What Is a Firewall and What Is It Used For?

A firewall, also known as a network security barrier, is a crucial component in the field of information security. It protects computer networks from unwanted traffic and malicious threats. In this article, we will take a detailed look at what a firewall is, the different types that exist, and how it works.

A firewall is a security system that controls incoming and outgoing network traffic. Its main purpose is to filter and block suspicious traffic, prevent intrusions, and protect against external threats. It can be either software-based or a hardware device.

A firewall operates based on preconfigured rules that determine which traffic is allowed and which should be blocked. For example, it can filter IP addresses, ports, and assess the threat level to block unwanted connections.

The primary function of a firewall is to provide protection against external and internal threats. It acts as a "shield" that inspects each incoming or outgoing connection and decides whether it should be allowed.

There are several types of firewalls, including:

• Packet filtering firewalls: These examine data packets based on IP addresses and port numbers.
• Software firewalls: These operate at the operating system level, protecting individual devices.
• Next-generation firewalls (NGFWs): These offer advanced functionalities, such as application filtering, traffic monitoring, and protection against sophisticated threats.

Firewalls can be divided into two main types: hardware and software. Each type has its own characteristics, advantages, and areas of application. Let’s take a closer look at them.

Hardware firewalls are devices installed between a corporate network and the external internet. They are typically used to protect large networks and enterprise systems. These firewalls are standalone physical devices that connect to the network and filter traffic at the entire network level.

Key Features of Hardware Firewalls:

• Power and Performance: Hardware solutions can usually handle much more traffic than software firewalls. This is especially important for large companies with high network loads.
• Network-Wide Protection: They protect the entire corporate network from external threats. All incoming and outgoing connections pass through the firewall, which inspects them for threats and blocks unwanted traffic.
• Centralized Management: For large organizations, having a centralized security management system is crucial. Hardware firewalls allow administrators to control network access and manage security policies from a single device for the entire network.
• Additional Features: Modern hardware firewalls often include features such as VPN (Virtual Private Network) support, application filtering, network traffic monitoring, antivirus protection, intrusion detection and prevention systems (IDS/IPS), and encryption support.

When to Use:

Hardware firewalls are best suited for organizations with a large number of devices and complex networks that require a high-performance security system. They are particularly beneficial for corporate networks, data centers, and companies handling sensitive information.

Software firewalls are solutions that are installed directly on devices such as personal computers, servers, or mobile devices. These firewalls are designed to protect against threats originating from the network. Software firewalls operate at the operating system level and control all incoming and outgoing traffic on the device.

Key Features of Software Firewalls:

• Personal Use: Software firewalls are often used by individual users to protect their computers, laptops, or servers. They help block unwanted connections and protect user data.
• Customization and Flexibility: They offer more flexible configuration options, as users can fine-tune rules for different programs and network connections. For example, traffic can be allowed for one application and blocked for another.
• Lower Network Load: Software firewalls impose less strain on the network since they operate only on a specific device. This can be useful for personal computers and small office networks.
• Less Resource-Intensive: Unlike hardware firewalls, software solutions do not require additional hardware resources and can run on existing devices.

When to Use:

Software firewalls are ideal for protecting personal devices or small to medium-sized servers. They are used to protect home users or small organizations where the need for entire network protection is not as critical.

Examples of Software Firewalls:

• Windows Firewall – a built-in solution for Windows operating systems.
• Comodo Firewall – a popular free solution for PC protection.
• ZoneAlarm – a firewall focused on protecting personal devices.

• Scalability: Hardware firewalls can provide protection for an entire network, whereas software firewalls operate only on a single device.
• Performance: Hardware firewalls have higher performance, making them suitable for handling large volumes of traffic. Software firewalls are limited by the power of the device they are installed on.
• Flexibility: Software firewalls offer more flexible configuration for protecting specific applications, while hardware solutions provide centralized security management for all connected devices.

