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Network Working Group                                         M. Bagnulo
Internet-Draft                                                      UC3M
Expires: January 12, 2006                                    E. Nordmark
                                                        Sun Microsystems
                                                           July 11, 2005


                        SHIM - MIPv6 Interaction
                       draft-bagnulo-shim6-mip-00

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Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   In this note, we explore the interaction between the SHIM protocol
   and MIPv6 protocol, identifying potential benefits and difficulties.
   The analysis will consider the two modes of operation of MIPv6: the
   Bidirectional Tunnel (BT) mode where the communication is routed
   through the Home Agent and the Route Optimization (RO) mode, where
   the communication flows directly between the Correspondent node and
   the mobile node.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Bidirectional Tunnel (BT) Mode . . . . . . . . . . . . . . . .  4
     2.1   Communication between the MN and the CN  . . . . . . . . .  4
   3.  RO mode  . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Security considerations  . . . . . . . . . . . . . . . . . . .  7
   5.  Normative References . . . . . . . . . . . . . . . . . . . . .  7
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  7
       Intellectual Property and Copyright Statements . . . . . . . .  8









































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1.  Introduction

   SHIM [1] is a host-based mechanism to provide site-multihoming
   support.  In this note, we explore the interaction between the SHIM
   protocol and MIPv6 protocol, identifying potential benefits and
   difficulties.

   The analysis contained in this document considers the most general
   case of shim and MIPv6 interaction, where the mobile node has both
   multiple Care-of-Addresses as well as multiple Home Addresses.  The
   MN can have multiple addresses for any number of reasons.  For
   example, the MN can have multiple CoAs due to the MN having multiple
   interfaces (connecting to different providers), or the MN visiting a
   link which has multiple address prefixes due to the visited site
   being multihomed.  Also, the MN can have multiple HoAs for different
   reasons, including having a home link which has multiple address
   prefixes due to being in a multihomed site, to having multiple,
   independent Home Agents that each provide it with a Home Address.

   Without loss of generality the analysis uses a single IP address for
   the correspondent node.

   The analysis will consider the two modes of operation of MIPv6: the
   Bidirectional Tunnel (BT) mode where the communication is routed
   through the Home Agent and the Route Optimization (RO) mode, where
   the communication flows directly between the Correspondent Node and
   the Mobile Node.
























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2.  Bidirectional Tunnel (BT) Mode

2.1  Communication between the MN and the CN

   In this case, we have a MN with multiple CoAs (CoA1,..., CoAj) and
   multiple HoAs (HoA1,..., HoAm) communicating with a Cn with address
   IPCN.

   We assume that the SHIM is layered above MIPv6.

   In this scenario, suppose that an application located above the SHIM
   layer, establishes a communication using one of the available HoAs,
   e.g.  HoAl and the address of the CN, IPCN, as ULIDs.  Because the
   SHIM is located above MIPv6, packets will be tunneled through the HA,
   i.e. packets will be encapsulated with an additional header that will
   contain IPHA and CoAj as addresses.

   At some point during the lifetime of the communication, a SHIM
   context is established.  Such context will contain:

   o  HoAl and IPCN as ULIDs

   o  HoA1,..., HoAm, as locator set for the MN.  (Optionally, the MN
      could choose not to provide the CoAs to the CN in the shim6
      signaling.)

   o  IPCN as locator set for the CN

   We will next consider the response in case of an outage:

   Suppose that an outage occurs and the communication path becomes
   unavailable.  If there is an outage affecting the path between the CN
   and the MN, then the SHIM layer will detect it, and will retry with
   an alternative locator.

   When an alternative HoA is used as alternative locator, packets will
   be tunneled through the HA associated with the new HoA, and will be
   received through the CoA associated with the new HoA.  In case that
   there is at least one HA and one CoA that are not affected by the
   outage, the communication will be preserved.  In this case, the
   communication will still flow in BT mode, but it will be routed
   through an alternative tunnel associated with the new HoA.

