Which company owns MAC address prefix F4:B3:81?

MAC address prefix F4:B3:81 is registered to WindowMaster A/S in the IEEE Organizationally Unique Identifier (OUI) registry. Any device whose MAC address begins with F4:B3:81 has a network interface built by WindowMaster A/S.

What is the OUI F4:B3:81?

F4:B3:81 is an Organizationally Unique Identifier — the first three octets (24 bits) of a MAC address, assigned by the IEEE to WindowMaster A/S. It covers every address from F4:B3:81:00:00:00 to F4:B3:81:FF:FF:FF, or 16,777,216 addresses in total. It is also written F4-B3-81.

How do I find the manufacturer of a MAC address?

Take the first three octets of the address — in F4:B3:81:00:00:00 that is F4:B3:81 — 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 WindowMaster A/S located?

WindowMaster A/S is listed at Skelstedet 13 Vedbaek DK 2950 in the IEEE OUI registry entry for F4:B3:81. This is the address the organization registered with the IEEE, which may differ from its current operating address.

WindowMaster A/S

MAC address prefix F4:B3:81 is registered to WindowMaster A/S in the IEEE OUI registry. Any device whose MAC address begins with F4:B3:81 has a network interface built by WindowMaster A/S. 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 F4:B3:81:00:00:00 to F4:B3:81:FF:FF:FF.

OUI prefix: F4:B3:81
Hyphen form: F4-B3-81
MAC range: F4:B3:81:00:00:00 – F4:B3:81:FF:FF:FF
Addresses in block: 16,777,216
Organization: WindowMaster A/S
Address: Skelstedet 13 Vedbaek DK 2950
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 "WindowMaster A/S"
archived source →
2026-07-17Assigned to "WindowMaster A/S"

Nearby in the registry

The prefixes assigned immediately before and after F4:B3:81:

FAQ

Which company owns MAC address prefix F4:B3:81?: MAC address prefix F4:B3:81 is registered to WindowMaster A/S in the IEEE Organizationally Unique Identifier (OUI) registry. Any device whose MAC address begins with F4:B3:81 has a network interface built by WindowMaster A/S.
What is the OUI F4:B3:81?: F4:B3:81 is an Organizationally Unique Identifier — the first three octets (24 bits) of a MAC address, assigned by the IEEE to WindowMaster A/S. It covers every address from F4:B3:81:00:00:00 to F4:B3:81:FF:FF:FF, or 16,777,216 addresses in total. It is also written F4-B3-81.
How do I find the manufacturer of a MAC address?: Take the first three octets of the address — in F4:B3:81:00:00:00 that is F4:B3:81 — 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 WindowMaster A/S located?: WindowMaster A/S is listed at Skelstedet 13 Vedbaek DK 2950 in the IEEE OUI registry entry for F4:B3:81. This is the address the organization registered with the IEEE, which may differ from its current operating address.