Troubleshooting • Pi3+ dropping network connection speed

I have a desktop switch which has three Pi3+ boards connected to it, along with a Synology NAS. The switch has LEDs which show that a device is connected, and is either at 1Gb/s (green) or 100Mb/s (orange).
(All are running latest bookworm arm64, freshly updated this morning)

When I boot the Pi3+ machines, they start as green, but soon after, they drop speed down to orange.

dmesg -e reveals the following:What is the most likely cause of this?
Is it possible to set the lan so it doesn't negotiate, but wants 1Gbps all the time?

I do have bluetooth and wifi enabled on the machines, although strictly speaking, it would be possible to turn both of these off, since neither is necessary for any of them. I had issues with a Pi4 which runs dnsmasq where I would get repeated 'Link is Down/Link is Up' which went away when I turned off bt/wifi on the Pi4. Do I need to do the same with these?

And yes, I understand that it's going over USB2, so won't be 1Gbps transfer rate (although these are headless, so USB contention should be fairly low...), I'm not expecting blistering speeds, just trying to understand what's happening in case there's an issue with any of the hardware.

I have tried different ports on the switch, and a different switch, and get the same results.

Any help, as always, greatfully received....

Statistics: Posted by SteveSpencer — Fri Jun 27, 2025 9:20 am

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