Firewalls are good for security, but just because you have a firewall does not mean that your machine is secure. There are two main firewall tools that come installed with Red Hat Linux. You can setup and manage firewalls with the ipchains and iptables tools. Both of these were written by a guy named Rusty, who suggests you use the iptables firewalls. Since ipchains was written first there is a lot more GUI support for it. The only real difference between the two is how much control you have. Both of these firewall tools are good and should be tried out.