Generate random MAC addresses with selectable format, count, unicast/multicast and locally-administered flags.
Random MACs on demand. Produce one or many MAC addresses in colon, hyphen, space or Cisco dot notation, with control over the unicast/multicast and locally-administered bits. Uses crypto randomness, runs in your browser.
A MAC address is 48 bits, normally written as six hex bytes. The first three bytes are the Organisationally Unique Identifier, a block the IEEE sells to hardware vendors; the last three are assigned by that vendor to individual devices. This is why a MAC can usually be traced to a manufacturer — the OUI is a public registry, and lookup tools simply match the first three bytes against it.
Notation varies by ecosystem rather than by meaning. Colons (00:1a:2b:3c:4d:5e) are the Unix and IEEE convention, hyphens (00-1A-2B-3C-4D-5E) are what Windows shows, and Cisco writes three dot-separated groups of four hex digits (001a.2b3c.4d5e). All three encode the same 48 bits.
The two lowest bits of the first byte are not part of the identifier at all. Bit 0 distinguishes unicast from multicast: 0 means the frame is for one interface, 1 means a group. That is why 01:00:5e:... is the IPv4 multicast prefix and ff:ff:ff:ff:ff:ff is broadcast — the bit is set.
Bit 1 is the local/global flag. Cleared, it says the address comes from an IEEE-assigned OUI. Set, it says the address was assigned locally and carries no vendor meaning. Any address you generate yourself should have this bit set, which is why the generated bytes here always land on the second hex digit values 2, 6, A or E. Skipping this step is how test fixtures end up colliding with a real vendor's range.
Because a MAC is broadcast in the clear by every Wi-Fi probe request, it became a convenient handle for tracking people across venues. Modern phones and laptops now present a different locally-administered MAC to each network by default, and rotate it periodically. This breaks passive tracking, but it also breaks anything that assumed a MAC was a stable device identifier: MAC-based allowlists, DHCP reservations and captive-portal sessions all need rethinking on networks with modern clients.
Generated addresses like these are useful for lab topologies, virtual machine templates, test fixtures and documentation, where you want plausible-looking addresses that are guaranteed not to belong to real hardware.