Types of Firewalls Defined and Explained (2024)

What Are the Different Types of Firewalls?

There are many types of firewalls, often categorized by system protected, form factor, network placement, and data filtering method, including:

Network firewall
Host-based firewall
Hardware firewall
Software firewall
Internal firewall
Distributed firewall
Perimeter firewall
Next-generation firewall (NGFW)
Packet filtering firewall
Circuit level gateway
Web application firewall
Proxy firewall
Stateful inspection firewall

Capabilities of Modern Firewalls

Since their inception, firewalls have remained a network security cornerstone. As technology has evolved, so have firewall capabilities and deployment methods.

Advancements in technology have led to the emergence of many firewall variations. The broad range of terms and options can be confusing. Different firewalls perform distinct functions, which is one way to establish distinctions between types. A common method for categorizing firewall types is by the system they protect, form factor, placement within network infrastructure, and data filtering method.

Organizations may require multiple firewall types for effective network security. It’s also important to note that one firewall product can deliver multiple firewall types.

Firewall Types by Systems Protected

Network Firewall

A network firewall is positioned at the juncture between trusted and untrusted networks, such as internal systems and the internet. Its primary role is to monitor, control, and decide on the validity of incoming and outgoing traffic based on a predefined set of rules. These rules are designed to prevent unauthorized access and maintain network integrity.

The operational function of a network firewall lies in its ability to scrutinize each data packet. By comparing packet attributes like source and destination IP addresses, protocol, and port numbers to its established rules, it effectively blocks potential threats or undesired data flow. Whether implemented as hardware, software, or both, its placement ensures comprehensive traffic screening.

Beyond simple traffic regulation, network firewalls offer logging capabilities. Logs assist administrators in tracking and probing suspicious activities.

Host-Based Firewall

A host-based firewall is software that operates on a singular device within a network. It is installed directly onto individual computers or devices, offering a focused layer of protection against potential threats. By examining the incoming and outgoing traffic of that specific device, it effectively filters harmful content, ensuring that malware, viruses, and other malicious activities do not infiltrate the system.

In environments where network security is paramount, host-based firewalls complement perimeter-based solutions. While perimeter defenses secure the broader network's boundaries, host-based firewalls bolster security at the device level. This dual protection strategy ensures that even if a threat surpasses the network's primary defenses, individual computers remain shielded.

Firewall Types by Form Factors

Hardware Firewall

A hardware firewall is a physical device placed between a computer or network and its connection to the internet. It operates independently of the host device, examining inbound and outbound traffic to ensure compliance with set security rules. By actively analyzing packets of data, the hardware firewall can identify and block threats, providing a robust barrier against potential cyber intrusions.

The operation of a hardware firewall involves connecting it directly between the internet source and the target network or system. Once implemented, all internet traffic, whether incoming or outgoing, must pass through this device. As it inspects each data packet, decisions are made based on predefined security policies. Malicious or suspicious traffic is blocked, so only safe and legitimate data reaches the internal network. Threats are intercepted before reaching internal systems, offering a proactive approach to network security.

Software Firewall

A software firewall is a firewall in a software form factor rather than a physical appliance, which can be deployed on servers or virtual machines to secure cloud environments.

Software firewalls are designed to protect sensitive data, workloads and applications in environments wherein it is difficult or impossible to deploy physical firewalls.

Types of Software Firewalls

Types of software firewalls include container firewalls, virtual firewalls (also known as cloud firewalls), and managed service firewalls.

Container Firewalls

A container firewall is a software version of a next-generation firewall, purpose-built for Kubernetes environments.

Container workloads embedded in Kubernetes environments can be difficult to secure with traditional firewalls. Consequently, container firewalls help network security teams safeguard developers with deep security integration into Kubernetes orchestration, preventing modern application attacks and data exfiltration.

Virtual Firewalls

A virtual firewall is a virtualized instance of a next-generation firewall, used in virtual and cloud environments to secure east-west and north-south traffic. They are sometimes referred to as “cloud firewalls.”

Virtual firewalls are a type of software firewall which can inspect and control north-south perimeter network traffic in public cloud environments, as well as segment east-west traffic inside physical data centers and branches. Virtual firewalls offer advanced threat prevention measures via microsegmentation.

