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Netext BOF                                                   S. Krishnan
Internet-Draft                                                  Ericsson
Intended status: Informational                                 H. Yokota
Expires: January 13, 2010                                       KDDI Lab
                                                                T. Melia
                                                          Alcatel-Lucent
                                                            C. Bernardos
                                                                    UC3M
                                                           July 12, 2009


          Issues with network based inter-technology handovers
                 draft-krishnan-netext-intertech-ps-02

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Abstract

   Proxy Mobile IPv6 (PMIPv6) is a network based mobility management
   protocol that enables IP mobility for a host without requiring its
   participation in any mobility-related signaling.  While the PMIPv6
   protocol itself supports handover across interfaces and between
   access types, there are several issues with effectively performing
   inter-technology handovers with network based mobility protocols.
   This document aims to enumerate some known issues with such
   handovers.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Conventions used in this document . . . . . . . . . . . . . 3
   2.  Issues occuring in the MN . . . . . . . . . . . . . . . . . . . 3
     2.1.  Formation of interface identifier for SLAAC . . . . . . . . 3
     2.2.  Use of DHCP for address configuration . . . . . . . . . . . 3
     2.3.  Usage of the same address on multiple interfaces  . . . . . 3
     2.4.  Limitations of interfaces . . . . . . . . . . . . . . . . . 4
     2.5.  Interface between MN and MAG  . . . . . . . . . . . . . . . 4
   3.  Issues occuring in the network  . . . . . . . . . . . . . . . . 4
     3.1.  Access selection  . . . . . . . . . . . . . . . . . . . . . 5
     3.2.  Handover vs. multi-homing . . . . . . . . . . . . . . . . . 5
     3.3.  Predictive handovers  . . . . . . . . . . . . . . . . . . . 5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6



















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1.  Introduction

   Proxy Mobile IPv6 (PMIPv6) [RFC5213] is a network based mobility
   management protocol enables IP mobility for a host without requiring
   its participation in any mobility-related signaling.  While the
   PMIPv6 protocol itself supports handover across interfaces and
   between access types, there are several issues with effectively
   performing inter-technology handovers with network based mobility
   protocols.  This document aims to enumerate some known issues with
   such handovers.  On a high level these can be classified into those
   issues occurring on the MN and those issues occurring in the network.

1.1.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL","SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


2.  Issues occuring in the MN

2.1.  Formation of interface identifier for SLAAC

   The IPv6 address of the MN is composed of two parts, the prefix and
   the interface identifier.  Even if the network correctly identified
   the handover and allocated the same prefix on the new interface, the
   MN might come up with a different interface identifier on the new
   interface than it was using on the old interface.  This is usually in
   several link-layer technologies because the interface identifier is
   formed based on a unique identifier of the link-layer interface.
   E.g. the modified EUI-64 based interface identifiers based on the MAC
   address of the link-layer interface.  If this is the case, the
   resulting address on the new interface is different than the address
   the MN was using prior to the handover and hence the applications
   bound to the earlier IPv6 address will lose connectivity.

2.2.  Use of DHCP for address configuration

   If the MN uses DHCP to configure the IP address and as long as it
   complies to recommendations highlighted in RFC 5213 the issue raised
   in the previous section does not apply.

2.3.  Usage of the same address on multiple interfaces

   Several MN operating system implementations do not allow the
   configuration of the same address on multiple interfaces.  Even on
   those that do, the resulting behavior is usually not predictable.
   e.g. after a handover all the traffic might still be directed to the



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   old interface (hence getting dropped) because the default route was
   pointing towards that interface.

2.4.  Limitations of interfaces

   Certain types of point-to-point interfaces are tightly bound to the
   underlying interface and could be torn down even if there is another
   viable interface that can carry the traffic.  For instance, some
   operating system dynamically creates a PPP interface with an IP
   address assigned to it when its connection is established and all
   transport sessions over that connection are maintained only while
   that PPP interface exists.  This implies that the address should not
   be bound directly to an interface that can go down during handovers
   but something a bit more stable.

2.5.  Interface between MN and MAG

   The PMIPv6 protocol needs to receive the right information fro the MN
   to form the PBU message for the LMA.  In particular the MN should
   indicate to the access network if the interface attachment
   corresponds to an initial attachment or to an handover.  This
   information is contained in the Handover Indicator option in the PBU
   message.  Conveying this information from the MN to the MAG implies
   discussing mobile node involvement in the mobility procedure.

   The MN to MAG interface can be based upon L2 signalling or L3
   signalling.

   If L2 signalling is used it is necessary that each wireless access
   technology connected to the PMIPv6 domain supports transferring of
   such information (e.g.  HI).  Although no changes to the IP stack
   would be required, the main drawback is that each L2 technology will
   need to implement their own mechanisms.

   If L3 signalling is used the MN can then include such info in IP
   based signalling being technology agnostic.  Major drawback is the
   modification of the IP stack.

   In any case to support inter-technology the MN needs to send the
   information required to fill the PBU message.  Withount this support,
   it might be hard to implement inter-hechnology handovers.


3.  Issues occuring in the network







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3.1.  Access selection

   The network nodes may not always be aware of the complete set of
   access technologies available to the MN.  This is especially true if
   the multiple accesses are administered by different entities.  Only
   the MN is guaranteed to have this information.  The network may also
   not know about the characteristics that the MN desires from the
   selected access technology.  Because of these reasons it is almost
   impossible for the network to perform access selection without some
   amount of co-operation from the MN.

3.2.  Handover vs. multi-homing

   The network nodes may not always be aware of the intent of the MN
   when it attaches to a new attachment point.  The MN may be performing
   a handover, or may wish to be simultaneously connected.  The access
   router at the new attachment point is unable to distinguish between
   these cases, but needs to communicate this information to the
   mobility anchor.  The mobility anchor point needs this information to
   determine whether to handover an existing mobility session or to
   create a new one.

3.3.  Predictive handovers

   An MN that is capable of being attached to multiple accesses can
   perform a predictive handover attaching to the target access even
   before detaching from the previous access.  This is done in order to
   reduce the handover latency and to reduce packet loss.  Most of the
   time, the intent of the MN is to continue using the previous access
   until it explicitly signals to the network to start using the new
   access.  The target access router cannot determine if this is the
   case and may end up prematurely moving the MNs binding over to the
   new access even while the MN is sending outgoing packets onto the old
   access.


4.  Security Considerations

   This document discusses issues with inter-technology handovers with
   network based mobility protocols, and does not raise any new security
   issues.


5.  IANA Considerations

   This document does not require any IANA action.





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6.  References

6.1.  Normative References

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

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

6.2.  Informative References


Authors' Addresses

   Suresh Krishnan
   Ericsson
   8400 Blvd Decarie
   Town of Mount Royal, Quebec
   Canada

   Email: suresh.krishnan@ericsson.com


   Hidetoshi Yokota
   KDDI Lab

   Email: yokota@kddilabs.jp


   Telemaco Melia
   Alcatel-Lucent
   Route de Villejust
   Nozay  91620
   France

   Email: telemaco.melia@alcatel-lucent.com














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   Carlos J. Bernardos
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   Leganes, Madrid  28911
   Spain

   Phone: +34 91624 6236
   Email: cjbc@it.uc3m.es
   URI:   http://www.it.uc3m.es/cjbc/










































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