Active Directory DNS Single Label Names


Hey everyone, Ace again. Let’s discuss this issue. I hardly see this issue any more, because it was a previously prevalent when Active Directory was introduced, since there were some confusion about AD domain naming, and many IT admins used NT4’s domain naming guidelines. Man of us are now familiar with AD’s naming convention, and have more than likely renamed or rebuilt their AD domains. However, there are still some installations with this issue. 

How did it happen? Many reasons, such as lack of research on AD’s DNS requirements, assumptions, or a simple typo when originally upgrading from NT4 or promoting your new AD domain. It doesn’t matter now, because you were brought here to find out what to do with it.

I hope you find this blog informative on this issue and what to do about it.

First, let’s discuss a little background on the necessary components at play…


First, let’s discuss the FQDN. What is an FQDN? It stands for “Fully Qualified Domain Name.” It is multi-level, or hierarchal, such as:

What is a Single Label DNS Domain name?
The name is reminiscent of the legacy style NT4 domain NetBIOS domain names, such as:


Unfortunately, since this does not work with DNS, and Active Directory relies on DNS, therefore, it does not work with Active Directory. Stay with me. I’ll explain…


DNS is a hierarchal database. Some call it a “tree” with a root (the ‘com’ or ‘net’, etc, name), then the trunk (the ‘domain’ portion of it), and the branches (such as www, servername, etc). The Root domain name, such as com, edu, net, etc, is also known as the TLD (Tope Level Domain name).

Basically you can look at a DNS domain name as having multiple levels separated by periods. The minimal requirment for an FQDN domain name, such as, is two levels. Then of course are your resource names, such as www, servername, or even child domain names under it.

Notice with a single label name there is only one name for the domain, or one level? Don’t get this confused with the NetBIOS domain name, that we were familiar with in the NT4 days. AD supports the NetBIOS domain name as well, but only as a NetBIOS domain name. It’s one of the domain names chosen when a machine is promoted into a domain controller for a brand new domain in a brand new forest. NT4 wasn’t reliant nor did it use DNS for NT4 domains. However, AD is reliant, therefore it must follow DNS naming rules.

Unfortunately the old NT4 style names are not hierarchal because there is only one level.
Since AD requires and relies on DNS, and DNS is a hierarchal database, a single label name does not follow any sort of hierarchy. DNS fails with single label names. Windows 2008, Windows 2003, XP and Vista have problems resolving single label names because it does not follow the proper format for a DNS domain name, such as, etc.

Also, Windows 2000 SP4 and all newer machines have problems querying single label names. It’s explained below by Alan Woods. Because clients query DNS for AD resources (domain controller locations and other services), they may have difficulty finding resources.

How did it happen? As I said earlier, it doesn’t matter now, because you were brought here to find out what to do with it.

Common Mistakes When Upgrading a Windows 2000 Domain To a Windows 2003 Domain (or any AD upgrade or installation):

Single Label Name Explanation

Another variation of the Single Label Name explanation that I had provided in a response to a post in the DNS and/or AD newsgroups at one time:

The issue is the single label name. Locally at HQ, it’s using NetBIOS to join, however remotely, it’s relying on DNS. DNS queries do not work properly with single label names on Windows 2000 SP4 and all newer machines.

Period. Why? good question. It’s based on the fact DNS is hierarchal. Hierarchal meaning it must have multi levels, a minimum of two levels.

The TLD (top level domain) is the root name, such as the com, net, etc., names. The client side resolver service algorithm (which is governed by the DHCP Client service which must be running on all machines, static or not),
relies on that name for the basis to find the second level name (the name “domain” in, etc.). If the name is a single label name, it thinks THAT name is the TLD.

Therefore it then hits the Internet Root servers to find how owns and is authoritative for that TLD.Such as when looking up It queries for the COM portion, which the roots return the nameservers responsible for the COM servers, then it queries for the servers responsible for zone.

