Just do what SirDice suggested to you in post #2, put your modem in bridge mode. Double NAT (which you're trying to do right now) is a bad idea/practice and serves no purpose at all. It'll just cause you more headache further down the road. Keep min mind that switching to bridge mode is a bit different between ISPs. Sometimes you need to wait for you DHCP lease to expire before you reboot the modem and renew. One of the ISPs here require you to reboot the modem without WAN (coax) connected, connect it after ~5 minutes after switching it to bridge mode.