1. RFC 4908
Network Working Group                                          K. Nagami
Request for Comments: 4908                                 INTEC NetCore
Category: Experimental                                            S. Uda
                                                             N. Ogashiwa
                                                            NOWARE, Inc.
                                                                H. Esaki
                                                     University of Tokyo
                                                             R. Wakikawa
                                                         Keio University
                                                              H. Ohnishi
                                                               June 2007

              Multihoming for Small-Scale Fixed Networks
              Using Mobile IP and Network Mobility (NEMO)

Status of This Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).


   This RFC is not a candidate for any level of Internet Standard.  The
   IETF disclaims any knowledge of the fitness of this RFC for any
   purpose and in particular notes that the decision to publish is not
   based on IETF review for such things as security, congestion control,
   or inappropriate interaction with deployed protocols.  The RFC Editor
   has chosen to publish this document at its discretion.  Readers of
   this document should exercise caution in evaluating its value for
   implementation and deployment.  See RFC 3932 for more information.

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RFC 4908             Multihoming for Fixed Network             June 2007


   Multihoming technology improves the availability of host and network
   connectivity.  Since the behaviors of fixed and mobile networks
   differ, distinct architectures for each have been discussed and
   proposed.  This document proposes a common architecture for both
   mobile and fixed networking environments, using mobile IP (RFC 3775)
   and Network Mobility (NEMO; RFC 3963).  The proposed architecture
   requires a modification of mobile IP and NEMO so that multiple Care-
   of Addresses (CoAs) can be used.  In addition, multiple Home Agents
   (HAs) that are located in different places are required for

1.  Motivation

   Users of small-scale networks need an easy method to improve network
   availability and to load balance several links.  Multihoming
   technology is one of the solutions to improve availability.
   Conventional major multihoming networks use BGP, but it has some
   issues.  Therefore, we propose a multihoming architecture using
   mobile IP [1] and NEMO [2] for small-scale fixed networks.

1.1.  General Benefits of Multihoming

   In a multihoming network environment, both users and network managers
   benefit from controlling outgoing traffic, incoming traffic, or both
   of them.  Those benefits are described in "Goals and Benefits of
   Multihoming" [3].  The following is a summary of those goals and

      o  Ubiquitous Access

      o  Redundancy/Fault-Recovery

      o  Load Sharing

      o  Load Balancing

      o  Bi-casting

      o  Preference Settings

1.2.  Problems to be Solved to Accomplish Multihoming

   Several multihoming technologies have been proposed so far.
   Conventional major multihoming networks use BGP, but it has some
   issues, as follows.

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   (1) Increasing route entries in the Internet

      In the multihoming environments, each user's network needs to
      advertise its address block to all ISPs connected to them.  If a
      multihomed user connects to only one ISP, the ISP can advertise
      routing information to aggregate them.  But some multihomed users
      need to connect with different ISPs to be prepared for ISP
      failure.  In this case, ISPs need to advertise routing information
      for multihomed users without aggregation.  Therefore, the number
      of routing entries in the Internet is increasing one by one.

   (2) Difficulty of using multiple links efficiently

      It is not easy to control incoming traffic in the case of the
      conventional multihoming architecture using BGP.  Therefore, load
      balancing of connected links is difficult.

1.3.  Using the Architecture of Mobile IP and NEMO to Solve the Problems

   Basically, mobile IP (MIP) and NEMO have been proposed for mobile
   hosts or mobile networks; however, their architecture and protocol
   can be used for fixed networks and to solve the problems mentioned
   above.  The details of the solution are described in the sections

   Moreover, by using the architecture and the protocol of MIP and the
   NEMO, the cost of network operation will be decreased.  For instance,
   in the architecture of MIP and NEMO, renumbering IP addresses when
   office or network equipment is relocated becomes unnecessary, as the
   network address prefix used by a user network in a mobile IP
   environment does not depend on the upstream ISP's network prefix.

2.  Multihoming Architecture Using Mobile IP and NEMO

2.1.  Mobile Network Includes Fixed Network

   By their nature, NEMO and mobile IP must work with multihoming.  This
   is because mobile nodes need to use multiple links to improve the
   availability of network connectivity since the wireless link is not
   always stable.  Therefore, we propose that multihoming for fixed
   nodes (routers and hosts) uses the framework of NEMO and mobile IP.

