IETF MIP6 Working Group                                     N. Montavont
Internet-Draft                                               LSIIT - ULP
Expires: January 17, 2005                                    R. Wakikawa
                                                         Keio University
                                                                T. Ernst
                                                 WIDE at Keio University
                                                                 T. Noel
                                                             LSIIT - ULP
                                                                   C. Ng
                                                Panasonic Singapore Labs
                                                           July 19, 2004


                 Analysis of Multihoming in Mobile IPv6
        draft-montavont-mobileip-multihoming-pb-statement-01.txt

Status of this Memo

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   This Internet-Draft will expire on January 17, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   Individual solutions have been proposed to extend Mobile IPv6 in
   order to allow mobile nodes to be multihomed, but all issues have not



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   been addressed by a single document.  In this document, we thus
   propose a taxonomy to classify the situations where a mobile node may
   be multihomed.  This taxonomy is then used to describe all multihomed
   scenarios.  Issues preventing mobile nodes to be multihomed while
   operating Mobile IPv6 are highlighted.  This document doesn't aim at
   proposing solutions, however, it is expected to raise discussion in
   order to make sure forthcoming solutions will address all the issues.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Taxonomy . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Scenarios  . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1   Issues Related to Mobile IPv6  . . . . . . . . . . . . . .  8
     4.2   Issues Not Related to Mobile IPv6  . . . . . . . . . . . .  8
     4.3   Issues Related to a Host Connected to Home Link  . . . . .  9
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 10
       Intellectual Property and Copyright Statements . . . . . . . . 12































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1.  Introduction

   Mobile IPv6 [4],[5] is designed to allow a mobile node to maintain
   its IPv6 communications while moving between IPv6 subnets.  However,
   the current specification does not give hints nor requirements to
   deal with mobile nodes with multiple points of attachement, i.e.  a
   multihomed mobile node.  We are thus proposing the current document
   to fill this gap.

   This document has two goals.  The first goal is to define a taxonomy
   which helps to represent the different situations where a mobile host
   is multihomed.  For each case, we show the configuration a multihomed
   host may have (number of interfaces, number of Home Addresses or
   number of Care-of Addresses).  We also give a concrete illustration
   for each scenario.

   The second goal of this document is to define the requirements needed
   to manage multihomed hosts.  Different issues will be raised in order
   to provide full support of multihomed hosts in Mobile IPv6.  The
   potentially needed solutions to support new features will be
   described in a separate document.

   The reader is assumed to have read our companion document [1] which
   outlines the goals and benefits of multihoming for both fixed and
   mobile nodes (i.e.  generic IPv6 nodes).  Real-life scenarios as
   illustrated in that document are the based motivations of this
   present study of multihomed issues peculiar to mobile nodes.  The
   terms used in this memo are the same as the ones used in Mobile IPv6
   [4].

   The document is organized as follows: in the first section, we
   propose a taxonomy to classify the different cases where mobile hosts
   are multihomed.  Then this taxonomy is used to describe the
   multihoming scenarios specific to Mobile IPv6.  In the next section,
   an analysis of each case is given in order to select the most
   interesting scenarios highlighted in the previous section.  The last
   section summarizes the different features needed in Mobile IPv6 to
   reach the goal defined in [1].













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2.  Taxonomy

   As detailed in [1], multihoming can provide a number of benefits:
   ubiquitous access, redundancy/fault recovery, load sharing, load
   balancing, bicasting and preferences settings.  In that document, the
   multihoming study is split into two main axes: either the node has
   only one interface (and several IPv6 addresses) or the node has
   several interfaces.  In this memo, we follow the same guidelines, but
   we conduct this study from the pespective of mobile nodes operating
   Mobile IPv6 specifically.  However, two more parameters are necessary
   to study the feasability of each goal: the multihoming management
   will be different according to the number of Home Addresses and the
   number of Care-of Addresses the mobile node has.  We then proposes
   the following taxonomy:

   o  x = number of active interfaces

   o  y = number of Home Addresses (HoAs)

   o  z = number of Care-of Addresses (CoAs)

   A value of '1' implies there is a single instance of the parameter,
   whereas a value of 'n' indicates that there are multiple instances of
   the parameter.  An illustration of this taxonomy is given in Figure
   1.


























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              Mobile Node

           HoA1         HoA2   ... HoAn   --> Mobile IP layer (x)
            |            |          |
      +-----+--------+   |          |
      |     |        |   |          |
     CoA1   +--CoA2  +---CoA3  ... CoAn   --> IP layer (y)
      |          |        |         |
     Link1      Link2    Link3 ... Linkn  --> IPv6 Link (n/a *)
      |          |        |         |
      +-----+----+        |         |
            |             |         |
           IF1            IF2  ... IFn    --> Physical layer (z)
                                            (z = the number of active interfaces)

   HoA1 ::= {CoA1, 2, 3} [IF1 and IF2]
   HoA2 ::= {CoA3}       [IF2]

   Mobile Node(x = 2, y = 3, z = 2)

   * because number of IPv6 link is equal to the number of CoAs, equal to y

             Figure 1: Illustration of the chosen taxonomy

   The variable y indicates the number of HoAs allocated to a host.  A
   host may have multiple HoAs (x=n) when either:

   o  The host has only one home link, and all its HoAs are based on the
      same IPv6 prefix (e.g.  the host may have multiple interfaces).

   o  The host has only one home link, and multiple HoAs with distinct
      prefixes because there are several IPv6 prefixes advertised on the
      home link.

   o  The host has several home links, and thus has at least two HoAs
      with different IPv6 prefixes.

