This section documents the callback function that is implemented by a filter-hook driver and the I/O control (IOCTL) that the filter-hook driver uses to register such a callback function. The filter-hook driver's callback function is also known as a filter hook. The Internet Protocol (IP) filter driver that is supplied with the system uses a filter hook to determine whether to either forward or drop incoming and outgoing packets.
A filter-hook driver supplies the symbolic address of its filter hook to register the filter hook's entry point with the system-supplied IP filter driver. The filter hook is defined by the PacketFilterExtensionPtr data type. Because a filter-hook driver supplies the address, and not the name, of its filter hook entry point, driver developers are free to name the filter hook whatever they wish.
This section includes the following topics: