The iperf application must be installed on both ends of a link (a host and a client). Once iperf is installed, start the server end:

$ iperf -s 

Then run the client side to generate throughput statistics:

$ iperf -c 192.168.1.36 
------------------------------------------------------------ 
Client connecting to 192.168.1.36, TCP port 5001 
TCP window size: 19.3 KByte (default) 
------------------------------------------------------------ 
[  3] local 192.168.1.44 port 46526 connected with 192.168.1.36 port 5001 
[ ID] Interval       Transfer     Bandwidth 
[  3]  0.0-10.0 sec   113 MBytes  94.7 Mbits/sec 

The -m option instructs iperf to also find the Maximum Transfer Size (MTU):

$ iperf -mc 192.168.1.36 
------------------------------------------------------------ 
Client connecting to 192.168.1.36, TCP port 5001 
TCP window size: 19.3 KByte (default) 
------------------------------------------------------------ 
[  3] local 192.168.1.44 port 46558 connected with 192.168.1.36 port 5001 
[ ID] Interval       Transfer     Bandwidth 
[  3]  0.0-10.0 sec   113 MBytes  94.7 Mbits/sec 
[  3] MSS size 1448 bytes (MTU 1500 bytes, ethernet)