What Is Firewall Security? How to Protect Your Infrastructure

A firewall is a network security device that monitors network traffic, allowing or blocking traffic based on certain security rules. Firewalls have evolved over the years; there are now different types, including next-generation network firewalls (NGFW) and web application firewalls (WAF).

Firewalls have been a first line of defense in network security for over 25 years. They establish a barrier between secured and controlled internal networks that can be trusted and untrusted outside networks. For example, firewalls are business-critical to protect the data of any company with an internal-only network, or one working on the Internet. A firewall can be hardware, software, software-as-a service (SaaS), public cloud, or private cloud (virtual).

Understanding Firewall Security

A firewall is a network security solution that protects your network from unwanted traffic. Firewalls block incoming threats such as malware based on a set of pre-programmed rules. Modern firewalls also include additional capabilities such as intrusion prevention systems (IPS) and URL filtering, allowing security teams to augment rules to prevent users within the network from accessing certain websites and applications.

The primary difference between an NGFW and a WAF is that an NGFW primarily monitors outbound traffic and the resultant return flows to prevent risks from coming back into the enterprise. On the other hand, a WAF protects web apps from incoming threats.

Firewalls are based on the simple idea that network traffic from less secure environments – like outside sources connected via the Internet – should be authenticated and inspected before moving to a more secure environment. This prevents unauthorized users, devices, and applications from entering a protected network environment or segment. Without firewalls, computers and devices in your network can be susceptible to hackers and make you an easy target for attacks. However, with the widespread adoption of cloud and SaaS-based apps, the network perimeter has largely dissolved.

Most organizations use additional security solutions along with their firewall deployment to help insure protection in today’s complex and ever-changing cyberthreat landscape. But firewalls are still considered a foundational building block for creating a proper cybersecurity system.

As part of the first line of defense against cyberattacks, firewalls offer essential monitoring and filtering of all traffic, including outgoing traffic, application-layer traffic, online transactions, communications and connectivity — such as IPSec or SSL VPN — and dynamic workflows. Proper firewall configuration is also essential, as default features may not provide maximum protection against cyberattacks. Modern firewalls like NGFWs may bundle these capabilities.

Today’s digital landscape is ever more complex because more devices, users, and applications are crossing through the network perimeters – including the growing volume of Internet of Things (IoT) and end user devices. We are also seeing less overall centralized control from IT and security teams.

All of this can leave companies more vulnerable to cyberattacks. That means it is essential to understand how firewalls work, what types are available, and which are the best for securing different areas of your network. 

How Firewall Security Works

Each type of firewall has its strengths and weaknesses, and organizations often use a combination of these types to create a layered network-level defense strategy. There are five main types of firewalls that offer progressively more advanced protection levels.

  1. Packet-filtering firewalls: These firewalls examine “packets” of data as they pass through a network. They analyze the packet header information, such as source and destination IP addresses, ports, and protocols. Based on predefined rules, they either allow or block the packets. Packet-filtering firewalls are relatively simple and efficient but lack the ability to inspect the contents of the packets.
  2. Stateful inspection firewalls:  combine the packet-filtering approach with additional capabilities. They maintain a record of the state of network connections and use this information to make more informed decisions about allowing or blocking packets. Because they track the state of connections, they can identify and protect against certain types of attacks, including  and IP spoofing.
  3. Application-level gateways (proxy firewalls): Application-level gateways, also known as proxy firewalls, operate at the application layer of the network stack. They act as intermediaries between clients and servers, inspecting and filtering traffic at the application level. They can analyze the content of packets, making them more effective at detecting and blocking specific types of threats. Sometimes, however, an organization will notice that the proxy feature can result in latency.
  4. Next generation firewalls (NGFW): These solutions bundle capabilities such as network firewall, IPS, URL filtering/Secure Web Gateway, malware prevention, and VPN connectivity and serve as a primary tool in enterprise defenses.
  5. Web application firewall (WAF): WAFs serve as a critical stopgap to mitigate critical vulnerabilities that can otherwise have a devastating impact on an organization. Modern WAFs use a combination of signatures, threat intelligence, and behavioral analytics and can defend against a variety of threats including application denial-of-service (L7 DoS) and exposure of sensitive data such as personally identifiable information (PII).

The Role of Firewalls in Cybersecurity

Firewalls remain a relevant and reliable defense against cyberthreats. Here’s how they work to help prevent unauthorized access to your network.

