What Is a MAC Address?

Computer networks are amazing things. They are a complex matrix of circuits and links forming webs of virtual communications. These networks give way to unimaginable and almost instantaneous virtual applications. Either through games, video streaming, chat, telephone or the internet, the link between the physical world and the virtual world sometimes seems like magic. But how do computers bridge that gap between the two worlds. Where on the network does the physical realm meet the virtual. How Do Computers Communicate? Every computer or device that needs to get on the network to talk to another computer needs a network interface card (NIC). Most NIC's are either built-in, like a wireless connection, or are installed in the computer. When a NIC is made, the manufacturer permanently encodes a unique hardware address into it. This permanently encoded hardware address is stored in the read only portion of memory with in the card and is known as the MAC (Media Access Control) address. A MAC address is a 48 bit hardware address that's used to physically identify the computer on the network. This 48 bit address is usually displayed in hexadecimal (base 16) as a 12 digit number. This is an example of a MAC: MM:MM:MM:HH:HH:HH A real MAC would look something like this: 00:1b:21:44:eb:8d The first half of the MAC, the first 6 digits (24 bits), of the address represents the vendor portion or manufacturer of the NIC card. Every network card manufacturer is assigned a unique identifier by the IEEE for all of their network cards. The last 24 bits (6 digits) are a unique identifier that represents the card itself. Each manufacturer will number their NIC's to be unique. No two MAC addresses are alike. This entire 48 bit MAC address represents the physical computing device on the network. It is the bridge between the physical world and the virtual world of computing. It is the link between the physical hardware and the virtual operating system. All computers communicate using the MAC address. Most people believe that computers use IP addresses to communicate. And they do, but beneath the IP address lies the MAC address and this is where the true communication takes place. So the next time you need to find a computer on your network remember to look for the MAC address. Once you find the MAC address you will find the computer itself.

Joseph L Wilson is a Senior Network Engineer in Austin TX, working with IP networks for over 15 years. Joe has recorded several network video tutorials on his network engineer blog to help engineers better grasp complex routing and switching topics.