lease problem

Glenn Satchell glenn.satchell at
Sat Jul 28 12:44:20 UTC 2012

Hi Julie

If you are worried about using up all your dynamic range with pxe leases,
you can use a class, such as this, to give PXE clients a short lease time:

class "PXE" {
  match if substring(option vendor-class-identifier, 0, 9) = "PXEClient";
  # 10 minutes should be long enough for PXE
  max-lease-time 600;

It doesn't solve the problem of having a different IP address for PXE and
Windows, but provides an alternative that hopefully gets around one of the

There does not appear to be any other way around this without hacking the
source code of the ISC dhcp server to ignore client-id, or using
fixed-address host statements.


On Sat, July 28, 2012 10:31 pm, Julie Xu wrote:
> Yes, it is for PXE/windown building process.
> So, "deny duplicate" and "on-lease-per-client"  all can not fix the
> problem.
> it is big issue for me now. Any way to work around? I mean to let machine
> keep same ip address after reboot?
> I can not give all the machines a host stattement. I need them on dynomic
> range.
> I guess this is a common problem for everyone who use isc dhcpd and
> windows, any know how to fix it ether on dhcpd site or windown site?
> Message: 3
> Date: Sat, 28 Jul 2012 08:23:20 +0100
> From: Simon Hobson <dhcp1 at>
> To: Users of ISC DHCP <dhcp-users at>
> Subject: Re: lease problem
> Message-ID: <p06240803cc3942929f6b at>
> Content-Type: text/plain; charset="us-ascii" ; format="flowed"
> Julie Xu wrote:
>>I get complain about new machines. the problem is :
>> when new machine come online first time, it get one ip
>>address. when the machine reinstall company image and reboot, even
>>it is in 10 minutes time, it get another ip address.
> let me guess, the company image is Windows, and the <something else>
> booted before that is not Windows ?
> It's most likely that the first system booted does not send a
> Client-ID - this is the default for pretty much everything other than
> Windows.
> Then when the system is booted with Windows, a Client-ID is used.
> The ISC server uses the Client-ID as the primary database key if one
> is supplied, and only falls back to the MAC (hardware) address if
> there is no Client-ID. So the two systems are different clients as
> far as the server is concerned.
> There used to be some patches that would "fix" this, but I've not
> heard of them for a while and I've no idea if they are maintained. If
> not maintained, they wouldn't work (I assume) against the current
> versions.
> But the obvious question is does it actually matter ?
> --
> Simon Hobson
> Visit for books by acclaimed
> author Gladys Hobson. Novels - poetry - short stories - ideal as
> Christmas stocking fillers. Some available as e-books.
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