How Does a Proxy Server Work?

Purpose

The basic idea of a proxy server is to act as an intermediary between the client computer and the Web server. The proxy server does all the work of connecting to the Web server. The main reasons for using a proxy are anonymity, security, speed and filtering. The client computer is invisible to the Web server; this protects it from malicious attacks and also keeps the client computer anonymous. A proxy server may speed up connections through caching. This means that the proxy servers keep a copy of files requested so that they can quickly send them if requested, avoiding the potentially slower download speeds of the host server. Finally, the proxy server may be used to filter or censor the information from before sending it to the client. For example, a school may blacklist sites considered inappropriate for students.

Connecting

The client computer is connected to the proxy server through the Web browser. The Web browser options include connection options that allow a proxy to be manually set. To do this the network address of the proxy server is put into the appropriate boxes. From that point forward any time the user enters a Web address in the browser it will talk to the proxy rather than directly to the Web server. This process is invisible to the average Web user.

Filtering

Once the proxy server receives a request from the client computer, such as a request for a Web page, it first checks that it passes filtering requirements such as a blacklist set up by the network administrator. Provided that it does, it will connect the to the server in question. Any malicious attacks from the Web server will automatically be directed to the proxy server, which has strong firewall protections. After the proxy server receives the Web page it will keep a copy in the cache so that if a client computer requests it again within a short period the proxy can send the cached version rather than having to download it again. Connections between a proxy server and client in the same physical LAN are usually faster than download speeds from distant Web servers, so caching saves time. Finally, the proxy server will pass the Web page to the client computer.