What Is a Firewall? Types & Role in Cybersecurity

What is Firewall?

Firewalls are network security products that monitor and filter internal or outgoing network traffic according to an organization's security policies. They are the wall between a private internal network and the public Internet.

Similarly, property fencing protects your house and keeps trespassers at bay; firewalls, in their place, secure a computer network. Firewalls are network security systems that prevent unauthorized access to a network. They may be hardware or software units that filter the incoming and outgoing traffic within a private network according to rules to spot and prevent cyberattacks.

Firewalls are vital to network security and are used in enterprise and personal environments. Most operating systems have basic built-in firewalls. However, protection using a third-party firewall application is well-implemented and liked.

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A Primer on Firewalls

A firewall is a device or software in a network that controls incoming and outgoing network traffic according to predetermined security rules. It can be set up as a barrier between an internal trusted network and external untrusted networks, such as the Internet. It typically allows only authorized traffic while blocking potentially harmful data.

Key Functions of Firewalls:

1. Traffic Filtering: Firewalls screen data packets (pieces of data) in the network's flow-in and flow-out directions, allowing or blocking them according to certain rules.

2. Access Control: They decide which applications, services, and devices can access the network, thus protecting sensitive resources.

3. Threat Detection: Some can detect and prevent other types of threats, such as viruses, malware, or suspicious behavior.

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Types of Firewalls

It can be software or hardware. Software firewalls are applications installed on each computer; they control network traffic through applications and port numbers. Hardware firewalls are devices set up between the gateway and your network. You also refer to a firewall provided by a cloud solution as a cloud firewall.

Depending on their methods of filtering traffic, structure, and functionality, there is more than one type of firewall. Some of the types of firewalls include:

1. Packet Filtering

A packet filtering firewall controls incoming and outgoing traffic across a network. It allows or rejects data flow depending on the packet's source address, destination address, application protocols involved in transmitting the data, and more.

2. Proxy Service Firewall

This type of firewall works by filtering messages at the application layer that are of interest to the network. A proxy firewall is a gateway between two networks for a specific application.

3. Stateful Inspection

A firewall permits or blocks network traffic based on state, port, and protocol. It decides on filtering based on administrator-defined rules and context. 

4. Next-Generation Firewall

According to Gartner, Inc., a 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.

5. Unified Threat Management (UTM) Firewall

Commonly, a UTM device combines a stateful inspection firewall, intrusion prevention, and antivirus functionalities in a loose coupling. A UTM could provide added services like cloud management. Simply put, UTMs have been designed to be simple and easy to use.

6. Web Application Firewall

It is a security solution that is used for filtering and monitoring inbound and outbound HTTP/HTTPS traffic towards or from a web application known as WAF. It protects against various threats targeting web applications, including SQL injection, cross-site scripting attacks, and other standard web weaknesses.

The WAF works at the application layer by obstructing malicious inputs and suspicious activities before they get to the web server. It will help prevent attacks on the OWASP Top 10 lists and provide real-time threat detection and bot mitigation to ensure integrity in web applications.

7. AI-Powered Firewall

An AI-powered firewall uses artificial intelligence to enhance network security by analyzing traffic patterns, detecting emerging threats, and adapting in real time. It provides advanced threat detection, including zero-day attacks, and reduces false positives by learning from data.

This makes AI firewalls more effective in identifying and blocking sophisticated, evolving cyber threats than traditional firewalls.

8. Virtual Firewall

A virtual firewall offers protection in the virtualized environment, including cloud platforms or VPNs. Like hardware firewalls, virtual firewalls work within VMs to filter and monitor network traffic, but they are virtual. They have the same functions as physical firewalls, like controlling traffic and detecting possible threats. Still, they've been designed to provide flexible and scalable protection in cloud and virtual infrastructures.

9. Cloud Native Firewall

Cloud-native firewalls are security solutions designed and fitted for cloud environments. Their seamless integration into the cloud platform ensures the protection of cloud applications and workloads. Unlike traditional firewalls, this new generation of cloud-native firewalls will provide features like scaling, flexibility, and handling dynamic and distributed cloud traffic. They offer advanced security features such as traffic filtering, threat detection, and compliance optimized for the unique needs of cloud architectures.

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How Does a Firewall Work?

