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. The origin all by itself may be referred to using ``@''.
All data contained in a master file is split up in resource records, or RRs for short. They make up the smallest unit of information available through DNS. Each resource record has a type. A records, for instance, map a hostname to an IP address, and a CNAME record associates an alias for a host with its official hostname. As an example, take a look at figure on page , which shows the named.hosts master file for the virtual brewery.
Resource record representations in master files share a common format, which is
Fields are separated by spaces or tabs. 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.
The following is an incomplete list of RRs to be used in DNS master files. There are a couple more of them, which we will not explain. They are experimental, and of little use generally.