A (host) Contains name-to-IP address mapping information, which is used to map a DNS domain name to a host IP address on the network. An A resource record is also referred to as a host record.NS (name server) Designates the DNS domain names for the servers that are authoritative for a certain zone or that contain the zone file for that domain.
CNAME (canonical name) Allows you to provide additional names to a server that already has a name in an A resource record. For example, if the server called webserver1.nwtraders.msft hosts the Web site for nwtraders.msft, this server must have the common name http://www.nwtraders.msft. A CNAME resource record is also referred to as an alias record.
MX (mail exchanger) Specifies the server to which e-mail applications can deliver mail. For example, if you have a mail server running on a computer named mail1.nwtraders.msft and you want all mail for firstname.lastname@example.org to be delivered to this mail server, the MX resource record must exist in the zone for nwtraders.msft and must point to the mail server for that domain.
SOA (start of authority) Indicates the starting point or original point of authority for information stored in a zone. The SOA resource record is the first resource record created when you add a new zone. It also contains several parameters used by other computers that use DNS to determine how long they will use information for the zone and how often updates are required.
PTR (pointer) Used in a reverse lookup zone created in the in-addr.arpa domain to designate a reverse mapping of a host IP address to a host DNS domain name.
SRV (service) Registered by services so that clients can locate a service by using DNS. SRV records are used to identify services in Active Directory and are also referred to as Service Location records.
NS Resource Records
The name server (NS) resource record indicates the servers authoritative for the zone. They indicate primary and secondary servers for the zone specified in the SOA resource record, and they indicate the servers for any delegated zones. Every zone must contain at least one NS record at the zone root.