Windows Server 2003 R2 DNS Issues

Hello Experts,

We do have a Win Server 2003 R2 with DNS , DHCP and Active Directory . For some strange reason our Win 7 stations and server sometimes drop the internet connection ( not the network connectivity). To be sure was not a ISP related issue I left one computer all day connected directly to the ISP router . The PC didn't had any issue. To test the internet connection I use a free software that basically connects to one site in this case Google or Yahoo as you may see on the attached file.

I left the software running all day and the internet drop is completely random . Sometimes it works for hours then it stops for 2 , 5 , 20 minutes then it goes back in.  To verify that again was Not a ISP related issue I left the same computer connected to the router where the router was the one giving the IP and not the DHCP on the Win server. When the server drops the Internet connection the PC was working perfectly.

I like to mention... when the server says Not Connected I try to ping via CMD  or any site and the ping didn't respond. However if i ping using the website or server IP  instead of the Name the ping respond without any issues. This makes me wondering that is something related to the DNS role.

Note: As soon the internet is back and working I open the CMD and ping the same website or server example and it reply without any issues.

Any advice or tips will be appreciated!
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prsnAuthor Commented:
I forgot to upload the image.
Natty GregIn Theory (IT)Commented:
Two things the nic facing the internet is going bad, and check the cable feeding the internet to your sever

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Miguel Angel Perez MuñozCommented:
Ensure you have marked secure cache against pollution on dns configuration.
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prsnAuthor Commented:
Hello I already replaced the Nic and network cable on the server . However the issue continue.
Don't use root hints, use forwarders only(preferably your ISP's DNS settings or & on the Server and make sure the workstations only have one DNS entry pointing to the server.
prsnAuthor Commented:
Hello Miguel

Secure cache against pollution was already check.
prsnAuthor Commented:
Hello Ktaczala,

Looking at the server configuration my Forwarders are from the ISP and the workstations DNS entry is basically my server IP .

Please take a look at this screen capture video on the link below. You will see when the monitoring software says "Not Connected" we still can reach websites or internet by using IP . However when I try to use the names or addresses like I can't reach them. As soon the system goes back alive I do the same procedure and all works. This scenario happens randomly.
Very strange!  Looks like it's definitely and server DNS issue.
To test theory try adding to a workstation as a secondary DNS entry, in theory the workstation should try server DNS first then the second one, which should succeed.
Any errors in the event logs for DNS?
Also can you post your routing table?  command prompt> route print
To state the obvious did you disable any firewalls & Antivirus apps?
Also try running this test In DNS Manager. Both when failing & working
prsnAuthor Commented:
Hello Group,

Turns out was a external Firewall issue in my scenario. Firewall had 2 cards ( 1 internal , 1 external) both cards where connected to the same switch.  This causes a loop on the network that affects the DNS . To solve the issue the external card was connected directly to the ISP router then the internal card was connected to the Network Switch . All workstations and server are connected to the switch. No more DNS resolution issues here.  

Thanks all for your tips.
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