What is a Firewall? Everything You Need to Know

By Tibor Moes / Updated: June 2023

What is a Firewall? Everything You Need to Know (2023)

What is a Firewall?

Imagine a world without firewalls. Your sensitive data would be exposed to constant threats, and cybercriminals would have a field day with your private network.

But, “what is a firewall?” you may ask. Firewalls are the heroes in the world of network security, keeping your devices and data safe from prying eyes. But how do they work, and what makes one type of firewall better than another? Read on to find out.


  • Firewalls are security systems that protect devices and networks from malicious attacks. They form a barrier (a “wall”) between your device and the outside world.

  • They operate by monitoring and filtering data that goes and in out of your device. They do so according to a rule set, that determines packet inspection & connection monitoring.

  • Firewalls come in many forms. Some firewalls protect a single PC. While others protect the network of entire organizations or countries (like the “Great Firewall of China”).

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Understanding Firewalls

A firewall is a digital security system that monitors all the traffic coming in and out of a network, based on certain rules. Think of it as a vigilant guard protecting your private network from malicious online attacks. Firewalls are often used for managing traffic filtering rules set by private network owners, detecting and blocking spam emails, controlling the type of traffic that can reach applications, and protecting devices from potential threats.

There are various types of firewalls, such as packet filtering firewalls, proxy firewalls, and next-generation firewalls, each with its unique features and functions. Understanding the differences between these firewalls is crucial to selecting the most suitable one for your network security needs.

How Firewalls Operate

Firewalls are responsible for monitoring and filtering all traffic, such as outgoing traffic, application-layer traffic, online transactions, communications, and dynamic workflows. They use a rule set to determine which traffic is safe and which is malicious. The two main types of firewalls are network firewalls and host-based firewalls, which are further classified into packet-filtering firewalls, basic gateway firewalls, advanced gateway firewalls, next-gen firewalls, and hybrid firewalls.

Configuring your firewall properly is essential because the default settings may not provide the best protection against cyberattacks. The two critical aspects of how firewalls operate are packet inspection and connection monitoring, which we’ll explore in the following subsections.

Packet Inspection

Packet inspection is the process of examining the contents of data packets as they pass through a network firewall. Firewalls use pre-set or dynamically learned rules to allow or deny attempted connections based on criteria such as source and destination IP addresses, ports, and protocols.

Application layer filtering is a more advanced form of packet inspection compared to packet-filtering and stateful inspection firewalls. Application layer filtering has an advantage, as it can block specific content such as malware or certain websites. Furthermore, it is capable of recognizing when certain applications and protocols are used improperly, like Hypertext Transfer Protocol, File Transfer Protocol, and Domain Name System.

Connection Monitoring

Stateful inspection firewalls monitor communication packets over time, examining both incoming and outgoing packets. They create a table to keep track of all open connections and use specific packet protocols, IP addresses, or ports to allow or deny traffic.

Despite their effectiveness, stateful inspection firewalls can be susceptible to Denial of Service (DoS) attacks that exploit already established connections that the firewall usually considers secure. Therefore, it’s crucial to employ additional security measures to complement the firewall’s protection capabilities.

Firewall Varieties

Now that we have a grasp of how firewalls operate, let’s dive deeper into the different types of firewalls available and their unique features and functions.

There are two categories of firewalls based on what they guard: network-based firewalls, which protect entire networks and are usually hardware-based, and host-based firewalls which secure individual devices and are usually software-based.

Within these categories, we have packet-filtering firewalls, advanced gateway firewalls, and next-gen & hybrid firewalls. Each type serves a specific purpose, and understanding their unique features is crucial for selecting the most suitable one for your network security needs.

Basic Packet-Filtering Firewall

Packet-filtering firewalls are designed to make sure that incoming traffic is safe. They do this by examining the data contained in each packet, making sure it matches certain security criteria. They examine the address and connection protocol in the header of data packets to decide if they’re safe or not. Packet-filtering firewalls are classified into two categories: stateful and stateless. Each category has its own way of filtering network traffic.

One of the drawbacks of packet-filtering firewalls is their heavy reliance on manual updates to stay up-to-date with the ever-changing landscape of threats. Without regular updates, they can quickly become outdated and vulnerable to attack.

Advanced Gateway Firewall

A circuit-level gateway firewall works on the session level and looks at the functional packets in an attempted connection. If the connection is successful, it will allow for a continuous open connection between the two networks. This type of firewall shares similarities with proxy firewalls, as both filter based on more detailed application-level data than just IP addresses, ports, and packet protocols.

The benefits of using a proxy firewall include a deeper look into data and the ability to cross-filter various data characteristics. However, the drawbacks include occasional interference with legitimate incoming data, resulting in slowdowns in performance.

Next-Gen & Hybrid Firewalls

Next-Generation and hybrid firewalls are cutting-edge in firewall technology. They combine multiple firewall technologies to offer more comprehensive protection against a wider array of threats. A Next-Generation Firewall (NGFW) looks at the application layer of the TCP/IP stack, allowing it to identify applications like Skype and Facebook.

Hybrid firewalls, on the other hand, combine two or more firewall types to protect a single private network. These advanced firewalls offer features like sandboxing technologies and threat prevention technologies like Intrusion Prevention Systems (IPS) and antivirus to keep malware and threats out of files.

The Evolution of Firewall Technology

The first generation of firewall technology was developed by Digital Equipment Corporation (DEC) back in the late 1980s, and it was called the Packet-Filter Firewall. Over the years, firewall technology has evolved to include advanced gateway firewalls, next-gen firewalls, and hybrid firewalls, which are designed to offer more comprehensive protection against a wider array of threats.

This evolution showcases the ever-increasing need for robust network security measures to combat the growing complexity and variety of cyber threats. Today’s firewalls are more advanced and sophisticated than ever, providing a critical line of defense in the ever-changing landscape of network security.

