A MAC, or Media Access Control, address is the unique 12-digit hexadecimal number hard-coded into a NIC or other ethernet device. The MAC address consists of two parts. The first half of the MAC address, the Organization Unique Identifier (OUI), identifies the manufacturer of the device. The second half is used to identify the device itself. The SonicWall's MAC address is its serial number. The IEEE OUI and Company_id Assignments searchable database may be used to locate the manufacturers of Ethernet devices by the OUI of their MAC addresses.