Stateful vs. stateless firewall

| By:
Sajal Sahay

A firewall provides network security by controlling the incoming and outgoing traffic between an organization's internal and external networks. Firewalls can provide:

  • Security
  • Access control
  • Traffic filtering
  • Network segmentation
  • Logging and auditing

There are several types of firewalls, each with its own characteristics and deployment scenarios depending on the needs of your clients’ business needs. More specifically, firewalls can be distinguished in different ways like stateful firewalls, stateless firewalls, proxy firewalls, and packet filtering firewalls. 

Here, we’ll focus on understanding how stateless vs. stateful firewalls work, the pros and cons of each, specific use cases, and how they factor into the MSP’s role in cybersecurity.

What is a stateful firewall?

A stateful firewall is a type of firewall that operates at the network layer, which is considered layers 3 and 4 of the Open Systems Interconnection (OSI) model. Stateful firewalls work to identify when unauthorized individuals try to access a client’s network and analyze data within packets to check if they contain malicious code. 

Stateful firewalls maintain a state table that records information about ongoing network connections. When a packet arrives at the firewall, it is checked against the state table to determine if it belongs to an established connection. If the packet matches an existing connection in the state table, it is allowed to pass through. This process is often referred to as stateful packet inspection.

The state table of a stateful firewall stores details about each connection including:

  • Source and destination IP addresses
  • Port numbers
  • Sequence numbers
  • Relevant information 

The primary advantage of a stateful firewall is its ability to understand the context of network connections. 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.

There are several benefits of stateful firewalls for both you and your clients, including: 

  • 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 and 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. For MSPs, this simplifies the process of rule management and reduces the chances of misconfigurations.
  • 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 for each individual packet, which 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.

While there are many pros to using a stateful firewall, there can be potential downsides:

  • Limited application-level inspection: Since stateful firewalls primarily focus on the network layer (Layer 3) and transport layer (Layer 4), they may not be able to detect and block certain application-level threats or attacks that require more granular inspection.
  • Performance impact as the number of connections increases: As your clients’ business grows, the state does too, which takes up more memory and processing resources. This can impact the performance of the firewall, especially if it is handling high volumes of traffic or dealing with many concurrent connections.
  • Difficulty handling changing environments like those where network connections change frequently, or dynamic IP addresses are used. It can be challenging to set up and configure in these types of environments.  

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. When comparing stateless vs. stateful firewalls, stateless firewalls make filtering decisions based only on the information present in each packet as opposed to stateful firewalls, which maintain a state table. 

Stateless firewalls examine packets by comparing their attributes against a set of predefined rules or access control lists (ACLs) including:

  • Source and destination IP addresses 
  • Port numbers
  • Protocols

Stateless firewalls are often used in situations where basic packet filtering is sufficient or when performance is a critical factor. Packet filtering involves examining individual packets of data as they travel between networks and making decisions to allow or block them based on predefined rules. For example, if you want to block traffic from certain IP addresses, you can create a rule to block those IP addresses with an action to deny access. 

Stateless firewalls are commonly deployed at the network perimeter to provide an initial level of protection against unauthorized network traffic. 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.

A few benefits of stateless firewalls include:

  • Simplicity. In the stateless firewall vs. stateful firewall conversation, stateless is simpler in design and operation, which can help you to 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 your 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 that you provide fewer system resources and have lower processing overhead, which can increase performance speed to help you serve your clients more quickly and efficiently.
  • Scalability. With more limited data processing, a stateless firewall may be able to process additional connections, making it more suitable when helping your clients scale their business. 
  • Cost. Since stateless firewalls are less complex, they may cost less than more complex stateful firewalls. This cost benefit helps MSPs save money because you don’t have to invest in more complex tools, which means cost savings can be passed onto clients.

A few downsides related to stateless firewalls include:

  • Limited application-level inspection. Like stateful firewalls, stateless firewalls also 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.

The difference between stateful and stateless firewalls

There are several differences when it comes to stateless vs. stateful firewalls; however, the main difference is in how they approach filtering network traffic and how they maintain a connection to state information. Understanding these differences can help you serve your clients by offering them the most appropriate tools and services.  

Other differences between stateless and stateful firewalls include: 

  • Filtering. Stateful firewalls analyze packets by examining their headers and maintain a state table that tracks the state of network connections. They make filtering decisions based on the information present in each packet and the context provided by the state table, which can provide more intelligent filtering. Stateless firewalls filter packets based only on the information contained in each individual packet. They don’t maintain any state information about connections, which gives less context but can be more efficient.
  • Connection state tracking. Stateful firewalls keep track of the state or context of connections by maintaining a state table. This allows them to differentiate between legitimate packets belonging to established connections and potentially malicious or unauthorized packets. Stateless firewalls do not track the state of connections. They treat each packet in isolation, without knowledge of whether it is part of an established connection or fits within the expected state of the communication.
  • 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 complex designs and operations because of the need for connection state tracking. Stateful provides 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 client’s organization. Factors like secure remote work environments may play a role in the types of firewalls you use to ensure the utmost protection. 

