[cisco-voip] Unity 4.x loses access to Exchange

[Joel P]

Here is an interesting one I have never ran across.
Today I get a call from a customer to let me know their VM is down.
This is Unified messaging with Unity 4.2 and Exchange 2k3.
I log in and see right away in the event viewer that Unity lost contact with
Exchange and to check the user accounts. I check the user accounts they are
all correct, then I check the mail server and that is also functioning. I
asked the customer if they rebooted exchange or unplugged it or something
along those line and they said no. After about 15 minutes everything starts
to work again. Eventually the customer tells me that he did some updates on
his main DC and rebooted that. His DC is also one of his DNS servers.
However he has 3 other DC's and another DNS server. 
The only thing that I can think of is that this DC is his GC server but he
couldn't verify that. Has anyone ran across this before?

Thanks,

Joel P