Even the most basic routers these days offer the NAT feature and firewall capabilities which protect your machines on the local network. But there are situations when you have to connect your Linutop directly to the Internet, or bypass the router’s firewall (for example, if you want to use Linutop as a server accessible from the outside). In this case, a decent firewall tool is essential. The problem is, though, that many firewall applications are not particularly user-friendly and you really have to know what you are doing when configuring them.
If tweaking a firewall via the command line is not your cup of tea, then you’ll appreciate Firestarter, a graphical application which significantly simplifies the process of setting up and configuring a firewall. To install Firestarter, run the sudo apt-get install firestarter command, or use the Synaptic package manager.