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Use the HOSTS File to Block Web Sites

By Stephen Bucaro

When you type a domain name into your Web browser, Internet Protocol contacts a computer that is a domain name server to look up the IP address of the Web site. In the early days, the Internet didn't need domain name servers. Every computer had a file named HOSTS that listed the domain name and IP address of the systems connected to the Internet.

Even today when your Web browser needs to resolve a domain name to an IP address, it first looks for a file named HOSTS on the local computer. In Windows NT, the HOSTS file is located in c:\windows\system32\drivers\. In Windows 9x, the HOSTS file is located in c:\windows\.

Because the HOSTS file is no longer required, you may not find it on your computer. Instead, you might find a file named HOSTS.SAM, the SAM extension meaning "SAMPLE". You might also find a file named LMHOSTS. The LMHOSTS file was used to resolve NetBIOS names to IP addresses.

The HOSTS file is simply a text file with a list of IP addresses and their respective domain names. You can open the file with Windows Notepad. The HOSTS file may list only one IP address, the loopback address, as shown below.

127.0.0.1 localhost

To block a Web site, enter an IP address that is not allowed for the Web. For example, any IP address with the first digit of 0 would be on the local network. Any IP address with the first digit of 127 is looped back. Then map that IP address to the domain name that you want to block.

For example, suppose you want to block a porn site that your teenager has been visiting, you might add an entry like the one shown below.

127.0.0.2 www.pornsite.com

Banner ads are usually hosted on an advertiser's domain and linked to sites all over the Web. Suppose you want to block annoying banner ads displayed at a site that you visit frequently. You might add an entry like the one shown below.

127.0.0.3 www.adserver.com

Then when a file from that domain name is requested, instead of the porn site or the banner being displayed, the browser will display the message "The Page Cannot be Displayed".

When you save the HOSTS file after editing, make sure that the file name does not have an extension. Sometimes Windows Notepad adds the extention .txt.

The HOSTS file is a quick, easy way to block access to a Web site. But if you use this method to block a porn site that your teenager has been visiting, make sure they don't find this article.