Bigfix Server and Client communication

Hi ,
How to force client to synchronize over HTTPs ? Below log shows it communicates over HTTP.

At 14:36:14 -0400 -
Entering service loop
Successful Synchronization with site ‘actionsite’ (version 385494) - 'http://bigfix.nsroot.net:52311/cgi-bin/bfgather.exe/actionsite
Successful Synchronization with site ‘mailboxsite’ (version 25) - ‘http://bigfix.nsroot.net:52311/cgi-bin/bfgather.exe/mailboxsite3100379’