How to disable firewalld and enable iptables instead?

To switch to from firewalld to iptables follow the steps given below.

1. Firstly ensure the iptables-services package is installed.

yum install -y -q iptables-services

2. Then prepare the iptables rules you wish to use by editing /etc/sysconfig/iptables and /etc/sysconfig/ipt6tables.

3. Next, disable and stop the firewalld service

4. Then start iptables services :

systemctl start iptables

systemctl start ip6tables

5. Enable iptables service to automatically start at boot :

# systemctl enable iptables
ln -s '/usr/lib/systemd/system/iptables.service' '/etc/systemd/system/basic.target.wants/iptables.service'
# systemctl enable ip6tables
ln -s '/usr/lib/systemd/system/ip6tables.service' '/etc/systemd/system/basic.target.wants/ip6tables.service'