What does "Private" mean in a MAC lookup?

In a MAC lookup, Private means the address belongs to a genuinely registered block whose registrant asked the IEEE Registration Authority to keep its details out of the public listings. The assignment exists and the block is real; what the registry publishes in place of the company name and address is the word PRIVATE. A Private result is therefore a match with the registrant withheld, not a missing record and not a randomized address.

Why a registration is private

The IEEE Registration Authority states that select assignments may be kept confidential for an annual fee, and that the difference between a public and a private assignment is the format of the listing: a public entry carries the company name and address, while a private one shows PRIVATE in their place. Private registrants are invoiced annually to keep that listing confidential. The block itself is assigned in the ordinary way — nothing about the addresses changes.

How it differs from a randomized address

The two look similar in a lookup because both hide the organization's name, but they are opposite cases:

• A private registration is assigned by the IEEE from its registry, so the address is universally administered: the local bit is 0 and the second hexadecimal digit of the first octet is not 2, 6, A or E. There is one organization behind it, and the block is unique to that organization.
• A randomized address is not registered with anyone. IEEE assignments are made with the local bit clear, so a locally generated address is recognisable by that bit, and randomization sets it. No organization is behind it at all.

So a Private result confirms that the address is a registered assignment; a no-vendor result on a locally administered address confirms the opposite.

What the lookup shows

MACLookup reports a private registration with isPrivate=true, and the company-name endpoint returns *PRIVATE* instead of a name. The other fields of the record — the matched prefix, the first and last address of the block, its size, the assignment type and the record's last update — are returned normally. The API documentation lists the full field set.

What Private does not mean

• It does not mean the device is hiding. The listing is confidential; the hardware behaves like any other registered address, and on a network it is visible in the ordinary way.
• It is not evidence of anything improper. Keeping a registration out of a public listing is a paid option the IEEE Registration Authority offers.
• It does not identify a device. The organization is withheld, so the result tells you less than a public record does, not more.

Check an address

Look up a prefix in the MAC address lookup; a Private result appears in the same place as any other registrant. Related guides: what an OUI is, why a lookup returns no vendor and what a lookup can identify.