Which of the following is NOT a valid DNS zone type?

A stub zone is a valid DNS zone type that holds only the SOA record, NS records, and glue A records necessary to locate the authoritative name servers for a delegated zone.

A secondary zone is a valid read-only DNS zone that receives a copy of zone data from a primary zone through zone transfer operations.

AlterNet zone does not exist as a valid DNS zone type in any DNS standard (RFC) or major DNS server such as Microsoft DNS or BIND. The recognized DNS zone types are primary, secondary, stub, and forward zones - no 'AlterNet' designation appears in any authoritative DNS specification.

A primary zone is a valid DNS zone type where the DNS server hosts the authoritative, read-write master copy of all resource records for that zone.