What Is a Virtual Firewall?

Cloud Firewalls

The term “cloud firewall” aligns most closely with the concept of a virtual firewall. These are software-based mechanisms anchored in the cloud, primarily responsible for sifting out malevolent network traffic. The delivery model in the cloud has led to common identification as firewall-as-a-service (FWaaS).

A noteworthy iteration of this terminology is the "public cloud firewall." Emphasizing public cloud deployment, this concept fundamentally mirrors hardware firewalls in function.

Definitions for the term "cloud firewall" vary. Predominantly, the term refers to firewalls situated in the cloud and offered by security providers, capabilities directly furnished by cloud hyperscalers, or appliances guarding applications within assorted public clouds. It appears that an industry standard definition has not yet emerged.

What Is a Public Cloud Firewall?

Managed Service Firewalls

Software firewalls are also available as a managed service, similar to many other software-as-a-service (SaaS) offerings. Some managed service firewall offerings provide a flexible way to deploy application-level (Layer 7) security without the need for management oversight. As managed services, some of these firewalls can be quickly scaled up and down

Hardware Firewall vs. Software Firewall

A hardware firewall is a standalone physical device positioned between the network and its connected devices. It monitors and controls both incoming and outgoing network traffic based on predefined security policies. Deployment of a hardware firewall requires skilled personnel to ensure proper setup and ongoing management.

On the other hand, a software firewall operates within a server or virtual machine. This type of firewall runs on a security-centric operating system, typically layered over generic hardware resources. It can often be rapidly implemented using cloud automation tools.

Both hardware and software firewalls provide essential protection for network security, with their choice determined by specific requirements and deployment contexts.

Firewall Types by Placement within Network Infrastructure

Internal Firewall

An internal firewall functions primarily within a network's confines, targeting security threats that may have already penetrated the perimeter defenses. Unlike external or perimeter firewalls which focus on incoming external threats, internal firewalls concentrate on the traffic between devices within the network. This is relevant because not all threats originate from the internet. Issues can arise from within an organization, be it unintentional employee errors or malicious intentions.

This type of firewall operates under the principle of Zero Trust. It doesn't automatically trust any activity just because it originates from within the network. By segmenting the network into distinct zones, each with its specific security measures, the firewall ensures potential threats don't spread unchecked across the entire system. Microsegmentation, for instance, is a technique wherein the network is divided into smaller, isolated zones, enhancing security. Additionally, these solutions may utilize intelligent automation to adapt and update security protocols based on observed and established safe behaviors, ensuring continuous and dynamic protection.

Distributed Firewall

A distributed firewall is a network security mechanism designed to safeguard an organization's entire infrastructure. Unlike traditional firewalls, which are typically concentrated on a single node or device, distributed firewalls operate across a network. They harness the capabilities of multiple devices to monitor and regulate traffic, ensuring consistent and complete protection.

One primary advantage of distributed firewalls is their ability to monitor both internal and external traffic. Conventional firewalls, historically, have focused on external threats. However, as security threats evolve, the need to monitor internal traffic for potential threats has become paramount. Distributed firewalls fill this gap, examining traffic both within and entering the network, thus offering a more comprehensive security layer.

Another notable characteristic of distributed firewalls is their scalability and efficiency. By decentralizing the traffic monitoring process across numerous devices or nodes, they prevent bottlenecks and points of congestion. This distributed nature ensures that as an organization expands or as traffic increases, the firewall system can scale accordingly without compromising performance or security.

Perimeter Firewall

A perimeter firewall establishes the boundary between a private network and the public domain of the internet. Functioning as the primary defense, this type of firewall meticulously inspects every data byte attempting to pass through. This safeguards the private network from unwarranted and potentially harmful data. A significant role of a perimeter firewall involves differentiating and subsequently allowing or disallowing traffic based on pre-defined parameters, ensuring only legitimate and safe data gains entry.

The efficacy of a perimeter firewall hinges on its ability to recognize and discern the nature of data packets. It examines both the header information and the payload of each packet to determine intent. This level of examination aids in the identification of potential threats, like malware or indications of a looming cyberattack, facilitating timely preventive action.

