Question 5

The name of the IP address 198.51.100.165 is stored in the PTR record for 165.100.51.198.in-addr.arpa.

The name of the IP address 198.51.100.165 is specifically stored in the PTR record for the reverse DNS entry 165.100.51.198.in-addr.arpa. This format is used to map an IP address back to its corresponding hostname.

A) In the A record for 165.100.51.198.ipv4.arpa.

This option is incorrect because the A record is used for forward DNS lookups, mapping hostnames to IP addresses, rather than reverse lookups. The correct format for reverse DNS entries involves the PTR record, not the A record.

B) In the PTR record for 165.100.51.198.in-addr.arpa.

This option is correct because PTR records are specifically designed for reverse DNS lookups. The address 198.51.100.165, when reversed, becomes 165.100.51.198, and is stored under the in-addr.arpa domain using a PTR record.

C) In the RNAME record for 198-51-100-165.rev.arpa.

This option is incorrect as RNAME records are used in certain DNS configurations to specify a responsible person's email address for a domain, rather than for mapping IP addresses to hostnames. The correct record type for reverse lookups is the PTR record.

D) In the ARPA record for 165.100.51.198 rev.

This option is incorrect because there is no specific "ARPA" record that stores hostname information. Reverse DNS uses PTR records within the in-addr.arpa domain, making this option misleading.

E) In the REV record for arpa.in-addr.198.51.100.165.

This option is incorrect as there is no standard DNS record type known as a "REV" record. Reverse DNS lookups are handled by PTR records, not by any record labeled REV.

Conclusion

The correct answer is definitively B, as it accurately describes the storage of the hostname associated with the IP address 198.51.100.165 using a PTR record in the specified format. All other options fail to align with the correct DNS record types and their purposes, specifically confusing forward and reverse lookup functions.