Firewalls: Your First Line of Defense

We all know about the dangers of clicking on unknown links or pop-up ads while browsing, but that isn’t really enough to keep your devices and network secure. That’s why a firewall is your first line of defense to protect your network and data.

Firewalls work by helping filter and block potential hackers from accessing your sensitive data.  There are many types of firewalls that use different strategies to keep your information safe. Firewalls protect your computer from malicious software as well, which can create all sorts of security issues.

Intrusion Prevention and Detection

Firewalls are set up to defend against a wide variety of potential threats to your network and system. Here are some of the major threats they are designed to thwart.

  • Unauthorized access: Firewalls protect your network from unauthorized access by hackers who use a variety of tools to gain entry, such as , backdoors, denial-of-service (DoS) attacks, remote logins, phishing emails, social engineering, and spam.
  • Cyberthreats: Firewalls act as a gatekeeper and are designed to mitigate external threats like viruses. They inspect and authenticate all data packets in network traffic before allowing them to move to a more secure environment.

Application Layer Filtering

Traffic filtering at the application layer is a security measure that allows you to control what enters or exits a network at a more granular level compared to traditional packet filtering. While packet filtering can be used to block or allow specific types of traffic based on IP addresses and port numbers, goes beyond that by examining the actual contents of the data.

ALF enables you to filter traffic based on application layer protocols, such as SMTP, POP3, DNS, and HTTP. By doing so, it can help prevent attacks that rely on vulnerabilities in these protocols, such as buffer overflows, web server attacks, and attack code hidden within SSL tunnels.

Traffic filtering at the application layer also allows you to:

  • Prevent application layer attacks: By analyzing the content of data packets, ALF can detect and block malicious traffic that is non-compliant or exploits vulnerabilities in application layer protocols.
  • Protect against data leakage: By inspecting the contents of data packets, ALF can detect and block sensitive information from leaving the network.
  • Control access to specific applications: ALF enables you to selectively allow or deny traffic based on the specific application or protocol used.
  • Enforce security policies: ALF allows you to define and enforce security policies at the application layer, ensuring that only authorized traffic is allowed.

Firewalls in Cyberthreat Prevention

Firewalls are a key weapon in preventing a variety of cyberthreats.

Distributed Denial of Service (DDoS) Protection

Firewalls help mitigate DDoS attacks by identifying and filtering out excessive traffic. While firewalls can employ techniques such as throttling, load balancing, and denylisting IP addresses to fight DDoS attacks, they may not be able to effectively distinguish between legitimate and malicious traffic. Additionally, firewalls’ stateful nature and reliance on stateful packet inspection (SPI) make them vulnerable to state exhaustion attacks.

To effectively protect against , it is recommended to implement an intelligent DDoS mitigation solution that operates in a stateless or semi-stateless manner, or that has robust connection management and reaping capabilities.. These solutions predominantly use stateless packet processing technology and integrate features such as traffic scrubbing at Layers 3, 4, and 7 of the OSI Model. By dealing with each incoming packet separately and without blocking all traffic from an IP address, these solutions can effectively mitigate DDoS attacks. In most cases, cloud-scrubbing is required to prevent ingress bandwidth from being exhausted during a volumetric DDoS attack.

Malware and Virus Defense

As for blocking malware and virus-infected data from infiltrating the network, firewalls can provide some level of protection by filtering incoming traffic based on predetermined security rules. They can block known malicious IP addresses, restrict access to certain ports, and inspect network packets for suspicious content. However, firewalls alone are not sufficient to provide comprehensive protection against malware and viruses.

To combat malware and virus threats effectively, organizations typically employ a combination of security measures, including:

  • Antivirus software: Antivirus software scans files and programs for known malware signatures and behavior patterns, helping to detect and remove malicious code from infected systems.
  • Intrusion detection/prevention systems (IDS/IPS): IDS/IPS solutions monitor network traffic for signs of malicious activity and can block or alert on suspicious behavior.
  • Email filtering: Email filtering solutions can help prevent malware and viruses from being delivered via email attachments or links.
  • User education and awareness: Educating users about safe browsing habits, avoiding suspicious downloads, and recognizing phishing attempts can significantly reduce the risk of malware infections.

Modern NGFWs have expanded into security architectures that can provide a unified defense across network, cloud, endpoint, and email threat vectors.

Additionally, modern WAFs have evolved into Web App and API Protection (WAAP) platforms that unify application security, API protection, bot management, and DDoS mitigation.

