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WiscNet hosted Iperf

Iperf is a measurement tool network testing tool used to help measure network throughput. It's developed by ESnet / Lawrence Berkeley National Laboratory. For more information please visit and


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  • Iperf is a commonly used network testing tool to help measure network throughputIperf is an open source tool. There are clients for Mac, Linux, BSD, etc. There is a port for Windows; however, in our testing we found it to lack certain features and to lag in performance. 
  • Iperf operates where one end is the client, the other is the server.

WiscNet Server Details

  • WiscNet runs an Iperf version 2 server in Eau Claire, WI
  • The server is restricted to WiscNet IP addresses
  • Iperf2 and iperf3 are incompatible
  • runs a TCP Iperf server on the default port 5001
  • runs a UDP Iperf server on port 5001
  • runs a v6 TCP Iperf server on port 5001
  • runs a v6 UDP Iperf server on port 5001

TCP vs UDP Testing

  • Iperf uses TCP by default. TCP has built in congestion avoidance. If TCP detects any packet loss, it assumes that the link capacity has been reached, and it slows down. This works very well, unless there is packet loss caused by something other than congestion. If there is packet loss due to errors, TCP will back off even if there is plenty of capacity. iperf allows TCP to send as fast as it can, which generally works to fill a clean, low latency link with packets. If a path is not clean/error free or has high latency, TCP will have a difficult time filling it. For testing higher capacity links and for links with higher latency, you will want to adjust the window size (-w option).

  • By using the -u option, you have told iperf to use UDP packets, rather than TCP. UDP has no built in congestion avoidance, and iperf doesn't implement it either. When doing a UDP test, iperf requires that the bandwidth of the test be specified. If it isn't, it defaults to 1Mb/s. You can use the -b option to specify bandwidth to test. iperf will then send packets at the request rate for the requested period of time. The other end measures how many packets are received vs how many were sent and reports its results.

Some Common Iperf Flags

  • Enter iperf -h or man iperf depending on your operating system. Here are some common flags:
-cClient mode-c
-tTime to run the test in seconds-t 30
-PNumber of parallel connections-P 2
-uUDP (default is TCP)-u
-bBandwidth per thread
-b 250m
-iInterval between bandwidth reports in seconds-i 1
Listen on port-L 5001
bidirectional test (individually)-r
bidirectional test (simultaneously)-d