Modern internet threats are becoming increasingly complex and sophisticated. Without a firewall, network-connected devices may be vulnerable to various types of attacks. A firewall is a crucial security measure that helps prevent numerous threats—malware, viruses, trojans, spyware, and even hacking attempts. All these threats can cause significant harm to both individual users and organizations.

One of the primary functions of a firewall is to protect against unauthorized access. The web is full of malicious actors looking for vulnerabilities to exploit in networks and devices. Without effective protection, hackers can infiltrate systems, gain access to sensitive data, and infect computers with viruses.

A firewall blocks access attempts from unknown IP addresses or devices trying to connect to your network without permission. It can use allowlists and blocklists, as well as analyze connection behavior to prevent attacks.

Example: If a cybercriminal attempts to infiltrate a network through an unused or vulnerable port, the firewall will immediately block the request. The firewall serves as the first line of defense, stopping malicious code from entering through network access.

Traffic filtering is the process of inspecting data passing through a network. Modern firewalls not only block access but also analyze the content of transmitted data to ensure it does not contain malicious elements.

This is especially important for protection against viruses, trojans, and other malware that may be hidden within network traffic. For example, if malicious code attempts to transfer data into your system, the firewall can recognize it by its virus signature or behavioral patterns and block it at the network level.

How Filtering Works:

• Packet Filtering: The firewall inspects data packets passing through its system. If a packet does not meet specified criteria (such as IP address, port, or protocol type), it will be rejected.
• Application-Level Analysis: The firewall can inspect data at the application level, meaning it can recognize and block not only suspicious traffic but also applications attempting to connect to the system with potentially harmful intent (e.g., unauthorized remote access to a database).

This process significantly reduces the risk of infections and intrusions, making the system more secure.

A firewall not only protects against threats but also provides the ability to monitor and manage network traffic. Next-generation security systems can generate detailed reports on incoming and outgoing traffic, intrusion attempts, and other suspicious activities.

Monitoring Functions:

• Event Logging: The firewall records all traffic-related events, including access attempts, successful and failed connections. These logs can be useful for subsequent security analysis.
• Anomaly Detection: Modern firewalls can analyze traffic and identify anomalies, such as unusually high traffic at specific times or suspicious requests from certain users. Such anomalies may indicate a potential attack or intrusion.
• Connection Management: Some firewalls offer real-time access management, allowing connections to be blocked or permitted as needed. This enables an effective response to evolving threats and allows security measures to adapt to current conditions.

Additionally, a firewall can integrate with other security systems (such as Intrusion Detection and Prevention Systems – IDS/IPS), creating a multi-layered network protection system.

Monitoring Example:

If a large number of connection attempts come from a single IP address, potentially indicating a Distributed Denial of Service (DDoS) attack, the firewall can automatically limit this traffic, preventing system overload and disruptions.

Internal users (employees or administrators) may accidentally or intentionally cause harm to the network. A firewall helps control data and applications interacting within the network, preventing data leaks and ensuring protection against internal threats.

Various types of attacks exploit vulnerabilities in internet protocols such as HTTP, FTP, DNS, as well as weaknesses in IoT devices. A firewall filters these protocols and defends against attacks by analyzing them, significantly reducing the risk of exploitation.

Firewall configuration depends on its type, purpose, and complexity. For most home users, simple settings of a built-in software firewall are sufficient, while large organizations and corporate networks require more complex configurations with centralized management and integration with other security systems. Let's look at how firewalls are configured in different scenarios.

Built-in Firewalls in Operating Systems

Many operating systems, such as Windows and Linux, include built-in firewalls. These firewalls provide basic protection and can be configured through control panels or the command line. They prevent unauthorized connection attempts and can be set up to allow or block specific traffic.

Example of Configuring a Firewall in Windows:

• Open the Control Panel.
• Go to Windows Firewall.
• Enable or disable the firewall for private and public networks.
• Click Advanced Settings to configure rules for inbound and outbound traffic.
• You can create new rules to allow or block ports, programs, and connections based on specific IP addresses.

