Generates random MAC addresses using your browser's crypto.getRandomValues (6 random bytes). Pick a separator and case, optionally force the "locally administered & unicast" bit for a safe test address, or choose a real vendor OUI prefix for a more realistic-looking address.
Like IP ranges, the OUI (first 3 bytes) is assigned by the IEEE to real manufacturers. This list is a small representative sample of 20 well-known prefixes and does not replace the full IEEE OUI database (intentionally out of scope).
When enabled, the first octet's two low-order bits are adjusted so the U/L bit (0x02) is set to 1 (locally administered) and the I/G bit (0x01) is set to 0 (unicast). Useful for test/virtual addresses that won't collide with real hardware. This option is automatically disabled when a vendor OUI is selected, since a real OUI is already a universally administered address. Regardless of this option, every generated address is always unicast (I/G bit = 0).
The lowest two bits of a MAC address's first byte carry special meaning: the I/G (Individual/Group) bit is 0 for unicast (a single device) and 1 for multicast. The U/L (Universal/Local) bit is 0 for a globally unique address assigned by the IEEE, and 1 for a locally administered address chosen by an administrator. Virtual machines, containers, and test environments commonly use locally administered unicast addresses (second hex digit of the first octet ending in 2, 6, A, or E) to avoid colliding with real hardware addresses.
A MAC (Media Access Control) address is 48 bits (6 bytes), usually written as six two-digit hex groups separated by colons or hyphens. The first 3 bytes (24 bits) are the OUI (Organizationally Unique Identifier) assigned by the IEEE to a manufacturer; the last 3 bytes are a serial number the manufacturer assigns itself. Cisco equipment conventionally shows addresses as three four-digit groups separated by dots (e.g. aabb.ccdd.eeff).
If the second-lowest bit of the first octet (U/L) is 0, the address is a globally unique one assigned by the IEEE; if 1, it was locally administered β chosen by software or an administrator. If the lowest bit (I/G) is 0, the address is unicast (one specific device); if 1, it's for multicast/broadcast. When assigning a new MAC to a test setup, virtual network interface, or container, using the locally-administered + unicast combination (bits set to 1 and 0 respectively) is the standard practice to avoid colliding with real hardware.
The OUI list offered by this tool is a representative sample of 20 well-known prefixes (Cisco, Apple, VMware, Raspberry Pi, and others) and does not replace the IEEE's full OUI database, which contains tens of thousands of entries. Choosing a vendor prefix only randomizes the last 3 bytes, so the resulting address looks like it belongs to that vendor but was never actually issued by them. Use this for testing, documentation, or teaching purposes only β not to impersonate real network hardware.