What Is a Firewall and Why Is It Vital?

With the increasing number of cybercrimes with every passing day, individuals and companies must secure their information. However, there are many challenges to implementing the same. A firewall is one such security device that can help you safeguard your network and device from an outsider. In this tutorial on ‘what is a firewall’, you will learn all you need to know about a firewall and how it acts as a shield to protect your network.

Now, let’s start by understanding what is firewall

What Is Firewall?

Firewalls prevent unauthorized access to networks through software or firmware. By utilizing a set of rules, the firewall examines and blocks incoming and outgoing traffic.

Fencing your property protects your house and keeps trespassers at bay; similarly, firewalls are used to secure a computer network. Firewalls are network security systems that prevent unauthorized access to a network. It can be a hardware or software unit that filters the incoming and outgoing traffic within a private network, according to a set of rules to spot and prevent cyberattacks. 

Firewalls are used in enterprise and personal settings. They are a vital component of network security. Most operating systems have a basic built-in firewall. However, using a third-party firewall application provides better protection.

Now that we have understood what is firewall, moving forward we will see the history of firewalls.

History of Firewall

Network firewalls have evolved over the years to address several threats in the security landscape. Firewalls will remain crucial to organizations and society. So, let’s look at a brief history of firewalls. 

  • 1989 - Birth of packet filtering firewalls
  • 1992 - First commercial firewall DEC SEAL
  • 1994 - First of the stateful firewalls appear
  • 2004 - IDC coins the term UTM (unified threat management)
  • 2009 - Next Generation Firewall (NGFW) was introduced by Gartner

Now that you know the what is firewall and its history, let’s dive deeper into understanding how a firewall works. 

Why Are Firewalls Important?

Firewalls are designed with modern security techniques that are used in a wide range of applications. In the early days of the internet, networks needed to be built with new security techniques, especially in the client-server model, a central architecture of modern computing. That's where firewalls have started to build the security for networks with varying complexities. Firewalls are known to inspect traffic and mitigate threats to the devices.   

Key Uses of Firewalls

  • Firewalls can be used in corporate as well as consumer settings.
  • Firewalls can incorporate a security information and event management strategy (SIEM) into cybersecurity devices concerning modern organizations and are installed at the network perimeter of organizations to guard against external threats as well as insider threats. 
  • Firewalls can perform logging and audit functions by identifying patterns and improving rules by updating them to defend the immediate threats.
  • Firewalls can be used for a home network, Digital Subscriber Line (DSL), or cable modem having static IP addresses. Firewalls can easily filter traffic and can signal the user about intrusions. 
  • They are also used for antivirus applications. 
  • When vendors discover new threats or patches, the firewalls update the rule sets to resolve the vendor issues.
  • In-home devices, we can set the restrictions using Hardware/firmware firewalls.

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Functions of Firewall

  • The most important function of a firewall is that it creates a border between an external network and the guarded network where the firewall inspects all packets (pieces of data for internet transfer) entering and leaving the guarded network. Once the inspection is completed, a firewall can differentiate between benign and malicious packets with the help of a set of pre-configured rules.
  • The firewall abides such packets, whether they come in a rule set or not, so that they should not enter into the guarded network. 
  • This packet form information includes the information source, its destination, and the content. These might differ at every level of the network, and so do the rule sets. Firewalls read these packets and reform them concerning rules to tell the protocol where to send them. 

How Does a Firewall Work?

As mentioned previously, firewalls filter the network traffic within a private network. It analyses which traffic should be allowed or restricted based on a set of rules. Think of the firewall like a gatekeeper at your computer’s entry point which only allows trusted sources, or IP addresses, to enter your network. 

A firewall welcomes only those incoming traffic that has been configured to accept. It distinguishes between good and malicious traffic and either allows or blocks specific data packets on pre-established security rules. 

These rules are based on several aspects indicated by the packet data, like their source, destination, content, and so on. They block traffic coming from suspicious sources to prevent cyberattacks. 

For example, the image depicted below shows how a firewall allows good traffic to pass to the user’s private network.


Fig: Firewall allowing Good Traffic

However, in the example below, the firewall blocks malicious traffic from entering the private network, thereby protecting the user’s network from being susceptible to a cyberattack.


Fig: Firewall blocking Bad Traffic

This way, a firewall carries out quick assessments to detect malware and other suspicious activities.

There are different types of firewalls to read data packets at different network levels. Now, you will move on to the next section of this tutorial and understand the different types of firewalls.