After understanding what a firewall is in a computer network, let us have a look at how it works. As earlier noted, firewalls filter the network traffic within a private network. They analyze which traffic should be allowed or restricted according to set rules. Think of a firewall as a gatekeeper at the entry to your computer, permitting access into your network to only trusted sources or IP addresses.

It only accepts incoming traffic that has been configured to do so. Firewalls will distinguish between good and malicious traffic and allow or block specific data packets based on pre-established security rules.

These rules depend on multiple aspects that the packet data indicates, such as source, destination, content, and so on. Thus, they block traffic coming from suspicious sources to avoid cyberattacks.

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

Firewall Allowing Good Traffic

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

Firewall Blocking Bad Traffic

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

Different types of firewalls can 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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Why Are Firewalls Important?

Firewalls are designed with state-of-the-art security techniques employed in different applications. The early days of the Internet required networks built with new security techniques, especially in the client-server model—a central architecture of modern computing. That's where firewalls have started to create security for networks with varying complexities. Firewalls are known to inspect traffic and mitigate threats to devices.

Key Uses of Firewalls

• Firewalls can be applied to corporate and consumer environments.
• Firewalls can implement a SIEM strategy in cybersecurity devices concerning modern organizations installed at the network perimeter of organizations to protect against external threats and insider threats.
• Firewalls can find patterns, perform logging and auditing, and enhance rules by updating them to defend against immediate threats.
• Firewalls can be used in a home network, Digital Subscriber Line, or cable modem with static IP addresses. They can easily filter out traffic and signal the user about intrusions.
• They are also utilized in antivirus applications.
• Firewalls perform updates of the rule sets to address vendor issues when vendors identify new threats or patches.
• For devices at home, restrictions can be implemented using Hardware/firmware firewalls.

Functions of Firewall

• The most crucial role of a firewall is to create a border between an external network and a guarded network. The firewall inspects all the packets entering and leaving the guarded network. Once the inspection has been done, a firewall can differentiate between benign and malicious packets with the help of a set of pre-configured rules.
• The firewall enforces such packets, whether in a rule set or without rules, to ensure that they do not enter the protected network.
• The source, destination, and content information is provided in packet form. Each may differ at each level of the network, and with it differs the set of rules. Firewalls read the packets and then reform the rules to instruct the protocol where to send them.

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How to Use Firewall Protection?

• Set up and maintain your firewall correctly to protect your network and devices. Here are some tips that will assist you in keeping your firewall very secure:
• Constantly update your firewalls: Firmware patches are used to update your firewalls against newly discovered vulnerabilities.
• Antivirus protection: In addition to firewalls, antivirus software is installed to help safeguard your system against viruses and other types of infections.
• Limit available ports and host: Disallow incoming and outgoing traffic to only a few known, trusted IP addresses.
• Active network: Establish active network redundancies to avoid downtime. Data backup for network hosts and other critical systems will enable you to avoid lost productivity in disasters.

Best Practices for Firewalls

1. Establishment and Implementation of the Firewall Policy: Stringent firewall policies to meet your company's security needs, ensuring that only required traffic and users are permitted for necessary services.

2. Principle of Least Privilege: Access will be given only when strictly needed by allowing only persons or systems authorized to connect with any particular resource.

3. Stateful Inspection: Configure your firewall to track the state of each network connection. This would enhance decision-making capabilities by analyzing patterns of incoming traffic in real-time.

4. Ensure Firewalls Are Up-to-Date and Patched: Regularly update the firewall software and firmware to defend against newly discovered vulnerabilities and exploits.

5. Segment Your Network: Segment your network into zones using firewalls, for example, internal, external, and DMZ, and apply different security levels against these; this may help you control access between them.

6. Activity Monitoring and Logging: Continuous monitoring shall be performed to look for suspicious activities or signs of intrusion in firewall logs. Automated log analysis tools shall be available to identify threats quickly.

7. IDS/IPS: IDS/IPS shall be set up on the respective firewall systems, which will be able to detect and block suspect traffic automatically.

8. Disabling Unnecessary Services: Unused ports, protocols, and services that an attacker might use shall be turned off.

9. Regular Firewall Rules Review: Periodically review the rules in your firewalls to remove obsolete or duplicated policies that may introduce risks.

