Understanding MAC Addresses: Structure, Importance, and How to Find Them in 2025

A media access control address, or a device’s MAC address, is a worldwide unique identifier assigned to a network interface controller. It is also known as “hardware address” or “physical address” and is very important for communication within network segments. Most IEEE 802 network technologies, including Ethernet, Wi-Fi, and Bluetooth, use a Media Access Control address for within-network segment communication.

It 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 letters from A to F. Where A= 10, B=11, C=12, D=13, E=14, and F=15.

MAC Structure

In an Ethernet LAN, each network device connects to shared media. Therefore, all nodes receive every frame transmitted over the shared media. MAC addresses identify the source and destination to prevent too much overhead in processing every frame. Media Access Control addressing also provides a method for device identification.

Vendors develop Ethernet Cards and assign them a unique address, following IEEE standards. IEEE requires registration of any organization that manufactures Ethernet Devices and NIC cards.

After registration, IEEE assigns a 3-byte code term, Organizational Unique Identifier(OUI). So, each MAC assigned to an Ethernet device must have a vendor OUI and a unique serial number. Media Access Control Addresses assigned to an Ethernet device must have a vendor OUI and a unique serial number assigned to them.

• MM:MM:MM:SS:SS: SS
• MM-MM-MM-SS-SS-SS
• MMM.MMM.SSS.SSS

The leftmost 6 digits (24 bits) are called an “OUI,” associated with the adapter manufacturer. Every manufacturer registers and obtains a MAC OUI as assigned by the IEEE. The manufacturer often possesses many OUI numbers related to their different products.

The rightmost digits of a Media Access Control address represent an identification number for the particular device. Devices manufactured by the same vendor, OUI, are each given their unique 24-bit number. The figure below illustrates the Media Access Control address OUI and the Interface controller-specific number.

IEEE requires a vendor to follow two simple rules:-

• MAC addresses assigned to a NIC and another 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.

Note: Duplicate MAC addresses can occur due to manufacturing errors, virtual machine cloning, or manual configuration mistakes. Resolution may require replacing the NIC, updating software, or reconfiguring the address, with potential security implications like MAC spoofing to consider.

How to find the MAC address for a Personal Computer

We can find the MAC on a Windows host using the command “ipconfig /all” shown in the figure below. This command identifies the MAC of an Ethernet adapter. The steps for finding a MAC are the following:-

1. Click Windows Start or press the Windows key.
2. In the search box, type cmd and press Enter
3. The command prompt you should see now.
4. Type ipconfig /all and press Enter. Look for the ‘Physical Address’ under your Ethernet adapter, which will be displayed in the format XX-XX-XX-XX-XX-XX (e.g., 34-E6-D7-10-4C-8B).”
5. A Physical Address is displayed for each adapter. The Physical Address is your device’s MAC address.

For non-Windows systems, you can find the MAC address on Linux or macOS by opening a terminal and typing ifconfig (older systems) or ip link (newer systems) and looking for the HWaddr or link/ether field. For example, on macOS, use the command ifconfig | grep ether.

Note: We often see various representations of MAC addresses, which depend on devices and operating systems. Cisco routers and switches also use the address XXXX.XXXX.XXXX, where X is a hexadecimal character.

Conclusion

Understanding the Media Access Control (MAC) address is essential for effective network communication and management as of June 2025. This 48-bit unique identifier, structured with a 24-bit Organizationally Unique Identifier (OUI) and a 24-bit device-specific number, plays a critical role in the Data Link layer of the OSI model, facilitating accurate data delivery across Ethernet, Wi-Fi, Bluetooth, and emerging technologies like IoT and 5G.

Whether troubleshooting network issues, configuring devices, or enhancing security, a solid grasp of MAC addresses—along with practical skills like finding them using ipconfig /all on Windows or ip link on Linux/macOS—remains indispensable for network professionals. As networking evolves, staying informed about MAC management, including potential duplicates and spoofing risks, will continue to be vital for maintaining robust and secure networks.