One (of two) 2008 DCs will not authenticate

[jlovelo]

"DC1" and "DC2" - both Server2008, same subnet, same 5 fsmo roles, both Global Catalog enabled, both run DNS. If DC1 is offline, AD seems to be unavailable - cannot login, cannot authenticate for Outlook/OWA/ISA2006 (Exchange 2007 also on same subnet). I suspect this is a DNS issue, but need assistance before diving into the zone. Thanks.

[JAMES_911]

The problem that you may be facing can be due to one of the possible reason that is unavailability of Global Catalog (GC). In your environment anouth DCS are GCs or not?. If its not make both DCs as GC. Then it will solve your problem. For enabling GC - http://technet.microsoft.com/en-us/l.../cc758330.aspx

[jlovelo]

Thanks James for your response - yes as mentioned both servers have GC enabled.
cheers

[jlovelo]

I was incorrect about fsmo roles - only one server (DC1) holds five roles.

Exchange MAD service can see both DCs (names substituted for privacy):

Process MAD.EXE (PID=3444). Exchange Active Directory Provider has discovered the following servers with the following characteristics:
(Server name | Roles | Enabled | Reachability | Synchronized | GC capable | PDC | SACL right | Critical Data | Netlogon | OS Version)
In-site:
"DC1" CDG 1 7 7 1 0 1 1 7 1
"DC2" CDG 1 7 7 1 0 0 1 7 1