how can i do NAT tunnel UDP hole punching in java?

how can i do NAT tunnel UDP hole punching in java?

because of th开发者_如何学Pythonis, the A and B computer behind the different NAT can not receice the UDP packs which they send to each other.....

how can i solve this?

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You need a server S with a public IP address. A and B should open a connection to S. This will open an UDP hole in the NAT. Then S can read the NAT translated address/port for A and B. Then S can send back this information to A and B who can start communicating directly on each other's open TCP port.