CCENT-CCNA：ICND1 100-105 Certification Guide

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Ethernet MAC addresses

An Ethernet MAC address, often known as a physical address, is a unique network address that identifies the network interface on a computer network, and it is used for communication in the Data Link layer. The size of the MAC address is 48 bits expressed in 12 hexadecimal digits, where each digit represents 4 bits. The Ethernet MAC address is burned on the Read Only Memory (ROM) of the NIC and is thus often referred to as the Burned-in Address (BIA). It consists of two fields like the Organizationally Unique Identifier (OUI) and Vendor Assigned, as shown in Figure 2.14. Both fields have an identical size of 3 bytes each (or 24 bits) and represent the vendor and the particular device. In literature and elsewhere, you will often see the Ethernet MAC addresses represented in three formats:

With dashes: Usually represented by Windows OS, for example, 00-11-22-AA-BB-CC
With colons: Usually represented by Mac OS and Linux, for example, 00:11:22:AA:BB:CC
With periods: Usually represented by Cisco IOS, for example, 0000.1111.AAAA

Figure 2.14. Ethernet MAC address structure

To find out the physical address of the NIC on your Windows computer, enter the ipconfig /all command in Command Prompt (CMD), or enter the ifconfig command on Mac and Linux computers.