8 Types of Firewalls: Know Which One Is Best for Your Network

a brick wall with three lights shining from the top. bricks are in different shades of brownish red and orange
A firewall is handy for blocking out threats.

You’ve just set up your network and are now ready to add some security to it. The first thing that comes to mind is—surprise, surprise—a firewall. Good call. But what type of firewall? As of this writing, I’d say you have 8 major types of firewalls to choose from. 

Before I go over each of those 8 types of firewalls, allow me to give a brief overview of what firewalls are.

What Is a Firewall?

A firewall is a network security tool that filters inbound and outbound traffic. To do that, it uses a set of rules or conditions. Previously, they sat at network perimeters. They protect your organization’s network from external threats. 

Today, organizations use firewalls in other areas of their network. That also provides additional layers of security. For example, a firewall prevents your employees from accessing your financial or human resource systems.

These capabilities allow firewalls to keep out unwanted traffic from your network. They also prevent unauthorized outbound connections from getting established. How do they do that? Well, it depends on the type of firewall, although they do have some similarities in the way they work. Speaking of ‘the way they work’, let’s talk about that now. 

How Do Firewalls Work?

Firewalls allow or deny network traffic based on certain rules or conditions. Depending on the type of firewall, these conditions operate on specific layers of the TCP/IP or OSI conceptual models. For example, packet-filtering firewalls operate in the network layer, while application firewalls operate in the application layer.

Basic firewalls can inspect one or two layers. They also usually focus on the lower layers, e.g., the network and transport layers. What’s more, the more advanced a firewall is, the more layers it can inspect and filter. If you want more granular inspections, select a more advanced firewall type. 

Let’s go over the 8 types of firewalls now.

8 Types of Firewalls

1. Packet-Filtering Firewalls

This is the most basic type of firewall. It filters out traffic based on a set of rules—a.k.a. the firewall’s ‘ruleset’—that applies to the network layer. In some cases, it also applies to the transport layer. However, this firewall only inspects a packet’s header

Besides, this firewall allows you to create the rules. For example, you can block incoming traffic from unapproved IP addresses. You can also allow only one transport layer to pass through. 

Advantages

  • Is faster
  • Has less impact on network performance 
  • Is more affordable

Disadvantages

  • Doesn’t inspect the packet’s payload. Malicious payload may pass by undetected 
  • Lacks awareness of the state of a connection. Hence, they can’t determine if a connection is truly authorized. As a result, this makes them vulnerable to spoofing attacks 
  • Has tedious access control lists (ACLs)

Although they provide decent protection, packet-filtering firewalls aren’t effective against sophisticated threats. Therefore, you’d use a packet-filtering firewall for networks with moderately valuable assets. You’d also use it as the first line of defense in a multi-layered defense strategy.  

2. Circuit-Level Gateways

Another basic firewall is the circuit-level gateway firewall. This firewall mainly operates in the session layer. This layer deals with TCP handshakes. It also handles other mechanisms related to connection establishment, management, and termination. Firstly, the firewall inspects the messages involved in these mechanisms. Then, it compares them with predefined session rules. This enables it to determine whether a session is legitimate or not.

For instance, let’s say a session is only valid if initiated by a recognized device. In this case, the firewall blocks any session initiated by unknown devices. 

Advantages

  • Is faster
  • Is more affordable
  • Has less impact on network performance 

Disadvantages

  • Doesn’t know any threats lurking in a packet’s payload
  • Operates only on a single layer—the session layer

You’d normally deploy a circuit-level gateway firewall when you have a limited budget. Although it isn’t the best, it’s still slightly better than a packet-filtering firewall. 

3. Stateful Inspection Firewalls

A stateful inspection firewall also operates in the network and transport layers. It inspects packets, then checks to see whether they satisfy the firewall’s ruleset. If they do, they can pass through. 

In addition, the firewall can record information about each packet into a ‘state table’. From this table, the firewall can determine if a packet aligns with the expected state. If it doesn’t, the firewall blocks this packet. A stateful inspection firewall can also determine if an inbound packet is part of a currently open connection. If it is, that packet is automatically safe.  

Advantages

  • Has better context than packet-filtering firewalls when determining what to block
  • Reduces exposure to potential threats such as port scanners. That’s because it opens and closes ports based on the connection state 
  • Generates detailed logs that can help in digital forensics

Disadvantages

  • Is more resource-intensive than packet-filtering firewalls
  • Is more expensive than packet-filtering firewalls
  • Faces TCP flood attacks or other DDoS attacks that exploit ‘stateful’ characteristics

Generally, this firewall offers more than simple packet filtering. It’s also a viable option when you’re looking for something less expensive than a proxy firewall (see below).

4. Proxy Firewalls (AKA Application-Level Gateways)

Proxy firewalls operate in the highest layer of the OSI and TCP/IP models—the application layer. They can also inspect a packet’s content, not just the headers. This is deep packet inspection (DPI)

Proxy firewalls can also prevent two communicating hosts/devices from connecting together directly. At the same time, it makes each device think it’s establishing a direct connection with the other.. 

