I have heard about WireShark software that what can it do. But it snif only my lan card. What if i wanted to snif the router that what other computers on the network are doing? Is there any way to do that?
Yes, you can plug a hub in between the target computer and the switch port and then plug the computer that has wire shark into that hub. Since a hub will send packets on all of its ports you'll see all traffic and can capture it.
Of course, if you have a manager switch, a span port or mirrored port would work in the same manner.
In general, getting all the traffic passing through a router is a difficult task. The only centralized point for collection is the router itself (without injecting multiple additional points into your network as JorgeM suggests).
Several things complicate this: The aggregate capacity of the router is usually much higher than the collection machine; the SPAN port on a switch is best-effort meaning it will be preempted at high loads and not get all traffic; finally, network users assume a certail level of privacy on a network and would likely not appreciate your 'snooping' on them.
You should check the rules and regulations of your network before trying any of the suggestions listed here to ensure you are not engaging in prohibited activity.
the truth is some people are using my wifi without my permission, my neighbours in fact. i want to teach them a lesson. :) I had a password over my router but then it was resetted and i forgot about the passowrd. i came to know yestereday that i did'nt have the password activated and all neighbours were using the net. So now its there time to payback. ;)
Sort of you fault for not remembering to put another password. looking at their packets isn't going to do that much unless you're going to try to take it a step further and mess with their systems from potential info you gather. Best bet: Just throw some WPA2 with a decent password and you'll keep every one of your neighbors out.