TCP/IP Tutorial and Technical Overview - IBM Redbooks

12.1 Domain Name System (DNS)
The Domain Name System is a standard protocol with STD number 13, and its
status is recommended. It is described in RFC 1034 and RFC 1035. This section
explains the implementation of the Domain Name System and the
implementation of name servers.
The early Internet configurations required the use of only numeric IP addresses.
Because this was burdensome and much harder to remember than just the name
of a system, this evolved into the use of symbolic host names. For example,
instead of typing:
TELNET 10.12.7.14
You can type:
TELNET MyHost
MyHost is then translated in some way to the IP address 10.12.7.14. Though
using host names makes the process of accessing a resource easier, it also
introduces the problem of maintaining the mappings between IP addresses and
high-level machine names in a coordinated and centralized way.
Initially, host names to address mappings were maintained by the Network
Information Center (NIC) in a single file (HOSTS.TXT), which was fetched by all
hosts using FTP. This is called a flat namespace. But due to the explosive growth
in the number of hosts, this mechanism became too cumbersome (consider the
work involved in the addition of just one host to the Internet) and was replaced by
a new concept: Domain Name System. Hosts on smaller networks can continue
to use a local flat namespace (the HOSTS.LOCAL file) instead of or in addition to
the Domain Name System. Outside of small networks, however, the Domain
Name System is essential. This system allows a program running on a host to
perform the mapping of a high-level symbolic name to an IP address for any
other host without requiring every host to have a complete database of host
names.
12.1.1 The hierarchical namespace
Consider the typical internal structure of a large organization. Because the chief
executive cannot do everything, the organization will probably be partitioned into
divisions, each of them having autonomy within certain limits. Specifically, the
executive in charge of a division has authority to make direct decisions, without
permission from the chief executive.
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