As you already know, information over a network travels in packets. A firewall screens and limits these packets as they flow between network interfaces. In smaller networks, firewalls are used to protect desktop and server machines from those nasty people in the outside world called crackers, who break into machines and do whatever they feel like to the machine and its information. In larger installations they are used wherever two untrusting networks meet (for example, to protect an internal network from being attacked by crackers taking advantage of security holes in a publicly accessible Web server).
Firewalls have been essential to business users for some time now, and with the increase in permanently connected, high bandwidth home Internet connections (which are attractive targets for crackers), they are becoming necessary for home users too. The Linux 2.2 and 2.4 kernels contain inbuilt firewalling tools. Additionally, the same tools can be used for IP masquerading — a method of sharing an Internet connection to a network.
There's a big difference between Linux 2.2 and 2.4 when it comes to firewalling, masquerading and other aspects of security-focused networking. Linux 2.4's new Netfilter system (which provides a way for applications to control networking functions) contains iptables, a simpler and more powerful firewalling and
Packages Service Name Configuration filets) Log files
Webmin configuration Service configuration Access control Network port
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