A zone is an administrative entity which is created on a DNS server to represent a discrete portion of namespace. Administrators divide DNS namespace into zones to delegate their administration and to store zones on different servers. The DNS server can store about 200,000 zones on a single server.
The DNS server in Windows 2003 server supports 3 types of zones.
1. Primary zone: It contains master copy or the read and writable copy of zone database. In the primary zone, the admin makes any changes to zone’s resource records. Any other zone cannot be created without a creating a primary zone .
2. Secondary zone: It contains only the readable copy of the DNS database. It copies the information from primary zone. It provides data redundancy or fault tolerance to primary DNS. Indirectly it is used to improve the performance of DNS.The contents in a secondary zone cannot be modified manually, it can only be updated by replicating primary master zone database file using a process called zone transfer.
3. Stub zone: A stub zone is a read-only copy of a zone, which obtains its resource records from other name servers. It contains copies of only three types of resource records are SOA record for the zone, Name server (NS) records for all name servers authoritative for the zone and Host (A) records for all name servers authoritative for the zone. These resource records are necessary to identify the authoritative DNS server for the zone.