From the Kenosha News on 2-24-08
Use commands in a DOS window to troubleshoot connection problems
If you’re old enough, you might remember back to when computers didn’t use a Windows operating system. The screen was black, and people had to type commands to make things happens. These were the day of DOS: Disk Operating System. While Windows and MacOS have made computer usage much easier by providing a Graphical User Interface (GUI), you can still access a DOS-like window and type in commands. Some of these commands are very helpful, especially to troubleshoot connectivity problems.
To access a DOS window in Windows XP, click Start, then click Run. At the prompt, type in “cmd” and press Enter. You will get a black window in which you can type commands. When finished, type “exit” and press Enter or click the Close box (X) at the upper right corner of the window to close it.
If you’re having a problem connecting to the internet, you can use the DOS window to determine if you’re getting a valid IP number. IP is “internet protocol” and in order to get onto a network or the internet, you need to have a valid IP number. Special servers run by your local network, your home router, or your internet service provider (called DHCP servers) give out IP numbers to computers trying to connect to the internet. To see if you have a valid IP number, open a DOS window, type “ipconfig” and press Enter. Wait for several lines of information to be displayed. If you have multiple types of connections on your computer (e.g. wired and wireless), you may have multiple IP numbers. Each section will be labeled with the connection type, usually Ethernet something. Look for the item labeled “IP Address.” Check it as follows:
If you don’t have a valid IP number, you can request one by typing “ipconfig /renew” at the prompt and pressing Enter. If you receive a message that no DHCP can be reached, then you are not physically (or wirelessly) connected to the internet. (If you use dial-up, you must initiate your dial-up connection before this will work. You can also use this /renew command if you get “page not found” or other error messages in your browser.
By Carol Sabbar from the Kenosha News on 2-24-08