How To Test Network Bandwidth With iperf3 in Linux

Testing network bandwidth in multiple flavors in Linux is simple with a tool called iperf. There’s two main versions – iperf2 and iperf3. Project maintainers apparently completely rewrote iperf3 from scratch to make the the tool simpler and to support some new features.

Update 12/12/2021: One of the authors of iperf2 reached out to me. Iperf2 is currently very much actively developed. You can find the most recent code on its sourceforge.net page. Iperf3 was indeed rewritten from scratch as the wikipedia page says, but mostly to meet the U.S. Department of Energy’s use cases. Iperf3’s github page clearly states the the DoE owns the project.

For testing bandwidth properly, you need to be running in server mode on one endpoint and client mode on the other. For this experiement, we will run the server on Rocky Linux 8.5 and the client on Ubuntu 20.04.

Topology

iperf3 test in GNS3

This is about as simple of a topology as I can think of. Two nodes on either end of a single link, Ubuntu at 10.0.0.1/30 running iperf3 client and Rocky at 10.0.0.2/30 running iperf3 server.

Iperf3 installation

On Ubuntu, iperf3 can be installed from distribution sources with apt-get:

apt-get install iperf3

Same on Rocky Linux but with yum:

yum install iperf3

Run iperf3 bandwidth test

First we need to start the server process on Rocky Linux with one command:

iperf3 -s

Then you should see the server listening for incoming tests:

iperf3 server listening on Rocky Linux 8.5

Then from the Ubuntu client, one command will run the test:

iperf3 -c 10.0.0.2

The output will give us our bandwith test results, which can be see on either the client or server:

Connecting to host 10.0.0.2, port 5201
[  5] local 10.0.0.1 port 59628 connected to 10.0.0.2 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   176 MBytes  1.48 Gbits/sec  685    230 KBytes       
[  5]   1.00-2.00   sec   173 MBytes  1.45 Gbits/sec  738    113 KBytes       
[  5]   2.00-3.00   sec   170 MBytes  1.42 Gbits/sec  1004    191 KBytes       
[  5]   3.00-4.00   sec   175 MBytes  1.47 Gbits/sec  714    123 KBytes       
[  5]   4.00-5.00   sec   182 MBytes  1.52 Gbits/sec  458    163 KBytes       
[  5]   5.00-6.00   sec   204 MBytes  1.71 Gbits/sec  443    314 KBytes       
[  5]   6.00-7.00   sec   180 MBytes  1.51 Gbits/sec  910    130 KBytes       
[  5]   7.00-8.00   sec   191 MBytes  1.60 Gbits/sec  849    123 KBytes       
[  5]   8.00-9.00   sec   172 MBytes  1.44 Gbits/sec  564    170 KBytes       
[  5]   9.00-10.00  sec   184 MBytes  1.54 Gbits/sec  412    225 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  1.76 GBytes  1.52 Gbits/sec  6777             sender
[  5]   0.00-10.04  sec  1.76 GBytes  1.51 Gbits/sec                  receiver

iperf Done.

A wireshark capture in GNS3 between the two hosts (or tcpdump on the links if you’re not in GNS3) will show the packets flying while the test is running:

Wireshark capture from GNS3 of iperf3 test

Hope you liked it!

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