SB8200 is just a cable modem so you can access internet from only one ethernet port since it will be getting only one IP address from the service provider to give internet. This is the situation , even though you have 2 Ethernet ports on the back of the modem , you will be able to connect one device at the time and the reason why its because the modem is getting just 1 valid IP address. If you want to use both ports at the same time you will need to contact your ISP and request a secondary IP Address.