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I have found that in all my years of use with Macs, multiple OS versions, multiple hardware configurations, that it never queries anything but the primary DNS server. Why is this? We have spun up many different internal DNS servers and have tried specifying both internal and external DNS servers on the client. It will only resolve hosts in the primary DNS and completely ignores any DNS specified after that.

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    I can't accept the premise. I'm using Mavericks and I changed my network configuration to list two IP addresses; the first is an unused IP address locally and the other is a functional DNS server. I can surf the net, outbound ssh works, etc. Net access is slower because queries to the first server have to time out before the second server is tried. – Kyle Jones Nov 19 '14 at 19:06
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    DNS will accept the first positive answer it gets. If the first on the list always has an answer, why would it then look elsewhere? – Tetsujin Nov 19 '14 at 19:34
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    If it gets a response from the first DNS lookup it won't try again with another DNS server, even if the first response is NXDOMAIN. All your DNS servers are supposed to return the same results; if you're relying on different DNS servers with different results then your architecture is broken. – Mike Scott Nov 20 '14 at 6:40
  • OS X can support multiple resolvers, and use the hostname to select which resolver to use. Check out this question – Alan Shutko Jan 21 '15 at 17:27
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If it gets a response from the first DNS lookup it won't try again with another DNS server, even if the first response is NXDOMAIN. All your DNS servers are supposed to return the same results; if you're relying on different DNS servers with different results then your architecture is broken.

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