Hi Delegatevoid, and thanks for the elaborate answer. I ran a test on my LAN by disconnecting the WAN at the modem level... and the BTSync clients ( 2 pcs) stopped synching. I reconnected to the internet (plugging the modem back in ) and synching started. I know very little about the bitorrent protocol but I guess that even machines on my LAN need to download a tracker from a server somewhere on the internet. Can you confirm or refute the results of my test ? Thanks