Reading a MAC address
A MAC address is 48 bits, written as six bytes in hex. The first three bytes are the OUI (organisationally unique identifier) that the IEEE assigns to a manufacturer; the last three are chosen by the manufacturer. Two bits in the first byte carry meaning of their own:
- Bit 0 (I/G): 0 = unicast, 1 = multicast / group.
01:00:5e:…is IPv4 multicast,33:33:…IPv6 multicast,ff:ff:ff:ff:ff:ffbroadcast. - Bit 1 (U/L): 0 = universally administered (burned in by the vendor), 1 = locally administered. Phones and laptops that randomise their Wi-Fi MAC for privacy set this bit, which is why those addresses have 2, 6, A or E as their second hex digit and no vendor.
Notations
| Form | Example | Used by |
|---|---|---|
| Colon | 00:0C:29:AB:CD:EF | Linux, macOS, most tools |
| Dash | 00-0C-29-AB-CD-EF | Windows ipconfig, IEEE documents |
| Cisco dotted | 000c.29ab.cdef | Cisco IOS, some Huawei gear |
| Plain | 000c29abcdef | Databases, DHCP reservation files |
EUI-64 and IPv6
Early IPv6 autoconfiguration built the host part of the address from the MAC: split it in half, insert ff:fe, and flip the U/L bit. 00:11:22:33:44:55 becomes interface ID 0211:22ff:fe33:4455 and link-local address fe80::211:22ff:fe33:4455. Modern systems prefer random or stable-private IDs (RFC 7217), but network gear and older Linux still use EUI-64, and recognising the ff:fe pattern is a quick way to recover a device's MAC from its IPv6 address.
Vendor data
The site ships a seed table of the most common vendors (virtualisation, Apple, Intel, Cisco, Ubiquiti, MikroTik, Raspberry Pi, TP-Link and so on). The full IEEE registry has about 45,000 entries; the build includes a script to refresh the table from standards-oui.ieee.org.
Questions
Why does my phone show a different MAC on each network?
MAC randomisation, on by default in iOS 14+ and Android 10+. The address has the locally administered bit set and is generated per SSID. Disable it per network (“Private Address” / “Randomised MAC”) if you rely on DHCP reservations or MAC filtering.
Can two devices have the same MAC?
They should not on the same network segment, but it happens: cheap clones, cloned VMs, and manually set addresses. Duplicates cause intermittent connectivity as the switch’s forwarding table flips between ports.
Is a MAC address visible on the internet?
No. MAC addresses only travel within the local network segment; routers replace them hop by hop. A website cannot see your MAC. (IPv6 EUI-64 addresses did leak it, which is why randomised interface IDs replaced them.)
What does the vendor lookup tell me about a device?
Only who made the network chip or device. A Realtek or Intel OUI could be any PC; an Apple or Samsung OUI narrows it to that brand; VMware, QEMU and VirtualBox OUIs mean a virtual machine.