Networking

Switching between domain controllers

Normally, promoting a backup domain controller to primary domain controller is no big deal, but as Brien Posey explains, when your primary domain controller is dead, there are a couple of things you have to remember.


Let me tell you about a frightening experience I had the other day. I’d implemented a Windows 2000 server in a production environment about a week earlier. As you may know, if you want your Windows 2000 server to be a domain controller, at least one other Windows 2000 server must already be the primary domain controller. Otherwise, you must make the new Windows 2000 server your primary domain controller. Therefore, I made this new Windows 2000 server my primary domain controller.

That fateful morning, my Windows 2000 server died because of a hard disk failure. I wasn’t too concerned about people not being able to log in because I knew that my backup domain controllers were still running. Since I wanted to get the server back on line as quickly as possible, I just loaded Windows NT 4 on it. Unfortunately, when it came time to join the domain, the new server couldn’t connect because there was no primary domain controller.

Promoting the backup domain controller
My first thought was, “No big deal; I’ll just promote one of my backup domain controllers.” I went to one of my backup domain controllers and opened Server Manager. This is where my heart just about stopped, because the list of servers was blank. I couldn’t promote a backup domain controller that I couldn’t see. Immediately, panic set in. I began to picture Windows 2000 doing all sorts of horrible things to my network. However, this wasn’t the case.

Once I’d calmed down a bit, I remembered that the Show Domain Members Only option was selected under the Server Manager’s View menu. Once I deselected the Show Domain Members Only option, all of my servers were displayed.

I was now free to promote my backup domain controller to a primary domain controller. However, this entire situation reminded me that swapping domain controllers is a critical skill. Unfortunately, it’s easy to become a bit rusty at this, because you hardly ever have to do it.

Normally, promoting a backup domain controller to primary domain controller is no big deal. You just select the backup domain controller and then use the Promote To Primary Domain Controller option on the Computer menu. Then, Windows NT will stop the net login services on both machines, synchronize the domains, make the switch, and restart the services. Piece of cake.

However, when your primary domain controller is dead, there are a couple of things you have to remember. The procedure begins the same way. Just select your backup domain controller and then select the Promote To Primary Domain Controller command from the Computer menu. Once you’ve done so, Windows NT will inform you that it can’t communicate with the primary domain controller and will ask you if you want to promote the backup domain controller anyway. If you select the Yes option, you’re in business.

However, you must remember that if you happen to revive your original primary domain controller, you’ll have two primary domain controllers on the same domain. Upon bringing up the original primary domain controller, you must immediately demote one of the primary domain controllers to a backup domain controller via the corresponding option on the Computer menu. Otherwise, you’ll have lots of problems.

Brien M. Posey is an MCSE who works as a freelance technical writer and as a network engineer for the Department of Defense. If you’d like to contact Brien, send him an e-mail. (Because of the large volume of e-mail he receives, it's impossible for him to respond to every message. However, he does read them all.)

The authors and editors have taken care in preparation of the content contained herein, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for any damages. Always have a verified backup before making any changes.

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