Reply To: can I invoke winpkfilter functions in C#?

ndisapi.dll is a Win32 DLL and you can call it from C#. Please check the links below about calling Win32 DLL from C#

http://www.codeproject.com/Purgatory/C_DLL_with_Csharp.asp
http://msdn.microsoft.com/msdnmag/issues/02/08/CQA/
http://msdn.microsoft.com/msdnmag/issues/03/07/NET/