Does Discovery ping a node initially?

New to Discovery and untrained, so I apologize in advance for a simple question.

Does the Discovery engine, for a scheduled IP range, initially ping each node before trying to probe that node's ports? i.e. for a 24 bit masked network, 254 ping requests are transmitted and those that get a response will trigger port probes.

Or does Discovery probe the ports of all 254 nodes?

Thanks.