INTERNET Draft                                           George Tsirtsis
Expires:  January 2006                                    Hesham Soliman
                                                               July 2005

              Mobility management for Dual stack mobile nodes
                            A Problem Statement

Status of this memo

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   This draft discusses the issues associated with mobility management
   for dual stack mobile nodes. Currently, two mobility management
   protocols are defined for IPv4 and IPv6. Deploying both in a dual
   stack mobile node introduces a number of inefficiencies. Deployment
   and operational issues motivate the use of a single mobility
   management protocol. This draft discusses such motivations. The draft
   also hints on how current MIPv4 and MIPv6 could be extended so that
   they can support mobility management for a dual stack node.

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1.0 Introduction and motivation

   A mobile IPv4 only node can today use Mobile IPv4 [MIPv4] to maintain
   connectivity while moving between IPv4 subnets. Similarly, a mobile
   IPv6 only node can today use Mobile IPv6 [MIPv6] to maintain
   connectivity while moving between IPv6 subnets.

   One of the ways of migrating to IPv6 is to deploy dual stack node
   running both IPv4 and IPv6. Such a node will be able to get both IPv4
   and IPv6 addresses and thus can communicate with the current IPv4
   Internet as well as any IPv6 nodes and networks as they become

   A dual stack node can use Mobile IPv4 for its IPv4 stack and Mobile
   IPv6 for its IPv6 stack so that it can move between IPv4 and IPv6
   subnets. While this is possible, it is also clearly inefficient since
   it requires:

   - Mobile nodes to support two sets of mobility management protocols
   - Mobile nodes to send two sets of signaling messages on every
   - Network Administrators to run and maintain two sets of mobility
     management systems on the same network. Each of these systems
     requiring their own sets of optimizations that may include any of
     the following mechanisms, FMIPv6, HMIPv6, FMIPv4, and many

   This draft discusses the potential inefficiencies and operational
   issues raised by running both mobility management protocols
   simultaneously. It also proposes a work area to be taken up by the
   IETF on the subject and hints on a possible direction for appropriate

2.0 Problem description

   Mobile IP (v4 and v6) uses a signaling protocol (Registration
   requests in MIPv4 and BUs in MIPv6) to set up tunnels between two end
   points. At the moment MIP "signaling" is tightly coupled with the
   "address family (i.e. IPv4 or IPv6)" used in the connections that it
   attempts to manipulate. There are no fundamental technical reasons
   for such coupling. If Mobile IP were viewed as a tunnel setup
   protocol, it should be able to setup IP in IP tunnels, independently
   of the IP version used in the outer and inner headers. Other
   protocols, for example SIP, are able to use either IPv4 or IPv6 based
   signaling plane to manipulate IPv4 andIPv6 bearers.

   A mobile node using both Mobile IPv4 and Mobile IPv6 to roam within
   the Internet will require the following:

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   - Both implementations available in the mobile node
   - The network operator needs to ensure that the home agent supports
     both protocols or that it has two separate Home Agents supporting
     the two protocols, each requiring its own management.
   - Double the amount of configuration in the mobile node and the home
     agent (e.g. security associations).
   - Local network optimizations for handovers will also need to be

   We argue that all of the above will hinder the deployment of Mobile
   IPv6 as well as any dual stack solution in a mobile environment. We
   will discuss some of the issues with the current approach separately
   in the following sections.

2.1. Implementation burdens

   As mentioned above, a dual stack mobile node would require both
   mobility protocols implemented to roam seamlessly within the
   Internet. Clearly this will add implementation efforts, which we
   argue are not necessary.

   In addition to the implementation efforts, some vendors may not
   support both protocols in either mobile nodes or home agents. This is
   more of a commercial issue; however, it does affect the large scale
   deployment of mobile devices on the Internet.

2.2. Operational burdens

   As mentioned earlier, deploying both protocols will require managing
   both protocols in the mobile node and the home agent. This adds
   significant operational issues for the network operator. It would
   certainly require the network operator to have deep knowledge in both
   protocols. This might add a significant cost for deployment that an
   operator cannot justify due to the lack of substantial gains.

2.3. Mobility management inefficiencies

   This is perhaps the most significant issue to consider. Suppose that
   a mobile node is moving within a dual stack access network. Every
   time the mobile node moves it needs to send two mobile IP messages to
   its home agent to allow its IPv4 and IPv6 connections to survive.
   There is no reason for doing this. If local mobility optimizations
   are deployed (e.g. HMIPv6, Fast handovers or local MIPv4 HA), the
   mobile node will need to update the local agents running each
   protocol. Ironically, one local agent might be running both HMIPv6
   and local MIPv4 home agent. Clearly, there is no need in this case to
   send two messages.

   Hence, such parallel operation of Mobile IPv4 and Mobile IPv6 will
   complicate mobility management within the Internet and increase the

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   amount of bandwidth needed at the critical handover time for no
   apparent gain.

2.4. The impossibility of maintaining connectivity

   A final point to consider is that even if both mobility protocols are
   supported by a mobile node seamless connectivity would not in fact be
   guarantied since that also depends on the IPv4/IPv6 capabilities of
   the networks the mobile is visiting i.e.: a dual stack node
   attempting to connect via a IPv4 only network would not be able to
   maintain connectivity of its IPv6 applications and vice versa.

3. Conclusion and recommendations

   The points above highlight the tight coupling in both Mobile IPv4 and
   Mobile IPv6 between signaling and the IP addresses used by upper
   layers. Given that Mobile IPv4 is currently deployed and Mobile IPv6
   is expected to be deployed, there is a need for gradual transition
   from IPv4 mobility management to IPv6. Running both protocols
   simultaneously is inefficient and has the problems described above.
   In order to allow for a gradual transition based on current standards
   and deployment, the following work areas seem to be reasonable:

   - it should be possible to create IPv4 extensions to Mobile IPv6 so
   that a dual stack mobile node can register its IPv4 and IPv6 HoAs to
   a dual stack Home Agent using MIPv6 signaling only.
   - it should be possible to create IPv6 extensions to MIPv4 so that a
   dual stack mobile node can register its IPv4 and IPv6 HoAs to a dual
   stack Home Agent using MIPv4 signaling only.
   - it should also be possible to extend MIPv4 and MIPv6 so that a
   mobile can register a single CoA (IPv4 or IPv6) to which IPv4 and/or
   IPv6 packets can be diverted to.

   Further work in this area, possibly independent of Mobile IP, may
   also be of interest to some parties in which case it should be dealt
   with separately from the incremental Mobile IP based changes.

4. Authors Addresses

   George Tsirtsis
   Flarion Technologies
   Phone:  +442088260073

   Hesham Soliman
   Flarion Technologies
   Phone:  +1 908 997 9775

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4. References

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

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This Internet-Draft expires January, 2006.

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