Random MAC Address Generator
Generate random MAC addresses in colon, hyphen, Cisco dotted or bare notation, in upper or lower case. By default the locally administered bit is set and the multicast bit cleared, which is what distinguishes an address you made up from one a manufacturer was assigned — the distinction most generators ignore. A vendor prefix can be fixed instead, for testing code that looks the manufacturer up. Everything is generated in your browser; nothing is uploaded and no result is recorded anywhere.
How it works
A MAC address has two meaningful bits in its first octet: one marks the address as locally administered rather than assigned to a manufacturer, and one marks it as multicast. Leaving "locally administered" on sets the first and clears the second, which is what a made-up unicast address should look like.
Setting a vendor prefix fixes the first three octets — the OUI — to a specific manufacturer, which is what you want when testing code that looks the vendor up.
Values are generated in your browser and never sent anywhere.
Adjust the settings above and values appear here.
Frequently asked questions
What does "locally administered" mean?
The second-least-significant bit of the first octet marks an address as assigned locally rather than by a manufacturer. Setting it is how you say "I made this up" — without it, a random address may collide with a real one and will look, to any tool that checks, like it belongs to a company that never issued it.
Why does the multicast bit matter?
The least significant bit of the first octet marks an address as multicast. A normal device address is unicast, so that bit must be clear — an unrestricted random address has a one in two chance of being multicast, which would be wrong for almost every use.
What is a vendor prefix or OUI?
The first three octets of a MAC address are the Organisationally Unique Identifier, assigned to a manufacturer. Fixing them makes the generated address look like it came from that manufacturer, which is what you want when testing code that resolves a vendor from an address.
Which format should I use?
Colon-separated lowercase is the common form on Linux and in most documentation. Hyphen-separated uppercase is the Windows convention, and the dotted form with three groups of four is how Cisco equipment displays them.
Can I use these addresses on a real network?
A locally administered address is exactly what is meant for that, but any address must still be unique on its local segment. Two devices sharing one will cause problems that are unpleasant to diagnose.
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