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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.² The author named it after the sound that sonar makes since its methodology is analogous to sonar's echolocation.³⁴ The backronym Packet InterNet Groper for PING has been used for over 30 years. Muuss says that, from his point of view, PING was not intended as an acronym but he has acknowledged Mills' expansion of the name.⁵⁶ 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.⁷ The FreeDOS version was developed by Erick Engelke and is licensed under the GPL.⁸ Tim Crawford developed the ReactOS version. It is licensed under the MIT License.⁹

Any host must process ICMP echo requests and issue echo replies in return.¹⁰

Invocation example

The following is the output of running ping on Linux for sending five probes (1-second interval by default, configurable via -i option) to the target host www.example.com:

$ ping -c 5 www.example.com PING www.example.com (93.184.216.34): 56 data bytes 64 bytes from 93.184.216.34: icmp_seq=0 ttl=56 time=11.632 ms 64 bytes from 93.184.216.34: icmp_seq=1 ttl=56 time=11.726 ms 64 bytes from 93.184.216.34: icmp_seq=2 ttl=56 time=10.683 ms 64 bytes from 93.184.216.34: icmp_seq=3 ttl=56 time=9.674 ms 64 bytes from 93.184.216.34: icmp_seq=4 ttl=56 time=11.127 ms --- www.example.com ping statistics --- 5 packets transmitted, 5 packets received, 0.0% packet loss round-trip min/avg/max/stddev = 9.674/10.968/11.726/0.748 ms

The output lists each probe message and the results obtained. Finally, it lists the statistics of the entire test. In this example, the shortest round-trip time was 9.674 ms, the average was 10.968 ms, and the maximum value was 11.726 ms. The measurement had a standard deviation of 0.748 ms.

Error indications

In cases of no response from the target host, most implementations display either nothing or periodically print notifications about timing out. Possible ping results indicating a problem include the following:

• H, !N or !P – host, network or protocol unreachable
• S – source route failed
• F – fragmentation needed
• U or !W – destination network/host unknown
• I – source host is isolated
• A – communication with destination network administratively prohibited
• Z – communication with destination host administratively prohibited
• Q – for this ToS the destination network is unreachable
• T – for this ToS the destination host is unreachable
• X – communication administratively prohibited
• V – host precedence violation
• C – precedence cutoff in effect

In case of error, the target host or an intermediate router sends back an ICMP error message, for example host unreachable or TTL exceeded in transit. In addition, these messages include the first eight bytes of the original message (in this case header of the ICMP echo request, including the quench value), so the ping utility can match responses to originating queries.¹¹

Message format

ICMP packet transported with IPv4

An ICMP packet transported with IPv4 looks like this.

IPv4 datagram

Offset	Octet	0								1								2								3
Octet	Bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
0	0	Version (4)				IHL (5)				DSCP (0)						ECN (0)		Total length
4	32	Identification																Flags			Fragment offset
8	64	Time to live								Protocol (1)								Header checksum
12	96	Source address
16	128	Destination address

ICMP Echo Request packet

20	160	Type (8)								Code (0)								Checksum
24	192	Identifier																Sequence number
28	224	(Payload)
32	256
⋮	⋮

Type: 8 bits Set to 8 to indicate 'Echo Request'.¹² Checksum: 16 bits Checksum is the 16-bit ones' complement of the ones' complement sum of the ICMP packet, starting with the Type field,¹³ including the Payload. The IP header is not included. Identifier: 16 bits Can be used by the client to match the reply with the request that caused the reply. Sequence number: 16 bits Can be used by the client to match the reply with the request that caused the reply. Payload: variable length Optional. Payload for the different kind of answers; can be an arbitrary length, left to implementation detail.

Most Linux systems use a unique Identifier for every ping process, and Sequence number is an increasing number within that process. Windows uses a fixed Identifier, which varies between Windows versions, and a Sequence number that is only reset at boot time.

The Echo Reply is returned as:

ICMP Echo Reply packet

20	160	Type (0)								Code (0)								Checksum
24	192	Identifier																Sequence number
28	224	(Payload)
32	256
⋮	⋮

Type: 8 bits Set to 0 to indicate 'Echo Reply'.¹⁴ Identifier: 16 bits Copied from the Echo Request and returned. Sequence number: 16 bits Copied from the Echo Request and returned. Payload: variable length Optional. Payload is copied from the Echo Request and returned.

ICMPv6 packet transported with IPv6

An ICMP packet transported with IPv6 looks like this.

IPv6 datagram

Offset	Octet	0								1								2								3
Octet	Bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
0	0	Version (6)				Traffic class								Flow label
4	32	Payload length																Next header (58)								Hop limit
8	64	Source address
12	96
16	128
20	160
24	192	Destination address
28	224
32	256
36	288

ICMPv6 Echo Request packet

40	320	Type (128)								Code (0)								Checksum
44	352	Identifier																Sequence number
48	384	(Payload)
52	416
⋮	⋮

Type: 8 bits Set to 128 to indicate 'Echo Request'. Identifier: 16 bits Can be used by the client to match the reply with the request that caused the reply. Sequence number: 16 bits Can be used by the client to match the reply with the request that caused the reply. Checksum: 16 bits The checksum is calculated from the ICMP message (starting with the Type field), prepended with an IPv6 pseudo-header.¹⁵ Payload: variable length Optional. Payload for the different kind of answers; can be an arbitrary length, left to implementation detail.

