Iptables

From TheLinuxVault

Iptables is the default firewall integrated into the Linux kernel. This means that any modern version of Linux comes with a firewall already installed, inside the kernel (unless Iptables has been disabled, which would only be done if an other firewall was used). This is one reason that Linux has much greater security than Microsoft Windows.

There are GUI programs to configure Iptables, such as Firestarter.

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