MAC Address Formatter
Normalise MAC addresses in bulk to colon, hyphen, Cisco dot or plain style and read the bits: OUI, multicast, locally administered, EUI-64 and IPv6 link-local.
Every line re-formatted, with its OUI and NIC parts, I/G and U/L flags, broadcast detection, the modified EUI-64 and fe80:: link-local address, duplicates across styles and invalid lines called out.
Example: 001a.2b3c.4d5e becomes 00:1a:2b:3c:4d:5e with OUI 00:1a:2b, EUI-64 02:1a:2b:ff:fe:3c:4d:5e and link-local fe80::21a:2bff:fe3c:4d5e; 02-00-00-00-00-01 is locally administered.
Six bytes,
read bit by bit.
The styles, the flag bits and the EUI-64 derivation — and why the vendor name is not looked up.
Styles
A MAC is six bytes; the page accepts them with colons, hyphens, Cisco dots, spaces or as plain hex (and an optional 0x), rejects anything else or any other length, and re-emits every line in the style and case you choose. Eight-byte EUI-64 values are formatted too. Duplicates are found across styles.
The bits
In the first byte, the least significant bit is I/G: 0 for an individual (unicast) address, 1 for a group (multicast); the next bit is U/L: 0 for a universally administered address burned in by the maker, 1 for a locally administered one — randomised Wi-Fi MACs, virtual machines, containers. The first three bytes are the OUI, the registrant’s block; ff:ff:ff:ff:ff:ff is broadcast.
EUI-64 and link-local
RFC 4291 derives an interface identifier by inserting ff:fe between the two halves and flipping the U/L bit; fe80:: followed by it is the classic IPv6 link-local address, written in RFC 5952 form. Most modern stacks use privacy or stable-random identifiers instead, so it is a derivation, not necessarily the address in use. The vendor behind an OUI is an IEEE registry lookup and is not embedded. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- IEEE 802 EUI-48: I/G bit (multicast) and U/L bit (locally administered) in the first octet, OUI = first three octets — vendor names are a registry lookup and are not embedded
- RFC 4291 Appendix A modified EUI-64 (ff:fe insertion, U/L flip) and RFC 5952 IPv6 text form
Last reviewed 21 September 2026. How results are checked: How we verify.