Checking data packets

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.

Note: In principle, Firewalls operate at the interconnection between two or more networks. For the following explanation, we only look as example at the passage between a local network of a company and the Internet. These explanations can be transferred however in a general manner also to other network constellations, e.g. for the protection of a subnetwork of the personnel department of a company against the remaining network users.