If the DNS zone is a Standard Primary or Secondary zone, the information is already in a .DNS file at %SystemRoot%\System32\Dns.

To extract an Active Directory-integrated zone to a file:

dnscmd /ZoneExport FQDN_ZoneName FileName

Examples

dsncmd /ZoneExport JSIINC.COM JSIINC.DNS
exports the JSIINC.COM zone to %SystemRoot%\System32\Dns\JSIINC.DNS.

dnscmd JSI002 /ZoneExport test.JSIINC.COM Test.DNS
exports the test.JSIINC.COM zone on server JSI002 to %SystemRoot%\System32\Dns\Test.DNS on JSI002.