The ping command sends one or more requests to a system asking for a response. It’s typically used to check that a system is up and running, verify an IP address, or prove that the sending system can reach the remote one (i.e., verify the route). The ping command is also one that network intruders often use as a first step in identifying systems on a network that they might next want to attack. In this post, we’re going to take a quick look at how ping works and then examine options for configuring systems to ignore these requests.
How ping works
The name “ping” came about because the ping command works in a way that is similar to sonar echo-location which used sound propogation for navigation. The sound pulses were called “pings”. The ping command on Unix and other systems sends an ICMP ECHO_REQUEST to a specified computer, which is then expected to send an ECHO_REPLY. The requests and replies are very small packets. On many systems, the default is to send four such packets and display the result of each request and each reply with a summary at the end. Others continue sending pings until the person issuing the command enters control-C to stop the process.
From: Network World