An Ethernet MAC address is a worldwide unique identifier assigned to network devices. Sometimes also referred to as hardware address or physical address. MAC address is a 48-bit binary value expressed as 12 hexadecimal digits. As we know that decimal is a base ten “(xxx)10” number system and Hexadecimal is a base sixteen “(xxx)16” number system. The base sixteen number system uses the numbers from 0 to 9 and the letters from A to F. Where A= 10, B=11, C=12, D=13, E=14, and F=15.
In Ethernet LAN, each network device is connected to share media. Therefore all nodes would receive every frame transmitted over the shared media. To stop the too much overhead involved in the processing of every frame, MAC addresses identify the actual source and destination. MAC addressing also provides a method for device identification.
MAC Address Structure
Vendor Develop Ethernet Card and assign to it a unique address followed by IEEE standards. IEEE required registration of any organization with them that manufactures Ethernet Devices and NIC cards. After registration, IEEE assigns a 3-byte code termed Organizational Unique Identifier(OUI). MAC Addresses assigned to an Ethernet device must have a vendor OUI and a unique serial number assigned to them.
IEEE requires a vendor to follow two simple rules, as shown in the figure:
- All MAC addresses assigned to a NIC or other Ethernet device must use that vendor’s assigned OUI as the first 3 bytes.
- All MAC addresses with the same OUI must be assigned a unique value in the last 3 bytes.
|OUI||Vendor Assigned Unique serial|
|24 bits||24 bits|
|6 Hexadecimal digits||6 Hexadecimal digits|
|Vendor ID assigned by IEEE||Unique device ID|
Note: Duplicate MAC addresses are possible to exist due to mistakes during manufacturing or in some virtual machine implementation methods. In either case, it will be necessary to modify the MAC address with a new NIC or in software.