Network Utility showing 2 different connection speeds - which is correct?

[AVR2]

My 2019 MBP is connected to a Gigabit switch which is connected to my fibre router. I'm using Cat6 cable throughout.

Network Utility is giving me two conflicting connection speed reports. When I choose "Ethernet", it says the link speed is 100 Mbit/s, when I choose "USB 10/100/1000 LAN" it says it's 1 Gbit/s. What's the reason for two different link speeds being reported?

According to the Network pane in System Preferences, the network speed is 1000baseT.

I've got a couple of non-Gigabit-capable devices connected to the switch, but I was under the impression that they wouldn't slow down comms between Gigabit-capable devices on the switch.

 

[lostngone]

It shows USB bridge. This could be on another USB device you have plugged in or a device that emulates a network interface.

I would unplug your USB devices one by one and see which one cause it to go away when plugged. You might have to remove all your USB devices and then delete the interface and then plug them in one by one and wait until it comes back.