What is Firewall in a Computer network

The firewall is a computer program whose objective is to filter the elements arriving on an internal network; dive into post for more.

Updated: 30 Aug, 23 by Antoniy Yushkevych 21 Min

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 Even users who are less familiar with technology know the usefulness of antivirus for the electronic security of our computers. However, as far as a firewall's meaning is concerned, some users may be unaware of its necessity and the reasons for its existence. In this article, we will explain what is a firewall; we will introduce you to the concept of a firewall, its usefulness, and the basic items found on our computers.

If you were to ask what is firewall in a computer network, that is to say, a firewall network security is a device that monitors incoming and outgoing network traffic and allows or blocks data packets based on a set of security rules. It is responsible for creating a barrier between your internal network and incoming traffic from external sources (like the Internet) to block malicious traffic from viruses and hackers.

Furthermore, the simplest way to describe the firewall is to liken it to the prison guard at the entrance.

The duties of the firewall network are as follows:

  • Controls who enters and exits the building based on certain rules.
  • Prohibits entry or exit to specific persons
  • If he or she does not know about the entry or exit rights of a particular person, he/she consults his superiors on how to do so.

A firewall is a program, device, or set of devices that does this for our computer: it controls communication, downloading, or sending data from specific programs over a network.

Some programs have free access to send and receive data on the network (such as the browser, e-mail program, or the service for operating system updates).

Other programs, such as recognized malware, have denied access - for these programs, it's basically like there's no network.

Finally, because no firewall has rules for the millions of programs on the market, most "home" firewalls ask the user when a new, unknown program first tries to access the network. In this question, the firewall almost always has the option to remember the rule (yes or no that the user will answer) and not to ask again.

The firewall designation came from the special walls, designed to contain a fire in the event of an event and not allow it to spread to the rest of the building. Later, firewalls were named metal plates on cars and planes to separate the passenger space from the engine.

Firewalls, especially next-generation firewalls, focus on blocking malware and application-layer attacks. With an integrated intrusion prevention system (IPS), these next-generation firewalls are able to react quickly and transparently to detect and combat attacks across the entire network.

Firewalls can act on previously defined policies to better protect your network and can perform quick assessments to detect invasive or suspicious activity, such as malware, and stop it. Using a firewall for your security infrastructure, you configure your network with specific policies to allow or block inbound and outbound traffic. 

Furthermore, there are many more reasons to want to know which programs on our computer are communicating with the network.

  • There are programs called keyloggers, which, if they have compromised our system, record everything we write on the keyboard (possibly including passwords and credit card numbers) and send them automatically to a server.
  • There are also remote administration programs that allow someone to see everything we see on our screen and additionally take full control of our computer, even the keyboard, mouse, and power button.
  • It has appeared at least one virus that infects machines that do not have a firewall just because it finds them unprotected.

Not having a Firewall on the computer is like sleeping in a detached house with windows wide open. It used to be relatively safe, but these days, it's rather risky. It may not happen, but there's no reason to risk it. And, of course, as in the case of Windows, there is always the possibility of some malware disabling or bypassing our firewall. 

Therefore, we should be careful about what kind of programs we download and run on our computers - especially if we visit suspicious sites.

Firewalls carefully analyze incoming traffic according to pre-established rules and filter traffic from unsecured or suspicious sources to prevent attacks. It sits between the user, their applications and the internet connection. The administrator is responsible for defining the rules that will authorize or, on the contrary, prohibit certain accesses. Thus, when a connection is established, the firewall analyzes it and applies the current rules. Filtering is done at the IP, port or application level.

Be careful; if the rules are not clearly defined, some legitimate applications could be blocked!

Moreover, firewalls monitor traffic at a computer's entry point, called a port, where information is exchanged with external devices. For example, “The source address is allowed to reach the destination through port 22”.

Think of IP addresses as houses and port numbers as rooms in that house. Only trusted people (source addresses) can enter the house (destination address). There is then further filtering so that people in the house can only access certain rooms (destination ports), depending on whether it is the owner, a child or a guest. The owner can access any room (any port), while children and guests can access a certain set of rooms (specific ports).

Firewalls are divided into software and hardware. In plain language, Firewalls can be software or hardware, but it is better to have both. A software firewall is a program installed on every computer that regulates traffic through port numbers and applications. A physical firewall is an equipment installed between your network and the access gateway.

Packet filtering firewalls, the most common type, examine packets and deny them passage if they do not match an established set of security rules. This type of firewall checks the packet's source and destination IP addresses. If the packets match those of an "allowed" rule on the firewall, it is trusted to enter the network.

Packet filtering firewalls are divided into stateful and stateless categories (with or without status). Stateless firewalls examine packets independently of each other and lack context, making them easy targets for hackers. In contrast, stateful firewalls retain information about previously transmitted packets and are considered much more secure.

While packet-filtering firewalls can be effective, they provide very basic protection and can be limited. For example, they cannot determine whether the content of the request sent will hurt the application that she reaches. If a malicious request authorized from a trusted source address led, for example, to the deletion of a database, the firewall would have no way of knowing. Next-generation firewalls and proxy firewalls are better equipped to detect these threats.

