transparent proxy?

Answer 1

An intercepting proxy, often incorrectly called transparent proxy (also known as a forced proxy) combines a proxy server with NAT. Connections made by client browsers through the NAT are intercepted and redirected to the proxy without client-side configuration (or often knowledge).

Intercepting proxies are commonly used in businesses to prevent avoidance of acceptable use policy, and to ease administrative burden, since no client browser configuration is required.

Intercepting proxies are also commonly used by Internet Service Providers in many countries in order to reduce upstream link bandwidth requirements by providing a shared cache to their customers.

It is often possible to detect the use of an intercepting proxy server by comparing the external IP address to the address seen by an external web server, or by examining the HTTP headers on the server side.