   As the taxonomy suggests, the fact that the mobile node has several
   HoAs is independent from the fact that the mobile node has multiple
   interfaces.  The fact that the mobile node has multiple interfaces
   does not imply that it has multiple HoAs and vice-versa.










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3.  Scenarios

   o  x = 1: only one interface on the host

      1.  One HoA, one CoA (1,1,1)

          The host is not multihomed.  The host has only one interface,
          with one HoA and is currently away from its home link (one CoA
          on the foreign link).

      2.  Several HoAs, one CoA (1,n,1)

          The host is multihomed, since it has several HoAs.  This case
          may happen when a host is getting access to Internet through
          different ISPs and each offers a Mobile IPv6 service to the
          host.  That way, the host will have a HoA per ISP.  Once the
          host is connected to a visited IPv6 subnet, it gets one CoA.
          This CoA may be registered with all the Home Agents provided
          by the ISPs, in order to remain simulteneously reachable
          through all its HoAs.

      3.  One HoA, several CoAs (1,1,n)

          The host is multihomed since it has several CoAs.  This case
          may occur when the interface of the host is connected to a
          link where multiple IPv6 prefixes are advertised.

      4.  Several HoAs, several CoAs (1,n,n)

          The host is multihomed, since it has multiple addresses.  This
          case can be viewed as a combination of the two cases described
          above: the host has several HoAs (e.g.  given by different
          ISPs) and several CoAs (e.g.  because the host is receiving
          multiple IPv6 prefixes).

   o  x = n: the host has multiple interfaces

      1.  One HoA, one CoA (n,1,1)

          The host is multihomed: this is a special case of a host with
          two interfaces connected to different IPv6 subnets; one of the
          subnet is the home network of the host and allows the host to
          use its HoA.  The host can build a temporary IPv6 address on
          its other interface but it cannot register the temporary
          address with its Home Agent (unless the host stops using its
          HoA, i.e.  its interface connected to the home link).

      2.  One HoA, several CoAs (n,1,n)



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          The host is multihomed: the host has several addresses to
          choose from.  For example, consider a host with several
          interfaces, each connected to an IPv6 network (the same or
          not).  In this example, at least one IPv6 address is
          configured on each interface.  The host has only one home
          link, and only one Home Agent.

      3.  Several HoA, one CoA (n,n,1)

          The host is multihomed.  This case extends the case (n,1,1)
          when the host has several HoAs, for example from multiple
          ISPs.

      4.  Several HoAs, several CoAs (n,n,n)

          The host is multihomed.  Many scenarios may lead to this case.
          For example, consider a host with three interfaces, two of
          them connected to their home link(two different HoAs) and the
          last one connected to a visited link where two IPv6 prefixes
          are advertised.

































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4.  Open Issues

   In this section we highlight open issues which have to be taken into
   account to handle a multihomed host using Mobile IPv6 and we list the
   requirements for a Mobile IPv6 node to benefit from its multihomed
   configuration in an optimized fashion.  To meet some of these
   requirements, specific procedures in the Mobile IPv6 specification
   will be required.  It's not the purpose of this document to provide
   solutions to meet these requirements but we give some hints.
   Solutions to meet these requirements will be defined in a separate
   document.

4.1  Issues Related to Mobile IPv6

   1.  In the (*,n,*) cases when the mobile host otains a new CoA, it's
       not clear to which HoA the new CoA would be bound to.  There is
       thus a need to define a relationship between HoAs and CoAs.

   2.  In the (*,1,n) case, several CoAs may be simultaneously used by a
       mobile node.  In this case, the host must be able to register all
       CoAs with a single HoA on a distant node (Correspondent Node or
       Home Agent).  This questions how to manage multiple CoAs bound to
       a single HoA and how to identify an entry in the Binding Cache.
       Solutions like [10] may be used.


4.2  Issues Not Related to Mobile IPv6

   1.  In the (n,*,*) cases, the solution should bring support to allow
       a mobile host to simultaneously use several interfaces,
       regardless the number of HoAs and CoAs the mobile node may have.

   2.  In the (*,n,*) case, a mechanism should be defined to detail how
       to bind multiple HoAs to a host.

   3.  In the (n,*,*) cases, a mechanism is needed to redirect flows
       from one interface to another: this functionality would allow a
       mobile node to pursue all communication flows that were initiated
       over the failed interface before it is down.

