This was recommended to me by the network engineers at work as being one of the fastest and efficient ways to measuring bandwidth on a link. IPerf does not have to be installed, it runs simply in a command prompt window. You need to setup IPerf on both ends to perform testing.
To use IPerf to test your network speed perform the following:
On one end run IPerf as the server:
On the other end run IPerf as the client including the name or ip address of the iperf server.
iperf -c 10.10.9.39
Here we can see we are getting 8.93mbps over the link to my other end.
Another handy trick is you can test bandiwidth both ways by using the -d switch for duel-test. This should be done if your network is full duplex only! If your running half-duplex this is not a good test to do!
iperf -c 10.10.9.39 -d
This testing was done over an MPLS cloud!