In a Windows NT Server V4 domain, if the connection between the PDC
and the BDC goes down, how long does it take for the BDC to
automatically promote itself to PDC, and where can this parameter be
changed?

mikeplokta-

Thanks for the question. It appears that many people are similarly
confused by this, as I found a lot of conflicting information.
However, a BDC will _not_ automatically promote itself to PDC- any
promotion must be performed manually. What is confounding about this
issue is that since Microsoft doesn't document everything that
_doesn't_ happen, there aren't any concrete references to this in
official documentation. However, every mention of BDC->PDC promotion
in Microsoft's documentation explicitly mentions the manual promotion
of the BDC. Additionally, I am relying on personl experience and
empirical evidence offered by trusted associates as well as the
Internet community at large.

When a PDC fails any BDCs that exist on a network will still handle
authentication records and provide NetBIOS names. However BDCs hold a
read-only copy of the domain SAM and thus, changes such as adding a
user or a user changing a password are impossible. If it is known that
a PDC will be unavailable for more than a few minutes, a PDC should be
manually promoted (this is done in the Server Manager application).
There are numerous USENET and mailing list theads on this topic. Some
of the highlights:

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=utf-8&threadm=ODGnrunA9GA.197%40uppssnewspub05.moswest.msn.net&rnum=14&prev=/groups%3Fq%3DPDC%2Bautomatic%2Bpromotion%2BNT%26start%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3Dutf-8%26scoring%3Dd%26selm%3DODGnrunA9GA.197%2540uppssnewspub05.moswest.msn.net%26rnum%3D14

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=utf-8&threadm=01bc07de%24080af040%24a97e2399%40barryhome&rnum=8&prev=/groups%3Fq%3DBDC%2Bautomatic%2Bpromotion%2Bwindows%2BNT%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3Dutf-8%26scoring%3Dd%26selm%3D01bc07de%2524080af040%2524a97e2399%2540barryhome%26rnum%3D8

Once a BDC has been promoted to PDC (we'll call the promoted BDC
PDC_2, and the original PDC PDC_1), a new issue arises- how to bring
PDC1 back into the mix. Since a domain is only allowed one PDC, there
is a conflict. However, you cannot just demote PDC_2 back to a BDC,
since any changes made to the SAM while the PDC_1 was offline will be
lost. Thus, it is best to demote PDC_1 to a BDC, have it synch with
PDC_2, then demote PDC_2 back to its original role as a BDC and
promote PDC_1 to its original role as PDC. There is a Knowledge Base
article that discusses this process:
http://support.microsoft.com/default.aspx?scid=KB;EN-US;Q112549&

I also discovered a useful Microsoft TechNet article that details the
sundry registry keys that control how PDC/BDC communication works. You
can find it at http://www.microsoft.com/technet/treeview/default.asp?url=/technet/prodtechnol/winntas/maintain/ntopt4.asp

Hopefully this helps you out. Please let me know if there is anything
that needs clarification.


Search strategy:

www.google.com
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BDC "automatic promotion" windows NT

groups.google.com (this was the most useful source)
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PDC "automatic promotion" NT
BDC "automatic promotion" NT

search.microsoft.com
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BDC automatic promotion

Thorough and well researched. Tells me everything I need to know.