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Our internal DNS server with windows 2003 has problems with querying specifically .co domains. I've done a Package capture and found that the DNS server does not do anything when querying .co domains(the others like .com .net etc are fine).

So I think this problem is related with the server cache. And when I look at the server cache, there's no A records for .co root name servers which might due to TTL. So I guess the cache stuck somewhere.

Once I clear the cache of the DNS server, it will no longer have the problem but after some time (I can't tell the exact time), the problem will appear again which is quite annoying.

Can anyone seen this before or help please?


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Is it doing recursive lookups or forwarding to another recursive server? – Shane Madden Feb 28 '12 at 16:22
Yes, it is doing recursive lookups but no forwarding. – Dongdong Mar 8 '12 at 14:05
One way to help troubleshoot issues like this is to see the NS records for the problem domain when the issue happens. Use nslookup for this (type in nslookup, type in set type=NS, then type in co. or whatever domain is having issues) – samiam Feb 1 '14 at 17:34

Is the server up to date with DNS hotfixes & security bulletins? There have been a couple that could apply in this situation. There may have been more than just these two.

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