We've got several machines running Dropbox (all mac osx desktops and laptops - no mobiles / tablet apps). 99% of the time we are syncing data between machines that are in the same room and on the same wifi network, but i dont think its using LAN, just by the amount of time it takes for the data to show up on the other machines. 

Is there a way to check if the data is being synced over LAN or back and forth to the Dropbox servers, is there some extra configuration we need to setup to get the LAN working properly ?