transparent firewall using iptables

i would like to know what i am missing IKnowNot...pls tell me what would u like to know more ........any how i will read this also...

What you are missing?

I too often times do not articulate in a manner to convey my meaning correctly, as powertoad5000 pointed out in Almost a tutorial

What you need is a way to set up the router side of the firewall box with an Ethernet card with NO IP address, since the router does the natting and/or masquerading for you and will be sending packets into it for numerous destinations, and you probably want the same thing for the switch side since you said you can not change the configurations of either: hence you want a bridge.

Another very important thing is what flavor ( or more precisely what version ) of Linux you are using.
If you are running a 2.0 kernel, IKNowNot.
If you are running a 2.2 kernel, there should be a patch for the bridging, but did you patch(?) the kernel for iptables?

If you are running a recent version of a 2.4 kernel, everything should be be there but you may have to rebuild the kernel to “activate” it.

With the links provided hopefully you should be able to then figure out the firewall rules and bridging you need.

another thought: will you have direct access to the firewall box or will you be accessing it via ssh from the LAN ? If the latter is true you may need a third ethernet card because the others won't have an IP address for the box to connect to otherwise.

Just something to concider.