You have the modem with the built-in router from flow? This is what I can recall about port-forwarding with the flow equipment. If it doesn't work, well someone else may help you.
The default address of the old modems without router is
http://192.168.100.1The modem is just a bridge, so you cannot configure anything there, only a tech can with the super-admin login credentials.
The default address of the modem/router is
http://192.168.0.1/ or the default gateway IPv4 address that your computer is using currently.
Default User Name:
admin and Password:
passwordObviously you will change this for your own security.
Then go under Firewall Tab and there should be a Virtual Servers tab under that. This is a picture from the old Arris modem/routers, so yours may look differently, but it's the same settings really.
And Enable the box 1 for whatever game/program you want to port forward. type in the same port number in all labelled port boxes, type in your local client ip address, i.e. the ip address that the router has assigned your computer. To check whether it's a TCP or UDP port check here:
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers. For example, the Call of Duty (PC) line of games are on port 28960 UDP.
Save settings, may have to reboot the router (not reset). Then go in your software firewall and open that port.
Then check if it's open with this
http://portforward.com/help/portcheck.htm. Don't worry, it's not a virus or any malicious software, even though your antivirus/firewall may tell you otherwise.
As an alternative, if forwarding specific ports doesn't work, you can DMZ your computer's client ip address, manually set your computer's ip address so it won't change with automatic DHCP and just open the ports in the software firewall on your computer (like ZoneAlarm or Comodo). This would leave your computer open though, and just the installed software you've got to protect you, or if you don't have, Windows Firewall. Your choice. If you've got good software, I think you would be safe from noob hackers if they find you...