Locally-Administered Unicast MAC Generator

Locally Administered MAC addresses (U/L bit = 1)

Every MAC address carries two control bits in its very first byte. The I/G bit (least significant) distinguishes unicast from multicast. The U/L bit (second least significant) distinguishes Universally Administered (UAA, U/L=0, assigned by the manufacturer from an IEEE-registered OUI) from Locally Administered (LAA, U/L=1, freely assignable by the operator). Forcing U/L=1 and I/G=0 means the first byte's hex value must end in 2, 6, A or E — addresses like 02:00:00:..., 06:..., 0A:..., 0E:... — guaranteed not to collide with any registered OUI.

Why this matters in 2026: MAC randomization

The biggest 2020s privacy improvement on consumer devices is automatic per-network MAC randomization. iOS 14 (September 2020) shipped "Private Wi-Fi Address" on by default — every SSID gets a fresh LAA, preventing tracking across coffee shops, hotels and airports. Android 10 introduced the same feature; Windows 10 calls it "Random Hardware Addresses". Without it, your physical Wi-Fi MAC is a stable identifier that retailers, ad networks and venue Wi-Fi systems use to follow you between locations.

Common use cases for LAA

• Privacy — per-network MAC rotation on phones and laptops.
• Virtualization — Docker (02:42:...), KVM/QEMU, VMware Workstation and Hyper-V assign LAA prefixes to virtual NICs to avoid OUI collision.
• Lab and test environments — generating many distinct MACs for switch and DHCP scale testing.
• Captive-portal evasion — getting around free-Wi-Fi time limits or MAC bans (legal grey area, depends on terms of service).
• Live migration — moving a VM between hosts while keeping the same MAC.

Spoofing the MAC on each OS

On Linux: ip link set dev eth0 down && ip link set dev eth0 address 02:00:00:11:22:33 && ip link set dev eth0 up. On macOS: sudo ifconfig en0 ether 02:00:00:11:22:33 (Wi-Fi may require disassociating first). On Windows: the device's Properties → Advanced → "Network Address" field, or via NetSh / PowerShell Set-NetAdapter -MacAddress. The change is volatile — most OSes revert on reboot unless persisted through NetworkManager, systemd-networkd or the Windows registry.

Caveats and side effects

MAC randomization breaks any system that pins authentication or quality-of-service to your MAC: home routers with MAC-allowlists, captive portals that remember your "free 30 minutes", enterprise 802.1X profiles tied to device identity. Sniffers can still see the LAA over the air — randomization is anti-correlation, not invisibility. Use an OUI lookup (standards-oui.ieee.org) to verify a candidate MAC has U/L=1 and does not accidentally fall inside an assigned multicast range.

FAQ

Does LAA stop Wi-Fi tracking? It prevents long-term correlation across networks and visits, but on a single network during a single session you remain identifiable.

Will it break my home Wi-Fi? It can — captive portals will ask you to re-authenticate, and routers configured with MAC allowlists will refuse the new address. Disable randomization for trusted SSIDs.

Can a sniffer still see my MAC? Yes. The LAA is broadcast on every probe and beacon — privacy comes from rotating it, not hiding it.

Is any data sent to a server? No. MAC generation is pure randomness in the browser; nothing leaves the device.