What is ICMP used for?

• A. Error reporting and network diagnostics.
• B. Data transfer
• C. Flow control
• D. Authentication

Answer: (A)

ICMP is used for error reporting and network diagnostics. It carries control messages between hosts and routers to signal problems or confirm reachability, rather than delivering application data. For example, Echo Request/Reply is used by ping to test whether a host is reachable and to measure round-trip time. Other ICMP types report issues, such as Destination Unreachable when a packet can’t be delivered or Time Exceeded when a packet’s TTL expires. This makes ICMP a tool for diagnosing network problems, but it does not move user data (that’s what TCP/UDP do), and it doesn’t provide flow control or authentication.