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What Are Firewalls, and How Do They Work?

13 September 2023

In today’s digital landscape where cyber threats loom large, businesses must take proactive measures to protect their networks and sensitive data. One crucial defence mechanism in their arsenal is a firewall. Firewalls act as the first line of defence against cyber attacks, preventing unauthorised access and filtering out malicious traffic. 

In this blog post, we will delve into the world of firewalls, exploring their definition, significance, and how they function to safeguard businesses from cyber threats.

Understanding Firewalls

A firewall is a network security device designed to monitor and control incoming and outgoing network traffic. Its primary objective is to establish a barrier between trusted internal networks and untrusted external networks, such as the internet. By doing so, firewalls help prevent unauthorised access to networks and protect sensitive data from being compromised.

The importance of firewalls cannot be overstated in the realm of cybersecurity. With the rise of sophisticated cyber attacks and the constant evolution of hacking techniques, firewalls play a critical role in mitigating these risks. They act as a proactive defence mechanism, reducing the attack surface and minimising the potential impact of breaches.

How Firewalls Work

Firewalls employ various techniques and mechanisms to ensure robust security. Here are some of the key methods:


  1. Packet Filtering 

Packet filtering is a fundamental technique used by firewalls to examine network packets and determine whether they should be allowed or blocked. This approach evaluates packet headers and filters traffic based on predetermined rules and filtering criteria. While packet filtering is effective and efficient, it may have limitations in dealing with more sophisticated attacks.

  1. Stateful Inspection 

Stateful inspection takes packet filtering to the next level by considering the context and state of network connections. In addition to examining packet headers, stateful firewalls maintain a record of the state of each connection, allowing them to make more informed decisions about which packets to permit or deny. This technique enhances firewall security by preventing certain types of attacks, such as IP spoofing.

  1. Application Proxy

 Application proxy, also known as application-level gateway, acts as an intermediary between internal and external networks. It establishes separate connections for each request, thoroughly inspecting traffic and validating it against application-specific rules. Application proxies offer enhanced security by providing deep packet inspection and protection against application-level vulnerabilities.

Types of Firewalls

There are different types of firewalls available, each catering to specific security needs and network configurations. Let’s explore some of the most common types:

  1. Network Firewalls 

Network firewalls are the most prevalent type and form the backbone of network security. They operate at the network level, inspecting packets of data as they travel across networks. Network firewalls can be hardware or software-based and use a set of predefined rules to determine whether to allow or block network traffic.

  1. Host-based Firewalls

 Unlike network firewalls, host-based firewalls operate at the individual device level, such as servers, workstations, or laptops. These firewalls provide an additional layer of protection by controlling inbound and outbound traffic specific to the device they are installed on.

  1. Application Firewalls

 Application firewalls, also known as proxy-based firewalls, focus on securing specific applications or protocols. They monitor and filter traffic based on application-specific rules, providing granular control over application-level threats.

Real-World Examples of Firewall Failures

There have been several incidents that highlight firewall failures, including:

  1. The Target Breach

The Target breach in 2013 remains one of the most notable data breaches in retail history. Attackers gained unauthorised access to Target’s network through a third-party HVAC vendor that lacked proper security measures. The absence of proper firewalls and network segmentation allowed the attackers to navigate freely, compromising millions of customer records. The attack highlighted the importance of network segmentation, conducting security assessments of third-party vendors, and continuous monitoring of network traffic.

  1. NotPetya Ransomware Attack

The NotPetya attack in 2017 demonstrated the limitations of relying solely on firewalls for protection against advanced malware. The attack exploited software vulnerabilities and spread rapidly, bypassing firewall configurations. It served as a reminder of the criticality of patch management, implementing a multi-layered defence strategy, robust incident response planning, and cybersecurity awareness training.

Protect Your Network With Firewalls

In an era dominated by cyber threats, businesses must prioritise their network security to safeguard sensitive data and protect against potential breaches. Firewalls serve as an indispensable component of an organisation’s cybersecurity infrastructure, offering crucial protection against unauthorised access and malicious traffic. 

Choose our managed firewall service and ICT Solutions will act as an extension of your IT staff, providing the hardware support and security expertise you need to secure your critical business information. 

Your chosen network users will have ‘anytime, anywhere’ access without putting your infrastructure, business assets, or employees at risk.

With ICT Solutions, you get strong on-site security, along with on-going maintenance and support off-site to make sure your site is fully protected.