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I condider myself to have a very good understanding of Active Directory and I am aware of the obvious benefits of having more than one domain controller in a domain.

My question is basically this. When one domain controller is not available, how does a PC in the domain know to revert to another domain controller?

Thanks for any help.

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1  
What does nslookup your.domain return? :) –  jscott Dec 10 '12 at 19:39
    
@jscott, thanks for the quick reply. It simply returns the IP address of the current domain controller/dns server (My current network only has a single domain controller). My question is simply curiosity based and not practical based. –  slickboy Dec 10 '12 at 19:42
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Here you go, the DC Locator process: blogs.technet.com/b/arnaud_jumelet/archive/2010/07/05/… –  joeqwerty Dec 10 '12 at 19:53
    
@joeqwerty Link answers suck but that is by far the best answer to this question. I'd post it anyway. –  Brent Pabst Dec 10 '12 at 19:55
    
I was being lazy so I posted the link as a comment instead of a full answer with the link included. It looks like @Greg Askew got it. –  joeqwerty Dec 10 '12 at 20:00

1 Answer 1

up vote 5 down vote accepted

It's known as the DC Locator process.

https://blogs.technet.com/b/arnaud_jumelet/archive/2010/07/11/domain-controller-locator-in-depth.aspx

How DNS Support for Active Directory Works
http://technet.microsoft.com/en-us/library/cc759550%28v=ws.10%29.aspx

DNS returns a list of DC's sorted by priority and weight. The client attempts to communicate with a DC, and moves to the next DC in the list if a response is not received in a brief period.

5.4.5.3 Ping the Candidate Domain Controllers for "Liveness" and Capability Verification Using LDAP Ping Mechanism
http://msdn.microsoft.com/en-us/library/ff718294%28v=prot.20%29.aspx

If the client cannot locate a DC in it's site, or if the client is not in a site, it will attempt to contact any domain controller in the domain.

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