /      | *    \
      |        update         |       +---*-+-'    +--+-*+    `+-----+
      |<-- PBU*---|           |       |   * |      |    *|     |     |
   route          |           |       |MAAR1|______|MAAR2+-----+MAAR3|
   update         |           |       |   **(______)**  *|     |     |
      |--- PBA*-->|           |       +-----+      +-*--*+     +-----+
      |         BCE           |                      *  *
      |        update         |                Pref1 *  *Pref2
      |           |--- PBA*-->|                     +*--*+
      |           |         route         ---move-->|*MN*|
      |           |         update                  +----+

         Operations sequence                  Data Packets flow
   PBU/PBA Messages with * contain
        a new mobility option

             Figure 2: Scenario after a handover, CMD as relay

   For MN's next movements the process is repeated except the number of
   P-MAARs involved increases (accordingly to the number of prefixes
   that the MN wishes to maintain).  Indeed, once the CMD receives the
   first PBU from the new S-MAAR, it forwards copies of the PBU to all
   the P-MAARs indicated in the BCE, namely the one registered as
   current P-CoA (i.e., the MAAR prior to handover) plus the ones in the
   P-MAARs list.  They reply with a PBA to the CMD, which aggregates
   them into a single one to notify the S-MAAR, that finally can
   establish the tunnels with the P-MAARs.

   It should be noted that this design separates the mobility management
   at the prefix granularity, and it can be tuned in order to erase old
   mobility sessions when not required, while the MN is reachable
   through the latest prefix acquired.  Moreover, the latency associated
   to the mobility update is bound to the PBA sent by the furthest
   P-MAAR, in terms of RTT, that takes the longest time to reach the
   CMD.  The drawback can be mitigated introducing a timeout at the CMD,
   by which, after its expiration, all the PBAs so far collected are
   transmitted, and the remaining are sent later upon their arrival.
   Note that in this case the S-MAAR might receive multiple PBAs from
   the CMD in response to a PBU.  The CMD SHOULD follow the



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   retransmissions and rate limiting considerations described in
   Section 3.6, especially when aggregating and relaying PBAs.

   When there are multiple previous MAARs, e.g., k MAARs, a single PBU
   received by the CMD triggers k outgoing packets from a single
   incoming packet.  This may lead to packet bursts originated from the
   CMD, albeit to different targets.  Pacing mechanisms MUST be
   introduced to avoid bursts on the outgoing link.

3.3.  The CMD as MAAR locator

   The handover latency experienced in the approach shown before can be
   reduced if the P-MAARs are allowed to signal directly their
   information to the new S-MAAR.  This procedure reflects what was
   described in Section 3.2 up to the moment the P-MAAR receives the PBU
   with the S-MAAR option.  At that point a P-MAAR is aware of the new
   MN's location (because of the S-MAAR's address in the S-MAAR option),
   and, besides sending a PBA to the CMD, it also sends a PBA to the
   S-MAAR including the prefix it is anchoring.  This latter PBA does
   not need to include new options, as the prefix is embedded in the HNP
   option and the P-MAAR's address is taken from the message's source
   address.  The CMD is relieved from forwarding the PBA to the S-MAAR,
   as the latter receives a copy directly from the P-MAAR with the
   necessary information to build the tunnels and set the appropriate
   routes.  Figure 3 illustrates the new message sequence, while the
   data forwarding is unaltered.

























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   +-----+      +---+      +-----+           +--+            +--+
   |MAAR1|      |CMD|      |MAAR2|           |CN|            |CN|
   +-----+      +---+      +-----+           +*-+            +*-+
      |           |           |               *               *
      |           |          MN               *     +---+     *
      |           |        attach.        *****    _|CMD|_    *
      |           |          det.   flow1 *       / +-+-+ \   *flow2
      |           |<-- PBU ---|           *      /    |    \  *
      |          BCE          |           *     /     | *******
      |        check+         |           *    /      | *    \
      |        update         |       +---*-+-'    +--+-*+    `+-----+
      |<-- PBU*---|           |       |   * |      |    *|     |     |
   route          |           |       |MAAR1|______|MAAR2+-----+MAAR3|
   update         |           |       |   **(______)**  *|     |     |
      |--------- PBA -------->|       +-----+      +-*--*+     +-----+
      |--- PBA*-->|         route                    *  *
      |          BCE        update             Pref1 *  *Pref2
      |         update        |                     +*--*+
      |           |           |           ---move-->|*MN*|
      |           |           |                     +----+

