How to Find an IP Address of an External Modem Through a MAC

By C. Taylor

External modems have two IP addresses used to route information to and from the Internet.
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An external modem has two Internet Protocol addresses. The first is the external IP address, which is assigned by your Internet service provider. The second is the internal IP address used to communicate between your modem and other hardware, such as your computer or a router. Both IP addresses are associated with the modem's MAC address, which is the static identifier for the modem.

Reference your modem's manual for the internal IP address. In most cases, this will be "" or less likely "" in older 3Com Tailfin modems. To verify the address, enter "" in your browser. If you see your modem's configuration, this is the internal IP address.

Find the MAC address by referencing the modem's manual or looking for a sticker on the side of the modem.

Click "Start," "All Programs," "Accessories" and "Command Prompt." Type "ipconfig" in the window and press "Enter." Look for "IP Address" (XP) or "IPv4 Address," and follow the dotted line to the four-part number formatted as XXX.XXX.XXX.XXX. This is your external IP address.

Go to an IP lookup website (see "Resources") and look at your displayed "IP Address" or "WAN" to find out your external IP address.