Active Directory dc offline

How long can a DC be offline? https://social.technet.microsoft.com/Forums/windowsserver/en-US/7ffe5c2d-3a20-4ede-8499-2688f4dc3719/how-long-can-a-dc-be-offline?forum=winserverDS
60 to 80 days depending on OS and SP level. It is ultimately determined by the ‘tombstone lifetime‘ in the forest. That being said, from personal experience, the longest we‘ve ever had one offline is a couple days.
http://technet.microsoft.com/en-us/library/cc779177%28WS.10%29.aspx

活動目錄域控制器最長可以離線多久？