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How Fast is Fast? Find out with iPerf! Speedtest Your Network

iPerf is a command line tool that allows you to test the throughput of a network using TCP or UDP protocols. This is helpful for knowing where bottlenecks exist in your network or if specific hardware is performing as intended.

rastacalavera

rastacalavera

— 3 min read
How Fast is Fast? Find out with iPerf! Speedtest Your Network

iPerf is a command line tool that allows you to test the throughput of a network using TCP or UDP protocols. This is helpful for knowing where bottlenecks exist in your network or if specific hardware is performing as intended. I personally used this tool to test my crimping of CAT5/6 cables as I was running them through my dwelling.

When using this tool, it is important to know that there are two versions and that these versions are not compatible with each other. So when you decide to install the tool on your machines, be sure you pick the same one. iPerf and iPerf3 are available in your Linux OS repos but also as pre-compiled binaries for Windows, Mac, Android, etc.

The iPerf tool runs as a client or server on your machine, so to test the speed of your network, you'll need two machines total and have one run the tool as the server and the other as a client.

On the machine you are running as the server, you'll want to put in the following command: iperf3 -s -p 5001

There are two options used in the command -s which tells the tool that it should run the server and -p which designates what port the server should listen to for traffic. If you don't designate a port, iPerf will pick one. You'll need to open up ports on your firewall for both machines so that they can reach out to each other. A common way to do this on systems that use ufw is to use the command:

sudo ufw allow 5001

This will open up port 5001 for IPv4 and IPv6 traffic. When you are done with your testing, you can close up the firewall ports again using sudo ufw deny 5001 on both of your machines.

On the machine acting as the client you'll want to put in the following command:

iPerf3 -c 10.10.0.140 -p 5001 -bidir

There are three options being performed in this command. The -c tells the tool that the machine is acting as the client. The -p is the port designation as discussed above and the -bidir tells the tool that we want to test the connection in both directions. This is helpful because it shows the amount of traffic to and from the server.

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The above option can be found in the man pages for iPerf3. 

Results from the server on a wired connection and laptop on wireless 5G

[  4] local 10.10.0.141 port 60252 connected to 10.10.0.140 port 5001
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec  5.62 MBytes  47.0 Mbits/sec
[  4]   1.00-2.01   sec  5.50 MBytes  45.8 Mbits/sec
[  4]   2.01-3.01   sec  5.62 MBytes  47.3 Mbits/sec
[  4]   3.01-4.00   sec  5.38 MBytes  45.4 Mbits/sec
[  4]   4.00-5.01   sec  1.00 MBytes  8.32 Mbits/sec
[  4]   5.01-6.01   sec  4.00 MBytes  33.4 Mbits/sec
[  4]   6.01-7.00   sec  3.50 MBytes  29.7 Mbits/sec
[  4]   7.00-8.01   sec  3.00 MBytes  25.0 Mbits/sec
[  4]   8.01-9.01   sec  4.75 MBytes  39.6 Mbits/sec
[  4]   9.01-10.02  sec  4.25 MBytes  35.6 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-10.02  sec  42.6 MBytes  35.7 Mbits/sec                  sender
[  4]   0.00-10.02  sec  42.6 MBytes  35.7 Mbits/sec                  receiver

[  4] local 10.10.0.166 port 58827 connected to 10.10.0.140 port 5001
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec  90.9 MBytes   761 Mbits/sec
[  4]   1.00-2.00   sec  88.8 MBytes   745 Mbits/sec
[  4]   2.00-3.00   sec  92.4 MBytes   775 Mbits/sec
[  4]   3.00-4.00   sec  91.5 MBytes   767 Mbits/sec
[  4]   4.00-5.00   sec  92.5 MBytes   777 Mbits/sec
[  4]   5.00-6.00   sec  92.1 MBytes   772 Mbits/sec
[  4]   6.00-7.00   sec  92.5 MBytes   776 Mbits/sec
[  4]   7.00-8.00   sec  91.2 MBytes   765 Mbits/sec
[  4]   8.00-9.00   sec  92.6 MBytes   777 Mbits/sec
[  4]   9.00-10.00  sec  92.9 MBytes   779 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-10.00  sec   917 MBytes   770 Mbits/sec                  sender
[  4]   0.00-10.00  sec   917 MBytes   770 Mbits/sec                  receiver

As you can see from the output above, I get much better speeds on the wired than wireless connection which is expected. Also, you'll notice that the last two lines in each output show the bandwidth from both machines. If these didn't match, then it can be helpful in trouble shooting issues.

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Have you used iPerf inside and outside your network? Maybe tried it on a mesh VPN network like Nebula or Tailscale? Let us know in the comments below how you've used it to solve problems or to share any other tips or tricks.

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