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Mobile communication is one of the things that didn't come to the mind of the people who invented the Internet 30 years ago. There was over-the-air communication even before, especially the ALOHAnet should be mentioned, but the computers were too large to be carried around. And all stations were within reach of each others (by using pretty strong signals — the Hawaii islands are not that small). Handover means that an end node regularly changes the station it's connected to. With a switching system like net2o, this means, the address changes. The communication however should continue even when such an address change happens frequently. And it should work even when both nodes hop from station to station. No complicated renegotiation should happen, and no routing server should be queried if such a thing happens on an open connection. The idea to achieve this is fairly trivial:

This overlap time is necessary if two connected nodes change station at the same time. As the communication itself is protected by encryption from intruders, this is save even without presenting some ticket for the handover. The overlap time can be also achieved by temporarily forwarding packets from the old destination — this is the preferred way to migrate virtual machines to new hosts — the old host temporarily forwards all received packets to the new host, and after a short time can be used for something else. From a firewall point of view, this approach looks scary. When a system opens a connection (which consists of some address ranges), this address range is open to anybody. And worse yet, since the address is not encrypted, everybody can know which are legitimate addresses, by observing the traffic for a while. The blocking of intruders happens solely through encryption, and that encryption is unknown to the firewall (which is the whole point of encryption, after all).