MAC Address Representations

Hardware and software manufacturers represent the Physical address or MAC address in different hexadecimal formats that are 12 digits (6 byte or 48 bits), as shown in the following:

• MM:MM:MM:SS:SS:SS

• MM-MM-MM-SS-SS-SS

• MMM.MMM.SSS.SSS

The leftmost 6 digits (24 bits) called an "OUI" is associated with the adapter manufacturer. Every manufacturer registers and obtains MAC OUI as assigned by the IEEE. the manufacturer often possesses many OUI numbers associated with their different products.

The rightmost digits of a MAC address represent an identification number for the particular device. Devices manufactured by the same vendor OUI, each is given their own unique 24-bit number.

Finding MAC Addresses on a computer

On a Windows host, open the command prompt and enter the command ipconfig /all as shown in figure 4.4.This command can be used to identify the MAC address of an Ethernet adapter. Notice that in result it display the Physical Address of the computer  00-21-70-B9-50-95. On a MAC or Linux host, the ifconfig command is used.

 

We often see various representations of MAC addresses which depend on devices and operating system. Cisco routers and switches use the form XXXX.XXXX.XXXX where X is a hexadecimal character.