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Network Layer Vs. Application Layer Inspection

Network Layer Inspection: Network Layer Inspection works at the third layer of the OSI model. Its prime focus is basic packet filtering, where filtering takes place based on IP addresses and protocols such as TCP, UDP, and port numbers.

It checks the source and destination addresses of the data packets and allows or blocks the transmission accordingly. This inspection type is fast and efficient but does not delve into the inside of the data contents.

Application Layer Inspection: On the other hand, Application Layer Inspection works at Layer 7 of the OSI model. It goes deeper, inspecting the actual content of the data being transmitted, such as the HTTP request, email, or file transfer.

Because this kind of inspection can comprehend specific application protocols and behaviors, this type of protection will find more sophisticated threats like malware, SQL injections, or cross-site scripting.

Key Differences:

1. Depth of Inspection: Attention is paid to IP addresses and ports at the network layer, while the application layer examines real data content and application behavior.

2. Speed versus Security: The inspection at the network layer is faster while less complete; application layer inspection is slower but will offer more comprehensive security.

3. Threat detection: Application layer inspection provides visibility into sophisticated, application-level attacks that may not be visible via network layer inspection.

Application Layer and Proxy Firewalls

A proxy firewall filters and parses the packet payload at the application layer to identify valid requests versus malicious code masquerading as valid requests for data. Proxy firewalls are rare at the application layer, keeping attacks against web servers from becoming more common. In addition, a proxy firewall gives security engineers better granularity when controlling network traffic.

On the other hand, proxy firewalls can allow filtering at an application-layer level to block malware and detect misuse among various protocols, including HTTP, FTP, applications, and DNS.

The Importance of NAT and VPN

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

• Nat (Network Address Translation).
• It hides or translates internal client or server IP addresses, which are usually in a "private address range." However, RFC 1918 defines it as a public IP address.
• NAT preserves the limited number of IPv4 addresses and 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 often be encrypted. However, the contents inside the packets are protected, especially when they are traversing the Internet. 
• VPN enables users to send and receive data safely across shared or public networks.

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The Future of Network Security

In recent years, virtualization trends and converged infrastructure have created more east-west traffic, and the most significant volume of traffic within a data center moves from server to server. This, in turn, compelled some enterprise organizations to migrate from the traditional three-layered data center architectures to leaf-spine architectures in various forms.

This shift in architecture has made some security experts warn that firewalls play an essential role in keeping 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

To have a clear understanding of what is a firewall, one must know the difference between a firewall and an antivirus.

Firewall

• Firewalls, in this respect software or firmware, block unauthorized access to a network.
• This works by inspecting the incoming and outgoing traffic using sets of rules to find and block threats and implement them in software or hardware form.
• Firewalls can be used in personal and enterprise environments, and many devices have one installed by default; examples include Macs, Windows, and Linux computers.

Antivirus

• Antivirus also falls under network security. It is basically an application or software used to provide security from malicious software on the Internet.
• Antivirus is based on three significant actions: threat detection, identification, and removal.
• Antivirus can deal with both external and interior threats based on implementing only software solutions.

Advantages of Using Firewalls

1. Improved Security: Firewalls block illegitimate access and prohibit entry into the network by cyber threats like hackers, malware, and phishing attacks.

2. It monitors incoming and outgoing traffic and lets the administrators control the incoming or outgoing data as the security policy instructs.

3. Firewalls block unauthorized remote access to your network and protect sensitive data and systems from illegal access.

4. Network Segmentation: Firewalls provide better control and protection between network segments by segmenting your network into different zones, such as internal, external, and DMZ.

5. DoS Attacks Protection: Firewalls can detect and block denial-of-service attacks, which aim to overload and render services useless.

6. Security Policies: Firewalls enable an organization to set rules and policies based on business needs, ensuring proper protection for a variety of services and applications.

7. Intrusion Detection and Prevention: Advanced firewalls possess intrusion detection and prevention capabilities that identify malicious traffic as it occurs and block it.

8. Logging and Reporting: Firewalls perform event logging and reporting to monitor possible suspicious activities and analyze security incidents for improvement in the future.

Disadvantages of Using Firewall

1. Cost: The cost of buying, installing, and maintaining high-end firewalls, particularly ones with advanced features like intrusion prevention and deep packet inspection, is relatively high.

2. Performance Impact: Firewalls may slow down network performance, especially when performing complex checks, such as deep packet inspection. They may also delay data on its path through the network.

