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If I have contradictory NS records for my domain:

dig +trace example.com

example.com.        172800  IN  NS  ns1.webfaction.com.
example.com.        172800  IN  NS  ns2.webfaction.com.
example.com.        172800  IN  NS  ns2.mydyndns.org.

Which one[s] will be queried by my DNS client? Does the ordering matter? How can I tell the ordering?

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I would remove the ns dns record if possible, tertiary ns is unlikely to be fired off in my experience; how big is your network? –  scape Nov 7 '12 at 18:13
    
There is no such thing as "tertiary ns" –  bortzmeyer Nov 7 '12 at 20:59

3 Answers 3

up vote 2 down vote accepted

The ordering in which the lists are presented to you is randomly ordered in most cases. But you (as the dns-admin) can also configure sequential output (round-robin) or static output. Depends on the administrators mood.

Which entry a client chooses is also up to the developer of the client.

dig +trace picks a random entry.

In any case, the only reason for this is load balancing. If all servers are running fine it doesn't matter which entry you actually use.

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I don't see the same output when running the same command.

But to answer your question, a random one will be chosen and the order you list them in does not matter. You can see this with successive runs:

$ dig +trace inburke.com

...
inburke.com.        3600    IN  A   108.59.11.111
;; Received 45 bytes from 173.230.141.144#53(ns4.webfaction.com) in 96 ms

$ dig +trace inburke.com
...
inburke.com.        3600    IN  A   108.59.11.111
;; Received 45 bytes from 178.79.142.142#53(ns2.webfaction.com) in 8 ms
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Sorry, just providing an example. I changed it to example.com –  Kevin Burke Nov 7 '12 at 19:00

I believe that the resolver uses round robin methodology to query DNS hosts.

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