Hello, Knock Knock, anyone there?

Sometimes you just need to know if anyone is home.

Call, text, knock, yell!

The computer equivalent to ‘Are you there’ in the Ping.

ICMP Ping to be exact.

Maybe you have seen Hunt For Red October where Sean Connery very dramatically said “Give me a ping, Vasili. One ping only, please.”  In the case of Hunt for Red October, the character played by Connery used echolocation, sound waves, to communicate with another submarine.  Normally it would be used by a ship or submarine to find submarines and other objects under the water.  The ship or submarine would send a ping, a sound signal, into the water and listen for the sound to be reflected back.  Based on the amount of time the sound takes to reflect back, the distance and direction of the submarine or object can be calculated.

A computer ping is similar.  A host sends an ICMP ping request to a destination IP address to see if it is “alive.”  The device at the remote IP address, if it exists, receives the request and sends an ICMP reply message back to the host that sent the request.  When the host that sent the ICMP request message receives the reply, they know that yes, the host at the remote IP is “alive” and responding.

Variations:
TCP Ping
UDP Ping

Related:
Traceroute