A zone file defines a Domain Name Service (DNS) serverís zone of authority. The zone file is a text file containing records for all the computers and services for which the server is responsible. In a small domain the zone file may contain the records for the whole domain. When a domain contains many computers or is spread geographically, the domain may have two or more DNS servers each responsible for its own zone within the domain.
The entries in a zone file are called resource records.
An A type resource record indicates the IP address associated with the host name.
ACNAME (canonical name) is an alias pointing to the actual server without giving its name.
TheSOA (Start Of Authority) resource record is at the beginning of each zone file defining the entity responsible for everything lower in the hierarchy.
The NS (Name Server) resource record indicates the Name Server.
The MX (email exchange) resource record and the RP (Responsible Person) record are self-explanatory.
Reverse Lookup Zone File
The reverse lookup zone file is used when the client provides the Internet Protocol (IP) address and needs the Host name. In this file each resource record consists of the network portion of the IP address in reverse followed by .in-addr.arpa. For example 18.104.22.168 would have the entry, 66.59.192.in-addr.arpa. In-addr stands for inverse address, the arpa portion is a Top-Level Domain (TLD) left over from the Internetís predecessor ARPAnet.