The perimeter firewall can oversee both internal and external traffic. While internal traffic flows between users, devices, and systems within the network, external traffic originates from the internet. Given the sheer volume and variability of threats on the internet, managing external traffic becomes a pivotal task for these firewalls.

Over time, advancements in technology have redefined perimeter firewall architecture. The introduction of next-generation firewalls (NGFWs) underscores this evolution. Incorporating the capabilities of basic packet filtering and stateful inspection, NGFWs integrate additional security functions, including deep packet inspection and intrusion detection/prevention mechanisms. Such advancements enhance the overall defense mechanism, ensuring private networks remain shielded.

Firewall Types by Data Filtering Method

A next-generation firewall (NGFW) extends the capabilities of traditional firewalls, offering more comprehensive security solutions. Unlike their predecessors focused primarily on stateful inspection, NGFWs provide enhanced features to understand and control application traffic, integrate intrusion prevention mechanisms, and utilize cloud-sourced threat intelligence. This evolved approach ensures a more meticulous inspection of data packets, accounting for the intricate nuances of modern cyber threats.

Beyond access control, NGFWs are adept at addressing modern challenges like advanced malware and sophisticated application-layer attacks. They delve deeper into the data, examining the nature of the traffic and identifying patterns that could signal potential threats. The integration of threat intelligence sources within NGFWs ensures they remain updated with the latest threat vectors, maintaining their effectiveness against evolving cybersecurity challenges.

The emergence of NGFWs represents a significant stride forward. By marrying the fundamental features of traditional firewalls with advanced security capabilities, NGFWs offer a robust, multi-faceted line of defense. Their ability to operate at the application layer and integrate additional protection mechanisms makes them an indispensable asset in safeguarding corporate networks from both conspicuous and covert threats.

Packet Filtering Firewall

Packet filtering firewalls operate at the network layer, responsible for regulating the flow of data packets between networks. These firewalls rely on pre-defined rules that evaluate specific attributes of the packets such as source IP, destination IP, ports, and protocols. If the attributes match the established rules, the packet is allowed to pass through. If not, the packet is blocked.

Types of packet filtering firewalls can be further broken down into static packet-filtering firewalls, dynamic packet-filtering firewalls, stateless packet-filtering firewalls, stateful packet-filtering firewalls.

Circuit Level Gateway

A circuit-level gateway functions primarily at the session layer of the OSI model. Its role is to oversee and validate the handshaking process between packets, specifically for TCP and UDP connections. By examining the handshake process and the IP addresses associated with packets, this firewall identifies legitimate traffic and deters unauthorized access. A circuit-level gateway primarily focuses on header information, ensuring the traffic aligns with the firewall's rule set without delving into the actual content of the data packets.

When a user seeks to initiate a connection with a remote host, the circuit-level gateway establishes a circuit, which is essentially a virtual connection between the user and intended host. This gateway then supervises the traffic traversing this circuit. It ensures traffic aligns with an already established connection, permitting only verified and authorized traffic to pass. When data packets meet these criteria, the firewall facilitates a connection, allowing either the transmission control protocol or user datagram protocol to communicate with the destination server on the user's behalf. If packets do not meet the criteria, the gateway rejects the connection, effectively ending the session.

The distinguishing factor for circuit-level gateways is their simplicity in design and implementation. Since they are not designed to understand or interpret application protocols, their deployment is often straightforward. A circuit-level gateway is distinct from basic port forwarding mechanisms. In a circuit-level gateway setup, the client recognizes an intermediate system, making the gateway's operations more comprehensive than mere port forwarding.

Web Application Firewall

A web application firewall, commonly referred to as WAF, serves as a specialized layer of protection for web applications, web servers, and APIs. It functions by examining and filtering HTTP traffic, thereby safeguarding web applications from threats like cross-site-scripting (XSS), SQL injection, and file inclusion. WAFs differentiate themselves by operating at Layer 7, specifically targeting application layer threats.

