Unable to reach certain websites DNS issues

Tim
Tim used Ask the Experts™
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Today I started having issue with my DNS resolution and can't quite find out how to fix this issue. I have two DNS servers on my network and the primary domain controller cannot reach UPS.com but the secondary server can. On the primary server I can reach most sites but when it comes to UPS it cannot. I have restarted the server and checked the DNS settings on the NIC and all looks good however I am unable to reach UPS on that computer and since this is the primary domain controller my users cannot access the site either.

What can I do to find out what is causing this configuration error
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Melissa DyerSenior Network Administrator

Commented:
First you need to clear the DNS cache. Run the following command: ipconfig /flushdns
Next make sure that the DNS server is using itself as the primary DNS and the secondary server is the other INTERNAL DNS server. Next verify that the forwarders setup are valid and responsive. Good luck!
TimSr. System Admin

Author

Commented:
Flushed the DNS and restarted both servers. The primary server can get to the UPS website but the secondary cannot. When I ping the ISP DNS servers the first server times out half the time and the secondary never times out. Could that be the issue? It really doesn't explain why one server can reach the same site while the other cannot.
Principal Support Engineer
Commented:
When I ping the ISP DNS servers the first server times out half the time and the secondary never times out. Could that be the issue?
It certainly could. If the "primary" DC has the ISP DNS servers configured as forwarders but is having issues connecting to them, it's most likely not getting responses to DNS queries that it forwards to them either.

Figuring out why you're having intermittent connectivity problems with the ISP DNS servers may be a real pain (the ISP is pretty much guaranteed to say it's not their fault, especially since your other DC doesn't seem to have the same problem), so in the meantime you may want to consider either using a different set of DNS servers as your forwarders (Google's 8.8.8.8 and 8.8.4.4, for example) or removing the forwarders altogether and using root hints instead.

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