There are two types of addresses found in Ethernet network. The logical addresses (TCP/IP) who works at OSI model Layer 3 and the physical (MAC), it works at OSI model Layer 2. The Ethernet address term specially referred to MAC addresses, it is also called burned in address (BIA), Ethernet address, hardware address, physical address or MAC address. The MAC address is the unique serial number burned into each network interface card that differentiates the network card from all others, just like your house number is unique on your street and identifies your home from all others. Being a part of any network each device must have a unique address so other communication devices can be reach to each other.
A MAC address has 48 bits (6 bytes) long and is made up of two parts, the organizational unique identifier (OUI) and the vendor-assigned address. The IEEE requires globally unique MAC addresses on all network adapters. To ensure a unique MAC address, the Ethernet card manufacturers burned the MAC address onto the card. This code, which is assigned to each manufacturer by the IEEE is called organizationally unique identifier (OUI). Each manufacturer assigns a MAC address with its own OUI as the first half of the address, with the second half the address being assigned a number that this manufacturer has never used on another card.
MAC addresses are represented as Hexadecimal numbers and might look like this 00-08-a1-08-c8-13. The OUI is 00-08-a1, and the vendor-assigned number is 08-c8-13. In CISCO devices, typically is written with periods separating each set of four hex digits like: 0000.0C12.2334 is a valid Ethernet address.
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