Developing Application Filters

This section describes the basic steps required to create 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 Firewall service, and the Firewall service works with Windows Sockets (Winsock), knowledge of Winsock is also helpful. Information about Winsock can be found in MSDN.

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

1. Read the description of Internet Security and Acceleration (ISA) architecture in About Internet Security and Acceleration Server.
2. Read Introducing Application Filters for information on the basics of filter functionality.
3. Study Filter Development Tools, particularly the general descriptions of the basic and advanced object interfaces needed for filter creation.
4. Work through the step-by-step procedure provided in How to Create an Application Filter.
5. Examine the logic and interface usage of the sample filters provided with ISA.
6. Develop a simple filter. See the Reference for details on interface methods and parameters.

Topics in this Section

This section contains the following topics:

• Introducing Application Filters
• Filter Development
• Application Filter Test Environment
• Filter Setup
• How to Create an Application Filter
• Sample Filters