2.2.  Overview of Multihoming Network Architecture Using Mobile IP

   Figure 1 shows the basic multihoming network architecture.  In this
   architecture, a mobile router (MR), which is a border router of the
   multihomed network, sets up several tunnels between the MR and the HA
   by multiple-CoA registration.  An HA (or a router to which the HA

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   belongs) advertises the user's network prefix (Prefix X in Figure 1)
   to ISPs via the routing protocol.  If the HA has several multihomed
   networks (Prefix X and Y in Figure 1), they can advertise an
   aggregated network prefix to ISPs.  Therefore, the Internet routing
   entries do not increase one by one when the number of multihomed
   users is increased.

                                 ||(Advertise aggregated prefix X and Y)
        |                   The Internet               |
          |          |                    |          |
        ISP-A      ISP-B               ISP-A'      ISP-B'
          |          |                    |          |
          |          |                    |          |
          +--- MR ---+                    +--- MR ---+
          CoA1 | CoA2                      CoA1|CoA2
               |                               |
        -------+--------- (Prefix X)    -------+------ (Prefix Y)
        Multihomed Network X            Multihomed Network Y

                 Figure 1: Advertisement of aggregated prefixes

   Packets to multihomed users go to the HA, and the HA sends packets to
   the MR using CoA1 and CoA2.  The HA selects a route in which a CoA is
   used.  The route selection algorithm is out for scope of this
   document.  This can improve the availability of the user network and
   control traffic going from the ISP to the MR.  In the basic
   architecture, HA1 is the single point of failure.  In order to
   improve the availability of the user network, multiple HAs are
   needed.  This is described in Section 3.2.

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                                ^ | |
       (1) Packets to prefix X  | | |  (2) HA forwards the packets
           are sent to HA       | | v      to CoA1 or CoA2
                          | The Internet |
                            |          |
                            |          | |(3) Packets are forwarded over
                            |          | |    the MIP tunnel selected by
                            |          | v    the HA1
                          ISP-A      ISP-B
                            |          | |
                            |          | |
                            +--- MR ---+ v
                            CoA1 | CoA2
                          -------+--------- (Prefix X)
                         Multihomed Network A

                       Figure 2: Packet Forwarding by HA

3.  Requirements for Mobile IP and NEMO

3.1.  Multiple Care-of-Addresses (CoAs)

   Multiple Care-of-Addresses are needed to improve the availability and
   to control incoming and outgoing traffic.  The current Mobile IPv6
   and the NEMO Basic Support protocol does not allow registration of
   more than one Care-of Address bound to a home address to the home
   agent.  Therefore, [4] proposes to extend MIP6 and NEMO Basic Support
   to allow multiple Care-of Address registrations for the particular
   home address.

3.2.  Multiple Home Agents

   Multiple Home Agents should be geographically distributed across the
   Internet to improve service availability and for the load balancing
   of the HA.  When all the networks that have HA advertise the same
   network prefix to their adjacent router/network, the traffic is
   automatically routed to the nearest Home Agent from the viewpoint of
   routing protocol topology.  This operation has already been proven to
   work in the area of Web server applications, such as CDN (Contents
   Delivery Network), with the Interior Gateway Protocol (IGP) and
   Exterior Gateway Protocol (EGP).

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   In order to operate multiple HAs, all HAs must have the same
   information such as binding information.  This synchronizes the
   databases among the HAs.  The HAHA protocol [5] introduces the
   binding synchronization among HAs.  This is the same architecture as
   Internal BGP (IBGP).  The database is synchronized by full-mesh
   topology.  In addition, in order to simplify operation of the HA, the
   database is synchronized using star topology.  This is analogous to
   the IBGP route reflector.

                             HA1 ------ HA2
                              |          |
                            | The Internet |
                              |          |
                            ISP-A      ISP-B
                              |          |
                              |          |
                              +--- MR ---+
                              CoA1 | CoA2
                            Multihomed Network

                             Figure 3: Architecture with HA Redundancy

4.  Discussion on the Mailing List

4.1.  Why the Proposed Architecture Uses NEMO Protocols

   The multihomed architecture proposed in this document is basically
   the same as the architecture of NEMO.  Furthermore, NEMO protocols
   meet the requirements of the proposed architecture in this document,
   which are:

   o  The protocol can be used by the MR to send information such as the
      CoA, Home Address (HoA), and Binding Unique Identifier (BID) [4]
      to the HA.

   o  The protocol can establish multiple tunnels between the MR and HA.

   o  The protocol supports multiple HAs and can synchronize Binding
      Caches among multiple HAs.

