Try to set up a peer-to-peer tunnel on bob.example.com host with a static key

openvpn

sudo openvpn --remote {{alice.example.com}} --dev {{tun1}} --ifconfig {{10.4.0.1}} {{10.4.0.2}} --secret {{path/to/key}}

click the source code to copy install openvpn on any operating system with command-not-found.com