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FREE TOOL
Enter a MAC address in any common form to see it written every standard way, find out whether it is an individual or a group address and whether its universal/local bit marks it as universally or locally administered, and look up which organization registered its prefix with the IEEE. The page does the work in your browser and does not send the address to a server. No account is required.
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The tool is ready. It runs in this page, and the page does not send what you enter to a server.
RouteSwitchU has asked the IEEE for permission to include its registry data in this page. Until that permission is in place, the page formats the address and reads its bits, and the lookup itself is done on the IEEE site.
Search the IEEE Registration Authority public listing
Registry data: the IEEE Registration Authority public listings for MA-L, MA-M, MA-S, and IAB, fetched 2026-10-14 at 12:12 UTC. IEEE updates the listings every day, so a block assigned after that date is missing here. The lookup runs in this page against a copy of that data loaded from this site, and the address you enter is not sent anywhere. "Private" means a block is registered but its owner chose not to publish a name. A match on a locally administered or group address does not say who made the hardware. RouteSwitchU is not affiliated with the IEEE, and the IEEE does not endorse this tool.
Each step shows the bits in binary, eight to a group, next to the same value in hexadecimal. Where a step uses only the first part of the address, those bits are shown in bold.
A MAC address is 48 bits, usually written as 12 hexadecimal digits. Linux and most documentation separate the six octets with colons, Windows and the IEEE's own text listing use hyphens and capital letters, and Cisco IOS writes three groups of four digits separated by dots. All of them hold the same 48 bits, so the tool removes the separators, checks that exactly 12 hex digits remain, and writes each form back out. A group with a single digit, as the macOS arp command prints 0:1b:63:84:45:e6, is read with a leading zero.
Two bits of the first octet change what the address means. The lowest bit is the individual/group (I/G) bit. When it is 0 the address belongs to one interface, and when it is 1 the address names a group, which is a multicast address or the broadcast address. The broadcast address has all 48 bits set to 1, written FF-FF-FF-FF-FF-FF.
The next bit up is the universal/local (U/L) bit. A 0 marks the address as universally administered. By convention, such an address begins with a prefix the IEEE assigns to an organization, and that organization controls the addresses under it. A 1 marks the address as locally administered, which by convention places it in the local address space, under the control of the local network administrator. The bit records only which space the address is marked as belonging to. It does not show how a given address was actually assigned, or whether its prefix is registered. For a local address, the two bits above that divide the local space into four quadrants under the optional IEEE Structured Local Address Plan (SLAP). The tool reports the quadrant, but nothing in the address says whether a network uses SLAP.
To practice, take the first octet of 01:00:5e:90:10:00 and write it in binary before you look it up. Decide from the last two bits whether it is individual or group and universal or local, then check your answer against the steps.
The IEEE assigns blocks of addresses in three sizes. An MA-L block has a 24-bit prefix, the older organizationally unique identifier (OUI). An MA-M block has a 28-bit prefix, and an MA-S block has a 36-bit prefix. The IEEE carves the MA-M and MA-S blocks, and the older 36-bit IAB blocks, out of 24-bit blocks registered to the IEEE Registration Authority itself. So the tool tries the first 36 bits, then 28, then 24, and reports the longest prefix that is listed, along with the registry it came from. Reading only the first 24 bits would report "IEEE Registration Authority" for thousands of addresses that belong to a smaller block.
A few early blocks break the usual pattern. About 18 prefixes assigned to early Ethernet makers, such as 02-60-8C (3COM) and AA-00-00 (Digital Equipment Corporation), have the universal/local bit set to 1. The tool looks up the address as written, so these still match, and it reports the local bit beside the match. For a group address with no match, it tries again with the group bit cleared, because a block's holder forms its group addresses that way, and it says when it did. Some prefixes list more than one organization, such as 08-00-30, and the tool shows every name.
A match says which organization registered the block. It does not prove who built the device. Companies are renamed and bought, and any interface can be set to use another address.
The data is a trimmed copy of the four public CSV listings the IEEE Registration Authority publishes for MA-L, MA-M, MA-S, and IAB, fetched 2026-10-14 at 12:12 UTC. It keeps each prefix and organization name and drops the street addresses. The page loads it from this site the first time you look up an address, not when the page opens. A refresh script downloads the listings again, records each file's source URL, fetch time, and SHA-256 hash, and stops without writing anything if a file's header changes or a registry suddenly has fewer entries.
The lookup knows only the blocks that were listed when the data was fetched, so a newly assigned prefix shows as unknown until the data is refreshed. It does not look up company IDs (CIDs), which the IEEE does not allow as the start of a universally administered address, and it reads 48-bit addresses only, not 64-bit EUI-64 identifiers. It cannot tell a manufacturer's address from one an administrator copied onto another device.
Sources: RFC 9542, IANA considerations and IETF use of IEEE 802 parameters, sections 2.1 to 2.3, for the address layout, the special bits, SLAP, company IDs, and the documentation and multicast blocks; RFC 894, IP over Ethernet, for the broadcast address; RFC 4291, IPv6 Addressing Architecture, Appendix A, for Modified EUI-64; the IEEE Registration Authority's Guidelines for Use of EUI, OUI, and CID, for the block sizes, the longest-prefix rule, and the early blocks; and the IEEE Registration Authority public listing.