This article will give further information on how the Search function in GateManager Agents works.
Clicking Search
When you click Search the SiteManager will make an opportunistic search for devices on the network, this means that it broadcasts to strategic addresses, this makes sure that it will not lose any packets as it would easily do if it broadcast searched on a big network where a lot of devices would answer at the same time. this in terms means that searching for all devices takes a little longer than you might expect.