What is Reddit's opinion of iPerf3?

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Per the iperf3 documentation, -n will stop the transfer after a specific number of bytes. So if you're combining that with -P, you'd want to multiply -n by -P.

https://software.es.net/iperf/invoking.html#iperf3-manual-page

That said, if you have any kind of local software distribution platform (Active Directory, etc), rolling it out that way is probably a better idea.

The iperf faq states that you should use iperf2 on windows instead of iperf3.

• iperf3 parallel stream performance is much less than iperf2. Why?
• I’m trying to use iperf3 on Windows, but having trouble. What should I do?

Using iperf2, I was able to get 60 Gbps on a 25 Gbps x 4 connection between to two Windows Server 2016 servers. At that point, the sender CPUs were maxed out.

If you already have a gigabit switch and your APs are new (802.11ac or 802.11ax), then it's likely either narrow channels, congested channels, or a failing link to an AP that's running at 100mb.

It's usually easy to test by setting up two machines and using a performance testing tool. iperf3 does a great job at this, and is available for every OS you can imagine, you just need to be able to run it from the command line. If you are running modern APs, have a gigabit switch and APs, use 5GHz WiFi with 40MHz channels or larger, you should get ~200-250Mb/s fairly easily. If you do, then look at your own router and ensure it's not traffic shaping and can support the higher speeds.

To do an extender to extender speed test, I’d say you’d need a PC of some sort connected via Ethernet to each one, then run iperf3 on each PC and see what you get (one client, one server)

https://software.es.net/iperf/