Ping is a computer network tool used to test whether a particular host is reachable across an IP network; it is also used to self test the network interface card of the computer, or as a speed test. It works by sending ICMP “echo request” packets to the target host and listening for ICMP “echo response” replies. Ping estimates the round-trip time, generally in milliseconds, records any packet loss, and prints a statistical summary when finished.

The word ping is also frequently used as a verb or noun, where it can refer directly to the round-trip time, the act of running a ping program or measuring the round-trip time.

History

Mike Muuss wrote the program in December, 1983, as a tool to troubleshoot odd behavior on an IP network. He named it after the pulses of sound made by a sonar, since its operation is analogous to active sonar in submarines, in which an operator issues a pulse of energy at the target, which then bounces from the target and is received by the operator. (The pulse of energy in sonar is analogous to a network packet in ping.) Later David L. Mills provided a backronym, "Packet InterNet Groper" (sometimes also defined as "Packet Inter-Network Groper").

The usefulness of ping in assisting the "diagnosis" of Internet connectivity issues was impaired from late in 2003, when a number of Internet Service Providers began filtering out ICMP Type 8 (echo request) messages at their network boundaries.

This was partly due to the increasing use of ping for target reconnaissance, for example by Internet worms such as Welchia that flood the Internet with ping requests in order to locate new hosts to infect. Not only did the availability of ping responses leak information to an attacker, it added to the overall load on networks, causing problems for routers across the Internet.

Although RFC 1122 prescribes that any host must accept an echo-request and issue an echo-reply in return, one finds that this standard is frequently not followed on the public Internet. Notably, Windows XP SP2 will not respond to an echo request on the public Internet in the default configuration. (See Troubleshooting Windows Firewall in Microsoft Windows XP Service Pack 2

Generic composition of an ICMP packet

• Header (in blue), with Protocol set to 1 and Type of Service set to 0.
• Type of ICMP message (8 bits)
• Code (8 bits)
• Checksum (16 bits), calculated with the ICMP part of the packet (the header is not used)
• The ICMP 'Quench' (32 bits) field, which in this case (ICMP echo request and replies), will be composed of identifier (16 bits) and sequence number (16 bits).
• Data load for the different kind of answers (Can be an arbitrary length, left to implementation detail. However must be less than the maximum MTU of the network needed; what about the ping of death ?).