Mastering iperf: Install, Configure, and Run TCP/UDP Bandwidth Tests

iperf Installation

iperf is a network performance testing tool that can measure TCP and UDP bandwidth, packet loss, and transmission quality. Download the appropriate version from https://iperf.fr/iperf-download.php . For Windows, copy iperf.exe and cygwin1.dll to the %systemroot% directory. For Linux, install with:

yum -y install iperf

TCP Bandwidth Test

Start the server: iperf -s -i 1 -p 3389 Start the client: iperf -c 172.19.16.97 -p 3389 -i 1 You can also omit the port and interval:

iperf -s

iperf -c 172.19.16.97

Example output (server on 10.0.0.14, client on 10.0.0.3) shows simultaneous upstream and downstream bandwidth:

Key parameters:

-s : start in server mode

-c : start in client mode

-t : test duration in seconds (e.g., -t 30)

-i : reporting interval (e.g., -i 5)

-d : simultaneous bidirectional test

-r : reverse test (server connects back to client)

-L : specify port for reverse connection

-w : set TCP window size

UDP Bandwidth Test

UDP mode is used to measure maximum bandwidth, jitter, and packet loss.

Server command: iperf -u -s Client command (example with 1000 Mbps target and 3‑second interval): iperf -u -c 10.0.0.14 -b 1000M -i 3 Result screenshot:

When testing high packet rates, adjust the UDP buffer size in /etc/sysctl.conf:

net.core.wmem_default = 8388608
net.core.rmem_default = 8388608
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216

Apply the changes:

sysctl -p

Network Packet Performance Test

Run the server with reporting interval and custom port: iperf -u -s -i 1 -p 3389 Run the client specifying packets per second and packet size:

iperf -u -c 172.19.16.97 -b 300000pps -l 100bit -i 1 -p 3389

Result images show no packet loss up to 300 kpps, with loss appearing around 320 kpps, indicating the network’s practical packet‑per‑second limit.

Summary of important iperf options:

-s: start server

-c: start client

-t: test duration (seconds)

-i: reporting interval (seconds)

-d: bidirectional test

-L: port for reverse connection

-w: TCP window size

-b: set UDP bandwidth (bit/s) or packet rate (pps)

-l: set packet size (default 8 KB for TCP, 1470 B for UDP)