Media Access Control (MAC) Tables
The term Media Access Control (MAC) probably sounds familiar. This term is typically introduced in lessons on the Open Systems Interconnection (OSI) model's Layer 2—data link layer addressing. Each Ethernet device that is manufactured is assigned a MAC address. This address is split into two different parts, the Organizationally Unique Identifier and the device ID:
- Organizationally Unique Identifier (OUI). The OUI is purchased by a manufacturer and assigned by the IEEE. In turn, a 24-bit OUI is given to be used in the manufacture of networking equipment (network interface card, switch, router, and so on).
- Device ID. The device ID is also a 24-bit number; it is assigned by the manufacturer to uniquely identify each device.
This means that every Ethernet networking device that is manufactured has a unique identifier, consisting of the OUI plus the device ID. As an example, let's take a look at the MAC address 5478.1a15.cf19, which breaks down to an OUI of 5478.1a and a device ID of 15.cf19. If you take the OUI 5478.1a and perform an OUI lookup, you will find that it links back to Cisco Systems, which is the manufacturer of the equipment from which I obtained that MAC address. This information is not used in the transmission of networking traffic, but it is helpful if you are troubleshooting a networking problem and you don't recognize a specific device; you can use the MAC address to look up the device's manufacturer.