After deletion and recreation of the reverse zone Bind9 started again. Thanks to Rowland for the hint. However, bind complains that virtually all zones are duplicate and thus at least one issue is ignored. Since it's samba_dlz complaining there's either something wrong in the AD or in the DLZ module. The Bind does not have any other zones than the DLZ. I have trouble connecting windows clients to my AD after the secondary DC took over. But as far as I can tell DNS works flawlessly. Oct 28 07:07:46 verdandi named[672]: sizing zone task pool based on 22 zones Oct 28 07:07:46 verdandi named[672]: Loading 'AD Zones' using driver dlopen Oct 28 07:07:46 verdandi named[672]: samba_dlz: starting configure Oct 28 07:07:46 verdandi named[672]: samba_dlz: Ignoring duplicate zone '1.16.172.in-addr.arpa' from 'DC=@,DC=1.16.172.in-addr.arpa,CN=MicrosoftDNS,DC=DomainDnsZones,DC=ad,DC=microsult,DC=de' Oct 28 07:07:46 verdandi named[672]: samba_dlz: Ignoring duplicate zone '6.16.172.in-addr.arpa' from 'DC=@,DC=6.16.172.in-addr.arpa,CN=MicrosoftDNS,DC=DomainDnsZones,DC=ad,DC=microsult,DC=de' Oct 28 07:07:46 verdandi named[672]: samba_dlz: Ignoring duplicate zone 'ad.microsult.de' from 'DC=@,DC=ad.microsult.de,CN=MicrosoftDNS,DC=DomainDnsZones,DC=ad,DC=microsult,DC=de' Oct 28 07:07:46 verdandi named[672]: samba_dlz: Ignoring duplicate zone '10.16.172.in-addr.arpa' from 'DC=@,DC=10.16.172.in-addr.arpa,CN=MicrosoftDNS,DC=ForestDnsZones,DC=ad,DC=microsult,DC=de' Oct 28 07:07:46 verdandi named[672]: samba_dlz: Ignoring duplicate zone '_msdcs.ad.microsult.de' from 'DC=@,DC=_msdcs.ad.microsult.de,CN=MicrosoftDNS,DC=ForestDnsZones,DC=ad,DC=microsult,DC=de' Any idea what could lead to these messages?