A resource record

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An A Resource Record is used to assign an IPv4 address to a DNS name . A resource records are the most common resource records in the DNS .

In addition to the host IP address assignment, A RRs are also used for DNSBLs or to specify subnet masks for backward resolutions in accordance with RFC 1101 .

The corresponding record type for IPv6 is AAAA .

construction

Name
published name
TTL
time to live : indicates how long in seconds this resource record may be valid in a cache (optional; if not specified, a previously explicitly defined default value is assumed - via a $ TTL statement at the beginning of the zone file )
IN
class: Internet (optional; alternatives are the classes HSfor HESIOD and CHfor CHAOS, two experimental network projects that have been obsolete for a long time; INassuming no information )
A
Record Type
Length
the length of the entry, in this case 4 for the 4 bytes of the IP address .
Adresse
the IP address at which the searched server can be reached

example

www.example.com.   3600  IN  A  172.27.171.106

Put equivalent: 

$TTL 3600
$ORIGIN example.com.
www    A  172.27.171.106

See also