v  In an enterprise that uses the Internet, a proxy server is a serverthat acts as an intermediary between a workstation user and the Internet so that the enterprise can ensure security, administrative control, and caching service. A proxy server is associated with or part of a gatewayserver that separates the enterprise network from the outside network and a firewallserver that protects the enterprise network from outside intrusion.

v  In computer networks, a proxy server is a server  which services the requests of its clients by forwarding requests to other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server. The proxy server provides the resource by connecting to the specified server and requesting the service on behalf of the client. A proxy server may optionally alter the client’s request or the server’s response, and sometimes it may serve the request without contacting the specified server. In this case, it would ‘cache’ the first request to the remote server, so it could save the information for later, and make everything as fast as possible.

v  A proxy server that passes all requests and replies unmodified is usually called a gateway or sometimes tunneling proxy.

v  A proxy server can be placed in the user’s local computer or at specific key points between the user and the destination servers or the Internet.

v  A proxy server receives a request for an Internet service (such as a Web page request) from a user. If it passes filtering requirements, the proxy server, assuming it is also a cache server, looks in its local cacheof previously downloaded Web pages.

v  If it finds the page, it returns it to the user without needing to forward the request to the Internet.

v  If the page is not in the cache, the proxy server, acting as a client on behalf of the user, uses one of its own IP addresses to request the page from the server out on the Internet. When the page is returned, the proxy server relates it to the original request and forwards it on to the user.

v  To the user, the proxy server is invisible; all Internet requests and returned responses appear to be directly with the addressed Internet server. (The proxy is not quite invisible; its IP address has to be specified as a configuration option to the browser or other protocol program.)

v  An advantage of a proxy server is that its cache can serve all users. If one or more Internet sites are frequently requested, these are likely to be in the proxy’s cache, which will improve user response time. In fact, there are special servers called cache servers. A proxy can also do logging.