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Unable to access Certain DNS name Internally

jburbach asked
Medium Priority
Last Modified: 2010-04-13
I am having some issues with DNS where it will not allow me to access certain DNS Names internally.... I am able to access them by their IP Address though.


-mail.7Medical.com- internal address is the outside address


I have verified that NSLOOKUP is working properly!

I have tried adding a A Host name in DSN for the outside address- Did not work!

Any help would be greatly appreciated... This is a high priority!!!!

Watch Question

Try stopping the dnscache service (on command line run net stop dnscache).  Then try to ping the hostname.  If this does not work, can you post the A record for the domain.


Tried stopping and starting dnscache and that did work. I am unable to ping mail.7medical.com as well... I have tried posting a Host A record and that did not work either.

Non-authoritative answer:
Name:    crm.7medical.com

The DNS resolution is ok for this record.

Do you have separated internal and external DNS servers?


We Currently have Internal Integrated DNS... The External DNS is provided by our ISP.

If stopping the dnscache service allows you to get the correct IP it could be related to Windows negative dns caching.  
See the following kb for a more through explanation:


Jon, can you post the results of a your nslookup internally, it appears the external record is working as intended.
I suspect that your registered DNS name is named identically to your internal AD domain name, is that setup in that way?


Nope my Internal domain name is pdnlan.local.


The DSN Cache really has nothing to do with this issue...


This is what I think is occuring

When you surf to crm.7medical.com from my office (or anywhere for that matter) DNS resolves crm.7medical.com to, the public IP for that webserver.   Your browser tries to go to that address, but since that is a NATed address, on the external interface of the firewall, when you try to go there from "inside" you are essentially trying to go out and right back in on the same (external) interface.  Most (if not all firewalls) take exception to that sort of thing.

 Unfortunately, editing the hosts file wouldn't be effective, because while the FQDN would work fine while you were on the 7medical LAN, it wouldn't work when you were out in the rest of the world.

i think you must add a zone 7medical.com to your internal DNS servers an put there A records for the private ip address of all your servers. Make sure you "Clear the DNS cache" on your server.

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