Re: [gentoo-user] Port Tracer Program Needed

[Heiko Wundram]

Am Dienstag, 14. März 2006 19:24 schrieben Sie:
> I created the script as you suggested, and when I executed it ALL the
> lights on the ports that have connections go nuts

Okay, your switches are layer 2 switches, not layer 3 switches then... (they 
don't understand IP traffic, only ethernet traffic; a broadcast ping is a 
broadcast ethernet packet which gets forwarded to every port by a layer 2 
switch). I didn't think of that when I sent out the snippet; our switches are 
layer 3 switches, and they won't forward packets between different network 
segments, even when they are in the same ethernet segment.

But, you can still make this work if you have two computers connected to the 
network, one which you know the switch port and IP of.

Your setup should look something like this:

------------------------------------
|     Switch                       |
--|------------------------------|--
  Port 1 (192.168.0.1)           Port x (your Laptop, fixed at 192.168.123.45,
                                         some address not on your network)

Port 1 mustn't necessarily be port 1, may also be any other port, just as you 
may use any other IP you know.

Then, try the following:

#!/bin/sh
# Set up networking, adjust to fit your network.
ifconfig $1 192.168.123.45 netmask 255.255.0.0 broadcast 192.168.255.255

# Standard loop.
while true
do
	ping -f -w $2 192.168.0.1 # Your known host IP
	sleep $2
done

When you call this script (just as before), only those two ports which are 
present in the diagram above should start to fire (and sleep), and as you 
know one of them, the other can't be hard to actually discern from the rest 
of the ports on the switch.

If the above doesn't work, there are other ways which involve creating 
ethernet packets with invalid recipient address at high speeds which 
shouldn't get forwarded by a layer 2 switch, but these involve a little more 
trickery than a small shell script. I'd be happy to write a little 
Python-Program which does just this, but before I do, test the above. ;-)

-- 
--- Heiko.

-- 
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