Testing ntttcp as an iperf3 alternative in Windows 11 (and Linux)

ntttcp (Windows NT Test TCP) is a network benchmarking utility similar to iperf3 that works in both Windows and Linux written and recommended by Microsoft over iperf3, so we’ll test the alternative in this mini review.

iperf3 is a utility of choice for our reviews of single board computers and mini PCs running either Windows or Linux, but we’ve noticed that while Ethernet (up to 2.5GbE) usually performs just as well in Windows and Linux, WiFi is generally much faster in Ubuntu 22.04 than in Windows 11. So when XDA developers noticed a post by Microsoft saying iperf3 should not be used on Windows 11, it caught my attention.

Microsoft explains iperf3 should not be used in Windows for three main reasons:

1. The maintainer of iperf – ESnet (Energy Sciences Network) – says “iperf3 is not officially supported on Windows, but iperf2 is. We recommend you use iperf2. Some people are using Cygwin to run iperf3 in Windows, but not all options will work”
2. iPerf3 is Emulated on Windows – iPerf3 does not make Windows native API calls as it only knows how to make Linux/POSIX calls, and this may impact performance.
3. I usually download iperf3 3.1.3 for Windows released in 2016, and Microsoft notes the one offered by ESnet (version 3.16)  is more recent but still 15 versions behind, so users are not running the latest version of the utilities.

So what’s the alternative for iperf3? Microsoft maintains two:

• ntttcp (Windows NT Test TCP) open-source utility for Windows and Linux with a command line similar to iperf3 according to Microsoft in the sense it aims to isolate network stack throughput.
• ctsTraffic for Windows-to-Windows testing only, also open-source and maintained on Github. ctsTraffic focuses on end-to-end goodput scenarios.

We can disqualify ctsTraffic immediately here at CNX Software since our tests typically involve a mix of Linux and Windows machines. Microsoft compared iperf3 to ntttcp utilities with high-speed network interfaces (10 GbE+), and the latter reports much higher performance. I only have hardware with 2.5GbE and WiFi 6, but I still wanted to test it, especially to check WiFi. So I decided to give ntttcp a try following the instructions on Microsoft Learn. It ended up being a challenge as those would not work on my system, and it took me a while to find the right parameters…

My testbed is comprised of four main components:

• Khadas Mind Premium mini PC and Khadas Dock with 2.5GbE and a WiFi 6 running Windows 11 Pro
• UP Xtreme i11 Edge mini PC with 2.5GbE acting as a server running Ubuntu 20.04
• A 2.5GbE TP-Link switch
• Xiaomi Mi AX6000 WiFi 6 router (not shown in the photo above)

The Khadas Mind Premium was selected as it’s the only spare Windows system with 2.5GbE and WiFi 6 that I own and have already reviewed. You’ll notice the network tests in Windows 11 and Ubuntu 22.04 using iperf3 reveal much lower performance in the Microsoft OS as summarized in the table below.

The Khadas mini PC is an outlier when it comes to 2.5GbE upload performance, but WiFi is faster in Linux in all mini PC reviews we’ve done. Since the Mind Premium review was done a while ago (August 2023), I updated Windows to the latest version and drivers and tested networking performance again with iperf3 and ntttcp in Windows 11 Home using the same command line as in the Microsoft blog post.

The first step was to install ntttcp (Linux) on UP Xtreme i11 mini PC running Ubuntu 20.04:

We can run the receiver command as follows.

Only one core is used to emulate iperf3 and the V (verbose) options help a lot to troubleshoot issues. After downloading the ntttcp.exe binary to Windows we can run it immediately as a sender in a command prompt:

But as you can see from the log above, it did not quite work as expected. It turns out that for Windows to Linux tests, we need to use the “ns” (No Sync) parameter. It’s mentioned in the Microsoft’s blog post

There is a known interoperability limitation when testing between Windows and Linux. Details can be found in this ntttcp for Linux wiki article on GitHub.

It took me a couple of hours to find out, but once I did that, I could complete the WiFi 6 Tx (upload) test:

98.125 MB/s or about 785 Mbps, slightly better than with iperf3, but still far from the performance in Linux.

I then connected an Ethernet cable to test 2.5GbE upload:

88 MB/s or 704 Mbps, so it’s basically the same as with iperf3 even after having updated the drivers.

iperf3 has a reverse transfer option, but I could not see any such option on ntttcp. So I had to type the commands to run ntttcp.exe in receiver mode on Windows and ntttcp in sender mode on Linux. We’ll need to run CMD as administrator, open the firewall, and the networking benchmark tool with other parameters:

The Linux command for the Ubuntu sender is quite different than the same command for the Windows sender as parameters are different:

But I still managed it. Needless to say, I did have an overly positive view of ntttcp utility so far. The only benefit I see is that we have some extra data such as CPU usage during the transfer.  2.28 Gbps is about what we would expect for a 2.5GbE connection.

I usually disconnect the Ethernet cable to test WiFi 6 with iperf3 and run the same command. But here we also need to change the IP address on both the server and client side to test it again:

604 Mbps so there’s no improvement here.

The table above summarizes the results after I ran iperf3 again. While ntttcp is faster for WiFi 6 upload, the results are not conclusive as the other results are more or less unchanged.  I suppose it only matters for high-speed networking with 10GbE or greater connections.

The tests above were done to compare ntttcp to iperf3 with similar parameters, but Microsoft says multithread and larger buffer sizes should be used to test bandwidth. Let’s try again with WiFi 6 download using 8 threads and 1024KB buffer size:

564 Mbps is slower than with only one thread and a 128KB buffer, although I reckon WiFi results can be fairly volatile.

Based on the tests done above there’s very little difference between iperf3 and ntttcp results, ntttcp Linux has not been updated for over three years, so I’m not convinced, and we’ll keep using iperf3 for the networking tests in reviews of Windows mini PCs…

Jean-Luc Aufranc (CNXSoft)

Jean-Luc started CNX Software in 2010 as a part-time endeavor, before quitting his job as a software engineering manager, and starting to write daily news, and reviews full time later in 2011.

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