A firewall is a program that monitors and controls your system's network interfaces' incoming and outgoing network traffic, and can restrict the transmission to only useful and non-harmful data into and out of a computer system or network. By default, CentOS is made available with an extremely powerful firewall, built right into the kernel, called netfilter. While, in older versions of CentOS, we used the famous iptables application to control it, in version 7, the new standard netfilter management program has changed to a service called firewalld, which is already installed and enabled on every CentOS 7 server by default.
It is a very powerful service to take full control over your server's firewall security, and is much easier to work with than iptables. Its main advantages are that it features a better structured and more logical approach to managing and configuring every aspect of a modern firewall solution. Therefore, it will be the foundation of your server's...