If it’s a single label, the query ends there, and it won’t go further. However what is funny (sic) is that even though the single label name is being hosted locally in DNS, it will NOT query locally first, because it believes it is a TLD, therefore goes through the normal resolution (recursion and devolution) process, which causes excessive query traffic to the internet Root servers.

How to fix it? Good question. Glad you’ve asked.

  1. The preferred “fix” (in a one line summary), is to install a fresh new domain properly named and use ADMT to migrate user, group and computer accounts into the new domain from the current domain.
  2. An alternative is to perform a domain rename, (difficulty depends on the operating system and which version of Exchange is installed).
  3. As a temporary resort, you can use the patch or band aid registry fix to force resolution and registration that is mentioned in the following link. This must be applied to every machine. Unfortunately it must be done on every machine in the domain, including the DCs, member servers, workstations and laptops.

Information About Configuring Windows 2000 for Domains with Single-Label DNS Names:

Single Label Names and being a better Internet Neighbor

The following was posted by Microsoft’s Alan Woods in 2004:

Single label names, from Alan Woods, [MSFT], posted:

—– Original Message —–
From: “Alan Wood” [MSFT]
Newsgroups: microsoft.public.win2000.dns
Sent: Wednesday, January 07, 2004 1:25 PM
Subject: Re: Single label DNS

Hi Roger,

We really would prefer to use FQDN over Single labled. There are
alot of other issues that you can run into when using a Single labeled
domain name with other AD integrated products. Exchange would be a great
example. Also note that the DNR (DNS RESOLVER) was and is designed to
Devolve DNS requests to the LAST 2 names.

Example: Single Labeled domain .domainA
then, you add additional domains on the forest.

If a client in the domain Child2 wants to resolve a name in domainA
Example. Host.DomainA and uses the following to connect to a share
\\host then it is not going to resolve. WHY, because the resolver is
first going to query for first for Host.Child2.child1.domainA, then it
next try HOST.Child1.domainA at that point the Devolution process is
DONE. We only go to the LAST 2 Domain Names.

Also note that if you have a single labeled domain name it causes excess
DNS traffic on the ROOT HINTS servers and being all Good Internet Community
users we definitely do not want to do that.   NOTE that in Windows 2003,
you get a big Pop UP Error Message when trying to create a single labeled
name telling you DON’T DO IT.  It will still allow you to do it, but you
will still be required to make the registry changes, which is really not

Microsoft is seriously asking you to NOT do this.  We will support you but
it the end results could be limiting as an end results depending on the
services you are using.

Thank you,

Alan Wood[MSFT]


Related Articles – Even though they seem old, they STILL APPLY!!!

Common Mistakes When Upgrading a Windows 2000 Domain To a Windows 2003 Domain

Best practices for DNS client settings in Windows 2000 Server and in Windows Server 2003:

DNS and AD (Windows 2000 & 2003) FAQ:

Naming conventions in Active Directory for computers, domains, sites, and OUs (Good article on DNS and other names)



I hope this helps!

Published 10/15/2016

Ace Fekay
MVP, MCT, MCSE 2012, MCITP EA & MCTS Windows 2008/R2, Exchange 2013, 2010 EA & 2007, MCSE & MCSA 2003/2000, MCSA Messaging 2003
Microsoft Certified Trainer
Microsoft MVP – Directory Services

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Active Directory FSMO Roles Explained

Original Publication 1/16/2011
Updated 11/20/2014
by Ace Fekay

Ace here again. I’ve updated this blog to just clean it up a bit, but as for the technical information about FSMOs, not much as changed. If you see anything that you feel is inaccurate, by all means please contact me.


This blog contains some quoted material from the Microsoft Official Curriculum (MOC) 6425B Course

Course 6425C: Configuring and Troubleshooting Windows Server 2008 R2 Active Directory Domain Services

If interested in taking this course, please see the following link to find a training center near you:

Find Microsoft Training

Key Points

In any replicated database, some changes must be performed by one and only one replica because they are impractical to perform in a multimaster fashion.

