iperf is a tool that can perform active measurements of a network by connecting a client instance to a server instance and measuring transfer performance between them.
On any of our nodes you can install iperf using:
apt install iperf
You can run iperf in TCP or UDP mode. It might be best to measure using both modes since they can reveal different networking issues. UDP mode is a little more useful since it can report packet loss and jitter in addition to overall bandwidth availability.
In either mode, start one instance in server mode using:
iperf -s
On a node on the other end of the network segment to measure, run an instance (or several) in client mode pointing at the node where you're running the server instance:
iperf -c HOST_OF_SERVER
By default, it will perform a measurement for 10 seconds and both server and client will report the results.
You can switch to UDP mode by adding -u to both server and client command lines.