What is an OUI in a MAC address?

An Organizationally Unique Identifier (OUI) comprises the first 24 bits (first 3 octets) of a MAC address, assigned by the IEEE to hardware manufacturers like Cisco, Intel, or Apple.

How do you tell if a MAC address is unicast or multicast?

The least significant bit of the first octet indicates transmission type: 0 = Unicast, 1 = Multicast. Broadcast (FF:FF:FF:FF:FF:FF) has all bits set to 1.

MAC Address & Hardware OUI Lookup

Identify network hardware manufacturers, parse IEEE Organizationally Unique Identifiers (OUIs), and format MAC strings.

Enter MAC Address

Format Output

Hardware Identification Vendor Identified

Hardware Manufacturer / Vendor

Cisco Systems, Inc.

IEEE OUI Prefix (24-bit)

00:1A:2B

Device Specific NIC ID (24-bit)

3C:4D:5E

Cast Type (Bit 0)

Unicast (Individual)

Administration (Bit 1)

Globally Unique (OUI Enforced)

🔍 IT Troubleshooting: In network switch ARP tables and DHCP server leases, identifying the MAC OUI allows network admins to rapidly locate rogue devices, unauthorized IoT hubs, or faulty NICs.

Media Access Control (MAC) Address Structure

A MAC address is a 48-bit (6-byte) physical identifier permanently burned into Network Interface Cards (NICs) at Layer 2 (Data Link Layer) of the OSI model.

48-Bit MAC Address Decomposition

Bytes 1–3 (OUI): Organizationally Unique Identifier assigned by the IEEE Registration Authority to hardware vendors (e.g. F0:18:98 for Apple, 00:50:56 for VMware).
Bytes 4–6 (NIC): Device identifier assigned by the manufacturer ensuring unique physical addressing.
I/G Bit (Individual / Group): Bit 0 of the first byte distinguishes Unicast (0) from Multicast/Broadcast (1).
U/L Bit (Universal / Local): Bit 1 of the first byte indicates if the address is globally unique (0) or locally administered (1, often used in MAC randomization for privacy).