          Operations sequence                  Data Packets flow
   PBU/PBA Messages with * contain
        a new mobility option

            Figure 3: Scenario after a handover, CMD as locator

3.4.  The CMD as MAAR proxy

   A further enhancement of previous solutions can be achieved when the
   CMD sends the PBA to the new S-MAAR before notifying the P-MAARs of
   the location change.  Indeed, when the CMD receives the PBU for the
   new registration, it is already in possession of all the information
   that the new S-MAAR requires to set up the tunnels and the routes.
   Thus the PBA is sent to the S-MAAR immediately after a PBU is
   received, including also in this case the P-MAAR option.  In
   parallel, a PBU is sent by the CMD to the P-MAARs containing the
   S-MAAR option, to notify them about the new MN's location, so they
   receive the information to establish the tunnels and routes on their
   side.  When P-MAARs complete the update, they send a PBA to the CMD
   to indicate that the operation is concluded and the information is
   updated in all network nodes.  This procedure is obtained from the
   first one re-arranging the order of the messages, but the parameters
   communicated are the same.  This scheme is depicted in Figure 4,
   where, again, the data forwarding is kept untouched.






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   +-----+      +---+      +-----+           +--+            +--+
   |MAAR1|      |CMD|      |MAAR2|           |CN|            |CN|
   +-----+      +---+      +-----+           +*-+            +*-+
      |           |           |               *               *
      |           |          MN               *     +---+     *
      |           |        attach.        *****    _|CMD|_    *
      |           |          det.   flow1 *       / +-+-+ \   *flow2
      |           |<-- PBU ---|           *      /    |    \  *
      |          BCE          |           *     /     | *******
      |        check+         |           *    /      | *    \
      |        update         |       +---*-+-'    +--+-*+    `+-----+
      |<-- PBU*---x--- PBA*-->|       |   * |      |    *|     |     |
   route          |         route     |MAAR1|______|MAAR2+-----+MAAR3|
   update         |         update    |   **(______)**  *|     |     |
      |--- PBA*-->|           |       +-----+      +-*--*+     +-----+
      |          BCE          |                      *  *
      |         update        |                Pref1 *  *Pref2
      |           |           |                     +*--*+
      |           |           |           ---move-->|*MN*|
      |           |           |                     +----+

          Operations sequence                 Data Packets flow
   PBU/PBA Messages with * contain
        a new mobility option

             Figure 4: Scenario after a handover, CMD as proxy

3.5.  De-registration

   The de-registration mechanism devised for PMIPv6 cannot be used as-is
   in this solution.  The reason for this is that each MAAR handles an
   independent mobility session (i.e., a single or a set of prefixes)
   for a given MN, whereas the aggregated session is stored at the CMD.
   Indeed, if a previous MAAR initiates a de-registration procedure,
   because the MN is no longer present on the MAAR's access link, it
   removes the routing state for that (those) prefix(es), that would be
   deleted by the CMD as well, hence defeating any prefix continuity
   attempt.  The simplest approach to overcome this limitation is to
   deny a P-MAAR to de-register a prefix, that is, allowing only a
   serving MAAR to de-register the whole MN session.  This can be
   achieved by first removing any layer-2 detachment event, so that de-
   registration is triggered only when the binding lifetime expires,
   hence providing a guard interval for the MN to connect to a new MAAR.
   Then, a change in the MAAR operations is required, and at this stage
   two possible solutions can be deployed:

   o  A previous MAAR stops the BCE timer upon receiving a PBU from the
      CMD containing a "Serving MAAR" option.  In this way only the



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      Serving MAAR is allowed to de-register the mobility session,
      arguing that the MN definitely left the domain.

   o  Previous MAARs can, upon BCE expiry, send de-registration messages
      to the CMD, which, instead of acknowledging the message with a 0
      lifetime, sends back a PBA with a non-zero lifetime, hence re-
      newing the session, if the MN is still connected to the domain.

