Enterprise Cloud Security and Governance

Stateful packet inspection

As the name suggests, stateful firewalls keep track of connection states. They know at which point the connection has reached (SYN state, SYN-ACK state, ESTABLISHED state, and so on).

In order to understand how it works, let's look at an example:

Let's assume that there is a server with a firewall. Now, it needs to download package updates, so it initiates a request to the CentOS update repository with IP 88.150.173.218. Considering that this is the firewall rule associated with the server, can the reply come back to 88.150.173.218 to the server or will it be blocked at the firewall?

This is illustrated by the following diagram:

The answer is YES if it's a stateful firewall and NO if it's a stateless firewall. ...