Stateful vs. stateless firewall

Firewalls provide network security by controlling the flow of traffic between an organization's internal systems and the outside world. However, they’re not one-size-fits-all. Several types exist, and each type uses different methods to filter traffic and protect networks. Two of the most common types are stateful and stateless firewalls, both of which make filtering decisions based on packet header data.  

However, stateful firewalls offer an added layer of protection by tracking the state of active network connections. In this guide, you’ll learn more about stateful vs. stateless firewalls, including how they work, their pros and cons, and how to choose the right one for your IT team or client.   

Key takeaways

• ​​​​​​​A stateful firewall filters traffic based on both packet header information and the state of active network connections. 

• A stateless firewall filters traffic based solely on individual packet information, such as IP addresses, port numbers, and protocols.  

• Stateful firewalls enhance protection by tracking active connections and making context-aware decisions. 

• Stateless firewalls simplify management and boost filtering speed, making them a good choice for basic or low-complexity networks.  

What is a stateful firewall?

​​​A stateful firewall is a type of network security device that inspects packet headers to determine if traffic is valid based on predefined rules, while also monitoring a dynamic record of active network connections in a database known as the state table. The state table is continuously updated as new packets are processed, enabling the firewall to detect patterns that indicate potential threats. For example, it could potentially identify a SYN flood attack, where a flood of TCP SYN packets is used to exhaust server resources. While each packet may appear legitimate on its own, the state table will register an unusually high number of incomplete connection attempts—a strong sign that an attack may be underway.  

​​​How stateful firewalls work

Stateful firewalls operate at Layers 3 and 4 of the Open Systems Interconnection (OSI) model. When a packet arrives, the firewall records details, such as the packet’s source and destination IP addresses, port numbers, and sequence numbers. It then checks the packet against the state table to determine if it belongs to an established, valid connection. If the packet matches an existing connection, it’s allowed to pass. If it doesn’t, the firewall evaluates the packet using both predefined rules and connection context to determine if the packet should be allowed or denied (dropped). This process is known as stateful inspection.  

The primary advantage of a stateful firewall is its ability to provide context-aware protection. By keeping track of the state of connections, stateful firewalls can make more intelligent decisions about which packets to allow and which to block. They can differentiate between legitimate packets that are part of an established connection and potentially malicious packets that are unauthorized or do not fit the expected state. 

What is a stateless firewall?

A stateless firewall is a type of firewall that filters network traffic based on individual packets without storing information about the state or context of connections. Stateless firewalls make filtering decisions based only on the information present in each packet, as opposed to stateful firewalls, which also maintain a state table.  

​​​How stateless firewalls work

Stateless firewalls are commonly deployed on network perimeters to provide a basic level of protection against unauthorized traffic. When a packet arrives, the firewall examines the header information, such as the source and destination IP addresses, port numbers, and protocol type. It then makes a filtering decision based on predefined rules or access control lists (ACLs). Because the firewall treats each packet independently, it applies the rules in a simple allow-or-deny fashion. If the packet matches an allow rule, it will be passed to the destination, if the packet matches a specific deny rule, or does not match a rule it will be  blocked accordingly. 

Stateless firewalls are often used in situations where basic packet filtering is sufficient or when performance is a critical factor. For example, if you want to block traffic from certain IP addresses, you can create a rule to deny traffic from specific addresses.  Or, in cases where no inbound rules are necessary and other security measures are in place to protect the environment. However, for more advanced security requirements or environments with complex networking needs, stateful firewalls or other security technologies with deeper inspection and stateful capabilities may be more suitable. 

The differences between stateful and stateless firewalls

​​​The main difference between stateful and stateless firewalls is that stateful firewalls maintain a database of active network connections while stateless firewalls don’t. The state table provides stateful firewalls with context about ongoing traffic, enabling more intelligent and dynamic filtering decisions. In contrast, stateless firewalls filter packets solely based on the information contained in each individual packet. While the latter approach involves less context, it can be faster and more resource-efficient. 

Beyond connection tracking, other differences between stateless and stateful firewalls include:  

• Application-level inspection. Stateful firewalls can offer more advanced application-level inspection by analyzing the content and behavior of higher-level protocols, allowing for deeper inspection and filtering at the application layer (Layer 7). Stateless firewalls typically lack advanced application-level inspection capabilities. They primarily focus on network and transport layer information, making filtering decisions based on packet headers rather than analyzing the content or behavior of higher-level protocols. 