3.6.  Retransmissions and Rate Limiting

   When sending PBUs, the node sending them (the CMD or S-MAAR) SHOULD
   make use of the timeout also to deal with missing PBAs (to retransmit
   PBUs).  The INITIAL_BINDACK_TIMEOUT [RFC6275] SHOULD be used for
   configuring the retransmission timer.  The retransmissions by the
   node MUST use an exponential backoff process in which the timeout
   period is doubled upon each retransmission, until either the node
   receives a response or the timeout period reaches the value
   MAX_BINDACK_TIMEOUT [RFC6275].  The node MAY continue to send these
   messages at this slower rate indefinitely.  The node MUST NOT send
   PBU messages to a particular node more than MAX_UPDATE_RATE times
   within a second [RFC6275].

3.7.  The Distributed Logical Interface (DLIF) concept

   One of the main challenges of a network-based DMM solution is how to
   allow a mobile node to simultaneously send/receive traffic which is
   anchored at different MAARs, and how to influence the mobile node's
   selection process of its source IPv6 address for a new flow, without
   requiring special support from the mobile node's IP stack.  This
   document defines the Distributed Logical Interface (DLIF), which is a
   software construct in the MAAR that allows to easily hide the change
   of associated anchors from the mobile node.



















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     +---------------------------------------------------+
    (                      Operator's                     )
    (                         core                        )
     +---------------------------------------------------+
               |                               |
       +---------------+     tunnel    +---------------+
       |   IP  stack   |===============|   IP  stack   |
       +---------------+               +-------+-------+
       |    mn1mar1    |--+ (DLIFs) +--|mn1mar1|mn1mar2|--+
       +---------------+  |         |  +-------+-------+  |
       | phy interface |  |         |  | phy interface |  |
       +---------------+  |         |  +---------------+  |
             MAAR1       (o)       (o)       MAAR2       (o)
                                      x                 x
                                        x             x
                           prefA::/64     x         x   prefB::/64
                         (AdvPrefLft=0)     x     x
                                              (o)
                                               |
                                            +-----+
                                prefA::MN1  | MN1 |  prefB::MN1
                               (deprecated) +-----+

        Figure 5: DLIF: exposing multiple routers (one per P-MAAR)

   The basic idea of the DLIF concept is the following: each serving
   MAAR exposes itself towards a given MN as multiple routers, one per
   P-MAAR associated to the MN.  Let's consider the example shown in
   Figure 5, MN1 initially attaches to MAAR1, configuring an IPv6
   address (prefA::MN1) from a prefix locally anchored at MAAR1
   (prefA::/64).  At this stage, MAAR1 plays both the role of anchoring
   and serving MAAR, and also behaves as a plain IPv6 access router.
   MAAR1 creates a distributed logical interface to communicate (point-
   to-point link) with MN1, exposing itself as a (logical) router with a
   specific MAC and IPv6 addresses (e.g., prefA::MAAR1/64 and
   fe80::MAAR1/64) using the DLIF mn1mar1.  As explained below, these
   addresses represent the "logical" identity of MAAR1 towards MN1, and
   will "follow" the mobile node while roaming within the domain (note
   that the place where all this information is maintained and updated
   is out-of-scope of this draft; potential examples are to keep it on
   the home subscriber server -- HSS -- or the user's profile).

   If MN1 moves and attaches to a different MAAR of the domain (MAAR2 in
   the example of Figure 5), this MAAR will create a new logical
   interface (mn1mar2) to expose itself towards MN1, providing it with a
   locally anchored prefix (prefB::/64).  In this case, since the MN1
   has another active IPv6 address anchored at a MAAR1, MAAR2 also needs
   to create an additional logical interface configured to resemble the



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   one used by MAAR1 to communicate with MN1.  In this example, there is
   only one P-MAAR (in addition to MAAR2, which is the serving one):
   MAAR1, so only the logical interface mn1mar1 is created, but the same
   process would be repeated in case there were more P-MAARs involved.
   In order to maintain the prefix anchored at MAAR1 reachable, a tunnel
   between MAAR1 and MAAR2 is established and the routing is modified
   accordingly.  The PBU/PBA signaling is used to set-up the bi-
   directional tunnel between MAAR1 and MAAR2, and it might also be used
   to convey to MAAR2 the information about the prefix(es) anchored at
   MAAR1 and about the addresses of the associated DLIF (i.e., mn1mar1).

