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I setup some CNAME entry on our Windows Small Business Server 2012 for our internal applications (git, bug ticketing etc), but every 30 min or so the alias name became un-resolvable until we restart DNS Client service on our individual pc. What could be the cause of this problem / how can I debug it further?

The CNAME entry I setup points to the FQDN. For example I have a dev server mycompanydev01.local and I setup CNAME mycompanygit pointing to mycompanydev01.local.

DNS alias not resolving

On DNS Manager the entry is listed as static (couldn't find a way to change it). I don't know if this has anything to do with the problem. What does static actually mean, does it mean it expire after certain period?

enter image description here

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When you say it becomes unresolvable, what is the exact error? –  Snellgrove May 3 '13 at 6:33
    
It says "could not find host" see screenshot above –  gerrytan May 3 '13 at 6:37

1 Answer 1

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+50

First, static is good. You want it to be static - it means the entry was manually added to the DNS zone and will stay there until manually removed.

One thing that may make your life a little easier is clearing the resolver cache. When a DNS client cannot find an answer for a query it puts a negative cache entry into the resolver cache. If you run ipconfig /displaydns on the client you see something like the following.

werwer.qwerwertr.wer
----------------------------------------
Name does not exist.

You can remove these without restarting the DNS Client service by executing ipconfig /flushdns.

Now, why is the DNS client not resolving the name? In the past, I've seen this happen in two situations. First, the DNS servers are overloaded and sometimes unresponsive. Second, the clients have multiple DNS servers entered in their network adaptor properties and the multiple DNS servers are not in sync.

To check the second situation, on the clients execute ipconfig /all. What DNS Servers are in the list, for all network cards? Are all the listed servers under your control? Are they all replicating to each other somehow?

Finally, does the name under the white scribble above have full stops in it? If you are using something like ping server5 then it may be using NetBIOS name resolution, which means broadcasts and/or WINS.

Note: ipconfig is a Microsoft Windows command. Other clients will have equivalent commands (ifconfig is probably the *nix equivalent).

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Thanks again for the answer, I just figured out the real cause of the problem is we had multiple DNS on our DHCP configuration. One is our internal DNS, and two are public DNS which doesn't contain the CNAMEs. I have updated the DHCP config to only use the internal DNS, and configure the 2 public DNS as a forwarder and it solves the problem –  gerrytan May 14 '13 at 7:20

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