What Is a Firewall? Protecting Against Cyber Attacks

What Is A Firewall

You can think of a firewall as an imaginary wall with a thick steel door that regulates the incoming and outgoing network traffic of a trusted internal network. Only traffic that abides by the network’s predefined set of strict security rules can enter or leave through the “steel door.”

To put it in simpler terms, a firewall establishes a barrier between a trusted internal network and untrusted external networks, like the internet — the last thing you need is to allow a cybercriminal unregulated access to your network!

The next-generation firewall (NGFW) industry is worth billions of dollars, and network security devices are a must-have for personal and professional use.

You must take all necessary steps to safeguard yourself against cyber attacks. The most basic of these include purchasing a robust antivirus and firewall, setting up bulletproof passwords, avoiding clicking on scammy links and attachments, and only accessing HTTPS websites.

Read on to learn how firewalls fight fire with fire!

How Firewalls Work

Firewalls monitor and filter data that enters or leaves your network or device (your computer system should be firewall-protected). Let’s explore how they work at an elementary level and their types.

PS We recommend installing a third-party firewall on your smartphone as well.

Basic Operation

Firewalls filter data packets based on the predetermined security rules in their table; if an incoming packet matches any of the rules, entry into the network will be permitted.

Simplified diagram of how firewalls work
This is the basic operation of a firewall.

These rules are ordered as access control lists (ACLs) — they consist of a default policy (actions: accept, reject, or drop) followed by a list of parameters or conditions traffic must meet for the action to go through.

If parameters or conditions aren’t defined for that particular instance, the action will go through by default. Remember to program your firewall to “deny by default” to ensure top-notch cybersecurity.

Types of Firewalls

There are numerous types of firewalls, the most popular of which are packet filtering firewalls, stateful inspection firewalls (AKA dynamic packet filtering), proxy service firewalls (AKA application-level gateways), and next-generation firewalls (so long, traditional firewalls!).

  • Packet filtering firewalls: A packet filtering firewall controls network access by monitoring incoming and outgoing data packets on the basis of incoming and outgoing IP addresses, port numbers, and protocols like TCP, UDP, and ICMP.
  • Stateful inspection firewalls: A stateful inspection firewall combines packet filtering with contextual information about active connections. It keeps a record of each connection’s state by tracking characteristics like source/destination IP addresses and port numbers and makes informed decisions accordingly.
  • Proxy service firewalls: A proxy service firewall operates at the application layer and sits between an internal network and the internet, isolating the former from the latter. It applies strict filtering rules to ensure malicious content from an application can’t enter the network.
  • Next-generation firewall (NGFW): An NGFW combines several advanced functionalities, like SSL/SSH inspection, application inspection, and deep packet inspection, to protect a network from modern cyber threats. Palo Alto Networks, Fortinet, and Check Point are some of the best NGFW vendors.

To check which firewall is installed on your computer system, navigate to Settings and type “Firewall” in the search query. I use a software firewall called Windows Defender Firewall on my laptop, for example (included by default).

Categories of Firewalls

Now, the types of firewalls above can be packaged into a physical network security device (a hardware firewall), software (a software firewall), or a firewall-as-a-service solution (a cloud-based firewall).

Windows Defender Firewall, for example, is a software firewall that’s included with Windows operating systems (OSes).

Hardware Firewalls

hardware firewall illustration

If you can afford to purchase a hardware firewall for your organization, go for it. However, a firewall-as-a-service (FWaaS) solution may entice you.

It’s a dedicated appliance that acts like a gatekeeper, regulating traffic between network devices and the internet.

It includes capabilities like packet filtering, basic or advanced packet inspection, network perimeter defense, and additional security features like intrusion prevention (IPS) and antivirus protection.

Software Firewalls

software firewall illustration

Software firewalls are applications installed on individual devices like computer systems, network servers, and smartphones to monitor and control traffic.

Like hardware firewalls, they inspect data packets to see whether they fit the profile of malicious code — if all is clear, the data packet is permitted to enter or exit the device.

Some firewalls provide provisions for the latter to ensure you can’t harm others.

Cloud-Based Firewalls

cloud-based firewall illustration

As the name suggests, cloud-based firewalls are hosted in the cloud and delivered as a software-as-a-service (SaaS) solution.

They can deliver the capabilities of a hardware firewall or a software firewall and can operate in any cloud setup (private, public, or hybrid).

They’re advantageous as they’re easy to deploy, highly scalable, guarantee high availability, and provide identity protection.

