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Network Working Group                                        G. TsirtsisRequest for Comments: 4977                                      QualcommCategory: Informational                                       H. Soliman                                                    Elevate Technologies                                                             August 2007Problem Statement: Dual Stack MobilityStatus of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Abstract   This document 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 problems.   Deployment and operational issues motivate the use of a single   mobility management protocol.  This document discusses such   motivations.  The document also discusses requirements for the Mobile   IPv4 (MIPv4) and Mobile IPv6 (MIPv6) protocol so that they can   support mobility management for a dual stack node.Table of Contents1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . .22.  Introduction and Motivation . . . . . . . . . . . . . . . . . .23.  Problem Description . . . . . . . . . . . . . . . . . . . . . .33.1.  The Impossibility of Maintaining IP Connectivity  . . . . .43.2.  Implementation Burdens  . . . . . . . . . . . . . . . . . .43.3.  Operational Burdens . . . . . . . . . . . . . . . . . . . .43.4.  Mobility Management Inefficiencies  . . . . . . . . . . . .43.5.  IPv4 to IPv6 Transition Mechanisms  . . . . . . . . . . . .54.  Conclusions and Recommendations . . . . . . . . . . . . . . . .55.  Security Considerations . . . . . . . . . . . . . . . . . . . .66.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .66.1.  Normative References  . . . . . . . . . . . . . . . . . . .66.2.  Informative References  . . . . . . . . . . . . . . . . . .6Tsirtsis & Soliman           Informational                      [Page 1]

RFC 4977         Problem Statement: Dual Stack Mobility      August 20071.  Terminology   This document uses the following terms as defined in Stateless IP/   ICMP Translation (SIIT) [RFC2765]: 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 [RFC3344] 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 IPv4-capable.   - MIPv6-capable node:      A node that supports MIPv6 [RFC3775] 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 [RFC3344] to maintain   connectivity while moving between IPv4 subnets.  Similarly, a MIPv6-   capable node can use Mobile IPv6 [RFC3775] 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   available.   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 does not   ensure connectivity since that also depends on the IP version support   of the network accessed.  Supporting Mobile IPv4 and Mobile IPv6 is   also more inefficient since it requires:Tsirtsis & Soliman           Informational                      [Page 2]

RFC 4977         Problem Statement: Dual Stack Mobility      August 2007   -  Mobile nodes to be both MIPv4 and MIPv6 capable.   -  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, with each of these systems      requiring its own set of optimizations.   This document 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 discusses   requirements for appropriate solutions.3.  Problem Description   Mobile IP (v4 and v6) uses a signaling protocol (Registration   requests in MIPv4 [RFC3344] and Binding updates in MIPv6 [RFC3775])   to set up tunnels between two end points.  At the moment, Mobile IP   signaling is tightly coupled to 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 set up   IP in IP tunnels, independently of the IP version used in the outer   and inner headers.  Other protocols -- for example, SIP [RFC3261] --   are able to use either an 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).   -  IP-layer local network optimizations for handovers will also need      to be duplicated.   We argue that all of the above will make the deployment of Mobile   IPv6, as well as any dual stack solution in a mobile environment,   harder.  We will discuss some of the issues with the current approach   separately in the following sections.Tsirtsis & Soliman           Informational                      [Page 3]

RFC 4977         Problem Statement: Dual Stack Mobility      August 20073.1.  The Impossibility of Maintaining IP Connectivity   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.3.2.  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.  The ability to   employ both IP versions from one mobility protocol makes it possible   to implement just that one protocol, assuming the protocol choice is   known.  However, in situations where the mobile node must be capable   of working in any network, it may still need two protocols.3.3.  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, 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.  Depending on the security   mechanisms used and with some further work, it might be possible to   rely on one set of common credentials.  Assuming nothing else   changes, however, such duplication is again significant with no gain   to the operator or the mobile node.3.4.  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   IPv6 (HMIPv6) [RFC4140], Fast handovers for Mobile IPv4 [RFC4068]),   the mobile node will need to update the local agents running each   protocol.  Ironically, one local agent might be running both HMIPv6Tsirtsis & Soliman           Informational                      [Page 4]

RFC 4977         Problem Statement: Dual Stack Mobility      August 2007   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 optimization.   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.3.5.  IPv4 to IPv6 Transition Mechanisms   The IETF has standardized a number of transition mechanisms to allow   networks and end nodes to gain IPv6 connectivity while the Internet   is migrating from IPv4 to IPv6.  However, while some transition   mechanisms can be combined with Mobile IPv4 or Mobile IPv6, none of   the known mechanisms have been shown to assist with the issues   described in this document.4.  Conclusions 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 meantime, it is important to   ensure that the problems listed above can be avoided.  Hence, this   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.   The Mobile IPv6 Working Group has reached the view that to allow for   a gradual transition based on current standards and deployment, the   following work areas would 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 to      perform such tasks.  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.Tsirtsis & Soliman           Informational                      [Page 5]

RFC 4977         Problem Statement: Dual Stack Mobility      August 2007   -  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 [RFC3344] and MIPv6      [RFC3775] 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.   If the IETF chooses to pursue all these paths, a vendor could choose   to support one mobility management protocol while avoiding the   incompatibility and inefficiency problems listed in this document.   Similarly, operators could decide to continue using one mobility   management protocol throughout the period of IPv4 and IPv6   coexistence.  However, a mobile node would be forced to choose one   approach or the other, or nevertheless to install both and use one or   the other according to circumstances.5.  Security Considerations   This document is a problem statement that does not by itself   introduce any security issues.6.  References6.1.  Normative References   [RFC2765]  Nordmark, E., "Stateless IP/ICMP Translation Algorithm              (SIIT)",RFC 2765, February 2000.   [RFC3344]  Perkins, C., "IP Mobility Support for IPv4",RFC 3344,              August 2002.   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support              in IPv6",RFC 3775, June 2004.6.2.  Informative References   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,              A., Peterson, J., Sparks, R., Handley, M., and E.              Schooler, "SIP: Session Initiation Protocol",RFC 3261,              June 2002.   [RFC4068]  Koodli, R., "Fast Handovers for Mobile IPv6",RFC 4068,              July 2005.Tsirtsis & Soliman           Informational                      [Page 6]

RFC 4977         Problem Statement: Dual Stack Mobility      August 2007   [RFC4140]  Soliman, H., Castelluccia, C., El Malki, K., and L.              Bellier, "Hierarchical Mobile IPv6 Mobility Management              (HMIPv6)",RFC 4140, August 2005.Authors' Addresses   George Tsirtsis   Qualcomm   Phone: +908-443-8174   EMail: tsirtsis@qualcomm.com   Hesham Soliman   Elevate Technologies   Phone: +614-111-410-445   EMail: hesham@elevatemobile.comTsirtsis & Soliman           Informational                      [Page 7]

RFC 4977         Problem Statement: Dual Stack Mobility      August 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Tsirtsis & Soliman           Informational                      [Page 8]