raspi Open VPN

[j.a.cole]

Bit of a support question, I've recently set up a Pi3b+ as an open vpn servers running Debian (PiOS)

however seem to be having bandwidth issue, and im not sure if its just a limitation of the Pi or of my setup.
At home i have a 150/150Mbps internet connection, and where I am remotely i have a 100/100Mbps connection. However when I connect using open VPN im only getting 20-25Mbps via speedtest.net

Is this a limitation of the Pi itself or are there optimizations i can do. I know the Pi3b+ has a 300Mbps limited ethernet port so this isnt the bottleneck, and I expect some overhead losses from the encryption, but not to the degree im only getting 1/5th of my theoretical capacity. Im not complaining too much, I can still do the things i need to do using it, but i expected higher speeds on my network file transfers.

[Levent]

RPI3B shares USB bandwidth across all USB devices and ethernet, so if you have a usb device plugged in thats instantly a penalty. Other than that, you can monitor your RPI and see if its CPU bottlenecked.

[Master Disaster]

RasPi 3 only has 100base NIC to start with on top of the USB limitation @Leventmentioned above. 25Mbps is about right TBH.

 

You need a RasPi 4 for 1000base.

[j.a.cole]

2 hours ago, Levent said:

RPI3B shares USB bandwidth across all USB devices and ethernet, so if you have a usb device plugged in thats instantly a penalty. Other than that, you can monitor your RPI and see if its CPU bottlenecked.

Nope Only Ethernet direct to the routers built in gigabit switch and power plugged into the device. no other USB devices. might need to have a look at the CPU utilization, haven't actually checked that yet. as i quickly set it up the other day and I'm remote working right now trying to use it for a few things.and tested the remote speed and was underwhelmed.

Edit - managed to test the cpu and network via ssh. speedtest shows the pi itself can use the full 150Mbps connection.
Using the VPN a single client maxed at 30bps with only 68% CPU usage. a second test with two clients at the same time maxed the cpu to 97% with one client reporting 33Mbps whilst the other 21Mbps. so clearly isnt a network bottleneck but maybe a CPU and software one.as its allowing upto 50Mbps combined
 

 

1 hour ago, Master Disaster said:

RasPi 3 only has 100base NIC to start with on top of the USB limitation @Leventmentioned above. 25Mbps is about right TBH.

 

You need a RasPi 4 for 1000base.

From Raspberry's own spec i was under the impression the Pi3B was like that but the Pi3B+ which I have had a gigabit port, but limited to 300Mbps due to the USB2.0 interface limitations.

[Master Disaster]

1 hour ago, j.a.cole said:

From Raspberry's own spec i was under the impression the Pi3B was like that but the Pi3B+ which I have had a gigabit port, but limited to 300Mbps due to the USB2.0 interface limitations.

That's probably correct considering 25Mbps is closer to 300base than 100base, I knew it couldn't do full Gigabit from anecdotal evidence, I ran a NAS from a Pi 3 and it also couldn't do much more than 20Mbps.

[charlie_root]

I'm not sure if the BCM2837B0 has hardware cryptographic acceleration. Some Cortex-A53 SoCs do, but it is optional. Without crypto acceleration, all that encryption overhead is going to be done in software on the CPU, and 25 Mb/s is about what I would expect for that.

 

You might find this discussion useful: https://www.raspberrypi.org/forums/viewtopic.php?t=141566