What is a MAC address and how is it used?

Short answer

A MAC (Media Access Control) address is a unique hardware identifier assigned to every network interface card. It operates at the Data Link layer and ensures devices communicate on the same local network segment.

How it works

Manufacturers burn MAC addresses into network hardware during production. The address is 48 bits long, typically displayed as six pairs of hexadecimal digits (e.g., AA:BB:CC:DD:EE:FF). The first three octets identify the manufacturer (OUI), and the last three identify the specific device.

When your device sends data locally, it uses ARP to map an IP address to a MAC address. Switches use MAC addresses to forward frames to the correct port.

Example

In an office, a computer with IP 192.168.1.10 sends a packet to 192.168.1.1. ARP resolves the router's MAC address, and the switch forwards the frame based on that MAC.

Why it matters

MAC addresses enable precise local delivery. They are used for DHCP reservations, MAC filtering, device tracking, and network security policies. Unlike IPs, MAC addresses generally do not change, making them useful for identifying hardware.