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  1. NetFilter Checklist Building a NetFilterbased firewall is not difficult. End users interested in setting up their own NetFilter firewall can use the following brief checklist: Step 1. Select a system to be used as the firewall. Step 2. Install additional network interfaces (minimum number of required interfaces is two). Step 3. Install at least the minimum recommended memory (preferably more if the firewall will be providing more than just filtering services). Step 4. Select a Linux version to install (Debian, Fedora Core, Red Hat, Gentoo, and so on). Step 5. Install the operating system. Step 6. Configure the operating system (assign addresses to interfaces, either by using Dynamic Host Configuration Protocol [DHCP] or static assigned addresses). Step 7. Define which services will be allowed through the firewall. Step 8. Define which hosts will be translated by the firewall. Step 9. Using the iptables utility, Firewall Builder, Firestarter, Webmin, or another utility, create the firewall filter ruleset. Step 10. Apply the ruleset to the external interface (that is, the public interface) of the firewall. Step 11. Test connectivity through the firewall. Step 12. If desired, define what outbound traffic is to be filtered. Step 13. Apply the outbound filter to the internal interface of the firewall. Step 14. Retest connectivity through the firewall.