Firewall Examples: The 3 Barriers You Need to Know (2023)

By Tibor Moes / Updated: June 2023

Firewall Examples: The 3 Barriers You Need to Know (2023)<br />

Firewall Examples

Imagine you’re hosting a party and you’ve appointed a security guard at the entrance. This guard checks everyone’s invitation and only lets in those you’ve approved. If anyone uninvited tries to enter, they’re stopped at the door. In the world of computers and the internet, that guard is called a firewall. In this article, we will explore some of the most interesting examples of firewalls that help keep your digital party safe.


A firewall is a network security device that monitors and filters incoming and outgoing network traffic based on pre-set security rules, protecting devices from various threats.

Example 1 – Packet Filters (Late 1980s): One of the earliest examples of firewalls, packet filters work at a low level by inspecting packets (small chunks of data) passing through them. They make decisions to allow or block packets based on factors like the source and destination addresses, and the type of traffic (such as email or web browsing).

Example 2 – Stateful Inspection Firewalls (Mid-1990s): These are a significant step forward from packet filters. They not only examine individual packets but also keep track of ongoing connections. This allows them to understand the context of a network request, which aids in determining whether to permit or deny traffic.

Example 3 – Next-Generation Firewalls (2010s): These firewalls take things to a new level by integrating additional functionality like intrusion prevention systems and the ability to enforce policies based on applications, users, and more. They can identify and control application usage within the network while providing in-depth visibility for better network control.

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Firewall Examples In-Depth

Packet Filters (Late 1980s)

Imagine you’re a postmaster in a small town. Every day, you’re handed a pile of letters and packages to sort and distribute. You don’t necessarily know what’s inside each package, but you can see where it’s from, where it’s going, and whether the sender and recipient seem legitimate based on your past experiences. If something doesn’t look right—for instance, if a package is addressed to a resident who’s told you they’re out of town—you might decide not to deliver it. That’s essentially how packet filtering works.

Introduced in the late 1980s, packet filters act as our diligent postmasters in the digital world. They scrutinize “packets,” or small chunks of data, traveling through the network, just like the postmaster examines every parcel that arrives at the post office.

Every packet of data contains a wealth of information. There’s the “header” — like the address on an envelope — which tells the packet filter where the data came from and where it’s going. There’s also the type of “service”— akin to the postage stamp on the letter, indicating whether it’s first-class mail, a package, etc. In data terms, this could be email traffic, web browsing, file transfers, and more.

Packet filters work on a simple yet effective principle: check every packet against a set of rules, or a “rule base.” You could think of this as the postmaster’s guidelines for sorting and delivering mail. If a packet’s header and type of service match a rule, the packet gets through. If not, it’s blocked, much like a suspicious parcel at the post office.

However, the packet filter’s simplicity is also its limitation. It’s like our postmaster who can only see the outside of each package but has no idea what’s inside. Packet filters can’t look at the content of the packets, so they can’t tell if a seemingly harmless packet is carrying malicious data. They also lack the ability to remember past packets, making them less effective against more complex threats.

Yet, despite these limitations, packet filters played a crucial role in the early days of internet security. They were the first line of defense in a world increasingly connected and vulnerable to threats. Like the pioneering postmasters of old, they laid the groundwork for more sophisticated systems that were to follow.

But that’s a story for another day. For now, let’s celebrate packet filters — the diligent postmasters of the early internet — and their contribution to the evolution of firewall technology.

Stateful Inspection Firewalls (Mid-1990s)

Imagine you’re a friendly neighborhood librarian. Not only do you know all the books in your library, but you also know all your regular visitors, what books they usually borrow, and when they typically visit. Whenever someone walks in, you don’t just check their library card (though you do that too!), but you also recall their borrowing history and their usual behavior. This helps you spot anything out of the ordinary, like a quiet regular suddenly borrowing a pile of noisy cookbooks. This is akin to how stateful inspection firewalls function.

Stateful inspection firewalls, which rose to prominence in the mid-1990s, are like these vigilant librarians. They represent a significant leap forward from packet filters. These advanced firewalls don’t just examine individual packets of data—they keep track of ongoing connections. They “remember” what has happened before, which enables them to understand the context of a network request.

To make this possible, stateful inspection firewalls maintain a “state table,” a kind of memory. You can think of it as our librarian’s ledger, keeping track of every book checked out and returned. The state table records all established connections passing through the firewall, detailing the source and destination IP addresses, the port numbers, and the connection state.

With the information in the state table, a stateful inspection firewall can make more informed decisions. It’s not just blindly applying rules to individual packets. Instead, it’s looking at each packet in the context of its connection. If a packet is part of an existing, approved connection—like our regular visitor returning a book—it’s allowed to pass through. But if it’s not part of an existing connection—like a stranger entering our library—the firewall scrutinizes it more closely.

