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We tested the popular open source tool IPERF to see how accurately it is at measuring bandwidth of a link and the reliability of its reporting. Our goal was to measure the bandwidth of a link that had a lot of buffering (i.e. a bufferbloat situation.)

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So we set up an Iperf server at one end and an Iperf client at the other.  We ran Iperf in UDP mode – we did not want our results affected by TCP congestion algorithms.  We ran a single-direction test.  The client was instructed to send traffic into the link much faster than we knew the link could handle – we expected substantial loss of packets and we also expected a significant time delay for may of those that did get through we.

We observed those expected effects.

And we observed more that we did not expect.  In particular we observed that Iperf was significantly under reporting the actual bandwidth of the link.


Key Topics Covered:

  • Converting IPERF Results to Real bandwith
  • Accuracy of Results
  • Alternative Testing Tools

Protocols Discussed:

  • User Datagram Protocol (UDP)
  • Transmission Control Protocol (TCP)
  •  Address Resolution Protocol (ARP)

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