Host And Domain Names; Overview; Host Tables - HP ProCurve 7000dl Series Basic Management And Configuration Manual

Domain Name System (DNS) Services

Overview

Overview
Domain Name System (DNS) is the Internet protocol for translating domain
names or hostnames into IP addresses. The hostname is the familiar, alpha-
numeric name for a host on the Internet (for example, www.hp.com), and the
IP address is the 32-bit address that machines use to reach each other. DNS
allows users to enter more readily memorable and intuitive hostnames rather
than IP addresses. It also allows a host to keep the same hostname even if it
changes its IP address.

Host and Domain Names

The domain name of a single host is also called a hostname. A hostname is
typically made up of at least three domain levels. For example, the top-level
domain of www.hp.com is "com." The Internet is divided into hundreds of top-
level domains. The most common include com, gov, org, and two-letter codes
for every country.
There are millions of first-level domains (hp, in our example), each designating
an organization. When you want to reserve a domain name, you work through
the proper channel for your top-level domain. The top-level organization
ensures that every first-level domain in the top-level domain is unique.
The second (or third or fourth) domain level refers to the specific machine.
For example, www often identifies a domain's Web server. An organization
can subdivide its domain, so a hostname might include four or more levels.

Host Tables

In the very early days of the Internet, Stanford Research Institute's Network
Information Center (SRI-NIC) maintained a single host table mapping all
hostnames in the Internet to their IP addresses. Individual network adminis-
trators would download new entries to their name servers. However, as the
Internet exploded with new domains, SRI-NIC simply could not manage all
the new entries, nor could name servers hold them all.
DNS distributes host tables throughout many DNS servers or name servers.
The host table is divided into many zones, and each name server only holds
the information for a few zones. Every organization maintains the host table
for its own domain on its name server or servers. It is up to the organization
to keep its own information accurate and up to date.
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