This document is meant as an introduction to how to setup a firewall - it is not a complete guide to securing systems. Firewalling is a complex issue that requires careful configuration. The scripts quoted here are simply intended to give examples as to how a firewall works, they are not intended to fit into any imaginable configuration and may not prevent any imaginable attack. The purpose of this text is simply to give you a hint on how to get started with a firewall. Customization of these scripts for your specific situation will be necessary for an optimal configuration, but you should make a serious study of the iptables documentation and creating firewalls in general before hacking away. Have a look at the list of at the end of this section for more details. Here you will find a list of URLs that contain quite comprehensive information about building your own firewall.