The name is derived from the real firewalls used to secure buildings. These physical firewalls are a set of doors that close in a building to keep the fire contained to one area, preventing the entire building from being destroyed. Similarly, an internet firewall is designed to shut down access to your operating system or to other computers connected to your network.
How does it work?
Firewalls carefully analyse inbound traffic to your computer based on a set of pre-established rules and filter traffic coming from unsecured or suspicious sources to prevent attacks. A firewall protects against inbound traffic from the computer's entry point, also known as a "port". This is where information is exchanged with external devices. For example, it could look like this: "Source address 172.18.1.1.1 is allowed to reach destination 172.18.2.1 via port 22".
It can be helpful to think of an IP address as a house and port numbers as rooms in the house. Only trusted people (source addresses) are allowed to enter the house (destination address). Access is further filtered so that only certain people in the house are allowed to access certain rooms (destination ports). The owner has access to any room, while guests only have access to certain ones.
How are the rules decided?
Your firewall may come with its own set of rules, but in most cases you will be able to customise them to your needs. The filter can be loose. It can also directly exclude certain websites by name.
Why should you have a firewall?
There are many reasons. Some people value them for their ability to keep private information safe. Identity theft is a growing problem and many see firewalls as a good defence against these specific types of criminals. Others, such as small business owners, believe firewalls are important because they keep their personal electronic information private. Not only is privacy important from a competitive perspective, but you also need to make sure that your customers' personal trading information is safe with you.
In theory, a firewall would be unnecessary if you only visit websites that you trust and know are secure. In these cases where you only visit a few websites, a firewall can still be useful, but it doesn't have to work quite as hard to filter out dangerous content.
