Test connection speed with iperf

Install iperf, for example on Ubuntu or Arch use one these commands:

Ubuntu/Debian:
apt-get install iperf

Arch:
yay iperf

On computer one, run iperf in server mode:

iperf -s

On the other, run iperf in client mode:

iperf -c 192.168.0.10

If you want to see the full duplex speed, try this instead:

iperf -d -c 192.168.0.10

Substitute 192.168.0.10 for the servers IP address