Port Forwarding
Just out of curiosity, does Cox currently allow Port Forwarding or is it blocked by the ISP? I have opened a number of ports through my third party router and Windows Firewall as necessary to temporarily host a dedicated server for some friends to play a game. It is not the first time I have done this either. Years ago, I would be able to open these ports and go to a website such as canyouseeme.org to verify the ports are open. However, now whenever I check these ports I am being told that they are still closed and my friends are unable to see or connect to the server when it is up.
I've tried updating my router's firmware, resetting it to factory defaults, power cycling both the router and modem, etc. I cannot for the life of me figure out why these ports are still showing as closed when the router indicates they are opened and that Port Forwarding is turned on.
+1 for modem and router you have. Cox does not block port forwarding. See thread here.
::edit:: Do you still have the MB8600? If so, try bypassing the router and connect direct to the MB8600 with ethernet and the power cycle the MB8600 to renew DHCP. See if the ports are open then. That will see if your firewall on your OS is open.