non-root server

I need to make my DNS server a NON-ROOT server by deleting the “.” domain in DNS manager on my first DNS server to put my ISP’s DNS server entries in the FORWARDER settings on the DNS server. My question is this. When I set up a second DNS server for fault tolerance on my network how do I set the primary and alternate settings in TCP/IP for the second server. Is the first DNS server in the network listed as the primary and the second the alternate? Or should each server be set as it’s own primary. I’m confused.