Final answer:
DNS, or Domain Name System, is the system that translates an IP address into an FQDN. It includes a Reverse DNS lookup feature for finding the domain name associated with a given IP address. Other protocols listed, like DHCP, VPN, and HTTP, have different roles and aren't involved in domain name resolution.
Step-by-step explanation:
The system that enables the determination of a Fully Qualified Domain Name (FQDN) by knowing the IP address is the Domain Name System (DNS). DNS is essentially an internet service that translates IP addresses into FQDNs. This is crucial because while computers use IP addresses to communicate with each other, humans find it easier to use domain names. The translation process in the opposite direction, from an IP address to a domain name, is known as Reverse DNS lookup (rDNS).
When a user wants to reach a website, they type in a domain name, and it is the DNS that helps translate this into an IP address that the network can understand. Conversely, if someone needs to find the domain name associated with an IP address, rDNS within DNS is used. The other options listed such as DHCP (Dynamic Host Configuration Protocol), VPN (Virtual Private Network), and HTTP (Hypertext Transfer Protocol), serve different purposes within a network but are not used for domain name resolution from an IP address.