What is a…
The A Record, (Address Record or IP Address), for a domain name is used to specify the physical address on the Internet that a user must connect to in order to use the information associated with that domain name, such as web site files or other types of data. For instance, if a web site for the domain name exampledomainname.com exists at the address 184.108.40.206, the IP Address for that domain name will be set to 220.127.116.11 in the zone file on that domain name's authoritative DNS.
The AAAA Record, (Address Record or IP Address), is very similar to an A record in that it is used to associate a domain name with the IP address of the corresponding service (i.e. a website such as www.register.com <http://www.register.com > ). However, these records are used to specify an IPv6 (Internet Protocol version 6) address record rather than an IPv4 (Internet Protocol version 4) address record as the A Record does. AAAA records are 128 bits in length and are typically represented in hexadecimal notation as such: 2001:06b0:1:00ea:0202:a5ff:fecd:13a6.
A CNAME (Canonical Name or Domain Alias) section of a zone file, is an extension to a domain name that allows the creation of derivatives of the domain name which can be pointed to the same (or any other) domain name on the Internet. An example of a Domain Alias is www.register.com points to Register.com, where "www" functions as the Domain Alias and accesses the same web site as Register.com.
The MX Record, (Mail Exchange Record), is the section of a domain name's zone file whose entries specify the mail server(s) on the Internet responsible for email distribution for a specific domain name. Any mail sent to an email address at a domain name must be routed on the Internet through the mail servers specified in the MX Record for that domain name, in order to reach the recipient.
TXT records are used to describe an entry in a zone file. The description can be anything that fits into 255 characters or less. TXT records are often used to support Sender Policy Framework, (SPF), an authentication system for email.
SRV (service) records allow flexibility and stability to services making use of them. Like a "general use" MX record, the SRV records relate to a particular service of the domain, like FTP or SIP, rather than a specific machine the way A or C-name records do.
Several programs are starting to make use of SRV records for such purposes as FTP, telnet and security applications, and they are commonly used for newer applications such as voice over IP.
A cluster of computers can be specified for a given service, with differing priority and "weighting" assigned, so a system or server administrator can specify both the order in which the machines are queried and the proportion of requests each server would handle. This allows a slower machine to take a smaller amount of the traffic, creating a greater efficiency of the service, and in other words, balancing the traffic load.
The PTR Record (Pointer or Reverse Record) can be thought of as the opposite of an A Record. This is what allows a reverse DNS lookup, (where an IP Address is used to map, or determine what your host/domain name is).
Not every IP address has a corresponding PTR record, however they are sometimes required for diagnostic or security purposes. PTR records are added to reverse zones.