What is the purpose of a PTR record?

• A. Mapping a hostname to an IP address
• B. Mapping an IP address to a hostname
• C. Providing routing information
• D. Storing DNS zones

Answer: (A)

PTR records are for reverse DNS lookups: they map an IP address back to a hostname. This is the opposite of how A records work, which map a hostname to its IPv4 address (and AAAA records map to IPv6). PTR records live in special reverse zones (in-addr.arpa for IPv4 and ip6.arpa for IPv6) and are commonly used by mail servers and other services to verify who is connecting, aiding in trust, logging, and anti-spam checks. They do not map hostnames to IPs, nor are they used to route traffic or to store DNS zones.