What Is a Firewall in Computer Networking? 

With the rise of cybercrimes and fraud around the world, network security has become essential. A computer network firewall is a shield that blocks, checks, and manages outgoing and incoming traffic according to the security provisions that have been programmed. Firewalls can be used whether you’re securing a single device or managing infrastructure at the enterprise level. Firewalls make it possible to combat unauthorized access, malware infection, and data breaches. The blog describes what a firewall is, its types, the way it functions, the distinction between a conventional and a next-gen firewall, and how to employ a firewall to keep an organization secure.

Table of Contents:

• What is the Purpose of a Firewall in a Computer Network?
• A Brief History of Firewalls in Computer Networks
• Evolution of Firewall Generations in Network Security
• How Firewalls Operate: Behind the Scenes of Network Filtering?
• Major Types of Firewalls in Network Security
• Core Functions of a Firewall in Securing Your Network
• Common Limitations of Firewalls
• Advantages and Disadvantages of Firewalls
• Difference Between Traditional Firewalls and Next-Gen Firewalls
• Best Practices for Maximum Protection
• Conclusion

What is the Purpose of a Firewall in a Computer Network?

Try to think of your network as a safe building that has a small number of doors to enter. You would not leave them open and allow anybody to come walking into them, would you? That’s where a firewall comes into play. In computer networking, a firewall is a security guard that blocks everything entering and leaving the network using a given set of rules. It has the mandate to pass or reject data packets based on whether they pass the security standards set or not. Essentially, a firewall in computer networking will assist in avoiding unauthorized users, hacking, viruses, and information loss. Whether you use a small-scale home setup or a huge business network, the main function of a firewall is to provide a security net between your local system and the potentially harmful external world, such as the internet. It tracks traffic in real-time and also ensures that the trusted sources pass through.

Firewalls are the backbone of any cybersecurity approach. With the increase of cyber threats, the importance of a correctly configured firewall is not only critical, but it is also necessary. A firewall helps ensure your safety, whether you’re conducting business or simply browsing at home.  A firewall will keep your network traffic clean and safe.

A Brief History of Firewalls in Computer Networks

The concept of firewalls in networking dates back to the late 1980s, when internet usage spread not only in institutions of research but also in commercial and general sectors. Originally, the networks were trusted and open by default to the public, but later on, cyber attacks rose, and it was evident that some sort of protection line had to be set up. The first kind of firewall was a basic packet filter thatonly examined the headers of data packets to either pass or block them according to pre-determined rules.

Check Point Technologies introduced the first stateful inspection firewall in the year 1993, and it was a significant breakthrough in security. With the passage of time, firewalls were developed to deal with more advanced traffic and application-level threats. Later in the mid-2010s, Next-Generation Firewalls (NGFWs) were introduced, which added more powerful capabilities, such as deep packet inspection, intrusion prevention, and threat intelligence. Such innovations do indicate an increasing level of digital attacks and the means necessary to fight them.

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Evolution of Firewall Generations in Network Security

Over the years, firewalls have evolved through several generations to accommodate the needs of increasing cybersecurity threats. The first were referred to as packet-filtering firewalls, as the only thing they analyzed was IP addresses, ports, and protocols, which is not much protection. Then there were stateful inspection firewalls, where the active connections were monitored and intelligent decisions on the filtering were made. The third generation, or user application-layer firewalls, had the potential to examine up to the application level, recognizing abuse in policies such as HTTP and FTP. Current Next-Generation Firewalls (NGFWs) add deep packet inspection, intrusion prevention, SSL decryption, and identity-based access to protect against sophisticated, modern attacks.

How Firewalls Operate: Behind the Scenes of Network Filtering?

Any firewall can boil down to a group of regulations, which are basically meant to curb incoming or outgoing data through your network. Upon receiving a data packet, the firewall scans its source and destination IP address, destination port number, and protocol in order to determine whether to permit, reject, or drop the packet. This filtering is in real time, depending on pre-defined security policies. The Next-Gen Firewalls (NGFWs) are more advanced in that the system goes further–to examine packet content including malware, and even inspecting traffic that is encrypted through SSL/SSH decryption.

Different types of firewalls operate at various layers of the OSI model. As an example, packets are normally blocked by packet-filtering firewalls acting on the network layer of the OSI model, whereas application-layer firewalls check data on the highest layer to prevent dangerous applications or data. Other firewalls also have state tables, which are used to monitor sessions, and only the understood traffic is permitted. When this flow is monitored and controlled, firewalls can become the alert guards as they provide protection to your internal systems against unpermitted access, malware, or cyberattacks.

Major Types of Firewalls in Network Security

1. Stateful Firewalls

A “stateful” application in computer science stores information from earlier interactions and occurrences. Instead of analyzing every packet, a stateful firewall stores information about open connections and uses this knowledge to evaluate incoming and outgoing traffic.

Stateful firewalls make decisions by heavily relying on context. For instance, if a connection’s outgoing packets require a specific type of response, the firewall will only permit incoming packets on that connection provided they also include the desired response.

2. Firewall-as-a-service (FWaaS)

The more recent paradigm for providing firewall capabilities through the cloud is firewall-as-a-service (FWaaS). Another name for this service is “cloud firewall.”

 Similar to how conventional firewalls enclose an organization’s internal network, FWaaS creates a virtual wall around cloud platforms, infrastructure, and applications. FWaaS is frequently more effective than traditional firewalls at securing cloud and multi-cloud assets.

3. Web application firewalls (WAF)

WAFs help protect online applications from dangerous users, whereas conventional firewalls protect private networks from harmful web apps. A WAF filters and observes HTTP traffic between a web application and the Internet.