   +------------------------------------------+ +----------------------+
   |                  MAAR1                   | |         MAAR2        |
   |+----------------------------------------+| |+--------------------+|
   ||+------------------++------------------+|| ||+------------------+||
   |||+-------++-------+||+-------++-------+||| |||+-------++-------+|||
   ||||mn3mar1||mn3mar2||||mn2mar1||mn2mar2|||| ||||mn1mar1||mn1mar2||||
   |||| LMAC1 || LMAC2 |||| LMAC3 || LMAC4 |||| |||| LMAC5 || LMAC6 ||||
   |||+-------++-------+||+-------++-------+||| |||+-------++-------+|||
   |||    LIFs of MN3   ||    LIFs of MN2   ||| |||   LIFs of MN1    |||
   ||+------------------++------------------+|| ||+------------------+||
   ||              MAC1   (phy if MAAR1)     || || MAC2 (phy if MAAR2)||
   |+----------------------------------------+| |+--------------------+|
   +------------------------------------------+ +----------------------+
                       x        x                            x
                      x          x                          x
                    (o)          (o)                      (o)
                     |            |                        |
                  +--+--+      +--+--+                  +--+--+
                  | MN3 |      | MN2 |                  | MN1 |
                  +-----+      +-----+                  +-----+

              Figure 6: Distributed Logical Interface concept

   Figure 6 shows the logical interface concept in more detail.  The
   figure shows two MAARs and three MNs.  MAAR1 is currently serving MN2
   and MN3, while MAAR2 is serving MN1.  Note that a serving MAAR always
   plays the role of anchoring MAAR for the attached (served) MNs.  Each
   MAAR has one single physical wireless interface as depicted in this
   example.

   As introduced before, each MN always "sees" multiple logical routers
   -- one per anchoring MAAR -- independently of its currently serving
   MAAR.  From the point of view of the MN, these MAARs are portrayed as
   different routers, although the MN is physically attached to one
   single interface.  The way this is achieved is by the serving MAAR
   configuring different logical interfaces.  Focusing on MN1, it is
   currently attached to MAAR2 (i.e., MAAR2 is its serving MAAR) and,



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   therefore, it has configured an IPv6 address from MAAR2's pool (e.g.,
   prefB::/64).  MAAR2 has set-up a logical interface (mn1mar2) on top
   of its wireless physical interface (phy if MAAR2) which is used to
   serve MN1.  This interface has a logical MAC address (LMAC6),
   different from the hardware MAC address (MAC2) of the physical
   interface of MAAR2.  Over the mn1mar2 interface, MAAR2 advertises its
   locally anchored prefix prefB::/64.  Before attaching to MAAR2, MN1
   was attached to MAAR1, configuring also an address locally anchored
   at that MAAR, which is still being used by MN1 in active
   communications.  MN1 keeps "seeing" an interface connecting to MAAR1,
   as if it were directly connected to the two MAARs.  This is achieved
   by the serving MAAR (MAAR2) configuring an additional distributed
   logical interface: mn1mar1, which behaves as the logical interface
   configured by MAAR1 when MN1 was attached to it.  This means that
   both the MAC and IPv6 addresses configured on this logical interface
   remain the same regardless of the physical MAAR which is serving the
   MN.  The information required by a serving MAAR to properly configure
   this logical interfaces can be obtained in different ways: as part of
   the information conveyed in the PBA, from an external database (e.g.,
   the HSS) or by other means.  As shown in the figure, each MAAR may
   have several logical interfaces associated to each attached MN,
   having always at least one (since a serving MAAR is also an anchoring
   MAAR for the attached MN).

