MAC Address Vendor Lookup: How OUI Lookup Works

A MAC address vendor lookup (also called an OUI lookup) identifies the company that made a network interface from its MAC address. It works because the first half of every globally assigned MAC address is a vendor prefix registered with the IEEE.

For example, a MAC address starting with B8:27:EB belongs to the Raspberry Pi Foundation, and 00:0C:29 belongs to VMware.

What is an OUI?

An OUI (Organizationally Unique Identifier) is the first 24 bits — the first three bytes, or six hex digits — of a MAC address. The IEEE Registration Authority assigns each OUI to one organization.

00:0C:29:4E:7A:B1
└─ OUI ─┘└─ device ┘
VMware    unique to this NIC

The vendor gives the remaining 24 bits to individual devices. Together they make the address unique. For the full address layout, see What Is a MAC Address?.

How to look up a MAC address vendor

Take the first six hex digits of the MAC address and ignore the separators (:, - or .). 00-0C-29-4E-7A-B1 becomes 000C29.
Search that prefix in the IEEE registry, or in a tool built on it.
Read the registered organization name.

The registry holds several block sizes, and the longer ones are shared between companies:

Registry	Prefix length	Notes
MA-L (large)	24 bits (6 hex digits)	The classic OUI
MA-M (medium)	28 bits (7 hex digits)	Block shared by up to 16 organizations
MA-S (small)	36 bits (9 hex digits)	Block shared by up to 4096 organizations

If a 6-digit lookup returns an unfamiliar or generic name, the address may sit inside an MA-M or MA-S block, which needs the longer prefix to resolve.

Why a MAC lookup sometimes finds nothing

Randomized MAC addresses. Modern phones and laptops (iOS, Android, Windows, macOS) use a random MAC per Wi-Fi network for privacy. These have no registered vendor.
Locally administered addresses. If the second hex digit of the first byte is 2, 6, A or E, the address was set by software (VMs, containers, bridges) and is not in the IEEE registry. 02:42:AC:11:00:02 is a typical Docker address.
Multicast addresses. If the lowest bit of the first byte is 1, the address is a group address, not a device.
Outdated database. New OUIs are assigned continuously, so a stale list misses recent vendors.
Spoofed addresses. A MAC can be changed in software, so a lookup shows who the prefix belongs to, not necessarily who built the device.

What a vendor lookup is useful for

Identifying unknown devices on your network from a router or DHCP client list
Spotting rogue devices or unexpected hardware
Tracing a MAC address in a switch's CAM table to a device type
Troubleshooting duplicate or conflicting addresses

It identifies the interface's manufacturer, not the end product. A Raspberry Pi vendor prefix tells you it's a Pi, but a router's prefix may show the chipset or ODM maker rather than the brand on the box.

FAQ

What is the difference between OUI lookup and MAC address lookup?

They are the same thing in practice. A MAC address lookup reads the OUI (the first three bytes) and returns the registered vendor.

How do I find the manufacturer of a MAC address?

Take the first six hex digits, remove any separators, and search them in an OUI database such as the IEEE registry. Check the longer MA-M and MA-S blocks if the 6-digit result is unclear.

Why does my phone's MAC address show no vendor?

Most phones use a randomized, locally administered MAC address per Wi-Fi network. Those addresses are not registered to any vendor. Turn off "private Wi-Fi address" for that network to see the real hardware address.

Is a MAC vendor lookup accurate?

It accurately shows who holds the prefix. It can't prove the device's brand, because MAC addresses can be spoofed and many brands use third-party chip makers.

How many hex digits do I need for an OUI lookup?

Six hex digits (24 bits) is the standard minimum. Seven or nine digits let you resolve addresses inside the smaller MA-M and MA-S blocks.

Related tools

MAC Address Formatter — normalize notation and look up common OUI prefixes
Subnet / CIDR Calculator