# MAC address

> The built-in name of a network card, used to deliver data inside a local network.

- Level: Intermediate
- Topics: Networks
- URL: https://tidbit.legios.com.ar/mac-address/
- In Spanish: [Dirección MAC](https://tidbit.legios.com.ar/es/mac-address/)

A **MAC address** is an identifier that comes with every network interface: the Wi-Fi chip in your phone, the Ethernet port in your laptop, the radio in a smart bulb. It is 48 bits long and usually written as six pairs of hexadecimal digits, like `3c:22:fb:9a:10:4e`. The first half says which manufacturer made the hardware, from blocks handed out by the IEEE; the second half is that maker's serial for the card. It has nothing to do with Apple's Mac computers: MAC stands for Media Access Control.

Its job is local delivery. Inside one network, say your home Wi-Fi, devices find each other by MAC address: the router knows that `3c:22:fb:9a:10:4e` is your laptop and sends its data there. To get from an IP address to the right MAC address, devices simply ask the network out loud, 'who has 192.168.1.20?', and the owner answers (that exchange is called **ARP**).

A MAC address never leaves your local network. When your data goes out to the internet, each router along the way rewraps it with its own MAC address for the next hop, while the IP address stays the same from end to end. That is why the IP address works like a postal address and the MAC address like the name of the person who opens the door.

Because it used to be fixed, a MAC address could be used to recognize the same phone in every café and shopping mall. Modern phones and laptops now use a **private** or **random MAC address**, a different one for each Wi-Fi network. It is also why 'MAC filtering' on a router is weak protection: any device can be told to announce a different address.

## An analogy

The IP address is the street address on an envelope; the MAC address is the name of the person inside the building. The mail carrier uses the street, and the doorman uses the name.

## Keep in mind

- 48 bits, written as six pairs like `3c:22:fb:9a:10:4e`.
- The first half identifies the manufacturer of the network hardware.
- Only used inside a local network; routers swap it at every hop.
- Phones now use a random MAC address per Wi-Fi network for privacy.

## Go deeper

- [MAC address on Wikipedia](https://en.wikipedia.org/wiki/MAC_address)
- [Address Resolution Protocol (ARP) on Wikipedia](https://en.wikipedia.org/wiki/Address_Resolution_Protocol)

## Related terms

- [Wi-Fi](https://tidbit.legios.com.ar/wi-fi/): Networking over radio waves: the internet without the cable, within a few rooms.
- [Chip](https://tidbit.legios.com.ar/semiconductor-chip/): A sliver of silicon carrying billions of tiny switches that compute and remember.
- [Port](https://tidbit.legios.com.ar/port/): The numbered door on a computer that says which program a connection is for.
- [Apple](https://tidbit.legios.com.ar/apple/): The company that sells the iPhone and the Mac, plus the services that run on them.
- [Router](https://tidbit.legios.com.ar/router/): The box that connects your devices to each other and to the internet.
- [IP address](https://tidbit.legios.com.ar/ip-address/): The number that identifies a device on a network, like a postal address.
- [Internet](https://tidbit.legios.com.ar/internet/): A worldwide network of networks that lets any connected device reach any other.