Pluggable 2.5Gbps USBC-E2500 Asymmetric Speeds

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New Member
Feb 1, 2024
Have an interesting problem - there might not be a solution (aka hardware limitation), but I figured I'd float it and see if anyone else has encountered it.

I have two WIN11 PCs, each with a USBC-E2500 adapter.
Using a crossover cable and iperf3, I can fully max out the UL and DL rates. I get between 2.3 - 2.4 Gbps. So it can get there.

When I connected both PCs to a CRS-310-8G+2S-+IN, the download is solid at full speed, but uploads are mysteriously capped at 2 Gbps.

The Switch is running router OS 7.14.2, and I have verified that no software processing is occurring - a) CPU usage stays at 0% during the tests, and b) the same PC using intel i226 NIC gets full upload via the same switch.

Two different PCs get the same 2 Gbps limit, both via the USB-C port on the motherboard. Clearly not a USB/PCI bandwidth limit, since the full download speed is achieved.

I've tried changing all the settings on the NIC itself - none of which had any effect (things like rx & tx offload, auto negotiation, etc.).

What on earth would be causing the bottleneck, specifically on uploads. Any thoughts?