We have an old 2003 server that used to be our primary server. It ran AD DC, DNS, DHCP, WINS, file shares, etc. Over the years we have added additional 2008, 2008 R2, 2012, and 2012 R2 servers and moved services to those other servers. We have finally migrated all services and all but one file share off it. We would like to DCPROMO it to be a standard server as we need to raise the AD functional level for some software that requires it. We have ensured that all services are pointed elsewhere, but we continue to get a large amount of authorization failures when it is demoted. I have increased the LDAP weight so it should not be a primary server for lookups, but watching the TCP connections to it, it is still getting hammered by clients and servers for lookups. We demoted it and when all the network authorization issues came up, we DCPROMOed the server and put AD back on and everything started working fine again. I have done a lot of research and the only thing I can find is It turns out that weird things can happen when you mix Windows Server 2003 and Windows Server 2012 R2 domain controllers
But this article is not exactly what we are dealing with so I am hesitant to apply the hotfix. It is only replicating to and from one other DC in Sites and Services. It is not a GC, does run DNS.
Any thoughts on what we can do to figure out what is breaking when we demote this server? We have multiple AD, DNS, DHCP, WINS, etc. servers in multiple locations so it shouldn't be dependent on this one server. One suggestion was to reboot servers and clients when we remove it but that would be a major undertaking. Should we add additional AD connections in sites and services so it replicates its changes out faster?