What does a PTR (Pointer) record do?

What does a PTR (Pointer) record do?

• A. Resolves a domain name to an IP address.
• B. Resolves an IP address to a domain name.
• C. Stores MX records for email.
• D. Assigns an IP address to a device via DHCP.

Answer: (B)

PTR records are used for reverse DNS lookups: they map an IP address back to a domain name. In DNS you usually look up a domain to find its IP (forward mapping with A or AAAA records), but a PTR lookup does the opposite—given an IP, it reveals the associated hostname if a PTR exists in the reverse DNS zone. For IPv4, the lookup lives under the in-addr.arpa domain with the IP octets reversed; for IPv6, it's in the ip6.arpa domain with the address nibble-reversed. This is commonly used by mail servers and logging to verify who is connecting from a given IP. The other options describe forward name resolution, email routing records stored as MX, or DHCP-based IP assignment, which are not what PTR records accomplish.

PTR records are used for reverse DNS lookups: they map an IP address back to a domain name. In DNS you usually look up a domain to find its IP (forward mapping with A or AAAA records), but a PTR lookup does the opposite—given an IP, it reveals the associated hostname if a PTR exists in the reverse DNS zone. For IPv4, the lookup lives under the in-addr.arpa domain with the IP octets reversed; for IPv6, it's in the ip6.arpa domain with the address nibble-reversed. This is commonly used by mail servers and logging to verify who is connecting from a given IP. The other options describe forward name resolution, email routing records stored as MX, or DHCP-based IP assignment, which are not what PTR records accomplish.