Portable and Powerful 2.5 GbE iperf3 Server Capable of 3 Gbps – Topton M6 Mini PC

After using FriendlyElec R5S single-board computer as a portable iperf3 server, I decided to also order and test Topton M6 Mini PC. It is more powerful, based on Intel CPU, and runs Windows 11 Pro or Ubuntu. I personally chose Windows (yes, I am brave), mainly because I also wanted to use this device as a Windows Wi-Fi client for other things than iperf3 testing.

Dimensions and case

Compared to the R5S, Topton M6 Mini PC is still portable, but about twice as large. Plastic case wraps the unit, but it is more fragile if you plan to carry it in your backpack or tool bag. There is a built-in fan which is always on. Not a big deal if you use it as an perf3 server, but little inconvenient when it runs on your desk for a longer period of time.

iperf3 performance

Topton M6 has a single onboard 2.5 Gigabit Ethernet port consistently capable of 2.35 Gbps up and down iperf3 throughput with default settings.

Consistent 2.35 Gbps iperf3 throughput

Now, can we make it go faster? Let’s see. We will use USB-A 5 Gigabit Ethernet capable Sabrent adapter. This can either be connected to a USB-A port or USB-C port of the Mini PC. In my tests, I have found that the USB-C port has limited throughput and only tops around 350 Mbps. When I connected the Sabrent 5GbE adapter to USB-C, it only auto negotiated 1 Gbps Full Duxplex.

Use any of the three USB-A 3.1 ports instead to avoid that limitation.

Use USB-A ports, not the USB-C
With the USB adapter, we get 2.94 Gbps down and 3.27 Gbps up

With the USB adapter, the whole setup get less portable. But it allows us to achieve 2.94 Gbps down and 3.27 Gbps up from clients perspective. Is it worth the extra spend? If you need to break the 2.35 Gbps barrier of the built-in 2.5 GbE port, this might be a workable solution for you.

Power adapter with an adapter

This Mini PC is quite strict when it comes to its power source. It requires 12V/2A USB-C PD adapter. Unfortunately, your USB-C MacBook or iPad chargers won’t work.

It draws around 7.5 Watts in idle mode.

If you happen to only use this PC in the US, happy days, as the power adapter ships with US plug. If you select UK during the ordering process, you will receive the US power adapter with UK adapter, which adds to its overall size.

My way around this is to use a standard non-USB-PD 12V/2A adapter with 5.5×2.1mm barrel jack connector, and a barrel jack to USB-C adapter. This particular “power brick” has a standard IEC C14 power cable connector, which you can find in any data centre and with the right European, UK, or Australian plug.

Power adapter with barrel jack + barrel jack 5.5×2.1mm to USB-C adapter
Detail of barrel jack 5.5×2.1mm to USB-C adapter

Battery power

Simply use a USB-C cable and USB PD battery pack capable of delivering 12V/2A. No surprises there.

Powered by PoE

I prefer powering equipment using PoE over local power bricks. If you are in the same boat, you can power this Mini PC by a PoE splitter.

Please pay close attention to the splitter specs. We want the one with a barrel jack and 12V/2A. Since the Mini PC uses USB-C power connector, we will use a barrel jack 5.5×2.1mm to USB-C adapter. Here is the complete setup. Press the power button and voila!

Under the hood

Most of the components are soldered to the main board with little room for upgrades. I ordered the lowest 8GB DDR4 and 128GB NVMe spec with Windows 11 Pro OEM preinstalled (no actual Windows license included).

I was hoping for the Wi-Fi adapter to be replaceable, but it is not the case. It is Intel AX201 and soldered to the board. Good enough, just not ideal for Wi-Fi professionals. M.2 slot would be ideal.

A quick look at the bottom side of the PCB shows the NVMe drive.

NVMe drive is practically the only replaceable component

Final verdict

Personally, I think this Mini PC has some great potential for certain use cases, but as an iperf3 server, I would rather use the FriendlyElec NanoPi R5S I reviewed here.

If you absolutely need to break the 2.3 Gbps barrier, it can be done with the help of a USB 5 GbE adapter, but it is not very cost effective. The Mini PC cost me £186 including shipping to the UK. The Sabrent 5GbE USB adapter costs around £65.

Finally, it you need top performance, don’t care that much about small form factor, and money is no object, the latest Apple M1 Mac Mini can be configured with built-in 10 GbE.

Portable and affordable 2.5 Gigabit Ethernet iperf3 Server – FriendlyElec NanoPi R5S

What problem am I trying to solve?

