This blogpost aims to explain some of the inner workings of the “uncomplicated firewall” (ufw) that is available for Ubuntu installations since 8.04 LTS and for Debian installations since 10.
Before going into detail, ufw is not a firewall but a frontend for iptables. Iptables is a frontend for the netfilter kernel module that is performing packet filtering within the Linux kernel. Therefore all actions that are performed via ufw can be directly queried using the iptables command. Firewalls under the hood - UFW
Rascals are always sociable, and the chief sign that a man has any nobility in his character is the little pleasure he takes in others company. Arthur Schopenhauer