A secondary name server acts as an alternate to the master name server if the master name server becomes unavailable or overloaded. The secondary name server receives zone data directly from the master name server in a process called zone transfer. Zone transfers occur only when data changes. Some name servers support zone change notification, which results in the zone transfer happening quickly after the data changes. Other name servers poll for changed data based on the refresh interval in the Start of Authority (SOA) resource record. For a description of the SOA resource record, see z/OS Communications Server: IP Configuration Reference. A secondary name server, like a master name server, is authoritative for a zone.