Active Directory replication error 1722: The RPC server is unavailable

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

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


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

  1. DCPROMO Promotion of a replica 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."
  2. 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:  
  3. REPADMIN.EXE reports that replication attempt has failed with status 1722 (0x6ba).

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


    Sample output from REPADMIN /SHOWREPS and REPADMIN /SYNCALL depicting The RPC server is unavailable error is shown below:

    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 RPC server is unavailable error is shown below:

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

    Right-clicking on 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 below:

    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

  5. 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.


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 for this are:

  1. Link local failure
  2. DHCP failure
  3. DNS failure
  4. WINS failure
  5. Routing failure (including blocked ports on firewalls)
  6. IPSec / Network authentication failures
  7. Resource limitations
  8. Higher layer protocol not running
  9. Higher layer protocol is returning this error


Basic troubleshooting steps to identify the problem.

Verify the startup value and service status are correct for RPC, RPC Locator, and Kerberos Key Distribution Center

Verify the startup value and service status are correct for the Remote Procedure Call (RPC), Remote Procedure Call (RPC) Locator and Kerberos Key Distribution Center.

The OS version will determine the correct values for the source and destination system that is logging the replication error. Use the following table to help validate the settings.

Service Name Windows 2000 Windows 2003 /R2 Windows 2008 Windows 2008 R2
Remote Procedure Call (RPC) Started / Automatic Started / Automatic Started / Automatic Started / Automatic
Remote Procedure Call (RPC) Locator Started / Automatic (Domain Controllers)

Not started / Manual(Member Servers)
Not started / Manual Not started / Manual Not started / Manual
Kerberos Key Distribution Center (KDC) Started / Automatic (Domain Controllers)

Not started / Disabled(Member Servers)
Started / Automatic (Domain Controllers)

Not started / Disabled(Member Servers)
Started / Automatic (Domain Controllers)

Not started / Disabled(Member Servers)
Started / Automatic (Domain Controllers)

Not started / Disabled(Member Servers)

If you make any changes to match the settings above, restart the machine. Verify both the startup value and service status match the values documented in the table above.

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

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> ( [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
      DC2 PASS PASS n/a  n/a  n/a  PASS n/a  
      Enterprise DNS infrastructure test results:  
      For parent domain 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  
      ......................... 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. For finding the Global Catalog, you must specify a tree name, which is the DNS domain name of the root domain.

    Sample output:

    DC: [\]  
    Address: \\<IP Address>  
    Dom Guid: 5499c0e6-2d33-429d-aab3-f45f6a06922b  
    Dom Name:  
    Forest Name:  
    Dc Site Name: Default-First-Site-Name  
    Our Site Name: Default-First-Site-Name  
    The command completed successfully
  • Netdiag -v

    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):  
    Authoritative zone:  
    Primary DNS server: <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:  
    UDP port 53 responding to queries: YES  
    TCP port 53 responding to queries: Not tested  
    Answering authoritatively for domain: NO

    SOA record data from server:

    Authoritative name server:  
    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 server: <IP Address>

    Alias (CNAME) and glue (A) records for forest GUIDs from server:

    • CNAME:

      • Alias:
      • Glue: <IP Adress>
    • CNAME:

      • Alias:
      • Glue: <IP Address>

      For more information, see 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.

Application protocol Protocol Ports
Global Catalog Server TCP 3269
Global Catalog Server TCP 3268
LDAP Server TCP 389
LDAP Server UDP 389
NAT-T UDP 4500
RPC randomly allocated high TCP ports¹ TCP 1024 - 5000
49152 - 65535*

* This is the range in Windows Server 2008, Windows Vista, Windows 7, and Windows 2008 R2.

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 below 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 & 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 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 = is server agrees (0,disable, 1 enable).

Additional Troubleshooting:

If the above don't provide a solution to the 1722, 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.