Active Directory replication failed because the remote procedure call was cancelled
The remote procedure call was cancelled.
The destination domain controller initiated an inbound replication request to a source DC, but did not receive a complete response within the RPC replication timeout window (default 5 minutes). Active Directory cancelled the call and logged error 1818. The root cause is almost always that the source DC is taking too long to gather and send the replication data — typically because it is under heavy load, the replication payload is very large, or there is a network bottleneck between the two DCs.
The source domain controller is under heavy CPU, disk I/O, or memory load and cannot service the replication request within the timeout window.
The replication delta between the source and destination DC is very large (e.g., after a long offline period or a major batch of directory changes), causing the source to take longer than the timeout to package the response.
Network latency or bandwidth constraints between the source and destination DC (especially over WAN links) are causing the replication data transfer to exceed the timeout.
A virus scanner, security product, or third-party process on the source DC is scanning NTDS-related files and causing disk I/O contention during the replication operation.
The RPC Replication Timeout registry value has not been tuned for the environment and the default 300-second window is insufficient for the scale of the directory or the bandwidth available.
How to fix it
Identify which source DC is the origin of the timeout using `repadmin /showrepl <DestinationDC>` and check the failing replication partner.
Check resource utilisation on the source DC at the time of the failure: CPU, disk I/O (perfmon counters: PhysicalDisk\Avg Disk Queue Length, NTDS\DS Replication Sync Requests Made), and available memory. Address any resource bottlenecks.
Check for virus scanners or backup agents configured to scan the NTDS database folder (default: C:\Windows\NTDS). Exclude NTDS directory and log files from real-time scanning per Microsoft guidance.
If the replication delta is large following an extended offline period, allow the sync to run during off-peak hours when the source DC has more available resources. Trigger replication manually with `repadmin /replicate <DestDC> <SourceDC> <NC>`.
If the timeout is genuinely too short for the environment (large directory or slow WAN link), increase the RPC replication timeout on the destination DC: `reg add "HKLM\SYSTEM\CurrentControlSet\Services\NTDS\Parameters" /v "Replicator RPC timeout (minutes)" /t REG_DWORD /d 10`. Adjust the value in minutes as needed (default is 5).
For intersite replication over slow WAN links, review the intersite link cost and schedule configuration in Active Directory Sites and Services to ensure replication is not being forced over undersized connections.