• Complexity and flexibility. Stateful firewalls have more c​​omplex designs and operations because of the need for connection state tracking. They also provide more advanced functionality and flexibility, which can accommodate more dynamic networking environments. Stateless firewalls are more suitable for basic packet filtering needs and scenarios where performance is a critical factor. However, they may struggle to handle complex networking requirements. 

The choice between stateful vs. stateless firewalls will depend on the specific security requirements, network environment, and performance considerations of your organization or your client’s. Factors like secure remote work environments may play a role in the types of firewalls you use to ensure the utmost protection.  

Pros and cons of stateful vs. stateless firewalls

Stateful and stateless firewalls each offer unique advantages but also have their drawbacks. Below, find the key pros and cons of each to help you determine which type of firewall may be best for your team or your client’s organization. 

Stateful firewall pros and cons

First, a closer look at the key pros and cons of stateful firewalls.  

Pros

• Improved security. By maintaining connection states, stateful firewalls can identify and block unauthorized or suspicious network traffic. They can also prevent various types of attacks, such as IP spoofing, port scanning, and connection hijacking. This can help quickly identify problems with less work for your IT team or less downtime for your clients. 

• Simplified rule configuration. Stateful firewalls can allow returning packets for outgoing connections without the need for explicit rules for each response packet. This simplifies the process of rule management and reduces the chances of misconfiguration. 

• Enhanced performance. Stateful firewalls can process packets more efficiently by leveraging the state information stored in the state table. They can quickly determine the state of a packet and make forwarding decisions without extensive ​​packet inspection. This saves your team time while supporting your clients’ business needs and goals. 

• Granular control. Stateful firewalls allow administrators to define policies based on the state of a connection. This gives you granular control and greater visibility over network traffic by allowing different rules for the initial connection establishment, ongoing communication, and connection termination phases. 

Cons

• Sizing of the firewall is critical:  As a business grows, the state table does as well, which takes up more memory and processing resources. This can impact the firewall’s performance, especially if it is handling high volumes of traffic or dealing with many concurrent connections.  Properly sizing any firewall is a critical step to ensure performance matches the needs of a business. 

Stateless firewall pros and cons

Next, here are the key advantages and drawbacks of stateless firewalls.  

Pros

• Simplicity. In the stateless vs. stateful firewall conversation, stateless is simpler in design and operation, which can help you configure and implement firewalls. Stateless firewalls focus on filtering packets based on basic header information and do not require the maintenance of connection states, streamlining IT processes. 

• Efficiency. Stateless firewalls are generally more efficient in terms of performance compared to stateful firewalls. Since they do not keep track of connection states, they require fewer system resources and have lower processing overhead, which can increase performance speed. 

• Scalability. With more limited data processing, a stateless firewall may be able to process additional connections, making it more suitable for large throughput needs in organizations that have other security measures in place. 

• Cost. Since stateless firewalls are less complex, they may cost less than more complex stateful firewalls—translating into savings for organizations.  

Cons

• Limited application-level inspection. Stateless firewalls typically have limited capabilities for deep inspection at the application layer (Layer 7). They primarily focus on network and transport layer information, making filtering decisions based on packet headers rather than analyzing the content or behavior of higher-level protocols. 

• Stateless nature. The stateless nature of these firewalls can pose challenges in environments that require more advanced functionality, such as handling dynamic IP addresses, Network Address Translation (NAT), or load balancing. Stateless firewalls may struggle to manage complex networking scenarios that rely on tracking connection states. 

Choosing the right firewalls

​​​Whether you’re evaluating options for your internal IT team or external clients, effective protection starts with selecting the right firewall. As you weigh your options, here are key factors to keep in mind: 

Security needs: Consider the sensitivity of the organization’s data, regulatory guidelines, the level of protection needed, and the potential threats they may face. This assessment will help you determine the specific features and capabilities the firewall should have. Stateful firewalls are particularly effective at blocking unauthorized or suspicious traffic and can protect against common cyberattacks like IP spoofing, port scanning, and connection hijacking. 

Network environment: Evaluate the network infrastructure and determine its complexity, size, and geographical distribution. Identify the types of devices, applications, and protocols used within the network. Consider if there are remote workers, branch offices, or cloud-based services, as these factors can influence the firewall requirements. The more complex the environment, the more likely you’ll want to rely on a stateful firewall. 

Required features: Consider features such as:

• Packet filtering
• Application-level filtering
• Intrusion detection and prevention
• VPN support
• Content filtering
• Identity-based controls
• Logging and reporting capabilities
• Integration with other security tools 

Scalability and performance: Evaluate expected growth in network traffic, concurrent connection volumes, and bandwidth requirements to ensure the firewall can handle current and future demands without performance issues. Additionally, plan to accommodate future changes, such as increased network complexity, additional security requirements, or integration with emerging technologies. Stateless firewalls do less data processing and may be able to process additional connections. However, a more complex network will likely require a stateful firewall that can offer more flexibility and functionality as the business grows.

