16.1. DNS resource records
On a large network, such as the Internet, it would be impractical to identify each system solely by its numerical Internet Protocol (IP) address. Names are more convenient; they help users and administrators locate network resources more easily. The Domain Name Service (DNS) is a distributed database holding the alphanumeric names and their corresponding IP addresses (and more) of every registered system on a Transmission Control Protocol (TCP)/IP network, such as the Internet or the IP Multimedia Subsystem (IMS). Each entry is referred to as a Resource Record (RR).
The alphanumeric names, better known as domain names, are hierarchical in nature where country, company, department and even a host (machine) name can be identified. Each step in the hierarchy is identified as a zone. The domain name below identifies a machine named pc27 in the engineering department of an Australian company called Foobar:
pc27.engineering.foobar.com.au
An entry in a DNS server that maps a domain name to an IP address is referred to as an address record, or A record. For IPv6 these records are referred to as AAAA records.
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