Fix AD Replication Error 0X000020FC – Quick Steps

Quick answer

Check DNS first – run nslookup on the source DC targeting the destination DC's IP. If that fails, fix DNS records. Then verify firewall rules allow RPC, LDAP, and Kerberos traffic. Run repadmin /replsummary to confirm.

Why this happens

I've seen this error pop up at least a dozen times in the last year alone. Last month, a client's branch office DC stopped replicating after a network upgrade. The error code 0X000020FC – ERROR_DS_DRA_CONNECTION_FAILED – means the destination domain controller can't be reached from the source. 90% of the time it's DNS. The replication process needs to resolve the name of the target DC to an IP address that's reachable. If DNS points to a stale IP, or the target DC has a firewall blocking ports, you get this error.

Common triggers: after a server rename, IP change, or when someone messes with firewall rules. Also happens when the KCC (Knowledge Consistency Checker) auto-generates a replication link but the network path is broken.

Fix steps

1. Verify DNS resolution

Open Command Prompt as admin on the source DC.
Run: nslookup
You should get the correct IP. If you get a different IP or a timeout, DNS is broken.
Check the target DC's DNS client settings – it should point to itself or another DC, not to an external DNS.

2. Check firewall rules on both DCs

AD replication uses dynamic RPC ports. The default range is 49152-65535 for Windows Server 2008 and later. Also need ports 389 (LDAP), 445 (SMB), 88 (Kerberos), and 53 (DNS). Had a client last month whose new firewall appliance blocked all RPC traffic. Took me an hour to find it. Test with telnet:

telnet  389

If telnet fails, port is blocked.

3. Validate replication topology

Run

repadmin /showrepl

on the source DC. Look for entries with status 0X000020FC. Then run repadmin /replsummary – this gives you a clean summary of all replication failures.

4. Force replication with a specific IP

If DNS is correct but the connection still fails, try forcing replication using the IP address instead of the hostname. Not a fix, just a test:

repadmin /syncall  /e /d /A /h

If that works, you've got a DNS registration or network route issue.

Alternative fixes

If DNS still fails

Clear the DNS cache on both DCs:

ipconfig /flushdns

and restart the Netlogon service. Then re-register DNS records: ipconfig /registerdns. Wait 10 minutes and retry replication.

If firewall is the culprit

Open Event Viewer on the destination DC, look for event ID 1925 or 5806. Those tell you exactly which port the KCC tried to use. Add that port to your firewall rules. Better yet, set a static RPC port range for AD replication (Google it, not gonna paste the whole thing here).

Last resort – delete and recreate the connection object

Open Active Directory Sites and Services. Navigate to the replication link between the two DCs. Delete the connection object. Wait for KCC to re-create it (usually within 15 minutes). Then force replication. This clears any corrupted state.

Prevention tip

Monitor DNS health weekly. Use

dcdiag /test:dns

on each DC. Also set up a scheduled task to run repadmin /replsummary and email you the results. I've done this for all my clients – catches problems before they cause downtime. And never change firewall rules without testing replication immediately after.