Installing and Administering Internet Services

62 Chapter 3

Conﬁguring and Administering the BIND Name Service

Overview of the BIND Name Service

• You can contact almost any host on the Internet. Because BIND

spans network boundaries, you can locate almost any host on the

network by starting at the root server and working down.

An NIS server can serve only the hosts on its local LAN. NIS clients

send out broadcasts to locate and bind to NIS servers, and broadcasts

do not cross network boundaries. Each NIS server must be able to

answer all the host name queries from the hosts on its local LAN.

Many people use BIND for host information and NIS or NIS+ for other

conﬁguration information, like the passwd and group databases. NIS or

NIS+ has the advantage that it can easily manage many different types

of information that would otherwise have to be maintained separately on

each host. However, NIS does not easily span networks, so the hosts in

an NIS domain do not have access to information from other domains.

The DNS Name Space

The DNS name space is a hierarchical organization of all the hosts on

the internet. It is a tree structure, like the structure of UNIX directories.

The root of the hierarchy is represented by a dot (.). Underneath the

root, top-level internet domains include com (commercial businesses),

edu (educational institutions), gov (government agencies), mil (military

and defense), net (network-related organizations), and org (other

organizations). Under each top-level domain are subdomains. For

example, the edu domain has subdomains like purdue, ukans, and

berkeley. In turn, each subdomain contains other subdomains. For

example, the purdue subdomain could contain econ, cs, and biol

subdomains.

At the deepest level of the hierarchy, the “leaves” of the name space are

hosts. A fully qualified host name begins with the host’s canonical

name and continues with a list of the subdomains in the path from the

host to the root of the name space. For example, the fully qualiﬁed host

name of host arthur in the cs domain at Purdue University would be

arthur.cs.purdue.edu.

Figure 3-1 shows the hierarchical structure of the DNS name space.