What is ICMP used for?

• A. Encrypts IP packets
• B. Translates domain names to IP addresses
• C. Error reporting and diagnostics (e.g., ping, traceroute)
• D. Provides end-to-end reliability

Answer: (C)

ICMP is the protocol used to report problems in the delivery of IP packets and to help diagnose connectivity. It carries messages that signal errors or provide diagnostic information, such as when a destination is unreachable or a packet’s time-to-live expires along the path. This is why tools like ping and traceroute rely on ICMP: ping sends an Echo Request and waits for an Echo Reply to verify reachability and measure round-trip time, while traceroute uses ICMP error or TTL-expired messages to learn the route packets take to a destination. ICMP does not encrypt packets, does not translate domain names to IP addresses, and does not provide end-to-end reliability (that role is handled by higher-layer protocols like TCP).