On CentOS 7, FirewallD a default firewall management tool is enabled.

In order to install iptables, we need FirewallD from server:

# systemctl stop firewalld

# systemctl disable firewalld

# systemctl mask –now firewalld

Once the FirewallD ins disabled, you can proceed to install iptables:

# yum install iptables-services

# systemctl start iptables

# systemctl start iptables6

Enable the iptables to start on boot:

# systemctl enable iptables

# systemctl enable iptables6

To check current iptables rules:

# iptables -nvL

By default, only port 22 is opened in iptables. You can now open other ports like 80, 53, 25, 587 etc. for the services you install.