How-To: OpenVPN – selective Routing and Killswitch on Asus with Merlin WRT

https://github.com/RMerl/asuswrt-merlin/wiki/Policy-based-routing

Running multiple OpenVPN instances (multi port)

Running multiple OpenVPN instances (multi port)

How To Install and Configure OpenVPN On Your DD-WRT Router

https://www.howtogeek.com/64433/how-to-install-and-configure-openvpn-on-your-dd-wrt-router/

Installing OpenVPN client and server on a DD-WRT router

How To Install OpenVPN On Ubuntu 16.04

Tutorial: Installing OpenVPN on Ubuntu 16.04

How To Install OpenVPN On Ubuntu 16.04

To configure iptables look here:

https://www.digitalocean.com/community/tutorials/how-to-set-up-an-openvpn-server-on-ubuntu-16-04

 

Site-To-Site Routed VPN Between Two or More Routers using dd-wrt/openvpn

Espresso

Install OpenVPN Access Server

https://www.linode.com/docs/networking/vpn/install-openvpn-access-server-on-linux