A proxy server is a device or a program that makes requests for information from the Internet on behalf of a client computer and then directs the response back to the client. Proxy servers can serve a wide variety of purposes, depending on how they're configured and where they're installed. For example, one popular use of a proxy server — a caching proxy server — is storing temporary copies of all files and web pages requested from the Internet. If a second computer later asks for the same file or web page, the proxy server can deliver it directly over the local network without having to download it again from scratch. This makes web browsing and downloading faster and reduces congestion on one's Internet connection.
For more on using proxy servers (outside your local network) to provide anonymous web-browsing capabilities, see Chapter 10.
If you set up a proxy server between your local network and your gateway and then direct all Internet traffic (or all traffic of a particular type, such as web or FTP) through it, the proxy can do other things too. For one thing, you can configure it to filter incoming and/or outgoing data — for example, preventing employees on your network from visiting certain websites or from sending out certain types of information. It can also provide some security (and a small measure of anonymity) by making all outbound requests appear to have originated from a single computer and by blocking some incoming requests directed ...