iperf3 is a free open-source, cross-platform command-line utility designed for real-time network throughput measurements. It ranks among the most effective tools for assessing maximum achievable bandwidth in IP networks (supporting both IPv4 and IPv6).

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With iperf, users can adjust various parameters related to timing, buffers, and protocols such as TCP, UDP, and SCTP. This makes it particularly useful during network performance optimization tasks.

To achieve enhanced or maximum network performance, it's essential to improve both the throughput and latency of your network’s sending and receiving capabilities.

However, before proceeding with tuning, you should conduct tests to gather comprehensive network performance statistics that will guide your optimization strategy.

The results from iperf include time intervals in seconds, data transferred, bandwidth (transfer rate), loss, and other relevant network performance metrics. Its primary purpose is to aid in tuning TCP connections across a specific path, which is the focus of this article.

Prerequisites:

• Two networked systems with iperf3 installed on both.

How to Install iPerf3 on Linux Systems

Before utilizing iperf3, install it on both machines intended for benchmarking. Since iperf3 is available in the official repositories of most major Linux distributions, installation is straightforward using the appropriate package manager as shown below.

<code>$ sudo apt install iperf3         [On <strong>Debian, Ubuntu and Mint</strong>]
$ sudo yum install iperf3         [On <strong>RHEL/CentOS/Fedora</strong> and <strong>Rocky/AlmaLinux</strong>]
$ sudo emerge -a net-misc/iperf   [On <strong>Gentoo Linux</strong>]
$ sudo apk add iperf3             [On <strong>Alpine Linux</strong>]
$ sudo pacman -S iperf3           [On <strong>Arch Linux</strong>]
$ sudo zypper install iperf3      [On <strong>OpenSUSE</strong>]    </code>

Once iperf3 is installed on both systems, you're ready to begin testing network throughput.

How to Test Network Speed Between Two Linux Servers

Begin by connecting to the remote machine that will act as the server, and start iperf3 in server mode using the -s option. By default, it listens on port 5201.

You may specify the format (k, m, g for Kbits, Mbits, Gbits or K, M, G for KBytes, Mbytes, Gbytes) for output using the -f parameter as shown.

<code>$ iperf3 -s -f K </code>

If port 5201 is already occupied by another process on the server, you can choose an alternate port (e.g., 3000) using the -p switch.

<code>$ iperf3 -s -p 3000</code>

Optionally, run the server as a background process using the -D flag and redirect messages to a log file.

<code>$ iperf3 -s -D > iperf3log </code>

Now, on your local machine, treated as the client (where the actual benchmarking occurs), launch iperf3 in client mode using the -c option and provide the hostname, domain name, or IP address of the server.

<code>$ iperf3 -c 192.168.10.1 -f K</code>

After approximately 18–20 seconds, the client will finish running and display results showing the average throughput, as illustrated in the screenshot below.

As seen in the above screenshot, there may be differences between values reported by the server and the client. However, always rely on the results from the iperf client when analyzing test outcomes.

How to Conduct Advanced Network Throughput Testing in Linux

There are several advanced options specific to the client for more detailed tests, explained below.

One key factor influencing the amount of data present on the network at any given time is the TCP window size – crucial in optimizing TCP connections. You can adjust this using the -w parameter as shown.

<code>$ iperf3 -c 192.168.10.1 -f K -w 500K   </code>

To perform a test in reverse mode, where the server sends and the client receives, use the -R flag.

<code>$ iperf3 -c 192.168.10.1 -f K -w 500K -R    </code>

For a bi-directional test, measuring bandwidth in both directions simultaneously, apply the -d option.

<code>$ iperf3 -c 192.168.10.1 -f K -w 500K -d</code>

If you wish to include server-side results in the client output, use the --get-server-output parameter.

<code>$ iperf3 -c 192.168.10.1 -f K -w 500K -R --get-server-output</code>

Additionally, you can define the number of simultaneous parallel streams (e.g., two) using the -P option.

<code>$ iperf3 -c 192.168.10.1 -f K -w 500K -P 2</code>

For more information, refer to the iperf3 manual page.

<code>$ man iperf3</code>

That concludes this guide! Always remember to conduct network performance tests before proceeding with actual tuning. iperf3 is a robust tool ideal for evaluating network throughput.

Do you have questions or thoughts to share? Use the comment section below.

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