Thanks a lot for those explanations
Here is what i undestood about the way it works.
All in coming frames , (which, of course, arrives by physical NIC) are send to applications listening; no mater IP because applications listen ports not IP + port.
All frame send throw Virtual IP are redirected to physical NIC and then to the router.
Router only know the real (class C) IP. All forward must be done to physical NIC IP address
Is it all right ?
Thanks again for you help