unsolicited DHCP parameters [was: dhcpd and Vista]

[Frank Bulk]

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.  

Frank

-----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 "255.255.255.255", 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
Offer.

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