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
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!