What is a MAC Address? Global Knowledge

What is a MAC Address? Global Knowledge

December 2, 2022 Off By Nick

Apple has created many amazing things, but they were not yet created by Xerox PARC researchers when they created Media Access Control addresses. These MAC addresses are 48 bytes long (6 bytes), and are also known as MAC-48 or EUI-48. EUI stands for Extended Unique Identifier. It is written in hexadecimal characters as shown below.

MAC addresses are local communication addresses. They can be found in all IEEE 802 networks.
The IEEE manages MAC addresses. Their current projections show that the 48-bit address space (more then 281 Trillion) is available until 2100. They have already begun to expand the MAC address area by 64 bits and will call it EUI-64.
There are three types of MAC addresses: Unicast, Multicast, and Broadcast. To determine the type of address you are looking at, simply look at the first byte. The unicast address’s first byte will be even. For example, 02, 04, 06, etc. Multicast addresses use an odd first byte, such as 01, 03, 06, etc. Broadcast addresses use all 1s binary or all FF hex. Any receiving interface can determine which type of destination address it’s reading by simply reading one byte.

For a network interface to function properly, it must have a unique address in every local segment of media. This address is known as the unicast address. This uniqueness can be supported by Ethernet card vendors. They are issued one or more Organizationally Unique Identifications. This OUI is referred in TCP/IP literature to as the vendor address component of the MAC address.
For any unicast address, the vendor address component of a MAC addresses is found in the first three bytes (pairs hexadecimal character pairs). The remaining three bytes contain the serial number of the vendor’s interface card.
OUIVendor00-00-36ATARI CorporationF0-4D-A2Dell, Inc.E8-06-88Apple, Inc.E8-E0-B7Toshiba00-02-A5Hewlett-Packard CompanyB4-A4-E3Cisco Systems2C-21-72Juniper Networks00-A0-C8ADTRAN, Inc.40-B2-C8Nortel Networks00-AA-02INTEL Corporation
Multiple OUIs are often registered by vendors for different reasons. One vendor may want to use one OUI for a specific product or because they have run out of serial numbers on an older OUI. The full list is available at http://standards.ieee.org/develop/regauth/oui/oui.txt.
Although many vendors follow the standards, some are more strict than others. A vendor could use a code registered to another vendor and create multiple NICs with the exact same Ethernet address. If cards with duplicate MAC addresses are installed on the same router side, it can lead to unpredictable results.

These skills can also be developed through courses in related fields
Understanding Networking Fundamentals
CompTIA Network+

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