How eavesdropping is performed? Can I perform eavesdropping by sitting on client side? Can eavesdropping be done in both wired and wireless transmission too?
closed as not a real question by Iszi, Rory Alsop♦ Nov 17 '11 at 8:52
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I suppose you are inside the network, meaning that your computer is part of the network, IP and all...
The most stright-forward approach will be either to physically connect to a router from the external side of it and to monitor the traffic with some sniffer, e.g. Wireshark, Tcpdump, dsniff
The second approach, which is the most probable for you is to go with ARP poisoning, it works either on wired and wireless connections (much more successful on a wired connection) and then go through what ever you like.
If you want something in particular - like listening to encrypted transmission like SSL you will have to go a step further and set yourself as a rogue proxy and make the connection for them (sslstrip or even Man in the Middle renegotiation attack can do the trick, if possible).