Disable Firewalld Service.

[root@rhel-centos7-tejas-barot-linux ~]# systemctl mask firewalld

Stop Firewalld Service.

[root@rhel-centos7-tejas-barot-linux ~]# systemctl stop firewalld

Install iptables service related packages.

[root@rhel-centos7-tejas-barot-linux ~]# yum -y install iptables-services

Make sure service starts at boot:

[root@rhel-centos7-tejas-barot-linux ~]# systemctl enable iptables

Now, Finally Let’s start the iptables services.

[root@rhel-centos7-tejas-barot-linux ~]# systemctl start iptables