Microsoft Internet Authentication Server (IAS) is a standard of the RADIUS (Remote Authentication Dial In User Service) server used to authenticate Users connecting to the ISA Server 2004 Firewall machine. You can use IAS to authenticate Web Proxy clients on your Internal Network or VPN clients, VPN gateways are making connections from an External Network location (eg from a corporate branch office). Alternatively, RADIUS can be used to authenticate remote users when these objects connect to Web servers that have been published through Web Publishing rules on ISA Server 2004.