Which DNS record is used for reverse DNS lookups to map an IP address back to a hostname?

Which DNS record is used for reverse DNS lookups to map an IP address back to a hostname?

• A. Pointer Record (PTR)
• B. Canonical Name (CNAME)
• C. Name Server (NS) record
• D. Address (A) record

Answer: (A)

Reverse DNS uses a Pointer record to map an IP address back to a hostname. In DNS, forward lookups resolve a hostname to an address using A (IPv4) or AAAA (IPv6) records. For reverse lookups, the IP is encoded into a special domain: for IPv4, the address is written in reverse order and appended to in-addr.arpa (for example, 23.113.0.203.in-addr.arpa for 203.0.113.23); for IPv6, the nibbles are reversed and appended to ip6.arpa. The Pointer record in that reverse zone then maps that reverse-domain name to the canonical hostname, enabling a reverse lookup from IP to name. So, a PTR record is the one that provides the hostname corresponding to an IP address. Other records like A map a hostname to an IP, CNAME aliases one name to another, and NS identifies authoritative name servers, which is why they don’t handle reverse IP-to-hostname lookups. Note that not every IP has a PTR record; reverse DNS can be absent or intentionally unconfigured.

Reverse DNS uses a Pointer record to map an IP address back to a hostname. In DNS, forward lookups resolve a hostname to an address using A (IPv4) or AAAA (IPv6) records. For reverse lookups, the IP is encoded into a special domain: for IPv4, the address is written in reverse order and appended to in-addr.arpa (for example, 23.113.0.203.in-addr.arpa for 203.0.113.23); for IPv6, the nibbles are reversed and appended to ip6.arpa. The Pointer record in that reverse zone then maps that reverse-domain name to the canonical hostname, enabling a reverse lookup from IP to name.

So, a PTR record is the one that provides the hostname corresponding to an IP address. Other records like A map a hostname to an IP, CNAME aliases one name to another, and NS identifies authoritative name servers, which is why they don’t handle reverse IP-to-hostname lookups. Note that not every IP has a PTR record; reverse DNS can be absent or intentionally unconfigured.