3. Limited Protection: Firewalls do not protect against an internal security breach, only external intrusion caused by employee misuse or insider attacks.

4. Configuration Risks: Poor configuration of firewall rules may cause security vulnerabilities, such as unauthorized access to traffic or blocking traffic that mustn't be blocked.

5. False sense of security: Firewalls do provide some measure of security, but reliance on them could make users complacent about other aspects of security, such as endpoint security and patch management.

6. Complexity: The rules and policies on firewalls can get complex, especially for large networks, requiring professionals with the necessary skills to ensure that they operate properly.

7. Application Layer Control Limited: Basic firewalls might not inspect or control traffic at the application layer. In that case, more sophisticated attacks could be launched by using vulnerabilities in applications.

8. No Protection Against Social Engineering: Firewalls do not guard against social engineering attacks, phishing, or scams. These types of attacks include targeting users directly rather than network vulnerabilities.

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Limitations of a Firewall

1. Firewalls also cannot prevent users from accessing malicious data or information from websites, making them more prone to internal threats or attacks.

2. It cannot protect against the transfer of virus-infected files or software in case of badly configured security rules or against non-technical security risks, such as social engineering.

3. It does not prevent the misuse of passwords and attackers with modems from dialing in or out of the internal network.

4. Firewalls cannot protect systems that are already infected.

Conclusion

You must now be clear on what a firewall is. You also learned the different types of firewalls and how to use them. Cybersecurity is a booming field today. If you are looking to learn ethical hacking to protect devices and networks from cyber criminals, you can opt for the Cybersecurity Experts Masters Program from Simplilearn.

FAQs

1. What is a computer firewall?

A computer firewall is a security system, which can be either hardware or software-based. It monitors and controls incoming and outgoing network traffic. Its purpose is to safeguard the computer or network against unauthorized access and potential cyber threats.

2. What is a firewall, and why is it used?

A firewall is a security device or software that creates a protective barrier between a reliable internal network and an untrusted external network, typically the Internet. It filters and controls network traffic, allowing only authorized and safe data packets to pass through while blocking or inspecting potentially harmful traffic.

3. What are the 3 types of firewalls?

The three main types of firewalls are:

1. Packet Filtering Firewalls: These examine data packets and allow or block them based on criteria like source/destination IP, ports, and protocols.
2. Stateful Inspection Firewalls: They keep track of the state of active connections and make decisions based on the context of the traffic.
3. Application-layer firewalls (Proxy Firewalls): These operate at the OSI model's application layer, offering more sophisticated filtering and content inspection abilities.

5. What are the benefits of a firewall?

The benefits of a firewall include:

• Protection against unauthorized access and cyber-attacks.
• Network traffic filtering to block malicious content.
• Prevention of data breaches and sensitive information leakage.
• Control over internet usage and access to specific resources.
• Enhanced network security and reduced risk of cyber threats.

6. Where are firewalls used?

Firewalls protect various environments, including homes, businesses, data centers, and networked systems, from unauthorized access and potential cyber threats.

7. How to use a firewall?

You can configure a firewall through its software interface or use the built-in firewall settings in your operating system. Define the rules for inbound and outbound traffic, specify allowed applications, and ensure regular updates for optimal protection.

8. Which type of firewall is best?

The best type of firewall depends on the specific requirements and context. A software firewall or a router's built-in firewall might suffice for home users. In enterprise environments, a combination of packet filtering, stateful inspection, and application-layer firewalls might be used for comprehensive protection. The best firewall choice depends on factors like security needs, budget, and network complexity.

9. Why do we need a firewall?

We need a firewall for protecting the networks and devices from unauthorized access, different kinds of cyber threats, and malicious attacks. Firewalls maintain a wall of security between the internal networks and other external sources, such as the Internet, by observing and controlling traffic according to predefined rules. It helps in evading hacking, malware, and various other threats that may compromise sensitive data, so that one can comfortably continue with safe and secure network operations.

10. Who builds firewalls?

Firewalls are built by specialized cybersecurity companies and technology providers. Major firewall manufacturers include Cisco, Palo Alto Networks, Fortinet, Check Point, Sophos, and Juniper Networks. A variety of companies provide hardware-based firewalls, software firewalls, and cloud-based firewall solutions, meaning a broad scale of security products protects various types of networks and infrastructures.