Page 776 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

the change, the change occurs on the hardware. When the OS

supports the change, the change is only in memory, but it looks like
a hardware change to all other network entities.

An IP address is temporary because it is a logical address and
could be changed at any time, either by DHCP or by an
administrator. However, there are instances where systems are
statically assigned an IP address. Likewise, computer names or
DNS names might appear permanent, but they are logical and thus

able to be modified by an administrator.

This system of naming and addressing grants each networking
component the information it needs while making its use of that

information as simple as possible. Humans get human-friendly
domain names, networking protocols get router-friendly IP addresses,
and the network interfaces get physical addresses. However, all three
of these schemes must be linked together to allow interoperability.
Thus, the Domain Name System (DNS) and the ARP system were
developed to interchange or resolve between domain names and IP

addresses or IP addresses and MAC addresses respectively. DNS
resolves a human-friendly domain name into its IP address equivalent.
Then, ARP resolves the IP address into its MAC address equivalent. It
is also possible to resolve an IP address into a domain name via a DNS
reverse lookup, if a PTR record is defined (see “Domain Name System”
later in this chapter).

The DNS is the hierarchical naming scheme used in both public and
private networks. DNS links IP addresses and human-friendly fully
qualified domain names (FQDNs) together. An FQDN consists of
three main parts:

Top-level domain (TLD)—The com in www.google.com

Registered domain name—The google in www.google.com

Subdomain(s) or hostname—The www in www.google.com

The TLD can be any number of official options, including six of the
original seven TLDs—com, org, edu, mil, gov, and net—as well as many

newer ones, such as info, museum, telephone, mobi, biz, and so on.