This ability to remember past connections and examine each packet in its context makes stateful inspection firewalls more secure than simple packet filters. They’re better at detecting and blocking unsolicited and potentially harmful traffic.

But as the digital world grew more complex and sophisticated, new challenges emerged that stateful inspection firewalls struggled to address. As we’ll explore in our next example, firewalls had to evolve again to keep pace with the changing landscape.

For now, let’s appreciate the stateful inspection firewall—a smart librarian who brought a new level of intelligence and context-awareness to the world of network security.

Next-Generation Firewalls (2010s)

Imagine you’re a tour guide at a popular museum. You’re not just responsible for letting visitors in and out based on their tickets, but you also keep an eye on their behavior inside the museum. You know what exhibits are currently on display, what rooms are off-limits, and you even recognize regular visitors and their interests. If you see someone lingering suspiciously in a restricted area, you’re going to take action. This is a lot like how next-generation firewalls operate.

Next-Generation Firewalls, or NGFWs, which emerged prominently in the 2010s, are the museum tour guides of the cyber security world. They’re not just content with checking packets and remembering connections, they go several steps further, offering a level of scrutiny that is as comprehensive as it is impressive.

These advanced firewalls integrate several additional features that were previously standalone technologies. For instance, they include intrusion prevention systems (IPS) which can detect and prevent attacks by examining network traffic in more depth. It’s like our tour guide spotting a visitor trying to touch a priceless painting and stepping in before any harm can be done.

Moreover, NGFWs can enforce policies based on users and applications. Instead of just looking at IP addresses and ports, they understand who is sending or receiving the data and what application is being used. This is like our guide knowing that a particular visitor is a museum member with privileges to access a members-only exhibit.

One of the most interesting aspects of NGFWs is their ability to inspect encrypted traffic. Encryption is a common way to protect sensitive data, but it can also be exploited by malicious actors to hide threats. An NGFW’s ability to peer into encrypted data is like our tour guide having the ability to check the contents of a visitor’s backpack.

While they’re complex and sophisticated, NGFWs are also designed to be user-friendly, with clear interfaces and detailed analytics. This makes it easier for network administrators to see what’s happening and respond accordingly, much like our tour guide has a map of the museum and a radio to call for assistance if needed.

In short, next-generation firewalls are the culmination of decades of innovation and improvement in network security. They’re powerful, adaptable, and intelligent, and while they can’t eliminate all threats, they provide a level of protection that earlier firewalls couldn’t match.

So, let’s celebrate the NGFW, the vigilant museum guide of the digital world, keeping an eye on our data as it moves through the labyrinthine corridors of the internet.


In our journey through the realm of firewall technology, we’ve traveled from the basic packet filters, akin to diligent postmasters, to stateful inspection firewalls, acting like vigilant librarians, and finally to the sophisticated next-generation firewalls, resembling mindful museum guides. Each evolution in this technology has aimed to enhance our defense against cyber threats and keep our digital world safer. As we embrace an increasingly connected future, these firewalls remain our steadfast guardians, watching over the ever-expanding frontier of the internet.

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.

Why do we need a firewall?

A firewall acts like a security guard for your computer or network. It monitors and filters incoming and outgoing traffic based on predefined rules, protecting your system from various cyber threats such as hacking attempts, viruses, or worms. Without a firewall, your system could be vulnerable to these threats.

What is the difference between a packet filter and a stateful inspection firewall?

Packet filters, the earliest form of firewall, inspect packets of data individually based on their headers and type of service. They don’t keep track of ongoing connections or inspect the content within the packets. In contrast, stateful inspection firewalls maintain a “state table” that records all established connections. This allows them to examine each packet in the context of its connection and make more informed decisions about whether to allow or block traffic.

Are next-generation firewalls (NGFWs) the ultimate solution in firewall technology?

While next-generation firewalls represent the most advanced firewall technology as of now, they aren’t the ultimate solution to all cybersecurity threats. Cyber threats are constantly evolving, and so must our defenses. NGFWs are a significant step forward, with features like intrusion prevention systems, user and application awareness, and encrypted traffic inspection. However, they need to be used in conjunction with other security measures for comprehensive protection.

Author: Tibor Moes

Author: Tibor Moes

Founder & Chief Editor at SoftwareLab

Tibor is a Dutch engineer and entrepreneur. He has tested security software since 2014.

Over the years, he has tested most of the best antivirus software for Windows, Mac, Android, and iOS, as well as many VPN providers.

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

This website is hosted on a Digital Ocean server via Cloudways and is built with DIVI on WordPress.

You can find him on LinkedIn or contact him here.

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