When first migrating to version 7 of CentOS I failed to understand the working of the new default firewalld product and kept with iptables/ufw. I am finally embracing the new methodology, and found an exellent article Understanding Firewalld in Multi-Zone Configurations. I hope this note helps you if you seek knowledge.
Due to the fact that RHEL/CentOS server software lags so far behind, today I converted one of my servers to an Ubuntu server. I almost regret installing from their live server image as opposed to their live workstation image. The basic install went well I thought all text based. But upon first boot I couldn't login. Thankfully google showed me how to boot into init 2, mode and after several tries to the key sequence right to get the grub menu I booted and discovered the admin user i specified was never created. After fixing that, rebooting and logging in as new user with admin, i discovered networking was not configured. After googling manual ubuntu network configure, I discover that bionic uses a new network configuring system called netplan. Anyway, the server is now networked and currently updating all the packages. Hopefully I will have it all up and running before my new ASUS Tinkerboard arrives today.