Developing Application Filters

This section describes the basic steps required to create, deploy, and test an application filter. This section is intended for developers who are familiar with Microsoft® Visual C++® and COM. For performance reasons, application filter interfaces are not automation interfaces, and filter objects are best implemented as free-threaded objects. Therefore, Visual Basic®, Java, and scripting languages are not suitable for creating application filters.

Because application filters work with the Microsoft Firewall service, and the Firewall service works with Windows Sockets (Winsock), knowledge of Winsock is also helpful. For information about Winsock, see MSDN.

To become familiar with the filter development process, the following approach is recommended:

1. For a description of ISA Server 2004 architecture, read About Internet Security and Acceleration Server 2004.
2. For information about the basics of filter functionality, read About Application Filters.
3. Examine the logic and interface usage of the sample filters provided with ISA Server.
4. Develop a simple filter. For details about interface methods and parameters, see Application Filter Reference.

This section contains the following topics:

• Filter Development
• Filter Setup
• Application Filter Test Environment