A MAC (Media Access Control) address is a unique hardware identifier assigned to a network interface, whether wired or wireless, at the data link layer. It consists of six pairs of hexadecimal digits (for example, 3A:97:0E:4C:1F:22), where the first three pairs identify the vendor (OUI) and the last three are a device-specific serial.
Within a local network, every Ethernet frame or Wi-Fi packet carries source and destination MAC addresses so switches and access points can forward traffic directly to the correct interface. When data crosses a router to another subnet, MAC addresses are replaced at each hop, ensuring internal hardware identifiers remain within the local broadcast domain.
MAC addresses also underpin protocols like ARP (Address Resolution Protocol) in IPv4 and neighbour discovery in IPv6, which map IP addresses to the corresponding MAC for seamless local delivery. Modern devices often randomise their MAC when scanning for Wi-Fi to protect privacy, reverting to their true address only upon secure connection. Administrators may use MAC filtering or 802.1X authentication for access control, but because MACs can be spoofed, these measures are typically combined with stronger security controls.