How to create a direct connection between two clients?

Question

Computer networks

How to establish a direct connection between two clients that do not have white IPs and without the participation of a central server?
I'm trying to make a small decentralized network, I'm considering an option in which none of the participants has their own IP.
For example, Skype uses some kind of P2P technology, while most users do not have a personal IP.

Answer 1

As a variant of pwnat.

Answer 2

you need at least one white sp. Buying it from the provider is not expensive now.
if it’s enough just to exchange files between offices, then you can look towards p2p file exchange: torrent and automatic exchange systems based on resilio sync (commerce) and syncthing (free)

Answer 3

How to establish a direct connection between two clients that do not have white IPs and without the participation of a central server?

No way.
Skype DOES have a central server that participates in the connection setup phase.
The only thing that can meet your postulates is a mesh network.