How does CentOS 7 open ports quickly

When CentOS was upgraded to 7, it was found that iptables could not be used to control the port of Linuxs. After google, it was found that Centos 7 used firewalld instead of the original iptables. The following documents how to open the Linux port using firewalld:

Open port

firewall-cmd --zone=public --add-port=80/tcp --permanent

Command meaning:
-- the zone # scope
-- add-port =80/tcp # add port, format: port/communication protocol
--permanent # is permanently in effect and will not be rebooted without this parameter

Restart the firewall

firewall-cmd --reload