Iperf is a simple client/server tool that you can use to test the bandwidth between 2 linux devices.

For our setup we'll consider the following:

Server = 10.20.30.40
Client = 50.60.70.80

on Server

$ apt-get install iperf
$ iperf -s

on Client

$ apt-get install iperf
$ iperf -c 10.20.30.40