11.4 Resource Records

Information on domain names and their IP addresses, as well as all the other information distributed via DNS is stored in the memory of name servers as Resource Records (RRs).

A name server (also referred to as a DNS server) loads data into its memory in several ways. Authoritative data are read from files on a disk or obtained via a zone transfer query from another server’s memory. Nonauthoritative data are obtained by the server from other servers’ memory as it answers individual DNS queries.

If a DNS client needs to obtain information from a DNS, it requests RRs from the DNS according to its requirements, i.e., a client can request from a domain server an A type RR with the IP addresses of the particular domain name. A client can be a resolver or a name server that cannot resolve the query on its own.

Each RR has the same structure in DNS protocol. The RR structure is shown in the following figure:

Figure 11.3: Resource Record structure

Each RR field...