Fullcone NAT

The fullcone NAT method allows any external host (regardless of whether the internal client has initiated any contact with it or not) to send packets to the internal client IP address and port, using the external natted address defined by the NAT binding. The reverse packet flow for the fullcone NAT binding can be from any server, port, using any protocol. The only requirement is that the sending server know the external public address of the fullcone NAT binding.

Fullcone NAT shows an example of fullcone NAT.