MAC Address Lookup (OUI / Vendor)

How MAC address lookup works

Every network interface card (NIC) in the world has a unique Media Access Control (MAC) address burned into its firmware by the manufacturer. The MAC address is 48 bits long, typically displayed as 12 hexadecimal digits grouped in pairs. The first 24 bits (6 hex digits) form the Organizationally Unique Identifier (OUI), which is assigned to the manufacturer by the IEEE Registration Authority. The remaining 24 bits are the device-specific extension assigned by the manufacturer.

When you enter a MAC address into this tool, the JavaScript extracts the first 6 hex characters (normalized to uppercase, stripping separators) and matches them against an embedded dictionary of known OUI prefixes. The dictionary contains around 100 OUI prefixes for 20 of the most common vendors, sourced from the official IEEE registry. If the OUI is found, the manufacturer name is displayed; if not, the tool reports that the prefix is unknown but valid.

The MAC address also encodes information about its type. If the least significant bit of the first octet (the I/G bit) is 1, the address is a group (multicast or broadcast) address. If the second-least significant bit (the U/L bit) is 1, the address is locally administered rather than universally assigned by the manufacturer. The tool parses these bits and displays the address type accordingly.

Understanding MAC address format

MAC addresses can be written in several formats. The most common are six pairs of hexadecimal digits separated by colons (00:1A:2B:3C:4D:5E), hyphens (00-1A-2B-3C-4D-5E), or three groups of four digits (001A.2B3C.4D5E, Cisco style). The lookup tool accepts all three formats and normalizes the input before matching. The first three octets (00:1A:2B in the example) form the OUI that identifies the vendor.

The first octet of a MAC address contains two significant flag bits. The least significant bit (bit 0) is the Individual/Group (I/G) bit. When set to 0, the address is unicast (addressed to a single interface). When set to 1, it is a multicast or broadcast address. The broadcast address FF:FF:FF:FF:FF:FF has all 48 bits set to 1. The second-least significant bit (bit 1) is the Universal/Local (U/L) bit. When set to 0, the address is universally administered (burned into hardware by the manufacturer). When set to 1, it is locally administered (set by software, such as in virtual machines or MAC spoofing).

The IEEE Registration Authority maintains the public OUI database at standards-oui.ieee.org. Companies pay a fee to register an OUI and are assigned a unique 24-bit prefix. Large manufacturers often have multiple OUI prefixes — for example, Cisco Systems owns dozens of OUIs covering different product lines and acquisitions. The complete database contains over 30,000 registered OUIs from manufacturers worldwide.

Practical uses of MAC address lookup

Network administrators use MAC address lookup for asset inventory, security auditing, and troubleshooting. By examining the MAC addresses of devices on a network, administrators can identify the make and model of connected hardware without physical access. This is particularly useful for detecting unauthorized devices, identifying rogue access points, and maintaining an accurate inventory of network-connected equipment.

In wireless networking, MAC address filtering was once a common security mechanism (though it is now considered weak since MACs can be spoofed). Knowing the OUI of devices helps administrators quickly identify device types in DHCP lease logs, ARP tables, and Wi-Fi controller client lists. For example, spotting multiple Apple OUIs might indicate employee iPhones, while a Samsung OUI on the guest network might be a personal device.

Forensic investigators use MAC address information to trace devices involved in security incidents. While MAC addresses do not directly identify individuals, they can link a device to a specific manufacturer and, when correlated with access point logs, place a device at a specific location at a specific time. This information is often used in corporate security investigations and, with proper legal authority, in law enforcement contexts.

MAC address privacy concerns

In recent years, privacy advocates have raised concerns about MAC address tracking. Because MAC addresses are unique and persistent, they can be used to track devices as they move between Wi-Fi networks. Retail stores, airports, and shopping malls have used Wi-Fi probe requests (which broadcast the device MAC address) to track customer movement and dwell times.

To address these concerns, modern operating systems including iOS 14+, Android 10+, Windows 10, and macOS Big Sur+ implement MAC address randomization. When scanning for Wi-Fi networks or connecting to public networks, the device uses a randomized MAC address instead of the real hardware address. This prevents tracking by passive monitoring systems. For enterprise networks and MAC-based authentication, users can disable randomization for trusted networks.

Limitations

The OUI dictionary included in this tool covers around 100 prefixes for 20 of the most common consumer and enterprise networking vendors. If your MAC address OUI is not in the dictionary, the tool will indicate an unknown prefix. The full IEEE OUI database contains over 30,000 entries and is updated regularly as new manufacturers register prefixes. For a complete lookup, refer to the official IEEE OUI database.

MAC addresses can be spoofed at the software level, so the OUI lookup identifies the claimed manufacturer of the interface, not necessarily the actual hardware in use. Virtual machines and containerized environments frequently use locally administered MAC addresses that may not correspond to any real manufacturer. The tool also does not look up MAC addresses in external APIs — all data is contained in the page and the lookup is instantaneous and fully private.

Frequently asked questions