This means that a large manufacturer, like Cisco, has been assigned hundreds of OUIs. As a result, more than 16 million unique OUIs exist, and each OUI can be used by the manufacturer for over 16 million NIC addresses. The first 24 bits of address space in MAC addresses are reserved for the OUI, and the last 24 bits are reserved for a unique ID for each NIC manufactured by the owner of the OUI. The OUI database was used originally to associate Ethernet cards with their manufacturers, but the OUI has been expanded to cover all types of NICs, including Wi-Fi and other wired and wireless network interfaces. The first three octets are the OUI assigned by the IEEE Registration Authority to the vendor of the NIC. These addresses are usually represented as 12 hexadecimal digits in six pairs, separated by colons or hyphens - for example:

Modern network interfaces like those used for Ethernet or Wi-Fi are uniquely identified in six octets (48 bits) of a MAC address. These addresses uniquely identify the network interfaces on physical networks and consist of two parts: The first three octets (bytes) of the addresses are associated with the manufacturer or vendor of the device's NIC, and the second three octets uniquely identify the NIC itself. Most networked devices use Ethernet or Wi-Fi NICs and have 48-bit MAC addresses. This tutorial shows how to use Wireshark's OUI lookup tool from within the Wireshark application, as well as how to do OUI lookup from any internet-connected device.

Wireshark mac lookup