"deny duplicates;" not working?

Neff, Glen glen.neff at emc.com
Tue Jan 8 21:23:51 UTC 2013

I guess i'm using the default, which is UID, so I guess I have to specify a class?

How do I specify a class that includes all MAC addresses?


 * Glen R. J. Neff
 * USD Lab Operations Infrastructure Team
 * glen.neff at emc.com
 * EMC^2 == E^2

From: dhcp-users-bounces+glen.neff=emc.com at lists.isc.org [dhcp-users-bounces+glen.neff=emc.com at lists.isc.org] On Behalf Of Sten Carlsen [stenc at s-carlsen.dk]
Sent: Tuesday, January 08, 2013 3:49 PM
To: dhcp-users at lists.isc.org
Subject: Re: "deny duplicates;" not working?

How is your configuration? do you specifically use the MAC or is it the default (which is UID)?

On 08/01/13 20:13, Neff, Glen wrote:
>The main piece of information to identify a client is actually the UID, so with a new UID -> a new client, obviously it >can not get the same IP, that is reserved for the old client.
>You may have luck looking into classes and subclasses. Possibly with "spawn". I have never used these features >but I have a feeling they may actually do what you need.
>Use the hardware = MAC to create your subclass and that could be independant from the UID - I think.
Is dhcpd.conf(5) erroneous then?:

       The duplicates keyword
        allow duplicates;
        deny duplicates;
       Host declarations can match client messages based on  the  DHCP  Client
       Identifier  option  or  based on the client's network hardware type and
       MAC address.   If the MAC address is used, the  host  declaration  will
       match  any  client  with that MAC address - even clients with different
       client identifiers.   This doesn't normally  happen,  but  is  possible
       when  one computer has more than one operating system installed on it -
       for example, Microsoft Windows and NetBSD or Linux.
       The duplicates flag tells the DHCP server that if a request is received
       from  a  client that matches the MAC address of a host declaration, any
       other leases matching that MAC  address  should  be  discarded  by  the
       server,  even  if the UID is not the same.   This is a violation of the
       DHCP protocol, but can prevent clients whose client identifiers  change
       regularly  from  holding  many  leases  at  the same time.  By default,
       duplicates are allowed.

 * Glen R. J. Neff
 * USD Lab Operations Infrastructure Team
 * glen.neff at emc.com<mailto:glen.neff at emc.com>
 * EMC^2 == E^2

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Best regards

Sten Carlsen

No improvements come from shouting:

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