26 May 2022 | 4 min read | Ignas Anfalovas
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MAC Address: Media Access Control Explained

What is a media access control (MAC) address? How does it function? What is it used for? Discover answers to these important questions here.

MAC (Media Access Control) Address next to a laptop.

Media access control, medium access control or simply MAC, is a specific network data transfer policy. It determines how data transmits through a regular network cable. The protocol exists to ease data packets’ transfer between two computers and ensure no collision or simultaneous data transit occurs.

The medium access control – commonly referred to as the MAC protocol – is, effectively, a sublayer or MAC sublayer that controls hardware responsible for the communication with a wired, wireless or optical transmission medium. 

The MAC sublayer is part of the two sublayers scheme: data link layer. The other part of the data link layer is the logical link control (LLC) sublayer. The LLC sublayer offers multiplexing and flow control for the logical link, and the MAC sublayer acts as the interface between the LLC sublayer and the physical layer within a transmission medium.

Media Access Control depicted as sublayer of the data link layer.
MAC sublayer in the Data Link Layer

Now that we’ve explained the media access control method of transfer, let’s cover the media access control addresses – MAC addresses – the actual hardware addresses of Ethernet network adapters. These are unique identifiers of network devices that enable data transmission. 

Continue reading as we explain what a MAC address is, how a specific media access control address works and what it’s used for. 

What is a MAC address?

Sending data between computers is only possible if both software and hardware are involved. However, for every device to know where to send the data, a third component is required – addresses. 

Since both hardware and software are involved, there are two types of addresses here. The software address is the IP address, while the hardware address is the media access control address. 

The MAC address ties to the network interface card, or network interface controller (NIC), located inside each computer today. The NIC acts as the transmission medium that turns data into electrical signals, which can then transmit over the web. 

It consists of six sets of two characters or digits that colons or hyphens may separate. The limitations of this number are due to the address itself being 48-bits in length. 

A typical MAC address has six groups of two hexadecimal digits. For example, 00:05:85:00:34:SG or 00-05-85-00-BZ-05. The first three groups here are intentionally the same, as they correspond to the same NIC manufacturer. In this case – Juniper

MAC address with organizationally unique identifier and universally administered address parts.
An example of a MAC address

Every NIC manufacturer has its own unique Organizationally Unique Identifier (OUI), or the first 24-bit part of the MAC address. This addressing scheme helps manufacturers distinguish themselves and their products. 

MAC addresses are static and never change, unlike dynamic IP addresses. Each MAC address is a unique identifier, making it more reliable for network administrators who have to identify the ones sending and those receiving data. 

How do MAC addresses function?

The primary function of MAC addresses is clear, but let’s dig a little deeper to explain how they work. 

Every data packet sent over the network is sent from one MAC address to another. So, when the network adapter receives a packet, it compares the packet’s MAC address to its own. These addresses need to match so that the network interface card or network adapter can receive information. 

This part is seamless, but it cannot happen without the help of IP addresses. Why are they important? They are a part of the data transmission process. 

In plain terms, MAC addresses use IP addresses to recognize devices on the wide web. IP is a protocol above ethernet networks, and ethernet solely uses MAC addresses. And since they cannot send packets between each other unless they are part of the same network, be it cable or wireless, they need to go above. 

In other words, there is no routing between MAC addresses. So, they use something called the Address Resolution Protocol (ARP). ARP’s primary function is to map IP addresses to MAC addresses. It’s also a protocol above ethernet, on the same level as IP. 

Thanks to APR, when a piece of hardware needs to know the MAC address of the IP address that sends information, it sends a packet asking that question. APR is responsible that the device with the proper MAC address can respond, confirming its identity. Once that’s ready, the two devices can finally exchange data packets. 

One computer sending a request to multiple computers and receiving a response.
How ARP works using a request-response system

What are MAC addresses used for?

Media access control addresses have several applications. For one, it ensures the filtering process on a regular Wi-Fi network. Every router accepts a specific MAC address so that no intruder can gain access. So, if the IP address changes, the device is still identifiable by the MAC address, which remains the same. 

You can also use these addresses to connect to a wireless device in the data recovery process and identify stolen hardware trying to connect to your network. Many companies acquire these addresses from their employees’ devices to make sure they know who’s accessing the network and disable intruders should they try to do the same using a stolen device. 

Wireless access points can also use a media access control address for access control. If needed, they can limit access to known devices with the right addresses and the correct passphrases. 

It’s also worth mentioning that DHCP servers use the MAC address system to identify specific devices and give some of them fixed IP addresses when necessary. 

Conclusion

The MAC layer – which interfaces between LLC sublayer within the data link layer and the physical layer – is essential when many computers sit on the same communication circuit. MAC addresses allow these computers and other devices to connect and share information. 

One could argue that the importance of MAC addresses is greater than that of IP addresses, even though the latter belong to a higher layer. That said, a MAC address is always static, so it’s possible to identify its corresponding computer and identify potential intruders.

Due to this, MAC addresses are a crucial component for many businesses and organizations. 


About the author

Ignas Anfalovas

Platform Engineering Manager

Ignas is a Platform Engineering Manager at IPXO with more than 7 years of experience in the IT sector. His expertise includes network design solutions and infrastructure maintenance. After working hours, you will find Ignas in Lithuanian folk-dance classes.