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DNS Client with multiple DNS, what is priority

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  • DNS Client with multiple DNS, what is priority

    In Windows 8 client with both Primary and Secondary DNS Servers set I have always believed the priorities worked something like this:
    The Primary DNS Server is always used if it is available and the Secondary DNS Server is only ever used in the event that the primary in unavailable.
    Is my understanding here correct?

    Reason for asking is because I have this from Microsoft:
    if you use multiple DNS servers, the client may also query the secondary server sometimes even if the first one is available
    And then this is this post:
    http://blogs.technet.com/b/ajayr/arc...alternate.aspx

    If Primary DNS is online and working why does DNSCache still seem to use Secondary DNS Server sometimes? I didn't think this should happen.

    How are clients with multiple DNS Servers meant to behave? Is this a bug in Win8 DNSCache?
    Last edited by Nick_C; 24th April 2013, 12:33.

  • #2
    Re: DNS Client with multiple DNS, what is priority

    Originally posted by Nick_C
    How are clients with multiple DNS Servers meant to behave?
    to get a better understanding, i will refer you to this page:
    DNS Processes and Interactions

    the short version is that windows will send the request to the first DNS. if the response isnt received within 1 second, then a second request is sent to the alternate. if the response from the secondary arrives before the primary, then m$ switches to secondary from there out until the process repeats itself.

    does that make sense? did you just want to know why or were you needing to change something?

    this creates issues for me on slow networks where i use internal server names for RDP or telnet stuff. if the internal response is slow, then it will try resolve internal names on a public DNS srvr, which doesnt work. so i have to ipconfig/flushdns ->/registerdns to resolve the internal names or get out my notebook and see what the IP is...
    its easier to beg forgiveness than ask permission.
    Give karma where karma is due...

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    • #3
      Re: DNS Client with multiple DNS, what is priority

      Thanks James, very informative article.

      Yes I had the same problem whereby the Primary (internal) DNS server was not replying in time and queries were getting redirected to the Secondary (external) DNS server.

      So it seems we can no-longer depend on DNS queries being resolved by the Primary DNS when it is online. Quite short timeouts could cause queries to get redirected to the external DNS server instead.

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