Which type of authoritative DNS zone maps IP addresses back to host names?

• A. Reverse Mapping
• B. Forward Mapping
• C. External Secondary
• D. Local Mapping

Answer: (A)

Mapping IP addresses back to host names is the reverse DNS concept. In DNS, the forward direction uses A and AAAA records to translate a name into an IP address. The reverse direction uses PTR records inside a reverse DNS zone to map an IP address back to its hostname. For IPv4, these records live under the in-addr.arpa domain (and for IPv6, under ip6.arpa). An authoritative reverse DNS zone contains the PTR records that provide the hostname for a given IP.

So this type of zone is about reverse mapping—from IPs to names—whereas forward mapping would use A/AAAA records to go from names to IPs. The other options describe different zone roles or don’t pertain to the direction of DNS lookups.