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Types of Firewalls

A firewall can either be software or hardware. Software firewalls are programs installed on each computer, and they regulate network traffic through applications and port numbers. Meanwhile, hardware firewalls are the equipment established between the gateway and your network. Additionally, you call a firewall delivered by a cloud solution as a cloud firewall.

There are multiple types of firewalls based on their traffic filtering methods, structure, and functionality. A few of the types of firewalls are:

  • Packet Filtering

A packet filtering firewall controls data flow to and from a network. It allows or blocks the data transfer based on the packet's source address, the destination address of the packet, the application protocols to transfer the data, and so on.

  • Proxy Service Firewall

This type of firewall protects the network by filtering messages at the application layer. For a specific application, a proxy firewall serves as the gateway from one network to another. 

  • Stateful Inspection

Such a firewall permits or blocks network traffic based on state, port, and protocol. Here, it decides filtering based on administrator-defined rules and context. 

  • Next-Generation Firewall

According to Gartner, Inc.’s definition, the next-generation firewall is a deep-packet inspection firewall that adds application-level inspection, intrusion prevention, and information from outside the firewall to go beyond port/protocol inspection and blocking.

  • Unified Threat Management (UTM) Firewall

A UTM device generally integrates the capabilities of a stateful inspection firewall, intrusion prevention, and antivirus in a loosely linked manner. It may include additional services and, in many cases, cloud management. UTMs are designed to be simple and easy to use.

  • Threat-Focused NGFW

These firewalls provide advanced threat detection and mitigation. With network and endpoint event correlation, they may detect evasive or suspicious behavior.

Advantages of Using Firewalls

Now that you have understood the types of firewalls, let us look at the advantages of using firewalls. 

  • Firewalls play an important role in the companies for security management. Below are some of the important advantages of using firewalls.
  • It provides enhanced security and privacy from vulnerable services. It prevents unauthorized users from accessing a private network that is connected to the internet.
  • Firewalls provide faster response time and can handle more traffic loads.
  • A firewall allows you to easily handle and update the security protocols from a single authorized device.
  • It safeguards your network from phishing attacks.

How to Use Firewall Protection?

To keep your network and devices safe, make sure your firewall is set up and maintained correctly. Here are some tips to help you improve your firewall security:

  • Constantly update your firewalls as soon as possible: Firmware patches keep your firewall updated against any newly discovered vulnerabilities.
  • Use antivirus protection: In addition to firewalls, you need to use antivirus software to protect your system from viruses and other infections.
  • Limit accessible ports and host: Limit inbound and outbound connections to a strict whitelist of trusted IP addresses. 
  • Have active network: To avoid downtime, have active network redundancies. Data backups for network hosts and other critical systems can help you avoid data loss and lost productivity in the case of a disaster.

Application Layer and Proxy Firewalls

Proxy firewalls can protect the application layer by filtering and examining the payload of a packet to distinguish valid requests from malicious code disguised as valid requests for data. Proxy firewalls prevent attacks against web servers from becoming more common at the application layer. Besides, proxy firewalls give security engineers more control over network traffic with a granular approach.  

On the other hand, application layer filtering by proxy firewalls enables us to block malware, and recognize the misused amongst various protocols such as Hypertext Transfer Protocol(HTTP), File Transfer Protocol (FTP), certain applications, and domain name system(DNS).  

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The Importance of NAT and VPN

NAT and VPN are both basic network translation functions in firewalls.

  • Nat (Network Address Translation)
  • It hides or translates internal client or server IP addresses that are usually in a “private address range”. It is defined in RFC 1918 as a public IP address.
  • NAT preserves the limited number of IPv4 addresses and also defends against network reconnaissance as the IP address from the Internet is hidden.
  • VPN (Virtual Private Network)
  • VPN is used to extend a private network across a public network inside a tunnel that can be often encrypted. However, the contents inside the packets are protected especially when they are traversing the Internet. 
  • VPN enables users to safely send and receive data across shared or public networks.

Next Generation Firewalls (NGFW)

Next-Generation Firewalls are used to inspect packets at the application level of the TCP/IP stack, enabling them to identify applications such as Skype, or Facebook and enforce security policies concerning the type of application. Next-Generation Firewalls also include sandboxing technologies, and threat prevention technologies such as intrusion prevention systems (IPS), or antivirus to detect and prevent malware and threats in the files. 


  • Insider Attacks

Insider attacks involve activities such as the transmission of sensitive data in plain text, resource access outside of business hours, sensitive resource access failure by the user, third-party users' network resource access, etc.

