Linux firewall ports are used to allow or deny incoming or outgoing connections to a Linux system. Different firewall products have different commands or methods to open ports, such as iptables, ufw, or firewalld. The port number, protocol, and zone are usually required to specify which port to open. The firewall status and rules should be checked before and after opening ports, and the service may need to be restarted for the changes to take effect.
Using netstat -a you can view a list of all open ports.
Using csf -l you can view all of the ports that CSF is utilizing.