IFWXFilter interface

Applies to: desktop apps only

The IFWXFilter interface is used by the Microsoft Firewall service to load and initialize a filter and to create session filters. When the Firewall service starts, it creates an instance of the COM object that implements the IFWXFilter interface in each application filter that is installed on the Forefront TMG computer and enabled, and then the Firewall service calls the FilterInit method for each application filter to initialize it.

For more information about how this interface is used in application filters, see Filter Object Model.

For more information about implementing the IFWXFilter interface, see Implementing a Filter Object.

When to implement

Every application filter must implement this interface on a COM object called the filter object.


The IFWXFilter interface inherits from the IUnknown interface. IFWXFilter also has these types of members:

  • Methods


The IFWXFilter interface has these methods.

Method Description

Creates an instance of the session filter object, returns a pointer to the IFWXSessionFilter interface on the object created, and populates an FwxFilterHookEvents structure created by the Firewall service with the set of events that the session filter will handle.


Initializes the filter, passes a pointer to the IFWXFirewall interface exposed by the Microsoft Firewall service to the filter, and populates an FwxFilterHookEvents structure created by the Firewall service with the initial set of events for which the filter should be notified.


Begins the shutdown sequence for the filter object when the Firewall service is shutting down.



Only one instance of the IFWXFilter interface is created for each application filter. In the IFWXFilter interface, you define a port, or range of ports, to be monitored, and the events that will trigger a call to the IFWXFilter::AttachToSession method.


Minimum supported client

None supported

Minimum supported server

Windows Server 2008 R2, Windows Server 2008 with SP2 (64-bit only)


Forefront Threat Management Gateway (TMG) 2010



See also

Filter Interfaces



Build date: 7/12/2010