Which utility makes use of ICMP to function?

The utility that makes use of ICMP (Internet Control Message Protocol) to function is traceroute. Traceroute is designed to map the route that packets take from one network device to another, providing information about the path as well as the time it takes for each hop along the way. It works by sending ICMP echo request packets or UDP packets to the destination and analyzing the ICMP time-exceeded messages that are returned from intermediate routers. This allows traceroute to determine all the gateways that the packets pass through.

In contrast, ping is also a utility that uses ICMP to determine whether a specific IP address is reachable, but it does not map the route taken by packets. Nslookup is used for querying DNS to obtain domain name or IP address mapping information, and it does not use ICMP. Netstat provides information about network connections, routing tables, and interface statistics, and is unrelated to ICMP as well. Thus, while both ping and traceroute use ICMP, traceroute specifically does so to trace the path taken by packets, making it the correct answer in this context.