In what cases is the ICMP protocol used in networks?

The ICMP (Internet Control Message Protocol) is used in networks for transmitting control messages between devices. Main use cases of ICMP:

• Network diagnostics — commands like ping and traceroute use ICMP to check the availability of nodes and determine the route.

• Error messages — if a packet cannot be delivered (for example, due to host unavailability, TTL expiration, routing errors), ICMP sends a corresponding notification to the sender.

• Flow control — ICMP can inform about congestion conditions or the need to slow down transmission.

ICMP is not used for transmitting user data but serves for network control and management.

Example: when executing the ping command, ICMP Echo Request packets are sent, and ICMP Echo Reply is received in response, allowing to check if the remote host is reachable.