Budget: Determine the budget for a firewall solution combined with other tools, including the initial purchase cost and ongoing maintenance or subscription fees. A stateless firewall can be a more budget-friendly option that still offers protection when an organization operates in a relatively static, low-complexity network environment.  

Ease of use and management of the firewall: Features such as a user-friendly interface, centralized management capabilities, reporting and monitoring tools, and integration with security management solutions are also important. A stateless firewall is simpler and can be easier to manage and configure, but doesn’t offer as many features. 

​​​Ideal firewall use case scenarios

With all this in mind, what are some of the best-suited potential fits for stateless and stateful firewalls? While it can vary based on the organization, here are some general rules of thumb to keep in mind.  

Ideal stateless firewall users: 

• Small Branch Office / Home Office: Stateless firewalls are often simpler and more cost-effective, making them a good fit for smaller SOHO organizations with limited network complexity and more basic security needs. 

• Guest Networks: A stateless firewall can often provide sufficient protection for guest networks that don’t need complex state tracking.  

Ideal stateful firewall users: 

• Large enterprises: Large enterprises often need the additional functionality provided by stateful firewalls due to their extensive network infrastructure and higher security demands. 

• High-traffic networks: Other organizations with high-traffic networks, like data centers, also tend to need stateful firewalls to perform deep packet inspection, session tracking, and advanced traffic filtering. 

• E-commerce, medical, and financial institutions: Businesses with publicly facing applications or who are dealing with sensitive  data, financial transactions, or online payment processing often need stateful firewalls to detect and prevent sophisticated attacks, such as session hijacking or application-layer attacks. 

Best practices for implementing firewalls

​​​Once you’ve selected the right type of firewall for an organization, the next step is proper implementation. The following steps can help ensure a smooth and successful deployment:  

1. Create a firewall strategy that aligns with the organization’s security policies and requirements. Clearly define the purpose, scope, and goals of a firewall implementation.
2. Perform a thorough assessment of the organization’s network infrastructure, including network topology, devices, applications, and protocols. Understand the flow of network traffic and identify critical assets and potential vulnerabilities.
3. Define rule sets that dictate how traffic should be allowed or denied by the firewall. Follow the principle of least privilege, allowing only the necessary traffic and blocking everything else. Regularly review and update rule sets to ensure they remain relevant and effective.
4. Implement a defense-in-depth approach by combining multiple layers of security controls, such as intrusion detection/prevention systems (IDS/IPS), antivirus software, web application firewalls (WAF), and secure network segmentation, in addition to stateless or stateful firewalls.
5. Adhere to industry-standard security practices when configuring and managing firewalls. Use strong, unique passwords for firewall administration accounts, enable multi-factor authentication (MFA), and regularly update firewall firmware or software to patch vulnerabilities.
6. Secure firewall management interfaces, such as the web console or command-line interface, with strong passwords and appropriate access controls. Limit access to the management interfaces from trusted networks or IP addresses.
7. Implement logging and monitoring capabilities on your firewall to detect and respond to potential security incidents. Regularly review firewall logs and analyze traffic patterns for signs of malicious activity. Perform periodic security audits to validate the effectiveness of your firewall configuration and ensure compliance.
8. Test and validate firewall rules to ensure they’re functioning as intended. Conduct regular penetration testing and vulnerability assessments to identify any weaknesses or misconfigurations that could be exploited.
9. Provide training programs to educate stakeholders about the importance of firewall security. Topics should include safe network practices, recognizing potential threats, and reporting suspicious activities.
10. Continuously review and update firewall policies and configurations to adapt to changes in the organization’s network environment, new threats, or business requirements.  

Improving your cybersecurity with ConnectWise

​​​For MSPs and IT teams alike, choosing the right firewall is just one part of building a resilient security stack. ConnectWise cybersecurity solutions help strengthen your frontline defenses by integrating tools like SIEM for advanced threat detection and MDR for 24/7 response support—both designed to complement firewall protections. Whether you're managing security in-house or across multiple client environments, ConnectWise delivers the visibility, automation, and support needed to reduce risk and stay ahead of evolving threats. 

Start your free ConnectWise cybersecurity demo to see how our software can elevate your protection strategy. You can also explore the ConnectWise Virtual Community to connect with cybersecurity experts and peers tackling the same challenges.