In promiscuous mode operation, a NIC picks up all frames on a segment, even those that are not addressed to it. Promiscuous mode must be supported by network adapter hardware as well as the software driver installed on the operating system.
Not all NICs support promiscuous mode operation.When you buy a NIC, check its specifications to make sure it supports promiscuous mode. If you are not sure, test it using Nexeye©. If all you see is unicast traffic destined to the Nexeye© machine as well as broadcasts and multicasts, the NIC is not running in promiscuous mode.