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I have 3 Win 2003 domain controllers across 3 sites. When one of those domain controllers goes offline connectivity to Exchange is intermittent. When users open Outlook some of them will be able to connect and others won't (seemingly random). All of the domain controllers say that they are GCs which I believe is a FSMO that Exchange cares about. What else is special about this DC that is causing problems with Exchange? This DC is at a different site than Exchange and I would like to get rid of this dependancy so if the site is offline it won't effect the other sites Exchange connectivity.

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check DNS? Also check to see if replication is working in the event log on the DCs or use repladmin. dcdiag might show you what's going on as well. – gravyface Jul 18 '11 at 14:59

We have exactly the same problem and it is a "feature" of exchange that it can take up to 30 minutes for Exchange to "notice" that a domain controller has gone offline.

If it is a planned outage then you can switch to using a different one in advance by right clicking on the "Organisation Configuration" node in the Exchange Management Console and selecting the "Modify Configuration Domain Controller" to specify a specific DC.

You will need to do this 30 minutes in advance of the downtime of the DC to allow the setting to take effect. Once the DC is back up set it back to "Use a default" domain controller

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In the couple times that it has gone down it has been longer than 30 minutes. I checked what DC was listed as the current configuration domain controller via those steps and it wasn't the DC that has been giving us problems. In fact it's set to the DC we'd like it to be b/c it's at the same site. – PHLiGHT Jul 18 '11 at 18:57

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