Creating a UDP peer-to-peer connection

Creating network connections with Godot is simple — as long as you have the other party’s IP address, and there’s no NAT gateway involved. Unfortunately, that’s exactly the problem in most cases. You don’t know the other party’s IP, and these days, just about everyone is behind a combination wifi router/gateway/firewall with NAT.

Conceptually, NAT hole-punching is pretty simple, and this video explains how it’s done with just netcat.

In a nutshell:

• listen on a particular port (e.g. 50001)
• nc -u -l 50001
• echo ‘hello’ | nc -u ipaddr 50001
• echo ‘hole punch’ | nc -u -p 50001 ipaddr 50002
• third party exchanges ip addresses

Putting it all together, player A (hosting a game) would require the game to connect to the directory server.

• The directory server would list the game as something a player can now connect to.
• player B (client who wants to join) will tell the directory service that it wants to connect, and will send its info
• The directory server forwards the information to player A (host), player A will then send a packet to player B, and respond to the directory server
• The directory server will then tell player B to go ahead and connect to player A.
• Player B should be able to punch through to player A

With Godot, the connections from client to host would use ENetMultiplayerPeer.create_client(), which can specify the local port.

Here’s an older example of a signaling server: https://github.com/Faless/gd-webrtc-signalling/tree/master