The Internet Control Message Protocol (ICMP) is one of the simplest yet most important diagnostic tools in networking. This episode explains how ICMP is used for basic network health checks, including the ubiquitous ping and traceroute utilities. You’ll learn about echo requests and replies, time exceeded messages, and destination unreachable codes that help identify where and why communication is failing.

We also explain how ICMP is sometimes blocked or rate-limited for security reasons, and how this can complicate troubleshooting. Understanding ICMP allows you to interpret connectivity tests accurately and identify whether packet loss, firewall rules, or routing loops are the cause of problems. This protocol forms the basis of nearly every first troubleshooting step and is a must-know for the Network Plus exam and beyond.