XP clients sometimes ignore DHCPOFFERs

Sebastian Hagedorn Hagedorn at uni-koeln.de
Fri Mar 17 09:30:38 UTC 2006

--On 16. März 2006 17:41:30 +0000 "David W. Hankins" 
<David_Hankins at isc.org> wrote:
> The technote quoted says it only happens on "non microsoft" DHCP servers.
> I wonder what MS's server is doing to get its clients out of this loop.

Maybe I misunderstand, but I read this differently. The technote doesn't 
apply to *any* non-Microsoft server, but only to those which are configured 
in a certain way:

"The non-Microsoft DHCP server is configured to ignore "duplicate" DHCP 
discover messages (DHCPDISCOVER)"

ISC dhcpd does *not* ignore duplicate DHCPDISCOVER messages. The server 
they give as an example is the Lucent VitalQIP DHCP server device. I think 
they say non-Microsoft, because the Microsoft server never ignores 
messages, but they don't know about all the others and want to cover all 
their bases.

> Someone should be able to find out by getting a client into this state (it
> sounds like you need to give it a really long lease) and then attach it to
> a network where someone enabled "share network" on a regular Windows XP
> box.

You are right that this would be a scenario where the client might fail, 
because it could ping the gateway it had in its previous lease. However, in 
the specific situation we are currently investigating that scenario can be 
ruled out. The client is the *only* computer in that particular subnet.

> A pcap of that would save me a lot of effort.

I hope that mine are of some use.

Cheers, Sebastian Hagedorn
     .:.Sebastian Hagedorn - RZKR-R1 (Gebäude 52), Zimmer 18.:.
Zentrum für angewandte Informatik - Universitätsweiter Service RRZK
.:.Universität zu Köln / Cologne University - Tel. +49-221-478-5587.:.
                   .:.:.:.Skype: shagedorn.:.:.:.

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