Data Communications Networking Devices - 4th Ed.pdf

804 ___________________________________________________________ SPECIALIZED DEVICESFigure7.44 Using the Technologic Interceptor ®rewall to create a policy allowing inboundHTTP from a speci®c IP address10.0.0.0 to 10.255.255.255172.16.0.0 to 172.31.255.255192.168.0.0 to 192.168.255.255Any of the addresses in the preceding IP address blocks can be used behind a®rewall, enabling the use of existing Class A, B, or C addresses to serve as translationaddresses for use on the public side of the ®rewall.Stateful inspectionThe term stateful inspection was originally coined by Checkpoint Systems toreference the examination of packets at the network layer. Although this feature issimilar to ®ltering, there are several key differences. First, the analysis is performedon each packet based upon the context of previous transmission. This is similar totracking a series of telephone calls and permits a ®rewall to become aware ofsuspicious trends for which it may be con®gured either to bar further accessattempts or to generate an alert to a designated person. Secondly, by tracking datafrom higher layers which are analyzed based upon the context of previous transmissions,the ®rewall becomes capable of providing a detailed audit trail of events.