mjhjmtu

I would like to create a system like this.

The user would connect through a wifi network which would reroute all http requests and responses through the network card on a computer thus allowing that computer to sniff the packets. I have debian running on the computer. How would i go about doing this?

Get a 10/100 ethernet hub, a real hub, like a Netgear DS104. Put it between the wifi and the router. Hubs replicate traffic on all ports, so you can connect a separate machine to another port on the hub and sniff everything.

Unless your brand of router specifically allows for that kind of interception (most don't unless you're talking about industrial grade stuff with triple digit costs and usage licenses) I'm afraid you're sunk; a better bet might be to install a wifi card in your computer and try to sniff the wireless traffic directly using something like wireshark or Kismet.

You can connect modem directly to your computer and make router so send all traffic through your debian system. In this case you may do anything you want with packets.

P.S.: do you need something like this?

tcpdump -i ethX -w capturefile net x.x.x.x/y

Where ethX the card which receives this traffic and x.x.x.x/y is the cidr of the wireless network. This should capture anything coming or going to this network and save it to "capturefile" file. Add and port 80 in the end if you want only web traffic.

This looks like a "honeypot" setup. If you are trying to capture http sessions and/or other private information, this is illegal. Even if those users are trying to steal your internet connection. Unless you've acquired permission from those who use the wireless network, this is probably illegal.

EDIT:

I thought you already had setup the rerouting part. If you're asking how to reroute the specific traffic, it is possible but it depends on the hardware you have and probably I can't help you on that.