Many vendors have chosen to register multiple different OUIs for lots of different reasons. The remaining three bytes carry the serial number of that vendor’s interface card. The first three bytes (pairs of hexadecimal characters) of any unicast address contain that vendor address component of the MAC address. TCP/IP literature refers to this OUI as the vendor address component of the MAC address. They get one or more Organizationally Unique Identifiers.
To help that process, Ethernet card vendors support that uniqueness by registering with the IEEE. To work correctly, each network interface has to have an address that is unique in its local segment of media. That way, any receiving interface can tell what kind of destination address it is reading after just reading one byte. The broadcast address uses all 1s binary or all FF hex. The first byte of a multicast address is odd, such as 01, 03, 05, etc. A unicast address’s first byte will be even, like 02, 04, 06, etc. The way to identify which address type you are viewing is simply look at the first byte. There are three types of MAC addresses: Unicast, Multicast, and Broadcast. They have already planned to extend the MAC address space to 64 bits and will call it EUI-64. Their current projection is that the amount of addresses available with 48 bits (over 281 Trillion) will last until 2100. They show up in most IEEE 802 networks including: 802.3 (as well as Ethernet II), 802.5, 802.11 (Wi-Fi), 802.15 (Bluetooth), and the ITU-T G.hn standards. MAC addresses act as the physical addresses for local communications. It is written in hexadecimal characters as shown below: EUI stands for Extended Unique Identifier. These MAC addresses are 48 bits or 6 bytes long, so they are also known as MAC-48 or EUI-48. While Apple has created many fine things, they were yet to be created themselves when Xerox PARC scientists created Media Access Control addresses.
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