IFWXSlowDataFilter Interface

The IFWXSlowDataFilter interface provides a method that the Firewall service can call to verify that the instance of the data filter object associated with a connection has completed the processing of all data for the connection before terminating it.


interface IFWXSlowDataFilter : IUnknown

When To Implement

An application filter may implement this interface to prevent data loss that results from the premature termination of connections.


The IFWXSlowDataFilter interface inherits the methods of the IUnknown interface.

In addition, IFWXSlowDataFilter defines the following method.

Method Description


Verifies that all data for this connection has been processed.


When a Firewall client application calls the Winsock WSACleanup function, the client DLL will close the Microsoft Firewall service session. As a result, the Firewall service will terminate all the connections that were created in this session.

Occasionally, this may lead to data loss, if the client application relies on TCP/IP for receipt acknowledgement. The connection could be closed after acknowledgement of a packet receipt because the slow connection delays the receipt of the remainder of the packets. This is not an issue if the client application uses application level acknowledgement.

To prevent data loss in these cases, an application filter should implement the IFWXSlowDataFilter interface.


Server Requires Windows Server 2008.
Version Requires Forefront Threat Management Gateway (TMG).

Declared in Wspfwext.idl.

See Also

Filter Interfaces

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Build date: 11/30/2009

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