Listen to incoming IP adresses with yun

Hello, I'm working on a project where I would like to "sniff" Incoming IP adresses on a small private network, using the Arduino yun. The network consists of a home router(AP), my Laptop, and the yun, and I need to gather the IP adresses on incoming packages send to my laptop.

This is not an area I'm proficient in, and I'm in doubt exactly where to start.

From what I have red, it seems like I'll need to configure the yun to act as a "middleman" router and let it listen to incoming packages by using tcpdump commands or similar. I've tried to do this by letting the yun create an access point, while having it connected to the router via an ethernet cable. I then hoped I could connect my laptop to the yun's AP and have connection to the internet, but that didn't work.

So my question is: What do I need to do, to make the yun work as an middleman router, sniff IP addresses, and let my laptop connect to the internet via the yun's AP? - and is this even the best way to accomplish what I want?

Network sniffer while ethernet port or wifi port?

I want to sniff on the packages send to my laptop, which should be connected to the internet via the Yún's AP. The Yún will be connected to the router via Ethernet, so I guess the sniffing should happen on the ethernet port?

Make arduino work as an AP to a Modem/Router:

http://forum.arduino.cc/index.php?topic=322588.msg2230844#msg2230844

Once completed, install tcpdump into Yun start dump.