AD server resiliency for two offices

If you configure both DCs in the same domain, they will replicate AD information between them automatically.

You need to configure two separate AD sites, one for each office, and configure the subnets that correspond to each office.  Because AD is "site-aware" you need to do this so that your US clients will authenticate to the US DC and the UK will authenticate to the UK, otherwise you'll be getting calls complaining of slow logon times as clients try to authenticate across the WAN.  (What kind of connectivity do you have between the two offices?)  Check out the following support webcast on configuring Sites & Subnets in AD 2003: http://support.microsoft.com/kb/909429

As far as client configuration is concerned, configure the US office to point to the US DC as its primary DNS with UK as their secondary, and vice versa.

Hope this helps.

Laura  E. Hunter - Microsoft MVP: Windows Server - Networking

Dear Sir,

Thx for your reply.   The connection between the two offices is just Internet, therefore I perfer two servers to provide AD service to local users only in normal case.  Only when there is problem on either server, the remaining server will provide service to users in both locations.

Do I need to manually create user account/service/permission in both servers or it will replicate automatically ?

thx
Eric

You should also reference https://www.experts-exchange.com/questions/22474493/MS-Exchange-AD-Server-Information-Synchronization-between-two-offices-in-different-locations.html for information that we've already provided to you on this topic.