[ReAzem]

Yes, it needs an exernal server.

By default, Syncthing is pre-configured with community-hosted discovery servers:

- https://github.com/syncthing/syncthing/blob/master/lib/confi...

The community also hosts relay servers, so if your two devices can't communicate with eachother directly, it will work anyway.

Relay servers take bandwidth. Anyone can run a relay server, and it will automatically join the relay pool and be available to Syncthing users. This is documented here:

- https://docs.syncthing.net/users/strelaysrv.html#strelaysrv

It would also be possible to host your own private relay and discovery pools, if you need that for some reason.