there's a couple ways:
1) your router has to support "port mirroring" (see attachment). you then tell it to take all the ports (in the case of my attachment, lets say port 1,2, and 3) and "mirror" all the data received on those ports to port 4 (at the bottom of the attachment).
Then, you'd have to connect a computer to port 4 and put a bandwidth sniffer on it.
2) Place a hub between the router (and optionally, a switch) and your clients:
Code:
ROUTER ----> HUB ----> (SWITCH) ----> COMPUTERS ON LAN
then, attach a computer to the hub:
Code:
ROUTER ----> HUB ----> (SWITCH) ----> COMPUTERS ON LAN
|
|------> COMPUTER Now, whenever the switch send something to the router, your hub will get it, and broadcast that traffic to everything connected to it (the router and the computer). you'd place a sniffer on the computer.
THE PROBLEM WITH EXAMPLE 2 is that if the computers on the lan send information to other computers on the lan, that information would never get to the router since the switch would never send it to the router.
also, you waste a lot of ports on your router with the hub solution, and the hub solution might introduce a bottleneck into your lan.