The ping Command
Checking for Connectivity with Ping
The ping command exists to test connectivity. It sends a series of packets to one destination IP address. The packets mean basically “if you get this packet, send a reply back.” Each time the sender sends the request, and the other host sends a reply, the ping command knows a packet made it from the source host, to the destination, and back.
More formally, the ping command uses the Internet Control Message Protocol (ICMP), specifically the ICMP Echo Request and ICMP Echo Reply messages. ICMP defines many other messages as well, but these two messages were made specifically for connectivity testing ...
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