MAC Address Tool

A MAC address (Media Access Control address) is a 48-bit unique identifier burned into the hardware of every Ethernet, Wi-Fi, and Bluetooth interface ever shipped. Written as six pairs of hex digits (e.g. 00:1A:11:23:45:67), the first three bytes are the Organisationally Unique Identifier (OUI) — assigned to the device manufacturer by the IEEE Registration Authority — and the last three bytes are the device serial number within that vendor's allocation. The combination gives every network interface in the world a globally-unique address.

OUI registration — how vendors get their prefix

Companies that build network hardware register OUIs with the IEEE. A standard OUI (MA-L, "Medium Allocation - Large") gives the registrant 24 bits of unique-device space — about 16.7 million MAC addresses. The current registration fee is roughly USD 3,495 for an MA-L (as of 2024); cheaper MA-M (4,096 addresses) and MA-S (4,096 addresses) options also exist for smaller vendors. The IEEE publishes the complete registry as a public CSV — about 50,000 entries totalling ~10MB. Apple alone holds over 600 OUI ranges; Cisco holds nearly 1,000. New vendor allocations are processed monthly.

The two flag bits — universal versus local, unicast versus multicast

The first byte of every MAC carries two flag bits with significant operational meaning. Bit 0 (LSB) distinguishes unicast (sent to one specific device) from multicast (sent to a group); when set, the MAC is multicast. Bit 1 distinguishes universally-administered (assigned by IEEE via OUI) from locally-administered (assigned by an OS, hypervisor, or admin); when set, the MAC is locally administered. For test labs and virtual machines, generating MACs with the locally-administered bit set is best practice — it guarantees you won't collide with any real-world hardware MAC, no matter how the IEEE expands the OUI registry in the future. The tool above defaults to locally-administered for exactly this reason.

MAC randomisation — privacy at the cost of analytics

Since iOS 14 (2020), Android 10 (2019), and Windows 10 (2017), every modern phone and many laptops randomise their MAC address when scanning for Wi-Fi networks they aren't already associated with. The behaviour matters for retail analytics (counting unique visitors via Wi-Fi probe requests), enterprise NAC (MAC-based access control), and ISP-issued home routers that use captive portals. Each platform's randomisation rules differ: iOS uses a fresh random MAC every 24 hours per network; Android uses the same MAC per saved network but a different one per network; Windows can be configured either way. The presence of 02:, 06:, 0A:, or 0E: as the first byte (locally-administered bits set) is a strong signal of MAC randomisation.

MAC versus IP — what each one actually identifies

The classic exam-question distinction: a MAC address identifies a network interface (Layer 2 of the OSI model); an IP address identifies a host on a network (Layer 3). MACs are used for delivery within a single broadcast domain (your local switch, your home Wi-Fi); IPs are used for routing across networks. Every packet has both — the IP doesn't change as it traverses the internet, but the source and destination MAC are rewritten at every hop. This is why ARP (Address Resolution Protocol) exists: to map a destination IP within your subnet to the corresponding MAC for the next-hop delivery. Most users will never see a MAC address consciously, but every byte of internet traffic depends on the layered MAC/IP cooperation working correctly.