I described Netdiag at How do I use the Network Diagnostics Tool (Netdiag.exe) in Windows 2000?

When Netdiag runs the DNS test on a domain controller, the /FIX switch verifies that all the DNS entries in the Netlogon.dns file are correct. If the entries are incorrect, Netdiag fixes them.

When Netdiag runs a domain controller test, the /fix switch causes it correct the cached domain GUID on the local computer if it is different than the domain GUID saved on a domain controller.