[UKLAN] RE: XP clients sometimes ignore DHCPOFFERs

Sebastian Hagedorn Hagedorn at uni-koeln.de
Thu Mar 16 15:10:27 UTC 2006

--On 15. März 2006 16:34:26 -0500 "King, Michael" <MKing at bridgew.edu> 
> Actually, I think it's the home routers that are killing you.  :-)

I thought of that. One thing I have noticed is that the leases form the 
home routers seem to be very long-lasting, i.e. several days. I haven't 
been able to ascertain whether XP saves leases between restarts.

> There is another Microsoft "Feature" you failed to mention:
> http://www.microsoft.com/technet/prodtechnol/windows2000serv/deploy/confe
> at/dhcpnt5.mspx
> If the DHCP client has previously obtained a lease from the DHCP server,
> the client tries to renew any unexpired lease with the DHCP server. If
> the client fails to locate any DHCP server, it attempts to ping the
> default gateway listed in the lease. If this succeeds, the client assumes
> it has not been moved and uses that lease. The client then seeks to
> automatically renew the lease when half of the lease time has expired.
> If the attempt to ping the default gateway fails, the client assumes that
> it has been moved to a network that has no DHCP services currently
> available, such as a home network and it configures itself. It then
> automatically keeps trying to find a DHCP server every five minutes.
> So.....
> Can these clients / you ping (or  If you can,
> that's why they won't let go of they're IP and take a new one.

No, they can't. We use "proper" addresses for our subnets. However, I 
wonder if the second paragraph might not be an indication of what goes 
wrong: if I understand this correctly it says that if the client can't ping 
the gateway from the old lease it will *first* configure itself (I take 
that to mean "assign itself a link-local IP") and only then five minutes 
later try to find a DHCP server!?

AFAIK, just waiting for the client to get a lease does not work, either, 
but I can't swear to that.

Thanks, 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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