Test bandwidth between two servers

http://stackoverflow.com/questions/426272/how-to-test-internet-connection-speed-from-command-line

on machine1 (host, this one will receive)

iperf -s -p 65000

on machine2 (client, this one will upload)

iperf -c [ip of server] -p 65000

Reverse the machines to test the other way (upload->download or vice versa).