Which company owns MAC address prefix A4:51:5E?

MAC address prefix A4:51:5E is registered to Juniper Networks in the IEEE Organizationally Unique Identifier (OUI) registry. Any device whose MAC address begins with A4:51:5E has a network interface built by Juniper Networks.

What is the OUI A4:51:5E?

A4:51:5E is an Organizationally Unique Identifier — the first three octets (24 bits) of a MAC address, assigned by the IEEE to Juniper Networks. It covers every address from A4:51:5E:00:00:00 to A4:51:5E:FF:FF:FF, or 16,777,216 addresses in total. It is also written A4-51-5E.

How do I find the manufacturer of a MAC address?

Take the first three octets of the address — in A4:51:5E:00:00:00 that is A4:51:5E — 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 Juniper Networks located?

Juniper Networks is listed at 1133 Innovation Way Sunnyvale CA US 94089 in the IEEE OUI registry entry for A4:51:5E. This is the address the organization registered with the IEEE, which may differ from its current operating address.

How many MAC prefixes does Juniper Networks own?

Juniper Networks holds 211 OUI prefixes in the IEEE registry, of which A4:51:5E is one. A device made by Juniper Networks could carry a MAC address from any of them.

Juniper Networks

MAC address prefix A4:51:5E is registered to Juniper Networks in the IEEE OUI registry. Any device whose MAC address begins with A4:51:5E has a network interface built by Juniper Networks. 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 A4:51:5E:00:00:00 to A4:51:5E:FF:FF:FF.

OUI prefix: A4:51:5E
Hyphen form: A4-51-5E
MAC range: A4:51:5E:00:00:00 – A4:51:5E:FF:FF:FF
Addresses in block: 16,777,216
Organization: Juniper Networks
Address: 1133 Innovation Way Sunnyvale CA US 94089
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.

Other prefixes from Juniper Networks

Juniper Networks holds 211 OUI prefixes in total. A device with this exact prefix could just as well carry any of these:

Assignment history (2)

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

2022-07-11Assigned to "Juniper Networks"
archived source →
2026-07-17Assigned to "Juniper Networks"

Nearby in the registry

The prefixes assigned immediately before and after A4:51:5E:

FAQ

Which company owns MAC address prefix A4:51:5E?: MAC address prefix A4:51:5E is registered to Juniper Networks in the IEEE Organizationally Unique Identifier (OUI) registry. Any device whose MAC address begins with A4:51:5E has a network interface built by Juniper Networks.
What is the OUI A4:51:5E?: A4:51:5E is an Organizationally Unique Identifier — the first three octets (24 bits) of a MAC address, assigned by the IEEE to Juniper Networks. It covers every address from A4:51:5E:00:00:00 to A4:51:5E:FF:FF:FF, or 16,777,216 addresses in total. It is also written A4-51-5E.
How do I find the manufacturer of a MAC address?: Take the first three octets of the address — in A4:51:5E:00:00:00 that is A4:51:5E — 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 Juniper Networks located?: Juniper Networks is listed at 1133 Innovation Way Sunnyvale CA US 94089 in the IEEE OUI registry entry for A4:51:5E. This is the address the organization registered with the IEEE, which may differ from its current operating address.
How many MAC prefixes does Juniper Networks own?: Juniper Networks holds 211 OUI prefixes in the IEEE registry, of which A4:51:5E is one. A device made by Juniper Networks could carry a MAC address from any of them.