I think you would enjoy this article from Tailscale: https://tailscale.com/blog/how-nat-traversal-works/ https://tailscale.com/blog/how-nat-traversal-works/ Th

I think you would enjoy this article from Tailscale: https://tailscale.com/blog/how-nat-traversal-works/ https://tailscale.com/blog/how-nat-traversal-works/ The poke a hole to outside world to a random server, log the port allocated to you by your router and have someone else use this to connect to you is the basis of STUN protocol.