Filter Types

You can develop a wide range of application filters by using the ISA Server Software Development Kit (SDK). Examples of filter types are:

1. Protocol-enabling filters: These filters enable the usage of a protocol through the Firewall service. These filters open dynamic secondary ports, and edit Secure Network Address Translation (SecureNAT) addresses. The FTP and H.323 filters provided with ISA Server are examples of protocol-enabling filters.
2. Protocol-scanning filters: These filters scan data from specific protocols for intrusion, viruses, and so on. Examples of protocol-scanning filters are the Internet Security Systems (ISS) POP and DNS filters that are provided with ISA Server.
3. Redirection filters: These filters may cause specific connections to be redirected into their control and act as a server. For example: The HTTP redirector filter provided with ISA Server redirects HTTP connections to the Web Proxy service.
4. Other filters, such as those that check content. ISA Server's architecture allows developers a great deal of latitude in creating filters.