Ubuntu does not have many open ports by default, but there are times when you want to restrict access to a port(ports) or a specific ip adress. Maybe you run a ssh server in your ubuntu machine and want to block everyone from connecting to it, except yourself. Have you ever thought how to accomplish such things or tried to do it? You need a firewall to do that. In this article I will explain what is a firewall and teach you how to use the ufw ubuntu firewall by giving real world examples of it.

Full article here:
Install And Learn How To Use ufw Firewall In Linux (LinOxide)