Unsolved DNS Server Issues

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I have a customer who is running Windows Server 2012 Standard. They have one physical server with two Hyper-V Virtual Machine Installations. One VM is their Domain Controller with DNS. The other VM is their Application server which they login to use a custom program that has a SQL Standard database. They have remote desktop services and licenses installed to allow remote desktop.

The customer is experiencing intermittent DNS issues where they will be connected to the Application Server and suddenly it will abruptly disconnect. If they attempt to reconnect via Remote Desktop, it will error out that client is not found. When this occurs they are also unable to navigate via their local web browser to any website by domain name.

How would you begin to troubleshoot this situation?

Do they have any support apps like hamatchi on the server?

@marc-vazquez No, support apps like Hamatchi.

I would start with looking at the vCPUs, RAM, NIC performance, and disk performance. Is anything maxed out? Can you ping the server when you can't connect? Any errors in event viewer. Did you try restarting the server and clearing out the RAM? Disk space filled?

I checked the ping of the server when I couldn't connect. I did both a ping by hostname and by IP Address. Both had a similar result. Since I was unable to continuously ping by IP address, that would seem to indicate that the DNS server is not the issue, wouldn't it?

Is it possible you have general VM networking issues? I have seen problems a few years ago related to bad NIC drivers while VMQ was enabled. If this applies to the NICs in your physical server, give it a try.

https://support.microsoft.com/en-ca/help/2986895/virtual-machines-lose-network-connectivity-when-you-use-broadcom-netxt

I went through issues with HP Gen7 blades. Only one set of NIC firmware and drivers would work reliably. I had the blades network disconnect. VMware has cookbooks that show for the NIC I am using the proper combination of firmware and drivers.

Hello James,
Just adding my contribution in this thread. if you are getting intermittent pings when pinging the hostname and IP address. chances are that there may be an issue with the VM itself. during this time can you ping the other VM with no issues? if you can then I would suggest starting at the VM in question. go though the system event log. see if there are any errors in regards to a NIC. also during this time are you able to access the VM from the Hyper-V management console?

@james-creen said in DNS Server Issues:

s running Windows Server 2012 Standard. They have one physical server with two Hyper-V Virtual Machine Installations. One VM is their Domain Controller with DNS.

I would suggest having another physical DNS (even a PC with raid 1 would be better than nothing) server as everything windows corporate network relies on DNS. The other issue with this type of setup; you may have time sync issues having everything on Hyper-V.

I hope this helps.

James,

Good evening, it sounds like you have been getting a lot of great advice so far, and I hope that you have made some headway towards solving the issue.

I wanted to step back to the beginning of your problem and see if I can help you to unravel what is going on here, as it seems to be a networking issue, but may not be DNS related.

Is the RDP session to the Application server done via an IP address or is it done via machine name / FQDN?