See…
- Understanding Synchronization – https://docs.syncthing.net/users/syncing.html
- Syncthing Discovery Server – https://docs.syncthing.net/users/stdiscosrv.html
- Syncthing Relay Server – https://docs.syncthing.net/users/strelaysrv.html
- Relaying – https://docs.syncthing.net/users/relaying.html