Networking
MAC Address
Also known as: Media Access Control Address, Hardware Address, Physical Address
A permanent hardware identifier assigned to a network interface at the factory — identifies the device itself, not its location.
A MAC address is a unique hardware identifier assigned to a network interface at the factory. Where an IP address tells the network where a device is, a MAC address identifies what the device is — permanently, at the hardware level.
Every network interface — wired NIC, Wi-Fi adapter, virtual adapter — has a MAC address: 48 bits written as six pairs of hexadecimal characters (e.g. 00:1A:2B:3C:4D:5E). The first three pairs identify the manufacturer (the OUI, or Organizationally Unique Identifier); the last three are unique to that specific device.
MAC addresses operate at Layer 2 (the Data Link layer). When traffic moves within your local network, switches use MAC address tables to decide which port to send a frame out of. IP addresses route traffic between networks; MAC addresses deliver it within one.
A few practical implications:
DHCP reservations use MAC addresses to assign a device the same IP address every time. You bind the MAC to the desired IP in your DHCP server.
MAC filtering on Wi-Fi networks restricts which devices can connect. It's a weak security control — MAC addresses are trivial to spoof — but it's still used for basic network access control in low-security environments.
Port security on managed switches can lock a port to specific MAC addresses, preventing unauthorized devices from plugging in.
Note that modern operating systems increasingly use MAC address randomization for Wi-Fi scanning and connections to prevent location tracking. If you're relying on MAC addresses for device identification in a BYOD environment, be aware that the MAC you see may not be the hardware MAC.