I made several change :
first, i set the server as "serveur only" instead of "private server and gateway" -> same problem
second, I remove one NIC (the WAN one), I reboot -> OK
I wonder the install process (or probably myself) has permute the two driver. I'm surprise because the driver is automaticaly selected ...
I'm going to re-install the second NIC. I hope i will be good now.