I am currently working on a little p2p basic system in python and I would like to know how do you make a TCP hole punch. I already successfully did one in UDP but I want the more organized TCP connection for the rest.
And yes, i've already googled the question but it does not seem that everybody has the same answer nor does it work.
You have to use a little trick. If you know the IP address and port of the peer you want to connect to, say 192.168.1.2:8081 , then you can punch the hole by connecting directly to it (using the same IP, of course) and telling it what your real IP is:
import socket
peer_ip = "192.168.1.2"
peer_port = 8081
my_ip = "192.168.1.1"
my_port = 8080
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((peer_ip, peer_port))
sock.send("OPEN %s:%d\n" % (my_ip, my_port))
If you connect to it then the firewall should open a port from your IP address to the peer's IP address and port that you specified in the OPEN command (this is a TCP hole punch protocol called ASYNC3 , which is described on the Async3 website).
To test this, you can use nc to connect to the peer and say hi. This should work if you are behind a NAT and have a firewall (even if it's not the same firewall that opened the hole):
$ nc 192.168.1.2 8081
hello, world!