Features of Effective Firewalls

You can’t use a traditional firewall solution on a PC and expect the best-in-class features. Unfortunately, Windows Defender Firewall is a traditional firewall and not the best solution around.

It has limited functionality and capacity, no traffic inspection, and low security. Listed are the features you should expect from an effective firewall (especially in a professional environment).

  • Access control: Using a firewall, you can define and enforce security policies to determine which users, devices, or IP addresses can access network resources. As stated earlier, the “deny by default” approach is the modern way.
  • Threat detection and prevention: An NGFW typically offers numerous features for identifying and mitigating various types of cyber threats, including signature-based detection, heuristics-based detection, sandbox-based detection, and layer 7 protocol analysis.
  • Logging and reporting: Firewalls store detailed logs and reports (numerous formats are available for this) of all network activity for monitoring and analysis. They’re valuable resources for compliance purposes, security analysis, and troubleshooting.
  • Scalability: By employing a cloud-based firewall you can take advantage of unrestricted scalability to meet increasing network demands. The firewall adapts to these demands and automatically scales resources to maintain peak system performance.
  • Ease of management: User-friendly interfaces and automation options make managing a firewall a breeze. Using a centralized firewall interface, you can manage access control, optimize firewall rules, change control systems, and integrate other security tools. The larger the network perimeter, the more difficult firewall management gets, though.

If you administer a business IT network, we recommend switching to a cloud-based NGFW as soon as possible. We’re in a cloud-first reality, and cloud firewalls easily integrate with existing cloud environments.

They’re also cost-effective, easy to deploy and manage, and feature-rich.

Common Firewall Configurations

A firewall is like the eight pawns on a chessboard — the first line of defense against the enemy.

Configuring firewalls for your organization may seem intimidating so we recommend dividing this into simpler tasks: network perimeter security, internal segmentation, and host-based security.

Network Perimeter Security

Using firewalls to protect the network edge is crucial, as these endpoints (PCs, modems, and adapters) serve as connection points between the internal network and the internet.

While the devices benefit from being closer to the data source, cybercriminals can exploit the slightest of network vulnerabilities to gain access and create havoc.

Strategically placing firewalls at the edge to monitor data packets in real time and prevent threats is of the essence.

Internal Segmentation

By segmenting an enterprise network into internal zones and setting up a firewall for each zone, you can minimize the attack surface even if a cyber attacker gains access to one.

For example, it makes little sense for the finance department to share the same firewall with the human resource department.

Each of these departments has valuable resources and through firewall segmentation, you can protect critical assets even if one of these zones has been compromised.

Host-Based Security

Host-based security is a critical component of enterprise security monitoring. Installing firewalls on individual devices like computers, servers, routers, and switches is a must for targeted protection — set them up properly for maximum efficiency.

Combine host-based firewalls with enterprise-level antivirus solutions and other valuable enterprise security technologies for layered protection.

Benefits and Limitations of Firewalls

Firewalls aren’t perfect and have certain limitations. You need to find ways to address them, as a firewall is a must-have in your security toolkit.

Let’s commence proceedings on a cheerier note, though — here are the benefits of firewalls.


Even if your business uses technology sporadically (a small grocery store with a single computer, for example), you must be proactive to be on the safer side.

A network firewall monitors network traffic, stops virus attacks, prevents hacking, stops spyware, and promotes privacy.

  • We create and consume tons of data daily. Incoming data, in particular, can be a threat and compromise business operations. Firewalls provide enhanced security and protection against unauthorized access (so long, cybercriminals!).
  • Firewalls leverage pre-defined rules and filters to monitor and control network traffic and keep your systems protected.
  • Through firewalls, you can build an environment of trust with your customers by ensuring that their data is safe in your hands. While data is regularly stolen from companies, your reputation will be severely damaged if customers learn you could have taken certain steps to avoid the intrusion.
  • Firewalls also help you remain compliant with security regulations.

Network firewalls have been around for more than 40 years, with traditional firewalls paving the way for NGFWs.

Firewalls are versatile, have simple infrastructure, offer multi-layered protection, provide updated threat protection, and promote consistent network speed — they offer countless benefits.


Unfortunately, firewalls (traditional firewalls, in particular) aren’t flawless and come with drawbacks. These limitations can compromise your security (surprise, surprise) and strain resources.

