logging on and authentication issues

I am one of several server admin managing a very large enviroment that is currently just finshed the W2K rollout for our servers. the desktop enviroment is primarily NT with a few Win95 machines.. We have several remote country sites plus 4 overseassites all with at least 1 DC. The problem is that at some of the sites when our users logon they are getting authenticated by a remote DC, not the local one.. in one case our tokyo users are getting authenticated by a DC in one of our mining sites in remote western australia. This involves several router hops and as can be expected frustrating. I would appreciate any help in trying to determine why this happening…