The AT&T modem setting is referred to as "IP passthrough". The reason I had to use that is that the range of acceptable IP's in the modem differe significantly from the router. It made the most sense to have the router control all that. The actual key to the last element was using the IP for the Modem (in passthrough mode) on each of the 3 HD DVRs....now everything works, since the modem flows the Internet connection on to the router, and then to the DVR's. What is a bit concerning is not only the time it took to make all this magic work, but most people's setups will vary, depending on their ISP provider, modem setup, and router. It would be great to have some simple documentation indicating the dependencies of what IP's should be used where, and what modem dependencies must be satisfied.....as without that.....there are countless individual elements that could possibly stop it all from working.