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List:       dhcp-client
Subject:    Re: Interpreting results of tcpdump (was Re: No working leases with cable modem and new linux server
From:       Robert Elz <kre () munnari ! OZ ! AU>
Date:       2001-07-23 2:03:58
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    Date:        Sun, 22 Jul 2001 12:58:16 -0400 (EDT)
    From:        Gary Nielson <gnielson@charlotte.infi.net>
    Message-ID:  <Pine.LNX.4.21.0107221248200.359-100000@localhost.localdomain>

  | For example, I downloaded ethereal after
  | Ted mentioned it and installed it. I ran it on my packets on eth0. It's a
  | whole lot more readable than tcpdump.

It is a lot more verbose.   But the tcpdump output that you sent totally
failed to decode the packet (which wasn't surprising, it managed to miss
finding an IP header at all - the ethernet header it detected looked
simply wild).   tcpdump output usually includes a lot more useful info
that you were seeing.   It is possible that your tcpdump doesn't match
your kernel, and needs to be recompiled (or reinstalled, or whatever you
do on linux).   But since you have a new etherreal that does much the
same thing, this probably doesn't matter.

  | I've included 1 of 5 frames, they all appear to be the same.
  | ethereal reports:

The packets look fine.

  | It also reports:
  |     Server host name not given

That's OK, that field is only relevant in replies, not requests.

  | Should my IP address, before getting an IP from the dhcp server, be
  | 0.0.0.0 as listed?

Yes.

  | When ethereal reports that the server host name not
  | given, is that the key here -- no communication with the dhcp
  | server?

Well, yes, no communication with the dhcp server.

  | Would that indicate that I am sending packets but getting nothing
  | back?

What indicates that more is that you aren't seeing any replies with
etherreal.   You need to talk to RR, and find out if they're seeing
your requests.  They might be able to tell you what is wrong with them.
Or, perhaps they disconnected you for some reason or other (accident or
deliberately).

  | Any help appreciated. I feel that if I can properly read the results from
  | ethereal, it will tell me the story here, so that I can speak with
  | authority when dealing with the anti-Linux Road Runner folks.

Yes, but all you're seeing here is a good looking dhcp discover packet
being sent to the right place (ethernet broadcast address appears here).

If they ask you what you're sending in any particular field (I doubt they're
going to, as a wintrash user would have no idea at all...) then you'll be
able to find that easily enough (if etherreal hasn't told you its value,
then you aren't sending it at all).

Talk to RR, pretend you're running wintrash if you like when you talk to
them, if they ask you to run the command which releases and renews the
lease, just kill dhclient and run it again.    That's close to all they
can ask a windows user to do.   If they ask what the addresses assigned
are, use ifconfig eth0 to tell them what is set.

kre

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