Friends can't connect to server even after pfwd'ing/sv_lan 0

[Sonicfan574]

I had a dedicated server a while back using the HlDsUpdateTool, and it worked fine. After updating everything though and installing TF2 content today, it's being an asshole.

I tried both port forwarding and using DMZ (which opens all ports, basically) but it still "fails after four retries" for my friends. I've tried sv_lan 0, heartbeat, ip (my ip), all that shit and it doesn't work.

Pages and pages of google results show this problem but hardly any of them were ever solved. This just shows how shitty networking on Steam games are. A lot of people can host on any game except HL/HL2 based games, including me.