When two hosts/devices connect through a proxy firewall, the firewall establishes two connections. Basically, the firewall stands between both devices. That means external clients can’t see your servers’ IP addresses. In effect, a proxy firewall can conceal internal IP addresses from external clients.

Advantages

  • Provides security that can complement what most types of firewalls provide
  • Examines packet content and headers
  • Conceals internal IP addresses. Prevents threat actors from gathering valuable intelligence about your internal network

Disadvantages

  • Can increase latency since it’s more thorough when inspecting a packet
  • Is more expensive than even stateful inspection firewalls
  • Supports a limited number of network protocols

Concealing internal IP addresses is very useful from a security standpoint. In fact, it adds a completely different element to firewall security. Still, proxy firewalls can’t support certain network protocols. For this reason, I’d recommend you use another type of firewall to complement it. 

5. Next-Generation Firewalls

Sitting at the top of the firewall hierarchy are the next-generation firewalls (NGFWs). On top of packet filtering and stateful inspection, NGFWs also have additional features. That includes DPI, intrusion detection system/intrusion prevention system (IDS/IPS), and malware protection.

A yellow road sign labeled: NEXT GENERATION AHEAD, backdropped by a setting or rising sun and a mountain range and clouds
Onward to the next generation.

In an NGFW, IDS/IPS analyzes packet information and behavior. To do that, they use various threat detection techniques. Among these are pattern matching, protocol-based detections, heuristic-based detections, and anomaly-based detections. I won’t go into the details, but these techniques detect potential threats

An NGFW combines DPI, IDS/IPS, and malware protection. That means, it can act on a wider range of threats.  

Advantages

  • Provides multiple security capabilities in one solution
  • Inspects almost all layers
  • Decrypts SSL/TLS-encrypted traffic to inspect the content

Disadvantages

  • Is very expensive; might be impractical for most small businesses 
  • Requires more system resources 

An NGFW won’t be equally useful in big and small businesses. In fact, its price reflects its extensive abilities. It might also be overkill in small businesses. Still, large organizations may benefit from it. 

In brief, I’ve classified the firewall types above based on their function and operation layers. Next, I’ll classify the rest based on their delivery methods. Shall we? 

6. Software Firewalls

Software firewalls, a.k.a. host firewalls, are basically software applications. Therefore, you install them on the devices you want to protect. Just like regular applications, these firewalls also take up CPU, RAM, and storage resources.

Since these firewalls operate on a specific device, they’re also more aware of processes on that device. Overall, this allows them to provide more granular security

Advantages

  • Can provide highly targeted restrictions
  • Is readily available. You can also install third-party alternatives

Disadvantages

  • Competes with other applications for CPU, RAM, and storage resources
  • Doesn’t offer full platform support. For example, if a particular software firewall only provides installers for Windows, you can’t use it to secure your Mac and Linux devices
  • Can be difficult to deploy third-party software since you have to install them on each of your devices

You may deploy software firewalls on mission-critical hosts to bolster that host’s defenses. You could also get these firewalls through third-party software.

7. Hardware Firewalls

Hardware firewalls, a.k.a. appliance firewalls, are network devices with firewall capabilities. Being a separate device, it takes up its own CPU, RAM, and storage resources. Hardware firewalls are normally positioned at a network’s perimeter. They’re a gatekeeper between the external and internal network. 

In most cases, that external network is the internet, while the internal network is your own. You can also position the firewall between two internal networks to separate them.

Advantages

  • Are fewer than software firewalls so they’re easier to manage
  • Don’t compete with the applications on your servers and other endpoint devices for computing resources
  • Protects a whole network single-handedly, while a software firewall can only protect the device you installed it on

Disadvantages

  • Requires trained administrators
  • Is more expensive than software firewalls 

One hardware firewall can secure multiple hosts and endpoint devices running in the same network. That’s why you should consider deploying one at your network’s perimeter. 

8. Cloud Firewalls

A cloud firewall, or Firewall-as-a-Service (FaaS), refers to any cloud-based service that acts as a firewall. As with other cloud solutions, third-party cloud solutions providers manage and operate these cloud firewalls. They also handle almost all administrative tasks, including installation, deployment, patching, and troubleshooting.

a glowing blue cloud wrapped with a network of illuminated nodes.
Cloud firewall in action.

Advantages

  • Frees your IT admins from firewall-related administrative responsibilities
  • Is scalable (just like all cloud solutions)
  • Poses zero upfront costs
  • Offers flexible pricing 

Disadvantages

  • Sends your traffic through a third party. For some businesses, that’s not very appealing from a privacy standpoint.
  • May be more expensive  in the long run.

You’d typically go for a cloud firewall if you have no concerns about routing your network traffic through a third party. Additionally, you’d go for this type of firewall if you can’t pay hefty upfront fees.

Now that I’ve discussed the 8 types of firewalls, I’d like to remind you that each firewall works based on the OSI layer they operate on

Operation OSI Layers

Here’s a simple table you can use to refer back to which firewall works on which layer.

