13-2 About the Domain Name System
About the Domain Name System
This section discusses key concept s of the domain name system.

Purpose of DNS

The domain name system maps domain names to information associated with these names, such as
IP addresses.

DNS Components

DNS components include:
• A distributed database consisting of domain names and associated information
• A hierarchical system of domain name servers that maintain the database and use it to respond to
requests for information about a particular domain name, such as its IP address
• Domain name resolvers that
— Accept requests from users
— Satisfy information requests by building and submitting properly formulated queries to one
or more name servers or by retrieving information from a local host file
— Return information to users
— Cache information for future use

Types of Name Servers

There are two types of name servers in the domain name system:
• Local servers maintain information for resources within a local zone. It is up to individual net-
work administrators to determine the scope of a local zone.
• Root servers maintain information in higher-level domains than do local servers.
Typically, when a user requires information about a domain name, the resolver queries a local server.
If local servers cannot provide the information, root servers are queried next.

Naming Conventions

Each node in the domain name system has a globally unique domain name that consists of its own
name, which is called a label, and the labels of all superior nodes.

DNS Name Example

Here is an example of a domain name. Note that labels are separated by periods:
mn07.amalgamated.com
In this example, mn07 is part of the higher-level domain called amalgamated.com.