Today after a power failure at my other site (yes power drops a lot) I noticed that after the main DC came back online that Exchange was complaining it could not see the DC. Normally the Topology for Exchange should be CDG177101171 it was showing CDG10010000.

I went to the DC in question and ran a DCDIAG and it reported the following error:

The host 661bcd5c-ba25-4e96-81b3-64c2db98a63b._domain name could not be resolved to an IP address. Check the DNS server, DHCP, server name, etc.
Got error while checking LDAP and RPC connectivity. Please check your firewall settings.
……………………. DC failed test Connectivity

Before doing anything else I tested from each Exchange server if I could ping the DC and I could. I went to Active Directory Sites and Services, forced replication and still got the same error. So before I make any changes I rebooted the DC.

After the reboot I ran a DCDIAG and found no more errors. What I could see in the logs was that the DC was complaining about DNS. After the server came up from the power failure it did not start DNS correctly.

15 min later when Exchange logs event 2080 regarding the AD Topology it was showing connectivity to the DC again with CDG177101171.

Hope it helps

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