ping is a computer network administration software utility used to test the reachability of a host on an Internet Protocol (IP) network. It is available for virtually all operating systems that have networking capability, including most embedded network administration software. Ping measures the round-trip time for messages sent from the originating host to a destination computer that are echoed back to the source. The name comes from active sonar terminology that sends a pulse of sound and listens for the echo to detect objects under water. Ping operates by means of Internet Control Message Protocol (ICMP) packets. Pinging involves sending an ICMP echo request to the target host and waiting for an ICMP echo reply. The program reports errors, packet loss, and a statistical summary of the results, typically including the minimum, maximum, the mean round-trip times, and standard deviation of the mean. The command-line options of the ping utility and its output vary between the numerous implementations. Options may include the size of the payload, count of tests, limits for the number of network hops (TTL) that probes traverse, interval between the requests and time to wait for a response. Many systems provide a companion utility ping6, for testing on Internet Protocol version 6 (IPv6) networks, which implement ICMPv6. History The ping utility was written by Mike Muuss in December 1983 during his employment at the Ballistic Research Laboratory, now the US Army Research Laboratory. A remark by David Mills on using ICMP echo packets for IP network diagnosis and measurements prompted Muuss to create the utility to troubleshoot network problems. The author named it after the sound that sonar makes, since its methodology is analogous to sonar's echolocation. The backronym Packet InterNet Groper for PING has been used for over 30 years, and although Muuss says that from his point of view PING was not intended as an acronym, he has acknowledged Mills' expansion of the name. The first released version was public domain software; all subsequent versions have been licensed under the BSD license. Ping was first included in 4.3BSD. The FreeDOS version was developed by Erick Engelke and is licensed under the GPL. Tim Crawford developed the ReactOS version. It is licensed under the MIT License. RFC 1122 prescribes that any host must process ICMP echo requests and issue echo replies in return. Invocation example The following is the output of running ping on Linux for