Information about configuring Active Directory domains by using single-label DNS names

This article contains information about the deployment and operation of Active Directory domains that are configured by using single-label DNS names.
For the following reasons, the best practice is to create new Active Directory domains that have fully qualified DNS names:

• Single-label DNS names cannot be registered by using an Internet registrar.
• Client computers and domain controllers that are joined to single-label domains require additional configuration to dynamically register DNS records in single-label DNS zones.
• Client computers and domain controllers may require additional configuration to resolve DNS queries in single-label DNS zones.
• Some server-based applications are incompatible with single-label domain names. Application support may not exist in the initial release of an application, or support may be dropped in a future release.
• Transitioning from a single-label DNS domain name to a fully qualified DNS name is non-trivial and consists of two options. Either migrate
  (http://technet.microsoft.com/en-us/library/cc974332(WS.10).aspx)
  users, computers, groups, and other states to a new forest. Or, perform a domain rename of the existing domain. Some server-based applications are incompatible with the domain rename feature that is supported in Windows Server 2003 and newer domain controllers. These incompatibilities either block the domain rename feature or make the use of the domain rename feature more difficult when you try to rename a single-label DNS name to a fully qualified domain name.
  
  Examples of applications that are incompatible with domain rename include, but are not limited to, the following products:
  • Microsoft Exchange 2000 Server
  • Microsoft Exchange Server 2007
  • Microsoft Internet Security and Acceleration (ISA) Server 2004
  • Microsoft Live Communications Server 2005
  • Microsoft Operations Manager 2005
  • Microsoft SharePoint Portal Server 2003
  • Microsoft Systems Management Server (SMS) 2003
  • Microsoft Office Communications Server 2007
  • Microsoft Office Communications Server 2007 R2
  • Microsoft System Center Operations Manager 2007 SP1
  • Microsoft System Center Operations Manager 2007 R2
  • Microsoft Lync Server 2010
  • Microsoft Lync Server 2013
• The Active Directory Installation Wizard (Dcpromo.exe) in Windows Server 2008 warns against creating new domains that have single-label DNS names. Because there is no business or technical reason to create new domains that have single-label DNS names, the Active Directory Installation Wizard in Windows Server 2008 R2 explicitly blocks creating such domains.

Best-practice Active Directory domain names consist of one or more subdomains that are combined with a top-level domain that is separated by a dot character ("."). The following are some examples:

• contoso.com
• corp.contoso.com
• contoso.local

Single-label names consist of a single word like "contoso."

The top-level domain occupies the rightmost label in a domain name. Common top-level domains include the following:

• .com
• .corp
• .net
• .org
• Two-letter country code top level domains (ccTLD) such as .nz
  

Active Directory domain names should consist of two or more labels for the current and the future operating system and for application experience and reliability.

DNS name registration with an Internet registrar

We recommend that you register DNS names for the top-most internal and external DNS namespaces with an Internet registrar. This includes the forest root domain of any Active Directory forests unless such names are sub-domains of DNS names that are registered by your organization name (For example, the forest root domain "corp.example.com" is a sub-domain of an internal "example.com." namespace.) When you register your DNS names with an Internet registrar, this lets Internet DNS servers resolve your domain now or at some point over the life of your Active Directory forest. And, this registration helps prevent possible name collisions by other organizations.

Possible symptoms when clients cannot dynamically register DNS records in a single-label forward lookup zone

If you use a single-label DNS name in your environment, clients may be unable to dynamically register DNS records in a single-label forward lookup zone. Specific symptoms vary according to the version of Microsoft Windows that is installed.

The following list describes the symptoms that may occur:

• After you configure Microsoft Windows for a single label domain name, all servers that have the domain controller role may be unable to register DNS records. The System log of the domain controller may consistently log NETLOGON 5781 warnings that resemble the following example:

  Event Type: Warning
  Event Source: NETLOGON
  Event Category: None
  Event ID: 5781
  Description:
  
  Dynamic registration or deregistration of one or more DNS records failed because no DNS servers are available.
  
