Internet Area                                                   M.Hui
Internet Draft                                                 H.Deng
Intended status: Informational                              China Mobile
Expires: September 9, 2009                                 March 9, 2009

     Problem Statement and Requirement of Simple IP Multi-homing of the

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   This document discusses current issues with simple IP multi-homing.
   In order to have deep understanding of the issue, the document also
   analyzes related works in IETF.  In the end gives the requirements of
   the simple IP multi-homing in concern of technical implements. Simple
   IP multi-homing focuses on simultaneous multiple IP connections of
   the host.

Table of Contents

   1. Introduction................................................3
   2. Problem statements of Simple IP Multi-homing.................4
      2.1. Default Gateway.........................................4
      2.2. Merging of parameters...................................4
      2.3. Source address selection for IPv4.......................5
   3. Analysis of Related Work in IETF.............................6
      3.1. Multi6.................................................6
      3.2. Shim6..................................................6
      3.3. Monami6................................................7
      3.4. Netlmm.................................................7
   4. Requirements for Simple IP Multi-homing......................9
   5. Security Considerations.....................................10
   6. IANA Considerations........................................11
   7. References.................................................12
      7.1. Normative References...................................12
      7.2. Informative References.................................12
   Author's Addresses............................................13
   Intellectual Property Statement....................
   Disclaimer of Validity............................

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          1. Introduction

   Simple IP Multi-homing means the host connects to more than one
   physical network through different network interfaces, and assigns
   different network flows to each interface, and ensure all the
   interfaces can deliver the flow simultaneously.

   Simple IP Multi-homing is a necessary part of daily life, i.e., you
   have to connect to your company office network through VPN connection
   by your Ethernet interface, at the same time you want to watch the
   stock market, which is not allowed through office network. And you
   have a GPRS card, so you would like to use ethernet and GPRS at the
   same time.

   Current the operating systems only allow one default network
   connection. If there are multiple connections of the host, all the
   flows will go to the default gateway based on RFC1122 description.
   One default gateway guarantees the host always has one entry to the
   network, but lead to the multiple connections be difficult. The most
   convenient way to make the host work under several networks at the
   same time is to add specific static route in the host route table, so
   that certain flow can use the assigned interface while others use the
   default one, but it is not easy for the ordinary users to handle it.

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          2. Problem statements of Simple IP Multi-homing

   As description above, simple IP multi-homing can not work based on
   the current specification. There are several reasons cause it invalid,
   and this section analyzes them in detail.

             2.1. Default Gateway

   The Windows operating system in the host follows the default gateway
   mechanism, which will choose the unify gateway among more than one
   default routes (''), the detail is described in RFC1122. The
   default gateway guarantees there always has a route to network when
   the host can not find a specific route for a datagram in the route

   But when it comes to multi-homing, the default gateway also causes
   all the flows go out through one interface, although there has more
   than one network connections.  Nowadays there are diverse networks
   can be chosen by the user, and the terminal have the capability and
   interfaces to connect to more than one networks at the same time. It
   is possible and necessary for the user to require connecting to
   different networks to ensure the best user experiences of different
   services, but the default gateway mechanism only allows one
   connection at once. Although you can connect your host to several
   networks physically, and each network has already assigned a IP
   address for your host interface, even you can see different default
   routes in the route table, all the flow goes to the default gateway
   chosen by the operation system other than different gateways actually.

         2.2. Merging of parameters

   In multiple interfaces host, each interface will get its own IP
   parameters in the procedure of IP address allocation all other policy
   deployment, such as DNS, metrics of routings, TOS. How to merge the
   same type of parameters derived form multiple interfaces to act
   harmoniously in the host is the problem presented in multiple
   interfaces host.

         2.2.1. DNS consideration

   DNS will be configured to the interface manually or by DHCP procedure,
   and multiple interfaces will obtain multiple DNS. The host will
   reserve several DNS in this situation. Referring to different domain
   names the host should query proper DNS so that the domain names can
   be resolved. The problem is current DNS selection mechanism is lack

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   to choose a right one for specific visited domain name, so that we
   need to merge multiple DNS to provide the host with the best

         2.2.2. Metrics consideration

   Metrics are used to measure the performance of routings, the lower
   metric it owns, the higher priority it has. For example, the default
   gateway is chosen based on the metric rule as RFC1122 description,
   The one have the lowest metric value becomes to the default gateway
   among several connected gateways, and the interface correspond to
   this gateway turns to be the default interface.

