I recently introduced a Windows Server 2012R2 domain controller into my environment since it was going to replace a Windows 2003R2 domain controller at some point. I went through all of the proper installation procedures including preparing the forest and domain to receive the new 2012R2 DC. Everything was working just fine, i.e. the netlogon share replicated fine, all group policies replicated fine, etc. They seemed to co-exist just fine. I transferred all FSMO roles and hosted applications from the 2003 server to the 2012R2 server in preparation to decommission it. To make sure things were going to be ok without it, I just powered down the 2003 DC to see if the 2012 server was going to be ok with everything. The next morning, people were saying it took forever to log in on some machines and I even had a couple of Windows 7 machines say the trust relationship failed so I had to leave the domain and rejoin to fix it. I am not sure where to start. The new DC is the only DNS server right now but I am going to add one very soon. All clients use the new DC as the DNS server and get the addressing via DHCP.
I am not seeing anything weird in Event Viewer on the 2012R2 DC. Where would you recommend I start in trying to troubleshoot the slow logons? I have not powered the 2003 DC back on and have no plans to demote it and decommission it totally until I get this figured out.