Proxy Mobile IPv6 Mobility Session Redirection Problem Statement
draft-korhonen-netext-redirect-ps-00

Versions: 00                                                            
Network Working Group                                        J. Korhonen
Internet-Draft                                    Nokia Siemens Networks
Intended status: Informational                          February 9, 2009
Expires: August 13, 2009


    Proxy Mobile IPv6 Mobility Session Redirection Problem Statement
                draft-korhonen-netext-redirect-ps-00.txt

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Abstract

   This document discusses a Proxy Mobile IPv6 mobility session
   redirection functionality at the Proxy Mobile IPv6 base protocol



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   level.  The redirection functionality would allow a Local Mobility
   Anchor to redirect the Mobile Access Gateway during the Proxy Binding
   Update and Acknowledgement exchange to an alternative Local Mobility
   Anchor.  The benefit of redirection at the protocol level is that it
   removes the dependence on having such functionality provided by the
   Authentication, Authorization and, Accounting elements or the Domain
   Name System in a Proxy Mobile IPv6 Domain.  Furthermore, doing the
   redirection at the base protocol level reduces the amount of
   signaling, unnecessary costly setup of mobility sessions and
   unnecessary costly interactions with backend systems.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Redirection Approaches  . . . . . . . . . . . . . . . . . . . . 4
   4.  Redirection Scenarios . . . . . . . . . . . . . . . . . . . . . 4
     4.1.  Redirection During the Initial Attach . . . . . . . . . . . 4
     4.2.  Redirection of an Active IP Mobility Session  . . . . . . . 5
   5.  Proxy Mobile IPv6 Domain Considerations . . . . . . . . . . . . 5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6
























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1.  Introduction

   This document discusses a mobility session redirection functionality
   for the Proxy Mobile IPv6 (PMIPv6) protocol.  The redirection
   functionality would allow a Local Mobility Anchor (LMA) to redirect
   the Mobile Access Gateway (MAG) during the Proxy Binding Update (PBU)
   and the Proxy Binding Acknowledgement (PBA) exchange to an
   alternative LMA.  The benefit of redirection at the protocol level is
   that it removes the dependence on having such functionality provided
   by the Authentication, Authorization and, Accounting (AAA) elements
   or the Domain Name System (DNS) in a PMIPv6 Domain.  Furthermore,
   doing the redirection at the base protocol level reduces the amount
   of signaling, unnecessary costly setup of mobility sessions and
   unnecessary costly interactions with backend systems.

   The redirection during the initial attach and the exchange of PBU/PBA
   messages seems to be the most natural place for redirection, because
   the mobility session setup is still in progress.  Therefore, the
   redirection during the initial attach is also the main problem
   interest area of this document.  The redirection of an active
   mobility session can be seen as a handover between LMAs.
   Accomplishing a handover between LMAs and maintaining the active
   mobility session, which may even include moving the Home Network
   Prefix (HNP) to a new topological location in the network, can be
   really challenging.  Therefore, the redirection of an active mobility
   session is the secondary problem interest area of this document.

   The following sections evaluate existing solutions for redirection
   that may be used with PMIPv6.  This document also briefly describes
   few use cases where redirection would be useful, and finally
   describes deployment consideration within a PMIPv6 Domain when
   redirection is used.


2.  Terminology

   In addition to the terminology defined in RFC 5213 [RFC5213], the
   following terminology is also used:

   rfLMA

      The LMA which receives the PBU from a MAG and decides to redirect
      the IP mobility session, and forwards the PBU to the target LMA
      (r2LMA).







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   r2LMA

      The LMA to which a MAG was redirected to.  During the redirection,
      the PBA is possibly sent to the MAG from this LMA.


3.  Redirection Approaches

   The dependency on DNS for redirection may not be deterministic enough
   from the PMIPv6 Domain point of view, for example in cases where MAGs
   cache DNS responses.  DNS based approach is also applicable only
   during the initial attach.  Furthermore, globally deployed DNS has
   unpredictable latencies on dynamic DNS updates that again make DNS
   suboptimal tool for redirection.  Using AAA for redirection is also
   another possibility.  However, relying on the AAA infrastructure
   would mean, in most cases, unnecessary updates to a remote Policy
   Store and subsequent Policy Profile downloads before and after
   redirection.  Compared to DNS based approach, the AAA infrastructure
   would allow initiating the redirection of an active mobility session.

