Event ID - 2070

Event Id2070
DescriptionProcess %1 (PID=%2). DSAccess lost contact with domain controller %3. Error was %4 (%5). DSAccess will attempt to reconnect with this domain controller when it is reachable.
Event InformationExplanation :
This event indicates that the DSAccess component on the Exchange Server lost contact with the domain controller specified in the Description section of the event. The error code in the Event Description will be in the format 0x800409ZZ, where ZZ is the hexadecimal value of a standard LDAP error. 

You can search the Microsoft Knowledge Base for the description of the LDAP error using string "Microsoft LDAP Error codes" to access an article that lists these LDAP Error codes.

The domain controller is either down or unreachable. 
DNS may be misconfigured. 

User Action :
Typically, no action is necessary. If it planned downtime, this event may be ignored, as long as there is sufficient capacity in alternative DCs/GCs. If the event is unplanned, DSAccess will attempt to reuse this domain controller automatically after some time period, and will reconnect when the domain controller is reachable. 
Check DNS and ensure that no records exist for GCs that are no longer available.
Reference Links Event ID 9074 and 2070 Messages Occur When You Run the System

Microsoft LDAP Error Codes

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