have a customer who is having issues with what I believe is replication. He recently was performing maintenance on his primary DC and shut it down. Unfortunately, when he did this, his internal employee's all lost access to the email /Exchange 2010 server and also to the internet. I checked for Event Logs entries and did not find anything. Likewise, when I checked the DC itself, I could not even see that the server was shutdown (using the net statistics command). Is there any other place that I could check to see what may have happened?

If name resolution failed when one DC was shut down, then it sounds like the computers on the network are not configured to use at least two internal DNS servers for name resolution. I would recommend that you have at least two DCs running DNS and that your internal hosts ONLY use the internal DNS servers for name resolution. None of your hosts should be configured to use an ISP's or OPEN Internet DNS server as a secondary. In addition, since you mentioned Exchange, make sure that there is more than one DC functioning as a Global Catalog (if this is one domain, ALL of your DCs should also be GCs). Visit: anITKB.com, an IT Knowledge Base.

Hi, How many domain controllers in this domain ? and it's appreciate that if you could discuss in detail topology of customer’s environment and network settings for clients(DNS , default gateway..etc.) . You may check if replication causes this issue by using repadmin utility ,for more information please refer to the link below: Monitoring and Troubleshooting Active Directory Replication Using Repadmin http://technet.microsoft.com/en-us/library/cc811551.aspx http://www.microsoft.com/downloads/en/details.aspx?FamilyID=C6054092-EE1E-4B57-B175-5AABDE591C5F&displaylang=en 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.