How to test your Fibre Line Health with iPerf

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. You can use iPerf UDP testing to detect small amounts of packet loss under load.

In some cases where basic speed tests do not solve an issue, running traffic load tests might be required to pinpoint a problem. As some issues can be intermittent, not reproducible during a site visit, or happen at odd times, it’s often quicker and more feasible for customers to run these tests when the problem occurs.

We host our iPerf servers 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 on our network is the Fibre Network Operator. In other words, if the tests show packet loss, we can ask the Fibre Network to investigate.

Before proceeding please keep in mind this is advanced troubleshooting, and requires tests to be run through your command prompt, with your computer connected directly via Ethernet to your Fibre ONT/CPE.

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.

How to install iPerf:

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

Local 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 flag 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.

Local 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 30 -O 3 -R -c -p 3334

IPv6 command

iperf3 -6 -V -t 30 -O 3 -R -c -p 3334


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