MAC Address Generator

Features

• Unicast, multicast and broadcast
• Fix a vendor prefix (OUI); accepts `00:1A:2B`, `00-1a-2b`, `001a2b` and more
• Errors when the OUI contradicts the type or the local bit instead of silently ignoring a choice
• Optional locally-administered bit (usually wanted for fake MACs)
• Four formats: colon, hyphen, no separator, Cisco dotted
• Uppercase or lowercase, up to 100 at a time
• No network access, no vendor database

How to use

1. Pick a type and a format
2. Fill in an OUI (first three octets) if you want a fixed prefix
3. Click “Generate again” for a fresh batch
4. Copy the result

FAQ

Why does supplying an OUI give me an error about the “lowest bit”?

Because the lowest bit of the first octet is the unicast/multicast flag, and your OUI has already fixed it. For example `00:1A:2B` starts with `00`, whose lowest bit is 0 — it can only be a unicast address. Selecting “multicast” at the same time cannot be satisfied. This errors rather than picking one silently, because the silent path would leave you believing your choice took effect. For a test-data prefix like `DE:AD:BE`, watch the second-lowest bit: `DE` is `11011110`, so that bit is 1 — it is a locally administered address, and the box must be checked.

What does “locally administered” mean? Should I check it?

The second-lowest bit of a MAC distinguishes two origins: 0 = vendor-assigned (the OUI comes from IEEE and is globally unique), 1 = locally administered (made up by an administrator; no registration needed, but no uniqueness guarantee). For test and fake data you usually do check it — the address then sits explicitly in the “made up locally” half of the space and cannot collide with any real vendor prefix. But if your OUI is a real vendor prefix (say `00:1A:2B`), you must not check it, because that prefix’s second-lowest bit is 0 to begin with. Checking it produces the error for exactly that reason.

Can I assign a generated MAC to a device?

Not on a device in a managed network. This tool generates random addresses and consults no allocation table, so it cannot guarantee uniqueness within your subnet — colliding with an existing MAC causes intermittent network faults (packet loss, disconnects, switch MAC table flapping) that are very hard to trace, because each device looks fine on its own. For an address that genuinely will not collide, use the NIC’s own randomization feature or ask your administrator. This tool is for test data, documentation examples and forms that merely require a MAC-shaped value.