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MAC Address

Also known as: Media Access Control address, Hardware address, Physical address

A 48-bit unique hardware identifier burned into every network interface card, used for local Ethernet and Wi-Fi delivery within a single network segment.

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What is a MAC address?

A MAC address (Media Access Control address) is a 48-bit hardware identifier assigned to a network interface — every Ethernet port, every Wi-Fi chip, every Bluetooth adapter has one. Unlike an IP address, which is logical and can change at any time, a MAC address is traditionally burned into the hardware at the factory and meant to uniquely identify that interface forever.

MAC addresses are used to deliver frames within a single Layer-2 network segment (a switch, an Ethernet LAN, a Wi-Fi network). IP addresses are used to route packets between such segments. Think of the MAC address as the physical apartment number and the IP address as the city-level postal address — you need both to deliver a letter end to end.

How MAC addresses look

A MAC address is written as six pairs of hexadecimal digits separated by colons or dashes:

00:1A:2B:3C:4D:5E
00-1A-2B-3C-4D-5E

The first three bytes (00:1A:2B) are the OUI (Organizationally Unique Identifier), assigned by IEEE to the NIC manufacturer (Intel, Broadcom, Apple, etc.). The last three bytes are assigned by that manufacturer. You can look up the OUI of any MAC in IEEE's public OUI database to find the vendor.

MAC address randomization

Because the OUI identifies the vendor and the full address stays stable across connections, MAC addresses are a very strong tracking signal — a shop's Wi-Fi, a coffee chain, or a city's public Wi-Fi can correlate your appearances across all their locations just by watching the MAC addresses probing for networks.

To defeat this, modern OSes now randomize the MAC address per network:

  • iOS has had per-SSID random MAC since iOS 14 (2020)
  • Android has had it since Android 10 (2019)
  • Windows 10/11 supports it per-SSID as a user setting
  • macOS got it for Wi-Fi scanning in Sonoma (2023)

The locally-administered bit (bit 1 of the first byte) indicates whether an address is locally assigned vs. burned-in — random MAC addresses set this bit so they cannot collide with any vendor's real OUI.

MAC addresses only traverse a single LAN segment. They never cross a router, so they don't appear in the logs of any remote server — only IP addresses do. That's why MAC addresses can't be used to geolocate or identify a remote visitor.

Frequently Asked Questions

No. MAC addresses only travel within a single Layer-2 network segment (one switch, one Wi-Fi network) and are stripped before a packet is forwarded to the next router. A remote web server, ad network, or any other internet host never sees your MAC — it only sees your public IP and any application-layer fingerprint (browser, cookies, etc.). MAC addresses are a tracking risk only on networks you connect to directly, like a shop's Wi-Fi.
Yes. Every modern OS lets you change ("spoof") the MAC address reported by a network interface, either temporarily or permanently. Linux uses `ip link set dev eth0 address aa:bb:cc...`, macOS uses `ifconfig en0 ether ...`, Windows lets you set it in the adapter's advanced properties or via `Set-NetAdapter`. Modern iOS and Android randomize the MAC per network automatically. Changing your MAC does not change your IP — they are independent identifiers at different layers.
The OUI (Organizationally Unique Identifier) is the first three bytes of a MAC address, assigned by IEEE to a network-equipment manufacturer. It identifies who built the network interface — for example, addresses starting `00:1A:2B` are assigned to Ayecom Technology, while `00:50:56` is VMware's OUI for virtual adapters. The IEEE OUI database is public, so you can look up any MAC's vendor. Randomized MAC addresses use OUIs with the locally-administered bit set, so they cannot collide with any vendor's real OUI.
Because the OUI plus serial portion of a fixed MAC address is a strong tracking signal — a coffee chain, airport, or shop can correlate your appearances across all their locations just by logging the MAC addresses your phone broadcasts when scanning for Wi-Fi. Per-network MAC randomization (default on iOS 14+, Android 10+, Windows 10/11, macOS Sonoma) breaks this by generating a fresh random MAC for each network you join, so the same device looks different to every observer.
In principle, yes — the IEEE assigns OUI ranges to vendors so that each globally-unique MAC is used exactly once. In practice, collisions happen: cheap NICs sometimes ship with duplicated addresses, manufacturers occasionally reuse a serial range, and randomized MAC addresses can statistically collide on the same network (extremely rare with 46-bit randomness). Within a single LAN segment, two devices with the same MAC will see traffic delivered unpredictably to either.
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