XP clients sometimes ignore DHCPOFFERs

Sebastian Hagedorn Hagedorn at uni-koeln.de
Fri Mar 24 11:17:20 UTC 2006

--On 21. März 2006 16:18:08 +0000 "David W. Hankins" 
<David_Hankins at isc.org> wrote:
> On Tue, Mar 21, 2006 at 10:56:34AM -0500, John Wobus wrote:
>> We made the change (xx.xx.xx.255 broadcast addresses
>> to broadcast addresses in the routers)
> This is actually a very well known problem with Windows DHCP
> clients of all versions (that I'm aware of), and the reason
> the ISC DHCP software package is so careful to make sure it
> forms packets precisely for Windows clients' needs (the BPF
> etc hacks).  It's also the reference behaviour (rfc2131 is
> specific in stating the address MUST be,
> which makes it more than a little hard to fault them.

I wasn't aware of that at all. We were blaming Microsoft all the time, when 
in fact it was a misconfiguration on our part.

> I forget sometimes that people don't always use ISC dhcrelay,
> so I often don't remember this.  It's an incredibly old problem,
> dating back to Windows 95 to my earliest memory.

Nobody really complained about this until very recently.

> At any rate, a Windows DHCP client may not receive DHCP packets
> if they are not being sent to  If you're using
> Cisco helper-address, I understand you may need to configure the
> broadcast address as well.

Actually it seems best to not configure it. It defaults to

>> P.S. There are excellent explanations of Windows' APIPA
>> feature that Googling "APIPA" will turn up.
> Supposedly there is now a DHCP option you can use to inform
> clients not to consider link-local addressing.
> It's an odd duck because it's the only one of its kind that may be
> present in DHCPNAK ("you may not have a dynamic lease, but don't
> autoconfigure one either").

I'd be interested in learning more about that. If anyone knows how to 
configure this, please let me know.

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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