I asked a question over on StackOverflow and was directed to ask a related one here to see if I could get any additional input. Basically, I am looking to have my application aware of what domain it's running under, if any at all. (I want to expose certain debugging facilities only in house, and due to our deployment model it isn't possible to have a different build.) Since I am over paranoid, I didn't want to just rely on the domain name to ensure we are in house. As such I noted the DOMAIN_CONTROLLER_INFO (http://msdn.microsoft.com/en-us/library/ms675912(v=vs.85).aspx ) returned from DsGetDcName (http://msdn.microsoft.com/en-us/library/ms675983(v=vs.85).aspx) has a GUID associated with it, however I can find little if any information on it. I am assuming this GUID is generated at the time the first DC in a domain is created, and that it would live on for the life of the domain. Does anyone else have any inner knowledge and would be kind enough to confirm or deny my assumptions?