How to Set Up: Wireless Router + Cable Modem
NOTE: This article provides the overall concept for setting up a wireless router to work with a cable modem instead of a DSL modem. It is not a step-by-step how to guide for beginners.
Setting up a wireless router to work with a cable modem is very different than with a DSL modem. The idea is to fool the cable modem into believing that your wireless router is actually a computer instead of a router. Don't worry, this isn't as hard as it sounds.
NOTE: The physical hookups in the end will be the same as when your router was using a DSL modem or its own built in DSL modem. Basically, your cable modem will use a standard Ethernet cable to connect to the wireless router and then everything else will connect to the wireless router.
First off, you need to hook up a computer to the cable modem using a standard Ethernet cable and do an IPCONFIG /ALL command from the CMD prompt to find the IP, Mask, Gateway, and (if shown) host domain pulled by the computer. You will also need to write down the DNS servers listed. If using a Linux computer the command is IFCONFIG. You can now unhook the computer and hook up the wireless router.
Next, you will put these exact settings into the wireless router on the external side that will connect to the cable modem. The internal side of the wireless router can be setup however you like. I would recommend a simple DHCP environment with security on the wireless side. After you save the settings unplug the power on both the cable modem and the wireless router. Now, plug in the cable modem and wait for it to fully establish. Then, and only then, plug in the wireless router.
NOTE: If you don't reboot the devices in this order it won't work right.
You should now be able to connect to the Internet on any device hooked up to the wireless router.
NOTE: All ISPs and hardware brands are different, so take this as a general concept and your situation may require further setup. For instance, some cases will require setting the MAC on the wireless router to match the MAC on the cable modem. This will essentially take it a step further and fool your ISP into thinking your wireless router is a cable modem.