Changes you make to iptables firewall rules only exist for the current boot, and if you don’t save the config, you will loose any changes upon rebooting.
CentOS 6 blocks most incoming ports by default, so you will generally have to make changes to the firewall if you install any new packages. Thankfully CentOS 6 provides the ability to easily save the configuration.
To save the current iptables firewall config, issue the following command:
# service iptables save
# service iptables save iptables: Saving firewall rules to /etc/sysconfig/iptables:[ OK ] #
During the next system boot up, or the next time the iptables rules are reloaded, your firewall settings will be reloaded.