Next-generation firewalls (NGFW) combine traditional firewall technology with additional features, such as inspection of encrypted traffic, intrusion prevention systems, antivirus, etc. In particular, they perform deep packet inspection (DPI, or deep packet inspection). While basic firewalls only examine packet headers, deep inspection examines the data within the packet itself, allowing users to effectively identify, classify, or shut down packets containing malicious data. Find more information about the NGFW Forcepoint here.

Proxy firewalls filter network traffic at the application level. Unlike basic firewalls, the proxy acts as an intermediary between two terminals. The client must send a request to the firewall, where it is evaluated against a set of security rules and allowed or blocked. Specifically, proxy firewalls monitor traffic for Layer 7 protocols such as HTTP and FTP and use stateful and deep packet inspection to detect malicious traffic.

Address Translation (NAT) firewalls allow multiple devices with independent network addresses to connect to the Internet using a single IP address while hiding individual IP addresses. Therefore, attackers scanning a network for IP addresses cannot capture specific details, ensuring greater security.

Software firewalls are programs that are installed on the computer in the same way that we install an antivirus to protect against viruses.

Advantages of a Software Firewall

  • It's cheaper than hardware firewalls
  • It is easier to set up and use
  • One can install a software firewall on a laptop that will be used anywhere.

Disadvantages of a Software Firewall

  • Protect only the computer on which they are installed, and multiple licenses are needed for multiple computers.
  • Consume power from processor and system memory
  • They have fewer options in their settings than hardware firewalls.

Hardware firewalls interfere with the computer or network and the Internet. Some better-quality routers have built-in hardware firewalls. 


  • A hardware firewall can protect an entire computer network
  • They have their processor and memory, so they do not burden the computer's resources at all
  • Hardware firewalls cannot be disabled by malware, as can be the case with software firewalls
  • Protect the system in whatever state the operating system is in - even if it is just installed
  • Some advanced Hardware firewalls include antivirus-antispyware protection


  • A hardware firewall costs more than a license for a software firewall.
  • Setting up hardware firewalls is more difficult and is aimed at more advanced users.
  • A hardware firewall is a machine that needs to be installed at a specific point and have access to power and the network.
  • If the firewall blocks a program, a message does not automatically appear on the user's computer; it should manually enter the firewall administrative system and allow it to function.
  • If a hardware firewall that protects an entire network of computers fails, all computers remain unprotected.
  • While there are some open-source or freeware firewall programs that are legally free, there is no corresponding solution for the hardware firewall.

In most cases, software firewalls are aimed at home users and hardware firewalls are aimed at businesses or large organizations with computer networks (schools, universities, public services, etc.).

As this article has an introductory tone of voice and is addressed to users unfamiliar with the technology, from now on, whenever we mention the firewall, we mean the software firewall.

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A next-generation firewall or Next-Generation Firewall (NGFW) is a security component that processes network traffic and applies rules to detect, alert and/or block potentially dangerous traffic. NGFWs evolve and push the capabilities of traditional firewalls for the better. They do everything traditional firewalls do, but more powerfully and with additional features. They have some super cool benefits for all of us that could even save small businesses from disaster.

Furthermore, next-generation firewalls inspect packets at the application level of the TCP/IP stack. They can identify applications such as Skype or Facebook and apply a security policy depending on the type of application.

Today, UTM (unified threat management) devices and next-generation firewalls include threat prevention technologies such as an intrusion prevention system (IPS) or antivirus to detect and stop malware and threats. These devices may also include sandboxing technologies to detect threats in files.

As the cybersecurity landscape continues to evolve and cyberattacks become more sophisticated, next-generation firewalls will remain an essential part of any enterprise's security solution, whether in the data center, networks or the Cloud. To learn more about the essential features that a Next-Generation Firewall should have, download the Next-Generation Firewall (NGFW) Buyer's Guide now.

Unlike the home router, the advantages of Next-Generation Firewalls are that they offer more visibility, robustness, flexibility and increased power to cybersecurity features.

Visibility is a big advantage to see and recognize activities and exchanges. This greatly helps decision-making to regulate access with rigour better to protect your network assets.

Interestingly enough, Controls are simplified as user interfaces continually improve.

The functionalities are greatly enhanced mainly by their Intrusion Detection and Prevention System (IDPS) modules.

The alerts are also super interesting. Detection features provide more visibility, including various alerts on activities that may be taking place. Once the activities are known, we can act by preventive controls for the future.

Another advantage of Next-Generation Firewalls is that their vendors offer more frequent and regular security updates, which is crucial for fixing vulnerabilities. Finally, their prices are more and more affordable.

The network layer or packet filters inspect packets at a relatively low TCP/IP protocol stack level, not allowing packets to pass through the firewall unless they obey the established rules. Where the source and destination of the rule set are based on Internet Protocol (IP) addresses and ports, firewalls that inspect the network layer perform better than those that inspect the application layer.

The disadvantage is that unwanted applications or malware can pass through authorized ports, for example, outgoing Internet traffic on the HTTP and HTTPS web protocols, respectively, on ports 80 and 443. 