   In order to enforce the use of the prefix locally anchored at the
   serving MAAR, the router advertisements sent over those logical
   interfaces playing the role of anchoring MAARs (different from the
   serving one) include a zero preferred prefix lifetime (and a non-zero
   valid prefix lifetime, so the prefix remains valid, while being
   deprecated).  The goal is to deprecate the prefixes delegated by
   these MAARs (so that they will no longer be serving the MN).  Note
   that on-going communications may keep on using those addresses, even
   if they are deprecated, so this only affects the establishment of new
   sessions.

   The distributed logical interface concept also enables the following
   use case: suppose that access to a local IP network is provided by a
   given MAAR (e.g., MAAR1 in the example shown in Figure 5) and that
   the resources available at that network cannot be reached from
   outside the local network (e.g., cannot be accessed by an MN attached
   to MAAR2).  This is similar to the local IP access scenario
   considered by 3GPP, where a local gateway node is selected for
   sessions requiring access to services provided locally (instead of
   going through a central gateway).  The goal is to allow an MN to be
   able to roam while still being able to have connectivity to this
   local IP network.  The solution adopted to support this case makes
   use of RFC 4191 [RFC4191] more specific routes when the MN moves to a
   MAAR different from the one providing access to the local IP network



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   (MAAR1 in the example).  These routes are advertised through the
   distributed logical interface representing the MAAR providing access
   to the local network (MAAR1 in this example).  In this way, if MN1
   moves from MAAR1 to MAAR2, any active session that MN1 may have with
   a node on the local network connected to MAAR1 will survive via the
   tunnel between MAAR1 and MAAR2.  Also, any potential future
   connection attempt towards the local network will be supported, even
   though MN1 is no longer attached to MAAR1.

4.  Message Format

   This section defines extensions to the Proxy Mobile IPv6 [RFC5213]
   protocol messages.

4.1.  Proxy Binding Update

   A new flag (D) is included in the Proxy Binding Update to indicate
   that the Proxy Binding Update is coming from a MAAR or a CMD and not
   from a mobile access gateway.  The rest of the Proxy Binding Update
   format remains the same as defined 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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |            Sequence #         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |A|H|L|K|M|R|P|F|T|B|S|D| Rsrvd |            Lifetime           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                                                               .
   .                        Mobility options                       .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   DMM Flag (D)

      The D Flag is set to indicate to the receiver of the message that
      the Proxy Binding Update is from a MAAR or a CMD.  When an LMA
      that does not support the extensions described in this document
      receives a message with the D-Flag set, the PBU in that case MUST
      NOT be processed by the LMA and an error MUST be returned.

   Mobility Options

      Variable-length field of such length that the complete Mobility
      Header is an integer multiple of 8 octets long.  This field
      contains zero or more TLV-encoded mobility options.  The encoding



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      and format of defined options are described in Section 6.2 of
      [RFC6275].  The receiving node MUST ignore and skip any options
      that it does not understand.

4.2.  Proxy Binding Acknowledgment

   A new flag (D) is included in the Proxy Binding Acknowledgment to
   indicate that the sender supports operating as a MAAR or CMD.  The
   rest of the Proxy Binding Acknowledgment format remains the same as
   defined 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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |   Status      |K|R|P|T|B|S|D| |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Sequence #            |           Lifetime            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                                                               .
   .                        Mobility options                       .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   DMM Flag (D)

      The D flag is set to indicate that the sender of the message
      supports operating as a MAAR or a CMD.  When a MAG that does not
      support the extensions described in this document receives a
      message with the D-Flag set, it MUST ignore the message and an
      error MUST be returned.

   Mobility Options

      Variable-length field of such length that the complete Mobility
      Header is an integer multiple of 8 octets long.  This field
      contains zero or more TLV-encoded mobility options.  The encoding
      and format of defined options are described in Section 6.2 of
      [RFC6275].  The MAAR MUST ignore and skip any options that it does
      not understand.

4.3.  Anchored Prefix Option

   A new Anchored Prefix option is defined for use with the Proxy
   Binding Update and Proxy Binding Acknowledgment messages exchanged
   between MAARs and CMDs.  Therefore, this option can only appear if
   the D bit is set in a PBU/PBA.  This option is used for exchanging



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   the mobile node's prefix anchored at the anchoring MAAR.  There can
   be multiple Anchored Prefix options present in the message.

