### About the Domain Name System

This section discusses key concepts 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 network 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.