Firewall in Ubuntu

     Ubuntu , as with all post 2.2/2.4 kernel Linux distributions comes with the netfilter/iptables framework. This framework is a set of kernel modules that can be utilized to create packet filtering rules at the kernel level. Rules are written in iptables format, which is the method of conveyance of instructions to netfilter, and in essence the Linux Kernel.

        Ubuntu also includes an application called Uncomplicated FireWall (UFW). This application is a userspace application that essentially can be used to create iptables rules. There is also a GUI for UFW called GUFW. It provides a graphical interface for UFW. 

         The command-line interface of UFW is installed by default in ubuntu.

Manual page can be seen by command :

                                    man ufw

If you want to see its current status, then it can be done by command :

                                  sudo ufw status

For enabling the firewall :

                                  sudo ufw enable

Note : The command for enabling the firewall, also puts it into the list of startup programs.