Terminology Index

Glossary

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ICMP

Internet Control Message Protocol: a network protocol used for diagnostics and error messages (such as ping and unreachable notifications). Defenders watch it because attackers can abuse it for scanning, tunneling, or covert channels.

ICMP carries control and diagnostic messages between network devices, underpinning tools like ping and traceroute and signaling conditions like unreachable hosts. While essential, it is also security-relevant: attackers use it to map networks (ping sweeps), and can tunnel data or command-and-control inside ICMP packets to evade controls. Understanding ICMP helps defenders interpret network behavior and recognize its abuse, and decide where to limit or monitor it.

Introduced in: Networking Foundations

Examples

  • Using ping (ICMP echo) to test whether a host is reachable.
  • Spotting an ICMP ping sweep used to map a network.
  • Detecting data smuggled inside ICMP packets as a covert channel.