Active Directory Replication Error Codes & Fixes

When repadmin /showrepl shows errors, they are usually accompanied by an HResult error code (e.g., 0x2105). Below is a list of common replication error codes, their causes, and solutions.

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🛠 Common AD Replication Error Codes & Fixes

1️⃣ Error: 1722 (0x6ba) - The RPC Server is Unavailable

📌 Cause:

• The destination domain controller (DC) is unreachable due to network/firewall issues.
• RPC endpoint mapper service is not running.
• DNS resolution issues.

✅ Fix:

• Ensure RPC is open: powershellCopyEditTest-NetConnection <DC-IP> -Port 135
• Verify DNS settings: powershellCopyEditnslookup <DC-Name>
• Restart services: powershellCopyEditnet stop ntds && net start ntds

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2️⃣ Error: 8453 (0x2105) - Replication Access Was Denied

📌 Cause:

• The DCs do not have proper permissions to replicate.
• The “Enterprise Admins” or “Domain Admins” group permissions are missing.

✅ Fix:

• Ensure the source DC has the correct permissions:
• powershell
• dsacls "CN=Configuration,DC=domain,DC=com"
• Manually trigger replication using elevated credentials:
• powershell
• repadmin /replicate <DestinationDC> <SourceDC> /force

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3️⃣ Error: 1818 (0x71A) - The Remote Procedure Call was Cancelled

📌 Cause:

• A timeout occurred due to network latency or overloaded DCs.

✅ Fix:

• Increase RPC timeout:
• powershell
• reg add HKLM\SYSTEM\CurrentControlSet\Services\NTDS\Parameters /v RpcTimeout /t REG_DWORD /d 120 /f
• Check network congestion using: powershellCopyEditpathping <DC-IP>

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4️⃣ Error: 8606 (0x219E) - Insufficient Attributes for Replication

📌 Cause:

• A DC is partially replicated and missing objects.
• Common after authoritative restores or schema mismatches.

✅ Fix:

• Check lingering objects:
• powershell
• repadmin /removelingeringobjects <SourceDC> <DestDC_GUID> <NamingContext>
• Re-register DNS and Global Catalog: powershellCopyEditnet stop netlogon ipconfig /registerdns net start netlogon

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5️⃣ Error: 8524 (0x214C) - The DSA Operation is Unable to Proceed Because of a DNS Lookup Failure

📌 Cause:

• The destination DC cannot resolve the source DC in DNS.
• Improper DNS delegation in multi-domain forests.

✅ Fix:

• Check current DCs in DNS:
• powershell
• nslookup -type=SRV _ldap._tcp.dc._msdcs.domain.com
• Ensure each DC points to a valid internal DNS.

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6️⃣ Error: 1908 (0x774) - Could Not Find the Domain Controller

📌 Cause:

• The DC is offline, or a decommissioned DC is still referenced.
• DNS has stale records.

✅ Fix:

• Remove old DC references:
• powershell
• nltest /dclist:domain.com
• Check for orphaned records:
• powershell
• dcdiag /test:dns
• If a DC is permanently offline, use metadata cleanup: powershellCopyEditntdsutil metadata cleanup

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7️⃣ Error: 8545 (0x2151) - The Replication Topology is Invalid

📌 Cause:

• A DC lost its connection to the replication topology.
• Occurs after improper site link configurations.

✅ Fix:

• Force KCC to regenerate topology: powershellCopyEditrepadmin /kcc <DC-Name>
• Verify site links and bridgeheads:
• powershell
• Get-ADReplicationSiteLink

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8️⃣ Error: 1396 (0x574) - Logon Failure: Unknown User Name or Bad Password

📌 Cause:

• The replication account has expired credentials.
• The DCs are in a different authentication realm (e.g., Trust issue).

✅ Fix:

• Reset the KRBTGT password:
• powershell
• netdom resetpwd /server:<PDC-Emulator> /userd:<Domain>\Administrator /passwordd:*
• Ensure time sync is correct: powershellCopyEditw32tm /query /status

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9️⃣ Error: 8457 (0x2109) - The Destination Server is Currently Rejecting Replication Requests

📌 Cause:

• The destination DC is in an invalid state (e.g., database corruption).

✅ Fix:

• Check if replication is disabled:
• powershell
• repadmin /options <DC-Name> If DISABLE_OUTBOUND_REPL or DISABLE_INBOUND_REPL is enabled, re-enable it: powershellCopyEditrepadmin /options <DC-Name> -DISABLE_OUTBOUND_REPL -DISABLE_INBOUND_REPL

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🔄 Final Checks

After fixing errors, verify that replication is working correctly:

1️⃣ Run a full diagnostic

powershell

dcdiag /c /v /e

2️⃣ Check replication health

powershell

repadmin /showrepl

3️⃣ Force synchronization

powershell

repadmin /syncall /AdeP