It typically guards against attacks such as cross-site scripting (XSS), file inclusion, SQL injection, and cross-site forgery.  

4. Next-generation firewalls (NGFW)

NGFWs are firewalls that combine traditional firewall functionality with a number of extra features to combat threats at various OSI model layers.

NGFWs examine packets significantly more thoroughly than conventional firewalls. Deep inspection can examine packet payloads and the applications they access, among other things. This enables the firewall to implement filtering rules with greater specificity.

5. Proxy-based firewalls

These intermediaries* between clients and servers are proxies. Clients connect to the firewall, which inspects the outgoing packets before establishing a connection with the target (the web server).

The firewall will also intercept a request from the web server trying to send a response to the client, inspect the packets, and then relay the response through a different connection to the client. Effectively preventing a direct connection between the client and server is a proxy-based firewall.

Core Functions of a Firewall in Securing Your Network

• Predefined Rule-based Traffic Filtering: Firewalls filter all the incoming and outgoing packets according to a group of security rules. Such rules may rest on IP addresses or port numbers or protocols, or application-level identifiers. The firewall filters traffic access by either allowing or disallowing any traffic that does not meet pre-approved standards, thus restricting unauthorized access and exposure to a risk that is untrusted.
• Implementation of access control: The ability to be able to control who or what gets to access your internal network is one of the most imperative firewall roles. Firewalls can also be configured with policies that may authorize or deny internet access to certain users, IP segments, or devices so that only endpoints that can be trusted to communicate with sensitive resources can do so.
• Network Activity Monitoring and Logging: Firewalls gather network traffic information to reveal user patterns, trace attempted intrusion, and audit access habits. This logging assists in identifying anomalies, responding to events, and meeting regulatory requirements such as GDPR, HIPAA, or PCI-DSS by preserving security audit trails.
• Intrusion Detection Prevention (IDP): The new generation of firewalls has incorporated intrusion detection and prevention systems that monitor the traffic to detect known attack signatures or abnormal patterns. Before they land within the network, brute-force attacks, SQL injections, DDoS attacks, and other threats that take place in real-time may be blocked with these systems.
• Blocking Data Exfiltration: Firewalls also prevent unauthorized shipping of internal data by screening the outbound traffic that does not match the permitted use cases. This helps prevent malicious insiders or malware from sending critical information such as customer records, intellectual properties, or login credentials to external command and control servers.
• Zone Isolations and Segmentation: Firewalls can partition a network into secure areas, e.g., the DMZs (demilitarized zones), internal and external segments, isolate critical assets, and decrease the propagation of breaches. The rules set may be different in each zone, which enables fine-grained access control between the zones.
• Application-Level Protection: Firewalls in the application layer are able to identify the abuse of a protocol like HTTP, FTP, or DNS. They determine and select traffic using the real application as opposed to ports or IPs. It particularly comes in handy in the prohibition of unsafe applications, such as remote desktop applications or web applications that have not been approved.
• Defense against Malware and Zero-Day Exploits: Some features provided by next-generation firewalls are antivirus, antimalware, and sandboxing. These modules scan files and executable code to filter out malicious materials before they get to your environment, and even scan compressed files or encrypted packets.
• VPN Support: Firewalls often support Virtual Private Network (VPN), allowing secure remote access to private networks over the public Internet. They can authenticate and encrypt VPN connections, ensuring that sensitive data transmitted between remote users and the network remains secure.

Common Limitations of Firewalls

• Impotent in Fighting Against Internal Threats: Firewalls are mainly oriented to protection against outside infiltration, not attacks carried out internally on the network. In case of a compromised user account of a trusted user or a rogue insider, the firewall cannot be the line of defense on its own, i.e., without being combined with other products and capabilities, such as endpoint detection or behavior analytics.
• Minimum Malware and Phishing Security Protection: Although contemporary firewalls provide certain malware prevention, these are not infallible. These malware, particularly of the zero-day type, or phishing emails that lure users into divulging confidential data, usually evade firewall settings. These threats should be addressed using firewalls alongside endpoint security, email filters, and user training.
• Has no Protection on Compromised Devices: Once a system in a network is attacked by malware, a firewall is not able to clean or delete the malware. When a machine is already infected, it is via a USB stick, faulty software, or even the carelessness of the user; the firewall by itself does not save the day. It is not a cure, it is a preventive layer.
• Prone to misconfiguration: The quality of firewalls is dependent on their configuration. If the firewall rules are not properly established, too liberal, or obsolete, attackers have a chance to get through. A gap of any kind, even a non-permitted open port or a forgotten rule, can turn into an entry point. Repeated checks and rule maintenance will be necessary.
• Not able to control Non-Network Threats: Firewalls are security controls of a network nature and, as such, cannot be used to prevent threats such as those propagated through physical access, removable media, and social engineering. Such attacks as shoulder surfing, insider sabotage, or evil USBs do not even require network-layer defenses.
• Bottlenecks in Performance during Heavy Load: Firewalls may also represent a bottleneck when not appropriately sized or optimized, in an enterprise environment with high traffic. By examining additional data packets, searching applications, and implementing deep packet inspection, they may experience a loss in performance, which may lead to slowing the network or loss of valid traffic.
• Cannot independently encrypt or decrypt end-to-end traffic: Some firewalls may allow inspection of the SSL traffic, but in most cases, the firewalls are not able to scan the encrypted traffic without being configured appropriately. The encrypted traffic can be circulating without the firewall catching on to it, and the threats remain hidden with no eyes to spot them unless the firewall is implemented with a decryption proxy that has blind spots.

Advantages and Disadvantages of Firewalls