Active Directory, 3rd Edition

Creating and Manipulating Resource Records

Resource records are the basic unit of information in DNS. A DNS server's primary job is to respond to queries for resource records . Most people don't realize they are generating resource record queries with nearly every network-based operation they do, including accessing a website, pinging a host via its Fully Qualified Domain Name (FQDN), or logging into Active Directory.

Resource records come in many different flavors or types. Each type corresponds to a certain type of name or address lookup. Each record type also has additional information encoded with the record that represents things such as the time to live of the record. The following is a textual example of what a CNAME record looks like:

www.mycorp.com.  1800  IN  CNAME  www1.mycorp.com.

Or, more generically:

Owner  TTL  Class  Type  RR-Data

Now let's break down the record into its individual parts:

Owner

The owner of the resource record. This field is typically what is specified during a query for the particular type.

TTL

The time to live, or length of time a nonauthoritative DNS server should cache the record. After the TTL expires, a nonauthoritative server should requery for an authoritative answer.

Class

Resource record classification. In nearly all cases, this will be "IN" for Internet.

Type

Name of the resource record type. Each type has a standard name that is used in zones (e.g., CNAME, A, PTR, SRV).

RR-Data

Resource record specific data. When you perform a query, you are ...