When NT4 servers can't find the PDC and all else fails

Recently I ran into a major problem with my Active Directory and NT4 setup. I maintain a network made up of 2 NT4 BDCs and about 10 Active Directory Domain Controllers. The domain is in 2003 interim mode and we also run Exchange 5.5 on 4 other NT4 member servers. Last week we renamed a few domain controllers and assigned new IP addresses (on the 2003 side). As a precaution I kept the old IP address on one of the major domain controllers until I could get time to manually modify all the legacy servers lmhosts files. We also shutdown the domain controller that was used to get us to Active Directory, basically I took a dell desktop that would run NT, and made it a BDC. Then I promoted it to a PDC and upgraded the OS to Server 2003 and installed Active Directory. Well its time to de-commission that box and we shut it down last week as well. On Monday, I created a new user account and immediately got reports of strange problems, the user was getting prompted for logon credentials in Outlook and could not stay online.

I looked around and couldn’t find anything wrong and wasn’t too concerned at this point. Later I realized that my NT4 BDCs were not able to find a PDC any longer. I assumed it was because we shutdown the upgraded domain controller and so we powered it back on hoping it would help. This did not fix the problem so I began working on the issue by online research and posting questions in newsgroups. Finally I found a guy on Experts-exchange that was very helpful and worked with me on EE for hours before we figured out the issue. By troubleshooting and much testing we found that NetBIOS lookups to the PDC emulator (running 2003) were failing. From 2003 we could map drives, browse to NT4 without a problem, only from NT4 to 2003 was there an issue. Lastly we found that its bad to have a multi-homed domain controller, especially the one we were using for the PDC Emulator. I removed the second (old) IP address from the server and everything started to work just fine. I could get into the user manager in NT4 and updates started to be processed without a problem.

So it turns out the main cause of the issue was not the renames, or IP change, or even shutting down an old DC. It was simply that we had more than 1 IP Address on our PDC Emulator server. Removing that fixed the issue. I think we can now power down the upgraded DC again and proceed further with the migration. Too bad it took so long to figure this out, but at least it is working normally now.