Which company owns MAC address prefix A4:B1:21?

MAC address prefix A4:B1:21 is registered to Arantia 2010 S.L. in the IEEE Organizationally Unique Identifier (OUI) registry. Any device whose MAC address begins with A4:B1:21 has a network interface built by Arantia 2010 S.L..

What is the OUI A4:B1:21?

A4:B1:21 is an Organizationally Unique Identifier — the first three octets (24 bits) of a MAC address, assigned by the IEEE to Arantia 2010 S.L.. It covers every address from A4:B1:21:00:00:00 to A4:B1:21:FF:FF:FF, or 16,777,216 addresses in total. It is also written A4-B1-21.

How do I find the manufacturer of a MAC address?

Take the first three octets of the address — in A4:B1:21:00:00:00 that is A4:B1:21 — and look that prefix up in the IEEE OUI registry. If the second-lowest bit of the first octet is set, the address is locally administered (a randomized or private MAC), which belongs to no manufacturer and will not resolve; modern phones and laptops use these by default on each network.

Where is Arantia 2010 S.L. located?

Arantia 2010 S.L. is listed at Volta do Castro s/n Santiago de Compostela A Coruña ES 15706 in the IEEE OUI registry entry for A4:B1:21. This is the address the organization registered with the IEEE, which may differ from its current operating address.

Arantia 2010 S.L.

MAC address prefix A4:B1:21 is registered to Arantia 2010 S.L. in the IEEE OUI registry. Any device whose MAC address begins with A4:B1:21 has a network interface built by Arantia 2010 S.L.. This prefix (the OUI, or Organizationally Unique Identifier) is assigned by the IEEE and is the first three octets of the address — it covers every MAC from A4:B1:21:00:00:00 to A4:B1:21:FF:FF:FF.

OUI prefix: A4:B1:21
Hyphen form: A4-B1-21
MAC range: A4:B1:21:00:00:00 – A4:B1:21:FF:FF:FF
Addresses in block: 16,777,216
Organization: Arantia 2010 S.L.
Address: Volta do Castro s/n Santiago de Compostela A Coruña ES 15706
Source: IEEE OUI registry

Have a full MAC address? Look it up— we'll also tell you if it's a randomized (private) address rather than a real manufacturer prefix.

Assignment history (2)

The IEEE registry publishes current state only — this is the change record we've kept since we started tracking it daily.

2016-07-29Assigned to "Arantia 2010 S.L."
archived source →
2026-07-17Assigned to "Arantia 2010 S.L."

Nearby in the registry

The prefixes assigned immediately before and after A4:B1:21:

FAQ

Which company owns MAC address prefix A4:B1:21?: MAC address prefix A4:B1:21 is registered to Arantia 2010 S.L. in the IEEE Organizationally Unique Identifier (OUI) registry. Any device whose MAC address begins with A4:B1:21 has a network interface built by Arantia 2010 S.L..
What is the OUI A4:B1:21?: A4:B1:21 is an Organizationally Unique Identifier — the first three octets (24 bits) of a MAC address, assigned by the IEEE to Arantia 2010 S.L.. It covers every address from A4:B1:21:00:00:00 to A4:B1:21:FF:FF:FF, or 16,777,216 addresses in total. It is also written A4-B1-21.
How do I find the manufacturer of a MAC address?: Take the first three octets of the address — in A4:B1:21:00:00:00 that is A4:B1:21 — and look that prefix up in the IEEE OUI registry. If the second-lowest bit of the first octet is set, the address is locally administered (a randomized or private MAC), which belongs to no manufacturer and will not resolve; modern phones and laptops use these by default on each network.
Where is Arantia 2010 S.L. located?: Arantia 2010 S.L. is listed at Volta do Castro s/n Santiago de Compostela A Coruña ES 15706 in the IEEE OUI registry entry for A4:B1:21. This is the address the organization registered with the IEEE, which may differ from its current operating address.