Ping Command Basics
The ping command tests connectivity by sending packets to an IP address, expecting the device at that address to send packets back. The command sends packets that mean “if you receive this packet, and it is addressed to you, send a reply back.” Each time the ping command sends one of these packets and receives back the message sent back by the other host, 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 by commands like ping. ...
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