Dropbox: LAN sync protocol

If all the dropbox clients have LAN sync enabled, then each of them should be able to understand and respond to the Discovery packet (assuming it’s able to distinguish between different user accounts. I believe it uses namespaces to identify them uniquely). This response packet called DB LAN sync(DB-LSP) is a TCP packet where the dropbox clients exchange data.

via Dropbox: LAN sync protocol – GeekLogs.