Proxy Automatic Configuration

PAC files script appropriate proxy routing by URL characteristics.

Proxy Automatic Configuration (PAC) is a way to automatically set the appropriate proxy for a given URL request. This is done by developing a JavaScript file with a .pac extension that is used by users' browsers and which evaluates their URL requests and forwards each request to the appropriate proxy. This approach has the advantage of being completely within the control of network administrators and of operating transparently from the perspective of end users. Explaining how to create, implement and maintain PAC files is beyond the scope of this documentation. For details on the development and use of PAC files, you can start with's PAC End User Guide for Firefox and Microsoft's Automatic Discovery of Firewall and Web Proxy Clients page.