Whenever you click on an enticing link on a web browser, the website you are looking at knows to send whatever the link contains to your computer not yours neighbors’ computer because your computer sends it IP address, kind of like a return address on letter. But as it turns out IP addresses only get you as far as the modem you have in your house, as most of have tons of things connected to it wirelessly like phones, tablets, laptops and other wireless device. All the freaking devices are connected to your home network. Then how does it decide to send those questionable videos to you and not to your parents sitting in the next room? Well each device on your network has something called a MAC address. MAC in this case stands for Media Access Control.
It basically identifies which device is which on your local network. So here is how they work, when data arrives at you home network from the worldwide internet your router needs to decide to which device to send that data, it does this by keeping track of the MAC addresses of all the devices connected to it. Then assigning what called a private IP address usually starting from 192.168 to every device. This is very different from a public IP which is what the rest of the internet sees as being your IP address for your entire hone network. Your router keeps a track of all outbound requests such as when you click on a link and the data you want reaches to your router and it attaches the correct private IP address to the data packets ensuring it’s you since all those private IP correspond to the correct MAC address.
Now this might understandably seem a little redundant since now a computer has both private IP and a MAC address that both can individually identify it. But in reality you need both since although both the public and private IP do the same throughout this process the MAC addresses on the data packets are constantly being changed. They will only tell the data where to go for its next hop. When your data gets to the next device the MAC address gets changed in order to tell it where to go next. Since your data might go through numerous servers and routers before it finally gets to your device, MAC address is crucial even though you have your private IP. Another upside of MAC address is normally they always stays the same with many devices having their MAC hard coded into the firmware at the factory making it easy to spot a malfunctioning device on the network if you are trying to troubleshoot and also to protect your device by allowing devices approved by you for which the router uses a MAC address to access to known devices. ISP’s also use predefined MAC address to make it easy to provide you the service you paid for and they also use this to block access if you aren’t paying the bill. It is possible to spoof a MAC address and you might want to if you are concerned about your privacy at a public network.