How Does a Firewall Work? Guide to Understanding Firewalls

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Firewalls are one of the most crucial tools in endpoint detection and protection (EDR) and network detection and protection (NDR) segments of the cybersecurity market.

There are many firewall offerings on the market, ranging in capability depending on the users, from individual users to small businesses and corporations.

A firewall is a network security tool that sits on the outer parameter of a computer network. It continuously monitors and scans incoming and outgoing network traffic between internal user devices, applications, databases, data centers, and third parties as well as the public internet connection.

The firewall software and hardware can be configured by the network admin to filter out and block network traffic that meets previously set criteria that are defined by the network security and privacy policies.

But what makes a firewall work, what’s involved with setting one up, and what’s the outcome?

How does a firewall work: Firewall technology

At its core, a firewall is packet inspection software. All traffic entering or exiting the protected network is monitored and scanned by the firewall — whether it’s software or hardware. Each packet of information is inspected to check whether its contents match those of previously known threats or if they don’t meet the criteria set by the network admin for authorized traffic.

The first application of firewall technology was in the 1980s. Since then, the technology making up the average firewall solution has evolved to keep up with more sophisticated cyberattacks and threats as well as the privacy and security requirements of organizations using it.

The following technologies can sometimes be found within their own dedicated cybersecurity and networking solutions. But they’re also available in most modern firewall offerings:

Machine learning and artificial intelligence

Machine learning (ML) and artificial intelligence (AI) algorithms can be integrated with the firewall’s software, enabling it to make smart and intuitive decisions regarding incoming and outgoing network traffic. 

ML and AI are especially present in next-generation firewalls (NGFW), allowing them to better determine whether incoming traffic contains a threat and if outgoing traffic is unauthorized and constitutes a data leak.

Network behavioral analysis

Behavioral analysis in firewalls is the combination of ML, AI, and big data analytics from logs the firewall gathered, in addition to previous training data by the firewall provider. This enables firewalls to detect unknown, concealed, and zero-day attacks launched at a network by analyzing the behavior preceding the attack and predicting it before it occurs.

Behavioral analysis can also be employed to mitigate insider attacks and data leaks by detecting unauthorized employee access to applications and databases as well as the transferring of massive amounts of data to a source outside the network.


Sandboxing technology can act as a fail-safe in case a piece of code or file entering the network wasn’t immediately detected as malicious. It enables a firewall to execute suspected files and code in an isolated environment, allowing it to observe and analyze the results.

Anything malicious would be immediately blocked without coming into contact with the internal components of your network, while legitimate commands proceed past the firewall.

Network admission and bandwidth control

Network admissions control, sometimes referred to as network access control, is a centralized management feature that lets network admins freely restrict, limit, or free the availability of network resources and bandwidth for various user devices, including access to any devices, applications, or sites outside the network.

This allows for the optimization of bandwidth and network resources, avoiding cases of overloading systems.

See more: How Firewalls are Used by Deakin University, Black Box, Palo Alto Networks, Modis, and Keysight: Case Studies

Setting up a firewall environment

Network security systems need to be aligned with the network’s architecture, from user devices to applications, and require access to internal databases and external resources. The same applies to firewall software and hardware. Here are a few key steps teams need to take to set up their environment for a firewall.

1. Securing the firewall

Whatever firewall software or hardware a team is using, make sure it’s up-to-date and capable of handling the number of devices and applications within the primary network.

The administrative capabilities and access authorities of the firewall are the most critical. Access should be limited to the assigned network administrators, each with unique login credentials.

2. Set up firewall-protected zones

Network resources a team is looking to protect should be divided into zones that vary according to the degree of security they need and the average level of access they need to support on a regular basis. 

The more zones a team has, the more flexibility they’ll have for securing each group of resources. However, that also increases the amount of work that goes into the firewall setup. Every zone would require setting up its own corresponding IP address, allowing it to communicate with other network parts internally as well as outside of it.

3. Access control configuration

After setting up secure zones and giving the needed access to the network admins, access control configurations should also be put in place for user devices and applications. Access permissions shouldn’t exceed what’s absolutely necessary, with temporary access permissions given out when needed.

4. Setting up firewall configurations

Most modern firewall software comes equipped with a number of additional tools and capabilities, such as logging, IP address management, virtual private network (VPN), and voice over internet protocol (VoIP) support.

Any activated service should be fully configured to meet the network’s security and privacy standards. Additionally, the team should disable any service they’re not looking to run in the firewall.

5. First-time firewall testing

Rigorously testing the firewall is the best way to find any gaps in configurations and ensure it’s performing up to standard. A team should verify the firewall’s ability to reliably block unwanted incoming traffic and unauthorized outgoing network traffic; the result should match up with their previously-set access control list (ACL) configurations.

6. Scheduling regular checkups

Firewall software must always be finely tuned to the needs of the network and the possible cyberthreats from outside. Furthermore, running tests at regular time intervals is also essential to ensure the firewall is still performing up to standard and up to date with the latest security capabilities.

See more: Why Firewalls are Important for Network Security

Core purpose and functions of firewalls

Firewalls were created to protect networks of devices and the data they regularly access. Any additional functionality that evolved over the years aided in making the firewall’s core purpose more effective, especially in a cyber world with growing threats and types of attacks.

Its ability to manage and protect the outer parameters of a network, spanning from personal devices to the many devices, applications, and databases of corporations, makes a firewall a solution, in particular, for a network seeking access to the public internet without sacrificing the security and privacy of its data.

While capabilities vary depending on the firewall solution, the following are some of the key functions of firewalls:

  • Network threat prevention
  • Network access verification
  • Resource optimization
  • Eliminating unauthorized user behavior
  • Network traffic and bandwidth management
  • Tracking and logging network user activity

See more: What is a Firewall? Definition & Ultimate Guide to Getting Started


How a firewall works relies heavily on the features available within each individual firewall offering. A firewall is a network security tool that focuses on monitoring and protecting the parameters of a network by controlling which data traffic can come in and which can leave.

Understanding the potential features of a firewall offering, such as next-gen functionality, allows a team to select the most appropriate solution for how to secure their network’s infrastructure and resources. Furthermore, the setup and installation of a firewall solution can be as critical as choosing a solution in the first place.

Anina Ot
Anina Ot
Anina Ot is a contributor to Enterprise Storage Forum and Datamation. She worked in online tech support before becoming a technology writer, and has authored more than 400 articles about cybersecurity, privacy, cloud computing, data science, and other topics. Anina is a digital nomad currently based in Turkey.

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