Information Security

Linux Netfilter and FreeS/WAN are popular tools for creating low cost firewall and VPN gateways. Creating firewall rules for these systems can be relatively straight forward if you understand how they work. There are many commercial and free firewall tools that provide GUI interfaces for creating firewall rules and VPN connections. These tools allow for less understanding of how the firewall works since the management tool is trusted to create the correct rules. People that manually configure or troubleshooting problems need an understanding how the Netfilter and FreeS/WAN work to correctly administer the gateways. This guide will discuss Netfilter and FreeS/WAN explaining how each tool works and how the two interact. The goal is to show how a packet will flow through these tools to provide a better understanding of these technologies and enabling the administrator to write firewall rules with fewer errors.