I don't believe that's true. You would still need something like UDP hole punching to bootstrap the inbound flow on both sides first. Also you would still only be limited to UDP traffic, TCP would still be blocked.
I don't believe that's true. You would still need something like UDP hole punching to bootstrap the inbound flow on both sides first. Also you would still only be limited to UDP traffic, TCP would still be blocked.
Sending one packet outbound is hole punching. It's really that simple. Since there's no NAT, you don't need to bother with all the complexity of trying to predict the port number on the public side of the NAT. You just have two sides send at least one packet to each other, and that opens the firewalls on both sides.