In CentOS 7, firewalld is used by default to administrate the firewall. If you want to switch back to iptables, you might run into the problem that your firewall rules are not automatically loaded when the system boots. So let’s look at this closer.

To remove firewalld and install iptables, I assume that you have executed something like

$ yum remove firewalld
$ yum install iptables iptables-services

The iptables service allows you to save the current ruleset.

$ service iptables save
iptables: Saving firewall rules to /etc/sysconfig/iptables:[  OK  ]

However, if we reboot now, we notice that iptables -L will print empty firewall tables.

The problem is that the service, which is responsible for restoring the ruleset at boot, does not start by default. We need to enable it manually:

$ systemctl enable iptables

This should be it. Rebooting should reload the configuration stored in /etc/sysconfig/iptables.