Great tutorial: https://www.digitalocean.com/community/tutorials/how-to-set-up-a-firewall-using-firewalld-on-centos-7

Start and Stop

systemctl start firewalld.service
systemctl stop firewalld.service
firewall-cmd –state

List open services

firewall-cmd --zone=public --list-services

Add service

firewall-cmd --zone=public --permanent --add-service=http
firewall-cmd --zone=public --permanent --add-port=53/udp
firewall-cmd --reload
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