How to use Rasbperry PI 3 or Raspberry PI 4 as VPN Router?

Question

I would like to use either Raspberry PI 3B 1GB or Raspberry PI 4 8GB version as VPN Router.

I have the following:

1. 4G Router
2. Either Raspberry PI 3B 1GB or Raspberry PI 4B 8GB
3. TP Link Router

My plan is to connect the Raspberry PI to the 4G Router via Ethernet and then with USB to Ethernet Adapter to the TP Link Router, where all my devices will be connected and have access to the Internet through the VPN configured on the Raspberry PI.

After I configure OpenVPN on the Raspberry PI, how should I proceed so that the traffic from TP Link router will go through the VPN configured in Raspberry PI ? Can this be done using only ufw on the Raspberry PI and then setting the Default Gateway to the TP Link Router to be from the Raspberry PI ?

Will a get a decent speed if I use the Raspberry PI 3B with 1GB RAM or is it better with the Raspberry PI 4B with 8GB RAM ? Using the VPN my internet speed is 50Mbps/s download and 30 Mbps upload.

Can you please give me more information and recommendation how to proceed ? Thanks for your help..

Answer 1

Anything before Pi 4 will be inherently slow due to the hardware architecture (all devices sharing a single USB root hub). Check out this question for example: a Pi 3 access point couldn't reach 20 Mbps even with an external 5 GHz WiFi dongle.

On a Pi 4, the built-in Ethernet and a USB Ethernet dongle will not share a single USB hub, so it should be possible to get a decent data rate out of it.