What is a primary and secondary Domain Name Server ?
Domain Name Servers (DNS) typically function in pairs; one server, called the Primary Server, will be responsible for updating the second DNS with relevant information about their domain names. The Secondary Server is dependent on the Primary Server for information. The relationship between the servers is established and maintained by the DNS administrator. As a result, when specifying a set of authoritative DNS in Domain Manager, it does not make a difference what order you specify the related entries.