Largest delta would report as unknown on Source DC while running Repadmin /replsummary for your Domain and Forest, since it’s showing unknown and didn’t see the replication delta value and unable to find the affected Destination DC, will describe how to find the Destination DC
Also Read: Force active directory replication
Why it’s reporting unknown?
Let’s say if the new replication connection object has been created by KCC and it’s failed before complete the first replication cycle or yet to complete the first replication cycle , so replication destination has never replicated from the source and Repadmin /showrep shows Last success @ (never). Then largest delta would report as unknown
How to find the affected Destination DC?
It’s not easy to find the Destination DC, since the connection object has not completed the first replication cycle, it won’t be available from Repadmin /replsummary output
Need to query each connection object from the Forest to find the Destination DC
Csvde -f c:\temp\list.csv -d "CN=Configuration,DC=Domainname,DC=com" -r (fromServer=*) -l fromserver
list.csv file contains all the connection object DN from your Forest and there fromserver attribute value
Search the list.csv with Source DC(fromserver attribute value), you will find the unknown Destination DC on the same line ( connection object DN), need to do many search till you get the correct Destination DC
This will also be used to check the opposite side of connection object, AD replication is two way pull replication and repadmin /showrep will show the connection object of respective Domain Controller and if you want to see what Domain Controller is pulling replication from this Domain Controller, then above method can be used
This can be easy in a very small environment with less then 10 Domain Controller, you can check this manually by running repadmin /showrep on each Domain Controller, let say you have a very large environment with more then a 100 DC then manual method can’t be easy and above procedure will find this in a easy way, hope this will help you to troubleshoot Active Directory replication issues