   The proposed multihomed architecture uses NEMO protocols as one of
   the applications of NEMO.  Needless to say, using the NEMO protocol
   is one of the solutions to accomplish the proposed multihome

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   architecture.  Another solution is to propose a new protocol just
   like NEMO.  Nevertheless, such a protocol would have functions just
   like those of NEMO.

4.2.  Route Announcement from Geographically Distributed Multiple HAs

   In the proposed architecture, the xSP (Multihomed Service Provider)
   is introduced.  The xSP is a conceptual service provider; it doesn't
   have to be connected to the Internet physically for all practical
   purposes.  xSP has one or more aggregatable mobile network prefixes.
   xSP contracts with some ISPs that are physically connected to the
   Internet.  The purpose of this contract is to set up some HAs in
   those ISPs' networks.  Those HAs announce the xSP's aggregated mobile
   network prefixes.  This means that HAs work just like border gateway
   routers, and this situation is the same as peering between the ISP
   and xSP.  In this case, the origin Autonomous System (AS) announced
   from the HAs is the xSP.

   On the other hand, a multihomed user (a small office user or home
   user) contracts with the xSP to acquire a mobile network prefix from
   the xSP.  Each multihomed user has an MR and multiple L3 connectivity
   to the Internet via multiple ISPs, and the MR will establish multiple
   tunnels to the HA.  Since the user's mobile network prefixes are
   aggregated and announced from the HA, the packets to the user's
   mobile network will be sent to the nearest HA depending on global
   routing information at that time.  The HA that received such packets
   will forward them to the user's network over the established multiple

   This model of route announcement from multiple HAs is compatible with
   the conventional scalable Internet architecture, and it doesn't have
   scalability problems.

5.  Implementation and Experimentation

   We have implemented and experimented with the proposed architecture.
   Currently, the system works well not only on our test-bed network,
   but on the Internet.  In our experimentation, the MR has two upstream
   organizations (ISPs) and two Care-of Addresses for each organization.
   The MR uses the multiple-CoA option to register the Care-of Addresses
   to the HA.

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RFC 4908             Multihoming for Fixed Network             June 2007

6.  Security Considerations

   This document describes requirements of multiple CoAs and HAs for
   redundancy.  It is necessary to enhance the protocols of MIP and NEMO
   to solve the requirements.  Security considerations of these
   multihoming networks must be considered in a specification of each

7.  References

   7.1.  Normative References

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

   [2]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
        "Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
        January 2005.

7.2.  Informative References

   [3]  Ernst, T., Montavont, N., Wakikawa, R., Paik, E., Ng, C.,
        Kuladinithi, K., and T. Noel, "Goals and Benefits of
        Multihoming", Work in Progress, February 2004.

   [4]  Wakikawa, R., Ernst, T., and K. Nagami, "Multiple Care-of
        Addresses Registration", Work in Progress, March 2007.

   [5]  Wakikawa, R., Thubert, P., and V. Devarapalli, "Inter Home
        Agents Protocol (HAHA)", Work in Progress, February 2004.

Authors' Addresses

   Kenichi Nagami
   INTEC NetCore Inc.
   1-3-3, Shin-suna
   Koto-ku, Tokyo  135-0075

   Phone: +81-3-5565-5069
   Fax:   +81-3-5565-5094
   EMail: nagami@inetcore.com

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   Satoshi Uda
   Japan Advanced Institute of Science and Technology
   1-1 Asahidai
   Nomi, Ishikawa  923-1292

   EMail: zin@jaist.ac.jp

   Nobuo Ogashiwa
   Network Oriented Software Institute, Inc.
   190-2, Yoshii,
   Yoshii, Tano, Gunma 370-2132

   EMail: ogashiwa@noware.co.jp

   Hiroshi Esaki
   The University of Tokyo
   7-3-1 Hongo
   Bunkyo-ku, Tokyo  113-8656

   EMail: hiroshi@wide.ad.jp

   Ryuji Wakikawa
   Keio University
   Department of Environmental Information, Keio University.
   5322 Endo
   Fujisawa, Kanagawa  252-8520

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

   Hiroyuki Ohnishi
   NTT Corporation
   9-11, Midori-Cho, 3-Chome
   Musashino-Shi, Tokyo  180-8585

   EMail: ohnishi.hiroyuki@lab.ntt.co.jp

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  1. RFC 4908