Some ISPs (most notably MediaOne) use your NIC’s MAC address to authenticate your service.  When you change the computer that you have connected to your cable modem service, you usually have to call up Tech Support and give them the MAC address of the NIC in the new machine.   Since hardware routers have the equivalent of a NIC on their WAN port in order to connect to your cable modem, you would have to do the same thing if you’re installing a router.

Recently, however, some ISPs have started to recognize the MAC addresses of popular routers and disconnect service if a router is detected.  Fortunately, many router manufacturers are including the capability to either set the router WAN port MAC address to anything you want, or copy it from a computer connected to the router LAN side.  You can check the Router comparison chart under “Mac addr. clone” to see which routers support this feature.  Then consult the router’s documentation for directions on using the feature.

If you use the feature, make sure you copy the MAC address from the computer that was used when your cable modem service was installed.  You can find the MAC address by using the winipcfg command in Win95 & 98, ipconfig command in Win NT, and the Info Button on the TCP/IP Control Panel on a MacOS machine.  Look for “Adapter Address”, “MAC address”, “Hardware Address”, or a number containing six pair of Hexadecimal digits such as: 03-EF-DF-5D-3E-23.

After you set the new address, you’ll probably need to power down your router, power cycle your cable modem, then power up your router in order to properly connect to your ISP.