   If an alternative CoA is used as alternative locator, then the
   communication will run directly between the MN and the CN in a kind
   of SHIM based RO mode, recovering from the outage.  However, in this
   case, care must be taken because the alternative CoA may become
   unavailable after movement.



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3.  RO mode

   We assume that the SHIM is layered above MIPv6.

   In this case, we have a MN with multiple CoAs (CoA1,..., CoAj) and
   multiple HoAs (HoA1,..., HoAm) communicating with a CN with address
   IPCN.

   Suppose that a communication is established between the MN and the CN
   using HoAl and IPCN.  In addition, through MIPv6 protocol, a Binding
   Cache Entry (BCE) is created in the CN associating the HoAl with one
   of the CoAs, CoAp.  So, packets associated with the communication are
   flowing directly between the CN and the MN carrying CoAp and IPCN in
   the source and destination address fields.

   Later on, at some point in time, a SHIM context is established
   between the MN and the CN.  In this case the SHIM context established
   contain the following information:

   o  ULIDs: HoAl and IPCN

   o  Locator set for MN: HoA1,...,HoAm, CoA1,..., CoAj.  (Optionally,
      the MN could choose not to provide the CoAs to the CN in the shim6
      signaling.)

   o  IPCN as locator set for the CN

   We will next analyze how this configuration reacts to different
   failure modes:

   o  The path between IPCN and CoAp fails.  The SHIM will detect the
      outage and will try with alternative locators available for the
      ULIDs of the session.  If an alternative HoA is used by the SHIM
      as alternative locator, when the SHIM passes the packet with an
      alternative HoA to the MIP layer, the MIP layer will route through
      the corresponding CoA available in the BCE associated with the new
      HoA, possibly falling back to BT mode but potentially recovering
      the failure.  If an alternative CoA is used by the SHIM as
      alternative locator, the MIP layer wonOt affect the packet
      carrying the alternative CoA, and packets will be routed directly
      between the MN and the CN, in a kind of SHIM-based RO mode.

   o  The path between the MN and the CN through the HA fails.  While
      data traffic is not routed through the HA, HoTI/HoT packets are
      exchanged through the HA.  If the path between the MN and the CN
      through the Ha fails, then HoTI/HoT exchange will fail.  A few
      minutes later, the corresponding BCE will expire, and the
      communication will fallback to the BT mode through the HA.



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      However, because we are considering the case where the path
      through the HA is down, the communication will fail.  At this
      point, the SHIM will detect the outage and use an alternative
      locator pair.  Analogously to the previous case, the SHIM can try
      with an alternative CoA or an alternative HoA as alternative
      locators for the communication.  In any case, similar
      considerations to the ones described above apply and the
      communications will be restored, whether in BT mode (alternative
      HoA) or in a SHIM-based RO mode (alternative CoA used).

   In any case, the presented setup seems to allow the preservation of
   the established communication through different failure modes.  It
   should be noted, that if CoAs are included as alternative locators
   for the SHIM, those will be short lived locators, and they may become
   unavailable sooner than the HoAs.




































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4.  Security considerations

   TBD

5.  Normative References

   [1]  Nordmark, E. and M. Bagnulo, "Multihoming L3 Shim Approach",
        draft-ietf-shim6-l3shim-00 (work in progress), October 2004.


Authors' Addresses

   Marcelo Bagnulo
   Universidad Carlos III de Madrid
   Av. Universidad 30
   Leganes, Madrid  28911
   SPAIN

   Phone: 34 91 6249500
   Email: marcelo@it.uc3m.es
   URI:   http://www.it.uc3m.es


   Erik Normark
   Sun Microsystems, Inc.
   17 Network Circle
   Mountain View, CA
   USA

   Phone: +1 650 786 2921
   Email: erik.nordmark@sun.com




















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   Copyright (C) The Internet Society (2005).  This document is subject
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Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




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