I am a big fan of Ubuntu’s Uncomplicated firewall because it is very simple to use. I cannot remember if ufw is installed by default so to be sure $ sudo apt-get install ufw As part of my project to use Sonofon Mobile Broadband as backup for my ADSL I needed ufw to NAT the connections through the ppp-connection. The solution is pretty straight forward: In the file /etc/default/ufw change the param