What is a MAC address?
Definition
A MAC address, short for media access control address, is a 48-bit hardware identifier assigned to every network interface by its manufacturer. It is written as six pairs of hexadecimal digits, such as A4:CF:12:38:8E:7F. Guest WiFi historically used it to recognise returning devices, but modern phones now randomise it.
MAC address explained
The MAC address identifies a device at Layer 2, the data link layer, which is how an access point knows which frames belong to which device. It is sent in clear text in 802.11 management frames, so anyone nearby with the right tools can read it, and anyone determined can copy it.
That weakness matters for MAC authentication, where the network lets a device in because its MAC address is on an approved list. It is still useful for devices that cannot do anything else, such as some printers and IoT sensors, but it is trivially spoofed, so it should never be the only control on a network that carries sensitive traffic.
Privacy law and operating systems have changed how MAC addresses can be used. Regulators treat them as personal information, because they can track a device and its owner. iOS, Android and Windows now use randomised addresses by default, which breaks MAC-based recognition of returning guests and inflates visitor counts in analytics that rely on it.
Guides on MAC address
- Technical guideWhat is MAC address authentication? When to use it and when to avoid it
- Technical guideMAC address randomisation: enterprise WiFi impact
- Technical guideHow MAC address randomisation affects guest WiFi analytics
Where it fits
- Pillar guideEnterprise WiFi security guide
- Purple productPurple Guest WiFi
- Free toolMAC address lookup
Related terms
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