Active Directory is no exception. A limited number of operations are not permitted to
occur at different places at the same time and must be the responsibility of only
one domain controller in a domain or forest. These operations, and the domain
controllers that perform them, are referred to by a variety of terms:

• Operations masters
• Operations master roles
• Single master roles
• Operations tokens
• Flexible single master operations (FSMOs)

Regardless of the term used, the idea is the same. One domain controller performs
a function, and while it does, no other domain controller performs that function.

All Active Directory domain controllers are capable of performing single master
operations. The domain controller that actually performs a single master operation is the
domain controller that currently holds the operation’s token, or the “role holder.”.

An operation token, and thus the role, can be transferred easily to another domain
controller without a reboot.

To reduce the risk of single points of failure, the operations tokens can be
distributed among multiple DCs.

AD DS contains five operations master roles. Two roles are performed for the
entire forest, and two roles are performed by three roles for each domain.

Forest Roles (two roles):

  • Domain naming
  • Schema

Domain Roles (three roles):

  • Relative identifier (RID)
  • Infrastructure
  • PDC Emulator

In a forest with a single domain, there are, therefore, five operations masters. In a forest with two domains, there are eight operations masters because the three domain master roles are implemented separately in each of the two domains.

Forest-Wide Operations Master Roles

The schema master and the domain naming master must be unique in the forest.
Each role is performed by only one domain controller in the entire forest.

Domain Naming Master Role:

The domain naming role is used when adding or removing domains in the forest. When you add or remove a domain, the domain naming master must beaccessible, or the operation will fail.

Schema Master Role:

The domain controller holding the schema master role is responsible for making any changes to the forest’s schema. All other DCs hold read-only replicas of the schema. If you want to modify the schema or install an application that modifies the schema, it is recommended you do so on the domain controller holding the schema master role. Otherwise, changes you request must be sent to the schema master to be written into the schema.

Domain-Wide Operations Master Roles

Each domain maintains three single master operations: RID, Infrastructure, and PDC Emulator. Each role is performed by only one domain controller in the domain.

RID Master Role

The RID master plays an integral part in the generation of security identifiers
(SIDs) for security principals such as users, groups, and computers. The SID of a
security principal must be unique. Because any domain controller can create
accounts, and therefore, SIDs, a mechanism is necessary to ensure that the SIDs
generated by a DC are unique. Active Directory domain controllers generate SIDs
by assigning a unique RID to the domain SID. The RID master for the domain
allocates pools of unique RIDs to each domain controller in the domain. Thus,
each domain controller can be confident that the SIDs it generates are unique.


The RID master role is like DHCP for SIDs. If you are familiar with the concept that
you allocate a scope of IP addresses for the Dynamic Host Configuration Protocol (DHCP) server to assign to clients, you can draw a parallel to the RID master, which allocates pools of RIDs to domain controllers for the creation of SIDs.

Infrastructure Master Role

In a multidomain environment, it’s common for an object to reference objects in other domains. For example, a group can include members from another domain.

Its multivalued member attribute contains the distinguished names of each
member. If the member in the other domain is moved or renamed, the infrastructure master of the group’s domain updates the group’s member attribute accordingly.

Note: The infrastructure master. You can think of the infrastructure master as a tracking device for group members from other domains. When those members are renamed or moved in the other domain, the infrastructure master identifies the change and makes appropriate changes to group memberships so that the memberships are kept up to date.

Also note: This role only pertains in a multi-domain forest. The infrastructure master if running on the same DC as a GC, will conflict and cause the infrastructure master role to fail its intended purpose. One way to eliminate any issues with the Infrastructure Master Role & GC conflict is to simply make all DCs a GC. More info on this can be found in the following link:

Global Catalog and FSMO Infrastructure Master Relationship

PDC Emulator Role

The PDC Emulator role performs multiple, crucial functions for a domain:

• Emulates a Primary Domain Controller (PDC) for backward compatibility
In the days of Windows NT® 4.0 domains, only the PDC could make changes
to the directory. Previous tools, utilities, and clients written to support
Windows NT 4.0 are unaware that all Active Directory domain controllers can
write to the directory, so such tools request a connection to the PDC. The
domain controller with the PDC emulator role registers itself as a PDC so that
down-level applications can locate a writable domain controller. Such
applications are less common now that Active Directory is nearly 10 years old,
and if your enterprise includes such applications, work to upgrade them for
full Active Directory compatibility.

