I got one of these - it came with 1.9 firmware. Possibly a return via Amazon ? In any case, I can't change Flow-Control for any port or group of ports.
Set it to ON and Apply, doesn't stick. I think it's kind of necessary though ...
As a test I have two systems,
backup (2.5G port 4) and
bondi2 (10G port 5). Running iperf3 from backup to bondi2 works fine, no retries. But running from bondi2 to backup,
tons of retries
❯ iperf3 -c backup.local
Connecting to host backup.local, port 5201
[ 5] local 192.168.2.115 port 35044 connected to 192.168.2.119 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 172 MBytes 1.45 Gbits/sec 1647 52.3 KBytes
[ 5] 1.00-2.00 sec 173 MBytes 1.45 Gbits/sec 1727 79.2 KBytes
[ 5] 2.00-3.00 sec 173 MBytes 1.45 Gbits/sec 1565 62.2 KBytes
[ 5] 3.00-4.00 sec 174 MBytes 1.46 Gbits/sec 1547 58.0 KBytes
[ 5] 4.00-5.00 sec 173 MBytes 1.45 Gbits/sec 1555 43.8 KBytes
[ 5] 5.00-6.00 sec 172 MBytes 1.45 Gbits/sec 1753 48.1 KBytes
[ 5] 6.00-7.00 sec 173 MBytes 1.45 Gbits/sec 1546 58.0 KBytes
[ 5] 7.00-8.00 sec 173 MBytes 1.45 Gbits/sec 1464 58.0 KBytes
[ 5] 8.00-9.00 sec 172 MBytes 1.45 Gbits/sec 1683 62.2 KBytes
[ 5] 9.00-10.00 sec 173 MBytes 1.45 Gbits/sec 1710 52.3 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 1.69 GBytes 1.45 Gbits/sec 16197 sender
[ 5] 0.00-10.00 sec 1.69 GBytes 1.45 Gbits/sec receiver
That's indicative of the 10G side just shoveling packets down the pipe to the 2.5G side, which can't handle the rate.