Wi-Fi standards have developed and also WAN links are fast and reasonably priced these days. When it comes to throughput testing tools like iperf3 servers, 1 Gigabit Ethernet has become a bottleneck. A Wi-Fi 6E client can now easily generate more than 1 Gbps of traffic, but how do we measure it?

To overcome that issue, I am looking for a reasonably priced portable single-board computer, which can push more than 1 Gbps of traffic. It should be powered via USB-C, battery, or PoE powered, and should be portable to fit in my “just in case I need it” tool bag.

FriendlyElec NanoPi R5S

This little FriendlyElec NanoPi R5S single-board computer (SBC) delivers everything I mentioned above. Let’s have a look.

Dimensions and case

It comes with a well designed aluminium case, which also serves as a heatsink. The whole unit is smaller than the smallest iPhone, slightly thicker obviously. It runs silent. There is no built-in fan whatsoever.

Portable? Tick! By the way, did you know that the original WLAN Pi uses NanoPi NEO2?
Left to right: WLAN Pi, R5S, Intel-based SBC I am also testing, WLAN Pi Pro


USB-C power input, two 2.5 GbE, one 1 GbE, HDMI useful troubleshooting or demos, two USB-A 3.0 ports

It has two 2.5 Gigabit Ethernet interfaces (LAN1 and LAN2) and one 1 Gigabit Ethernet interface (WAN). Either of the LAN ports delivers 2.3 Gbps of actual useful iperf3 throughput with default 1500-byte MTU and single stream. I used MacBook with OWC 10 Gigabit Ethernet Thunderbolt 3 Adapter and Cisco WS-C3560CX-8XPD switch.

From client’s perspective that’s 2.27 Gbps down and 2.35 Gbps up


The R5S only draws 4 Watts in idle, and can be powered by any USB-C 5V power source. Your MacBook USB-C charger, iPad/iPhone charger, or USB-C battery pack would do. Alternatively, use a 1 Gigabit Ethernet 5V PoE splitter and PoE power the unit. In my lab with a 2 meter cable, the 1 Gigabit Ethernet PoE splitter actually allowed the R5S auto negotiate stable 2.5 Gbps connection with the switch.

PoE powered


FriedlyElec built and published two operating system SD card images for the R5S – Ubuntu and FriendlyWRT. I tested both, and for my use case FriendlyWRT works best. It has a network-centric and easy to use web UI, has iperf3 preinstalled, and delivers great performance.

Initial setup and tips

R5S ships without any micro SD card, so make sure you have one ready to use. Flash the software image to it using Balena Etcher or similar tool.

Connect the WAN port to a network with existing DHCP server. If you are in the same subnet, simply ping FriendlyWrt.local to get the IP address of the R5S.

Then access the web UI or SSH to the unit, SSH is enabled by default. Change the root password now.

Now, this is important! To achieve maximum throughput, delete the pre-configured bridge interface br0, and configure both multigigabit eth1 (LAN1 port) and eth2 (LAN2 port) as standalone unbridged interfaces. Also, tweak IP address settings to your liking while you are there.

eth1 configured as a standalone interface. Bridge interface removed.

Make iperf3 automatically start by going to System > Startup > Local Startup and add iperf3 -s and hit the Save button.

Change CPU Governor setting to Performance. And CPU Minimum Frequency to the maximum value.

Here is the FriendlyElec documentation and introduction to their FriendlyWRT distribution.

Final verdict

This little single-board computer absolutely deserves its space in my tool bag. For the 2 GB RAM model with case I paid $88 including shipping to the UK. Add a Micro SD card and that’s all you need to get started.

Finally, it you need top performance, don’t care that much about small form factor, and money is no object, the latest Apple M1 Mac Mini can be configured with built-in 10 GbE.

Use SSH key stored on GitHub instead of an SSH password to access your WLAN Pi

By default WLAN Pi, and Linux in general, uses a username and password-based SSH authentication. It involves quite some typing, some brain capacity to remember the password, and it is not the most secure method either.

You can create a public and private key pair. Your SSH client automatically logs in using the private key. The SSH server uses the public key to confirm that you possess the right private key. No password needed, and it also is more secure. The private key is never sent over the network, and this method protects you against man-in-the-middle attacks.

The beauty of this GitHub method is that GitHub stores your SSH public key centrally, which you can easily update, and you can install it to the machine you want to SSH to, by a single command ssh-import-id-gh. You can even add this to a startup script so that it automatically updates your trusted keys.