  • Distributed Denial of Service (DDoS) Attacks

Distributed denial of service (DDoS) attack is a malicious attempt to disrupt normal traffic of a targeted network by overwhelming the target or its surrounding infrastructure with a flood of traffic. The DDoS attack is used to mitigate the difference between an attack and normal traffic. Nevertheless, the traffic in this attack type can come from seemingly legitimate sources that require cross-checking and auditing from several security components.

  • Malware

Malware threats are usually difficult due to their varied, complex, and constantly evolving nature. These days, with the rise of IoT, networks are becoming more complex and dynamic so that sometimes it becomes difficult for firewalls to defend against malware.

  • Patching/Configuration

Patching/Configuration is a firewall with a poor configuration or a missed update from the vendor that may damage network security. Thus, IT admins need to be very proactive concerning their maintenance of security components.

The Future of Network Security

In the last few years, virtualization and trends in converged infrastructure created more east-west traffic and the largest volume of traffic in a data center is moving from server to server. Some enterprise organizations have migrated from the traditional three-layer data center architectures to various forms of leaf-spine architectures in order to with this change. This change in architecture made some security experts warn that firewalls have an important role to play to keep the network secure in a risk-free environment. Thus, the importance and future of firewalls have no end. However, there may be many advanced alternatives to firewalls in the future. 

Difference Between a Firewall and Antivirus


  • A firewall is essential software or firmware in network security that is used to prevent unauthorized access to a network. 
  • It is used to inspect the incoming and outgoing traffic with the help of a set of rules to identify and block threats by implementing it in software or hardware form. 
  • Firewalls can be used in both personal and enterprise settings, and many devices come with one built-in, including Mac, Windows, and Linux computers.


  • Antivirus is also an essential component of network security. It is basically an application or software used to provide security from malicious software coming from the internet. 
  • An antivirus working is based upon 3 main actions, Detection, Identification, and Removal of threats. 
  • Antivirus can deal with external threats as well as internal threats by implementing only through software. 

Limitations of a Firewall

  • Firewalls are not able to stop the users from accessing the data or information from malicious websites, making them vulnerable to internal threats or attacks.
  • It is not able to protect against the transfer of virus-infected files or software if security rules are misconfigured, against non-technical security risks (social engineering)
  • It does not prevent misuse of passwords and attackers with modems from dialing in to or out of the internal network.
  • Already infected systems are not secured by Firewalls. 
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1. What is Firewall?

A firewall is a network security device that analyses network traffic entering and leaving your network. It permits or denies traffic based on a set of security rules.

2. How is Firewall Useful In Network Security?

A firewall is a security mechanism that prevents unwanted access to private data on your network. Firewalls also protect systems from harmful malware by establishing a barrier between trusted internal networks and untrusted external networks.

3. What Is The Difference Between Firewall And Network Security?

A firewall may protect both software and hardware on a network, whereas an antivirus can protect other software as an impartial software. A firewall prevents harmful software from accessing the system, whereas antivirus software removes corrupt files and software from your computer and network.

4. How does the firewall work?

A firewall protects your network by acting as a 24/7 filter, examining data that seeks to enter your network and blocking anything that appears suspect.

5. What Is The Purpose of a Firewall?

Firewalls defend your computer or network from outside cyber attackers by filtering out dangerous or superfluous network traffic. Firewalls can also prevent harmful malware from gaining access to a computer or network through the internet.

6. What are the 3 types of firewalls?

Depending on their construction, firewalls can be classified as software firewalls, hardware firewalls, or both. Each sort of firewall serves a distinct purpose but has the same functionality. However, it is best practice to have both for optimal protection.


In this tutorial on what is a firewall, you have understood what a firewall is and how it works. You also learned the different types of firewalls and how to use a firewall. Cybersecurity is a booming field in today's times. If you are looking to learn ethical hacking to protect devices and networks from cybercriminals. In that case, Simplilearn's CEH v11 - Certified Ethical Hacking Course will help you master advanced network packet analysis and penetration testing techniques to build your network security skill-set.

Do you have any questions on this tutorial on ‘what is a firewall’? If you do, please drop them in the comments section. We will help you solve your queries at the earliest. 

About the Author

Chinmayee DeshpandeChinmayee Deshpande

Chinmayee is a Research Analyst and a passionate writer. Being a technology enthusiast, her thorough knowledge about the subject helps her develop structured content and deliver accordingly.

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