What I'm trying to do is configure my Linux box as an IDS/Firewall box. I have two nics and also enabled ipv4 forwarding on the machine. I was hoping that this is all that I need but it isnt. My goal is to just have the machine pass packets from eth0 to eth1 and visa versa so I can use the IDS to pick up intrusions from my router to my internal machines. The router is a Cisco 2611 and is configured to do nat on the inside so I don't need to make the linux box into another nat/router. I just want to pass the packets between the nics. Any ideas?