So I just started my Garry’s mod dedicated server and to my knowledge did everything right, installed everything with the hldsupdate tool, forwarded the ports, put my addons in the addons folder, edited the server.cfg, and made myself admin. But for some reason I can join, either using the lan tab or my external ip address but my friends cannot join because they get a “connection failed after four retries” I’ve tried to have them join using the console and my external ip address and that does not work either. Any ideas?
Make sure you forwarded UDP port 27015 to your computers internal IP port 27015 in your router config. Its easy to make a mistake when doing this and it wont work if its not done right. I use DDWRT on my router, so my config page may be different from what you have on yours. It should look similar regardless.
Also, make sure your firewall on your PC allows traffic on port 27015 or you will still experience this.
Thanks so much man, that was the problem!