   4.  In the (n,1,1) case again, the node may want to use each
       interface differently according to some policies and preferences
       that would define which flow would be mapped to which interface
       and/or which flow should not be used over a given interface.  In
       order to optimize the global connectivity of a multihomed host, a
       solution may be defined to allow multihomed hosts to set filters
       on flows on distant nodes (Correspondent Node or Home Agent),
       such as mechanisms proposed by [7], [8] and [9].



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4.3  Issues Related to a Host Connected to Home Link

   In the (n,*,*) cases listed in Section 3, the host may have one of
   its interfaces directly connected to a home link.  This may have an
   impact on the multihoming management.

   For example, if we consider the case (n,n,n) with a host having three
   interfaces, three HoAs and two CoAs (connected to two visited IPv6
   subnets), the CoAs cannot be registered with the Home Agent serving
   the host on the home link it is connected to.

   Otherwise, the case (n,n,n) can translate into either case (n,n,1) or
   (n,n,0) according to the way the host is connected to the Internet.
   Case (n,n,1) only happens when the host is connected to a visited
   link with only one interface and obtain only one CoA.  Other
   interfaces are connected to the home link(s).  In the case (n,n,0),
   i.e.  several interfaces, several HoAs, and no CoA, all interfaces of
   the host are connected to their respective home links.

   Some Mobile IPv6 features cannot be used when the host is connected
   to the same link as its Home Agent (e.g.  home registration).  So,
   such specific scenrarios must be considered by the solutions.

5  References

   [1]   Ernst, T., "Goals and Benefits of Multihoming",
         draft-multihoming-generic-goals-and-benefits-00 (work in
         progress), February 2004.

   [2]   Manner, J. and M. Kojo, "Mobility Related Terminology", RFC
         3753, June 2004.

   [3]   Ernst, T. and H. Lach, "Network Mobility Support Terminology",
         draft-ietf-nemo-terminology-01 (work in progress), February
         2004.

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

   [5]   Arkko, J., Devarapalli, V. and F. Dupont, "Using IPsec to
         Protect Mobile IPv6 Signaling Between Mobile Nodes and Home
         Agents", RFC 3776, June 2004.

   [6]   Montavont, N., Noel, T. and M. Kassi-Lahlou, "MIPv6 for
         Multiple Interfaces", draft-montavont-mobileip-mmi-00 (work in
         progress), July 2002.

   [7]   Soliman, H., Malki, K. and C. Castelluccia, "Per-flow movement



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         in MIPv6", draft-soliman-mobileip-flow-move-02 (work in
         progress), July 2002.

   [8]   Montavont, N. and T. Noel, "Home Agent Filtering for Mobile
         IPv6", draft-montavont-mobileip-ha-filtering-v6-00 (work in
         progress), January 2004.

   [9]   Kuladinithi, K., "Filters for Mobile IPv6 Bindings (NOMADv6)",
         draft-nomadv6-mobileip-filters-02 (work in progress), June
         2004.

   [10]  Wakikawa, R., "Multiple Care-of Addresses Registration",
         draft-wakikawa-mobileip-multiplecoa-02 (work in progress),
         September 2003.

   [11]  Stemm, M. and R. Katz, "Vertical Handoffs in Wireless Overlay
         Networks", Journal Mobile Networks and Applications, vol. 3,
         number 4, pages 335-350, 1998.


Authors' Addresses

   Nicolas Montavont
   LSIIT - Univerity Louis Pasteur
   Pole API, bureau C444
   Boulevard Sebastien Brant
   Illkirch  67400
   FRANCE

   Phone: (33) 3 90 24 45 87
   EMail: montavont@dpt-info.u-strasbg.fr
   URI:   http://www-r2.u-strasbg.fr/~montavont/


   Wakikawa Ryuji
   Keio University
   Jun Murai Lab., Keio University.
   5322 Endo
   Fujisawa, Kanagawa  252-8520
   Japan

   Phone: +81-466-49-1100
   Fax:   +81-466-49-1395
   EMail: ryuji@sfc.wide.ad.jp
   URI:   http://www.mobileip.jp/






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   Ernst Thierry
   WIDE at Keio University
   Jun Murai Lab., Keio University.
   K-square Town Campus, 1488-8 Ogura, Saiwa-Ku
   Kawasaki, Kanagawa  212-0054
   Japan

   Phone: +81-44-580-1600
   Fax:   +81-44-580-1437
   EMail: ernst@sfc.wide.ad.jp
   URI:   http://www.sfc.wide.ad.jp/~ernst/


   Thomas Noel
   LSIIT - Univerity Louis Pasteur
   Pole API, bureau C444
   Boulevard Sebastien Brant
   Illkirch  67400
   FRANCE

   Phone: (33) 3 90 24 45 92
   EMail: noel@dpt-info.u-strasbg.fr
   URI:   http://www-r2.u-strasbg.fr/~noel/


   Chan-Wah Ng
   Panasonic Singapore Laboratories Pte Ltd
   Blk 1022 Tai Seng Ave #06-3530
   Tai Seng Industrial Estate
   Singapore  534415
   SG

   Phone: +65 65505420
   EMail: cwng@psl.com.sg

















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