What Is a MAC Address? EUI-48 and OUI Explained

What Is a MAC Address?

A MAC address (Media Access Control) is a 48-bit hardware identifier assigned to a network interface. Also called EUI-48, it operates at Layer 2 — below IP addresses — and is used for local Ethernet/Wi-Fi delivery.

Example: 00:1B:63:12:34:56

Format with the MAC Address Formatter.

Structure

00 : 1B : 63 : 12 : 34 : 56
└── OUI ──┘ └── NIC-specific ──┘
  (vendor)     (device serial)

OUI (first 3 bytes / 24 bits) — assigned by IEEE to a manufacturer
Last 3 bytes — assigned by the vendor to the specific device

Common notation formats

Format	Example
Colon (IEEE)	`00:1B:63:12:34:56`
Dash	`00-1B-63-12-34-56`
Cisco dot	`001B.6312.3456`
Plain	`001B63123456`

Unicast vs multicast

The least significant bit of the first octet:

0 = unicast (one specific interface)
1 = multicast (group of interfaces)

The second least significant bit:

0 = globally unique (OUI from IEEE)
1 = locally administered (software-defined, common in VMs)

OUI lookup

The first half identifies the vendor — e.g. 00:0C:29 is VMware, B8:27:EB is Raspberry Pi Foundation. Our tool bundles common OUIs for instant lookup.

See MAC Address Vendor Lookup for how lookups work and why some addresses return no vendor.

MAC vs IP address

	MAC	IP
Layer	2 (Data link)	3 (Network)
Scope	Local segment	End-to-end routable
Changes	Fixed (usually)	Can change (DHCP, roaming)
Used for	Switching	Routing

ARP maps IP → MAC on the local subnet.

What Is a MAC Address? EUI-48 and OUI Explained