If you are migrating from CentOS 6 to CentOS 7, verify whether you have the iptables-services packages installed after performing the upgrade by running the "rpm -q iptables-services" command as root. Also, verify that iptables and ip6tables services are enabled by running the "systemctl is-enabled iptables" and "systemctl is-enabled ip6tables" commands as root.

For more details about migrating the firewall service from CentOS 6, see the section about the firewalld service in the Red Hat Enterprise Linux 7 Migration Planning guide at [link:https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Migration_Planning_Guide/].

If you perform a clean installation of CentOS 7, the firewalld service will be installed on your system instead of iptables and ip6tables.

For further details about the firewalld service, see the section about firewalls in Red Hat Enterprise Linux 7 Security Guide. You can access the guide at [link:https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Security_Guide/].