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The word ping (Packet INternet Groper) comes from the way submarines estimate distances to underwater objects by bouncing sonar sound waves (or pings) off of the underwater objects. In IP networks, "pings" are used to test the existence and functionality of IP addresses by measuring the time it takes a data signal to go from a client to a server and then back from the server to the client. The round-trip time (RTT) is known as latency. Because of asymmetry, the latency from client to server is not necessarily the same as the latency from server to client.
Ping is useful for network troubleshooting. A long latency from client to server could indicate network congestion, routing problems, and/or network failure. Input for the Ping command can be either an IPv4 address, an IPv6 address, a domain name or your current IP address. Output will usually be 10 ICMP (Internet Control Message Protocol) messages. Below is the first and last message of a ping to google.com:
Packets are 64 bytes, ICMP seq numbers are 1 through 10, TTL * = 119, round trip time was 2.81 ms for the first ICMP message and 1.35 ms for the 10th ICMP message. TTL (Time-to-Live) is discussed in "Traceroute" previously. Ping statistics are displayed after the 10 ICMP messages: --- google.com ping statistics ---
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