Example of Configuring a Firewall in Linux (Using UFW – Uncomplicated Firewall):

• For basic settings, simple commands are sufficient:

sudo ufw enable   # Enable the firewall  
sudo ufw status   # Check firewall status  
sudo ufw allow 22  # Allow access on port 22 (SSH)  
sudo ufw deny 80   # Block access on port 80 (HTTP)  

• UFW provides a user-friendly interface for configuration, allowing users to permit or block access to specific ports or addresses.

Advantages of Built-in Firewalls:

• Easy to configure and use.
• Suitable for protecting home computers and small offices.
• Provides basic protection against common threats and unauthorized connections.

For large organizations with high security requirements and complex infrastructures, more powerful solutions are needed. Corporate firewalls are usually hardware devices or specialized software installed at the perimeter of the network, providing protection for the entire infrastructure.

Features of Configuring Corporate Firewalls:

Centralized Management: In large companies, centralized management solutions are often used. This allows administrators to securely and efficiently manage access to the entire corporate network. Centralized management enables firewall configuration from a single location and the application of security policies to all devices connected to the network.

Integration with Other Security Systems: Corporate firewalls are often integrated with other security systems, such as IDS/IPS (Intrusion Detection/Prevention Systems), SIEM (Security Information and Event Management) systems, and traffic monitoring and analysis solutions. This improves the effectiveness of protection, as the firewall can work in combination with other tools for threat analysis and more precise data filtering.

Role of the Firewall in Access Management: In corporate networks, firewalls are often used to manage access to various segments of the network. For example, they can block or allow access to specific parts of the network, restrict access to certain applications or data, and use VPNs (Virtual Private Networks) for secure remote connections.

Example of Configuring a Firewall for a Corporate Network:

Access Policies: Set up a policy that allows access to specific services only for trusted users or devices.
 Network Segmentation: Divide the network into different segments, such as for internal employees, guests, or database servers. The firewall can restrict access between these segments.
 Analysis and Reporting: Enable log collection and traffic analysis for further monitoring and threat detection. This will help quickly identify traffic anomalies, such as intrusion attempts or unusual connections.
 Application Security Configuration: Use application filtering to allow or block traffic for specific applications (e.g., blocking insecure services or allowing only corporate applications).

Software Solutions for Corporate Firewalls:

• Cisco ASA (Adaptive Security Appliance) — a solution for protecting corporate networks.
• Fortinet FortiGate — firewalls integrated with intrusion prevention and access management solutions.
• Palo Alto Networks Next-Generation Firewalls — offers advanced filtering, threat protection, and traffic management capabilities.

Monitoring and Reporting: After configuring the firewall, it is essential to set up monitoring and data collection for security status analysis. In corporate systems, monitoring is carried out using centralized platforms such as SIEM systems, which analyze the logs of the firewall and other security systems to detect potential threats.

Example of Monitoring:

• Regular reports on traffic and access attempts.
• Analysis of abnormal connection attempts (e.g., DDoS attacks).
• Alerts on blocked threats or security policy violations.

Configuring Notifications and Alerts: The system can be configured to send notifications via email or other communication channels if suspicious activities are detected. This helps to respond promptly to threats and mitigate them at an early stage.

It is important to regularly update firewall settings, as well as update software and databases to protect against new threats. Some firewalls update automatically, but for large corporate solutions, updates will need to be checked and configured manually.

Regular Updates Include:

• Threat database updates.
• Security patches to fix vulnerabilities.
• New rules and security policies to protect against modern threats.

A firewall plays a key role in securing network infrastructures, protecting devices and networks from external and internal threats. It is a necessary tool for both home users and large organizations, filtering traffic, preventing unauthorized access, and blocking malicious data. It is essential that the firewall configuration and management align with the threat level and security requirements of the specific network. Modern firewalls are powerful tools for monitoring, traffic filtering, and integration with other security systems — helping to respond quickly to potential attacks and minimize risks. Regular updates and maintenance of the firewall are essential for successful protection against evolving threats.

NB: As a reminder, the product is used to automate testing on your own sites and on sites to which you have legal access.