What is a Firewall?

A firewall is a security layer that sits between your device or network and the wider internet, filtering traffic to block unauthorised access while allowing legitimate data to pass through. It acts as a gatekeeper, deciding which connections are safe and which should be stopped.

Firewalls can be software-based, running on individual devices, or hardware-based, protecting entire networks. In both cases, the goal is to control how data enters and leaves a system to reduce exposure to threats.

This article explains how firewalls work, what they protect against, and how they fit into a broader approach to online security.

How does a firewall work?

A firewall works by inspecting data packets as they move between your device and the internet, applying a set of rules to determine whether each request should be allowed or blocked. These rules are based on factors such as IP addresses, port numbers, and the type of traffic being transmitted.

When a connection attempt is made, the firewall evaluates it in real time. If the traffic matches trusted criteria, it is allowed through, but if it appears suspicious or unauthorised, it is blocked before it can reach the system.

This process happens continuously in the background, creating a controlled boundary that helps prevent unwanted access.

What types of firewalls are commonly used?

Firewalls come in different forms depending on how they are deployed and what level of control they provide. Each type is designed to manage traffic in a slightly different way.

Some of the most common include:

• Software firewalls: Run directly on a device and protect individual systems
• Hardware firewalls: Sit between a network and the internet to protect multiple devices
• Network firewalls: Filter traffic across larger systems or organisations
• Application-level firewalls: Monitor specific types of data and behaviour

These variations allow firewalls to be used across everything from personal devices to large-scale infrastructure.

What threats does a firewall help prevent?

A firewall is designed to reduce exposure to external threats by controlling how connections are made. It does not eliminate all risks, but it acts as a strong first line of defence.

It helps protect against:

• Unauthorised access attempts from external sources
• Malicious traffic trying to exploit open ports or services
• Certain types of malware that rely on network communication
• Suspicious or unexpected inbound connections

A firewall limits the number of potential entry points by filtering traffic before it reaches your system, 

How does a firewall fit into overall security?

A firewall is one part of a wider security setup, focusing specifically on controlling network access rather than securing the data itself. It works best when combined with other tools that protect different layers of your online activity.

For example, using an Edge VPN adds encryption to your internet traffic, which means that even if data passes through a network, it cannot be easily read or intercepted. While the firewall controls what gets through, a VPN protects what is being transmitted.

Together, they create a more balanced approach, where both access and data are managed more effectively.

What are the limitations of a firewall?

Although firewalls are essential for controlling traffic, they are not designed to handle every type of threat. Their focus is on filtering connections, not detecting all forms of malicious behaviour.

There are several limitations to keep in mind:

• They cannot prevent attacks that originate from trusted or internal sources
• They do not protect against phishing or user-driven threats
• They cannot fully stop malware that is already inside a system
• They rely on correctly configured rules to be effective

Understanding these limits helps ensure firewalls are used as part of a broader strategy rather than a complete solution.