I'm wondering if someone can explain what happens to Exchange 2010 when a domain controller goes down. I currently have two domain controllers, here is their information from the Event Viewer on the Exchange server: dc1.contoso.com CDG 1 7 7 1 0 1 1 7 1 dc2.contoso.com CDG 1 7 7 1 0 1 1 7 1 What I'd like to see happen is when one of these machines goes down (schedule reboot or catastrophe) Exchange will continue working with the second domain controller. However, it seems as though Exchange goes down for a while and finally comes back up 10-15 minutes later. My users will either reconnect in Outlook automatically or it will prompt them for a username and password. Can someone explain to me why this happens, and if it is possible, make the fallover to the second domain controller seamless? Thanks!

The behaviour you are seeing is correct. Exchange doesn't look for another DC immediately, and therefore there is a delay. 35 minutes isn't unusual. Then you have the issue with Outlook, which isn't always Exchange related, but due to the way Windows works with domain controllers. Don't schedule a reboot in the middle of the day and in the event of a failure, tell users to log out and log back in again and restart the Exchange services. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources

From the EMC, you can also try to change the config DC , ORg right click and maybe changing of the DC should help

Hi, The Exchange DSACCESS uses Round Robin to contact the DC. And the default query time is 5 minutes. If the workload is high, that should be long. Thanks Allen Allen Song

Hi, Hope these articles will help you in understanding how DSACCESS works. http://exchangeserverinfo.com/2007/09/02/understanding-dsaccess.aspx http://support.microsoft.com/kb/250570/en-us Thanks. Nagaraj N

Thanks for explaining that, I guess there is no immediate fallover like I was hoping there would be.