The Importance of Implementing Firewalls

Implementing firewalls is vital for safeguarding networks from malicious threats like malware, identity theft, and cyber attacks. Firewalls face challenges in keeping up with the constant changes in malware and the rise of the Internet of Things (IoT). However, a well-configured and regularly updated firewall can provide a strong layer of protection for your network and devices.

In addition to firewalls, other security measures like antivirus software, intrusion detection systems, and regular software updates are necessary to ensure comprehensive network security. The combination of these security measures helps create a robust defense against the ever-evolving threats in the digital world.

Firewall Security Measures

Firewalls perform various security functions, including narrowing attack surfaces, filtering traffic, and creating audit trails. These functions help keep your system secure and provide valuable information for security operations teams to analyze and improve network security.

To maximize firewall protection and ensure effective implementation, it’s crucial to follow best practices such as blocking traffic by default, monitoring user access, planning for firewall configuration changes, and using monitor mode to watch current traffic. These practices help maintain a strong and adaptable security posture for your network.

Notable Firewall Applications & Incidents

Real-life examples of firewall use, both successful and compromised, offer valuable insights into their effectiveness and the lessons that can be learned from these cases. The Great Firewall of China is a notable example of a nation-state using a firewall to restrict access to content deemed politically or socially sensitive, as well as monitor online activity and collect personal information.

On the other hand, the breach of a US federal agency in 2020 highlights the importance of proper firewall configuration and regular updates. The agency’s network was compromised due to a misconfigured firewall with many outbound ports inappropriately open to traffic. This incident emphasizes the need for organizations to implement robust firewall security measures and stay vigilant to potential threats.

Firewall Best Practices

To maximize firewall protection and ensure effective implementation, certain best practices should be followed. These include setting up deny any/any rules, being specific and purposeful with the rules you create, configuring your network firewalls to automatically block any traffic that doesn’t meet the criteria, and following the principle of least privilege when it comes to user access.

In addition to these best practices, regular firewall security audits and network access control can help maintain a strong and adaptable security posture for your network. By implementing these best practices, organizations can reduce the risk of security breaches and maintain a more secure network environment.

Comparing Firewalls with Other Security Solutions

While firewalls play a crucial role in filtering network traffic, other security solutions like antivirus software and intrusion detection systems complement their functions to provide comprehensive network security. While firewalls act as a filter for incoming and outgoing traffic, antivirus software checks devices and storage systems for threats that have already made it in, and intrusion detection systems protect endpoints and detect threats.

Combining firewalls with other security tools is essential for maintaining a robust and resilient network security posture. These security solutions work together to provide a multi-layered defense against cyber threats, ensuring that networks remain secure and protected from potential attacks.

Limitations & Future Developments in Firewall Technology

Despite their effectiveness, firewalls have limitations when it comes to shielding against all types of attacks, and they can’t stop attacks that come from within the network. As cyber threats continue to evolve, so too must firewall technology to stay ahead of potential attackers.

Future developments in network security include the use of artificial intelligence and machine learning to detect and respond to threats, as well as cloud-based security solutions to provide an extra layer of protection. By continuously advancing and adapting to the ever-changing threat landscape, firewalls and other security solutions can help maintain a secure and resilient network environment.


In conclusion, firewalls play a crucial role in the world of network security, protecting private networks from malicious online attacks. Understanding the different types of firewalls, their unique features, and how they operate, is essential for selecting the most suitable one for your network security needs. By implementing best practices, staying up-to-date with technological advancements, and combining firewalls with other security solutions, organizations can maintain a robust and resilient network security posture. As cyber threats continue to evolve, so too must our defense mechanisms to ensure a safer digital world for all.

How to stay safe online:

  • Practice Strong Password Hygiene: Use a unique and complex password for each account. A password manager can help generate and store them. In addition, enable two-factor authentication (2FA) whenever available.
  • Invest in Your Safety: Buying the best antivirus for Windows 11 is key for your online security. A high-quality antivirus like Norton, McAfee, or Bitdefender will safeguard your PC from various online threats, including malware, ransomware, and spyware.
  • Be Wary of Phishing Attempts: Be cautious when receiving suspicious communications that ask for personal information. Legitimate businesses will never ask for sensitive details via email or text. Before clicking on any links, ensure the sender's authenticity.
  • Stay Informed. We cover a wide range of cybersecurity topics on our blog. And there are several credible sources offering threat reports and recommendations, such as NIST, CISA, FBI, ENISA, Symantec, Verizon, Cisco, Crowdstrike, and many more.

Happy surfing!

Frequently Asked Questions

Below are the most frequently asked questions.

What is a firewall?

Firewalls are security systems that protect devices and networks from malicious attacks. They act as a barrier between an internal, trusted network and an external, untrusted network such as the internet.

Firewalls can monitor and filter incoming and outgoing traffic to protect data from malicious intruders.

Should I turn my firewall on or off?

Given the importance of firewalls in protecting your device from malicious attacks, it’s highly recommended to keep your firewall on. This will give you an extra layer of protection and security as you navigate through the internet.

Is a firewall installed on a computer or router?

Both options are possible. A firewall can be either a software or a hardware device, or a combination of the two. And it can be used to protect a device, like your computer, or a network, like your Wi-Fi at home. In this first case, it would be installed on your computer. In the second case, it would be installed on your router.

Author: Tibor Moes

Author: Tibor Moes

Founder & Chief Editor at SoftwareLab

Tibor has tested 39 antivirus programs and 30 VPN services, and holds a Cybersecurity Graduate Certificate from Stanford University.

He uses Norton to protect his devices, CyberGhost for his privacy, and Dashlane for his passwords.

You can find him on LinkedIn or contact him here.