   The Anchored Prefix Option has an alignment requirement of 8n+4.  Its
   format 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |   Length      |   Reserved    | Prefix Length |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                        Anchored Prefix                        +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      IANA-1.

   Length

      8-bit unsigned integer indicating the length of the option in
      octets, excluding the type and length fields.  This field MUST be
      set to 18.

   Reserved

      This field is unused for now.  The value MUST be initialized to 0
      by the sender and MUST be ignored by the receiver.

   Prefix Length

      8-bit unsigned integer indicating the prefix length in bits of the
      IPv6 prefix contained in the option.

   Anchored Prefix

      A sixteen-octet field containing the mobile node's IPv6 Anchored
      Prefix.  Only the first Prefix Length bits are valid for the
      Anchored Prefix.  The rest of the bits MUST be ignored.






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4.4.  Local Prefix Option

   A new Local Prefix option is defined for use with the Proxy Binding
   Update and Proxy Binding Acknowledgment messages exchanged between
   MAARs or between a MAAR and a CMD.  Therefore, this option can only
   appear if the D bit is set in a PBU/PBA.  This option is used for
   exchanging a prefix of a local network that is only reachable via the
   anchoring MAAR.  There can be multiple Local Prefix options present
   in the message.

   The Local Prefix Option has an alignment requirement of 8n+4.  Its
   format 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |   Length      |   Reserved    | Prefix Length |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                         Local Prefix                          +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      IANA-2.

   Length

      8-bit unsigned integer indicating the length of the option in
      octets, excluding the type and length fields.  This field MUST be
      set to 18.

   Reserved

      This field is unused for now.  The value MUST be initialized to 0
      by the sender and MUST be ignored by the receiver.

   Prefix Length

      8-bit unsigned integer indicating the prefix length in bits of the
      IPv6 prefix contained in the option.

   Local Prefix



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      A sixteen-octet field containing the IPv6 Local Prefix.  Only the
      first Prefix Length bits are valid for the IPv6 Local Prefix.  The
      rest of the bits MUST be ignored.

4.5.  Previous MAAR Option

   This new option is defined for use with the Proxy Binding
   Acknowledgement messages exchanged by the CMD to a MAAR.  This option
   is used to notify the S-MAAR about the previous MAAR's global address
   and the prefix anchored to it.  There can be multiple Previous MAAR
   options present in the message.  Its format is as follows:

   The Previous MAAR Option has an alignment requirement of 8n+4.  Its
   format 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |     Length    |   Reserved    | Prefix Length |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                     P-MAAR's address                          +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                    Home Network Prefix                        +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      IANA-3.

   Length

      8-bit unsigned integer indicating the length of the option in
      octets, excluding the type and length fields.  This field MUST be
      set to 34.

   Reserved



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      This field is unused for now.  The value MUST be initialized to 0
      by the sender and MUST be ignored by the receiver.

   Prefix Length

      8-bit unsigned integer indicating the prefix length in bits of the
      IPv6 prefix contained in the option.

   Previous MAAR's address

      A sixteen-octet field containing the P-MAAR's IPv6 global address.

   Home Network Prefix

      A sixteen-octet field containing the mobile node's IPv6 Home
      Network Prefix.  Only the first Prefix Length bits are valid for
      the mobile node's IPv6 Home Network Prefix.  The rest of the bits
      MUST be ignored.

4.6.  Serving MAAR Option

   This new option is defined for use with the Proxy Binding Update
   message exchanged between the CMD and a Previous MAAR.  This option
   is used to notify the P-MAAR about the current Serving MAAR's global
   address.  Its format is as follows:

   The Serving MAAR Option has an alignment requirement of 8n+6.  Its
   format 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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |      Type     |     Length    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                     S-MAAR's address                          +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      IANA-4.




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   Length

      8-bit unsigned integer indicating the length of the option in
      octets, excluding the type and length fields.  This field MUST be
      set to 16.

