Resource Contents
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 RDATANAME: 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
| TYPE | RDATA | Example |
Description |
| A | Dotted quad | 206.102.12.130 |
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 | 2001:6B0:1:EA:A00:20FF:FE8F:708F |
Contains the IPv6 (post-experimental replacement for IPv4) equivalent of A. |
| NS | Domain name | dns2.easystreet.com. |
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 | dns1.easystreet.com. 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) ) |
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 | 100 smtp.easystreet.com. |
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. |
| CNAME | Domain name | easystreet.com. |
A canonical domain name for the queried domain. The specified domain is considered equivalent to the queried domain for mailers and other programs. |
| PTR | Domain name | easystreet.com. |
A pointer to another domain. Similar to CNAME, except that the queried domain is not equivalent to the referenced domain. |
| TXT | Arbitrary text | "You" "should" "follow" "standards" "and" "use" "www." |
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. | |
| MD | Domain name | mail.easystreet.com. |
Mail destination capable of acting as a mail agent and accepting mail for the domain. |
| MF | Domain name | mail.easystreet.com. |
Mail forwarder capable of accepting mail and sending it to another system. |
| HINFO | CPU type string, OS type string | "sun-ultra1" "unix" |
Host information used by some special software. |
| MINFO | RMAILBX, EMAILBX | mail.easystreet.com. mail.easystreet.com. |
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. |
Examples
| NAME | TTL | CLASS | TYPE | RDATA |
| easystreet.com. | 3600 | IN | NS | dns1.easystreet.com. |
| easystreet.com. | 3600 | IN | NS | dns2.easystreet.com. |
| easystreet.com. | 3600 | IN | NS | dns3.easystreet.com. |
| 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) ) |
| easystreet.com. | 3600 | IN | A | 206.102.12.130 |
| easystreet.com. | 3600 | IN | MX | 100 smtp.easystreet.com. |
| easystreet.com. | 3600 | IN | MX | 120 mxqueue.easystreet.com. |