What it does
A MAC address is a 48-bit hardware address, usually written as six hex bytes like 00:1b:54:11:22:33. The first three bytes are the OUI - the Organizationally Unique Identifier - which the IEEE assigns to a manufacturer. This tool takes a MAC (in any common format) or a bare OUI, looks the OUI up in an embedded snapshot of the IEEE MA-L registry to name the manufacturer, and reads the two meaningful bits of the first byte. It all runs in your browser.
The two bits that matter
The very first byte of a MAC carries two flags in its low bits:
- The I/G bit (least significant bit) is unicast when 0 and multicast when 1. A multicast address is a group address, not a single interface.
- The U/L bit (second-least significant bit) is universal when 0 and locally administered when 1. A universally administered address is globally unique and drawn from a manufacturer's OUI; a locally administered address was set by software (a hypervisor, a bonded interface, a randomized Wi-Fi MAC) and has no manufacturer.
So 02:... is locally administered (there is no vendor to find), and 01:... is multicast.
Formats it accepts
Colon (00:1b:54:...), hyphen (00-1b-54-...), Cisco dotted (001b.5411.2233), and unseparated (001b5411...) forms all work, in upper or lower case, as does a bare six-hex OUI.
About the data
The vendor names come from the IEEE MA-L (OUI) public listing, embedded here as a point-in-time snapshot. Because it is a snapshot, a very recently assigned block may not be present yet, and this build covers the MA-L (24-bit) registry, not the smaller MA-M (28-bit) or MA-S (36-bit) blocks. The snapshot is lazy-loaded when you do your first lookup, so opening the page is fast and nothing is ever fetched from a server at lookup time.
Using it
Type or paste a MAC address or an OUI. A locally administered or unknown address is reported honestly rather than guessed at.