   Serving MAAR's address

      A sixteen-octet field containing the S-MAAR's IPv6 global address.

4.7.  DLIF Link-local Address Option

   A new DLIF Link-local Address option is defined for use with the
   Proxy Binding Acknowledgment message exchanged between MAARs and
   between a MAAR and a CMD.  This option is used for exchanging the
   link-local address of the DLIF to be configured on the serving MAAR
   so it resembles the DLIF configured on the P-MAAR.

   The DLIF Link-local Address option has an alignment requirement of
   8n+6.  Its format 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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |   Type        |    Length     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                  DLIF Link-local Address                      +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      IANA-5.

   Length

      8-bit unsigned integer indicating the length of the option in
      octets, excluding the type and length fields.  This field MUST be
      set to 16.

   DLIF Link-local Address





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      A sixteen-octet field containing the link-local address of the
      logical interface.

4.8.  DLIF Link-layer Address Option

   A new DLIF Link-layer Address option is defined for use with the
   Proxy Binding Acknowledgment message exchanged between MAARs and
   betwwe a MAAR and a CMD.  This option is used for exchanging the
   link-layer address of the DLIF to be configured on the serving MAAR
   so it resembles the DLIF configured on the P-MAAR.

   The format of the DLIF Link-layer Address option is shown below.
   Based on the size of the address, the option MUST be aligned
   appropriately, as per mobility option alignment requirements
   specified in [RFC6275].

    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     |          Reserved             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                    DLIF Link-layer Address                    +
   .                              ...                              .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      IANA-6.

   Length

      8-bit unsigned integer indicating the length of the option in
      octets, excluding the type and length fields.

   Reserved

      This field is unused for now.  The value MUST be initialized to 0
      by the sender and MUST be ignored by the receiver.

   DLIF Link-layer Address

      A variable length field containing the link-layer address of the
      logical interface to be configured on the S-MAAR.

      The content and format of this field (including octet and bit
      ordering) is as specified in Section 4.6 of [RFC4861] for carrying



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      link-layer addresses.  On certain access links, where the link-
      layer address is not used or cannot be determined, this option
      cannot be used.

5.  IANA Considerations

   This document defines six new mobility options, the Anchored Prefix
   Option, the Local Prefix Option, the Previous MAAR Option, the
   Serving MAAR Option, the DLIF Link-local Address Option and the DLIF
   Link-layer Address Option.  The Type value for these options needs to
   be assigned from the same numbering space as allocated for the other
   mobility options in the "Mobility Options" registry defined in
   http://www.iana.org/assignments/mobility-parameters.  The required
   IANA actions are marked as IANA-1 to IANA-6.

   This document reserves a new flag (D) in the "Binding Update Flags"
   and a new flag (D) in the "Binding Acknowledgment Flags" of the
   "Mobile IPv6 parameters" registry http://www.iana.org/assignments/
   mobility-parameters.

6.  Security Considerations

   The protocol extensions defined in this document share the same
   security concerns of Proxy Mobile IPv6 [RFC5213].  It is recommended
   that the signaling messages, Proxy Binding Update and Proxy Binding
   Acknowledgment, exchanged between the MAARs are protected using IPsec
   using the established security association between them.  This
   essentially eliminates the threats related to the impersonation of a
   MAAR.

   When the CMD acts as a PBU/PBA relay, the CMD may act as a relay of a
   single PBU to multiple previous MAARs.  In situations of many fast
   handovers (e.g., with vehicular networks), there may exist multiple
   previous (e.g., k) MAARs.  In this situation, the CMD creates k
   outgoing packets from a single incoming packet.  This bears a certain
   amplification risk.  The CMD MUST use a pacing approach in the
   outgoing queue to cap the output traffic (i.e., the rate of PBUs
   sent) to limit this amplification risk.

   When the CMD acts as MAAR locator, mobility signaling (PBAs) is
   exchanged between P-MAARs and current S-MAAR.  Hence, security
   associations are REQUIRED to exist between the involved MAARs (in
   addition to the ones needed with the CMD).