Note: This only applies to the first 5 types of firewalls outlined in this post. The remaining are simply classified based on their deployment

Type of FirewallOSI Layer(s) They Operate On
Packet-FilteringNetwork and transport layers
Circuit-Level GatewaySession layer
Stateful InspectionNetwork and transport layers
ProxyApplication layer
Next-GenerationAll layers except the physical layer
First thing to remember is the operation layer!

At this point, you’re probably asking yourself: how do I choose the right firewall with so many options?  I’ll help you answer this question in the next section.

Which Firewall Is Best for Your Business?

Your organization is unique. In fact, no two companies have the same assets, resources, risk appetite, and network layouts. Hence, the firewall or firewalls ideal for your business will be unique to your specific needs. Here are 5 factors to consider before making a decision

1. Level of Security Required

To know how much security you need, you should consider many factors. What do you have behind your firewall? Do you have much personal information? Do you store your trade secrets behind your firewall? How about financial or customer data? Are you running a business-critical server behind it? 

If your hosts and endpoint devices are specifically critical, deploy one of the advanced types of firewalls. If not, then perhaps a simple packet-filtering or circuit-level gateway firewall will suffice.

2. Budget Constraints

In a perfect world, everyone will have NGFWs. Still, not everyone has an unlimited budget. If you need to protect sensitive data but simply can’t afford a next-generation firewall, then you’ll probably have to go for more affordable options. Even a stateful inspection or a packet-filtering firewall is better than no firewall at all. 

3. Risk Appetite

Before you opt for the cheapest option, you need to consider how much risk you’re willing to take. Even more, consider how much risk you can afford  to take. If your data is covered by data privacy/protection laws and regulations, you also need to consider the potential costs if you suffer a data breach. 

4. Network Size

The size of your network can also help determine the types of firewalls you include in your shortlist. If you have a massive network, a software-based third-party firewall might be too impractical. It’d also be better from an administrative and cost-efficient perspective to purchase a hardware-based firewall. 

5. Combinations Available

Ideally, because different firewalls have different strengths, you might also want to consider using multiple firewalls. That way, you can also apply a defense-in-depth approach to network security. You can use basic firewalls with more advanced firewalls. 

I believe I’ve covered enough for now. Let’s wrap things up before we go our separate ways.  

Final Words

Many different types of firewalls are available in the market, and each one works for a particular purpose. You have firewalls for companies with limited budgets, firewalls for business-critical networks, firewalls for large or small businesses, and so on. Before you can pick the right firewall, you need to know the use cases of each one. We took care of that earlier. 

In this post, you learned 8 different types of firewalls, their advantages, and disadvantages. You also discovered how to choose between these types of firewalls for your business. Overall, consider your business needs when deciding which firewall to go for.

Do you have more questions about the different types of firewalls? Check out the FAQ and Resources sections below!

FAQ

What is a spoofing attack?

In a spoofing attack, a malicious entity impersonates another entity. To do so, the cybercriminal uses information associated with that second entity. For example, in an IP spoofing attack, threat actors modify IP packet source addresses. That way, these packets look like they’re coming from a different source.  

What is an access control list (ACL)?

A firewall ACL is a list of allow/deny conditions, or rules. This list allows firewalls to determine whether a packet can pass through or not. Depending on the hosts, services, and applications behind that firewall, these lists can be quite long.

What is a DDoS attack?

A Distributed Denial of Service attack is a type of cyber attack that overwhelms a network or network device (such as a firewall). In turn, it prevents it from receiving connections. In other words, it denies users access to whatever service the network or device normally provides.

What is a TCP flood attack and how does it exploit a stateful inspection firewall?

A TCP flood attack is a DDoS attack that floods the firewall with SYN packets. After that, the firewall can no longer receive additional inbound connections. SYN packets are normally sent by a client that’s attempting to establish a TCP connection. In turn, the device records these requests in a state table. Then, it responds with an SYN-ACK message. Since the client in this case is malicious, it doesn’t respond with the expected ACK message. This forces the device to keep the TCP connection and the state entry in the table open as the firewall keeps track of the connection’s state. Finally, this consumes so much memory. Consequently, as more SYN packets come in, more memory gets consumed. That continues until the device can’t accept more requests.

What is digital forensics?

Digital forensics is the science of identifying, processing, and analyzing electronic data. Usually, it helps find evidence of cybercriminal activities. It also clarifies the implementation of these activities.

Resources

TechGenix: Newsletters

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TechGenix: Article on Firewall as a Service

Find out everything you need to know about FaaS.

TechGenix: Article on Runbook Scripts and Azure Firewall

Learn how to start and stop your Azure Firewall using a Runbook script.

TechGenix: Article on Top Firewalls

Discover the top firewalls for enterprises and SMBs.

TechGenix: Article on Best Practices for Azure Storage 

Learn best practices for enabling firewalls and VMs in Azure Storage.

Explore various articles about firewalls.

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