   Metric rules are different depending on the access technology and
   routing protocol, if the multiple interfaces connect to multiple
   access networks which have different measurements of metrics, the
   metric will not reflect the routing performances correctly. For
   example, current metric rules define the 100M bps Ethernet network
   card to be 20 and 10M bps to be 30, but the CDMA data card set its
   metric value as 1, although its speed is lower than 100M bps Ethernet
   network card. The merging of metrics is necessary in multiple
   interfaces condition.

         2.2.3. TOS consideration

   TOS can be a parameter of routing item to indicate which kind of IP
   data is suitable to deliver by this routing. The multiple interfaces
   will connect to multiple access networks, so that the preference of
   TOS need to be merged to have a better performance of data delivery.
   For example, the WiFi access could indicate itself has broader
   bandwidth comparing with 2G access, and set the TOS as broad
   bandwidth. When another interface connects the Ethernet, the TOS is
   also set as broad bandwidth preferred. In this situation, it needs
   some mechanism to merge and reorder the TOS getting form multiple

         2.3. Source address selection for IPv4

   For the host has more than one IP addresses which are obtained by
   multiple interfaces, the source address selection is the key issue in
   order to use multiple interfaces reasonably. The application needs to
   select right source address so that the data will be delivered by the
   corresponding interface. This mechanism is lack currently which needs
   to be solved in multiple interfaces situation.

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          3. Analysis of Related Work in IETF

   Multi-homing is a wide topic contains different aspects, and there
   are some work groups in IETF worked on a certain aspect of multi-

   This section explains their work, and compares the covered field with
   the simple IP multi-homing.  In the end we will find the simple IP
   multi-homing is still a problem which is not solved yet.

             3.1. Multi6

   Multi6 WG in IETF focuses on the multi-homed site, which has more
   than one connection to the public internet with those connections
   through either the same or different ISPs.  The reasons to choose
   site multi-homing are to improve fault tolerance, perform load
   balancing, etc.

   The Multi6 WG mainly focuses on site multi-homing solutions that tend
   to minimize adverse impacts on the end-to-end routing system and
   limit the number of prefixes that need to be advertised in the
   Default-Free Zone (DFZ).  The background is site multi-homing today
   is done largely by having a site obtain a dedicated block of address
   space and then advertising a route for its prefix through each of its
   ISP connections.  A site's ISPs in turn advertise the prefix to some
   or all of their upstream connections and the route for the prefix may
   propagate to all of the routers connected to the default-free zone.
   As the number of sites multi-homing in this manner increase, the
   number of routes propagated throughout the DFZ increases and overall
   routing stability decreases because of the burden on convergence time.

   Multi6 WG tries to solve this by defining a set of goals for IPv6
   site multi-homing architecture, and analyzing the current limitations
   and the approaches to the site multi-homing.  What's need to notice
   is that the working group is not chartered to make significant
   changes to the nature of IP addresses or to inter-domain routing.
   Obviously, the site multi-homing does not consider the host multiple
   connection which is the key problem of this document.

             3.2. Shim6

   Shim6 is another WG in IETF aims at site multi-homing.  Shim6 work is
   based on the architecture developed by the Multi6 WG, and completes
   the required protocol developments and the architecture and security
   analysis of the required protocols.  Different form Multi6, Shim6

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   focuses on surviving hosts on the multi-homing site from the changes
   or for creating new associations, when one or more of the site's
   address prefixes becomes unreachable.

   Shim6 WG produces specifications for an IPv6-based site multi-homing
   solution that inserts a new sub-layer (shim) into the IP stack of
   end-system hosts.  It enables hosts on multi-homed sites to use a set
   of provider-assigned IP address prefixes and switch between them
   without upsetting transport protocols or applications.  But it can
   not support connecting to all the ISPs simultaneously.

