State-full Packet inspection is a software module that is designed for inspecting the packets forwarded. This software is configured in the operating systems of UNIX of windows PC firewalls, and are used for inspecting the packets that are received. The rules of inspection are configured buy the security officer in to the machine and the inspection of packets is done based on these rules only.

Using this software in the ISO model the inspection is done in all the headers of 7 layers and the data related to the packets in the headers are stored in the dynamic state tables, these tables will preserve the information related to the connection. Packet filters can be run in the dual homed computers as they are designed in the form of software, these can filter the packets but at various networks they cannot be routed.

A firewall is also sometimes called as a bastion host when it is placed in the layer 5 of Internet model and layer 7 in ISO model. It is also called as guardian system, application gateway and proxy server. The services that are offered by the application are filtered as a main aim of these firewalls. Then the consequent packets are evaluated on the consequent connection trails and same connections by using the information that is stored in the tables.

Despite the fact that when compared to the simple packet filtering routers, this technology is very much secure, but when compared to the application gateways these are not that much secured because the information in the application is not completely inspected. Yet when compared to the application proxies, this technology is performed very fast. When compared to the security guards the concept of state-full inspection is almost similar in asking the questions like “who are you”, “where are going” and then permits the users.