In this article we will explain you how to measure bandwidth between two computers on the same network, by using Iperf software and related utilities. Iperf is a free software tool that can measure the bandwidth between two nodes in a computer network and the quality of a network link.
Idea is to run Iperf on both computers and measure bandwidth between them, where one computer is a client and the other is a server. Computer is assigned as a client (or server) within the application by using appropriate switches.
Iperf is a console application, which means you have to type commands in terminal (command prompt). If you find that annoying, try a graphical front-end for Iperf called Jperf – a graphical front-end written in Java, and it will be mentioned in the section regarding how to measure bandwidth between computer and Android smartphone (I performed a test and took screenshots in my home network).
OK, let’s get to work and perform a simple bandwidth test, and other features will be provided in examples and the further reading section.
How to measure bandwidth between two computers in network by using Iperf
You can see this concept on how to measure bandwidth between two computers on the same network in the chart below:
OK, you’ve downloaded Iperf (I downloaded v2) and copied it on computers that you want to measure bandwidth between them; open command prompt and run Iperf on the computer you want to be a server (there is no formal rule on which computer must have a server or client role. Any computer can be a client or a server), and type the command: iperf.exe -s
Use this tip to open the command prompt on specific path (where you have put Iperf): navigate to folder which contains your Iperf executable (iperf205, in my case), hold the Shift key and right mouse click on that folder; extended contextual menu will appear where you have to click on Open command window here option.
In my case, I used a computer with Windows 7 as a server and computer with Windows 8.1 as a client. On the diagram above, you can see that server is marked with “1”, because that’s always the first step – to define a server. Take a note of your server’s IP address (if you don’t know it), and the easiest way to achieve that, provided that you are already in command prompt, is by typing ipconfig command (IP address on the diagram is: 10.1.1.1).
When it comes to a client, take a look at the diagram – I marked it as “2”; open your command prompt on the client computer and type: iperf -c server_address
And that’s it, default settings are enough to show you the bandwidth between two computers in your network. Of course, you can add some extra switches to use this software according to your needs.
This method we used to measure bandwidth is through TCP tests; besides that, you can measure jitter (latency variation) or datagram loss with an UDP test.
I mentioned iperf v3, which is a rewrite of Iperf from scratch, with the goal of a smaller, simpler code base and a library version of the functionality that can be used in other programs. Iperf3 is not backwards compatible with iperf2.x. Opinions on which version is better are divided, so many users would still recommend you Iperf 2.0.x. (Iperf 3 is not as well respected).
Iperf usage examples:
- iperf -s —> runs iperf in the server mode.
- iperf -c 10.1.1.1 –> runs iperf in the client mode, where the server’s IP address is 10.1.1.1 (by default, only the bandwidth from the client to the server is measured).
- iperf -c 10.1.1.1 -r –> connects back to the client allowing the bi-directional bandwidth measurement.
- iperf -c 10.1.1.1 -d –> implies simultaneous bi-directional bandwidth measurement. If you want to test the bandwidths sequentially, use the -r argument (see the previous example).
- iperf -c 10.1.1.1 -w 4000 –> w switch defines TCP window size – amount of data that can be buffered during a connection without a validation from the receiver (it can be between 2 and 65,535 bytes).
- server side: iperf -s -p 12000 and client side: iperf -c 10.1.1.1 -p 12000 –> p switch must be set on both sides and its value defines a communication port. By default, the Iperf client connects to the Iperf server on the TCP port 5001 and the bandwidth displayed by Iperf is the bandwidth from the client to the server.
- iperf -c 10.1.1.1 -t 30 –> specifies the test duration time in seconds (default is 10 seconds).
- iperf -c 10.1.1.1 -t 30 -i 3 –> i argument specifies the interval in seconds between periodic bandwidth reports.
- iperf -h –> provides you with detailed help starting with command format: iperf [-s|-c host] [options], then explanation of the arguments/switches, etc.
Great reference manual that describes how to use these switches (e.g. how to use -u switch to perform UDP test) can be found here: https://iperf.fr/ , and here: https://code.google.com/p/iperf/wiki/ManPage
How to measure bandwidth between computer and Android device on the same network
As I mentioned in the beginning (where I placed download links) there is a software Iperf for Android, that can turn your smartphone or tablet into a iperf server or client. My test environment is as follows:
- Server: Samsung Galaxy S2 smartphone (GT-I9100), rooted and with Cyanogen Mod custom ROM,
- Klijent: Fujitsu Amilo laptop, Windows 8.1, x64, where I tested both Iperf and Jperf.
Install Iperf for Android onto your Android device and run this application; type iperf -s or just -s in the text field and tap on off button (Aus, in my case, because my phone interface is in German). So you’ll get something similar to this (An is On):
Note server’s IP address from the screenshot: 192.168.1.3
Run Iperf on the client computer and type the next command (make sure you use an IP from your server):
Android application will show info when a client connects to it:
Jperf can be associated with Iperf to provide a graphical frontend written in Java. So, if you’d like to try Jperf, you must have Java Runtime installed onto your operating system (I have Java JRE 8). Download Jperf from the download link I provided; extract the downloaded archive, find jperf.bat and run it:
In the screenshot above can be seen that I chose client mode, entered the IP address of my server (smartphone), and set test duration to 20 seconds (instead 10, which is default). Graph is provided to show you measured bandwidth between my computer and smartphone in my home network.
[ Further reading ]:
IPERF for Windows (native Windows port, not Cygwin), trial: http://www.iperfwindows.com/
Iperf2 vs Iperf3: https://fasterdata.es.net/performance-testing/network-troubleshooting-tools/iperf-and-iperf3/
bwctl (ensures that just one test is executed in a moment): https://fasterdata.es.net/performance-testing/network-troubleshooting-tools/bwctl/