AD replication isn't working with event 1865 logged

This article helps fix an issue where Active Directory replication doesn't work and event IDs 1865 and 1311 are logged.

Applies to:   Windows Server 2012 R2, Windows Server 2016, Windows Server 2019
Original KB number:   944351

Symptoms

You have multiple sites in the forest. On some sites, you find that AD replication isn't working.

On the Inter-Site Topology Generator (ISTG) Domain Controllers, the following events are logged every 15 minutes.

Event Type: Warning
Event Source: NTDS KCC
Event Category: Knowledge Consistency Checker
Event ID: 1865
Date: <date>
Time: <time>
User: NT AUTHORITY\ANONYMOUS LOGON
Computer: <computername>
Description:
The Knowledge Consistency Checker (KCC) was unable to form a complete spanning tree network topology. As a result, the following list of sites cannot be reached from the local site.

Sites: CN=<sitename>,CN=Sites,CN=Configuration,DC=<domain>,DC=com

Event Type: Error
Event Source: NTDS KCC
Event Category: Knowledge Consistency Checker
Event ID: 1311
Date: <date>
Time: <time>
User: NT AUTHORITY\ANONYMOUS LOGON
Computer: <computername>
Description:
The Knowledge Consistency Checker (KCC) has detected problems with the following directory partition.

Directory partition:
CN=Configuration,DC=<domain>,DC=com

Cause

This may happen when there are connectivity issues between the ISTG servers. For example, if a firewall has blocked the ports, the issue would occur.

Resolution

Use the portqry tool to troubleshoot the connectivity issues to the Bridgehead servers of the sites that are listed in Event 1865. If the ports are blocked by the firewall, configure the firewall to open the ports.

Data collection

If you need assistance from Microsoft support, we recommend you collect the information by following the steps mentioned in Gather information by using TSS for Active Directory replication issues.

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