Overview of DNS

The Domain Name System (DNS) is the mechanism by which a domain name is automatically translated into its corresponding IP address for use by the Internet.

The Domain Name System (DNS) uses the DNS service to make these translations or lookups.

# Lookups

The DNS maintains a database that enables resolution of domain names to their corresponding IP addresses (forward lookup) and IP addresses to their corresponding domain names (reverse lookup).

# Zones

A zone is a section of the domain name space that is represented by the data stored on a particular name server. The name server has authority over that particular zone, or the particular section of the domain name space described by that data. The DNS server manages the lookups for one or more domain name spaces.

# Records

The DNS server also maintains a list of all domain names and their associated IP addresses. The elements on this list are known as records. Once you have created a zone, you add records to that zone. A zone can contain the following types of records:

- Host or Address (A) record. A record that translates a domain or sub-domain to its IP Address. There should be one A record for each host address.

- Alias or Canonical (CNAME) record. A record that specifies to the DNS server that any requests made to the alias name must be redirected to the host to which the alias points. The target host does not have to be within the local domain.

- Mail Exchanger (MX) record. A record that specifies which mail server should process the email messages for that domain.

- Name Server (NS) record. A record that specifies the host name of a DNS server that is authoritative for the domain. A DNS zone requires at least one NS record. If there is only one NS record in a zone, it cannot be removed.

- Pointer (PTR) or Reverse record. A record that associates an IP address with a canonical or alias name. PTR records are used to convert IP addresses to host names. This is known as reverse lookup.

- Start of Authority (SOA) records. The Start of Authority (SOA) record contains information about the DNS zone and its records. Each zone contains a single SOA record. When you add a zone for a domain, an SOA record is automatically created.

The SOA record:

- Designates the start of the zone and specifies where in the domain name space the name server has authority.

- Provides contact information for a zone. Every zone’s SOA record contains the email address of the zone’s technical contact.