unsolicited DHCP parameters [was: dhcpd and Vista]

Frank Bulk frnkblk at iname.com
Fri Dec 1 03:04:51 UTC 2006

Microsoft Win2K DHCP server gives out responses for parameters the client
does not even ask for.  I discovered this with a V-Brick product several
years ago.  

We were setting these up for non-static deployment across campus, and for
the life of me I couldn't make it work.  So I connect to the serial
interface and learn that the gateway and subnet mask aren't correct, they
seem semi-random.  I then tried the V-Brick against a test Win2K box on a
separate subnet and it works just fine!

Certain that ISC's DHCP server was in a good shape, I whipped out Ethereal
to look at the packet exchanges of both Win2K's DHCP server and ISC.  The
DHCP request from the V-Brick only asked for an IP address -- not even a
subnet mask!  So ISC's DHCP server wasn't handing it out.  And Win2K was
providing it, unannounced.

To resolve the problem I found an option in ISC's DHCP to give out the
subnet mask and gateway anyways -- problem solved.

I filed a bug report with V-Brick, but it was not addressed for at least a
year, after which I left the school.  


-----Original Message-----
From: dhcp-users-bounce at isc.org [mailto:dhcp-users-bounce at isc.org] On Behalf
Of David W. Hankins
Sent: Thursday, November 30, 2006 6:10 PM
To: dhcp-users at isc.org
Subject: Re: dhcpd and Vista

On Fri, Dec 01, 2006 at 12:04:24AM +0100, Lluís Batlle i Rossell wrote:
> The Discover is made with "Broadcast" flag enabled, so the Offer is sent
> to broadcast ethernet and ip addresses. For sure it should receive it, I
> think.

Make sure the destination address is "", not the
interface's broadcast address (but then XP shouldn't work either).

> > Because the Vista client doesn't put them on the parameter request
> > list.
> But the other dhcp server (I don't know what is it) puts them in the

That's their perogative.

> I may try.

I think this is documented in the manpage, if not look at PXELINUX
example configs floating around google (just change the option codes).

David W. Hankins	"If you don't do it right the first time,
Software Engineer		you'll just have to do it again."
Internet Systems Consortium, Inc.	-- Jack T. Hankins

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