What is a Firewall? What Does It Do?

In today's world, where data has become the lifeblood of businesses, the need for robust cybersecurity measures is no longer optional, but a necessity. In an environment of constantly evolving cyber threats, firewalls serve as a powerful shield, successfully defending against numerous malicious attacks. By tirelessly filtering incoming and outgoing traffic, they create a barrier against unauthorized access, malware infections, and service attacks. Essentially, they allow non-threatening traffic to enter while keeping dangerous traffic out.

Next-generation firewalls can swiftly and seamlessly detect and respond to external threats across the entire network. Moreover, they can establish policies for a more effective defense strategy, rapidly identifying and shutting down malicious or suspicious activities and malware. Firewalls that can work with an integrated intrusion prevention system (IPS) aim to inspect and verify all data packets in network traffic before allowing them into a more secure environment. This system, which will be useful at nearly every point of your digital activity, is worth exploring further.

What is a Firewall?

Also known as a network security firewall, a firewall is a security system designed to prevent unauthorized access to a computer network. It is often used to ensure that unauthorized internet users cannot interface with private networks or intranets connected to the internet. When a network or computer is linked to another network, such as the internet, the firewall monitors and controls the traffic entering and leaving the network. Without a firewall, almost any data could exit a computer or network, and anyone or any program could easily gain access.

A firewall can come in various forms, such as physical hardware, digital software, a software service (SaaS), or a virtual private cloud. Considered a crucial component of network security, this system is used in both personal and corporate environments. Many devices, including Windows, Linux, and Mac systems, come with a built-in firewall. Most organizations use firewall systems that are integrated with cybersecurity devices and include a security information and event management (SIEM) strategy. Firewalls that work alongside antivirus programs provide comprehensive protection.

How Does a Firewall Work?

In the physical world, a firewall is a tool designed to prevent the spread of a fire. This physical barrier can significantly minimize the damage caused by flames. So, how does a firewall work in the digital world to protect a network?

In computer networks, a firewall is a software or hardware tool designed to block unauthorized access to or from a private network. Firewalls monitor incoming and outgoing network traffic and decide whether to allow or block traffic based on a set of security rules. You can think of a firewall as a security guard at the entrance of a nightclub; it stands at the gate of corporate networks, applications, databases, and other resources, inspecting incoming and outgoing traffic to determine which data packets can pass through and which should be rejected.

What Does a Firewall Do?

The most critical function of a firewall is to create a boundary between the external network and the protected network, ensuring security. It inspects all data packets entering and leaving the protected network. After inspection, it can distinguish between benign and malicious actions based on pre-configured rules. Even if certain activities fall outside these rules, the firewall will alert and prevent them from entering the protected network. These activities involve the source, destination, and content of the information. Firewalls analyze these actions and reorganize them according to routing rules.

Major risks that network firewalls protect computers from include denial of service (DoS) attacks, macros, remote logins, backdoors, spam, and viruses. Backdoors are vulnerabilities in applications that attackers exploit to gain access. DoS attacks occur when a hacker requests access to a server, and the server responds, only to find that the requesting system is unreachable. Macros hide within seemingly innocent data and cause damage to systems once inside. In such cases, the firewall forms a barrier that checks whether connection requests are legitimate and protects the network.

Types of Firewalls

Firewalls can be either software- or hardware-based. Software firewalls are programs that can be installed on computers and regulate network traffic through port numbers. Hardware firewalls are devices installed between the gateway and the network. There is also cloud firewall, known as cloud security firewall. Additionally, various firewall types exist depending on traffic filtering methods, structures, and functions.

Packet Filtering

A packet-filtering firewall controls the flow of data between networks. Whether the data packet is allowed to pass is determined by factors like the source or destination address of the packet and the protocols the data will use.

Proxy Service

This type of firewall filters messages at the application layer to protect the network. It acts as a gateway between certain applications from one network to another.

Stateful Inspection

A stateful firewall allows or blocks traffic based on the state, port, or protocol of the network. You can define the rules and filtering preferences yourself.

Next-Generation Firewall (NGFW)

Next-generation firewalls offer more features beyond port/protocol control and blocking. They are known for strengthening the network with deep packet inspection, intrusion prevention, and control over information added outside the firewall.

Unified Threat Management (UTM)

UTM devices typically integrate stateful firewall, intrusion prevention, and antivirus features in a connected manner. These devices are designed to include additional services and often cloud-based management, making them simple and user-friendly.

Threat-Focused NGFW

A threat-focused NGFW allows you to add advanced threat detection and mitigation features to your firewall. This system correlates network and endpoint events, making it easier to detect evasive or suspicious behavior.

How to Set Up a Firewall?

There are four key steps to setting up a firewall system on any network.

1. We don’t want hackers accessing the firewall management system, so it’s wise to grant administrative access only to trusted individuals who really need it. Login credentials can then be secured with strong passwords, and users with limited privileges can be created.
2. After setting access controls, create multiple network zones by placing resources containing sensitive data deep within the network, where internet traffic is more restricted.
3. Configure and adjust rules to control network traffic. Traffic to different zones of the network is filtered according to various rules. Select the ‘Deny All’ setting to restrict any type of traffic outside of what is allowed by the ACL.
4. In the final step, test the firewall to verify that it blocks the traffic intended to be filtered by the rules configured in previous steps. A penetration test can be conducted to assess the strength of the firewall.

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