What am i sure about is that your modem gives only one public ip adress, not private.
easiest solution, if you have any router, wifi router, attach cable modem in wan port, and any lan port into ruckus. That will solve your problem
If you doesnt have any router, you will need to set local subnet(s), and virtual lan, in addition to set dhcp that will give your devices local ip, not public (that is problem with your setup).
Maybe you'll need to set proper port setup (i am not very skilled in that area)