Fully detailed tutorial on how to play with friends
Before someone responds with that forum post by chase, that doesn't really cover T4 at the moment. It just says to turn on UPNP, and to port forward. I use Hamachi for that. While T6 works fine, T4 has no option to start a custom match by yourself, while T6 does.
Start a solo match then have them connect. I have edited the guide.
Still doesn't work for some reason, I did all the things necessary, I even dug up an old wifi adapter instead of using ethernet, nothing. I port forwarded, I used hamachi, I used the UPNP, every time I would try it, it just wouldn't work.