Domain Name System (DNS),  contains information about valid domain or sub-domain on the internet.  Each and every active web site has an IP address.  This IP address is the only way to reach a given web site using a given domain name.  A domain name server will use the name of the web site to lookup its actual IP address and other critical information that must be available to reach the servers which house a web site or other applications.

Major DNS Record Types

A Record:  This record is the “address” record which displays the IP address of a given web site or other domain entities.  The AAAA record is an IPV6 address record and maps a hostname to a 128-bit Ipv6 address.

The CNAME record stands for “canonical name”. This is often used to make one domain an alias of another domain.  CNAME is also used to map a new subdomains with an existing domain’s DNS records.

The MX record stands for “mail exchange”.  This is a list of mail  servers  used by he domain.

The PTR record stands for “pointer record”.  It maps an IPV4 address to the CNAME on the host.

The NS record stands for “name server” and indicates which Domain Name Server is authoritative for the domain.

SOA record stands for “State of Authority”.   It include information such as TTL (time to live),  domain server information, refresh time, retry time, expiration time and many other fields.

SRV record stands for “service” and is used to define a TCP service on which the domain operates.

A TXT record lets the administrator include any text in the  DNS record.   Among other uses, it is often used by webmaster utilities run by search engine companies  to validate ownership of a domain.