|Microsoft Internet Security and Acceleration Server 2004 SDK|
Unlike Microsoft Proxy Server 2.0, which implemented the Web proxy service as an ISAPI filter that was loaded by the local IIS Web server, the proxy service has been replaced by the Web proxy. IIS Server can be installed on an ISA Server computer but it is not required.
The incoming Web request and outgoing Web request properties can now run on different TCP ports. For example, by default, ISA Server listens for outgoing Web requests on TCP port 8080, while ISA Server listens for incoming Web requests on TCP port 80. In this way, ISA Server ensures that outgoing Web requests do not interfere with Web publishing on port 80.
If IIS Server is installed on the ISA Server computer, it must be configured to not use the ports that ISA Server uses for outgoing Web requests (by default, 8080) and for incoming Web requests (by default, 80). For example, you can change IIS Server to listen on port 81. Then you can configure the ISA Server computer to direct the incoming Web requests to port 81 on the local IIS Server.
If there is a conflict between ports used by ISA Server and those used by IIS Server, the setup program will stop the IIS publishing service. You can then change IIS Server to listen on a different port and restart the IIS Server publishing service.