We have a machine with an Intel x550 and a Cisco Nexus N9K-C9372-PX-E.
For whatever reason, it will only negotiate at 1Gb, even though it is 10Gb capable and is being plugged into a 10Gb switch. This is on an Asus x299 10Gb board.
We have about 15 other machines with a mixture of Intel x550, Intel x540 and other various 10Gb cards that do negotiate fine on this same switch. All negotiate (slow to negotiate but does) to 10Gb without problems except this one machine with its onboard X550. To me this would rule out the switch as an issue.
To rule out cabling issue I pulled a cable from a current working 10Gb machine and used the working cable and plugged it into the machine I’m having trouble with. I got the same result, the non working machine (X550 ports) negotiates at 1Gb and not the expected 10Gb.
However, if I plug the non working X550 directly into another machine with a 10Gb NIC, both machines will negotiate at 10Gb without issue.
I put an Intel X540-T1 card into the machine and that card negotiates fine to 10Gb. If I move the cable to the on board X550 ports, those will only negotiate to 1Gb
I’ve upgraded the non working machine to the latest 18.04 Ubuntu. I've upgraded the networking card drivers to test, I've upgraded the motherboard BIOS, I've upgraded the x550 firmware. Not sure what else the issue could be.