Mobile IPv6 (MIPv6) allow mobile nodes to roam between Internet domains while maintaining ongoing sessions and reachability. This is done by using an IPv6 home address or prefix. Since IPv6 is not widely deployed, however it is unlikely that mobile nodes will use IPv6 addresses just for their connections alone. It is assumed that mobile nodes be requiring an IPv4 home address for a long time, which can be used by upper layers. It is fair to assume that mobile nodes will be moving to networks that might not be IPv6-ready and would therefore require an IPv4 Care-of need capability support.
IPv6 compared to IPv4, offers a number of functional improvements, mostly due to its large address space and additional functional fields. The same goes for Mobile IPv6 compared to Mobile IPv4, which offers a number of improvements inheriting from IPv6 additional capabilities, including: Dynamic Home Agent Discovery (DHAD) and route optimization, which can only be achieved in Mobile IPv6 systems.
An advantage of having a large address space (as in IPv6) is to allows mobile nodes to obtain a globally unique care-of address disregarding their current location Hence, there is no need to use Network Address Translator (NAT) traversal techniques, which are required for Mobile IPv4. This further simplifies Mobile IPv6 system architectures and increases the efficiency of mobility management protocol and bandwidth allocations. However for existing private IPv4 networks, NAT traversal needs to be considered during the transition towards IPv6.
In order to minimize the need to changing the mobility stack because of the IPv6introduction within a deployed network and to allow for a long lasting mobility solution Mobile IPv6 should be used with dual stack mobile nodes capability.
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