For ASCII-art fans, the chains are arranged like so: (Note: this is a very different arrangement from the 2.0 and 2.2 kernels!) _____ Incoming / \ Outgoing -->[Routing ]--->|FORWARD|-------> [Decision] \_____/ ^ | | v ____ ___ / \ / \ |OUTPUT| |INPUT| \____/ \___/ ^ | | ----> Local Process ---- The three circles represent the three chains mentioned above. When a packet reaches a circle in the diagram, that chain is examined to decide the fate of the packet. If the chain says to DROP the packet, it is killed there, but if the chain says to ACCEPT the packet, it continues traversing the diagram.