reference:http://technet.microsoft.com/en-us/library/cc776854(WS.10).aspx

This is for my use.  It is from the link above.

Domain Controller Diagnostics Tool (dcdiag.exe)

Applies To: Windows Server 2003 with SP1

What does DCDiag.exe do?

This command-line tool analyzes the state of one or all domain controllers in a forest and reports any problems to assist in troubleshooting. DCDiag.exe consists of a variety of tests that can be run individually or as part of a suite to verify domain controller health.

Tool Requirements

• Except as noted below, all commands in DCDiag can be run on Windows XP Professional and Windows Server 2003 family (member servers and domain controllers).

Overview
1 DS3 Point to Point
VPN (Borderware Firewall)
2003 Server Standard

   Site A has 2 Domain Controllers (192.168.200.xx)
            DCA-0
            DCA-1
            25 to 35 servers (members)
   Site B has 1 Domain Controller   (192.168.201.xx)
            DCB-0
            SQL
            WebServer
This location by the end of May will have 1/2 the servers hardware but all the servers. (VMWare) DR.
DCPROMO at Site B.  This helps to make sure VPN works as it should and that all configuration is correct on the DC at both locations.