|Title||Problem Statement: Dual Stack Mobility
|Author||G. Tsirtsis, H. Soliman
Network Working Group G. Tsirtsis
Request for Comments: 4977 Qualcomm
Category: Informational H. Soliman
Problem Statement: Dual Stack Mobility
Status 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.
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 Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction and Motivation . . . . . . . . . . . . . . . . . . 2
3. Problem Description . . . . . . . . . . . . . . . . . . . . . . 3
3.1. The Impossibility of Maintaining IP Connectivity . . . . . 4
3.2. Implementation Burdens . . . . . . . . . . . . . . . . . . 4
3.3. Operational Burdens . . . . . . . . . . . . . . . . . . . . 4
3.4. Mobility Management Inefficiencies . . . . . . . . . . . . 4
3.5. IPv4 to IPv6 Transition Mechanisms . . . . . . . . . . . . 5
4. Conclusions and Recommendations . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . . 6
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
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
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:
- 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, 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.
3.1. 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 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
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
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.
- 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
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.
6.1. 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,
[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,
[RFC4068] Koodli, R., "Fast Handovers for Mobile IPv6", RFC 4068,
[RFC4140] Soliman, H., Castelluccia, C., El Malki, K., and L.
Bellier, "Hierarchical Mobile IPv6 Mobility Management
(HMIPv6)", RFC 4140, August 2005.
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