one-lease-per-client... seriously

Glenn Satchell glenn.satchell at
Mon Sep 19 01:17:25 UTC 2016

On Sun, September 18, 2016 5:21 pm, Chuck Anderson wrote:
> On Fri, Sep 16, 2016 at 08:00:15AM +0100, Simon Hobson wrote:
>> On 15 Sep 2016, at 21:00, Brian Rak <brak at> wrote:
>> > I'm running into an issue where DHCPD (v4.3.4 and older versions) is
>> issuing multiple leases to the same mac address.  It appears to be
>> looking at the DHCP Client-ID field to determine what a unique client
>> is.
>> That is by design as is **REQUIRED** by the RFCs.
>> It's a long standing problem that some real-world situations clash with
>> this - most notably when there is multi-boot with Windoze and anything
>> else since Windows defaults to using the MAC address as client-id and
>> everything else defaults to not sending one. But that's what the
>> standards require and the ISC implementation has always been intended to
>> be a "reference" implementation that completely meets the standards as
>> laid down (unlike several other servers which really do break the rules
>> a lot).
>> >  I'd much rather it ignore everything except for the client's mac
>> address, but I can't seem to find an option to do this.
>> It used to require patches, but I see Jeff has suggested an option to
>> deal with this.
> A better way might be to identify the various boot stages and hand out
> very short leases for PXE, etc.  That way you don't violate the
> standard, but the extra leases don't hang around for very long.

Here is how I do it:

# PXE boots for jumpstarting x86 boxes
class "PXE" {
  match if substring(option vendor-class-identifier, 0, 9) = "PXEClient";
  filename "pxegrub.I86PC.Solaris_10-1";
  # 10 minutes should be long enough for PXE
  max-lease-time 600;


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