Stateful vs Stateless Firewalls: Comparing the Differences

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Stateful and stateless firewalls both play an important role against today’s cybersecurity threats. Their use is based on the security demand and applicability. Firewalls are an essential part of network protection against persistent threats to the information system. Firewalls can often be broken down into stateless and stateful: stateless firewalls perform based on static information such as destination and source, while stateful firewalls filter data packets based on full context. They have their own strengths and weaknesses in filtering network traffic.

Continue reading to learn all about stateless and stateful firewalls, and when you should use one or the other.

What are Stateless Firewalls?

A stateless firewall processes network packets independently according to a predefined ruleset and determines if an arriving data packet is considered “safe” based on the set of security rules the firewall allows it to access. Usually, the rules are chosen by the network administrator and do not change despite the context. New incoming or outgoing packets are not influenced by the results of previous network traffic or connection. 

A stateless firewall defines the rules for both incoming and outgoing packets in a system and does not differentiate between traffic. They do not inspect the traffic or store information on the connection state. A stateless firewall is only intended to match predefined patterns and rules so they can avoid bottlenecks in the networks when needed.

A stateless firewall is also known as an access control list and applies to both the network layer and physical layer (as well as the transport layer on occasion) of the Open Systems Interconnection (OSI) model. The firewalls are designed to deliver network security based on static information. They perform network filtering based on header information in the packets such as Source IP, Destination IP, port number, and so on. The stateless firewalls are not connection-oriented and the process is less rigorous. Stateless firewalls are simple network security solutions yet are typically more performative and still very relevant in today’s threat protection.

Stateless firewalls pros

  • Stateless firewalls are less complex compared to stateful firewalls.
  • They can perform quite well under pressure and heavy traffic networks.
  • Stateless firewalls are considered to be less rigorous and simple to implement.
  • Performance delivery of stateless firewalls is very fast.
  • Stateless firewalls are generally cheaper compared to stateful firewalls.

Stateless firewall cons

  • Stateless firewalls do not analyze the entire packet, only check to satisfy existing rules.
  • The firewall does not monitor or inspect the traffic and cannot identify the traffic types.
  • When malicious traffic matches a forwarding rule, the stateless firewalls will be forwarded even if not logically valid. 
  • Configuration should be done by someone familiar with the traffic and attacks.
  • Stateless firewalls are less secure and may need extra energy.

What are Stateful Firewalls?

A stateful firewall inspects each packet according to a set of rules. If the packets match the rules then the firewall approves them to travel freely in the network: otherwise the packets will be blocked. The firewall tracks the state of active network connections and can perform at multiple stages. A stateful firewall is aware of the communication path and can monitor the traffic streams end to end. The firewall keeps the logical context of data exchanged in a stream and can avoid forwarding non-logical network traffic. A stateful firewall always monitors the state of network connections. Once a particular traffic has been approved by the firewall only then is it added to a state table.

Stateful firewalls can be considered an evolution of stateless firewalls meant to deal with modern threats efficiently. The firewalls constantly analyze the complete context of traffic and data packets. They check the data packet behaviors and can filter out suspicious data if there is any security risk. Stateful firewalls can observe traffic streams in their entirety and they can be used at the edge of the network or within. The firewalls are suitable at the transport layer and network layer of the OSI model. They investigate transport layer headers and above, analyze traffic flow and support application-aware inspections. Stateful inspection keeps track of each incoming and outgoing connection by analyzing the header of the packets and additional payload information.

Stateful firewall pros

  • Stateful firewalls are intelligent systems that can make future filtering decisions.
  • They are highly skilled in detecting forged or unauthorized access.
  • Stateful firewalls have a powerful memory to keep key aspects of connections.
  • The firewalls offer extensive logging capabilities and robust attack prevention.
  • Stateful firewalls do not require many ports to open effective communication.

Stateless firewall cons

  • The system demands a high memory and processing power to maintain state tables.
  • The data transfer rate of stateful firewalls is slower compared to stateless firewalls.
  • Stateful firewalls must be updated with the latest software, as vulnerabilities can allow them to be compromised by hackers.
  • In some cases, the firewalls can be tricked to allow or attract harmful connections.
  • Stateful firewalls can be vulnerable to distributed denial-of-service attacks.

Read more: 7 Different Types of Firewalls & Deployment Options Explained

When You Should Use Stateful Firewalls vs Stateless Firewalls

Stateful and stateless firewalls are both used widely according to security demands and usability of different areas of applications. You have to understand which firewall applies to your security needs for your organization and how much you may want to spend on them. 

A stateless firewall may be a good choice for a limited storage system or small network due to cost efficiency. It should be noted that stateful firewalls offer an “intelligent” solution, whereas stateless firewalls may need to be carefully configured by someone familiar with the traffic and attacks.

Therefore, stateless firewalls could be a better option for small businesses  due to affordability and can keep their business running safely. Stateless firewalls attract small business owners for faster performance with the ability to perform quite well under pressure and heavy traffic networks.

For larger enterprises, stateful firewalls are highly skilled in detecting forged or unauthorized access and have a powerful memory to keep key aspects of connections. Therefore, for larger enterprises, stateful firewalls could be a better option with intelligent solutions and robust attack prevention.

Bottom Line: Differences Between Stateful and Stateless Firewalls

Parameter Stateless Firewalls Stateful Firewalls
Working principle Stateless firewalls based on static information Stateful Firewalls based on full context
Processes network packets According to a predefined ruleset and determined independently According to a predefined ruleset and influenced by the previous results
Applies to OSI model Network and physical layer, sometimes transport layer Transport and network layer
Suitable to Small network and less complex situations Large network and more complex situations
Connection based filtering No Yes
Performance delivery Fast Slow
Entire packet analyze No Yes
Implementation Simple Complex
Attack prevention skills Low High
Application-aware inspections No Yes
Memory and CPU intensive Less High
Product Cost Inexpensive Expensive

The primary difference between stateful and stateless firewalls is the level of information used to make decisions about whether to allow or block network traffic. Stateful firewalls maintain a record or “state” of all active connections passing through them: if the packet is part of an established connection, the firewall allows it through. 

Stateless firewalls do not store information about the current state of a network connection: the firewalls decide whether to allow or block network traffic based solely on the data it contains.

Stateful firewalls provide more robust security and better performance, but require more processing power and memory. On the other hand, stateless firewalls are less resource-intensive and are easier to configure but offer less robust security. The choice between stateful and stateless firewalls depends on the specific security needs and available resources of the network being protected.

Learn more about firewall placement and why it is important.

Al Mahmud Al Mamun
Al Mahmud Al Mamun
Al Mahmud Al Mamun is a writer for TechnologyAdvice. He earned his B.S. in computer science and engineering from Prime University, Bangladesh. He attained more than 25 diploma courses and 100 certificate courses. His expertise and research interests include artificial intelligence (AI), artificial neural networks, and convolutional neural networks.

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