In comp.os.linux.networking Bob <email@example.com> wrote:
> Have you tried SNAT? I noticed it on YouTube last week.
I'm not sure how robust this:
This action is the one I really like. With the help of it you can
check if a host on your network is running a sniffer (well,
technically your checking if the NIC of that host is running in
promiscuous mode). The idea behind this is to use an arp request
with a forged destination address. First all of let me explain
what is a promiscuous and a normal mode for the NIC. In the first
one the network card simply picks up all of the packets (even
those that are not directed to it), the second mode only picks up
the packets that are directed to it and drops any other
packets. But, all networks cards that work in normal mode will
pick up a packet with the destination address equal
FF:FF:FF:FF:FF:FF (broadcast). So where is the trick ? In a
network with all NICs working in a normal mode if you send an arp
request with the destination address = FF:FF:FF:FF:FF:FE none of
the cards will reply. All of them will simply drop it. But when a
card works in promiscuous mode it will pick up that packets
(remember that it picks up all the packets regardless) and reply
to the request. So when you get a reply from a host after sending
such forged packet it means that the NIC is working in the promisc
mode , so probably a network sniffer is running on that
machine. Let me demonstrate it for you. I'm 192.168.1.6 and the
host I want to check is 192.168.1.8 As usual go to the directory
where you have snat.jar and execute the command (if you have any
problems go here) :
will be. First, I suppose that 99 times out of 10 a host responding
to that MAC address will be in promiscuous mode, but since the group
bit is set... And I would think all it takes is a small change to the
ARP code to verify that the destination MAC was a full broadcast...
The upshot is it is probably best to ass-u-me that unless you have
complete physical control of your network - all the wires, all the
ports, no wireless - that someone is listening.
oxymoron n, Hummer H2 with California Save Our Coasts and Oceans plates
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...