What is a MAC address?

A MAC address (media access control address) is a 48-bit number assigned to a network interface: the Wi-Fi radio in your laptop, the Ethernet port on a switch, the Bluetooth chip in a pair of headphones. It's usually written as six pairs of hex digits separated by colons or dashes, like 28:6F:B9:00:00:00. Unlike an IP address, which describes where a device is on a network and can change from one connection to the next, a MAC address is tied to the interface itself: assigned once, at manufacture, and meant to stay put.

"MAC" is short for Media Access Control, the sublayer of the OSI model's data link layer responsible for getting frames onto a shared medium (a cable, a wireless channel) without every device talking over every other one. The address is how that sublayer tells devices apart. Ethernet, Wi-Fi (802.11), and most other IEEE 802 link-layer technologies all use the same 48-bit format, which is also called an EUI-48 (Extended Unique Identifier, 48 bits) in IEEE's own terminology.

What it's used for

Two things, mainly:

• Local delivery. On an Ethernet or Wi-Fi segment, frames are addressed by MAC, not IP. A switch keeps a table of which MAC address lives on which port and forwards accordingly; ARP is the protocol that maps a known IP address to the MAC address it should actually send the frame to.
• Vendor identification. The first half of the address (see how MAC addresses are structured) identifies the manufacturer, assigned by IEEE. That's what powers device fingerprinting, network inventory tools, and this site's own lookup tool.

Where it comes from

Every network interface controller (NIC) ships with a MAC address burned in at the factory, drawn from a block of addresses the manufacturer registered with IEEE. That's the "universally administered" case, and it's still the common one. Software can also assign a MAC address on the fly, locally administered rather than burned in: virtual machines, containers, and, increasingly, phones and laptops doing MAC randomization for privacy all generate addresses this way. Both kinds follow the same 48-bit format; a single bit in the address itself is what tells you which kind you're looking at, covered in the structure guide.

Go deeper

• How MAC addresses are structured: the OUI, the device-specific half, and the two bits that carry real meaning.
• A brief history: from Xerox PARC's original Ethernet to today's randomized addresses.
• MAC address vs. IP address: what each one actually does, and how they work together.
• How to find your own MAC address on Windows, macOS, Linux, iOS, or Android.

Have an actual address in hand? Look it up and we'll tell you the vendor, whether it's randomized, and everything else it encodes.