Most routers do not handle routing to themselves. Thus, when your router sees you trying to connect to your global IP, it just forwards it along to your ISP. The ISP notices that you are trying to connect to yourself, so it just drops the packet. Edit your zone.dat file so your IP is 127.0.0.1 or use Custom Zone in the zone menu editor and set your IP as that.
Unless by over the internet, you mean someone other than you behind your own router, then I don't think you forwarded the correct ports. In your server.cfg, go to the [Misc] section and find the Port value there. Say it is set to 5000. You need to forward UDP 5000 and UDP 5001 to your computer. You do not need any TCP.