Page 777 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

There are also country variations known as country codes. (See
www.iana.org/domains/root/db/ for details on current TLDs and

country codes.) Note that the seventh original TLD was int, for
international, which was replaced by the two-letter country codes.

The registered domain name must be officially registered with one of
any number of approved domain registrars, such as Network Solutions
or 1and1.com.

The far-left section of an FQDN can be either a single hostname, such
as www, ftp, and so on, or a multisectioned subdomain designation,
such as server1.group3.bldg5 .mycompany.com.

The total length of an FQDN can’t exceed 253 characters (including
the dots). Any single section can’t exceed 63 characters. FQDNs can
only contain letters, numbers, and hyphens.

Every registered domain name has an assigned authoritative name
server. The primary authoritative name server hosts the original zone
file for the domain. Secondary authoritative name servers can be

used to host read-only copies of the zone file. A zone file is the
collection of resource records or details about the specific domain.
There are dozens of possible resource records (see
http://en.wikipedia.org/wiki/List_of_DNS_record_types); the most
common are listed in Table 11.6.

TABLE 11.6 Common resource records

Record Type Description

A Address Links an FQDN to an IPv4 address
record

AAAA Address Links an FQDN to an IPv6 address
record

PTR Pointer Links an IP address to a FQDN (for reverse
record lookups)

CNAME Canonical Links an FQDN alias to another FQDN
name

MX Mail Links a mail- and messaging-related FQDN to an
exchange IP address