31.3 Name Resolution
DNS assists in assigning an IP address to one or more names and assigning
a name to an IP address. In Linux, this conversion is usually carried out
by a special type of software known as bind. The machine that takes care
of this conversion is called a name server. The
names make up a hierarchical system in which each name component is
separated by dots. The name hierarchy is, however, independent of the IP
address hierarchy described above.
Consider a complete name, such as
in the format
hostname.domain. A full
name, referred to as a fully qualified domain name
(FQDN), consists of a hostname and a domain name
(example.com). The latter
also includes the top level domain or TLD
TLD assignment has become quite confusing for historical reasons.
Traditionally, three-letter domain names are used in the USA. In the rest
of the world, the two-letter ISO national codes are the standard. In
addition to that, longer TLDs were introduced in 2000 that represent
certain spheres of activity (for example,
In the early days of the Internet (before 1990), the file
/etc/hosts was used to store the names of all the
machines represented over the Internet. This quickly proved to be
impractical in the face of the rapidly growing number of computers
connected to the Internet. For this reason, a decentralized database was
developed to store the hostnames in a widely distributed manner. This
database, similar to the name server, does not have the data pertaining
to all hosts in the Internet readily available, but can dispatch requests
to other name servers.
The top of the hierarchy is occupied by root name
servers. These root name servers manage the top level domains
and are run by the Network Information Center (NIC). Each root name
server knows about the name servers responsible for a given top level
domain. Information about top level domain NICs is available at
DNS can do more than just resolve hostnames. The name server also knows
which host is receiving e-mails for an entire domain—the
mail exchanger (MX).
For your machine to resolve an IP address, it must know about at least
one name server and its IP address. Easily specify such a name server
with the help of YaST. If you have a modem dial-up connection, you may
not need to configure a name server manually at all. The dial-up protocol
provides the name server address as the connection is made. The
configuration of name server access with SUSE® Linux Enterprise is described in
The Domain Name System.
The protocol whois is closely related to DNS. With
this program, quickly find out who is responsible for any given domain.