• Participates in special password update handling for the domain
When a user’s password is reset or changed, the domain controller that makes
the change replicates the change immediately to the PDC emulator. This
special replication ensures that the domain controllers know about the new
password as quickly as possible. If a user attempts to log on immediately after
changing passwords, the domain controller responding to the user’s logon
request might not know about the new password. Before it rejects the logon
attempt, that domain controller forwards the authentication request to a PDC
emulator, which verifies that the new password is correct and instructs the
domain controller to accept the logon request. This function means that any
time a user enters an incorrect password, the authentication is forwarded to
the PDC emulator for a second opinion. The PDC emulator, therefore, should
be highly accessible to all clients in the domain. It should be a well-connected,
high-performance DC.

• Manages Group Policy updates within a domain
If a Group Policy object (GPO) is modified on two DCs at approximately the
same time, there could be conflicts between the two versions that could not be
reconciled as the GPO replicates. To avoid this situation, the PDC emulator
acts as the focal point for all Group Policy changes. When you open a GPO in
the Group Policy Management Editor (GPME), the GPME binds to the domain
controller performing the PDC emulator role. Therefore, all changes to GPOs
are made on the PDC emulator by default.

• Provides a master time source for the domain
Active Directory, Kerberos, File Replication Service (FRS), and DFS-R each rely
on timestamps, so synchronizing the time across all systems in a domain is
crucial. The PDC emulator in the forest root domain is the time master for the
entire forest, by default. The PDC emulator in each domain synchronizes its
time with the forest root PDC emulator. Other domain controllers in the
domain synchronize their clocks against that domain’s PDC emulator. All
other domain members synchronize their time with their preferred domain
controller. This hierarchical structure of time synchronization, all implemented
through the Win32Time service, ensures consistency of time. Universal
Coordinated Time (UTC) is synchronized, and the time displayed to users is
adjusted based on the time zone setting of the computer.

Note: Change the time service only one way. It is highly recommended to allow Windows to maintain its native, default time synchronization mechanisms. The only change you should make is to configure the PDC emulator of the forest root domain to synchronize with an extra time source. If you do not specify a time source for the PDC emulator, the System event log will contain errors reminding you to do so. See the following link and the articles it refers to, for more information.

Configure the Windows Time service on the PDC emulator in the Forest Root Domain

Configuring the Windows Time Service – A step by step with a Contingency Plan – This is a procedure I put together for an enterprise.

Configuring the Windows Time Service for Windows Server, explanation of the time service hierarchy, and more

Acts as the domain master browser
When you open Network in Windows, you see a list of workgroups and
domains, and when you open a workgroup or domain, you see a list of
computers. These two lists, called browse lists, are created by the Browser
service. In each network segment, a master browser creates the browse list: the
lists of workgroups, domains, and servers in that segment. The domain master
browser serves to merge the lists of each master browser so that browse clients
can retrieve a comprehensive browse list.

What happens when a FSMO Role Fails

PDC Emulator failure

The PDC Emulator is the operations master that will have the most immediate
impact on normal operations and on users if it becomes unavailable. Fortunately,
the PDC Emulator role can be seized to another domain controller and then
transferred back to the original role holder when the system comes back online.

Infrastructure master failure

A failure of the infrastructure master will be noticeable to administrators but not to users. Because the master is responsible for updating the names of group members from other domains, it can appear as if group membership is incorrect although, as mentioned earlier in this lesson, membership is not actually affected. You can seize the infrastructure master role to another domain controller and then transfer it back to the previous role holder when that system comes online.

