Define the AD server for authentication

Hi,

I am having some issues with the SharePoint 2010 authentication. 

The current environment is the following: There are many offices (locations) using the same domain (global.domain.com) and each office has a replicated local AD server. The issue is that the users logging in the office are "supposed" to log in to the local server instead of using an AD server in the central office, but the computers, somehow, bypass the local AD and request authentication in a central AD server. Other IT staff are working on this issue but I mention it since it might be related to the SharePoint authentication.

SharePoint is also trying to search for user authentication in another AD server and not in the local one, making the authentication to either take too long, or the site to request the user the username / password three times and then give an error page.

The main question is, is it possible to define in SharePoint which AD server to use for authentication?

Thank you,

Luis