"deny duplicates;" not working?

sthaug at nethelp.no sthaug at nethelp.no
Wed Jan 9 07:02:01 UTC 2013

> The third entry is after the firmware update.  Notice that the MAC address remains the same, however the UID has changed, so the server issued it a new IP.
> In consulting dhcpd.conf(5) I found "deny duplicates;" which sounded like a magic bullet workaround, so I added it to the subnet declaration in dhcpd.conf file, but the problem remains the same (in tests with other of the same type devices and firmware upgrade scenario).

By default (and according to the RFC) UID is preferred if it exists in
the DHCP request.

What you really want is the long asked for ability to prefer MAC address
(only) and ignore the UID. This is unfortunately not possible with the
current ISC DHCP.

I believe that if you look back in the archives you may find a patch
which implements this - but for a previous version of ISC DHCP. Current
status of this patch is unknown.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no

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