In one of the many responses I found to your issue they mentioned that also - that Cox has a NAT further up the line. I have two routers on my system but one just piggy-backs off of the main one which is connected to the cable modem (the second one is just to add a VPN gateway). Your EA8500 is what should be issuing the IP via DHCP to the NAS and the NAS should just be set in Obtain IP Automatically mode. It should be noted that I'm not running an NAS here I've just had to configure them in the past (it's been awhile though, lol).