Reverse DNS assigns hostnames to IP addresses. How is the name of the IP address 198.51.100.165 stored on a DNS server?A. In the A record for 165.100.51.198.ipv4.arpa.B. In the PTR record for 165.100.51.198.in-addr.arpa.C. In the RNAME record for 198-51-100-165.rev.arpa.D. In the ARPA record for 165.100.51.198.rev.E. In the REV record for arpa.in-addr.198.51.100.165.

The name of the IP address 198.51.100.165 is stored on a DNS server in the PTR record for 165.100.51.198.in-addr.arpa. So, the correct answer is B. "In the PTR record for 165.100.51.198.in-addr.arpa."

Here's a step-by-step explanation:

1. Reverse DNS (rDNS) is a method of resolving an IP address into a domain name, just as the domain name system (DNS) resolves domain names into associated IP addresses.

2. One of the applications of reverse DNS is as a spam filter. Here's how it works: Suppose you receive an email from the IP address 198.51.100.165. You can use reverse DNS to check which domain name is associated with this IP address.

3. The way reverse DNS entries are stored is slightly different from 'forward' DNS entries. For an IP address like 198.51.100.165, the reverse DNS entry would be stored as a PTR record for the reversed IP address followed by '.in-addr.arpa'.

4. So, for the IP address 198.51.100.165, the reverse DNS entry is stored as a PTR record for 165.100.51.198.in-addr.arpa.

5. Therefore, the correct answer is B. "In the PTR record for 165.100.51.198.in-addr.arpa."

The name of the IP address 198.51.100.165 is stored in the PTR record for 165.100.51.198.in-addr.arpa. This is how reverse DNS works, it uses PTR records (pointer records) to map IP addresses to domain names. The IP address is reversed and appended with in-addr.arpa. in IPv4 and ip6.arpa. in IPv6.