| Hex | Binary (first 2 bits) | Valid? | Notes | |------|----------------------|--------|-------| | 0x0? | 00 | No | Globally unique, not locally administered | | 0x1? | 01 | No | Multicast + global | | 0x2? | 10 | | ✅ Locally administered, unicast | | 0x3? | 11 | No | Multicast + local | | 0x4? | 00 | No | Global | | 0x5? | 01 | No | Multicast + global | | 0x6? | 10 | Yes | ✅ Locally administered, unicast | | 0x7? | 11 | No | Multicast + local | | 0x8? | 00 | No | Global | | 0x9? | 01 | No | Multicast + global | | 0xA? | 10 | Yes | ✅ Locally administered, unicast | | 0xB? | 11 | No | Multicast + local | | 0xC? | 00 | No | Global | | 0xD? | 01 | No | Multicast + global | | 0xE? | 10 | Yes | ✅ Locally administered, unicast | | 0xF? | 11 | No | Multicast + local |
When you attempt to set a custom MAC address through Windows settings (like the NetworkAddress property in the Device Manager) or third-party changers, the operating system often has a hidden validation rule. If the address you input is not a locally administered address, the change will be rejected. A 2022 Microsoft Q&A thread shows a user experiencing this exact error, describing that setting the first number to 02 works, but their desired address does not. A SuperUser thread about a similar Windows 8.1 restriction breaks it down further: | Hex | Binary (first 2 bits) | Valid
A MAC (Media Access Control) address is a unique 48-bit address assigned to a network interface controller (NIC) for use as a network address in the data link layer of a network segment. It's often referred to as a physical address or hardware address. MAC addresses are usually represented in a six-octet format, separated by hyphens or colons, like this: 00:11:22:33:44:55 . | 01 | No | Multicast + global | | 0x2
00:11:22:33:44:55 First octet: 00 (binary 00000000 ) → Bit 2 = 0 → Global, invalid → Error: "failed to change mac address – set the first octet" | 00 | No | Global | | 0x5
Follow these steps systematically. The solution is almost always in choosing a valid first octet.
Sometimes the GUI fails to write the change to the Windows Registry. You can manually check this path: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\4d36e972-e325-11ce-bfc1-08002be10318 Inside, you will find numbered folders (0001, 0002). Look for the one containing your adapter's name and ensure the "NetworkAddress" string matches your desired input. Verifying the Change
For a spoofed MAC address to be recognized as valid by a Windows wireless network driver, the must be a 2, 6, A, or E . This requirement corresponds to a specific bit configuration defining the address as "locally administered" rather than universally assigned.