I am answering this from my knowledge of bittorrent It maybe wrong for btsync. With the default set up it should not download the same bits from W1 because it check for availability of the chucks from everything it is connected it. If you leave it a while you should see that there is transfers from W1 -> H1, H2 and H1 <-> H2. However when it first starts it may pick to download the same first file, by chance. (To make sure you could just leave H1 running for a bit then turn on H2 later to make sure). So you shouldn't need to set one for lan only sync. However you may bring up a interesting question "Bitorrent checks availability of the 4MB chucks does BTSync check the availability of files?" Here is a topic on lan only sync. http://forum.bittorrent.com/topic/21286-lan-only-sync/ Hope that helps