The DNS Database Files Master files included by named, like named.hosts, always have a domain associated with them, which is called the origin . This is the domain name specified with the cache and primary commands. Within a master file, you are allowed to specify domain and host names relative to this domain. A name given in a configuration file is considered absolute if it ends in a single dot, otherwise it is considered relative to the origin.
All data contained in a master file is split up in resource records , or RRs for short.
Each resource record has a type. An entry may be continued across several lines if an opening brace occurs before the first newline, and the last field is followed by a closing brace. Anything between a semicolon and a newline is ignored. This is the domain name to which the entry applies. The ttl field specifies the time in seconds the information is valid after it has been retrieved from the server.