I have been waiting for a sync service that I trust that does not rely on external servers out of my control. I think I now have the solution, thanks to the known hosts setting of my synced folders. Environment: Two MacBooks used in and out of the house. One Mac mini server in the house. One AirPort Extreme router firewall. DDNS service pointing to the server host name. Setup: On the server; Installed the client, Configured a sync folder with no peer discovery boxes checked and no known hosts defined. On the firewall; Configured port forwarding to the UDP port and IP of BTSync on the server (not TCP), On the MacBooks; Installed the client, Configured a sync folder with no peer discovery boxes checked and one known host defined pointing to the server's full host name and port, Used the secret generated by the server client. Result: Any file or folder dropped into the BTSync folder on one of the MacBooks is synced to the other MacBook via the server at home. This happens whether at home or traveling. While I haven't captured packets to prove it yet, I think that no broadcasts are being sent to the LAN I am on advertising the service. Also, I am not reliant on someone else's server being up for the sync to function. Now to see if I can move shared password databases to it...