The Linux operating system has its own built-in, enterprise-grade firewall. However, not all Linux distributions ship with a graphical client fro configure and manage it. Mandriva (Linux 2009) One is one of a handful that ships with a fully configured graphical firewall client.
The gui firewall client is accessible from the Mandriva Linux Control Center: Control Center -> Security -> Personal Firewall. By default, the firewall is enabled and configured to allow Internet traffic. However, non-local network access to servers running on the system are denied. You may allow access to any of the servers, for example, ssh or ftp, by clicking the check box next to the servers name. This is the first screen you see when viewing the firewall gui.
The second screen of the firewall configuration shows you the services that will be accessible from the Internet and your local internet into your computer. Two other options shown on this screen are Portscan Detection and Use Interactive Firewall. When enabled (it is enabled by default), the interactive firewall feature configures the firewall to alert you whenever it detects unwanted intrusive activity.
The third screen shows you all the network interfaces that’s been detected on your PC. Here you choose which ones you want the firewall to protect. As the instructions says on the screen, if an interface is not facing the Internet, then you may uncheck it and not have the firewall protect it.
By default, the firewall is configured to protect the following services: FTP, SSH, Mail server, DNS, Web server, BitTorrent, and Ping (Echo Request). If there is a service, for example IPSEC, that you want to allow access through the firewall, then use the advanced screen to enable that service.
Unless you want to create a custom rule, you do not really need to tweak the firewall. It is configured to allow normal Internet traffic though, and you do not have to be an expert to use it. If you are not using Mandriva, and your distro does not install a gui firewall client, you may want to read graphical firewall clients for Linux desktops for a list of some of the best firewall gui clients.