What is a common ICMP message type?

• A. Echo request/reply (ping)
• B. Destination unreachable
• C. Time exceeded
• D. Redirect message

Answer: (A)

ICMP is used for diagnosing reachability and reporting problems in IP networks. The most familiar and widely used ICMP message pair is the Echo Request and Echo Reply, which power the ping utility. A host sends an Echo Request to a destination, and if the destination is reachable, it responds with an Echo Reply. This simple exchange lets you quickly verify that a host can be reached and measure round-trip time, making it the most common ICMP message type people rely on for basic network checks. Other ICMP types like Destination Unreachable, Time Exceeded, or Redirect are important for signaling specific issues or routing hints, but they aren’t as universally recognized for everyday reachability testing as the ping exchange.