Managing multicard net in a FTP client

Hallo to everybody,
I'm in a deep trouble. I'm developing a Gateway between two FTP servers. In the 1st server the gateway has to read only the files, while in the 2nd has to write and nothing else. A simple transporting data. While developing I've seen that my code cannot establish exactly the right network card to use. I know that the Operative System manages automatically the binding of the pool of network cards. I'm using MFC: do you think there a way to keep control on it?
Thank you in advance :wave:
Stefano