By combining these security measures with firewalls, organizations can create a more robust defense against emerging threats.

Network Firewall Security

Complex networks are typically thought of as network segments, smaller physical or logical components of a larger network. This allows security teams to quickly close off sections of a network if a threat arises and streamlines the management of sprawling enterprise network architecture.

For communication to flow between segments, traffic flows through routers or firewalls so that it can be inspected before passing through to other network segments. This strategy adds security redundancies throughout the system and strengthens overall network security. 

Implementing Network-Level Firewalls

Placing firewalls at network entry and exit points assists security by monitoring and controlling traffic flow. While internal networks do handle confidential data, connections between these networks can be more permissive than network connections between internal and external traffic. Still, there are unique network threats to consider because sensitive data needs to be transmitted frequently between users. In each network segment, security teams can create a variety of boundaries with varying degrees of security protection. 

Traffic Monitoring and Access Control

Firewalls, both physical and software, analyze incoming and outgoing data, using rules created and enabled by the firewall provider, your IT service, or other software that engages with the firewall. By filtering this data, the firewall can determine if traffic is legitimate and if it should be allowed through to its end destination.

Access control lists (ACLs) are ordered lists of permissions that define traffic allowed or denied by a firewall. Firewalls use ACLs to filter traffic based on source, destination, port, and other criteria. ACLs are applied to firewall interfaces, either on the inbound or outbound direction. The firewall examines traffic passing through a part of the network and makes decisions based on the ACLs. NGFW and WAFs are application aware and can inspect other aspects of traffic flows including DNS, URL queries, and web content.


Virtual Private Networks (VPNs) and Firewalls

Companies that rely on VPN connections use firewalls to help secure those connections. A firewall facilitates VPN by acting as a filter for your network traffic, preventing any instances when you receive incoming traffic from suspicious sources. The firewall safeguards the data moving from your device and network against threats. When the firewall is installed at the back of a VPN server, it is configured with filters to allow only VPN-specific packets to pass. Similarly, when the firewall is installed at the front of a VPN, the firewall is configured to allow only tunnel data on its Internet interface to be passed to the server.

Transport Layer Security (TLS) and Firewalls

TLS is a widely adopted security protocol designed to facilitate privacy and data security for communications over the Internet. Firewalls can be configured to inspect and filter network traffic at the application layer, including traffic encrypted with TLS. By decrypting and inspecting TLS-encrypted traffic, firewalls can analyze the contents of the data packets and apply security policies to protect against threats and vulnerabilities.

Some firewalls support TLS inspection, which involves decrypting TLS-encrypted traffic, inspecting it for potential threats or policy violations, and then re-encrypting it before forwarding it to its destination. This allows the firewall to analyze the encrypted traffic and apply security measures based on the decrypted content, such as blocking malicious or unauthorized traffic. TLS inspection should be implemented carefully to ensure the privacy and integrity of encrypted communications. 

Internet Firewall Security

In today’s business landscape, doing business via the Internet is not really optional. To reach customers and employees, wherever they are, and respond to their requests in near-real-time, your Internet presence must be broad, reliable – and secure. If your company accepts and transmits data to and from the Internet, it’s critical to have a firewall as part of your network security protocol.

Firewalls for Internet connections operate in much the same way as ones for internal networks. If a piece of data wants to come into your network from the Internet, the firewall makes the first assessment. If the firewall deems the data safe, it can proceed into your company network. If not, it’s stopped in its tracks.

Securing Web Applications

It is highly important to place strong controls on firewalls protecting the internal network from external connections (the Internet). Not only can malicious attacks occur from outside sources, but data leakage is a significant concern. A firewall can prevent unwanted content or unauthorized users from accessing your network or applications. It can also help guarantee security based on protocol settings and IP addresses. A firewall is designed to protect your data and operations on many fronts. However, the complexity of modern applications driven by the evolution to API-based systems, and an expanding risk surface from vulnerabilities, abuse, misconfiguration, and access control bypass requires more specialized defenses found in WAF and WAAP platforms.

Content Filtering and URL Blocking

On a more granular level, firewalls can help with and by acting as a gatekeeper between your computer or network and the Internet. They can also be configured to block web traffic using predefined categorizations and other specifications for determining which types of traffic are let through the firewall. For example, content filtering can be set to block all websites that are known to be categorized as “games” or “social networking.”

