No doubt we could come up with other examples. Most of us will not need to
set up or run a DNS server, but you are the type of person who reads books
like Ubuntu Unleashed, so you probably like to tinker with technology. It is
likely that most people reading this just want to play something new and have
some fun. This chapter will get you started.
Understanding Domain Names
Simply put, a domain name is a string of characters that is used to represent
an IP address. Domain names are intended to be easier to remember than
strings of numbers. Generally, they are set up as a set of letters separated by
dots. Each of these sets of letters is called a label. The label on the far right
denotes the widest group, or top-level domain (TLD). Each label to the left is
a subdomain of the one to the right of it. news.google.com is an example.
Here we see three labels:
The top-level domain here is com. The original set of top-level domains
is com, edu, gov, mil, net, and org. Other top-level domains include
country-code TLDs such as uk or in, sponsored TLDs like aero for
the Société Internationale de Télécommunications Aéronautiques, and
geographic TLDs like asia. Others also exist. All TLDs are controlled
by a group called ICANN, the Internet Corporation for Assigned Names
and Numbers, with which domain names must be registered to work on
the Internet (see www.icann.org). The TLD generally defines, with
varying firmness, the content permitted on subdomains; some TLDs are
far more controlled than others.
The first subdomain, in this case google, is called the root zone. The
root zone is required to create a fully qualified domain name (FQDN),
which is the combination of the root zone and the TLD. When you
register a domain name with a registrar, so you can put a website on the
Internet, you register a root zone for a TLD, as in
matthewhelmke.com or matthewhelmke.net. The complete
FQDN is required for DNS to work across the Internet.
After the first subdomain, others may be created, such as news in our
example. These are optional. Some standard ones are www, mail, and
ftp, which each denote specific uses for defined subdomains. They are
not required, but if you want to host more than one thing using a FQDN,
you must define and use subdomains. Subdomains are defined in a DNS
server in the same manner as TLDs.