A MAC address is a physical address unique to your computer.

Think of it like this: you want to send a letter to your friend so you put your friend’s mailing address on the envelope. This is good enough at first. But right before the post office puts your letter in your friend’s mailbox, the address gets changed to you friend’s fingerprint instead.

This is because computers don’t have a simple mailbox where letters and other messages can be delivered until somebody goes to check the mail.

But why switch from an address to a fingerprint in the first place?

The reason is because there are different layers to the communication. I won’t go into all the details, but in 1984 there was a standard document that was published called the Open Systems Interconnection Reference Model, or just the OSI model for short. This document describes a design that consists of seven layers. Each layer is responsible for specific functionality. And in order to get something running such as browsing the internet, you need pieces from each of these seven layers.

I’ve already described IP which exists in layer 3 of this document and both TCP and UDP which can both be found in layer 4. I didn’t want to go right into this document because it would seem too much like a bunch of theory. But now that you understand a few distributed computing concepts, it’s time to describe where everything fits in the OSI model.

Listen to the full episode for a description of the first four layers as well as why MAC addresses are needed and how they fit into the OSI model.