I recently get Comcast Internet and want to own my own cable modem instead of pay Comcast every month to rent one . Everything go well have to contact Comcast with Mac ID and serial # but after set everything up my modem keep cycling through and the Comcast guy say my modem would go online and then go offline . he think I have a faulty modem and they be go to charge I $ 50 to send a rep out to check if it be a line problem or a modem problem . luckly I google the problem and find that these modem sometimes have a problem with receive too powerful a signal from the cable line and say a attenuator or cable line splitter would do the trick . so I have a line splitter that take the 1 line and split it into 3 seperate line and then it work perfectly with a less powerful signal . Everything work perfectly now and the modem be great but I be surprised Comcast do not suggest to try this since it be a issue that be know .