[puetzk]

If your nodes have direct network access to each other, no.

But if two nodes that have added each other's keys cannot reach each other directly (e.g. are in separate private networks/behind firewalls/etc) but both can reach an external relay server, it may act as a dumb pipe bouncing encrypted traffic between them.

https://docs.syncthing.net/users/relaying.html

There is a public pool of such relay servers (https://relays.syncthing.net/), and by default syncthing will reach out and connect/announce its itself there so other nodes looking for it could contact it via a relay.

You can host your own relay server and configure your clients to use it exclusively: https://docs.syncthing.net/users/strelaysrv.html#client-conf... or if you only want syncing when your nodes are on the same local network you should be able to just not configure any relays at all.