Significant Resource Records (RR’s)

Significant Resource Records (RR’s)

The zone file that is consulted for each query received by a name server
and propagated throughout the zone on request, is compiled from a
variety of individual records known as Resource Records (RR’s). There
are many different types of RR’s each one performing a different
function and containing different information. The most significant of
these are listed and explained below.
Start Of Authority Record (SOA)
This is the first record in a zone. It is used to determine the version of
the zone file for the name server where it is kept. Each time a change
occurs within the zone file, e.g. a new host is added, the primary server
increments the serial number within this record. Other name servers for
the zone can then request the SOA and compare it to there own to
determine whether they require an updated zone file.
For the purposes of information gathering, this file also contains the email
address of the person responsible for administrating the zone.
Name Server Record (NS)
This record indicates the name servers authoritative for the zone. There
will be NS records for the primary and secondary name servers as well
as NS records for name servers authoritative for other zones so they can
be queried appropriately. Here is a NS record that would be found on
dns2, the primary name server for the sales zone (it is the sales zone as
this is the node closest to the root node, example):
sales.advertising.example.com IN NS dns3.advertising.example.com
The first field states which host or DNS domain this record belongs to.
The IN indicates that the default class, Internet, is used. NS defines this
record to be a name server record and the data field provides the name
of a name server.