Focus on WatchGuard

WatchGuard protects your bandwidth with URL filtering. Indeed, the establishment of traffic quotas reduces the risk of misuse of the web. This firewall ensures Quality of Service (QoS) through its comprehensive traffic management settings.

Let's take a concrete example to visualize the type of protection that a firewall could provide.

One of your employees received a fraudulent email containing a zip file. He opens this file and runs it, thinking it is legitimate. Unfortunately for him, this zip contains Trojan-type malware. Without protection, he could steal information from you. To interpret the code download and execute the virus, Windows needs to use wscript.exe.

Your administrator is known to be a far-sighted person and has previously created a rule that disallows outgoing connections on wscript.exe. There will, therefore, be no permission to connect to the site where the malicious program is hosted. Windows is, therefore, protected and will not be infected. Your business continues without a hitch, and your information is protected.

If you're still using a home router to protect your small business, then it might be time to reconsider and plan to leap to Next-Generation Firewalls (NGFW). It will give you a lot of benefits for your money, mainly for these functions of intrusion detection and prevention systems. With these latest features, you will gain visibility and detection.

It can even alert you in critical situations to help you avoid the worst scenarios of data exfiltration, data breaches and “Ransomware” extortion. In addition, the controls are much less technical and more understandable for all of us to make the changes sometimes necessary with simplicity. Be aware, of course, that the offer of features varies between firewall brands.

Overall, a firewall system does not protect you completely. Indeed, firewalls can be circumvented. For example, if connections are made from an internal network, using a modem or any other means of connection beyond its control. For better or worse, home firewall network security largely depends on the user's judgment. Users who uncritically press "yes" or "no" on what the firewall shows them are like young children who can open the door to anyone or, on the contrary, not open the door to their mother who forgot her keys.

If it is So Necessary, Why Does My Computer Not Already Have a Firewall?

It does. All Windows Vista, Windows 7, and Windows 10-based computers have Windows Firewall built-in, which is by default enabled.Of course, there are several who question its effectiveness. If you want a more flexible firewall with more features, you need to choose a third-party firewall, free or paid for.

Note that if you install a firewall, it is good to turn off the Windows firewall, not to run both simultaneously. To do this, in Windows 7, go to Control Panel -> System and Security and select the Windows Firewall.

Then, you'll find the option to turn it off on the left.

If I have an Antivirus, Why Have a Firewall?

Unfortunately, antivirus is only useful for malware recognized as a threat. If a virus that intercepts credit card details, for example, is very new, and the way it is manufactured does not resemble a known virus, Antivirus will not recognize it as a virus. Until Antivirus downloads the latest security updates from its company, it will let the virus act undisturbed on our system.

The firewall, however, is suspicious. If any new program tries to gain access to the internet - in our example, if the virus tries to send our credit card details to an external server - the firewall will immediately ask if we want to let that program communicate over a network. Our card details remain secure by answering "No" to this question.

So, with a Firewall, I Am Completely Safe, Even if I Do Not Have an Antivirus?

Antivirus and firewalls are two completely different products that serve different purposes. For example, if our system is infected with a virus that destroys Word files, the firewall will not detect or stop it, as it does not attempt to contact the network.

If my Antivirus is Internet Security, Do I Need a Firewall?

Most antivirus companies have products that identify them as Internet Security, which include antivirus and firewall in the same suite of applications. In this case, you do not need a separate firewall, as an internet security product already works.

So if I have antivirus and firewall or Internet Security, I'm completely safe, right?

Subject to conditions. Antivirus must be constantly updated with the latest security files to recognize all newer viruses. Regarding the firewall, you should be very careful when asking you to permit a program to access the network.

If you press "Yes" where you shouldn't, you'll let a malicious program communicate - so it's like you don't have a firewall for that particular problem.

Instead, if you press No to a question about a legitimate program, you'll block it from the network, and it won't work properly. For example, if it is the update program for your printer drivers, the program will not be able to communicate with the internet and download the latest version.

Essentially, all responsibility for the firewall's operation in a home environment falls more or less on the user.

How am I supposed to be sure if I have to press Yes or No?

When they ask permission for a program, most firewalls have some details option, which also shows the path of the program file.

For example, if the firewall asks about the C:\programfiles\HewlettPackard\HPupdat.exe, and recently you or a technician had installed the drivers for a Hewlett Packard device on your system, then 90% of that file is safe to access the internet.

On the contrary, if you do nothing, a screen appears that says that the file c:\Windows\Temp\23kjgskjg.js wants to access the network; logic says it is something malicious, so you must deny it access and make sure to delete it from your system as well.

The third case is to open a file that you believe is an image file or mp3 song and the firewall to detect that the program is requesting access to the internet. In this case, the image file or song you attempted to run is a camouflaged executable file with notoriously malicious code, so you still need to deny access and erase it as soon as possible from the system.

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Antoniy Yushkevych

Antoniy Yushkevych

Master of word when it comes to technology, internet and privacy. I'm also your usual guy that always aims for the best result and takes a skateboard to work. If you need me, you will find me at the office's Counter-Strike championships on Fridays or at a.yushkevych@monovm.com