A proxy server protects another computer by representing itself as that computer. That is, Computer A contacts Computer B, but Computer C intervenes without Computer A realizing it is not dealing with Computer B. In a network connection, a client contacts a server to request a resource. There are two types of servers -- those that protect clients and those that protect servers.

Forward Proxy Server

The forward proxy server protects the client. It presents requests to a server on the client's behalf, receives the response and then delivers the required resource to the client. This service is implemented in a number of different ways. The first method requires the proxy address to be entered in the network settings of the browser's configuration. Once this is set, all traffic from the browser will not go to the addresses entered in the browser's address bar, but instead they will be presented to the proxy server with the required address as a parameter. The other method is for the user to visit a proxy server website and enter the address of the required destination. This method enables the user to employ a proxy for one specific visit and to keep all other traffic from his browser free from proxy services.

Purpose

Most implementations of proxy servers are corporate. The network administrator sets all browsers in the company to send traffic to the company's proxy server. The proxy server can then implement company policy over access to the Internet. The proxy is configured with a list of banned websites, which may be an explicit list, or a pattern so that any website name containing a particular word is blocked. Similarly, the contents of the returned Web page can be checked for any banned words. The proxy server also acts as a firewall and blocks any programs that a website might try to download onto a client computer. The company proxy server makes all access to the Internet and then delivers the content to the requester on a separate connection. The proxy can also store data received from a particular website if it notices that the same page is frequently requested. It then delivers the page from its own memory, thus speeding up response times.

Reverse Proxy Server

The reverse proxy server receives requests on behalf of a server. It then refers to the server to gather the required information and then delivers this information directly to the client. The client does not know it is dealing with a proxy server. As with the forward proxy server, the reverse proxy server also saves -- or "caches" -- regularly requested information so that it can deliver a response without reference to the server.

Protection

Reverse proxy servers protect servers from infection, from denial-of-service attacks and also from overloading by regular traffic. Where a website has such demand, it needs a series of servers to fulfill all requests, the reverse proxy server provides one entry point with one IP address, or Web address. The proxy then distributes incoming requests between the cluster of servers it is guarding. This is called load balancing. The load-balancing proxy also caches and also protects the servers from malicious attack.