  Data Words: 0000: 0000232a

  Note Status code 0000232a maps to the following error code:
  DNS_ERROR_RCODE_SERVER_FAILURE
• The following additional status codes and error codes may appear in log files such as Netdiag.log:
  DNS Error Code: 0x0000251D = DNS_INFO_NO_RECORDS
  
  DNS_ERROR_RCODE_ERROR
  
  RCODE_SERVER_FAILURE
• Windows-based computers that are configured for DNS dynamic updates will not register in a single-label domain. Warning events that resemble the following examples are recorded in the System log of the computer:

  Event Type: Warning
  Event Source: DnsApi
  Event
  Category: None
  Event ID: 11151
  Description: The system failed to register network adapter with settings:
  Adapter Name : {Network adapter GUID}
  Host Name : <hostname>
  Adapter-specific Domain Suffix : local
  DNS server list : <DNS Server IP address 1>.<DNS Server IP address 2>,<DNS Server IP address 3>
  Sent update to server : None
  IP Address(es) : <IP address>
  The cause of this DNS registration failure was because of DNS server failure. This may be due to a zone transfer that has locked the DNS server for the applicable zone that your computer needs to register itself with.
  (The applicable zone should typically correspond to the Adapter-specific Domain Suffix that was indicated above.)
  You can manually retry registration of the network adapter and its settings by typing "ipconfig /registerdns" at the command prompt. If problems still persist, contact your network systems administrator to verify network conditions.

  Event Type: Warning
  Event ID: 11165
  Source: DnsApi
  Description: The system failed to register host (A) resource records (RRs) for network adapter with settings:
  Adapter Name : {Network adapter GUID}
  Host Name : <Host name>
  Primary Domain Suffix : <single label domain>
  DNS server list : <DNS Server IP address 1>.<DNS Server IP address 2>,<DNS Server IP address 3>
  Sent update to server :
  IP Address(es) : <IP address>
  
  The reason the system could not register these RRs was because the DNS server contacted refused the update request.
  The reasons for this might be (a) you are not allowed to update the specified DNS domain name, or (b) because the DNS server authoritative for this name does not support the DNS dynamic update protocol.
  
  To register the DNS host (A) resource records using the specific DNS domain name and IP addresses for this adapter, contact your DNS server or network systems administrator.

How to enable Windows-based clients to perform dynamic updates to single-label DNS zones

By default, Windows does not send updates to top-level domains. However, you can change this behavior by using one of the methods that are described in this section. Use one of the following methods to enable Windows-based clients to perform dynamic updates to single-label DNS zones.

Method 1: Use Registry Editor

Domain controller locator configuration for Windows XP Professional and later versions of Windows

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: On a Windows-based computer, an Active Directory domain member requires additional configuration to support single-label DNS names for domains. Specifically, the domain controller locator on the Active Directory domain member does not use the DNS server service to locate domain controllers in a domain that has a single-label DNS name unless that Active Directory domain member is joined to a forest that contains at least one domain, and this domain has a single-label DNS name.

Without modification, an Active Directory domain member in a forest that contains no domains that have single-label DNS names does not use the DNS Server service to locate domain controllers in domains that have single-label DNS names that are in other forests. Client access to the domains that have single-label DNS names fails if NetBIOS name resolution is not configured correctly.

To enable an Active Directory domain member to use DNS to locate domain controllers in domains that have single-label DNS names that are in other forests, follow these steps:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters
3. In the details pane, locate the AllowSingleLabelDnsDomain entry. If the AllowSingleLabelDnsDomain entry does not exist, follow these steps:
   1. On the Edit menu, point to New, and then click DWORD Value.
   2. Type AllowSingleLabelDnsDomain as the entry name, and then press ENTER.
4. Double-click the AllowSingleLabelDnsDomain entry.
5. In the Value data box, type 1, and then click OK.
6. Exit Registry Editor.

DNS client configuration

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: Active Directory domain members and domain controllers that are in a domain that has a single-label DNS name typically must dynamically register DNS records in a single-label DNS zone that matches the DNS name of that domain. If an Active Directory forest root domain has a single-label DNS name, all domain controllers in that forest typically must dynamically register DNS records in a single-label DNS zone that matches the DNS name of the forest root.

By default, Windows-based DNS client computers do not attempt dynamic updates of the root zone "." or of single-label DNS zones. To enable Windows-based DNS client computers to try dynamic updates of a single-label DNS zone, follow these steps:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DnsCache\Parameters
3. In the details pane, locate the UpdateTopLevelDomainZones entry. If the UpdateTopLevelDomainZones entry does not exist, follow these steps:
   1. On the Edit menu, point to New, and then click DWORD Value.
   2. Type UpdateTopLevelDomainZones as the entry name, and then press ENTER.
4. Double-click the UpdateTopLevelDomainZones entry.
5. In the Value data box, type 1, and then click OK.
6. Exit Registry Editor.

These configuration changes should be applied to all domain controllers and members of a domain that have single-label DNS names. If a domain that has a single-label domain name is a forest root, these configuration changes should be applied to all the domain controllers in the forest, unless the separate zones _msdcs.ForestName, _sites.ForestName, _tcp.ForestName, and _udp.ForestName are delegated from the ForestName zone.

For the changes to take effect, restart the computers where you changed the registry entries.

