A transparent proxy server, also known as an intercepting proxy server or a forced proxy server, is a server that intercepts outbound information on a network before it hits the Internet, without requiring any configuration on the client computer. Unlike explicit proxies, which require configuration on a software-by-software basis, transparent proxies require only server-side configuration, which means that they might be in use on a network without the end user’s knowledge. These servers are often employed to optimize load balance or filter content. Many schools and workplaces use this kind of proxy server.
Like an explicit proxy server, a transparent proxy server can increase network performance through a process known as caching. Data is stored locally on the first request, which enables subsequent requests to process much faster. On a network using a transparent proxy server, all requests from client computers go through a single host, so the host can store much of the frequently requested data locally, saving any need to transfer the data via the Internet. When a large number of web requests are being made — such as on many school or business networks — caching can conserve a great deal of time and bandwidth.
A transparent proxy server also can be used to filter or block specific web content from being accessed on a network. The network administrator can establish a list of websites that the proxy server will filter out before they can be accessed by the end user. For instance, an employer may wish to prevent employees from browsing sports websites while at work. With the proper transparent proxy server configuration, an attempt to check yesterday’s sports scores will instead result in an error page for the employee, preventing him or her from wasting working hours on a non-work-related website. Although this method of filtering will often be enough to prevent casual users from accessing undesirable content, savvy users might find means of bypassing the filtering process because of limits in the technology.
Transparent proxies are useful for many educational and commercial computer networks. A transparent proxy requires no configuration on each client computer, so network administrators often use them as a means of saving time on individual system setups. Although a transparent proxy offers the same caching and filtering benefits as most explicit proxies, it does not offer any Internet Protocol (IP) address masking functionality. Therefore, a transparent proxy is not suitable for many of the online security purposes often associated with web proxy servers.