system-config-securitylevel provides the user an easy interface to edit firewall rules. If you only need to open up certain tcp and udp ports, this tool may prove handy. For more complex routing rules, you are tempted to edit /etc/sysconfig/iptables directly.
If you have used system-config-securitylevel before, check out the iptables file and you will see this in the header:
# Firewall configuration written by system-config-securitylevel # Manual customization of this file is not recommended.
You were warned!! The problem with this is that the next time you run system-config-securitylevel (even if accidental), all your custom rules will be overwritten… sucks. So remember to backup /etc/sysconfig/iptables or use some sort of version control everytime you decide to edit the file directly.