DNS-SERVER & DNS-RECORDS

DNS is the Domain Name System. DNS converts machine names to the IP addresses that
 all machines on the net have. It translates (or "maps") from name to address and from address
 to name, and some other things. A mapping is simply an association between two things,
 in this case a machine name, like ftp.domainname.org, and the machine's IP number
 (or address) 192.168.X.X. DNS also contains mappings the other way, from the IP number
 to the machine name; this is called a "reverse mapping".  DNS is a directory of resource
 records organized as a tree.

DNS Records

Records	Description
1.A {Address} records	DNS A resource records map host names to their 32 bit IPv4 address. The A record mainly associate a hostname with an IP address,  It also used for storing subnet mask.
2.AAAA records	DNS AAAA resource records map hostnames to their 128 bit IPv6 address.
3.PTR {pointer} records	DNS PTR resource records map IP address to their corresponding hostname. The most common use is for implementing reverse DNS lookups.
4.CNAME {canonical name} records	DNS CNAME resource records denote the “canonical name”. It create an Alias of one name to another which maps a name to another hostname which has an A or AAAA records.  This helps when running multiple services {like a FTP  server & a web server, each running on different posts}  from a single IP address. Each service can have its own entry in DNS server {like ftp.domainname.com.& www.domainname.com .}.  Network administrators also use CNAMEs when running multiple HTTP servers on the same port, with different names, on the same physical host. The DNS lookup will continue by retrying the lookup with the new name.
5.DNAME {delegation name} records	DNAME creates an alias for a name and all its sub-names, unlike CNAME, which aliases only the exact name in its  label. Like the CNAME record, the DNS lookup will continue  by retrying the lookup with the new name.
5.MX records	DNS MX resource records denote the “MAIL EXCHANGER”.  It used to maps a domain name to a list of message transfer agents  {MTAs} for that domain. The MX records specifies a  mail server responsible for accepting email messages on  behalf of a recipient’s domain and a preference value used to  prioritize mail delivery if multiple mail servers are available.  The set of MX records of a domain name specifies how  email should be routed with the Simple Mail Transfer Protocol  {SMTP}.
6.NS records	DNS NS resource records denote the authoritative name  server for a domain. All public masters & slave servers  should have a NS record for the domains zones they manage.
7.SOA records {start of authority record}	Specifies authoritative information about a DNS zone, including  the primary name server, the email of the domain administrator , the domain serial number, and several timers relating to refreshing  the zone.