Re: Is it possible to record a DHCP handshake?
From: Tauno Voipio (tauno.voipio_at_iki.fi.NOSPAM.invalid)
Date: Mon, 06 Dec 2004 15:15:47 GMT
Elias Aarnio wrote:
> It is very common among the ISP's to refuse any responsibility even if
> there is a malfunction in their hardware devices. A very common problem
> these days is low-end HomaPNA switches that all of the sudden stop
> functioning as DHCP servers.
> This causes all clients (customer's computers) behind that switch to be
> unable to use the connection. These "layman" HPNA services often also
> state in the user guide that the the ISP has the right to change the IP
> addresses of the default gateways etc. without prior notice.
> So, when I go to help somebody with a problem like this, I would like to
> "record" the DHCP handshake. This would be extremely useful when the
> customer wants to get his/her money back from the ISP.
> How do you record a DHCP handshake?
The sure-fire method is a hub (not switch) and another
computer to catch the traffic.
You have to be root on the computer.
Use ifconfig to get the interface up, then start tcpdump
(or whatever sniffer) on it. Start the DHCP client manually
after the capture tool is up.
If the tool refuses to start capturing, get the interface
up with IP address of 0.0.0.0
My favourite sniffer is Ethereal (or tethereal if no graphic
environment is available).
-- Tauno Voipio tauno voipio (at) iki fi