Active Directory replication error 1722: The RPC server is unavailable

Article
06/04/2024

This article helps fix the error 1722 of Active Directory replication.

Applies to: All supported versions of Windows Server
Original KB number: 2102154

Symptoms

This article describes the symptoms, cause, and resolution for resolving Active Directory replication failing with Win32 error 1722: "The RPC server is unavailable."

DCPROMO Promotion of a replica domain controller (DC) fails to create an NTDS Settings object on the helper DC with error 1722.

Dialog title text: Active Directory Domain Services Installation Wizard

Dialog message text:

The operation failed because: Active Directory Domain Services could not create the NTDS Settings object for this Active Directory Domain Controller CN=NTDS Settings,CN=<Name of DC being promoted),CN=Servers,CN=<site name>,CN=Sites,CN=Configuration,DC=<forest root domain> on the remote AD DC <helper DC>.<domain name>.<top level domain>. Ensure the provided network credentials have sufficient permissions. "The RPC server is unavailable."

DCDIAG reports that the Active Directory Replications test has failed with error 1722: "The RPC Server is unavailable."

[Replications Check,<DC Name>] A recent replication attempt failed:
From <source DC> to <destination DC>  
Naming Context: <DN path of directory partition>  
The replication generated an error (1722):  
The RPC server is unavailable.  
The failure occurred at <date> <time>.  
The last success occurred at <date> <time>.  
<X> failures have occurred since the last success.  
[<DC name>] DsBindWithSpnEx() failed with error 1722,  
The RPC server is unavailable..  
Printing RPC Extended Error Info:  
<snip>

REPADMIN.EXE reports that the replication attempt has failed with status 1722 (0x6ba).

REPADMIN commands that commonly cite the -1722 (0x6ba) status include but are not limited to:

REPADMIN /REPLSUM
REPADMIN /SHOWREPL
REPADMIN /SHOWREPS
REPADMIN /SYNCALL

Sample output from REPADMIN /SHOWREPS and REPADMIN /SYNCALL depicting the error "The RPC server is unavailable" is shown as follows:

c:\> repadmin /showreps  
<site name><destination DC>  
DC Options: <list of flags>  
Site Options: (none)  
DC object GUID: <NTDS settings object object GUID>  
DC invocationID: <invocation ID string>  
==== INBOUND NEIGHBORS ======================================  
DC=<DN path for directory partition>  
    <site name><source DC via RPC  
        DC object GUID: <source DCs ntds settings object object guid>  
        Last attempt @ <date> <time> failed, result **1722 (0x6ba):  
The RPC server is unavailable.  
        <X #> consecutive failure(s).  
        Last success @ <date> <time>

Sample output of REPADMIN /SYNCALL depicting the error "The RPC server is unavailable" is shown as follows:

 C:\>repadmin /syncall  
 CALLBACK MESSAGE: Error contacting server \<object guid of NTDS Settings object>._msdcs.\<forest root domain>.\<top level domain> (network error): 1722 (0x6ba):  
 The RPC server is unavailable.

The replicate now command in Active Directory Sites and Services returns "The RPC server is unavailable."

Right-clicking the connection object from a source DC and choosing replicate now fails with "The RPC server is unavailable." The on-screen error message is shown as follows:

Dialog title text: Replicate Now

Dialog message text:

The following error occurred during the attempt to synchronize naming context <DNS name of directory partition> from domain controller <source DC host name> to domain controller <destination DC hostname>:The RPC server is unavailable. This operation will not continue. This condition may be caused by a DNS lookup problem. For information about troubleshooting common DNS lookup problems, see the following Microsoft Web site: DNS Lookup Problem

NTDS Knowledge Consistency Checker (KCC), NTDS General, or Microsoft-Windows-ActiveDirectory_DomainService events with the 1722 status are logged in the directory service event log.

Active Directory events that commonly cite the 1722 status include but are not limited to:

Event source	Event ID	Event string
Microsoft-Windows-ActiveDirectory_DomainService	1125	The Active Directory Domain Services Installation Wizard (Dcpromo) was unable to establish connection with the following domain controller.
NTDS KCC	1311	The Knowledge Consistency Checker (KCC) has detected problems with the following directory partition.
NTDS KCC	1865	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.
NTDS KCC	1925	The attempt to establish a replication link for the following writable directory partition failed.
NTDS Replication	1960	Internal event: The following domain controller received an exception from a remote procedure call (RPC) connection. The operation may have failed.

Cause

RPC is an intermediate layer between the network transport and the application protocol. RPC itself has no special insight into failures but attempts to map lower-layer protocol failures into an error at the RPC layer.

