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INTERNET Draft                                     George Tsirtsis 
Expires: August 2004                               Hesham Soliman 
                                                   Flarion 
                                                   February 2004 

                                      

              Mobility management for Dual stack mobile nodes 
                            A Problem Statement 
                   <draft-tsirtsis-DSMIP-problem-02.txt> 
    
Status of this memo 
    
   This document is an Internet-Draft and is in full conformance with 
   all provisions of Section 10 of RFC2026. 
    
   Internet-Drafts are working documents of the Internet Engineering 
   Task Force (IETF), its areas, and its working groups. Note that other 
   groups may also distribute working documents as Internet-Drafts. 
    
   Internet-Drafts are draft documents valid for a maximum of six months 
   and may be updated, replaced, or obsoleted by other documents at any 
   time. It is inappropriate to use Internet-Drafts as reference 
   material or cite them other than as "work in progress". 
    
   The list of current Internet-Drafts can be accessed at 
   http://www.ietf.org/ietf/lid-abstracts.txt 
   The list of Internet-Draft Shadow Directories can be accessed at 
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Abstract 
    
   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. 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 
   available. 

   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   
     handoff 
   - 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    
     others. 
    
   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 
   solutions. 
    
2. 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 AND IPv6 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  
     duplicated. 
    
   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.  
    




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

   It is reasonable to assume that the separation between mobility 
   signaling and IP version used in media planes could be adopted by the 
   Mobile IP protocol.  
    
   To that effect, 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. 

4. Author's Addresses 

   George Tsirtsis 
   Flarion Technologies 
   Phone:  +442088260073        
   EMail:  G.Tsirtsis@Flarion.com 
    
   Hesham Soliman 
   Flarion Technologies 
    
   Phone:  +61400500321 
   E-mail: H.Soliman@Flarion.com 
    
4. References 
    
   [MIPv4] C. Perkins, Editor, "IP Mobility Support for IPv4", RFC 3220,  
           January 2002. 
   [MIPv6] D. Johnson, C. Perkins and J. Arkko, "Mobility Support in  
           IPv6", draft-ietf-mobileip-ipv6-24.txt, June 2003.  



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