Parece que um pacote de transmissão UDP é enviado pela LAN.
Eu encontrei esses links para apoiar:
"we've experimented with various service discovery protocols, both standardized and our own. right now we're using UDP broadcast, but we're testing a few different ideas to see what'll work best for most people. the server is only involved in lansync negotiation to enforce our security model."
For example, if I look at a packet capture for my LAN I see "[source IP] 255.255.255.255 DB-LSP-Dropbox LAN Sync Discovery Protocol" every few seconds.