Let’s do this

ssh-keygen is the program that generates a public/private key pair on your local system. The private key is stored in ~/.ssh/id_rsa, and the public key is stored in ~/.ssh/id_rsa.pub.

The security of this method depends on keeping the private key safe and secure. Make sure not to leave the private key behind.

ssh-keygen -t rsa -C "your@email.com"
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/jiri/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /Users/jiri/.ssh/id_rsa
Your public key has been saved in /Users/jiri/.ssh/id_rsa.pub
The key fingerprint is:
The key's randomart image is:
+---[RSA 3072]----+

Display the public key, which is a text file at the end of the day, and copy its content to clipboard:

cat ~/.ssh/id_rsa.pub

Save this public key to your GitHub account. Browse to github.com, log in, and open Settings:

Click New SSH key, name the key, paste your public key from the clipboard and save it:

To verify that your key has been added you can browse to https://api.github.com/users/jiribrejcha/keys, where jiribrejcha is your GitHub username:

The last step is to SSH into your WLAN Pi or Linux machine and tell it to use this public key from my GitHub, where jiribrejcha is my GitHub username:

ssh-import-id-gh jiribrejcha

If the command isn’t installed, you can fix that by:

sudo apt install ssh-import-id

Passwordless SSH access

When you authenticate to a server using public key authentication, the SSH client offers a copy of the public key to the server and the server then compares it against the keys listed in your ~/.ssh/authorized_keys file. This key was added automatically by the ssh-import-id-gh command. If the key matches, the server indicates that it is able to proceed with the authentication. The private key is then used to sign a message that includes data specific to the SSH session. The server can then use its copy of the public key to verify the signature.

We have just SSH’d to the Pi without a password prompt.

Special thanks

To Colin Vallance for sharing this tip.

Cisco Catalyst C-ANT9103 antenna unboxing

If you have not had a chance to see the new Cisco Catalyst antennas for Catalyst 9130AXE access points, here are a few photos of the C-ANT9103 antenna for your reference.

Size, weight, mounting options

The official installation guide provides all this information and much more.

The optional access point “pocket”

Optionally, you can order an AP + antenna collocation “pocket”, which the Catalyst 9130AXE slides nicely in. It is aesthetically pleasing it, and all it takes to install the AP and antenna is a single mounting bracket. You don’t have to worry about mounting the access point and antenna separately. This drastically simplifies temporary deployments – just think about Cisco Live for example.

Previous generation with a separate AP bracket and antenna bracket
The new collocated, and aesthetically pleasing, solution with AP installed just behind the antenna


Please always refer to the official Cisco documentation for the latest information and package contents.

Multigigabit Ethernet on the Raspberry Pi 4

With the first consumer Wi-Fi 6E routers already shipping, and enterprise access points being worked on, I think it is now time to up my iperf3 game. While the standard 1 Gbps adapters push around 950 Mbps of TCP traffic, the iperf3 server will sooner or later become a bottleneck for throughput measurements.

Raspberry Pi 4 (RPi4) is widely available, and there is a chance that you might already own one. So, the question is, can it support multigigabit speeds?

Although it does not have any PCI Express slot available, it does have a couple of USB 3.0 ports. I researched USB 3.0 multigigabit NBASE-T Ethernet adapters, and purchased a few. At the time of writing, Linux kernel 5.10 is the Raspberry Pi OS gold standard, and that’s what I used for all tests.

TL;DR … give me the short answer

The maximum TCP throughput Raspberry Pi 4 iperf3 server can handle with a 5 Gbps USB 3.0 Ethernet adapter. These were 90-second iperf3 tests with standard 1500-byte MTU and a single iperf3 stream.

  • Download (from RPi4 server to a client): 2.05 Gbps
  • Upload (from a client to RPi4 server): 528 Mbps

If you can enable 9000-byte Jumbo frames on all devices involved in the data path, the upload speed becomes much healthier.

  • Download (from RPi4 server to a client): 2.05 Gbps
  • Upload (from a client to RPi4 server): 1.73 Gbps

USB multigigabit adapters

There are a few available on the market. After reading a dozen of reviews, I decided to get 3 adapters from a company called Sabrent. They make adapters with nice metal cases, which helps with dealing with the heat they dissipate.

