DC migration cause DNS outage. I don't know why it happened!


  • Hi,

    Last weekend I migrated most of our DC's from Windows Server 2008R2 to Windows 2012. The 2008R2 servers were also DHCP servers. This role was migrated to a non DC Windows 2008R2 server during the migration. Most of the 2008R2 DC's were demoted, replication took place, then new Windows 2012 servers were promoted using the old name/IP address. 

    At headquarters, we previously had two Windows Server 2008R2. Ill call them Headquarter-DC1 and Headquarter-DC2. Headquarter-DC2 was demoted but never shutdown or had DNS service stopped (a mistake on my part) which means it was configured with no zones. Headquarter-DC1 was demoted and then a Windows Server 2012 server was promoted with the same name/ip address as Headquarter-DC1. 

    When users came in Monday morning, they couldn't resolve hostnames. After checking DNS, I realized I hadn't removed Headquarters-DC2 which was the tertiary DNS server (and also had no DNS zones configured)given out from DHCP. After replacing the tertiary address, the clients started resolving the hostnames again. I also restarted DNS during this time. Some things to note is before the tertiary was replaced and DNS restarted, some clients just started resolving on their own while other clients logging in couldn't resolve hostnames until I made the changes noted above (about 15 minutes from when they booted up).

    My question is did the tertiary DNS server with no zones entry affect the clients ability to resolve the name even though the first to DNS servers were resolving names properly (which doesn't make sense to me). Or is there another likely scenario I am missing? 

    • Edited by Ray Jasutis Thursday, December 22, 2016 3:52 PM
    Thursday, December 22, 2016 3:50 PM

All replies

  • If your primary and secondary servers were responding to queries correctly then it is very unlikely the clients were even contacting the tertiary server for queries.

    So I would say no that shouldn't have affected it. Did you check to ensure that the clients didn't have any static entries configured incorrectly and the DHCP scopes were giving the DNS server addresses you expected them to?

    Thursday, December 22, 2016 3:59 PM
  • The clients were configured to get the DNS servers via DHCP. They didn't have statically set DNS server entries.

    I didn't check if the clients were getting the correct entries, I could only assume they were.

    • Edited by Ray Jasutis Thursday, December 22, 2016 4:05 PM
    Thursday, December 22, 2016 4:03 PM
  • If they had the correct entries then they shouldn't have contacted the tertiary DNS server (assuming at least either the Primary or Secondary was up and working) so that shouldn't have caused your issue.

    It is probably worth checking your event logs on your primary/secondary if they go back that far for any DNS errors/warnings. You could also check for error/warning events on a client that had the issue for DNS Client errors.

    Thursday, December 22, 2016 4:48 PM
  • Hi,

    Are there any updates?

    Best Regards,


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    Friday, December 30, 2016 1:10 AM
  • Hi Ray,

    do you have any more feedback?

    If you believe my response answered your question please 'mark as answer'


    Thursday, January 26, 2017 7:44 PM