If memory serves me right, keith tokash wrote:
I'm sorry I should have been more specific. I'm referring to the *percentage* of a circuit's bandwidth. For example if you order a 20Mb site to site circuit and iperf shows 17Mb. Well ... that's 15% off, which sounds hefty, but I'm not sure what's realistic to expect.
This doesn't exactly answer your original question, but... iperf (as well as its follow-on, iperf3) runs between two end hosts, so an iperf test will be measuring other effects, such as congestion (as others have pointed out), but also end-host tuning, the LANs to which the end hosts are attached, etc. ${WORK} maintains a good reference to tuning networks for high-performance R&E networks...some of these techniques are applicable to other environments as well. http://fasterdata.es.net/ Bruce.