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To identify the organization associated with a switch’s MAC address, look up its applicable prefix in the IEEE Registration Authority’s assignment listings. A match can point to the organization registered for that address block, but it cannot establish a switch model or prove the address belongs to a switch. Check the address’s administration bit and block size before drawing conclusions.
What a MAC prefix lookup can—and cannot—tell you
An OUI is a 24-bit identifier assigned to an organization. In a conventional OUI-based EUI-48 address, it forms the first three octets; the remaining bits identify an address within the block. IEEE describes an OUI as “a 24-bit globally unique assigned number referenced by various standards.”
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The registry identifies the organization associated with an assigned block. That organization may not be the device’s retail brand, and the entry is not a model number. A prefix match also does not prove that the observed interface is a switch. To establish the device role, check network inventory or management records.
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- Get the interface’s actual MAC address. Confirm that you have the address for the interface you want to identify, rather than an address for another port or a neighboring device.
- Normalize its notation. Separate the address into six hexadecimal octets consistently—for example,
AA:BB:CC:DD:EE:FF. - Check the applicable IEEE assignment. For an OUI-based address, start with the first 24 bits (the first three octets), then search the IEEE Registration Authority listings. Use the matching entry for the full applicable block if the registry offers a more specific match.
- Check whether the address is locally administered. In the first octet, the U/L bit is the second least significant bit. If it is set, the address is locally administered; its prefix may not identify the hardware manufacturer’s globally assigned block.
- Verify the device separately. Use device inventory or network management evidence to confirm that the endpoint is a switch and identify its model or location.
Why a three-octet match may be too broad
IEEE assigns blocks of different sizes. MA-L includes a 24-bit OUI, while MA-M and MA-S assignments use more specific block prefixes. Searching only the first three octets can miss a more specific assignment or return a result that is too broad. Match the full applicable block in the registry rather than treating every first-three-octet match as definitive.
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| IEEE assignment | Block capacity | What to keep in mind |
|---|---|---|
| MA-L | 224 EUI-48 identifiers (16,777,216) | Includes a 24-bit OUI. |
| MA-M | 220 EUI-48 identifiers (1,048,576) | A 24-bit-only lookup can be too coarse. |
| MA-S | 212 EUI-48 identifiers (4,096) | A 24-bit-only lookup can be too coarse. |
These are IEEE block capacities, not counts of switch manufacturers or measures of lookup accuracy. IEEE’s cited guidance does not state a publication year for these figures.
How local or generated MAC addresses change the result
The first octet contains the U/L bit, which distinguishes universal from local administration. IEEE says a universally administered address is intended to be globally unique. When the U/L bit is set, software or network policy may have chosen the address instead of using a globally assigned hardware prefix. Randomized or generated addresses can also change over time, so a registry match may not expose the device manufacturer’s assignment.
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The IETF notes that per-vendor OUI selection is the historical default for MAC address selection. That does not mean every address currently observed uses a vendor-assigned prefix; check the U/L bit and address context before interpreting the lookup.
Keep IANA allocations separate from IEEE assignments
IANA’s OUI Ethernet Numbers registry is a separate reference. It lists IANA allocations under 00-00-5E, which are specified separately from IEEE Registration Authority assignments. The IANA page was last updated on 2026-08-18. Use the relevant registry for the kind of allocation you are checking; do not treat an IANA allocation as an IEEE vendor assignment.
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What to do when the lookup does not identify the switch
- No confident organization match: Check whether a more specific MA-M or MA-S block applies instead of relying only on the first three octets.
- The U/L bit is set: Treat the address as locally administered; the prefix may not indicate the hardware manufacturer.
- The organization is unfamiliar or differs from the product brand: The registry names the organization associated with the block, not necessarily the retail brand or manufacturer you expected.
- You need the model, role, firmware, configuration, or physical location: A prefix lookup cannot supply those details. Confirm them in device inventory or network management records.
IEEE’s public listing page provides downloadable MA-L, MA-M, MA-S, IAB, and CID datasets. Registry entries can change, so check the live listing when identifying a real device.
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