The OUI (Organizationally Unique Identifier) is the first 24 bits of a MAC address. The IEEE assigns each OUI to a specific manufacturer, so it reveals who made the hardware.

Can a MAC address be changed?

Yes. The burned-in address is fixed, but most operating systems allow MAC spoofing, which temporarily overrides it in software. Spoofed addresses may still show a real vendor OUI if copied from another device.

What Is a MAC Address? OUI, Format & How It Works

Q: What is a MAC address?

A MAC (Media Access Control) address is a 48-bit hardware identifier assigned to a network interface. It is written as six pairs of hex digits, like 28:6F:B9:12:34:56, and identifies a device on a local network.

The basics

A MAC address (Media Access Control address) is a 48-bit identifier assigned to a network interface such as a Wi-Fi card, Ethernet port or Bluetooth radio. It is written as six pairs of hexadecimal digits, for example 28:6F:B9:12:34:56. Unlike an IP address, which can change, the MAC identifies the physical hardware and is used to move data on the local network.

What is an OUI?

The first 24 bits, called the OUI (Organizationally Unique Identifier), are assigned by the IEEE to a manufacturer. In 28:6F:B9:12:34:56 the OUI is 28:6F:B9. Every device that company builds gets a MAC starting with one of its assigned OUIs, so looking up the OUI tells you who made the hardware. The remaining 24 bits are chosen by the manufacturer to make each device unique.

MA-L, MA-M and MA-S blocks

The IEEE sells address space in three block sizes. An MA-L block gives a company a full 24-bit OUI (16.7 million addresses). Smaller makers buy MA-M (28-bit) or MA-S (36-bit) blocks that share a 24-bit prefix among several companies, so accurate lookup checks the longer prefix first. MacVendorCheck reads all three registries.

Why look up a MAC address

Network administrators identify unknown devices on a network, spot hardware that should not be there, and audit inventory by vendor. If your router lists a connected device by MAC only, the OUI reveals whether it is a phone, a smart plug, or something you do not recognise. Try it on the lookup tool.

Can websites read my MAC address?

No. A MAC address only travels on the local network segment and is never sent to websites, so no site can read your device's MAC. Tools like this one only look up a MAC that you type in yourself.