I need to setup a small router that can connect to an openvpn server as a client. I want any wired computer or hardware to use the vpn connection.
The wifi dont need to go trough the vpn but if it does it is ok.
What would you recommand as an hardware base?
It dependents from OpenVPN.
In general OpenVPN prefer AES encryption. But AES encryption is slow on low-end MIPS devices. It's fast only on mid or high-end devices built with ARM CPUs. This happens because mostly servers are on x86 and have AES-NI instructions for hardware accelerated AES.
But... you can setup OpenVPN with Chacha20-Poly1305 encryption in order to improve performance on low-end device.
Here you can see an benchmark:
So on low-end device you can get 10-20 Mbps and this is maximum from that hardware.
Other recommendation is to use WireGuard:
because this is different VPN that can get more from same hardware.
I would really like to change the Openvpn server setup but I just can't.
The way I see this I think I will go toward a small form arm computer with dual NIC So that it will run with out bottleneck. I have a router that run Openwrt already. I will use it as a simple switch and AP.
Yes, this is good idea.
But keep in mind that even Raspberry Pi doesn't comes with ARM AES instructions so everything is little bit slow. That's why try CHACHA20-POLY1305 too.
If fast VPN is the most important thing, than i personally would rather go with a Celeron J series x86_64 CPU, that has the AES-Ni instruction set. Those are used in most cheap NAS and work also well as a Media-PC. The older boards+cpu combo go for like 50-80€ and there a several barebones ~130€. Should also be dirt cheap on ebay.
PC: Ofc at this price-point you could also get a top of the line ARM-router, yet the Celeron based system might be more usefully if you also add NAS+Media-PC+Docker server workload on it.