Any answer from a DNS nameserver query takes the form of a resource record (generally referred to as an RR).
Resource records look like this:
NAME TTL CLASS TYPE RDATA
NAME: The host is that which is being queried. If we were querying dns1.easystreet.com for “www.easystreet.com”, “www.easystreet.com” would be the NAME.
TTL: Time To Live is a 32-bit integer stating how long in seconds a nameserver or the user making the query should cache the results returned for this record. Values of zero in this section declare the record uncachable.
CLASS: This is assumed to be 1 or IN in all cases. Other classes (CSNet (2), BIND’s Chaos (3), MIT’s Hesiod (4)) are essentially deprecated and unlikely to be found.
TYPE: Any one of many possible RR types (RRTs). A fairly full listing of relevant TYPES can be found on IANA.
RDATA: Dependent upon RRT and described below.
Resource Record Types
||Contains the IPv4 address that the domain resolves to. If there are multiple, generally a random one is chosen by the system making the query to use.|
|AAAA||hexadecimals seperated by colons||
||Contains the IPv6 (post-experimental replacement for IPv4) equivalent of A.|
||Contains the domain name a nameserver of the domain. Any domain must have at least two nameservers.|
|SOA||Domain name of primary, domain name of hostmaster, serial, refresh, retry, expiration, default time to live||
||Start of a zone of authority. This declares a nameserver which is “authoritative” for the domain; any queries (about any domains under the authority) sent to this nameserver will be firsthand and accurate, not cached.|
|MX||Preference number, domain name||
||The domain specified is designed to deal with all email sent to NAME. Also given is a mailing priority in case one machine rejects or fails to respond to sent emails. “1” is first priority.|
||A canonical domain name for the queried domain. The specified domain is considered equivalent to the queried domain for mailers and other programs.|
||A pointer to another domain. Similar to CNAME, except that the queried domain is not equivalent to the referenced domain.|
||Descriptive text for the queried domain.|
|NULL||Unstandardized data||Space used when testing experimental DNS functions. The “NULL” record can safely be ignored by users and isn’t allowed on master servers.|
||Mail destination capable of acting as a mail agent and accepting mail for the domain.|
||Mail forwarder capable of accepting mail and sending it to another system.|
|HINFO||CPU type string, OS type string||
||Host information used by some special software.|
||Mailing information generally used for mailing lists. RMAILBX is the responsible mail box used for the mailing list, EMAILBX is the error mail box to which problems are sent.|
|easystreet.com.||3600||IN||SOA||hostmaster.easystreet.com. ( 2003042840 ;serial (version) 14400 ;refresh period (4 hours) 900 ;retry interval (15 minutes) 604800 ;expire time (1 week) 3600 ;default ttl (1 hour) )|