INTERNET Draft                                           George Tsirtsis

Expires:  Jan 2007                                        Hesham Soliman


                                                               June 2006

              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 the current [MIPv4] and [MIPv6] protocols could be
   extended so that they can support mobility management for a dual
   stack node.

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1. Terminology

   In addition to [KEYWORDS], this draft uses the following terms as
   defined in [SIIT]: IPv4-capable node, IPv4-enabled node, IPv6-capable

   node, IPv6-enabled node.

   The following terms are introduced in this document:

   - MIPv4-capable node: A node that supports [MIPv4] in its
                         implementation. This allows the mobile node to
                         configure a home address (statically or
                         dynamically) and use such address in its Mobile

                         IPv4 signaling. A MIPv4-capable node may also
                         be IPv6-capable or IPv6-enabled and must be

   - MIPv6-capable node: A node that supports [MIPv6] by configuring a
                         home address and using such address in its
                         Mobile IPv6 signaling. A MIPv6-enabled node may

                         also be IPv4-capable or IPv4-enabled and must
                         be IPv6-capable.

2. Introduction and motivation

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

   One of the ways of migrating to IPv6 is to deploy nodes that are both

   IPv4 and IPv6 capable. Such nodes 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 node that is both IPv4 and IPv6 capable 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 be both MIPv4 and MIPv6 capable.
   - 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
     hierarchical Mobile IPv4, hierarchical Mobile IPv6 and Fast
     Handoffs for Mobile IPv4, mechanisms that are currently in
     development in the IETF.

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   This draft discusses the potential inefficiencies, IP connectivity
   problems, and operational issues that are evident when 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 solutions.

3.0 Problem description

   Mobile IP (v4 and v6) uses a signaling protocol (Registration
   requests in [MIPv4] and Binding updates in [MIPv6]) to set up tunnels

   between two end points. At the moment Mobile IP signaling is tightly
   coupled with the "address family (i.e., IPv4 or IPv6)" used in the
   connections 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 and IPv6 connections.

   A node that is both MIPv4 and MIPv6 capable, will require the
   following to roam within the Internet:

   - 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.

3.1. Implementation burdens

   As mentioned above, a node that is IPv4 and IPv6 capable must also be

   MIPv4 and MIPv6 capable to roam 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.
   Although this is more of a commercial issue, it does affect the
   large-scale deployment of mobile devices on the Internet.

3.2. Operational burdens

   As mentioned earlier, deploying both protocols will require managing
   both protocols in the mobile node and the home agent. This adds

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   significant operational issues for the network operator. It would
   certainly require the network operator to have deep knowledge in both

   protocols which is something an operator may not be able to justify
   due to the lack of substantial gains.
   In addition, deploying both protocols will require duplication of
   security credentials on mobile nodes and home agents. This includes,
   IPsec security associations, keying material, and new authentication
   protocols for Mobile IPv6, in addition to the security credentials
   and associations required by Mobile IPv4. Such duplication is again
   significant with no gain to the operator or the mobile node.

3.3. Mobility management inefficiencies

   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 such duplication. If local
   mobility optimizations were deployed (e.g., hierarchical Mobile IP,
   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, it is not desirable to have to send two messages and
   complete two sets of transactions for the same fundamental

   Hence, such parallel operation of Mobile IPv4 and Mobile IPv6 will
   complicate mobility management within the Internet and increase the
   amount of bandwidth needed at the critical handover time for no
   apparent gain.

3.4. The impossibility of maintaining IP connectivity

   A final point to consider is that even if a mobile node is both MIPv4

   and MIPv6 capable, connectivity across different networks would not
   in fact be guaranteed since that also depends on the IPv4/IPv6
   capabilities of the networks the mobile is visiting; i.e., a node
   attempting to connect via a IPv4 only network would not be able to
   maintain connectivity of its IPv6 applications and vice versa. This
   is potentially the most serious problem discussed in this document.

4. 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.
   The gradual transition can be done when needed or deemed appropriate
   by operators or implementers. In the mean time, it is important to
   ensure that the problems listed above can be avoided. Hence, this

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   section lists some actions that should be taken by the IETF to
   address the problems listed above, without mandating the use of two
   mobility management protocols simultaneously.

   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 run one mobility management protocol that
   can manage mobility for both IPv4 and IPv6 addresses used by upper
   layers. Both Mobile IPv4 and Mobile IPv6 should be able of performing

   such task. It may not be possible to support route optimization for
   Mobile IPv6 in all cases; however, mobility management and session
   continuity can be supported.

   - It should be possible to create IPv4 extensions to Mobile IPv6 so
   that an IPv4 and IPv6 capable mobile node can register its IPv4 and
   IPv6 home addresses to an IPv4 and IPv6 enabled Home Agent using
   MIPv6 signaling only.
   - It should be possible to create IPv6 extensions to Mobile IPv4 so
   that an IPv4 and IPv6 capable mobile node can register its IPv4 and
   IPv6 home addresses to an IPv4 and IPv6 enabled Home Agent using
   Mobile IPv4 signaling only.
   - It should also be possible to extend [MIPv4] and [MIPv6] so that a
   mobile node can register a single care-of address (IPv4 or IPv6) to
   which IPv4 and/or IPv6 packets can be tunneled.

   Following the steps listed above, a vendor can choose to support one
   mobility management protocol while avoiding the incompatibility and
   inefficiency problems listed in this document. Similarly, operators
   can decide to continue using one mobility management protocol while
   addressing the transition scenarios that a mobile node is likely to
   face when roaming within the Internet.

   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.

5. Authors Addresses

   George Tsirtsis
   Qualcomm Flarion Technologies
   Phone:  +1 908 947 7059

   Hesham Soliman
   Qualcomm Flarion Technologies
   Phone:  +1 908 997 9775

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6. References

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

   [MIPv4]      Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
                August  2002.

   [MIPv6]      Conta, A. and S. Deering, "Generic Packet Tunneling in
                IPv6 Specification", RFC 2473, December 1998.

   [SIIT]       Nordmark, E., "Stateless IP/ICMP Translator (SIIT)", RFC

                2765, February 2000.

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This Internet-Draft expires January, 2007.

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