To decommission an Active Directory Domain Controller (Windows Server 2003/2008) is a fairly straightforward task so long as you make sure nothing is relying on that server specifically. I will cover off the demotions steps (fairly easy) but I will go through a checklist (and how-to) of gotchas that you might get caught out when doing this.

What to check before demoting your DC?

The most important things to look out for are the following components that are either running or registered against the system:

• Global Catalog
• FSMO Roles
• Bridgehead server
• General server checks
• You have enterprise admin credentials

Global Catalog

If you remove the last remaining Global Catalog server from a domain, you will experience logon issues across the domain along with other functions like searches and lookups.

If you remove the last Global Catalog server from a site, users/machines will have to contact a Global Catalog server from a different site. This may not cause problems with small branch offices, however large sites may suffer with the additional overhead in traffic.

To check what servers are functioning as a Domain Controller in your domain, type the following command:

dsquery server -domain #DomainName# | dsget server -isgc -dnsname

Note: replace #DomainName# with the domain of the DC that you are demoting. The output should look similar to this:

If you have more than just the DC that you are preparing the demote, then you have nothing else to do as the DCPROMO steps will remove it automatically. If you don’t have any more, follow MS article 296882 to make another DC a GC.

Resources:

• Global Catalog Servers
  http://technet.microsoft.com/en-us/library/cc977998.aspx
• Determine whether a domain controller is a global catalog server (Windows Server 2003)
  http://technet.microsoft.com/en-us/library/cc786686%28v=ws.10%29.aspx
• Determine whether a domain controller is a global catalog server (Windows Server 2008)
  http://technet.microsoft.com/en-us/library/cc794880%28v=ws.10%29.aspx
• How to promote a domain controller to a global catalog server
  http://support.microsoft.com/kb/296882

FSMO roles

Flexible Single Master Operation roles (FSMO) are a feature of Microsoft’s Active Directory and you need to make sure they are not present on the server you are demoting.

To check that the the current server is not a FSMO role holder, simply run the following command:

netdom query fsmo

The output should look similar to this:

If none of the server names are the one you are demoting then you have nothing else to do. If you are then follow the MS KB Article 324801 noted below.

Resources:

• Flexible Single Master Operations
  http://en.wikipedia.org/wiki/Flexible_single_master_operation
• How to view and transfer FSMO roles in Windows Server
  http://support.microsoft.com/kb/324801
• Understanding FSMO Roles in Active Directory
  http://www.petri.co.il/understanding_fsmo_roles_in_ad.htm

Bridgehead Server

As Microsoft have described it here, ‘A bridgehead server is a domain controller that has been either administratively assigned or automatically chosen to replicate changes collected from other domain controllers in the site to bridgehead servers in other sites.’ If you have multiple sites you want to make sure the server you are demoting is not a Bridgehead server. To check if this server is, run the following command on the server console that is being demoted:

repadmin /bridgeheads

The output should be all the bridgeheads that are configured on that server. If it looks like the below screenshot, then you dont have any configured, otherwise you will need to reconfigure this before proceeding.

To do a whole check on the site, simply extend the command to

repadmin /bridgeheads site:#sitename#

where #sitename# is the name if the Active Directory site. The output for that looks like this:

Resources:

• Description of Bridgehead Servers in Windows 2000
  http://support.microsoft.com/kb/271997
• What is bridgehead server , preferred bridgehead server and Knowledge Consistency Checker (KCC)
  http://www.omnisecu.com/windows-2003/active-directory/what-is-bridgehead-server.htm

General Server Checks

There are some general server checks that you should run on your servers/domain to make sure it is healthy before running a DCPromo. There are a couple of reports that give you plenty of info, and they are quite easy to read. Search for the term ‘error’ or ‘fail’ on dcdiag and netdiag reports to locate the problem areas, but i do recommend reading through the entire logs to familiarise yourself.

DCDiag (part of WS03 SP1 Support tools) displays all information about Domain Controller information.

dcdiag.exe /V /C /D /E /s:#DomainControllerName# > c:\dcdiag.log

NetDiag provides information about specific network configuration for the local machine.

netdiag.exe /v > c:\netdiag.log

RepAdmin helps diagnise AD replication issues with WS03 and WS08 DC’s.

repadmin.exe /showrepl dc* /verbose /all /intersite > c:\repl.txt

DNSLint is a Microsoft Windows utility that helps you to diagnose common DNS name resolution issues.

dnslint /ad /s #IPAddressOfServer#

Resources

• Windows Server 2003 Service Pack 1 Support Tools
  http://support.microsoft.com/kb/892777
• Repadmin
  http://technet.microsoft.com/en-us/library/cc770963%28v=ws.10%29.aspx
• Description of the DNSLint utility
  http://support.microsoft.com/kb/321045

Admin Credentials

There are two types of Administrator Credentials you may need to use:

If you need to move all FSMO roles the logged-on user should be a member of the Enterprise Administrators group. This is required to transfer Schema master or Domain naming master roles.The rest of the operations can be done with a user who is a member of the Domain Administrators group.

How to decommission a Windows Server 2003/2008

The procedure involved is fairly straight forward so I will only document the steps. For more details and screenshots of the steps, refer to the resources below.

To demote a domain controller

1. On a domain controller, click Start, and then click Run.
2. In Open (or Run), type dcpromo to open the Active Directory Installation Wizard, and then click Next.
3. On the Remove Active Directory page, click Next, and then continue to follow the wizard.

Resources

• Demoting a Domain Controller
  http://www.vmadmin.co.uk/microsoft/43-winserver2008/136-svr2008dcdemote
• Demote a domain controller
  http://technet.microsoft.com/en-us/library/cc740017%28v=WS.10%29.aspx

Having Problems?

So you may have tried the above steps and it didn’t work? Or maybe your server crashed and you don’t want to try recovering it? There are a number of reasons why you may end up in this scenario – although not favorable its not all doom and gloom. Below are some resources to get you out of a pickle.

• Complete Step by Step to Remove an Orphaned Domain controller
  http://msmvps.com/blogs/acefekay/archive/2010/10/05/complete-step-by-step-to-remove-an-orphaned-domain-controller.aspx
• Forceful removal of DC
  http://support.microsoft.com/kb/332199
• Metadata cleanup
  http://www.petri.co.il/delete_failed_dcs_from_ad.htm
• How to remove data in Active Directory after an unsuccessful domain controller demotion
  http://support.microsoft.com/kb/216498
• Seize FSMO role
  http://www.petri.co.il/seizing_fsmo_roles.htm
• Configuring the time service on the PDC Emulator FSMO role holder
  http://msmvps.com/blogs/acefekay/archive/2009/09/18/configuring-the-windows-time-service-for-windows-server.aspx