Hole punching

A number of techniques exist for ‘hole-punching’ network address tables, in order to allow connections to be made between two computers, neither of which are directly connected to the internet. These generally rely on having some sort of ‘rendez-vous server’ used in order for the NAT to allow the connection. That is to say, the technique only works with ‘help’ from a server which is not behind a NAT, which means that although the server’s role is minimal, it does not give us complete independence.

– Seeding the Wild