What it does
iperf3 actively measures IP-network bandwidth and reports throughput, loss and other parameters, with configurable test settings and JSON output.
Run iperf3 in server mode at one endpoint and point the client at its hostname or IP address. Both sides must use the same listening port; the documented default is TCP 5201. The client normally sends data, while reverse mode measures delivery from the server. Reports distinguish sender and receiver results, and JSON output supports later analysis. This is active test traffic across that chosen path and endpoint pair, with device capacity and settings affecting the result. Official development platforms are Ubuntu Linux, FreeBSD and macOS. iperf3 is BSD-licensed and does not interoperate with iperf2; check options against the installed manual.
Strengths
- Configurable active bandwidth measurements
- Machine-readable JSON output
Watch out for
- Not backward-compatible with the original iperf protocol
Best for
- Controlled network-path throughput tests
Sources
- iperf3 — iperf3 3.22 documentation (Oct 26, 2026)
- Invoking iperf3 (Oct 26, 2026)