MAC Address Formatter & Generator
Convert a MAC address between every vendor notation, decode its address bits, and generate valid locally administered addresses.
Result
Decoded
- OUI (first 24 bits)
- 00:1B:44
- Device identifier
- 11:3A:B7
- I/G bit (bit 0 of byte 0)
- 0 - individual address
- U/L bit (bit 1 of byte 0)
- 0 - universally administered
- IPv6 link-local (EUI-64)
- fe80::21b:44ff:fe11:3ab7
- Integer value
- 117106096823
About MAC Address Formatter & Generator
Four vendors, four notations, one 48-bit address. This converts between all of them and decodes the two bits in the first byte that determine whether an address is unicast or multicast, and globally unique or locally assigned.
MAC randomisation and what it broke
iOS, Android, Windows and macOS now present a randomised, locally administered MAC per network by default. That ends MAC-based device identification for guest tracking, and it breaks any access control built on a MAC allow-list — the device presents a different address on each network, and sometimes after each rejoin. Use 802.1X with certificates or credentials for authentication, and treat MAB as the fallback for printers and cameras that cannot do better.
The two bits that matter
Bit 0 of the first byte is I/G: set means a group (multicast) address. Bit 1 is U/L: set means locally administered. So 02:... is a valid locally administered unicast address, while 01:... is multicast and will never appear as a source address. A source MAC with the I/G bit set in a capture indicates a malformed or spoofed frame.
Common use cases
- Converting a MAC between a Cisco MAC table and a Linux ARP table.
- Assigning a locally administered address to a virtual interface or bond.
- Checking whether an address in a log is randomised device privacy addressing.
Edge cases and gotchas
- Modern phones randomise their MAC per network - MAC-based access control and per-device tracking no longer work reliably.
- Do not invent MACs from a manufacturer OUI; use the locally administered range.