What is a MAC address?

A MAC (Media Access Control) address is a unique 48-bit hardware identifier assigned to every network interface card (NIC). It is written as six pairs of hexadecimal digits (e.g. AA:BB:CC:DD:EE:FF). MAC addresses are used at layer 2 of the network stack for communication within a local network segment.

OUI (Organizationally Unique Identifier) is the first 3 octets (24 bits) of a MAC address. OUIs are assigned by the IEEE to hardware manufacturers. For example, the OUI 00:1A:2B is assigned to Apple. The remaining 3 octets are assigned by the manufacturer to individual devices, creating a globally unique address.

Can a MAC address be changed or spoofed?

Yes. The MAC address is stored in hardware (burned into the NIC) but can typically be overridden by software. This is called MAC spoofing and is used for privacy, to bypass network access restrictions, and to impersonate other devices. Modern phones use MAC address randomization by default when scanning for Wi-Fi to prevent tracking.

What is MAC address randomization?

MAC address randomization is a privacy feature in modern mobile operating systems (iOS 14+, Android 10+, Windows 10+) that generates a random MAC address when scanning for or connecting to Wi-Fi networks. This prevents location tracking based on MAC addresses by retail analytics systems and public Wi-Fi networks.

What is the difference between unicast and multicast MAC addresses?

The least significant bit of the first octet determines this: if it is 0, the address is unicast (intended for a single device); if it is 1, it is multicast (intended for a group of devices). The broadcast address FF:FF:FF:FF:FF:FF is a special case of multicast sent to all devices on a segment.

What does globally vs locally administered mean?

The second least significant bit of the first octet indicates administration: 0 means globally administered (the OUI was assigned by the IEEE to a manufacturer), 1 means locally administered (the address was set by software rather than burned in by the manufacturer). Randomly generated MAC addresses for testing should use locally administered to avoid conflicts.

Is MAC Address Lookup free?

Yes. OUI vendor lookup uses the free macvendors.com API (1 request per second on the free tier). MAC address generation runs entirely in your browser using the Web Crypto API. No sign-up or account is required.

MAC Address Lookup

About MAC Address Lookup

MAC Address Lookup has two functions: it identifies the manufacturer (vendor) of any network device from its MAC address, and it generates valid random MAC addresses for testing. On the Lookup tab, enter a MAC address in any common format (AA:BB:CC:DD:EE:FF, AA-BB-CC-DD-EE-FF, or AABBCCDDEEFF) and the tool queries the macvendors.com OUI database to return the manufacturer name and OUI prefix. On the Generate tab, configure unicast or multicast bit and globally or locally administered bit, optionally specify the first 3 octets (OUI prefix), and generate one or five random MAC addresses. MAC address data is used in network troubleshooting, device identification, and access control list (ACL) configuration. For looking up the network details of a specific IP, use IP Address Lookup. For a full picture of your current browser and device, see What Is My Browser.

MAC addresses are fundamental to how Ethernet and Wi-Fi networks operate at layer 2. When a device sends a packet on a local network, it includes both the source and destination MAC addresses in the Ethernet frame header. Switches use MAC address tables to learn which port each device is connected to, enabling them to forward frames directly to the right port rather than broadcasting to all ports. This is how switches differ from hubs. The IEEE assigns OUI blocks to manufacturers in blocks of 24 bits (16.7 million addresses per block), which manufacturers then subdivide for their products. Some manufacturers have multiple OUI assignments. The macvendors.com API used for lookups maintains a regularly updated database of OUI-to-manufacturer mappings derived from the IEEE public registry. MAC-based access control lists (MAC ACLs or port security) are used on managed switches to allow or deny network access based on device MAC addresses. However, because MAC addresses can be spoofed, MAC ACLs are not considered a strong security control on their own and should be used alongside other authentication mechanisms like 802.1X (port-based network access control). For home and small business networks, MAC filtering on Wi-Fi routers is a common but easily bypassed security measure: an attacker can observe a legitimate device's MAC address and spoof it to gain access.

How to use MAC Address Lookup

Vendor Lookup tab: enter a MAC address and click Lookup Vendor to find the manufacturer.
Generate tab: choose unicast or multicast, set prefix if needed, click Generate.
Copy any generated MAC address individually with the Copy button.

Frequently Asked Questions

What is a MAC address?: A MAC (Media Access Control) address is a unique 48-bit hardware identifier assigned to every network interface card (NIC). It is written as six pairs of hexadecimal digits (e.g. AA:BB:CC:DD:EE:FF). MAC addresses are used at layer 2 of the network stack for communication within a local network segment.
What is an OUI?: OUI (Organizationally Unique Identifier) is the first 3 octets (24 bits) of a MAC address. OUIs are assigned by the IEEE to hardware manufacturers. For example, the OUI 00:1A:2B is assigned to Apple. The remaining 3 octets are assigned by the manufacturer to individual devices, creating a globally unique address.
Can a MAC address be changed or spoofed?: Yes. The MAC address is stored in hardware (burned into the NIC) but can typically be overridden by software. This is called MAC spoofing and is used for privacy, to bypass network access restrictions, and to impersonate other devices. Modern phones use MAC address randomization by default when scanning for Wi-Fi to prevent tracking.
What is MAC address randomization?: MAC address randomization is a privacy feature in modern mobile operating systems (iOS 14+, Android 10+, Windows 10+) that generates a random MAC address when scanning for or connecting to Wi-Fi networks. This prevents location tracking based on MAC addresses by retail analytics systems and public Wi-Fi networks.
What is the difference between unicast and multicast MAC addresses?: The least significant bit of the first octet determines this: if it is 0, the address is unicast (intended for a single device); if it is 1, it is multicast (intended for a group of devices). The broadcast address FF:FF:FF:FF:FF:FF is a special case of multicast sent to all devices on a segment.
What does globally vs locally administered mean?: The second least significant bit of the first octet indicates administration: 0 means globally administered (the OUI was assigned by the IEEE to a manufacturer), 1 means locally administered (the address was set by software rather than burned in by the manufacturer). Randomly generated MAC addresses for testing should use locally administered to avoid conflicts.
Is MAC Address Lookup free?: Yes. OUI vendor lookup uses the free macvendors.com API (1 request per second on the free tier). MAC address generation runs entirely in your browser using the Web Crypto API. No sign-up or account is required.

MAC Address Lookup

About MAC Address Lookup

How to use MAC Address Lookup

Frequently Asked Questions

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