Statefull Inspection

A newer method used by firewalls is called "stateful inspection". Instead of examining the chunks of data coming through the network, a stateful inspection firewall compares certain key parts of the packet to a database of trusted information. Information traveling from inside the firewall to the outside is monitored for specific defining characteristics, then incoming information is compared to these characteristics. If the comparison yields a reasonable match, the information is allowed through. Otherwise it is discarded.