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Preferred and Alternate DNS servers

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  #1  
Old 15-01-2008
Sandy Proesch
 
Posts: n/a
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



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  #2  
Old 15-01-2008
Kevin D. Goodknecht Sr. [MVP]
 
Posts: n/a
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  
Old 15-01-2008
Sandy Proesch
 
Posts: n/a
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
> ===================================
>
>



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  #4  
Old 15-01-2008
Ace Fekay [MVP]
 
Posts: n/a
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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