If you are not familar with firewalld and the firewall-cmd, check out our Getting Started article.
The --add-port=port_number/protocol option can be used to allow connections to a port number. This is typically used when a protocol is not using the default port associated with the protocol, such as when HTTP is using 8080. --add-service is used when the protocol is using it's common port, such as when HTTP is using port 80.
firewall-cmd --add-port=12345/tcp --permanent firewall-cmd --reload
Or --remove-port=port_number/protocol to remove a port.
firewall-cmd --remove-port=8080/tcp --permanent firewall-cmd --reload
firewall-cmd --list-all will show the allowed ports.
~]# firewall-cmd --list-all public target: default icmp-block-inversion: no interfaces: eth0 sources: services: ports: 12345/tcp protocols: masquerade: no forward-ports: sourceports: icmp-blocks: rich rules: