In Active Directory Sites and Services, duplicate Active Directory replication connections are created for one or more domain controllers across one or more sites.
Symptoms
This issue is caused by either a lack of network connectivity or by another problem that disrupts replication on the Intersite Topology Generator (ISTG) in the site. If the ISTG cannot reach other domain controllers, it tries to create new (duplicate) Active Directory replication connections for domain controllers in the same site. Note If this is a transient condition, nothing will clean up the duplicate connection objects. If the connectivity and replication problem is no longer occurring on the ISTG, you must manually delete the duplicate connection objects and then rerun repadmin /kcc against the ISTG to make sure that the duplicates are not re-created.
Data collection
To collect the relevant data for this issue, follow these steps.Notes
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Repadmin /kcc <DCNAME> is the command to force KCC to run. However it won’t create a new connection if the other one is still in place.
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Replace <DCNAME> with the name of the domain controller that serves as the ISTG for the site.
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Run repadmin /showconn <DCNAME> >showconn.txt.
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Run repadmin /failcache <DCNAME> >failcache.txt.
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Run PortQRYUI on <DCNAME>, and target a remote domain controller that you have duplicate connections with, as follows:
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“Domains and Trusts test” File / Save Result
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On <DCNAME>, run repadmin /bind RemoteDC ( from step 3).
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Example: repadmin /bind RemoteDC1
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If repadmin /bind fails to connect, take a network trace by using netsh on both domain controllers, as follows:
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Run netsh trace start capture=yes tracefile=c:\%computername%.etl.
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Run repadmin /bind <DCNAME>.
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Connect by using the FQDN instead of the host name, if possible.
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Run netsh trace stop.
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Run repadmin /showrepl * /csv >showrepl.csv.
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Run repadmin /viewlist * >DCs.txt.
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Run repadmin /istg >istg.txt.
Cause
To resolve this issue, open ports in the site to allow the ISTG to connect to the domain controllers. After the connectivity issue is resolved, delete the duplicate connection objects, and then rerun KCC on the ISTG.
Resolution
For more information about this issue, see How Active Directory replication topology works. Particularly focus on the KCC and topology generation section and the “Excluded nonresponding servers” subtopic.
