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DHCP not working after demoting old DC

Posted on 2014-07-23
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Last Modified: 2014-07-24
Hi,

Today we demoted a legacy windows 2008 domain controller. It had previously been the PDC but we have since mad another 2008R2 server the PDC and have a 2012 server as a secondary DC. So I will call the servers as this -

Demoted server: Leg (2008 - DC/DHCP/DNS)
PDC (2008R2 - DC/DHCP/DNS)
SDC (2012 - DC/DNS)

After demoting the Leg server and removing the roles everything seemed fine. Until a user notified us later in the day that they could not log in. Tested and no machine can get DHCP. The Leg server had been powered down for a couple of weeks and all clients had been getting DHCP from the PDC. Why once we power it back on and demote it would all clients be unable to contact the PDC to obtain an IP address?

I have logged into the PDC and checked DNS. All the clients are registered there with the leases. But no machine can log on to the domain. They all get the message that no DC could be contacted.

I have logged in to the local machine and set a static IP address to see if they can connect this way but they are still unable to connect. But I am on a machine now that is still connected using a DHCP IP address.

Can anyone please give me some assistance in troubleshooting this issue? Please let me know what other info you need and I can supply it.

Thanks in advance.

Cheers,

Rory.
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Question by:rorymurphy
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Author Comment

by:rorymurphy
ID: 40213922
Hi,

Some further info. This is a virtual server environment running on VMware ESX v5.1.

The Leg server is backed up using Veeam however I am reluctant to restore the server given that it was a DC an has since been demoted. If I restore it back into the forest I would imagine that would cause further issues.

I am currently restoring it to a sandbox location so I can get any required files/settings from it if required.

Cheers,

Rory
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Accepted Solution

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sda100 earned 500 total points
ID: 40213974
You can restore the old server, just not as a domain controller, DHCP will still work.  However, you can test dhcp by using this little program, here: http://blog.thecybershadow.net/2013/01/10/dhcp-test-client/

I had to wait 20 seconds or so (after pressing "d") before I got a response from the DHCP server, but the response was correct.

Have you checked the firewall on both server and client (and anything in between)?

And now the red-herring, you said you changed a particular computer to static IP information, but it still didn't work?  That's where you should really start - lack of DHCP might be a result of this.
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Author Closing Comment

by:rorymurphy
ID: 40216411
I'm an idiot! A long day lead to my judgement being more than a little bit off. Was in fact a network issue in the end which we resolved and did not need to resurrect the old DC. But thank you for your post sda100. As you said a red herring indeed. Cheers!
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