Today was an interesting, over the bank holiday I demoted an old 2003 domain controller, let’s call it Server1.
All went to plan, changed the IP address of the DNS on the network card and ran DCPROMO, nexting through all the options.
Reboot, ran a few tests:
DCDIAG on all the remaining domain controllers, REPADMIN /REPLSUMMARY to test replication, Logged onto a few PC’s to check they could authenticate ok.
Well that all seemed fine and all the results were great.
Tuesday comes round and I turn up to bedlam!!
Around 20 or 30 machines were referencing Server1 for DNS and since the dcpromo the DNS server only had Active Directory integrated DNS running meaning users couldn’t get to a host of sites!!
The question was though, why on earth were they referencing Server1?
To try and resolve I did the normal client side:
Rebooted the client, IPCONFIG /Release, IPCONFIG /Renew, IPCONFIG /FlushDNS, Changed the settings in the registry: HKLM/CCS/Services/TCP/Parameters
But no matter what I did the DNS server reverted back.
So after some thought I logged onto Sercver1 and checked DHCP because as you know DHCP assigns DNS and the default gateway etc to clients.
The service was enabled which worried me slightly and the Scopes were disabled but more importantly the Server options were all referencing the wrong server!! So I quickly changed the options then disabled the DHCP service.
Rebooted the clients and Bam, everything was back up and running as it should.
For some strange reason the clients were using the wrong DHCP server along with its incorrect settings.
So I urge you if you have this problem check all your DHCP server first!!