How to test your Fibre Line Health with iPerf

We host an iPerf server on our network, so if you have a device (laptop or desktop computer) plugged into your Fibre ONT/CPE the only thing between your device and the iPerf server is your Fibre Network Operator. In other words, if the tests show packet loss, we can ask the Fibre Network to investigate. You can use iPerf UDP testing to detect small amounts of packet loss under load.

Slow International with Fast Local Speeds

iPerf testing can be very useful when you see slow international speeds while getting fast local speeds. Small amounts of packet loss (1%) on your fibre line, will have a big impact on international speeds with higher latency (140ms+), while local speeds with low latency (16ms) will still be fast.


Before proceeding please keep in mind this is advanced troubleshooting, and requires tests to be run through your command prompt.

Please note these tests are only for Atomic Access customers. If your ISP doesn’t have clear steps to test for packet loss, please consider switching to Atomic so we can help.

✅  Make sure you run these tests with a laptop/PC plugged directly into the Fibre ONT/CPE, with a Cat5 or Cat6 Ethernet cable and make sure the laptop has a Gigabit Ethernet interface. For Openserve customers, you can test in the router or configure PPP on the laptop port.


How to install iPerf:

Install a recent iperf3 version, ideally version 3.9 or newer.
Here is the link to the installation files:

80% UDP Test – Detect Packet Loss Under Load

iperf3 -4 -V -t 30 -O 3 -u -b 80M -l 1440 -R -c -p 3334

Change ‘-b’ parameter to 80% of your line speed. This should run with very little loss – ideally 0%. Up to about 0.5% for short intervals is usually ok. Please include all commands used when you make screenshots of the results. To be extra sure you can also run this test in the upload direction by removing the ‘-R’ flag.

TCP Test – Maximum Speed

Shows the maximum speed of a single TCP session from the data centre to you. This should be close to your fibre line speed.

IPv4 command (most common)

iperf3 -4 -V -t 20 -O 3 -R -c -p 3334

IPv6 command

iperf3 -6 -V -t 20 -O 3 -R -c -p 3334


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