Hello ecos66

                       SB8200 is just a cable modem so you will be getting one IP from the internet service provider for after activation and so if your able to access internet from direct connection you can access internet from the router connecting to the same ethernet port on the modem and when you are swapping the device you need to restart modem for a minute because cable modem can read only one MAC address at a time and then connect the router to the modem to access internet from the router. If still you face same issue on the router then we would suggest you to check with your router manufacturer.