Each network interface on your computer or any other networked device has a unique MAC address. These MAC addresses are assigned in the factory, but you can change, or “spoof,” MAC addresses in software.
MAC stands for “media access control.” MAC addresses are also commonly referred to as physical addresses or hardware addresses, because they correspond to a hardware adapter.
What MAC Addresses Are Used For
- Static IP Assignment: Routers allow you to assign static IP addresses to your computers. When a device connects, it always receives a specific IP address if it has a matching MAC address
- MAC Address Filtering: Networks can use MAC address filtering, only allowing devices with specific MAC addresses to connect to a network. This isn’t a great security tool because people can spoof their MAC addresses.
- MAC Authentication: Some Internet service providers may require authentication with a MAC address and only allow a device with that MAC address to connect to the Internet. You may need to change your router or computer’s MAC address to connect.
- Device Identification: Many airport Wi-Fi networks and other public Wi-Fi networks use a device’s MAC address to identify it. For example, an airport Wi-Fi network might offer a free 30 minutes and then ban your MAC address from receiving more Wi-Fi. Change your MAC address and you could get more Wi-Fi. (Free, limited Wi-Fi may also be tracked using browser cookies or an account system.)
- Device Tracking: Because they’re unique, MAC addresses can be used to track you. When you walk around, your smartphone scans for nearby Wi-Fi networks and broadcasts its MAC address. A company named Renew London used trash bins in the city of London to track people’s movements around the city based on their MAC addresses. Apple’s iOS 8 will use a random MAC address each time it scans for nearby Wi-Fi networks to prevent this sort of tracking.
Bear in mind that each network interface has its own MAC address. So, on a typical laptop with both a Wi-Fi radio and a wired Ethernet port, the wireless and wired network interface each have unique, separate MAC addresses.