Firewall system structure and its development

There are three firewalls of a couple of host computer system structure, scree ned host computer system structure, screened net host computer system structure. Their merits and demerits are analysed. Screened host computer system structur e is safer than a couple of host computer system structure, and internal net is separated from internet by screened net host computer. Stronghold computer, data filter, acting system may give some net safe way, none of the system structures is quite safe. When building firewalls, often several ways are used. The third firewall system is the direction firewall technology will take.