EXPERT RESPONSE
The use of extension headers with IPv6 to carry options (that are carried in the basic IP header with IPv4) makes IPv6 much more flexible for mobile communication. Some of the extension headers are used to optimize routing in a mobile environment. So for instance, when a host wants to roam from network to network without loosing its TCP connections, it will use mobile IP to do so. It then uses a home agent in its home network that will hold its TCP connections on its behalf while the mobile node is roaming. With IPv4 therefore, all communications from the mobile node with any service it is connected to will always go through its home agent. With IPv6, by using extension headers, if the mobile node is in a remote network connecting to a service in another network, it can, after a few initial packets through its home agent, route packets to the service directly, thereby optimizing the route. In the future, when we have to expect large numbers of mobile users roaming about using mobile IP, the old IPv4 scenario would create a heavy bottleneck at the home agent as all traffic from all mobile nodes of its network would be routed through that home agent.
Other features that will be very helpful in mobile networks are the much more flexible address space and above all the autoconfiguration possibilities IPv6 offers.
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