Basic Explanation of MAC Address (Media Access Controller Address)

MAC stands for “Media Access Control”. All devices on a network have different MAC addresses. MAC addresses are very useful in diagnosing network issues. MAC addresses are useful for network diagnosis because they never change, as opposed to a dynamic IP address, which can change from time to time.

For example, an Ethernet card may have a MAC address of 00:0d:83:b1:c0:8e.

Sub-parts of MAC Address

Following are the sub-parts of MAC Address:

  • OUI
  • EUI


An organizationally Unique Identifier is a 24-bit number that identifies a vendor. They are purchased and assigned by the IEEE. For example, these are examples of OUI:

  • 00:00:0A – this is owned by Omron
  • 00-0D-4B – this is owned by Roku, LLC


An extended Unique Identifier is a 48-bit number. EUI MAC is separated into two 24-bits, with one being OUI (Organizationally Unique Identifier) and the other being NIC specific.