Internet domain names are easier to remember than IP addresses such as 2.166 (IPv4) or 2001:db8:1f70::999:de48:6e8 (IPv6).
Users take advantage of this when they recite meaningful Uniform Resource Locators (URLs) and e-mail addresses without having to know how the computer actually locates them.
By default, named is not allowed by the SELinux policy to write, create or delete any files EXCEPT in these directories: $ROOTDIR/var/named/slaves$ROOTDIR/var/named/data$ROOTDIR/var/tmp where $ROOTDIR may be set in /etc/sysconfig/named if bind-chroot is installed.
The SELinux policy particularly does NOT allow named to modify the $ROOTDIR/var/named directory, the default location for master zone database files.
Zone files are optional for slave nameservers, but strongly recommended otherwise the slave will lose all knowledge of the zone content whenever it is restarted.
It will not then be able to start serving the zone again until it has performed a zone transfer, and if the master is unavailable for any reason then the period of downtime could be substantial.
But after that, any new DNS entries on master zone are not updated to slave zone.
These need not be masters in the sense defined above: it is possible (and sometimes necessary) for a slave to obtain zone data from another slave.
Masters must be specified as IP addresses, not as domain names, however it is possible to define a ‘masters list’ containing the required addresses which can then be referred to symbolically (see below).
It associates various information with domain names assigned to each of the participating entities.
Most importantly, it translates domain names meaningful to humans into the numerical identifiers associated with networking equipment for the purpose of locating and addressing these devices worldwide.