What Is a MAC Address?

What a MAC Address Identifies

A MAC (Media Access Control) address is a unique identifier physically burned into every network interface - a network card, Wi-Fi adapter, or similar device - used to identify it specifically on a local network segment.

The Format of a MAC Address

AA:BB:CC:11:22:33
<-- OUI --><-- Device ID -->
(48 bits total, written as six pairs of hexadecimal digits)

The First Half: Identifying the Manufacturer

The first 24 bits (three hex pairs) form an OUI (Organizationally Unique Identifier), assigned to the specific manufacturer of the network hardware. This is why looking up a MAC address's OUI can often reveal exactly which company made that particular device.

The Second Half: A Unique Device Identifier

The remaining 24 bits are assigned by the manufacturer itself, intended to make each individual device unique - together with the OUI, this is meant to guarantee that no two network devices anywhere share the exact same MAC address.

Why MAC Addresses Only Matter Locally

Unlike an IP address (covered extensively elsewhere in this project), which can identify a device anywhere on a routed network, a MAC address is only meaningful within the local network segment a device is directly connected to - routers do not forward MAC addresses across separate networks the way they forward IP packets.

Why MAC Addresses Can Still Be Changed in Software

Despite being "burned in" at the hardware level, most operating systems allow a device's MAC address to be overridden in software - a legitimate feature used for privacy on public Wi-Fi, but also a technique attackers can misuse, as covered in the ARP spoofing note later in this section.