Directly Connecting Two Computers

This is probably a stupid question with no solution, but I’ll ask anyways since I cannot find anything else on this subject anywhere.

Me and a buddy of mine who lives relatively close-by are trying to create a server in Garry’s Mod that just the two of us can use. Is there any way to do this without having to deal with opening up ports in the firewall?

In other words, we’re trying to directly link up our computers and only our computers without having to go through a firewall.

I think there’s a program called Hamachi, which will allow you to setup a private connection together, I am not sure though, try googling it.