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.

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.

Related tools

• MAC Address Formatter
• Subnet / CIDR Calculator