A MAC address, the hardware address a device uses on its local network, carries two flag bits and, if it came from a factory, a prefix pointing to the organisation that bought its block: not always the device's maker, and never a person or a place. On 12 October 2026 the IEEE's listings held 58,310 address blocks assigned to organisations, and by our count 18,429 of them (31.6%) are smaller blocks sharing their first three bytes with other holders, so a three-byte lookup can name at most the IEEE; together they cover about 1% of assigned addresses. Android 10 and later use a randomised, locally administered Wi-Fi address by default, and Apple says its devices use a different address for each network by default, a feature requiring iOS 14 or later.
A registry search finds 18 early blocks with the local bit set
A MAC address is 48 bits, written as six octets (bytes) of two hexadecimal digits; the IEEE calls the factory kind an EUI-48. Its guidelines for EUI, OUI and CID, dated 2017, make the lowest bit of the first octet the I/G bit (individual or group) and the next the U/L bit (universal or local). Both sit in the second hex digit, so 2, 6, A or E there marks a unicast address with the local bit set: usually randomised, virtual or chosen by an administrator. The IEEE warns that local addresses "are not globally unique". It recommends all-ones, the broadcast value, as the null for an unknown address, and says the all-zeros value has "not been and will not be used by that assignee as an EUI".
Searching the large-block listing for the local bit, we found 18 rows, matching the tutorial's "approximately 18" identifiers given to early Ethernet implementers before IEEE Std 802.3-1985 was approved; five, AA:00:00 to AA:00:04, belong to Digital Equipment Corporation. All 221 company IDs (CIDs) also have A as their second digit, and a CID "shall not be used to create an EUI-48 or EUI-64". Yet one popular lookup site, checked on 12 October 2026, gives the CID 6A:0E:20 a vendor name, GeoFrenzy, Inc, and a count of about 16 million addresses.
Most names on the large-block list return a single hit
The MA-L listing, the IEEE's large blocks, held 40,319 rows on 12 October 2026. Leave out 438 held by the IEEE Registration Authority and 107 listed as "Private", and 39,774 blocks remain under 20,124 distinct registered names. Of those names, 18,888 (93.9%) hold exactly one block, and together they hold 47.5% of the blocks; the top ten names hold a fifth.
Apple, Inc. leads by registered name with 1,573 blocks, though Huawei's two main entities hold 2,086 between them. A name is the block's buyer, and the IEEE's registration FAQ says parent and subsidiary companies "can and are heavily encouraged to share assignments". "Private" is a paid option: "Select assignments may be kept confidential for an annual fee."
Short-prefix lookups miss the holder of 31.6% of assignee blocks
Since 1 January 2014 the IEEE has also assigned medium (MA-M) and small (MA-S) blocks, the small ones replacing the older IAB, all carved from prefixes the IEEE keeps: the first 24 bits of an MA-M block are "an OUI assigned to IEEE that will not be reassigned".
| Listing | Bits naming the holder | Addresses per block | Blocks, 12 Oct 2026 | "Private" |
|---|---|---|---|---|
| MA-L (large) | 24 | 16,777,216 | 40,319 | 107 |
| MA-M (medium) | 28 | 1,048,576 | 6,628 | 76 |
| MA-S (small) | 36 | 4,096 | 7,226 | 31 |
| IAB (closed 2014) | 36 | 4,096 | 4,575 | 24 |
| CID (company ID) | 24 | None | 221 | 0 |
Every MA-S and IAB block, and all but 128 MA-M blocks, sit under one of those 438 IEEE rows. So the 18,429 smaller blocks, 31.6% of the 58,310, cannot be named from three bytes, yet they cover only about 1% of assigned addresses.
Our MAC address tool reads 24 bits and carries 155 MA-L prefixes. The revision of 12 October 2026 adds the container prefixes, so it says how many bits name the holder, reads a locally administered address as having no registered maker, and refuses a vendor prefix while its "Locally administered" box is ticked. Until 12 October 2026 the tool honoured the prefix: in our test, 500 of 500 addresses generated that way were universal addresses inside Apple's real 00:0A:27 block. It also labelled the IAB prefix 00:50:C2 as an MA-M or MA-S block, and read the broadcast address as locally administered.
Searching the address field brings up Intel's Kulim address behind most rows registered in Malaysia
Reading the place code at the end of each holder's registered address across the 39,774 assignee blocks (98 did not parse), we found 13,165 registered in the US (33.1%) and 9,871 in China (24.8%). Registered addresses in ASEAN member states account for 1,133 (2.85%). Malaysia has 785, and 666 of those are "Intel Corporate", every one at the same address in Kulim, Kedah. Singapore has 213, led by D-Link International with 58.
The field records where a holder registered rather than where devices are made or used. The FAQ says assignments "should not be used on a per-product basis or by manufacturing location", so Malaysia's figure is mostly one company's choice of address.
Android's randomised Wi-Fi addresses draw a blank in the IEEE lists
The Android Open Source Project says that from Android 10 the framework randomises the MAC address by default, setting "the locally administered bit to 1, and the unicast bit to 0" and randomising the other 46 bits; the default address "remains the same until a factory reset" for each network profile. Such an address belongs to no block; by our arithmetic, the 18 early blocks and 221 CIDs cover 239 of 4,194,304 possible local unicast prefixes, about 0.006%.
Apple's support page says that since iOS 18 a device picks Fixed when joining a new network with WPA2 or stronger security, and Rotating, a new private address every 2 weeks, on weak or open ones; it does not say which bits those addresses set. Microsoft's Windows page says "you can turn on random hardware addresses" where the hardware supports it, and states no default.
Experiments at IETF meetings found identifiers sent alongside a fresh address
RFC 9724, published in March 2025, reports that experiments at IETF and IEEE meetings in 2014 and 2015 found "other protocol identifiers (e.g., the DHCP client identifier) can be correlated". That identifier is a value a device sends when asking for an IP address. The RFC also notes that a device shows its MAC address in probe requests, the frames it sends while scanning for networks.
A MAC address has also travelled beyond the local network inside IPv6 addresses, the kind of identifier covered in what an IP address shows. RFC 4291 of 2006 formed the interface identifier, the part of an IPv6 address naming a device's interface, from the hardware address, "inverting the “u” bit". RFC 8064 of February 2017 "recommends against embedding stable link-layer addresses in IPv6 IIDs", and RFC 8981 of February 2021, which obsoletes RFC 4941, sets out temporary addresses.
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