How to Use This Tool
Paste an address in any notation. You get every other notation, plus what the two flag bits say about it.
Why there are four formats
They are the same 48 bits with different punctuation, and which one you see depends on who wrote the tool:
- Colons — Linux, macOS, most standards documents and packet captures.
- Hyphens — Windows, and the IEEE's own printed form.
- Dot-separated groups of four — Cisco equipment.
- No separators — logs, config files, anywhere the punctuation was inconvenient.
Case carries no meaning either, though tools disagree on which they prefer. Any comparison between addresses should normalise both before checking, or you get false mismatches on formatting alone.
The two bits worth reading
Bit 0 — unicast or multicast. Set means the frame is for a group rather than one
device. Broadcast, FF:FF:FF:FF:FF:FF, is the extreme case. You will not see a multicast
address as a device's own MAC.
Bit 1 — globally unique or locally administered. Clear means the manufacturer was assigned this range by the IEEE and it should be unique worldwide. Set means someone made it up locally, which is legitimate and increasingly common.
The practical tell: the second hex digit. If it is 2, 6, A or E, the address is locally administered.
Randomised MAC addresses
Phones and laptops now generate a fresh MAC for each network they join, specifically so that a shop or airport cannot track the same device across visits. Those addresses set the locally-administered bit, which has two consequences worth knowing:
- Vendor lookup returns nothing — not a gap in the database, but an address that was never assigned to anyone.
- MAC-based allow-lists stop working, because the device arrives as a different address each time. This surprises a lot of home network setups, and the fix is to turn off randomisation for that specific network on the device.
Which is a reasonable moment to note that MAC filtering was never a security measure. Addresses are sent unencrypted in every frame and can be changed in software in one command, so anyone who can see your network can copy an address off it.
Making up your own
If you need a MAC for a virtual machine or container, set the locally-administered bit and clear the multicast bit — the generator above does this. That guarantees it cannot collide with any hardware address the IEEE has assigned, which is exactly what the bit exists for.
