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All machines are running Windows Server 2012.

We have a Domain Controller, DC1, that is also our primary DNS server. We have a secondary DNS server, DNS2.

All servers and desktops in the environment (60+) use DC1 as their primary DNS. All servers also use DNS2 as their secondary DNS. DC1 uses DNS2 as its primary DNS with loopback as secondary. DNS2 uses DC1 as primary and loopback as secondary. DC1 is set to notify DNS2 on changes for Zone Transfers. All desktop machines in the environment use DHCP. All servers have static IPs.

DNS2 is having an issue with its NIC that causes it to lose network connectivity. When that happens, all internal DNS resolutions immediately fail on all desktops and servers for 15-30 seconds. We're working on fixing the connectivity issue, but shouldn't DNS successfully resolve if the secondary is offline?

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Yes, within reasonable time-outs the secondary DNS server should take over.

You didn't indicate which server is the primary for DNS in the DHCP leases but I assume it's DNS2 with DC1 as secondary? Is there a reason you couldn't set it to be DC1 as primary?

You'll want to use various tools and logs to determine if the DNS on DC1 is actually available or not. Open nslookup and pass the config server=DC1 then do a lookup. Try this from everywhere (DC1, DNS2, DHCP server, Desktops). Then try the same thing with DNS2 as the server. Make sure both are actually available.

Double check the configuration for DNS Zone Transfers to ensure that they are actually transferring. Make sure your TTLs aren't ridiculously high. Check event logs on the DC DNS service.

Sometimes there's a race condition where AD tries to come up before DNS which causes DNS/AD to fail on the DC. Usually I fix this the way you have with a secondary DC as the primary DNS on the DC, not sure if a non-DC DNS server has the same effect.

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  • The issue is that the secondary DNS server is the one going offline and all DNS resolutions are then failing. I've done the NSLookup checks you suggest and both servers are available. I've confirmed the Zone Transfers are happening, TTLs are reasonable and logs don't have any smoking guns.
    – Jacob G
    Apr 18, 2019 at 15:44
  • And when you do ipconfig /all on the workstations, do they list both DNS servers?
    – duct_tape_coder
    Apr 18, 2019 at 22:03
  • No, the workstations do not point to both DNS servers, only the primary. I just realized I had that wrong in my original question. Sigh :( The DC points to DNS2 as its primary. All Servers point to DNS2 as their secondary. All Workstations only point to DC1. When DNS2 goes offline, all DNS fails.
    – Jacob G
    Apr 19, 2019 at 13:23
  • Unless you point the workstations to both DNS servers, they won't be able to use both. The fact that one DNS server is pointed to the other won't help if the only server listed on the NICs is unavailable.
    – duct_tape_coder
    Apr 25, 2019 at 18:04

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