I had a client recently who has all 2008 DCs and wanted to introduce 2016 DCs. No big deal. Prep the domain and forest and off you go. Except that this client was running in 2003 forest mode. And that led to a different discovery: FRS was being used for SYSVOL/NETLOGON replication. And this is not going
to cut it in a modern AD. Migrating is not especially difficult but it requires a little know how, patience and perserverance.
This article by Patrick van den Born was a wonderful resource that had almost all that I needed to get the pieces in place.
*** Make sure to install DFS on all the 2008 DCs but do not create a namespace.
http://www.rebeladmin.com/2015/04/step-by-step-guide-for-upgrading-sysvol-replication-to-dfsr-distributed-file-system-replication/ – also good!
Test replication by going to the “scripts” folder in SYSVOL, adding a text file, and making sure that it IMMEDIATELY appears in all the other DCs’ Scripts folder.