Left to right: 2.5 GE USB 3.0 Sabrent NT-S25G, 5 GE USB 3.1 Sabrent NT-SS5G, 10 GE Thunderbolt 3 Sabrent TH-S3EA

The 5 GE USB 3.1 Sabrent NT-SS5G is the only I recommend for use with the RPi4:

  • It uses the Marvell Aquantia AQC111U chipset
  • It works out of the box with Raspberry Pi OS and
  • It works on Windows 10 after you install the driver
  • It ships with USB-C and USB-A cables so you can connect it to your laptop using USB-C or RPi4 using USB-A
  • Unlike other brands it does not overhead or disconnect due to instability

Here is what’s in the box

5 GE USB 3.1 Sabrent NT-SS5G ships with both USB-A and USB-C cables

RPi4 for scale

ServeTheHome team did a great job of comparing the 5 GE adapters using the same chipset as the 5 GE USB 3.1 Sabrent NT-SS5G. It came out as a clear winner:

USB 3.1 Gen1 To 5GbE Comparison Table AQC111U Based Q1 2021
Credit and kudos to ServeTheHome

Why not use the cheaper 2.5 GE USB 3.0 Sabrent NT-S25G? Because it uses Realtek 8156 chipset, and there is no suitable Linux driver available at the time of writing.

Why not the 10 GE Thunderbolt 3 Sabrent TH-S3EA? Although it has a USB-C connector, it is not a USB adapter. It uses Thunderbolt 3 protocol, which is not supported by the RPi4.

Test setup

I use RPi4 with PoE HAT, because it has a fan on it, and I power the unit by a USB-C charger. Both multigigabit adapters involved in the test are 5-Gigabit Ethernet capable Sabrent NT-SS5G. The best part is that these work out of the box on the Raspberry Pi OS with no action required on your part.

But, if you are considering the purchase of these adapters for your Mac, please stop. After you plug the adapter in, it uses Apple’s 1 Gigabit Ethernet adapter driver, and it would only auto-negotiate 1 Gbps. To enable 2.5 and 5 Gigabit speeds, and support for Jumbo frames on Mac, you have to disable Apple System Integrity Protection (SIP) tool, and install a legacy kext Sabrent driver. I would discourage you from making these security compromises. If you are interested in a multigigabit adapter that works with macOS out of the box, tune in later and read this review (link to be added).

How to increase the MTU and enable Jumbo frames?

On the Raspberry Pi:

sudo ip link set dev eth1 mtu 9000

On the Cisco Catalyst switch running IOS:

Configure, save config, reload
Verify after reloading
System Preferences > Network > Adapter settings > Hardware > MTU on macOS


The RPi4 allows you to test download-only throughput up to 2 Gbps with standard MTU. Upload speeds are really poor and you would be better off using the built-in 1 Gibabit Ethernet adapter. You can use the RPi4 to run a few other tools, scripts, or take wall attenuation measurements.

With Jumbo frames enabled, 2 Gbps/1.7 Gbps is good enough for lab use or demonstrations. Keep in mind that you would have to enable Jumbo frames on all devices (RPi4, MacBook and the switch in my case).

The main cause of the relatively low performance is the storm of IRQ hammering the RPi4 CPU:

In a computer, an interrupt request (or IRQ) is a hardware signal sent to the processor that temporarily stops a running program and allows a special program, an interrupt handler, to run instead. Hardware interrupts are used to handle events such as receiving data from a modem or network card, key presses, or mouse movements.

Source: Wikipedia.org

If your use case requires a powerful iperf3 server, Apple’s Mac Mini with built-in 10 Gigabit Ethernet adapter would be something to consider today. It won’t be the cheapest option, but you won’t have to worry about performance or USB dongles. From what I’ve found, it uses Marvell AQC 1113 chipset and does 9.4 Gbps with 4 parallel iperf3 streams.


I purchased these adapters myself. No one asked me, or paid me, to write this blog post. I was as curious as you to see how the RPi4 performs when it comes to multigigabit Ethernet.

Hot-swappable tripod adapter for Cisco Aironet 1560 outdoor access points

If you have followed my hot-swappable series, my goal was to find a solution to swapping multiple outdoor AP + antenna combinations and a variety of AP models on the same tripod. What is the use case? I only wanted to carry a single tripod on the site survey day while still having the flexibility to survey with variety of antennas and different AP models.

After making the adapter for MR86 and MA-ANT-20 dipoles and MR86 with two MA-ANT-25 directional antennas, I realised I needed one for Aironet 1560, which, at the time of the writing, is my go-to outdoor AP.

