Which company owns MAC address prefix 00:21:81?

MAC address prefix 00:21:81 is registered to Si2 Microsystems Limited in the IEEE Organizationally Unique Identifier (OUI) registry. Any device whose MAC address begins with 00:21:81 has a network interface built by Si2 Microsystems Limited.

What is the OUI 00:21:81?

00:21:81 is an Organizationally Unique Identifier — the first three octets (24 bits) of a MAC address, assigned by the IEEE to Si2 Microsystems Limited. It covers every address from 00:21:81:00:00:00 to 00:21:81:FF:FF:FF, or 16,777,216 addresses in total. It is also written 00-21-81.

How do I find the manufacturer of a MAC address?

Take the first three octets of the address — in 00:21:81:00:00:00 that is 00:21:81 — 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 Si2 Microsystems Limited located?

Si2 Microsystems Limited is listed at No 84, Sy No 150, EPIP, Whitefield Industrial Area Bangalore Karnataka IN 560066 in the IEEE OUI registry entry for 00:21:81. This is the address the organization registered with the IEEE, which may differ from its current operating address.

Si2 Microsystems Limited

MAC address prefix 00:21:81 is registered to Si2 Microsystems Limited in the IEEE OUI registry. Any device whose MAC address begins with 00:21:81 has a network interface built by Si2 Microsystems Limited. 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 00:21:81:00:00:00 to 00:21:81:FF:FF:FF.

OUI prefix: 00:21:81
Hyphen form: 00-21-81
MAC range: 00:21:81:00:00:00 – 00:21:81:FF:FF:FF
Addresses in block: 16,777,216
Organization: Si2 Microsystems Limited
Address: No 84, Sy No 150, EPIP, Whitefield Industrial Area Bangalore Karnataka IN 560066
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 "Si2 Microsystems Limited"
archived source →
2026-07-17Assigned to "Si2 Microsystems Limited"

Nearby in the registry

The prefixes assigned immediately before and after 00:21:81:

FAQ

Which company owns MAC address prefix 00:21:81?: MAC address prefix 00:21:81 is registered to Si2 Microsystems Limited in the IEEE Organizationally Unique Identifier (OUI) registry. Any device whose MAC address begins with 00:21:81 has a network interface built by Si2 Microsystems Limited.
What is the OUI 00:21:81?: 00:21:81 is an Organizationally Unique Identifier — the first three octets (24 bits) of a MAC address, assigned by the IEEE to Si2 Microsystems Limited. It covers every address from 00:21:81:00:00:00 to 00:21:81:FF:FF:FF, or 16,777,216 addresses in total. It is also written 00-21-81.
How do I find the manufacturer of a MAC address?: Take the first three octets of the address — in 00:21:81:00:00:00 that is 00:21:81 — 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 Si2 Microsystems Limited located?: Si2 Microsystems Limited is listed at No 84, Sy No 150, EPIP, Whitefield Industrial Area Bangalore Karnataka IN 560066 in the IEEE OUI registry entry for 00:21:81. This is the address the organization registered with the IEEE, which may differ from its current operating address.