I want to connect both my router and an Ethernet cable to my modem. I can only get a connection from one at a time and not both. If I get my Ethernet cable working, my router won't work and if my router is working, my Ethernet cable won't. I can get both working by plugging in my Ethernet cable to my router, but its not long enough for my setup. I have an Xfinity dual band wifi 802.11ac modem and a D-Link DIR-655 router.