UFW Essentials: Common Firewall Rules and Commands (DigitalOcean)
UFW (uncomplicated firewall) is a firewall configuration tool that runs on top of iptables, included by default within Ubuntu distributions. It provides a streamlined interface for configuring common firewall use cases via the command line. This cheat sheet-style guide provides a quick reference to common UFW use cases and commands, including examples of how to allow and block services by port, network interface, and source IP address.