How does a MAC address lookup work?

A MAC address lookup compares the beginning of an address against the address blocks that registration data lists, and returns the organization the matching block is registered to. MACLookup matches the first six hexadecimal digits against MA-L blocks, seven against MA-M blocks and nine against MA-S blocks, because all three sizes exist in the IEEE registry; an address that falls in no listed block returns no vendor.

Why the prefix length changes the answer

IEEE assignments are not all 24 bits. A lookup that only read the first three octets would report the parent block for anything smaller, and the parent is often the IEEE Registration Authority itself, because MA-M and MA-S blocks are carved out of an IEEE-held base. These three records were read from the live lookup:

• MA-L, 24-bit prefix. EC:0D:51 → Apple, Inc., block EC:0D:51:00:00:00–EC:0D:51:FF:FF:FF.
• MA-M, 28-bit prefix. 38:B1:4E:6 → Universal Robots A/S, 1,048,576 addresses. The first three octets alone, 38:B1:4E, resolve to the IEEE Registration Authority instead.
• MA-S, 36-bit prefix. 70:B3:D5:00:1 → SOREDI touch systems GmbH, 4,096 addresses. As with the MA-M case, 70:B3:D5 on its own is an IEEE Registration Authority block.

This is why the same six hexadecimal digits can lead to two different records depending on how many digits you submit.

What the lookup returns

MACLookup answers from the IEEE registration data and the Wireshark manufacturer database, and reports the matched prefix, the registered organization, its registered address and country, the first and last address of the block, the number of addresses, the assignment type and the date the record was last updated. The API documentation lists every field and its meaning; the database used for offline lookups is on the JSON and CSV download pages.

What a lookup cannot answer

The record describes an address block, not a device. It does not contain a model, an owner, a location or a user, and it does not prove that a specific device was present on a network. See Can a MAC address identify a device?

When a lookup returns nothing

No match is a normal result, not an error: the address may be locally administered, randomized, outside every block in the data, or simply not listed. Why does a MAC address lookup return no vendor? covers each case and how to tell them apart.

Run a lookup

Use the MAC address lookup for a single address, or call the REST API with https://api.maclookup.app/v2/macs/<mac>.