Measuring network performance with iperf

August 16th, 2010 by Jeff

My new place in Austin came with a huge perk for a tech geek like me – it came pre-wired for ethernet in every room.  (Well, technically not every room is wired.  The laundry room, bathrooms, and garage are not, an understandable oversight.)

After installing a new D-Link Gigabit Ethernet Switch, I wanted to check the throughput to see if I was actually getting gigabit speeds – particularly because the house is wired with CAT-5e cable (and not the recommended CAT-6).

There are many ways to measure network throughput.  In the past I have usually copied a file across the network and used a stopwatch to get a relative sense of speed.  However, due to file sharing protocol overhead I always got disappointing results and never knew maximum capability of my network.

This time, based on the advice of a more network-savvy friend, I decided to use a command-line tool called iperf.

iperf is a command-line tool to measure network performance.  It is very powerful, but also easy to use for simple tests.  For a more complete overview of what iperf is and what it can be used for, check out this tutorial or the iperf page on Wikipedia.  iperf has a lot of options, and I won’t cover the majority of them here.  For more usage information, consult the iperf manual.

If you run Debian or Ubuntu (Linux), iperf can be installed by executing

sudo apt-get install iperf

I did these tests with OS X on the Mac since both of my Macs have gigabit ethernet ports and my older PCs don’t.  A package for iperf is conveniently available from Macports.  It can be installed via the graphical package manager Porticus or opening a Terminal window and typing

sudo port install iperf

In my case, all I wanted was a quick test of TCP/IP network performance.  This is easy to do, but it requires two computers, a client and a server, both connected to the network under test.  Ideally, there should be no other network traffic during the test, as this will affect the results.

On the first computer, launch the iperf server by executing

iperf -s

You should see something like this:

Server listening on TCP port 5001
TCP window size: 64.0 KByte (default)

On the 2nd computer (the client), open a Terminal window and run

iperf -c <IP address or hostname of server> -i 1

Within a few seconds, you should start to see reports coming in on both the client and server terminal windows:

Client connecting to mini.home, TCP port 5001
TCP window size:   129 KByte (default)
[  3] local port 65142 connected with port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0- 1.0 sec    110 MBytes    924 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  1.0- 2.0 sec    101 MBytes    850 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  2.0- 3.0 sec    109 MBytes    914 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  3.0- 4.0 sec    100 MBytes    841 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  4.0- 5.0 sec    111 MBytes    927 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  5.0- 6.0 sec    102 MBytes    853 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  6.0- 7.0 sec    110 MBytes    923 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  7.0- 8.0 sec    102 MBytes    858 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  8.0- 9.0 sec  79.4 MBytes    666 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  9.0-10.0 sec  93.6 MBytes    785 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  1018 MBytes    854 Mbits/sec

The last report (for the interval 0.0-10.0 sec) is the average throughput for the entire test.  I’m more than happy with 854 Mbits (927 Mbits/sec peak!) given my fairly long runs of CAT-5e cable and other machines using the network.   Contrast this with my results over 802.11g wireless:

[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  24.9 MBytes  20.9 Mbits/sec

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2 Responses to “Measuring network performance with iperf”

  1. Josh says:

    I have had that same switch for a few months now and it is a pretty sweet deal at only $45. I have never done a speed test on it so I will have to try it out and see if I get the same results as you.

  2. Jeff says:

    I have the smaller 5-port version as well, and it has been running flawlessly for about a year now. It runs much cooler than the rest of my network gear, cool enough that I can stick it in a closet with zero airflow and it barely gets warm.
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