Choosing the right firewalls for your clients

When supporting your clients, you want to provide the right tools to meet their needs and provide total protection. Consider these factors when choosing firewalls:

  • Assess their security needs: Consider the sensitivity of their 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 your firewall should have. Stateful firewalls are designed to identify and block unauthorized or suspicious network traffic and protect against various types of cyberattacks like IP spoofing or port scanning.
  • Define the network environment: Evaluate your network infrastructure and determine its complexity, size, and geographical distribution. Identify the types of devices, applications, and protocols used within your network. Consider if you have remote workers, branch offices, or cloud-based services, as these factors can influence your firewall requirements. The more complex the environment, the more likely you’ll want to rely on a stateful firewall.
  • Identify required features: Consider aspects 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: Discuss your client’s expected growth in network traffic, the number of concurrent connections, and the bandwidth requirements. Ensure that the firewall can handle the anticipated traffic volume without disrupting performance and can 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, which is more suitable when trying to scale; however, a more complex network will likely require a stateful firewall that can offer more flexibility and functionality as the business grows. 
  • Budget: Determine their budget for a firewall solution combined with other tools, including the initial purchase cost and ongoing maintenance or subscription fees. If your clients don’t have less dynamic network environments and less complexity, a stateless firewall is a more budget-friendly option that still provides protection. 
  • 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 platforms can be useful to you and your clients when choosing the type of firewall. A stateless firewall is simpler and can be easier to manage and configure but doesn’t offer as many features.

So, with this in mind, what are some of the best-suited potential clients for stateless and stateful firewalls? While this can vary based on client, here are some general rules of thumb you can keep in mind:

Ideal Stateless Firewall Users:

  • Small businesses: Your typical state firewalls are often simpler and more cost-effective, making them a great fit for businesses with limited network complexity and fewer security requirements.
  • Low-traffic networks: This typically includes small offices or home networks, where a stateless firewall can provide sufficient protection without the need for complex state tracking.
  • Public internet-facing services: This encompasses any publicly accessible services, such as web servers or FTP servers, where connections are initiated from the outside. Stateless firewalls can filter traffic based on IP addresses, ports, and protocols.

Ideal Stateful Firewall Users:

  • Large enterprises: Because of their extensive network infrastructure and higher security demands, these often need the additional functionality provided by stateful firewalls.
  • High-traffic networks: Enterprise networks also fall into this category, but so do networks like data centers. Stateful firewalls help perform deep packet inspection, session tracking, and advanced traffic filtering to ensure optimal security and performance.
  • E-commerce, medical and financial institutions: All of these are businesses dealing with sensitive customer data, financial transactions, or online payment processing. They need the advanced security capabilities of stateful firewalls to detect and prevent sophisticated attacks, such as session hijacking or application-layer attacks.

Managed service providers face unique cybersecurity challenges when working to secure their client’s business. Learn how to stay ahead of common threats by downloading our MSP Threat Report, updated with new predictions from our ConnectWise Cyber Research Unit (CRU).

Best practices for implementing firewalls

Firewall security is an ongoing process, so it’s crucial to stay informed about emerging threats and new firewall technologies to make sure you’re implementing the proper firewalls for your clients. The following tips can be helpful when implementing firewalls:

  • Create a firewall strategy that aligns with your client’s security policies and requirements. Clearly define the purpose, scope, and goals of a firewall implementation.
  • Perform a thorough assessment of your client’s network infrastructure, including network topology, devices, applications, and protocols. Understand the flow of network traffic and identify critical assets and potential vulnerabilities.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Test and validate firewall rules to ensure they are functioning as intended. Conduct regular penetration testing and vulnerability assessments to identify any weaknesses or misconfigurations that could be exploited.
  • 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.
  • Continuously review and update firewall policies and configurations to adapt to changes in your client’s network environment, new threats, or business requirements. 

There’s a lot to consider when helping your clients get the utmost protection for their business, and selecting the right security tech stack is the cornerstone. Start your free ConnectWise cybersecurity demo to see firsthand how our suite of cybersecurity tools can help you provide the security and protection your clients deserve. Also, to discuss more cybersecurity details and news with your peers and our experts, visit the ConnectWise Virtual Community.


Yes, a stateful firewall typically provides better visibility into network traffic compared to a stateless firewall because of its connection tracking, packet inspection, and application-level inspection capabilities.

Yes, stateless firewalls can offer performance advantages over stateful firewalls, like fewer resource requirements, more quickly process packets, simpler design, and easier to scale.

Yes, a stateful firewall can be configured to provide the same level of security as a stateless firewall and often offers greater security capabilities. While stateful firewalls have additional functionality and features compared to stateless firewalls, it is possible to configure them to operate in a stateless mode, effectively behaving like a stateless firewall.

Stateful firewalls are generally not more prone to false positives compared to stateless firewalls because the nature of stateful firewalls lends to more accurate filtering and reduces the likelihood of false positives. 

Yes, a stateless firewall can provide sufficient protection for a small business network depending on the specific security requirements and network environment. While stateless firewalls have certain limitations compared to stateful firewalls, they can still be effective in providing basic network security.

Stateful firewalls generally have better compatibility with third-party security software compared to stateless firewalls because they’re designed to be integrated into more complex security ecosystems. However, compatibility can vary depending on the types of tools being used, versions, and necessary configurations.