Firewall Explained

What is a Firewall?

Firewalls existed long before computers. In the real world, they are used in large buildings to prevent fire from moving from one area to the next. The purpose of a computer firewall is similar because it is used to prevent threats from moving from one area to another. It does this by filtering incoming data so that uninvited or undesirable traffic is unable to pass through. It can also be used to prevent data from moving from one part of the system to another – for example, there may be access to the internet on one office computer but not the rest.

How a Firewall Works

There are different types of firewall available, and these work in slightly different ways. Basically, they all function by inspecting incoming data to see if it meets certain criteria. If the data does not meet these criteria, it is not allowed in. One way to imagine this is to see the firewall as the doorman at a fancy nightclub. These bouncers will have certain criteria for deciding who gets in (e.g. a dress code), and anyone who does not meet this criteria will be left outside.

Types of Firewall

There are a number of different types of firewall including:

  • One of the oldest types of computer firewall is the packet filtering system which is usually located in the router for a network. It works by analysing IP addresses and either accepting or rejecting data packages based on where it is coming from.
  • Application firewalls are configured to only allow certain types of data to pass through. In order words, they are designed for dealing with specific types of traffic.
  • A circuit-level entry firewall is a virtual circuit between an internal client and a proxy server. It uses transmission control protocol (TCP) to determine which data passes through – in other words, it looks much deeper into the incoming data than just the IP address.
  • A stateful inspection firewalls is like a mix of the other three firewalls.

Configuring Firewalls

A firewall could be a bit of a blunt tool if it wasn’t for the fact that it is customisable. This means that the administrator can have a say in what data gets into the system. The filters in the firewall can usually be configured in such a way as to:

  • Block certain IP addresses
  • Block specific domain names – this can be easier than blocking an IP address
  • Block certain ports on machines – managers may do this if they do not want employees going online.
  • Block specific content – this can be done by instructing the filter to stop data containing certain words and phrases.
  • Allow only certain domain names or IP addresses – this would mean that these are the only places that the user can reach online.

Benefits of Firewalls

Firewalls will usually play a key role in keeping your computer or computer network secure. The benefits of this type of filtering include:

  • It helps to protect your computer from external and internal threats
  • It can stop many types of malware from gaining access to your network
  • It can be used to prevent certain content being accessed from a computer
  • It can block users from accessing certain websites – this can be very important in a business environment.
  • It can work alongside antivirus software to keep your network safe
  • It can keep a log of activity, and this can be really helpful when investigating any problems.
  • It can be used to create alarms if people try to access certain areas of the system
  • It makes it easier to monitor what is happening on a computer network


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