MAC address generator

A MAC address is 48 bits, and the first byte carries two flags that matter. The lowest bit marks multicast — set it and the address is not a host address at all. The next bit up marks locally administered, meaning the address was assigned by whoever runs the network rather than burned in by a manufacturer. Setting it is what makes a generated address safe: the entire locally-administered space is disjoint from every manufacturer allocation, so a collision with real hardware is impossible by construction. A generator that ignores this can hand you an address belonging to a real Cisco or Intel device.

The first three bytes of a manufacturer-assigned address are the OUI, bought from the IEEE, which is how a network scanner names the vendor of a device it finds. A locally-administered address has no OUI and will show as unknown — that is correct, not a fault.

Worth knowing about privacy: phones and laptops now randomise their MAC per network by default, precisely because a fixed one let shops and airports track a device across visits. Those randomised addresses are locally administered too, for the same reason as here.