My router is a sagemCOM f@st 1740n, and by special, I mean that there technically is no port forwarding, it's just called virtual servers. The only things you set are external port start and end, protocol, and ip address. I've only tried to host gm and minecraft servers. Yes, I've tried the garry's mod ports (3478, 4379, and 27000), and they come up as closed on port checker websites, which has to be wrong, else my gm server would never have worked in the first place.