Hello,

I have a CRS312-4C+8XG https://mikrotik.com/product/crs312_4c_8xg_rm
Using RouterOS version 6.49.6. No queues or firewall rules. Plain switching.
PC connected via cooper 10 Gbps to it. ( 5 meters )
NAS connected via cooper 10 Gbps to it ( 1 meter )

Problem
When connecting a 1 Gbps client to this switch and try to download something from my PC ( 10 Gbps ), I get horrible speeds, fluctuating between 60 Mbps and 100 Mbps. I would say a median of ~75 Mbps downloading single large files.
When downloading/uploading between my PC ( 10 Gbps ) and my NAS ( 10 Gbps ) the speed is decent at around 5 Gbps and close to 8.5 Gbps using iperf3. My NAS is limited by its CPU.

Downloading from my PC ( 10 Gbps ) to a 1 Gbps client. Downloading from my PC ( 1 Gbps forced from WinBox ) to a 1 Gbps client Downloading from my PC ( 1 Gbps ) to a 1 Gbps client via a 1 Gbps switch ( not Mikrotik ) Using the same cables for all tests.
CPU on CRS312-4C+8XG barely used.
Repeated the tests numerous times and 100% is not a fluke.
Found some posts mentioning this issue but could not find a fix also.

Anyone experienced this and able to pinpoint the cause?

Thank you.

try checking your PC 10g nic windows advanced settings

try checking your PC 10g nic windows advanced settings

Thank you. This little piggy was to blame. Was disabled. Enabled it and problem is gone.

thank you for sharing the solution