Free Wireshark Training Course Online

Take a free Wireshark Jumpstart training class online at

Tuesday, September 8, 2009

Do You Know Where Your Throughput is Today?

iPerf Might Scream "This Stinks!"

Last night I was laughing and crying at the same time while reading a local small town newspaper and the dissertation on bandwidth problems at the local library. They actually shut off half the computers to aleviate the problem. One quote really grabbed me - "We don't notice the bandwidth problem when no one is using the computers." Hunh?

There were a few puzzling comments in the article such as the comment that the bandwidth problem "started 3 weeks ago." That sudden onset of the problem feels like something else to me. It feels like a device along the path that is causing the problems. A quick look at the traffic would validate that.

The article tied in nicely to the iPerf Throughput Testing materials I am finishing up. The reaction to the live iPerf testing done during the Analyze and Improve Throughput course and numerous requests for more information on iPerf prompted me to start developing a course that shows how to perform a series of throughput tests for UDP and TCP traffic.

iPerf is simple and complex at the same time. The one application can be run either in client mode or server mode.

Tests can be run in one direction (from the client to the server, which is the default) or bi-directionally. Here is one of my favorite tests for iPerf:

Client: -c -u -t 60 -i 5
Server: iperf -s -u -i 5

This test enables me to locate jitter and packet loss along a path using a UDP stream sent over a 60 second time with results displayed every five seconds at both the server and the client.As you can see from the screenshot above, the path suffers packet loss reaching 39%. We were sending a steady stream at 1.05 Mbit/second specifically to identify packet loss. Well... we found it. Running the test for a full 24 hours would help us identify specific times of the day when packet loss is at its highest.

I hope to get into the local library and run Wireshark and iPerf on the network soon. I have no idea if the systems are locked down - a slight problem that might require some workaround. Meanwhile I'll peruse the shelves for those network troubleshooting books.

The "iPerf Throughput Testing" modules will be included in the Summit 09 course in December ( - the "Analyze and Improve Throughput" course is available now at

Enjoy life one bit at a time.