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Test LAN transfer speed with iperf3

Measure the real throughput between two machines on your network — great for checking Wi-Fi vs Ethernet.

Linuxnetworkiperf3speed-testlanLow risk
Start iperf3 -s on one machine, then run iperf3 -c ITS-IP on the other and read the Gbits/sec summary.

01Command

Command
$ iperf3 -s   # on the receiving machine; then: iperf3 -c 192.168.1.20

02What it does

Internet speed tests can't tell you why copying to your NAS is slow — iperf3 measures the raw path between two of your own machines. One machine acts as the server (-s), the other as the client (-c), and the 10-second test reports sustained throughput. Add -R to test the reverse direction and -P 4 for parallel streams, which Wi-Fi usually needs to show its best.

03Risk

RiskLow risk
Requirementsiperf3 installed on BOTH machines (Debian/Ubuntu: sudo apt install iperf3)
!Warning: Both machines need iperf3, and the server listens on port 5201 — don't leave iperf3 -s running on a laptop you take to public networks.

04Undo

✓No undo needed — this command does not change persistent state.

05Sources

  • iperf3(1) — manual page
    Arch Linux · community · 2026-09-17
    Evidence: iperf3 measures bandwidth between two hosts; -R reverses the direction to test download throughput from the server.
  • iperf3(1) — Ubuntu manual page
    Ubuntu · community · 2026-09-17
    Evidence: iperf3 -s runs a server and iperf3 -c host runs a client that measures achievable TCP/UDP throughput to that host.

Last verified: 2026-09-18 · Category: Network

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