INTERNET Draft George Tsirtsis
Expires: Jan 2007 Hesham Soliman
Qualcomm
June 2006
Mobility management for Dual stack mobile nodes
A Problem Statement
<draft-ietf-mip6-dsmip-problem-02.txt>
Status of this memo
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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 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
IPv4-capable.
- 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
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 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
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
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
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.
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
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.
3.4. 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
E-Mail: Tsirtsis@Qualcomm.com
E-Mail2: tsirtsisg@yahoo.com
Hesham Soliman
Qualcomm Flarion Technologies
Phone: +1 908 997 9775
E-mail: HSoliman@Qualcomm.com
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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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