This section introduces Windows Filtering Platform callout drivers. For a more information about the Windows Filtering Platform, see the Windows Filtering Platform documentation in the Microsoft Windows SDK.
Purpose of Callout Drivers
A callout driver implements one or more callouts. Callouts extend the capabilities of the Windows Filtering Platform by processing TCP/IP-based network data in ways that are beyond the scope of the simple filtering functionality. Callouts are typically used to do the following tasks:
Perform complex inspection of the network data to determine which data should be blocked, which data should be permitted, and which data should be passed to another filter. An antivirus product, for example, could look for virus signatures.
Perform modification and reinjection of the network packet headers or data, or both. A network address translation (NAT) product, for example, could modify the headers on IPv4 packets.
In addition to processing network data, callout drivers can perform other Windows Filtering Platform management tasks, such as adding filters to the base filtering engine. For more information about other tasks that a callout driver can perform, see Calling Other Windows Filtering Platform Functions.