I am hoping you can help me with some suggestions how to debug this issue. Periodically, browser requests on the network fail, then a refresh works; the failures looked like a DNS failure. So I decided to research it. I downloaded and used the GRC DNS test at http://www.grc.com/dns/benchmark.htm. I have 2 DNS servers, the primary is a later model 64 bit Win Srv 2008 R2 full patched. Backup DNS is 32 bit older PC, Win Srv 2008 (since R2 won't run on 32 bit). I use DHCP to pass DNS IP addresses to clients. What I see in the GRC test is that the primary is much faster in response as I would expect. However, the backup is 100% "reliable" in the test, meaning all DNS queries in the test were replied to. The primary though, typically is only 70% - 90% reliable, meaning a number of requests are not replied to. The problem is, I can't figure out why. I turned on detailed logging of any errors or warnings, and event log or DNS log shows nothing. I changed the forwarders from our ISP's to others (like Google), and that did not affect the outcome, so I eliminated forwarders on the internet not replying as an issue. I made sure nothing else was running at the time, CPU and network usage during this off-hours test were both 0%.This really has me baffled as it's a newer faster machine that in such a small test should be doing fine. It NEVER responds to 100% of the queries, I have run the test about 15 times over the last few days. No errors/warnings in general in the event log either. How can I figure out why the primary does not reply 100% of the time? Is this an Win Srv 2008 R2/DNS issue? Thanks for your help!

Hi Don, Thanks for posting here. Is this issue just occurred on one particular client computer? Have you tried exchange the primary and second DNS server entry on that client and would this issue still persist? You may capture the DNS query packet by using network monitor on that client host, so that could determine if name resolution would relate this issue. Microsoft Network Monitor 3.4 http://www.microsoft.com/downloads/en/details.aspx?FamilyID=983b941d-06cb-4658-b7f6-3088333d062f&displaylang=en I suspect that network connectivity may the root cause of this issue , you may start troubleshooting by replace cable or upgrade NIC driver software first, some good methods could be found in the article below: Advanced network adapter troubleshooting for Windows workstations http://support.microsoft.com/kb/325487 Network Connectivity http://technet.microsoft.com/en-us/library/cc961803.aspx Thanks. Tiger LiPlease remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.