ntop/n2n — reverse-engineered prompt

Build me a lightweight command line VPN tool in C that lets two or more computers join the same private virtual network, even if they’re behind normal home or office firewalls.

I want one program that runs on a public server as a discovery and relay server, and another program that runs on each computer that wants to join the network. The computers should use a shared community name and secret key, get virtual IP addresses, and then be able to ping and talk to each other like they’re on the same LAN. Try to connect them directly over UDP when possible, but fall back to relaying through the public server when needed.

Please include simple setup commands for Linux, a way to run the server and client as services, basic encryption for traffic, clear config examples, manual build steps from source, and a few tests or demo scripts so I can prove two machines can connect. Look up current docs online if you need to.