Hi Rob,
Multicasting does not start on its own. By default if you deploy an image to a group of machines it will unicast. To multicast you will have to go to to “Task Management” and search a group of hosts and there will be a double arrow icon next to the group name that you can click to multicast.
more info here:
[url]http://www.fogproject.org/wiki/index.php/Managing_FOG#General_Tasks[/url]
Cheers