If a packet gets “sucked down a black hole” (figuratively speaking) and is not received by its sender, and no message is sent back explaining the situation, then something is wrong. The failure to send a message means something is wrong with the _____.

ICMP is used to send network error and diagnostic messages, such as notifications that a packet could not be delivered. If a packet disappears and no message reports the problem, the failure concerns ICMP. TCP/IP is the broader networking suite, while HTTP handles web communication.

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