Re: DHCP
- From: "d" <kevindu28@xxxxxxxxx>
- Date: 19 Dec 2005 19:02:24 -0800
A reconfiguration of the TCP properties on this XP laptop seems to have
fixed or should I say stop the DHCPINFOM messages coming from the bogus
address of 4.0.0.0. Specifically I turned off the default NetBIOS
setting on the WINS tab and set it to "Enable NetBIOS over TCP/IP",
since my Linux server isn't a NetBIOS server. This client setting
isn't required. All cleared up now. Another XP gotcha??? Maybe.
d wrote:
> Using ethereal has help me discover the source and destination of these
> errand DHCP packets. The source address is a laptop machine on the
> network that has an address of 192.168.0.100. The destination address
> is 255.255.255.255. ethereal also reports that the MAC address of the
> destination is [ ff : ff : ff : ff : ff : ff ]. The laptop is a
> WIndows XPSP1 machine. Lots of other information in the output
> sections of ethereal. Nothing that jumps out to me as a problem. So I
> guess I have to keep on digging.
>
>
> prg wrote:
> > [snipped/moved top post to bottom]
> > > prg wrote:
> > > > d wrote:
> > > > > I expect to see these messages.
> > > > >
> > > > > dhcpd: DHCPINFORM from 192.168.0.111 via eth0
> > > >
> > > > Why do you expect this? DHCPINFORM is used only if the client has
> > > > already obtained an IP address by some other (non-dhcp) means.
> > > >
> > > > > dhcpd: DHCPACK to 192.168.0.111
> > > > >
> > > > > The messages that appear like below make no sence.
> > > > >
> > > > > dhcpd: DHCPINFORM from 4.0.0.0 via eth0: unknown subnet 0.0.0.0
> > > >
> > > > This indicates that the client _has_, by some mysterious means,
> > > > obtained the IP 4.0.0.0. The dhcpd server, if it made sense, would
> > > > return a unicast (since client has an IP) with other condig params. It
> > > > does _not_ make sense, thus the error message.
> > > >
> > > > >
> > > > > Please help me resolve them if there is a problem with my dhcpd
> > > > > configuration.
> > > >
> > > > I don't think it's a dhcpd.conf problem -- looks OK to me, though why
> > > > use dhcp for just two hosts is beyond me.
> > > >
> > > > See RFC2131 for info on DHCPINFORM:
> > > > http://www.faqs.org/rfcs/rfc2131.html
> > > >
> > > > I would run ethereal on the server and catch all the packets exchanged
> > > > between the client and server. Also check the client for a clue as to
> > > > why/how it is obtaining this IP _before_ sending its dhcp request.
> >
> >
> > d wrote:
> > > First, I'm just trying to get an understanding about how DHCPD works
> > > within Linux. Thus, I have two Windows XP clients to play with and
> > > therefore configured to obtain addresses from the server. (Start small
> > > and work up)
> >
> > I understand. But beware that Windows has a few wrinkles compared to
> > the way Linux boxes will behave. To really understand what's going on
> > -- especially with dhcp -- using ethereal to examine the packet
> > exchange will be invaluable help. Combined with the RFC 2131 you
> > should catch on pretty quickly to how it works.
> >
> > > When I saw the 1st message, I thought it was just the client
> > > (192.168.01.111) confirming to the server about its present on the
> > > network and that its IP is valid.
> > >
> > > Please the explain the term "return a unicast"?
> >
> > When the client first "contacts" the dhcpd server, it does not know
> > (normally) just where the server is, ie., it does not know the IP
> > address of the server, so it _broadcasts_ its initial packet. If the
> > client does not have an IP address (yet) the server would respond with
> > a _broadcast_ also (it works because the server has learned the
> > client's MAC/nic hardware address).
> >
> > A unicast packet is directed to a single ( ie., uni-) host and it
> > implies that the host has a "working" IP address. Most all normal
> > packets are unicast -- ie., directed from one host to another single
> > host.
> >
> > > Thanks for the FAQ, I'll give it a read.
> >
> > You will almost certainly need some MS docs or XP how-tos to work
> > through any MS wrinkles.
> >
> > http://www.microsoft.com/resources/documentation/Windows/XP/all/reskit/en-us/Default.asp?url=/resources/documentation/Windows/XP/all/reskit/en-us/prjj_ipa_xhku.asp
> > http://www.google.com/search?q=windows%20xp%20dhcp
> >
> > The question remains how the client acquired an IP of 4.0.0.0 (a class
> > A network's address -- not normally assigned to _any_ host). Something
> > very wrong here ;-)
> >
> > hth,
> > prg
.
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