Check the security log in the event viewer on both DCs.

"Robert" <Robert@discussions.microsoft.com> wrote in message
news:8D7CE83E-8FBF-44D6-8941-2577E1382056@microsoft.com...
> Hello.
> In a NT domain with PDC and BDC, how could I know which one is doing the
> domain user validation?
> Thanks in advance
> Roberto