Multiple Leases

David W. Hankins David_Hankins at
Fri Jun 30 16:08:07 UTC 2006

On Fri, Jun 30, 2006 at 10:53:34AM +1200, Eustace, Glen wrote:
> Before:
>  1800    IN      TXT
> "00de8d5f7d6c03c62f0c82b19c47b8441e"
> After:
>  43200   IN      TXT
> "31de8d5f7d6c03c62f0c82b19c47b8441e"

The first is a client that is identified by hardware address.

The second is a client that is identified by a client-identifier
that is equal to its MAC address (note that they are otherwise

Looking at logs you sent dhcp-bugs@, I notice that there are some
'DHCPACK to ' messages which only appear in response to DHCPINFORMs
(but the DHCPINFORMs are missing...).

This behaviour I'm only aware Windows boxes participate in with the
kind of frequency I'm seeing here (but I can easily be wrong about

But I would bet dollars for donuts that it's the Windows 'Automatic
Update' widget trying to find an http cache (via the "WPAD" option,

So it appears that the client is given a different address because
of these differences in identification, but has selected the same
hostname somehow.  That confuses ddns but otherwise seems to work

Also, examining the way the logs flow:

	DISCOVER ... get one address.
	Deleted 31... TXT string, added new binding successfully.
	REQUEST for a different address.
	Deleted 00... TXT string, added new binding successfully.

Implies that the 'brains' in these MACs that decides to boot without
a client identiifer starts at DISCOVER (network booting agent?  This
follows if the boot device doesn't have long-term storage to cache the
last known lease in).  The 'brains' that decides to start off with a
REQUEST uses a client identifier equal to the hardware address.  Both
of these are actions I would expect of Windows.

I think your MACs are booting Windows, a trick I'm told they
learned recently when they moved to Intel chips.

If that's the case, I'm very sorry Glen.

To be sure, you can try syslogging the vendor-class-identifier.

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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