On Jan 2, 2009, at 11:21 PM, Sdävtaker wrote:

I got a subnet with 5 machines and a cablemodem who provides 5 public ips
All is conected to a switch.
One of the machines is not ours and we want to check it is not
abuseing our internet link, so we want to know if there is any way to
monitor bandwich usage from one of the other machines in the subnet
with no need to modify the foreing machine config. Something like use
tcpdump in promiscuos mode or something like that, we doesnt matter
the content, we just need a bandwich conssumption meassure.
Thanks for any ideas.

Buy a smarter switch and do the traffic counts in the switch.

As things stand the switch is isolating all 5 machines from each other, none hear what the others have to say to the cable modem, so there is no way you can sniff the other's traffic.

If instead of a switch you had a dumb hub then all machines would hear what all the other machines were saying to each other and the cable modem. Is very hard to buy a dumb hub these days. Is easier to buy a smarter switch. A configurable smart switch can deliver the questionable machine's traffic to both the cable modem and to one of your machines but there is no point unless you want/need to see the contents of the packets. A switch that smart should also be able to count packets and tally total byte counts. If I understand correctly that is all you want.

David Kelly N4HHE, dke...@hiwaay.net
Whom computers would destroy, they must first drive mad.

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