As mentioned previously, name servers in an administrative domain maintain the DNS database. They also run the in.named daemon, which implements DNS services, most significantly, name-to-address mapping. in.named is a public domain TCP/IP program and included with the Solaris operating environment.
The in.named daemon is also called the Berkeley Internet Name Domain service, or BIND, because it was developed at the University of California at Berkeley.
Each domain must have one primary server and should have at least one secondary server to provide backup. "Zones" explains primary and secondary servers in detail.