About the MAC Address Generator & Formatter
This MAC address generator creates random 48-bit Ethernet (EUI-48) addresses for virtual machines, containers, test networks and lab equipment. By default it produces locally administered unicast addresses — the second hex digit is 2, 6, A or E — which are reserved for exactly this purpose and can never clash with a manufacturer-assigned address. You can also keep a vendor prefix (OUI) of your choice and randomise only the last three bytes.
The formatter half converts any MAC address between the notations different systems expect: colon-separated (Linux, macOS), hyphen-separated (Windows), Cisco dotted (aaaa.bbbb.cccc) or bare hex, in upper or lower case. It also tells you whether an address is unicast or multicast, universally or locally administered, and shows the IPv6 link-local address derived from it with the modified EUI-64 method.
Randomness comes from the browser's cryptographic generator and nothing leaves your device. Add a seed if you want the same list every time for repeatable test fixtures.
How to use the mac address generator & formatter
- 1Choose how many addresses you need and the address type (locally administered is safest).
- 2Optionally enter a vendor prefix to keep the first three bytes fixed.
- 3Pick the separator style and case your system expects.
- 4Copy the list, or paste an existing MAC in the reformat box to convert and inspect it.
Formula and method
A MAC address is 48 bits written as six bytes. The first three bytes are the organisationally unique identifier (OUI) the IEEE assigns to a manufacturer, and the last three identify the device. Two bits of the first byte carry flags: the least significant bit (I/G) is 0 for unicast and 1 for multicast, and the next bit (U/L) is 0 for universally administered (factory) addresses and 1 for locally administered ones.
The generator fills all 48 bits with random data and then forces those two flag bits to match the type you picked, so a locally administered unicast address always has a first byte ending in binary 10 (second hex digit 2, 6, A or E). For IPv6, the modified EUI-64 interface identifier inserts FF:FE in the middle of the MAC and flips the U/L bit, giving the fe80:: link-local address shown.
- I/G
- Individual/Group bit — unicast (0) or multicast (1)
- U/L
- Universal/Local bit — vendor-assigned (0) or locally administered (1)
- OUI
- First 24 bits: the manufacturer prefix
Worked examples
Five random MACs for virtual machines
Five locally administered unicast addresses are produced in colon format. Each has 12 hex digits plus 5 colons = 17 characters, and the second digit is always 2, 6, A or E.
Twenty addresses in Cisco dot notation
Cisco IOS writes MACs as three groups of four lowercase hex digits, e.g. 021a.2b3c.4d5e — 12 digits plus 2 dots = 14 characters each.
Reformat and inspect a Windows-style MAC
The hyphens become colons. First byte 0x00 has both flag bits clear, so it is a factory-assigned unicast address with OUI 00:1A:2B. For the IPv6 link-local address, FF:FE is inserted in the middle and the U/L bit is flipped (00 → 02), giving fe80::21a:2bff:fe3c:4d5e.
Spot a locally administered address
First byte 0x3A is 0011 1010 in binary: bit 0 is 0 (unicast) and bit 1 is 1 (locally administered). Phones use addresses like this for Wi-Fi MAC randomisation.
Frequently asked questions
What is a locally administered MAC address?+
It is an address with the U/L bit (second-lowest bit of the first byte) set to 1, so the second hex digit is 2, 6, A or E. These are assigned by software or administrators rather than the IEEE, which is why they are the right choice for virtual machines and random MACs.
Can I use a random MAC address on my network?+
Yes, as long as it is unicast and unique on that local network. Use a locally administered address so it cannot collide with a real device; many operating systems already randomise Wi-Fi MACs this way for privacy.
What are the different MAC address formats?+
The same address can be written 00:1A:2B:3C:4D:5E (Linux and macOS), 00-1A-2B-3C-4D-5E (Windows), 001a.2b3c.4d5e (Cisco) or 001A2B3C4D5E. They are equivalent; case does not matter.
How do I find the manufacturer from a MAC address?+
Take the first three bytes — the OUI — and look them up in the IEEE public registry. Locally administered and randomised addresses have no registered manufacturer.
How is an IPv6 link-local address made from a MAC?+
With modified EUI-64: split the MAC in half, insert FF:FE in the middle, flip the second-lowest bit of the first byte, and prefix fe80::. Many modern systems use random interface IDs instead for privacy.