How does the ping utility relate to ICMP?

• A. Ping uses ICMP Echo Request and Echo Reply messages to test reachability.
• B. Ping uses TCP connections to test reachability.
• C. Ping uses UDP packets.
• D. Ping uses ICMP Destination Unreachable messages to test.

Answer: (A)

Ping relies on ICMP to test reachability. It sends an ICMP Echo Request to a target, and if the destination is reachable and willing to respond, it replies with an ICMP Echo Reply. The time between sending the request and receiving the reply gives you the round-trip time, and whether you get a reply at all indicates reachability. This behavior uses ICMP, not TCP or UDP, which are different transport-layer protocols. Destination Unreachable messages do exist in ICMP as error signals, but they’re not how ping operates in its normal test; they’re only responses when a destination can’t be reached. So the best description is that ping uses ICMP Echo Request and Echo Reply messages to test reachability.