RPC error 1722/0x6ba/RPC_S_SERVER_UNAVAILABLE is logged when a lower-layer protocol reports a connectivity failure. The common case is that the abstract TCP CONNECT operation failed. In the context of AD replication, the RPC client on the destination DC was not able to successfully connect to the RPC server on the source DC. Common causes of this are:

Link local failure
DHCP failure
DNS failure
WINS failure
Routing failure (including blocked ports on firewalls)
IPSec/Network authentication failures
Resource limitations
Higher-layer protocol not running
Higher-layer protocol returning this error

Resolution

Basic troubleshooting steps to identify the problem.

Verify the ClientProtocols key exists under HKEY_LOCAL_MACHINE\Software\Microsoft\Rpc and that it contains the correct default protocols

Protocol name	Type	Data value
ncacn_http	REG_SZ	rpcrt4.dll
ncacn_ip_tcp	REG_SZ	rpcrt4.dll
ncacn_np	REG_SZ	rpcrt4.dll
ncacn_ip_udp	REG_SZ	rpcrt4.dll

If the ClientProtocols key or any of the four default values are missing, import the key from a known good server.

Verify DNS is working

Domain Name System (DNS) lookup failures are the cause of a large number of 1722 RPC errors when it comes to replication.

There are a few tools to use to help identify DNS errors:

DCDIAG /TEST:DNS /V /E /F:<filename.log>

The DCDIAG /TEST:DNS command can validate DNS health of Windows 2000 Server (SP3 or later), Windows Server 2003, and Windows Server 2008 family domain controllers. This test was first introduced with Windows Server 2003 Service Pack 1.

There are seven test groups for this command.

Authentication (Auth)
Basic (Basc)
Records registration (RReg)
Dynamic update (Dyn)
Delegations (Del)

Forwarders/Root hints (Forw)

Sample output:

TEST: Authentication (Auth)  
Authentication test: Successfully completed

TEST: Basic (Basc)  
Microsoft(R) Windows(R) Server 2003, Enterprise Edition (Service Pack level: 2.0) is supported  
NETLOGON service is running  
kdc service is running  
DNSCACHE service is running  
DNS service is running  
DC is a DNS server  
Network adapters information:  
Adapter [00000009] Microsoft Virtual Machine Bus Network Adapter:  
MAC address is 00:15:5D:40:CF:92  
IP address is static  
IP address: <IP Address>  
DNS servers:  
<DNS IP Address> (DC.domain.com.) [Valid]  
The A record for this DC was found  
The SOA record for the Active Directory zone was found  
The Active Directory zone on this DC/DNS server was found (primary)  
Root zone on this DC/DNS server was not found  
<omitted other tests for readability>

Summary of DNS test results:

Auth Basc Forw Del  Dyn  RReg Ext

Domain: fragale.contoso.com
DC1 PASS PASS FAIL PASS PASS PASS n/a  
Domain: child.fragale.contoso.com  
DC2 PASS PASS n/a  n/a  n/a  PASS n/a  

Enterprise DNS infrastructure test results:  
For parent domain domain.com and subordinate domain child:  
Forwarders or root hints are not misconfigured from parent domain to subordinate domain  
Error: Forwarders are configured from subordinate to parent domain but some of them failed DNS server tests  

(See DNS servers section for error details)  
Delegation is configured properly from parent to subordinate domain  
......................... domain.com failed test DNS

The summary provides remediation steps for the more common failures from this test.

Explanation and additional options for this test can be found at Domain Controller Diagnostics Tool (dcdiag.exe).

NLTEST /DSGETDC:<netbios or DNS domain name>

Nltest /dsgetdc is used to exercise the DC locator process. Thus /dsgetdc:<domain name> tries to find the domain controller for the domain. Using the force flag forces domain controller location rather than using the cache. You can also specify options such as /gc or /pdc to locate a Global Catalog or a primary domain controller emulator. To find the Global Catalog, you must specify a tree name, which is the DNS domain name of the root domain.

Sample output:
```
DC: [\DC.fabrikam.com]  
Address: \\<IP Address>  
Dom Guid: 5499c0e6-2d33-429d-aab3-f45f6a06922b  
Dom Name: fabrikam.com  
Forest Name: fabrikam.com  
Dc Site Name: Default-First-Site-Name  
Our Site Name: Default-First-Site-Name  
Flags: PDC GC DS LDAP KDC TIMESERV WRITABLE DNS_DC DNS_DOMAIN DNS_FOREST CLOSE_SITE  
The command completed successfully
```

Netdiag -v

It can be used with Windows 2003 and earlier versions to gather specific information for networking configuration and error. This tool takes some time to run when executing the -v switch.

