Our Main DC will sometimes not load AD after it restarts from automatic updates. DNS is also offline when this happens.
I can fix it by going to ADUC, actions->connect to another domain controller. Selecting DC2. Then redo the process but select DC1 the second time. The fix is easy, but I need to figure out why this is happening to prevent it. The first time it happened I thought it was a fluke, but it has happened twice in the past 2 or 3 months.
DC1 (AD, DNS, DHCP, GC) (one crashing)
DC2 (AD, Exchange 2007)
Branch offices (2 connected through VPN)
DC3 and DC 4 (AD, DNS, DHCP GC)