URL filtering is a way of blocking certain URLs from loading on a company network. Firewalls can be configured to block specific URLs by entering them manually or by selecting categories of URLs to block. If an employee attempts to visit a blocked URL, they will be redirected to a page notifying them that this content is blocked.

In so doing, these firewalls deliver consistent, reliable user experiences, with access to everything users need, and to nothing they do not.

Challenges with Internet-Facing Firewalls

With constant change the norm on the Internet, Internet-facing firewalls can encounter a variety of challenges that can affect their effectiveness. Here are some common ones:

  • Software vulnerabilities: Firewalls, like any software, can have vulnerabilities that attackers may exploit. Firmware vulnerabilities also pose a risk and can lead to security breaches. Regularly updating your firewall’s software and firmware is crucial to address known vulnerabilities and protect your network.
  • Misconfiguration:  is a leading cause of firewall breaches.  It occurs when the firewall’s settings are inaccurate due to user error or insufficient investigation. Misconfigurations can leave your organization vulnerable to unauthorized access, data breaches, and unplanned outages.
  • Reliance on proprietary threat intelligence: Some firewalls rely on proprietary and closed threat intelligence to detect and block threats, which limit their ability to evolve along with the ever-changing threat landscape. It’s important to ensure that your firewall has access to up-to-date threat intelligence to effectively protect your network.
  • Application-level attacks: Traditional network firewalls may not be effective at stopping application-level attacks that exploit vulnerabilities such as cross-site scripting, SQL injection, forceful browsing, and cookie poisoning. These attacks specifically target applications and require specialized protection mechanisms like web application firewalls (WAFs) to mitigate the risks.
  • Pervasive SSL/TLS connectivity: Internet traffic is largely encrypted and many traditional and NGFW firewalls are not designed to perform decryption at scale. Additionally, most security ecosystems require inspection by a variety of tools, necessitating a centralized decryption and encryption broker to balance security and user privacy.

Best Practices for Firewall Management

To ensure the best performance from your firewall, it’s important to stay on top of configuration, capabilities, and operational excellence. The following are some best practices in getting the most out of your firewall solution.

Thoroughly plan your firewall deployment: When deploying a firewall, consider the network interfaces, zones, and management requirements. Deploying two or more firewalls in a high availability cluster ensures security continuity.

Harden and properly configure the firewall: Ensure that the firewall’s operating system is patched and hardened. You can find guides from vendors and third parties like the Center for Internet Security (CIS) and the SANS Firewall Checklist.

Secure the firewall: Disable insecure protocols, schedule periodic backups, enable auditing of system changes, and send logs to an external, secured,  or firewall management solution.

Clean up the network: Identify and notify server administrators about servers, PCs, or specific applications hitting the firewall directly with outbound denied requests and malware-infected data packets. 

Remove unused rules and objects: As you continue to modify and adapt your firewall rule base, it can become weighed down with unused rules and software. That can slow traffic and efficiency and even potentially allow unsafe traffic to pass. Periodically schedule maintenance to remove outdated rules and objects.

Prioritize your most important firewall policy rules: Ensure that frequently used firewall policy rules align with your operating system, like Windows, and handle incoming traffic efficiently.

Evade DNS objects: Avoid DNS objects that call for constant DNS lookups on all traffic, which is especially crucial for small businesses relying on steady Internet connections.

Segregate Firewalls from VPNs: Separate firewalls from VPNs to manage VPN traffic and reduce strain on the network firewalls.

Manage broadcast traffic: Minimize logging of broadcast traffic to improve network traffic flow and bandwidth.

These tips, and keeping your software up to date, will help keep your firewall solutions functioning at peak performance.

How F5 Can Help

Firewalls are critical to protecting your data, both on an internal network and on the Internet. They are the first line of defense to keep out unwanted and unsafe traffic and can be configured to keep your data safe in other ways too. Yet selecting the appropriate firewall for your needs can be challenging. There are many options available, ranging from basic packet-filtering firewalls to advanced next-generation solutions with additional features like intrusion prevention systems and complex rule management tools. It’s important to consider your specific requirements and consult with experts to make an informed decision.

At F5, we live and breathe consistent, comprehensive and agile cybersecurity. We have deep experience in implementing the right type of firewall security for your organization’s needs.

At F5, we live and breathe consistent, comprehensive and agile cybersecurity. We have deep experience in implementing the right type of firewall security for your organization’s needs.

Protect your network from outside threats by maintaining a robust firewall security infrastructure.

Keep your data, your traffic, and your users’ information safe – behind the right firewall.