A MAC address (Media Access Control address) is a unique identifier assigned to a network interface controller (NIC) by its manufacturer. Unlike an IP address, which can change and is used for internet routing, a MAC address is (traditionally) fixed to the hardware and used only for communication within a local network segment.
MAC Address Format
A MAC address is 48 bits (6 bytes) written as six pairs of hexadecimal digits:
A4:C3:F0:85:AC:2D
- First 3 bytes (OUI) — Organizationally Unique Identifier, assigned by IEEE to the manufacturer (e.g., Apple, Intel, Qualcomm)
- Last 3 bytes — Unique identifier assigned by the manufacturer to the specific device
MAC vs IP Address
| Feature | MAC Address | IP Address |
|---|---|---|
| Layer | Layer 2 (Data Link) | Layer 3 (Network) |
| Scope | Local network only | Global (internet routing) |
| Assigned by | Manufacturer | ISP / DHCP server |
| Changes? | Rarely (hardware-fixed) | Regularly (dynamic IP) |
| Format | AA:BB:CC:DD:EE:FF | 192.168.1.1 / 2001:db8::1 |
MAC Address Randomization
Modern operating systems (iOS 14+, Android 10+, Windows 11, macOS Monterey+) randomize MAC addresses by default when scanning for Wi-Fi networks and when connecting to new networks. This prevents passive tracking via MAC address — for example, a mall that tracks your movement by logging when your device probes its access points.
Privacy and Security Implications
- Network fingerprinting — On a local network, your MAC address is visible to the router and all devices on the same subnet
- Device tracking — Before randomization, your MAC could be used to track your physical location across Wi-Fi networks
- ARP poisoning — Attackers can forge MAC addresses in ARP tables to intercept local network traffic
- MAC filtering — Routers can restrict access to specific MAC addresses, but this is easily bypassed by spoofing an allowed MAC
People Also Ask
- Can websites see my MAC address?
- No. MAC addresses are stripped at the router — they only travel as far as the next network hop. When your traffic reaches a website, the server sees your public IP address, not your MAC address. MAC addresses never leave your local network segment.
- Can I change my MAC address?
- Yes — this is called MAC spoofing. On Linux:
ip link set dev eth0 address AA:BB:CC:DD:EE:FF. On macOS and Windows you can change the MAC through network adapter settings. Most modern devices also randomize MACs automatically. The hardware-burned MAC (the "real" MAC) cannot be changed, but the software-visible MAC can be overridden.
Related: ARP poisoning | Packet sniffing | Network segmentation