Two PDCs in One Domain

Last reviewed: December 31, 1997
Article ID: Q112549

The information in this article applies to:

Microsoft Windows NT Advanced Server version 3.1
Microsoft Windows NT Server versions 3.5, 3.51, and 4.0

SUMMARY

When two different Windows NT Advanced Servers or Windows NT Servers in a domain think they are the Primary Domain Controller (PDC), the following error message may appear in the Event Log:

   A domain controller is already running in this domain.

MORE INFORMATION

It may be necessary to promote a Backup Domain Controller (BDC) to PDC when the original PDC fails. In the event that the original PDC is unavailable during this process, it is necessary to promote the BDC without having the PDC on-line. This should only be done when the PDC is expected to be down for a long period of time because demotion of the original PDC to BDC will not occur. The following message occurs in Server Manager during promotion of a BDC to PDC when the original PDC is unavailable:

   Cannot find the Primary DC for Domain xxxxxx.

You can administer this domain, but certain domain-wide operations are disabled. Promoting the BDC to PDC should work properly at this point. When the original PDC is restarted, it attempts to also become the PDC, and two Windows NT Advanced Server computers will both think they are PDCs for the same domain. As a result, the NetLogon service fails on the original PDC because a PDC already exists in the domain. Server Manager shows two PDCs for the domain. The original PDC has a transparent icon representing a domain controller while the current PDC has the correct colored domain controller icon.

To demote one of the PDCs:

Stop the NetLogon service on the current PDC by typing:
```
      Net Stop NetLogon
```
Highlight the machine name of the original PDC and then select Demote To Server from the Computer menu. This changes the role of the original PDC to BDC.
Restart the NetLogon server by typing:
```
      Net Start NetLogon
```

The original PDC can be promoted to PDC in step 2, if you want. The current PDC needs to be demoted to a server immediately after this step.

Additional query words: prodnt 3.10 3.50 3.51 two primary domain
controllers
Keywords : ntdomain ntnetserv kbnetwork
Version : 3.1 3.5 3.51 4.0
Platform : winnt

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Last reviewed: December 31, 1997
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