IP address vs. MAC address: what's actually different
The one-sentence version
An IP address says where a device is on a network right now and can change; a MAC address says which physical network card it is and — barring rare tricks — never changes, because it's burned into the hardware at the factory.
Why you need both, not just one
A MAC address operates at the local level — think of it as an apartment number that only means something inside one specific building. An IP address operates at the routing level — a full postal address that means something anywhere in the world. A packet traveling across the internet keeps the exact same source and destination IP the whole way, but its MAC address gets swapped out at every single router it passes through.
The concrete walkthrough
When your laptop sends a packet to a website, your OS already knows the destination IP address. But to actually put a frame on the wire, it needs the MAC address of the next hop — usually your router — not the final destination on the other side of the internet. It asks via ARP ("who has 192.168.1.1? tell 192.168.1.42"), the router replies with its own MAC, and only then does the frame go out addressed to that MAC, carrying the far-away IP inside it. The router receives it, strips the old MAC information, and re-wraps the same packet with a new MAC for the next hop — repeating this all the way to the destination. The IP address inside never changes across that whole journey; the MAC address changes literally at every single hop.
Side by side
| MAC address | IP address | |
|---|---|---|
| Set by | Hardware manufacturer | The network you join |
| Format | 6 bytes, e.g. 3C:22:FB:4A:9B:01 | 4 bytes (IPv4), e.g. 192.168.1.42 |
| Scope | Local network segment only | Can route across the whole internet |
| Changes | Rarely (only spoofed deliberately) | Routinely — new network, new IP |
What people get wrong
"My MAC address can be tracked across the internet" — mostly not true in practice. A MAC address doesn't survive past your first router hop; it gets replaced at every hop along the way, exactly as shown above, so a remote website never actually sees it. Modern operating systems also randomize the MAC address per Wi-Fi network specifically for privacy reasons — a real, deliberate exception worth knowing about.
One caveat worth knowing
Most home devices actually share a single public IP address through a technique called NAT, while each still keeps its own private IP internally — a related but genuinely separate question from "where is the IP address actually visible from," and worth understanding on its own once this part clicks.