   Since deregistration is performed by timeout, measures SHOULD be
   implemented to minimize the risks associated to continued resource
   consumption (DoS attacks), e.g., imposing a limit of the number of
   P-MAARs associated to a given MN.



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   The CMD and the participating MAARs MUST be trusted parties,
   authorized perform all operations relevant to their role.

   There are some privacy considerations to consider.  While the
   involved parties trust each other, the signalling involves disclosing
   information about the previous locations visited by each MN, as well
   as the active prefixes they are using at a given point of time.
   Therefore, mechanisms MUST be in place to ensure that MAARs and CMD
   do not disclose this information to other parties nor use it for
   other ends that providing the distributed mobility support specified
   in this document.

7.  Acknowledgments

   The authors would like to thank Dirk von Hugo, John Kaippallimalil,
   Ines Robles, Joerg Ott, Carlos Pignataro, Vincent Roca, Mirja
   Kuehlewind, Eric Vyncke, Adam Roach, Benjamin Kaduk and Roman Danyliw
   for the comments on this document.  The authors would also like to
   thank Marco Liebsch, Dirk von Hugo, Alex Petrescu, Daniel Corujo,
   Akbar Rahman, Danny Moses, Xinpeng Wei and Satoru Matsushima for
   their comments and discussion on the documents
   [I-D.bernardos-dmm-distributed-anchoring] and
   [I-D.bernardos-dmm-pmip] on which the present document is based.

   The authors would also like to thank Lyle Bertz and Danny Moses for
   their in-deep review of this document and their very valuable
   comments and suggestions.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
              November 2005, <https://www.rfc-editor.org/info/rfc4191>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/info/rfc4861>.






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   [RFC5213]  Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
              Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
              RFC 5213, DOI 10.17487/RFC5213, August 2008,
              <https://www.rfc-editor.org/info/rfc5213>.

   [RFC6275]  Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
              Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
              2011, <https://www.rfc-editor.org/info/rfc6275>.

   [RFC7333]  Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J.
              Korhonen, "Requirements for Distributed Mobility
              Management", RFC 7333, DOI 10.17487/RFC7333, August 2014,
              <https://www.rfc-editor.org/info/rfc7333>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References

   [I-D.bernardos-dmm-distributed-anchoring]
              Bernardos, C. and J. Zuniga, "PMIPv6-based distributed
              anchoring", draft-bernardos-dmm-distributed-anchoring-09
              (work in progress), May 2017.

   [I-D.bernardos-dmm-pmip]
              Bernardos, C., Oliva, A., and F. Giust, "A PMIPv6-based
              solution for Distributed Mobility Management", draft-
              bernardos-dmm-pmip-09 (work in progress), September 2017.

   [RFC7429]  Liu, D., Ed., Zuniga, JC., Ed., Seite, P., Chan, H., and
              CJ. Bernardos, "Distributed Mobility Management: Current
              Practices and Gap Analysis", RFC 7429,
              DOI 10.17487/RFC7429, January 2015,
              <https://www.rfc-editor.org/info/rfc7429>.

   [RFC8563]  Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
              Ed., "Bidirectional Forwarding Detection (BFD) Multipoint
              Active Tails", RFC 8563, DOI 10.17487/RFC8563, April 2019,
              <https://www.rfc-editor.org/info/rfc8563>.

Authors' Addresses









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   Carlos J. Bernardos
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   Leganes, Madrid  28911
   Spain

   Phone: +34 91624 6236
   Email: cjbc@it.uc3m.es
   URI:   http://www.it.uc3m.es/cjbc/


   Antonio de la Oliva
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   Leganes, Madrid  28911
   Spain

   Phone: +34 91624 8803
   Email: aoliva@it.uc3m.es
   URI:   http://www.it.uc3m.es/aoliva/


   Fabio Giust
   Athonet S.r.l.

   Email: fabio.giust.2011@ieee.org


   Juan Carlos Zuniga
   SIGFOX
   425 rue Jean Rostand
   Labege  31670
   France

   Email: j.c.zuniga@ieee.org
   URI:   http://www.sigfox.com/


   Alain Mourad
   InterDigital Europe

   Email: Alain.Mourad@InterDigital.com
   URI:   http://www.InterDigital.com/








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