  • Firewalls can’t protect against all types of cyber threats. While it’s obvious why a firewall can’t stop social engineering, it should do a better job fighting phishing — criminals can sometimes work around firewalls.
  • Imagine managing firewall rules and filters across a major network! You must have a firm grip on security rules, which may require significant resources and expertise to operate effectively.
  • Overly strict or improper policy rules could have damaging consequences. Legitimate traffic could be blocked (false positives), and illegitimate traffic could be granted network access (hello, cyber attacks and malware!).

Having a firewall is infinitely better than not having one at all. Carefully tune firewall configuration settings to balance access needs and security — a small mistake could compromise everything.

Setting Up and Managing a Firewall

Don’t just purchase the first firewall product that appears when you Google “best NGFW solutions.”

Clearly define the organization’s requirements (type, performance, compliance, and specifications), simulate potential firewall products to verify their effectiveness, and select the best one.

Initial Setup

After you have physically installed the firewall, it’s time to configure firewall rules and policies based on IP addresses, port numbers, and protocols.

You should thoroughly test configurations before deployment, including advanced features like intrusion prevention and web category filtering.

Next, establish your network zone structure to set up access controls and permissions. Please test and audit your firewall before deployment.

Ongoing Management

Your job doesn’t end when you deploy the firewall. You must regularly monitor and update rules and policies, monitor logs and alerts in real time, and conduct periodic security audits.

Doing so helps you prevent failure, aid recovery and incident response, and avoid false negatives and illegitimate traffic access.

You can assure compliance through regular security audits to verify rules and policies and check firewall logs.

Advanced Firewall Features

A basic firewall monitors, filters, and controls network traffic. It has limited filtering capabilities (based on specific ports, IP addresses, and web addresses only) and simple rule sets. It lacks granularity and can’t effectively detect malicious activity or advanced threats.

Advanced firewalls (like NGFWs), on the other hand, offer advanced capabilities like application-level scanning, enhanced threat detection, intrusion prevention, and content filtering.

Basic FirewallsNext-Gen Firewalls
No application awarenessCan set unique rules for different applications
No intrusion preventionSupport intrusion prevention
Traditional packet filteringDeep packet filtering
Rules are set by systems administratorsRules enhanced by threat intelligence
Work from Layers 1 – 4Work from Layers 2 – 7

Choose an advanced firewall for peace of mind.

Stateful Inspection and Deep Packet Inspection

The key features of stateful inspection include connection tracking, context monitoring, and, you guessed it, packet inspection.

Unfortunately, its scope of “inspection” is limited to packet header information like IP addresses, the port number, and the protocol version.

Deep packet inspection (DPI) provides a more comprehensive data analysis within a packet as it goes beyond its header. It also provides enhanced protection and can detect malware.

Intrusion Prevention Systems

An intrusion prevention system (IPS) is like a second set of more robust pawns behind a firewall (remember the pawn analogy?) — it serves as a second line of defense.

Intrusion prevention systems use advanced threat detection mechanisms to identify and stop attacks. They intercept malicious content and dangerous connections that have managed to bypass the network firewall and terminate them.

Web Application Firewalls

A web application firewall (WAF) is all about Hypertext Transfer Protocol (HTTP) traffic.

It protects web applications and APIs from attacks and vulnerabilities like file inclusion, SQL injections, and cross-site scripting (XSS) by monitoring, filtering, and blocking HTTP traffic traveling to and from a web app.

Basically, it acts like an invisible shield between a web app and the internet.

Next-Generation Firewall Technologies

The cream of the crop is next-generation firewall technologies.

NGFWs include all standard firewall capabilities (like stateful inspection), intrusion prevention, threat intelligence sources, application awareness and control, and leading security techniques to defend against the evolving cybercrime space.

Pro tip: Palo Alto, Fortinet, Check Point, Barracuda, and Cisco offer some of the best NGFWs around, so take them for a spin.

Why Firewalls Are a Vital Security Tool

Purchasing and deploying a network firewall is the first step toward protecting your PC or internal network. A computer system without a firewall is like a house without a door — a criminal could walk in unannounced.

While setting up a consumer-level firewall is relatively easy, a successful enterprise-level deployment requires mindful design, implementation, and maintenance. Failure to do so may lead to a compromised network, defeating the purpose of employing a firewall in the first place.

We recommend watching firewall setup tutorials and reading detailed configuration guides to avoid typical errors — a small mistake could cost you dearly.

We expect hybrid mesh firewalls to be the talk of the town soon and artificial intelligence (AI) and machine learning (ML) to take center stage in firewall technology evolution.

Cyber attacks are getting more devastating, and while firewall technology is evolving slower than the cybercrime industry, solutions that take advantage of AI/ML will hopefully defend better than existing ones.