how to debug dhcp?

[dragoran]

John Reiser wrote:
>> when I try to use dhcp for my network device (eth0 - forcedeth) it does
>> not get an IP with the result: failed
>>     
>
>   
>> 2) how can I debug it to find out what is causing it?
>>     
>
> Boot single-user, invoke the dhcp program from a console in "non-daemon"
> mode, and watch.
how do I do this (found nothing in the man page)
>   For dhcpd, consider flags -d -tf and perhaps -play.
> Also, consider running under strace.
I am talking about dhclient not dhcpd
>   For lowest-level packet trouble,
> use a program such as tcpdump or ethereal to check what goes over the wire.
>
>   
used ethreal an have not found anything that looks like an error...