Here is my network configuration: My computer is inside a LAN. All the internet traffic goes through a default gateway. I wish to conduct an experiment. I want to monitor user traffic pattern. I want to setup a proxy server to which other users will connect to for accessing the internet. I wish to log the URLs that they visited and forward their traffic to the gateway. Is there a tool which will help me do this?
Pretty much any proxy/gateway will do this. Squid is a good one. PFSense is a good complete solution if you don't feel like doing much work yourself. You can install PFSense on a server (a virtual server is OK), and then install the Squid plugin for it.
Then, you point all your computers to the squid/PFSense machine as their gateway, and your current gateway becomes the gateway of the squid/PFSense machine.
So it goes:
Computer > Squid/PFSense > Gateway