MAC address
termStands for: Media Access Control address
The hardware address that identifies a network interface on a local network.
A MAC address is the 48-bit identifier burned into (or assigned to) a network card, used to deliver frames on the local segment; its first half, the OUI, identifies the manufacturer. Unlike an IP address it does not route across networks, it is strictly local.
A MAC address is 48 bits, which the IEEE now calls an EUI-48; its registration guidelines declare the older name, MAC-48, obsolete. Two bits of the first octet change what the rest means: the lowest says whether the address is one interface or a group, the next whether it came from a purchased block or was set locally by software. Only a universal, individual address has a manufacturer behind its first three octets, the OUI.
That distinction matters more every year. Phones and laptops now join each Wi-Fi network with a random, locally administered address, by default on Android since version 10 and on Apple devices since iOS 14, so one device shows a different MAC on every network and none of them names a vendor. Group addresses are mostly computed rather than assigned: broadcast is all ones, IPv4 multicast maps into 01-00-5E, IPv6 multicast into 33-33.
A MAC address never leaves its link. Every router rewrites the frame, so the address in a capture is the last hop's, and what connects an IP address to it on the local segment is ARP.
Also known as: mac address, hardware address, physical address, OUI