To start IP tables on your RedHat server,
# service iptables start

You can run the following command to stop iptabes:
# service iptables stop

It is also important to save your iptables configuration so that it is loaded again on the next reboot. This can be done by running:

# service iptables save

You can also set the iptables program to start on boot by running:
# chkconfig iptables on