most broadband ISp's use dynamic TCP/IP to make it difficult for hackers. But that doesn't mean the ISP does not know who is connected. I would think they would want to guard the data to prevent hackers getting too much of a foothold. But I have no concrete information.

Some large companies refuse to recieve e-mail from a user who has dynamic TCP/IP which is a pain. So the ISP provides a static one, but it costs more so we can assume they have engage protection which is not as cost effective.