Comcast modems connect to the central Comcast network when they are plugged in and retrieve an IP address to assign to your computer or router, whichever is plugged in to the modem. If you are using a Comcast modem, you can easily find out what its IP address is through a few methods. These methods only require a basic understanding of computers to carry out and offer a variety of options for finding out the IP address based on what your current setup happens to be.
Open a web browser on a computer connected to the modem or to a router that is connected to the modem and use an online IP checking website. The IP address displayed on these sites is the IP address that is currently assigned to your modem.
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Directly connect your computer to the Comcast modem, click "Start," click "Run," type "CMD" into the Run window and wait for the command prompt to appear. Type "IPCONFIG" in the Run window and look at the IP address that is returned, as it will be the current IP of your Comcast modem.
Connect your computer to a router that is connected to the Comcast modem. Open the web interface of the modem and look at the settings of the router. An IP address will be displayed that is the currently assigned IP address of the Comcast modem.