Notes

• For Windows Server 2003 and later versions, the UpdateTopLevelDomainZones entry has moved to the following registry subkey:
  HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\DNSClient
• On a Microsoft Windows 2000 SP4-based domain controller, the computer will report the following name registration error in the System event log if the UpdateTopLevelDomainZones setting is not enabled:

  Event Type: Warning
  Event Source: NETLOGON
  Event Category: None
  Event ID: 5781
  User: N/A
  Description: Dynamic registration or deregistration of one or more DNS records failed because no DNS servers are available.
  Data: 0000: 0000232a

• On a Windows 2000 SP4-based domain controller, you must restart your computer after you add the UpdateTopLevelDomainZones setting.

Method 2: Use Group Policy

Use Group Policy to enable the Update Top Level Domain Zones policy and the Location of the DCs hosting a domain with single label DNS name policy as specified in the following table under the folder location on the root domain container in Users and Computers, or on all organizational units (OUs) that host computer accounts for member computers, and for domain controllers in the domain.Note These policies are supported only on Windows Server 2003-based computers and on Windows XP-based computers.

To enable these policies, follow these steps on the root domain container:

1. Click Start, click Run, type gpedit.msc, and then click OK.
2. Under Local Computer Policy, expand Computer Configuration.
3. Expand Administrative Templates.
4. Enable the Update Top Level Domain Zones policy. To do this, follow these steps:
   1. Expand Network.
   2. Click DNS Client.
   3. In the details pane, double-click Update Top Level Domain Zones.
   4. Click Enabled.
   5. Click Apply, and then click OK.
5. Enable the Location of the DCs hosting a domain with single label DNS name policy. To do this, follow these steps:
   1. Expand System.
   2. Expand Net Logon.
   3. Click DC Locator DNS Records.
   4. In the details pane, double-click Location of the DCs hosting a domain with single label DNS name.
   5. Click Enabled.
   6. Click Apply, and then click OK.
6. Exit Group Policy.

For more information about how to use the Group Policy Object Editor to manage local computer policy, click the following article number to view the article in the Microsoft Knowledge Base: On Windows Server 2003-based and later versions DNS servers, make sure that root servers are not created unintentionally.

On Windows 2000-based DNS servers, you may have to delete the root zone "." to have the DNS records correctly declared. The root zone is automatically created when the DNS server service is installed because the DNS server service cannot reach the root hints. This issue was corrected in later versions of Windows.

Root servers may be created by the DCpromo Wizard. If the "." zone exists, a root server has been created. For name resolution to work correctly, you may have to remove this zone.

New and modified DNS policy settings for Windows Server 2003 and later versions

• The Update Top Level Domain Zones policy
  
  If this policy is specified, it creates a REG_DWORD UpdateTopLevelDomainZones entry under the following registry subkey:
  HKLM\Software\Policies\Microsoft\Windows NT\DNSClient
  The following are the entry values for UpdateTopLevelDomainZones:
  • Enabled (0x1). A 0x1 setting means that computers may try to update the TopLevelDomain zones. That is, if the UpdateTopLevelDomainZones setting is enabled, computers to which this policy is applied send dynamic updates to any zone that is authoritative for the resource records that the computer must update, except for the root zone.
  • Disabled (0x0). A 0x0 setting means that computers are not permitted to try to update the TopLevelDomain zones. That is, if this setting is disabled, computers to which this policy is applied do not send dynamic updates to the root zone or to the top-level domain zones that are authoritative for the resource records that the computer must update. If this setting is not configured, the policy is not applied to any computers, and computers use their local configuration.
• The Register PTR Records policy
  
  A new possible value, 0x2, of the REG_DWORD RegisterReverseLookup entry was added under the following registry subkey:
  HKLM\Software\Policies\Microsoft\Windows NT\DNSClient
  The following are the entry values for RegisterReverseLookup:
  • 0x2. Register only if "A" record registration succeeds. Computers try to implement PTR resource records registration only if they successfully registered the corresponding "A" resource records.
  • 0x1. Register. Computers try to implement PTR resource records registration regardless of the success of the "A" records registration.
  • 0x0. Do not register. Computers never try to implement PTR resource records registration.

For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:

2002584: Unable to select DNS Server role when adding a domain controller into an existing Active Directory domain

2992634: Warnings when promoting Windows Server 2008 and Windows Server 2008 R2 DCPROMO in domains with single-label DNS names

ADMT Guide: Migrating and Restructuring Active Directory Domains

Active Directory Migration Tool (ADMT) Guide: Migrating and Restructuring Active Directory Domains

Active Directory Migration Tool version 3.1

Active Directory Migration Tool version 3.2

Product Compatibility page on the DNS Namespace Planning Solution Center