INTERNET Draft George Tsirtsis
Expires: January 2006 Hesham Soliman
Flarion
July 2005
Mobility management for Dual stack mobile nodes
A Problem Statement
<draft-ietf-mip6-dsmip-problem-00.txt>
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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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1.0 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
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.
2.0 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
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.
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
E-Mail: G.Tsirtsis@Flarion.com
E-Mail2: tsirtsisg@yahoo.com
Hesham Soliman
Flarion Technologies
Phone: +1 908 997 9775
E-mail: H.Soliman@Flarion.com
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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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