Please excuse the DYI approach. I did this during UK’s second COVID-19 lockdown. Shops were closed, access to tools was limited and I had no access to my lab.

How it turned out?

It went surprisingly well this time as I’ve already built a similar adapter for Cisco Meraki MR APs and this time it was even easier. Same as last time, the alu tube slides inside the top tripod tube and we are ready to roll.

The actual steps

I stocked up on M6 x 30 mm bolts, cut the 16 mm aluminium tube to the right length and reused the last bit of decking from a different project.

M6 x 30 mm bolt

I thought I will try making a template, which I then transferred onto the wood. That wasn’t the best idea and it seems to work best when you watch someone using this “trick” on YouTube. Next time I will go for an analog pencil and ruler, lesson learned;-)

That trick did not go as well as I thought :)

The decking is quite thick so I ended up shaving few millimeters off it. And here is the final adapter.

Ready to go on a tripod

Did you say tripod?

Yes, here is more about this 4-meter tripod I use.

How to achieve down tilt?

Thanks to Alan Wang, who suggested I use the official articulating pole mount AIR-ACC1530PMK2 and attach it to my “back board”. Obviously azimuth you can adjust by rotating the tripod, and this allow you to change the elevation angle.

Articulating pole mount
Articulating pole mount

Tern GSD self-adhesive silicon case for Apple AirTag

I enjoyed testing the under-seat and water bottle bike mounts for AirTags on our Tern GSD bike, and thought I should explore other mounting options.

This self-adhesive sleeve looks like a universal option, as it can be attached practically to any flat surface.

It has a silicone sleeve on one side and self-adhesive on the other.

Silicon sleeve with AirTag
Detail of the slot

The self-adhesive layer seems to be a good choice. It is not extremely sticky as some other products, it does not seem to leave marks, and I actually managed to remove the case from the Storm Box on our Tern GSD bike, move it to a more suitable spot and re-apply it.

Self-adhesive layer
That sounds of peeling off the protective plastic sheet

It fits nicely inside the sleeve and as far as I can tell, there is no chance of it slipping out. The silicone keeps it from moving. In fact, it takes some effort to insert and remove the AirTag, which is great.

Fully inserted AirTag

There are many accessories available for the GSD. Storm Box is a great candidate for an AirTag in this sleeve. Mine is still holding tight. It has a few internal pockets and you can easily attach a dozen of AirTags to it and still have some space left for more;-)

Tern GSD with Storm Box

Bottom of the front rack might also be a good place for an AirTag.

A word of caution

Wherever you mount it, please keep your own safety in mind. Don’t mount it near the motor or anywhere near the chain/belt. It might cause you some bumpy ride should the self-adhesive fail.

Where can I buy one?

I bought mine on eBay and it was very affordable. Here is a link if you are considering getting one or two.

Other bike mounts

If you are looking for inspiration, I tested an under-seat and water bottle bike mounts. Here are a couple of photos and you can find more of them in the respective blog posts.

Water bottle mount with more mounting options available on the GSD
Under-saddle mount

Tern GSD water bottle bike mount for Apple AirTag

I’ve recently tested an under-saddle mount. On its own, it is an easy target and it can be easily found if the thief knows where to look. To make the most out of AirTags, I also have one inside my Storm Box.

To complement the two, I am now also using this AirTag mount, which can either sit between your water bottle and the bike frame. Alternatively, if you do not have a bottle, it can sit directly on the frame secured using the bottle holder bolts.

Mounted using the “too-easy-to-spot” water bottle bolts
Let’s unzoom to put its size into perspective

Let’s play hide and seek!

Here is where the GSD comes to the rescue. It has a couple of other mounting options with the exact same distance between the bolts as the water bottle bolts.

Can you spot the AirTag?
What about now? Look between the pedal and battery.

Note the two silver bolts inside the triangle on the right hand side. They can be used for this AirTag mount.

Assembly and installation

It is super easy to install. The original Tern screws are too short. So, let’s replace them with the 2 bolts supplied with the mount. The only tool you need is a standard hex head 3 mm screwdriver bit.

On Tern GSD Generation 2, you can choose between the upper or lower position. Personally, I prefer the upper one.

Installed in the upper position
Installed in the lower position
It is not much thicker than the AirTag itself

Where can I buy one?

I am in the UK and I purchased one on eBay. Here is the link if you want to check it out and get yours.

What other mounts are available?

I’ve also tested an under-saddle mount. You can see more photos of it and read more about it here.

Comparison of the under-saddle and water bottle mounts