How Is Stateful Inspection Different From A Traditional Firewall?

A Stateful Inspection firewall inspects the payload of packets and the state in which they were sent or received. For example, if an email server receives a message with an attachment and then sends it on to another user inside its organization. This would be considered “stateful” because both sides are aware that there was an exchange of data between them.

This is different from just looking at what’s in the packet itself. The main benefit of this method is that it can catch malicious activity before it enters your network. It allows you to detect breaches much earlier than other methods by inspecting packet content, the ports used, and the IP addresses involved. 

It can even keep track of data flows. This is to detect data leaks or attempts to install malware on hosts inside your network. We have made a detailed piece about What a stateful inspection firewall is [What Is A Stateful Firewall article here].

How Is Stateful Inspection Different From A Traditional Firewall?

There are several differences between a Stateful Inspection and a Traditional Firewall. Stateful Inspection is a firewall that offers some of the best protection against newer attack methods. It can be seen in packet payloads as the data transfers. On the other hand, traditional firewalls only look at packet headers and concentrate mainly on intrusion prevention. 

Stateful InspectionTraditional Firewall
Stateful Inspection can monitor the actual contents of packets as they pass through the router. This allows it to detect attacks during data transfer between users and servers, such as SQL injections or cross-site scripting. Traditional firewalls cannot catch many types of modern breaches because they can only see into packet headers.
Stateful Inspection is proactive so that it can detect unexpected traffic. Traditional firewalls are only reactive, so they typically stop attacks that have already compromised a system. 
Stateful Inspection can be read into each packet, allowing it to inspect headers and payloads separately.Traditional firewalls can block or allow entire packets based on information in the header.
The proactive nature of Stateful Inspection makes it more suitable for organizations vulnerable to state-sponsored cybersecurity risks.Many traditional firewalls use stateless inspection and are only suitable for home networks or small businesses with no security threats.

What Is Stateful Inspection And How Does It Work?

A stateful firewall works by looking at state information in conjunction with packet content. This is to determine whether to allow, block, or modify the packet. 

It does not look for specific data in packets. A stateful firewall checks for changes in the network that may be the cause of the traffic being monitored.

Stateful inspection is a method of analyzing packets on a network. The stateful inspection looks at the flow of data and how it has changed from one point to another. 

This allows an analyst to decide which packets are legitimate and which ones are not. This technology also monitors how data flows from one computer to another. This is because the malicious activity can be blocked before it causes any damage.

What Are The Advantages Of Using Stateful Inspection Over A Traditional Firewall?

Ability To Inspect Packets

The advantages of using a stateful inspection firewall over a traditional one mainly have to do with their ability to inspect packets. This type of firewall can inspect all packets it receives, not just packets destined for TCP port 80. 

Ability To Detect Inactive Connections

In addition, because it’s inspecting all of the packets, it will detect inactive connections and clean them up by kicking inactive connections from the connection pool.

This is a massive advantage over traditional firewalls with connection limits and must drop new connections if they reach the limit. 

Ability To Keep Track Of The Traffic

In addition, stateful inspection firewalls can keep track of all of the traffic that crosses it; this means that it can keep track of its internal sessions (outbound connections) and keep track of the traffic on its external interface. 

This means that it can detect when an expected connection cannot be made and act accordingly (for example, if an external web crawler attempts to find your website on port 80 but drops off, a stateful inspection firewall would notice this immediately take action).

Easier To Understand

The additional benefit of stateful inspection firewalls is that they are easier for an administrator to understand than traditional firewalls, requiring networking protocols. Stateful inspection firewalls operate on the application level, meaning that an administrator needs only to know what the applications are supposed to be doing to configure it.

What Are The Disadvantages Of Using Stateful Inspection Over A Traditional Firewall?

Inability To Use In A DMZ

In general, the disadvantages of using stateful inspection over a traditional firewall include the inability to use it in a DMZ and the lack of a one-zone deployment. 

High Overhead

The stateful inspection also has a higher overhead with regards to packets and CPU cycles.

The advantages of stateful inspection over a traditional firewall include inspecting packets before they pass on to other levels in the network stack. The state of each packet is also known at the network layer, unlike with a traditional firewall where this information can only be gathered on an application level. This difference allows for more intelligible rule sets and better security policies for networks.

In short, the most significant disadvantage of using stateful inspection over a traditional firewall is that it cannot be used in a DMZ. The lack of one-zone deployment and higher overhead are also problems using stateful inspection versus a traditional firewall. 


Stateful inspection is a type of firewall that will analyze the state or content of an incoming packet. Stateful inspection, unlike traditional firewalls, can detect and mitigate any potential threats within packets before they reach their intended target destination. 

This makes it much more difficult for hackers to penetrate your system. This is because they cannot predict how the firewall reacts if they send certain data packets through. 

The main disadvantage of using stateful inspection is that there is an increase in resource usage on server resources. This results in slower performance due to high load times.  

However, the significantly reduced number of packets that penetrate your system makes stateful inspection very useful for maintaining a secure network.

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