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I have two Windows DNS instances. One is on an older physical machine with Windows 2008, the other is on a Hyper-V guest with Windows 2012 R2. The latter is the primary DNS.

I've noticed that the amount of cached forwarded requests on my secondary is a good bit higher on average than the primary. Both machines have ~<1ms ping times and are up 100%.

Why would a secondary keep getting more requests, or at least seems like it's getting more requests? Thanks.

Grant
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Ryan Peters
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  • You need to give more information about your network, and more specifically, *your network clients making the requests*. – Avery Payne Jan 26 '14 at 03:47

1 Answers1

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When the primary DNS server times out, Windows switches to the secondary. Even a momentary delay can cause this switch. By default, Windows reverts back to using the primary first after 15 minutes.

If the primary times out a lot, then each time it happens, the secondary will become the primary for 15 minutes. If it times out, say, on average once every five minutes and the alternate never times out, then 3/4 of the time, the alternate will be effectively primary.

If you want strict priority, change the timeout to zero, causing the priorities to be reset for each query. The registry key is HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters. The value is ServerPriorityTimeLimit. It's a DWORD, and setting it to zero will cause the primary to always be tried first.

David Schwartz
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