What Is A Stateful Inspection Firewall?

Stateful inspection firewalls are typically deployed on networks with both business-critical data and sensitive information. Stateful inspection firewalls provide greater security than other types of firewalls.

In stateful inspection, the firewall keeps track of both sides of a conversation between two computers and decides whether to allow it based on what’s been seen so far. This contrasts with how other firewalls work, which only look at packets themselves while they pass through.

What Is A Stateful Inspection

A stateful inspection firewall is a type of network security system that monitors the data packets sent to and from your computer, examining each packet for signs of malicious activity. It also blocks any packets that are not part of an established connection. 

Stateful Inspection Firewall can dynamically create rules for recognizing legitimate data exchange by analyzing its characteristics such as protocol type and port number. The entire network connection, including all related TCP handshake exchanges, is monitored before permitting access from one host to another across a public or private IP infrastructure (network).

A stateful firewall is a firewall that analyses each packet of data and determines whether the packet should be allowed into the network. Hence a stateful firewall is important as it can help protect against most types of attacks and block traffic.

Critical Features Of Stateful Inspection Firewall

  • Block Denial Of Service Attacks
  • Prevent unencrypted communications over Internet Protocol
  • Prevent IP spoofing
  • Protect from internal attacks using packets with a false source address
  • Save system resources by stopping nonessential traffic such as those without an established connection or those that do not contain data.

Unsolicited connections are blocked automatically at the firewall level, rather than relying on services running inside individual applications to take action. 

In other words, Stateful Inspection Firewall saves you time and money because it is fast and efficient in protecting against various threats. It uses unique techniques to inspect network traffic for bad actors looking to infiltrate your computer systems through unencrypted communication channels like email attachments, instant messaging clients, web browsers, etc.

How Does Stateful Inspection Firewall Work?

Stateful Inspection Firewall inspects incoming packets and creates a state table of all the connections passing through it. It tracks packets from each link, thereby maintaining their states by information kept within its ruleset. Every packet is checked against the ruleset to determine if access should be allowed or denied for that particular session in a Stateful Inspection firewall.

How a stateful inspection firewall works varies by implementation; however, there are two basic types: passive or active.

Passive Stateful Inspection

Passive stateful inspection firewalls are more efficient, but they are unable to prevent certain types of attacks. These include address spoofing attacks and denial-of-service (DoS) attacks. More advanced systems use passive rules to detect suspicious traffic patterns rather than immediately receiving packets that violate protocol standards or port usage.

Active Stateful Inspection

Active stateful inspection firewalls are more complex, but they use the same technologies as passive systems. The difference is that active firewalls can prevent attacks by taking action when suspicious activity occurs. Active firewalls also enable traffic filtering based on specific characteristics of an established connection or network session between two hosts communicating over a TCP/IP network.

Is A Stateful Inspection Firewall The Same As Traditional Packet Filtering?

With Stateful Inspection Firewall, all connections are automatically tracked in a two-way fashion using advanced memory techniques to ensure complete tracking of open TCP/IP exchanges even if they span multiple network segments or egress through different gateways at either end of the communication.

Stateful Inspection Firewalls work on the same principle as Packet Filtering, except they track all information for two-way communication sessions, which is considerably more complex.

Stateful VS Stateless Firewalls

Stateful Firewalls Stateless Firewalls
Every packet sent by any device within its purview gets analyzed for potential threats before it’s allowed past the front line (i.e., into your private networks). Stateless firewalls do not track the state of a network connection. They simply let packets through as they arrive and block those that don’t fit an already established pattern, such as unsolicited traffic from the Internet.
This type of firewall has two parts: one placed at the perimeter of your network infrastructure architecture to monitor incoming traffic for threats. The other needs to be placed within each internal workgroup or a virtual private server (VPS) to keep track of allowed packets. Stateless firewalls are less resource-hungry than their stateful cousins. Therefore, they can be run on lower specification hardware, but there is no guarantee that only legitimate data will get through to your computer systems or servers they protect.
It is a reverse proxy because it sends requests from Internet clients towards web servers running on internal networks behind them.


A stateful inspection firewall is a more advanced form of packet filtering that provides full session awareness. It can handle new connections quickly while simultaneously analyzing existing ones for potential issues, thus taking on heavy traffic loads without slowing down the regular operation. A stateful inspection firewall is the best way to protect your business from security threats such as cyberattacks and unauthorized access.

Recent Posts