   Another redirection approach would be utilizing Home Agent Switch
   [RFC5142] type of solution, which appears to be suitable especially
   initiating the redirection of an active mobility session.  The
   drawback of this approach during the initial attach is increased
   signaling.  One additional roundtrip is required to inform the MAG of
   a LMA redirection, one roundtrip to remove the existing binding on
   the old rfLMA, and one roundtrip to establish a new mobility session
   at the target r2LMA.  Also, there is no guarantee that the mobility
   session continuity can be preserved.  Furthermore, this approach
   would mean unnecessary creation of a "temporary" state in the rfLMA
   and unnecessary interactions with the backend systems.

   Based on the above observations, a more efficient redirection
   mechanism can be justified that would be part of the PMIPv6 base
   protocol and independent of external supporting infrastructures.  The
   details of how a LMA determines the redirection and possibly the
   communication between LMAs in a PMIP6 Domain to maintain a list of
   available LMAs is outside the scope of this document.


4.  Redirection Scenarios

4.1.  Redirection During the Initial Attach

   This is the basic use case for the redirection functionality.  A MAG
   sends an initial PBU for establishing a mobility session to a known
   LMA address within the PMIPv6 Domain.  The MAG may find out the "well
   known" IP address or addresses of the LMA through various PMIPv6



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   bootstrapping mechanisms [I-D.ietf-dime-pmip6]
   [I-D.korhonen-netlmm-lma-discovery].  The MAG receives the PBA from
   the r2LMA and will send subsequent PBUs and user traffic to the
   r2LMA.  The MAG updates its Binding Cache and Policy Profile to
   reflect the r2LMA to which PBUs associated with the MN need to be
   sent.

4.2.  Redirection of an Active IP Mobility Session

   This use case would allow a redirection of an active mobility
   session.  The MAG would be redirected to a new r2LMA during a normal
   Binding Lifetime Extension PBU/PBA exchange.  Reasons for doing so
   is, for example, moving Mobile Nodes (MS) anchored to a certain LMA
   to another in order to allow graceful shutdown of the LMA for
   maintenance purposes.  Another reason could again be load balancing
   in abrupt change of load condition on the LMA, and therefore redirect
   some of the mobility sessions to another less loaded LMA.

   If there is a need to maintain mobility session continuity during the
   redirection, then additional functionality is required in LMAs and
   possibly in the PMIPv6 Domain routing system.  A context transfer
   mechanism directly between LMAs, via a remote Policy Store or via
   some other control function would be an obvious requirement.
   However, context transfer specifics are outside the scope of this
   document.


5.  Proxy Mobile IPv6 Domain Considerations

   The redirection problem discussed in this document is only possible
   between MAGs and LMAs that have an existing SA set up.  It is the
   responsibility of the rfLMA that receives a PBU from a MAG to
   redirect the MAG to a such r2LMA whom the MAG already has a SA set up
   with.  Furthermore, the rfLMA and the r2LMA must have a prior
   agreement and an established trust relationship to perform
   redirection.  How a LMA learns and knows of other LMAs (where the
   mobility session can be redirected), is not covered by this problem
   statement.  Dynamic establishment of a SA during redirection is not
   covered in this problem statement.


6.  Security Considerations

   The security considerations of PMIPv6 signaling described in RFC 5213
   [RFC5213] apply to this document.  An incorrectly configured
   redirection functionality may cause unwanted redirection attempts to
   non-existing LMAs or to other LMAs that do not have and will not have
   a SA with the redirected MAG.  At the same time, a falsely redirected



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   MAG will experience failing binding updates and failing creation of
   mobility sessions.  An incorrectly configured redirection
   functionality may also cause biased load distribution within a PMIPv6
   Domain.  This document also assumes that the LMAs participating to
   the redirection have adequate prior agreement and trust relationship
   between each other.


7.  IANA Considerations

   This document has no IANA actions.


8.  References

8.1.  Normative References

   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

8.2.  Informative References

   [I-D.ietf-dime-pmip6]
              Korhonen, J., Bournelle, J., Muhanna, A., Chowdhury, K.,
              and U. Meyer, "Diameter Proxy Mobile IPv6: Support For
              Mobile Access Gateway and Local  Mobility Anchor to
              Diameter Server Interaction", draft-ietf-dime-pmip6-00
              (work in progress), January 2009.

   [I-D.korhonen-netlmm-lma-discovery]
              Korhonen, J. and V. Devarapalli, "LMA Discovery for Proxy
              Mobile IPv6", draft-korhonen-netlmm-lma-discovery-00 (work
              in progress), October 2008.

   [RFC5142]  Haley, B., Devarapalli, V., Deng, H., and J. Kempf,
              "Mobility Header Home Agent Switch Message", RFC 5142,
              January 2008.














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Author's Address

   Jouni Korhonen
   Nokia Siemens Networks
   Linnoitustie 6
   FIN-02600 Espoo
   FINLAND

   Email: jouni.nospam@gmail.com










































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