Secondary zones provide redundancy and load balancing.The secondary zone must have network access to the remote DNS server that hosts the zone in order to get the updated zone information from the master ( this is called a zone transfer and requires permissions from the master server where the zone is being copied).Secondary: is a read-only copy of a zone from the master DNS server and is a secondary source of information for the zone.
Primary: hosts a writable master copy of the zone data and is authoritative for the zone.
