In DNS, which record maps an IP address back to a hostname in reverse DNS?

In DNS, which record maps an IP address back to a hostname in reverse DNS?

• A. PTR
• B. A
• C. MX
• D. CNAME

Answer: (A)

PTR records enable reverse DNS by mapping an IP address back to a hostname. In forward DNS, A records map a hostname to an IPv4 address (and AAAA for IPv6). For reverse lookups, the IP is used within the reverse DNS zones (in-addr.arpa for IPv4 and ip6.arpa for IPv6) to retrieve the PTR record, which returns the canonical hostname. This mechanism is often used by mail servers and security checks to verify an IP is associated with a legitimate domain. The other options don’t fit because A maps name to address, MX specifies the mail server for a domain, and CNAME provides an alias for another name.

PTR records enable reverse DNS by mapping an IP address back to a hostname. In forward DNS, A records map a hostname to an IPv4 address (and AAAA for IPv6). For reverse lookups, the IP is used within the reverse DNS zones (in-addr.arpa for IPv4 and ip6.arpa for IPv6) to retrieve the PTR record, which returns the canonical hostname. This mechanism is often used by mail servers and security checks to verify an IP is associated with a legitimate domain. The other options don’t fit because A maps name to address, MX specifies the mail server for a domain, and CNAME provides an alias for another name.