Use iptables on CentOS 7 instead of firewalld

• log in to your CentOS 7 installation
• disable firewalld

systemctl stop firewalld
systemctl mask firewalld

• install the iptables-services package

yum install iptables-services

• enable the services at boot-time

systemctl enable iptables
systemctl enable ip6tables

• start the services

systemctl start iptables
systemctl start ip6tables

• save the iptables configuration

service iptables save
service ip6tables save

• the configuration can now be found in the file /etc/sysconfig/iptables