| The TCP/IP Protocol Suite |
The previously discussed
protocols do not use any concept of a host name. These protocols always use
32-bit IP addresses to locate source and destination hosts. Of course, no
one wants to specify a remote computer using an address such as 192.22.31.05.
The Domain Name System (DNS) maps IP addresses to alphabetic names. One of
the most important features of DNS is distributed management.
Each organization has the ability to control names within
its own domain. Domains are arranged in a hierarchy. For example, the XYZ
Company, Inc., may have names all ending in the following:
.xyz.com
The names could be further divided into several groups
such as the following:
For example,
abcvm.vm.xyz.com
might be the primary VM system at the XYZ Company, Inc. DNS enables
you to use a File Transfer Program command such as
ftp abcvm.vm.xyz.com
instead of
ftp 123.45.67.89
when transferring a file to this VM system.
Although it is possible to locate the mapping of host
addresses to host names in a file (for example,
/etc/hosts
on UNIX), DNS is more versatile than a system that maps
addresses to names in a file. Under a system that maps names to addresses,
the file containing the mapped names and addresses: must be replicated on
every host, does not have the capacity to contain the mappings for all computers
on a system as large as the Internet, and cannot be updated on a real-time
basis.
DNS uses server processes called name servers to stay current with the names assigned within a particular domain.
The network administrator provides the name servers with configuration files.
Each configuration file contains the mapping for the domain that it controls.
Name servers in a particular domain can refer to the addresses of name servers
for higher- and lower-level domains if the configuration files that they control
do not contain a particular name or address.
Name servers typically run on only a few machines in
an organization. Programs can use a set of routines, known as the resolver, to query their organization's name server. The resolver routines
are associated with the application and provide all the message formatting
and TCP or UDP communications logic necessary to talk to their organization's
name server.
DNS is general enough to allow distributed management
of other types of information, such as mailbox locations, and it does not
require any correspondence between domains and IP addresses or physical network
connections.
Copyright © 2001
by SAS Institute Inc., Cary, NC, USA. All rights reserved.
