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Thread: Preferred and Alternate DNS servers

  1. #1
    Sandy Proesch Guest

    Preferred and Alternate DNS servers

    I thought I knew the answer to this until someone asked. We have a W2K3
    domain with AD integrated dns servers. We put in one server as the
    preferred and one as the alternate dns server when we set up TCP/IP on a
    network adapter. What happens when someone tries to resolve a name that the
    preferred server knows nothing about? I say it looks at the forwarder which
    lists our external DNS servers and goes out the gateway to that address to
    resolve the name.

    Does the alternate server get queried as well? The only role I think it has
    is in case the preferred server is down. Is this correct, or does it look
    here as well?

    --Sandy



  2. #2
    Kevin D. Goodknecht Sr. [MVP] Guest

    Re: Preferred and Alternate DNS servers

    Read inline please.

    In news:eOeIbbuVIHA.1164@TK2MSFTNGP02.phx.gbl,
    Sandy Proesch <sproe@spamcop.net> typed:
    > I thought I knew the answer to this until someone asked. We have a
    > W2K3 domain with AD integrated dns servers. We put in one server as
    > the preferred and one as the alternate dns server when we set up
    > TCP/IP on a network adapter. What happens when someone tries to
    > resolve a name that the preferred server knows nothing about? I say
    > it looks at the forwarder which lists our external DNS servers and
    > goes out the gateway to that address to resolve the name.


    The DNS will try the forwarder for domains it does not know, if the
    forwarder has failed, it will use Root Hints.

    >
    > Does the alternate server get queried as well? The only role I think
    > it has is in case the preferred server is down. Is this correct, or
    > does it look here as well?


    The only time the Alternate is queried is when the Preferred does not
    respond quick enough (1 second). If the Alternate then responds with an
    Answer, the DNS Client service will use the Alternate for the preferred DNS
    until the TCP/IP stack is reset or until 10 min (IIRC, it could also be 15
    min, I'd have to look it up to verify the exact period)
    At any rate, if the Preferred says it cannot find the name, the query stops,
    the DNS client does not try a different server, it considers the answer to
    be correct.



    --
    Best regards,
    Kevin D. Goodknecht Sr. [MVP]
    Hope This Helps

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  3. #3
    Sandy Proesch Guest

    Re: Preferred and Alternate DNS servers

    Thank you very much. That was pretty much what I thought would happen, but
    you said it so much better than I did when I tried to explain it here!

    --Sandy

    "Kevin D. Goodknecht Sr. [MVP]" <admin@nospam.WFTX.US> wrote in message
    news:uFyAXuuVIHA.2268@TK2MSFTNGP02.phx.gbl...
    > Read inline please.
    >
    > In news:eOeIbbuVIHA.1164@TK2MSFTNGP02.phx.gbl,
    > Sandy Proesch <sproe@spamcop.net> typed:
    >> I thought I knew the answer to this until someone asked. We have a
    >> W2K3 domain with AD integrated dns servers. We put in one server as
    >> the preferred and one as the alternate dns server when we set up
    >> TCP/IP on a network adapter. What happens when someone tries to
    >> resolve a name that the preferred server knows nothing about? I say
    >> it looks at the forwarder which lists our external DNS servers and
    >> goes out the gateway to that address to resolve the name.

    >
    > The DNS will try the forwarder for domains it does not know, if the
    > forwarder has failed, it will use Root Hints.
    >
    >>
    >> Does the alternate server get queried as well? The only role I think
    >> it has is in case the preferred server is down. Is this correct, or
    >> does it look here as well?

    >
    > The only time the Alternate is queried is when the Preferred does not
    > respond quick enough (1 second). If the Alternate then responds with an
    > Answer, the DNS Client service will use the Alternate for the preferred
    > DNS
    > until the TCP/IP stack is reset or until 10 min (IIRC, it could also be 15
    > min, I'd have to look it up to verify the exact period)
    > At any rate, if the Preferred says it cannot find the name, the query
    > stops,
    > the DNS client does not try a different server, it considers the answer to
    > be correct.
    >
    >
    >
    > --
    > Best regards,
    > Kevin D. Goodknecht Sr. [MVP]
    > Hope This Helps
    >
    > ===================================
    > When responding to posts, please "Reply to Group"
    > via your newsreader so that others may learn and
    > benefit from your issue, to respond directly to
    > me remove the nospam. from my email address.
    > ===================================
    > http://www.lonestaramerica.com/
    > http://support.wftx.us/
    > http://message.wftx.us/
    > ===================================
    > Use Outlook Express?... Get OE_Quotefix:
    > It will strip signature out and more
    > http://home.in.tum.de/~jain/software/oe-quotefix/
    > ===================================
    > Keep a back up of your OE settings and folders
    > with OEBackup:
    > http://www.oehelp.com/OEBackup/Default.aspx
    > ===================================
    >
    >




  4. #4
    Ace Fekay [MVP] Guest

    Re: Preferred and Alternate DNS servers

    In news:O0NVdavVIHA.1168@TK2MSFTNGP02.phx.gbl,
    Sandy Proesch <sproe@spamcop.net> typed:
    > Thank you very much. That was pretty much what I thought would
    > happen, but you said it so much better than I did when I tried to
    > explain it here!
    > --Sandy


    It's actually 15 minutes, so Kevin was correct on his second guess. Here's
    an old article for Windows 2000 talking about a hotfix, but after the
    hotfix, the algorithm hasn't changed with Windows 2003, XP or Vista. The one
    second part is correct for how long it waits.

    The DNS Client Service Does Not Revert to Using the First Server in the List
    http://support.microsoft.com/?id=286834

    261968 - Explanation of the Server List Management Feature in the Domain
    Name Resolver Client:
    http://support.microsoft.com/?id=261968

    Here it is in more detail.
    Microsoft Windows 2003 Server - How DNS Works (includes how the query
    process works with multiple DNS addresses):
    http://technet2.microsoft.com/window...7fb7c1033.mspx

    --
    Regards,
    Ace

    This posting is provided "AS-IS" with no warranties or guarantees and
    confers no rights.

    Ace Fekay, MCSE 2003 & 2000, MCSA 2003 & 2000, MCSE+I, MCT,
    MVP Microsoft MVP - Directory Services
    Microsoft Certified Trainer

    Infinite Diversities in Infinite Combinations



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