sniffing and passing data

Hello All,
I am new to this and have a question.
I have recently bought two Arduino Ethernet Shields. http://arduino.cc/en/Main/ArduinoEthernetShield
My goal is to have two Ethernet shields 1 input, 1 output and basically connect the input to lets say a wall jack and pass it though to the second shield to connect to the client. However through this process i will be sniffing traffic

I already have the code written for the sniffing portion of this however I can not get it to pass the data when i connect the two Arduino Ethernet Shields. I would ultimately like to be able to plug the one shield into a wall port (input) and use the other shield to pass any traffic (output) to the client.
I was hoping that this was going to simply be a plug and play however it is not. Any thoughts or suggestions on how to get these two Ethernet shields to play together and allow the traffic to pass through the two of them would be greatly appreciated.

I am open to other ideas and thoughts as well.

Find yourself a good old-fashioned Ethernet hub (not switch). Connect your sniffer and the device being sniffed to the hub and your sniffer will see all the traffic going to and from the device.

Bear in mind that an Arduino is pretty unlikely to keep up with a loaded Ethernet connection anyway. If you want to do high speed packet processing, you'd be better off doing it on a PC or a router.

What if we were to use my suggested rout above (connecting two Ethernet shields) and just pass the network data (typical everyday traffic)? Would that still be too much for the arduino?
Would using a raspberry pi work better for this situation?

Any thoughts/ideas/comments would be greatly appreciated!

watkins272:
What if we were to use my suggested rout above (connecting two Ethernet shields)

...

any thoughts/ideas/comments would be greatly appreciated!

You've already had them. The proposed solution is not sensible.