What is a Proxy Server

As defined by RFC 2068, a proxy is "an intermediary program which acts as both a server and a client for the purpose of making requests on behalf of other clients." RFC 2068 continues, "requests are serviced internally or by passing them on, with possible translation, to other servers. A proxy must implement both the client and server requirements of this specification."

The type of a proxy is determined by, among other things, the amount of information that the proxy reveals about the person using it. For example, transparent proxies add, to their HTTP requests, one of two HTTP headers - VIA or PROXY_CONNECTION - that are unique to proxies, and another HTTP header - X_FOWARDED_FOR - from which the original IP address can be determined. In contrast, Anonymous proxies, lack the X_FOWARDED_FOR header. High Anonymity proxies (also known as Elite proxies), unlike Anonymous proxies, can't be identified at all as proxies from their HTTP requests (ie. their requests don't include any of the three afore mentioned HTTP headers). A proxy which sends out HTTP requests from a different IP address than the ones it recevies them from is known as a Gateway proxy.