iperf3 - benchmarking Wifi - strange behaviour for traffic from wifi to 10 GbE

Hi!

I have a strange behaviour, that I do not really understand.

I am benchmarking a Wifi6-AP with iperf3.

Everything is working fine, if the remote-station to the wifi-client has a 1 GbE interface.

IF the remote station is using a 10 GbE-interface, ONLY traffic TO the wifi-device is slow:

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1 GbE remote station:

Wifi -> remote station: 600 MBit/s

Wifi <- remote station: 600 MBit/s

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10 GbE remote station:

Wifi -> remote station: 600 MBit/s

Wifi <- remote station: 340 MBit/s

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My first thought was about flow control. I did tests with and without - no success.

I did tests with different NIC chipsets and devices - no success.

I did tests in the same subnet and over the router - same values.

I did a test with VMs and BareMetal servers - same values.

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Do you have any idea, how this can happen?

Thank you for your help!

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ITStril