VS 2012 How Make Packet Block PC

I wanna make program can filter packet. Can Anyone Help me?

Example PC A And PC B

Then PC A Access PC B. But some program in PC A Blocked by PC B that mean filter access so no one make crash or do modify on B

I looked blocked system access can detected internet protocol...and scan IP who access in PC B. so i can filtered. many there(internet) using C# and i not understand C#.

thank you for advance