Web Filter Basics

When a Web (ISAPI) filter is loaded, the filter passes a structure to the ISA Web proxy service, which contains, in addition to other information, a bit field that specifies the types of filter events of which the filter should be notified. Each time one of those events occurs, an event notification is sent, and every Web filter that has specified interest in that event is notified.

Designing a Web filter requires you to consider what events your want the filter to react to, and decide what processing the filter will perform when the vent occurs. In addition to those basic design considerations, you have to select a priority for the filter, and ensure that it will be properly registered so that it is loaded by the Web proxy service.