RID master failure

A failed RID master will eventually prevent domain controllers from creating new
SIDs and, therefore, will prevent you from creating new accounts for users, groups,
or computers. However, domain controllers receive a sizable pool of RIDs from the
RID master, so unless you are generating numerous new accounts, you can often
go for some time without the RID master online while it is being repaired. Seizing
this role to another domain controller is a significant action. After the RID master
role has been seized, the domain controller that had been performing the role
cannot be brought back online.

Schema master failure

The schema master role is necessary only when schema modifications are being
made, either directly by an administrator or by installing an Active Directory
integrated application that changes the schema. At other times, the role is not
necessary. It can remain offline indefinitely until schema changes are necessary.
Seizing this role to another domain controller is a significant action. After the
schema master role has been seized, the domain controller that had been
performing the role cannot be brought back online.

Domain naming master failure

The domain naming master role is necessary only when you add a domain to the
forest or remove a domain from a forest. Until such changes are required to your
domain infrastructure, the domain naming master role can remain offline for an
indefinite period of time. Seizing this role to another domain controller is a
significant action. After the domain naming master role has been seized, the
domain controller that had been performing the role cannot be brought back

Recovering from FSMO Role Failures

There are a number of steps that must be performed if any of the FSMO roles fail, and keep in mind, it’s not just based
on the FSMO role failure itself, rather you must also take into account the DC, too, because it usually means the DC itself
has failed, therefore the DC failure must be addressed.

If a DC fails, then you must address the DC failure as a whole, and not just the FSMO roles. This is because the DC’s account is referenced in the AD database by other DCs, and it expects it to be there to contribute and work with replication, among other AD functions. Therefore you must clean out the DC’s reference from the AD database, which also includes seizing the roles it held to other DCs.

This also includes the services a specific FSMO role held, such as the Time Service. This service runs on the PDC Emulator and must be moved to the new PDC Emulator you are seizing the role to.

For more information, with a complete and specific step by step, including any services the DC held which was FSMO role specific, please see the following article for more information:

Complete Step by Step to Remove an Orphaned Domain controller

Monitoring DCs for failures

Microsoft Monitoring Products

There are a number of tools to monitor your domain controllers from native Windows event logs, to using SCOM.

System Center Operations Manager 2007 (SCOM) – Platform MonitoringOct 6, 2010 … Take advantage of System Center Operations Manager 2007 for cross-platform monitoring, beta software and management packs.

To learn how to use SCOM, Microsoft has a specific course just for this product. For more information on the course, please see:

Microsoft Official Curriculum Course 50028B:
Installing and Configuring System Center Operations Manager 2007

Third Party Monitoring Tools

There are also numerous third party monitoring utilities available such as the following list:

Quest – Windows Management Solutions – Trust the Experts for Simplified Windows Management

Network Monitor Software and Windows Development ToolsNetwork Monitor Tool site – Network Monitoring Tools for Windows, Linux, Unix and Novell.

NetVision Audit for Active Directory – Monitoring Active Directory – Active Directory Reports – Easy Audit Reporting and Real-Time Monitoring

Windows Monitoring, Windows Server Monitoring, Windows Application …Download Windows monitoring tool for Windows server monitoring, IIS Server, . … Monitor Windows CPU, disk, process monitoring, memory and ensure high …

Windows Server Monitoring and Windows Event Log Management SoftwareDevelopers of Windows administration tools that monitor in real-time system performance, security logs, and event logs, and send automated, user-defined …

Nagios Core – Monitoring Windows Machines:

Network Management Software | Server Monitoring | WhatsUp GoldWhatsUp Gold is an award-winning network monitoring software, managing over 100000 networks worldwide. Download trials & free tools now!

Comments, suggestions and corrections are welcomed!



I hope this helps!

Original Publication Date: 11/1/2011
Updated 11/4/2014

Ace Fekay
MVP, MCT, MCSE 2012, MCITP EA & MCTS Windows 2008/R2, Exchange 2013, 2010 EA & 2007, MCSE & MCSA 2003/2000, MCSA Messaging 2003
Microsoft Certified Trainer
Microsoft MVP – Directory Services

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