Linuxiso.org - Storm Firewall for Linux. A firewall is a system or group of systems that enforces an access control policy between two networks. Firewalls can be configured to protect against unauthenticated logins from external networks, and to limit access to external networks from systems on an internal network. All packets enter or exit through the firewall, where they are filtered by the type, source address, destination address, and port information contained in each packet. This filtering is controlled by rules that are setup within the firewall's configuration.
Packets are discreet bundles of information that pass through a network.
A packet is made up of the packet body , which contains the information you want to transmit, and the packet header , which contains the source and destination address of the packet, along with other information. Physically, a network is comprised of nodes , such as a computer, that are interconnected by cables like phone lines, ethernet cables, fiber optic cable, and so on. Packets are sent from one node to another using protocols , which are a set of rules governing data transmission. These protocols operate at four different layers in this communication process. An Internet layer protocol, such as IP , is responsible for routing packets across networks to their destination, using IP addresses, which are unique for each node on the Internet.