             3.3. Monami6

   The objective of the Monami6 WG is to produce a clear problem
   statement and to produce standard track specifications to the
   straight-forward problems associated with the simultaneous use of
   multiple addresses for either mobile hosts using Mobile IPv6 or
   mobile routers using NEMO Basic Support and their variants (FMIPv6,

   The WG does not define a tunnel selection mechanism, but document how
   to use existing mechanisms based upon preferences or policies.  They
   explain the limitations for mobile hosts using multiple simultaneous
   Care-of Addresses and Home Agent addresses using Mobile IPv6, whether
   issues are specific to Mobile IPv6 or not.  They also deliver a
   protocol extension to Mobile IPv6 (RFC 3775) and NEMO Basic Support
   (RFC 3963) to support the registration of multiple Care-of Addresses
   at a given Home Agent address [Standard Track].  What's more, Monami6
   WG makes a "Flow/binding policies exchange" solution for an exchange
   of policies from the mobile host/router to the Home Agent and from
   the Home Agent to the mobile host/router influencing the choice of
   the Care-of Address and Home Agent address.

   Monami6 focus the same field with simple IP multi-homing, which is
   ensuring simultaneous use of multiple addresses for the host.  The
   difference is Monami6 puts this aim to under a certain condition, the
   mobile host using MIP6, while the simple IP multi-homing focuses on
   ordinary host using IPv4/6.

             3.4. Netlmm

   Netlmm WG studies Proxy Mobile IPv6 (PMIPv6) which supports multiple
   interfaces binding, by maintaining multiple binding cache entries for
   a given MN. The scenario concerned by PMIPv6 is each interfaces gets
   different prefix form others, however, there are many other scenarios
   associated with multiple interface attachment are not covered. The
   specific scenario needs specific solutions which require some

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   enhancement/modification to the current PMIPv6 protocol, and the
   simple IP multi-homing hasn't supported in the PMIPv6 environment as

   What's more, the multi-homing in PMIPv6 lacks flow filtering support.
   The LMA must has filter rules to allocate certain flow to traverse
   via a certain care-of address, but the mechanism in PMIPv6 is
   currently not supported.

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          4. Requirements for Simple IP Multi-homing

   Based on problem statements and related work analysis, the
   requirements for simple IP multi-homing is concluded and listed as

   1) The host with multiple network interfaces should be capable to
   connect with different networks simultaneously.

   2) The default gateway mechanism needs to be improved to support
   several gateways working at the same time.

   3) New metric mechanism must be defined to adapt to various network
   cards nowadays.

   4) The policies to assign different flows to the appropriate
   interface are required, and how to apply the policies to the host
   need to be considered as well.

   5 Network side should be capable of distributing the IP flow
   according to some parameters, such as IP address prefix, network type
   and so on.

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          5. Security Considerations

   This document doesn't propose any new protocol.

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          6. IANA Considerations

   This document doesn't require any new number from IANA.

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          7. References

             7.1. Normative References

   [RFC1122]  Braden, R., "Requirements for Internet Hosts-communication
              Layers", STD 3, RFC 1122, October 1989.

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

   [RFC3582]  Abley, J., Black, B., and V. Gill, "Goals for IPv6 Site-
              Multihoming Architectures", RFC 3582, August 2003.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [RFC4177]  Huston, G., "Architectural Approaches to Multi-homing for
              IPv6", RFC 4177, September 2005.

   [RFC4191]  R. Draves, D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, November 2005.

   [RFC5213]  S. Gundavelli, Ed., K. Leung, ''Proxy Mobile IPv6'', RFC5213,
              August 2008

             7.2. Informative References

   [MONAMI6] Ernst, T., "Motivations and Scenarios for Using Multiple
             Interfaces and global Addresses", May 2008, <draft-ietf-
             monami6-multihoming-motivation-scenario-03(work in

   [NETLMM]  M. Jeyatharan, C. Ng, J. Hirano, "Multiple Interfaced
             Mobile Nodes in NetlMM", June 2008, <draft-jeyatharan-
             netlmm-multi-interface-ps-02(work in progress)>.

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Author's Addresses

   Min Hui
   China Mobile
   53A,Xibianmennei Ave.,
   Xuanwu District,
   Beijing 100053

   Hui Deng
   China Mobile
   53A,Xibianmennei Ave.,
   Xuanwu District,
   Beijing 100053

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