I have had this set up for some time and have always wondered why I have almost continuous activity on my cable modem. Here is my setup. Roadrunner cable modem (surfboard sb3100) connected to my router which is connected to a simple hub to connect to my two desktop computers. Currently I have the router running with DHCP enabled and desktops with dynamic ip. I believe I have run with DHCP disabled and didn't notice any change. The activity light blinks constantly even when the computers are shutdown.

My question here is is this normal or am I wasting bandwith?