Ever wonder how the computing world knows the difference between a web browser request and an email send? Although there are quite a few technologies involved, the common way to separate these types of communication is through port numbers.  

For example, when you make a normal web request with your browser and type in “HTTP,” you’re telling the end server two things: 1) what computer address you’d like to connect to, and 2) what port number it should use. By default, HTTP will connect on port 80 (and HTTPS is generally port 443), but your web browser saves you the trouble of having to know this. There are thousands of ports and generally the standard communication ports will be the same wherever you go.

Ports on computers can be imagined as docking bays for delivery trucks. When a delivery truck leaves the shipping dock with a certain type of good, it not only needs to know which building to deliver to, but also which door. Ports are the doors of your computer. When you use your email server to send a message, you normally send through port 25. When you later check your email from your POP3 server, you’ll request your messages through port 110.

When you turn on your computer, you open up channels of communication through possibly hundreds of different ports that could be used to communicate with you. If someone wants to attack your computer, they’ll scan for open ports on your machine and try to use any they find as a way to install software or completely take over your machine.

The best way to make sure you only have the ports of communication open that you want, is to use the internet from behind a firewall (see my previous post), as the firewall does the work of closing all of those dangerous ports for you and keeps you from receiving a delivery you didn’t ask for!