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 firewalling 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 firewalling. 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 firewalling 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.