Hi Guys,
I have been having an issue for the past couple of days with 4 out of 5 of our production Remote Desktop Session Hosts (Windows Server 2008 R2 Enterprise) where they will intermittently (about half of the time) not resolve external DNS queries.
We have two Windows Server 2008 R2 Domain Controllers which also host DNS. Three forwarders are set up to our ISP's DNS server and two Google DNS servers. The Google servers were added when this issue started.
I have been able to replicate the issue on the four servers mentioned above using nslookup. I am able to ping both DNS servers from all affected servers and internal DNS lookup does not seem to be affected. From all four servers I have tried using nslookup to directly query both of our DNS servers and the two Google DNS servers in turn however I see the same behaviour of DNS not being resolved about half of the time.
I have run Network Monitor on both the DNS server and the Client which replicating the issue and can see all of the successful queries at both sides as you would expect however the unsuccessful queries don't appear in the trace at either side.
Can anyone point me in the right direction for what to try next?
Thanks In Advance
Alex