@Gordonwv yes it was the cable after all! I changed the cable with an other one and it worked fine. I had a homemade CAT6 cable, I guess I wired it bad!

Anybody had this issue where your router is plugged in a Gigabit Switch and the port negotiate 100Mbps Full duplex instead of 1000Mbps? I have the latest firmeware - tried to reboot both my switch...