What is a MAC address?

Two addresses, not one

In the last lesson you met the IP address, the address that tells the network where to deliver data. It can change every time you join a different network.

Your device has a second address too: the MAC address (MAC stands for Media Access Control). It belongs to the network chip inside your phone, laptop or game console, and it's set when the chip is made. It's sometimes called the physical address or hardware address.

How to read one

A MAC address is six pairs of letters and numbers, usually separated by colons or dashes:

3C:22:FB:9A:10:7E

Each pair is a number written in hexadecimal, which uses the digits 0 to 9 plus the letters A to F. The address has two halves:

• The first half, 3C:22:FB, names the maker of the chip. Each manufacturer is given its own prefix by the IEEE, the group that manages these numbers. The prefix is called an OUI (Organizationally Unique Identifier).
• The second half, 9A:10:7E, is that chip's own serial number, chosen by the maker so no two of their chips match.

How the two addresses work together

Think of sending a letter to someone in an apartment building.

• The IP address is the street address. It gets the letter to the right building, which is the right network.
• The MAC address is the name on the apartment door. Once the letter is inside the building, it picks out the one device it's meant for.

On your home network, the switch inside your router does this every second. It keeps a list of which MAC address is plugged into which port or connected over Wi-Fi, and sends each piece of data only to the device it's for.

Try it yourself

On an iPhone, open Settings > Wi-Fi, tap the network you're on, and look for Wi-Fi Address. On Android, look under Settings > About phone or in the Wi-Fi network's details. You'll see six pairs, like the example above.

Good to know

• Your phone might not use its factory MAC address. Many phones and laptops now show each Wi-Fi network a different, randomly made "private" MAC address, so networks can't track you from place to place. On an iPhone this is the Private Wi-Fi Address switch.
• MAC addresses are meant to be unique, but they can be changed in software, so they aren't proof of who a device is.
• MAC addresses only matter inside your local network. They don't travel across the internet; at each stop along the way, a router swaps in new ones. How your device finds the MAC address that goes with an IP address is a lesson of its own (it's called ARP).

For CCNA learners

This lines up with CCNA 200-301 exam topic 1.13, describe switching concepts, including MAC learning: a switch learns which MAC address lives on each port by reading the sender's address on incoming frames.