Memo

How do I enable IP forwarding?

 echo 1 > /proc/sys/net/ipv4/ip_forward

Client Debian-like: use DNS sent by the server

 sudo apt install openvpn-systemd-resolved
 # add the following lines into client.ovpn
 script-security 2
 up /etc/openvpn/update-systemd-resolved
 down /etc/openvpn/update-systemd-resolved
 down-pre