Configuring ISAPI Filters in IIS 7
Applies To: Windows 7, Windows Server 2008, Windows Server 2008 R2, Windows Vista
Internet Server Application Programming Interface (ISAPI) filters are programs that you can add to IIS to enhance Web server behavior. ISAPI filters receive every HTTP request made to the Web server to provide additional functionality for the server, such as logging request information, authenticating and authorizing users, rewriting URLs, and compressing Web content to reduce bandwidth cost.
In IIS 7, modules replace ISAPI filters, but you can still add ISAPI filters if you require the functionality that they provide.
For information about the levels at which you can perform these procedures, and the modules, handlers, and permissions that are required to perform these procedures, see ISAPI Filters Feature Requirements (IIS 7).