Positioned in front of web applications, WAFs act as reverse proxies. This means that they intercept and inspect requests bound for the web application, ensuring only legitimate traffic passes through. Any suspicious or malicious traffic is promptly blocked, preventing potential attacks. This architecture not only enhances the security of web applications but aids in shielding applications from direct exposure to internet threats.

To maintain efficiency, WAFs employ policies or sets of rules. These rules help the firewall discern between benign and potentially malicious traffic. Adjustments to these policies can be executed swiftly, allowing for immediate response to emerging threats or changing attack patterns. Regular updates to these rules are crucial.

What Is a WAF? | Web Application Firewall Explained

Proxy Firewall

A proxy firewall stands as a vital defense mechanism for networks, operating at the application layer. Also referred to as an application firewall or gateway firewall, it primarily functions as an intermediary, filtering messages between computer systems and external servers. By doing so, it safeguards network resources from potential cyber threats.

Unlike conventional firewalls, which do not decrypt or extensively inspect application protocol traffic, proxy firewalls delve deeper. They scrutinize traffic entering and leaving a network, identifying signs of potential cyberattacks or malware. Central to their operation, firewalls maintain their own Internet Protocol (IP) addresses. This design ensures that external networks cannot directly access the protected internal network.

The operational process of a proxy firewall is straightforward yet effective. Computers within a network connect to the internet using the proxy as their gateway. When a user attempts to access an external website or service, their request is intercepted by the proxy firewall. This firewall evaluates the request against its set policies. If deemed safe, it establishes a connection on behalf of the user. Through this method, the proxy firewall ensures only authorized and safe connections are established.

Stateful Inspection Firewall

Stateful inspection firewalls are integral in active network connection monitoring. By tracking these connections, they analyze the context of incoming and outgoing traffic, ensuring only safe data packets traverse the network. Located at Layers 3 and 4 of the Open Systems Interconnection (OSI) model, their primary function is to filter traffic based on its state and context. This method is more thorough than mere packet-level protection because it understands the broader context of data exchanges.

The underlying technology of a stateful firewall is its ability to perform packet inspection. It scrutinizes the contents of each data packet to determine if it matches the attributes of previously recognized safe connections. If there's a match, the data is allowed through. However, if discrepancies arise, the packet undergoes policy checks to ascertain its safety.

A practical example of stateful inspection's ability is its interaction with Transmission Control Protocol (TCP). TCP facilitates the simultaneous sending and receiving of data and uses a three-way handshake process to establish connections. The handshake involves synchronization (SYN), synchronization-acknowledge (SYN-ACK), and acknowledgment (ACK). The stateful firewall utilizes this process to recognize potential threats by examining packet contents during the handshake. If any red flags arise, such as suspicious origins or destinations, the firewall immediately discards the data. This approach ensures that only legitimate and secure connections are maintained.

Layer 3 vs. Layer 7 Firewall

A Layer 3 firewall functions at the network layer of the Open Systems Interconnection (OSI) model. It primarily focuses on filtering traffic based on parameters like IP addresses, port numbers, and specific protocols, making its approach broad and akin to routers' operations. This type of firewall offers efficient and wide-ranging coverage, providing protection by allowing or denying packets based on their source and destination details.

Conversely, a Layer 7 firewall operates at the application layer of the OSI model. Its main advantage lies in its ability to deeply inspect the content within data packets. By analyzing the specific contents, it can discern between benign and malicious application-specific traffic, effectively guarding against threats like SQL injections or other application-layer attacks.

In the realm of network security, it's not about choosing one over the other. Both types of firewalls offer unique advantages. While Layer 3 firewalls provide rapid, broad-spectrum filtering, Layer 7 firewalls delve into the intricate details of data, ensuring a deeper level of protection. Combining their strengths offers a robust defense-in-depth strategy for optimal security.

How to Choose the Right Firewall for a Business Network

Selecting an appropriate firewall for a business network requires a clear understanding of the network architecture, protected assets, and specific organizational needs.

Start by defining the technical objectives of the firewall. Determine if the network requires a comprehensive solution or if a more straightforward firewall suffices. It's crucial to consider the type of network, importance of assets, budget, and expected traffic, for starters. Assess how firewall products integrate into existing infrastructure. Finally, be sure to consider compliance requirements and relevant data protection laws.