010-160 · Question #2
Reverse DNS assigns hostnames to IP addresses. How is the name of the IP address 198.51.100.165 stored on a DNS server?
The correct answer is B. In the PTR record for 165.100.51.198.in-addr.arpa.. Reverse DNS uses PTR records stored in the in-addr.arpa zone, with the IPv4 address written in reversed octet order to align with DNS hierarchy.
Question
Options
- AIn the A record for 165.100.51.198.ipv4.arpa.
- BIn the PTR record for 165.100.51.198.in-addr.arpa.
- CIn the CNAME record for 198-51-100-165.rev.arpa.
- DIn the AAAA record for 165.100.51.198.rev.
- EIn the REV record for arpa.in-addr.198.51.100.165.
How the community answered
(42 responses)- A7% (3)
- B74% (31)
- C2% (1)
- D14% (6)
- E2% (1)
Why each option
Reverse DNS uses PTR records stored in the in-addr.arpa zone, with the IPv4 address written in reversed octet order to align with DNS hierarchy.
A records perform forward lookups, mapping hostnames to IPv4 addresses, not the reverse, and ipv4.arpa is not a valid or standard reverse DNS zone.
PTR (pointer) records are the DNS record type designated specifically for reverse lookups, mapping an IP address back to a hostname. The in-addr.arpa zone is the IANA-defined namespace for IPv4 reverse DNS, and the octets of the IP address are reversed so that 198.51.100.165 becomes 165.100.51.198.in-addr.arpa, mirroring the way DNS delegation works from right (most general) to left (most specific).
CNAME records create canonical name aliases between hostnames and are never used for reverse DNS PTR lookups.
AAAA records are used for IPv6 forward lookups only, and rev.arpa is not a defined DNS zone for reverse resolution.
There is no REV record type defined in any DNS RFC; PTR is the only standard record type used for reverse DNS resolution.
Concept tested: Reverse DNS PTR records in in-addr.arpa zone
Source: https://www.rfc-editor.org/rfc/rfc1035
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