Install iperf3 on a Ubuntu/Debian Linux server
apt-get install iperf3
Start an iperf3 server on serverA (server mode)
iperf3 -s
Start an iperf3 server on serverB (client mode)
iperf3 -c ip serverA here
How to use UDP rather than TCP
iperf3 -s -u (on serverA)
iperf3 -c ip serverA -u