Event ID 1865. is generated when the. KCC does not manage to build a complete topology of Active Directory replication. Start with. repadmin /replsummary, then control connectivity, DNS, Active Directory Sites and Services and replication partners before any manual topology changes.
What does this error mean?
Active Directory cannot properly build the necessary replication connections.
Probable causes
An Event ID 1865 may result from a offline DC, an isolated site, an absent or poorly planned link site, a failed DNS resolution or a already broken replication. Do not create a manual NTDS connection to hide the, error before, having identified the cause: the.KCC must normally be able to recalculate a healthy topology.
Verification and resolution
Pick up the sites listed in the, event, and run. repadmin /replsummary and. repadmin /showrepl Check that the partners are reachable, that DNS resolves DC names and that the ports required for Active Directory are not filtered. Finally, check the subnets, sites and links that need to link the locations concerned.
How to validate the correction — Event ID 1865 — Unable to form the replication topology.
Once the cause has been corrected, restart replication controls and let the KCC recalculate the topology. repadmin /replsummary no longer shows of failure and that the events 1865/1311 do not reappear. If a DC is permanently lost, first properly treat its deletion and metadata before considering the problem solved.
FAQ — Event ID 1865 — Unable to form replication topology
Event ID 1865 means that, Active Directory is completely stopped?
No, but some of the topology can be inaccessible and some partitions may no longer replicate properly.
Which order should you use first?
repadmin /replsummary gives a quick view of the failures, then repadmin /showrepl details the partners.
Should we create a manual connection?
Not in first intention: correct first DNS, connectivity, sites and partners so that KCC can rebuild topology.