contain the resource records such as A, AAAA, CNAME, MX, SRV, TXT
e.g.,
given a name record, a forward lookup returns an IP address
MX record returns a host record associated with the domain’s mail service
reverse lookup
aka reverse DNS querying
returns the host name associated with a given IP address
info is stored in a reverse lookup zone as a pointer (PTR) record
uses a special domain name by the first three octets of IP addresses in the zone in reverse order and appended with in-addr.arpa
name server is configured with a reverse lookup zone
zone contains PTR records consisting of the final octet of each host record
e.g., reverse lookup for a host record containing the IP address 198.51.100.1 is 1.100.51.198.in-addr.arpa
IPv6 uses the ip6.arpa domain
each of the 32 hex characters is expressed in reverse order as a subdomain
e.g., 2001:0db8:0000:0000:0bcd:abcd:ef12:1234 is represented by the pointer record: 4.3.2.1.2.1.f.e.d.c.b.a.d.c.b.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa