Get the Whitepaper called UFW – A Beginners Guide to Linux Firewall. The white paper is intended to provide information about a Linux firewall using a simple tool called UFW. It provides complete information on the tool and various ways through which users can create their own firewall rules to protects their assets.
You can download it from the following link: https://packetstormsecurity.com/files/download/160970/ufw-beginnersguide.pdf
Source: https://packetstormsecurity.com/files/160970/UFW-A-Beginners-Guide-To-Linux-Firewall.html