MAC OUI Lookup
Find the vendor behind a MAC address or OUI prefix using an IEEE public registry snapshot.
Supported MAC Address Formats
00:1A:2B:3C:4D:5E00-1A-2B001A.2B3C.4D5E001A2BWhat is an OUI Prefix?
An Organizationally Unique Identifier (OUI) is a 24-bit number assigned by the IEEE to uniquely identify a vendor or manufacturer of networked devices. It appears as the first three bytes of a standard 48-bit MAC address and helps identify the maker of a network interface controller.
Larger registries include MA-M (28-bit) and MA-S (36-bit) assignments, which allow smaller organizations to receive a more specific prefix block.
Unicast vs Multicast MAC Addresses
The least significant bit of the first byte of a MAC address determines whether it is a unicast or multicast address. A value of 0 indicates a unicast address used for one-to-one communication.
A value of 1 indicates a multicast address used to send traffic to a group of devices simultaneously, such as IPv6 neighbor discovery or streaming protocols.
Universally vs Locally Administered MAC Addresses
The second least significant bit of the first byte distinguishes universal from local administration. When this bit is 0, the address is universally administered by the IEEE and tied to a registered vendor.
When this bit is 1, the address is locally administered. Virtual machines, software bridges, and privacy features can set this bit to avoid conflicts with hardware addresses.
Related Resources
MAC OUI Lookup FAQ
What is an OUI prefix?
An OUI (Organizationally Unique Identifier) is a 24-bit prefix assigned by the IEEE to uniquely identify a hardware manufacturer or vendor. It forms the first three bytes of a standard 48-bit MAC address.
What MAC address formats are supported?
The tool supports colon-separated (00:1A:2B), hyphen-separated (00-1A-2B), Cisco dot notation (001A.2B3C.4D5E), and plain hex strings (001A2B).
What is the difference between unicast and multicast MAC addresses?
The least significant bit of the first byte determines the address type. If it is 0, the address is unicast (one-to-one). If it is 1, the address is multicast (one-to-many).
What does universally vs locally administered mean?
The second least significant bit of the first byte indicates administration. A 0 means the address is universally administered by the IEEE. A 1 means it is locally administered and may be assigned by network administrators or virtualization software.
Where does the OUI registry data come from?
The lookup uses a public IEEE registry snapshot stored server-side. It covers MA-L, MA-M, and MA-S assignments and is updated periodically from IEEE standards publications.