DNS Conditional forwarder issue

Question

We have created conditional forwarder zone with 3 IP and it goes fail when first DNS server goes down.

Ex: configured a zone name called test.com (10.0.0.1,10.0.0.2,10.0.0.3)
Could not able to resolve if 10.0.0.1 goes down and no issue with 10.0.0.2 and 10.0.0.3. So please let me know that why it is failing only with first IP.

Answer 1

Hi,
Theoretically, under the normal circumstance, if the first conditional forwarder does not answer (meaning that the DNS server is down), then DNS server will go to the second conditional forwarder, et cetera, until they resolve or not.

If the first conditional forwarder gives answer (even a negative response, such as "name not found" is also considered a valid response), then DNS server will NOT go to the second conditional forwarder, et cetera.

You mentioned the first conditional forwarder goes down, and DNS server could not be able to resolve. To correct your situation, here is my method: first make sure your first conditional forwarder (the one which goes down) cannot ping through the destination IP address, then please submit your nslookup result. Is there any chance the server is waiting for the first conditional forwarder responding, which leads you to believe DNS server could not be able to resolve? There may be many possibilities to cause such problem.

Actually, there may be a way you can try. You may adjust the order of conditional forwarders by moving 10.0.0.2 and10.0.0.3 up in the Edit Conditional Forwarder window, then disable 10.0.0.2, and to see if the DNS server could resolve. In theory, the DNS server should go to 10.0.0.3 directly.

Please refer to the following link as a guide to learn more details.
https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/forwarders-resolution-timeouts#what-is-the-default-behavior-of-a-dns-server-when-more-than-two-dns-servers-are-configured-as-conditional-forwarders

Best Regards,

Mulder Zhang

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Answer 2

Thanks for your reply. How to check current configured RecursionTimeout value

Answer 3

Hi,
For checking current configured RecursionTimeout value, you can simply input dnscmd /info recursiontimeout in Command Prompt. The Dword number you get means the default value. (Here in my test machine is 8 seconds.)

Please refer to the following link as a guide to learn more details.
https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2003/cc784399(v=ws.10)#example-5-display-the-recursiontimeout-setting-from-a-dns-server
Best Regards,
Mulder Zhang

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Answer 4

Thanks for your reply again