HOSTS file

A text file in a TCP/IP network that specifies the IP addresses of computer names and domain names. It is used to convert a request by name to a numeric IP address on the local network or the Internet.

Testing and Quick Retrieval

HOSTS files are used to override the DNS system for testing purposes so that a Web browser or other application can be redirected to a specific IP address. In addition, by explicitly stating an IP address in a HOSTS file, a website can be retrieved more quickly, because the multiple transmit/receive steps a normal DNS query takes have been eliminated. See DNS.

Denying Access to Websites

websites can be denied access from a computer if the URLs of those sites are added to the HOSTS file and directed to the loopback address of 127.0.0.1. For example, the following entry in a HOSTS file prevents users from reaching YouTube or eBay.

  127.0.0.1   youtube.com
  127.0.0.1   ebay.com

HOSTS File Locations

In Windows, the HOSTS file is in the \windows\system32\drivers\etc folder. In the Mac, it is in /private/etc. The first line of a HOSTS file contains the following. See localhost.

  127.0.0.1   localhost