How does the Firewall supervises the data traffic? The Firewall works in principle like a door keeper for data packets: Each packet will be checked, whether it may pass the door of the network (Firewall) in the desired direction or not. For such a checking different criteria are used, in common language of Firewalls called “rules” or “guidelines”. Depending on the kind of information, which are used for creation of the rules and which are checked during the operation of the Firewall, one distinguishes different types of Firewalls.
Above all, the aspect of the “central” positioning is very Important: Only when the entire data traffic between “inside” and “outside” goes through the Firewall, it can fulfil its task reliably under any circumstances. Each alternative way can reduce or even turn off the security of the Firewall. This central position of the Firewall simplifies by the way also the maintenance: One Firewall as common passage between two networks is certainly easier to maintain than a “Personal Firewall” on each of the workstations belonging to the LAN.