Sample output for the DNS test:

DNS test . . . . . . . . . . . . . : Passed  
Interface {34FDC272-55DC-4103-B4B7-89234BC30C4A}  
DNS Domain:  
DNS Servers: <DNS Server IP address>  
IP Address:         Expected registration with PDN (primary DNS domain name):  
Hostname: DC.fabrikam.com.  
Authoritative zone: fabrikam.com.  
Primary DNS server: DC.fabrikam.com <IP Address>  
Authoritative NS:<IP Address>  
Check the DNS registration for DCs entries on DNS server <DNS Server IP address>  
The Record is correct on DNS server '<DNS Server IP address>'.  
(You will see this line repeated several times for every entry for this DC.  Including srv records.)  
The Record is correct on DNS server '<DNS Server IP address>'.  
PASS - All the DNS entries for DC are registered on DNS server '<DNS Server IP address>'.

ping -a <IP_of_problem_server>

It's a simple, quick test to validate the host record for a domain controller is resolving to the correct machine.

dnslint /s IP /ad IP

DNSLint is a Windows utility that helps you to diagnose common DNS name resolution issues. The output is an HTM file with much information, including:

DNS server: localhost

IP Address: 127.0.0.1  
UDP port 53 responding to queries: YES  
TCP port 53 responding to queries: Not tested  
Answering authoritatively for domain: NO

SOA record data from the server:

Authoritative name server: DC.domain.com  
Hostmaster: hostmaster  
Zone serial number: 14  
Zone expires in: 1.00 day(s)  
Refresh period: 900 seconds  
Retry delay: 600 seconds  
Default (minimum) TTL: 3600 seconds

Additional authoritative (NS) records from the server: DC2.fabrikam.com <IP Address>

Alias (CNAME) and glue (A) records for forest GUIDs from the server:
- CNAME: 98d4aa0c-d8e2-499a-8f90-9730b0440d9b._msdcs.fabrikam.com
  - Alias: DC.fabrikam.com
  - Glue: <IP Address>
- CNAME: a2c5007f-7082-4adb-ba7d-a9c47db1efc3._msdcs.fabrikam.com
  - Alias: dc2.child.fabrikam.com
  - Glue: <IP Address>
  For more information, see the Description of the DNSLint utility.

Verify network ports are not blocked by a firewall or third-party application listening on the required ports

The endpoint mapper (listening on port 135) tells the client which randomly assigned port a service (FRS, AD replication, MAPI, and so on) is listening on.

Refer to the list of required ports in How to configure a firewall for Active Directory domains and trusts.

Portqry can be used to identify if a port is blocked from a DC when targeting another DC. It can be downloaded at PortQry Command Line Port Scanner Version 2.0.

Example syntax:

portqry -n <problem_server> -e 135
portqry -n <problem_server> -r 1024-5000

A graphical version of portqry, called Portqryui, can be found at PortQryUI - User Interface for the PortQry Command Line Port Scanner.

If the Dynamic Port range has ports being blocked, use the following links to configure a port range that is manageable for the customer.

Additional important links for configuration and working with firewalls and domain controllers:

Bad NIC drivers

See network card vendors or OEMs for the latest drivers.

UDP fragmentation can cause replication errors that appear to have a source of RPC server is unavailable

Event ID 40960 and 40961 errors with a source of LSASRV are common for this particular cause.

For more information, see How to force Kerberos to use TCP instead of UDP in Windows.

SMB signing mismatches between DCs

Using the Default Domain Controllers Policy to configure consistent settings for SMB Signing under the following section will help address this cause:

Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options

Microsoft network client: Digitally sign communications (always) Disabled.
Microsoft network client: Digitally sign communications (if server agrees) Enabled.
Microsoft network server: Digitally sign communications (always) Disabled.
Microsoft network server: Digitally sign communications (if client agrees) Enabled.

The settings can be found under the following registry keys:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanManWorkstation\Parameters and HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanManServer\Parameters
- RequireSecuritySignature = always (0 = disable, 1 = enable).
- EnableSecuritySignature = if server agrees (0 = disable, 1 = enable).

Additional troubleshooting:

If the preceding methods don't provide a solution to the 1722 error, use the following diagnostic logging to gather more information:

Windows Server 2003 SP2 computers logs extended RPC Server info in NTDS Replication events 1960, 1961, 1962 and 1963.  
Crank up NTDS Diagnostic logging

1 = basic, 2 and 3 add continually verbose info and 5 logs extended info.

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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