dnsonly master server

Hi, I have 3 servers. 1 is dnsonly and others are for normal accounts (cpanel/whm) I want to setup dnsonly as a master dns server, so that if any of the two main servers are down, it will redirect to the "backup" dnsonly server so there won't be any downtime. How do i setup all servers, nameservers, IP's etc? Thank you so much.