Promoting the secondary DNS to primary DNS server
Despite the fact that a secondary nameserver automatically copies its information from the primary, the DNS does not differentiate between primary and secondary nameservers. More-or-less, they are used equally whenever a domain name lookup is performed. These Secondary servers are equally necessary as the primary DNS servers. Mitigation of the load over the primary DNS server is handled by the Secondary servers as well.
Changing zone types from (secondary) to (primary)
Changing a zone from secondary to primary can affect other zone activities, including the management of dynamic updates and zone transfers and the use of DNS notify lists to notify other servers about changes in the zone.
You can perform this procedure by using the DNS snap-in or by using the Dnscmd command-line tool.
Promoting the primary DNS to secondary DNS server
The terms 'primary' and 'secondary' may not mean what common usage suggests... depending on the DNS client side, DNS resolution requests may be sent (first) to the DNS server that most recently responded, or it may be sent to both or all configured DNS servers [some clients may allow more than 2 to be specified...] and the first reply received is considered the 'winner' The secondary DNS server is referred as the Slave server.
Changing zone types from (primary) to (secondary)
Before you use these options, you must first convert the zone to the appropriate type, if necessary. The DNS Server service provides for three types of zones: Primary zone, Secondary zone, Stub zone. If the DNS server is also an Active Directory Domain Services (AD DS) domain controller, primary zones and stub zones can be stored in AD DS