Most Linux systems use a unique Identifier for every ping process, and Sequence number is an increasing number within that process. Windows uses a fixed Identifier, which varies between Windows versions, and a Sequence number that is only reset at boot time.

The Echo Reply is returned as:

ICMPv6 Echo Reply packet

40	320	Type (129)								Code (0)								Checksum
44	352	Identifier																Sequence number
48	384	(Payload)
52	416
⋮	⋮

Type: 8 bits Set to 129 to indicate 'Echo Reply'. Identifier: 16 bits Copied from the Echo Request and returned. Sequence number: 16 bits Copied from the Echo Request and returned. Payload: variable length Optional. Payload is copied from the Echo Request and returned.

Payload

The payload of the packet is generally filled with ASCII characters, as the output of the tcpdump utility shows in the last 32 bytes of the following example (after the eight-byte ICMP header starting with 0x0800):

16:24:47.966461 IP (tos 0x0, ttl 128, id 15103, offset 0, flags [none], proto: ICMP (1), length: 60) 192.168.146.22 > 192.168.144.5: ICMP echo request, id 1, seq 38, length 40 0x0000: 4500 003c 3aff 0000 8001 5c55 c0a8 9216 E..<:.....\U.... 0x0010: c0a8 9005 0800 4d35 0001 0026 6162 6364 ......M5...&abcd 0x0020: 6566 6768 696a 6b6c 6d6e 6f70 7172 7374 efghijklmnopqrst 0x0030: 7576 7761 6263 6465 6667 6869 uvwabcdefghi

The payload may include a timestamp indicating the time of transmission and a sequence number, which are not found in this example. This allows ping to compute the round-trip time in a stateless manner without needing to record the time of transmission of each packet.

The payload may also include a magic packet for the Wake-on-LAN protocol, but the minimum payload, in that case, is longer than shown. The Echo Request typically does not receive any reply if the host was sleeping in hibernation state, but the host still wakes up from sleep state if its interface is configured to accept wakeup requests. If the host is already active and configured to allow replies to incoming ICMP Echo Request packets, the returned reply should include the same payload. This may be used to detect that the remote host was effectively woken up, by repeating a new request after some delay to allow the host to resume its network services. If the host was just sleeping in low power active state, a single request wakes up that host just enough to allow its Echo Reply service to reply instantly if that service was enabled. The host does not need to wake up all devices completely and may return to low-power mode after a short delay. Such configuration may be used to avoid a host to enter in hibernation state, with much longer wake-up delay, after some time passed in low power active mode.

A packet including IP and ICMP headers must not be greater than the maximum transmission unit of the network, or risk being fragmented.

Security loopholes

To conduct a denial-of-service attack, an attacker may send ping requests as fast as possible, possibly overwhelming the victim with ICMP echo requests. This technique is called a ping flood.¹⁶

Ping requests to multiple addresses, ping sweeps, may be used to obtain a list of all hosts on a network.

See also

• fping
• hping
• Keepalive
• nping
• PathPing
• Ping of death
• Ping-pong scheme
• Smurf attack
• Traceroute

Further reading

• Dyson, Peter (1995). Mastering OS/2 Warp. Sybex. ISBN 978-0782116632.
• John Paul Mueller (2007). Windows Administration at the Command Line for Windows Vista, Windows 2003, Windows XP, and Windows 2000. John Wiley & Sons. ISBN 978-0470165799.
• McElhearn, Kirk (2006). The Mac OS X Command Line: Unix Under the Hood. John Wiley & Sons. ISBN 978-0470113851.

External links

Wikibooks has a book on the topic of: Guide to Windows Commands

• ping(1M) – Solaris 11.4 Reference Manual
• ping(8) – FreeBSD System Manager's Manual
• ping(8) – Linux Programmer's Manual – Administration and Privileged Commands
• ping at Microsoft Docs

References

1. Mike Muuss. "The Story of the PING Program". U.S. Army Research Laboratory. Archived from the original on 25 October 2019. Retrieved 8 September 2010. My original impetus for writing PING for 4.2a BSD UNIX came from an offhand remark in July 1983 by Dr. Dave Mills ... I named it after the sound that a sonar makes, inspired by the whole principle of echo-location ... From my point of view PING is not an acronym standing for Packet InterNet Grouper, it's a sonar analogy. However, I've heard second-hand that Dave Mills offered this expansion of the name, so perhaps we're both right. /wiki/Mike_Muuss ↩

2. Mike Muuss. "The Story of the PING Program". U.S. Army Research Laboratory. Archived from the original on 25 October 2019. Retrieved 8 September 2010. My original impetus for writing PING for 4.2a BSD UNIX came from an offhand remark in July 1983 by Dr. Dave Mills ... I named it after the sound that a sonar makes, inspired by the whole principle of echo-location ... From my point of view PING is not an acronym standing for Packet InterNet Grouper, it's a sonar analogy. However, I've heard second-hand that Dave Mills offered this expansion of the name, so perhaps we're both right. /wiki/Mike_Muuss ↩

3. Mike Muuss. "The Story of the PING Program". U.S. Army Research Laboratory. Archived from the original on 25 October 2019. Retrieved 8 September 2010. My original impetus for writing PING for 4.2a BSD UNIX came from an offhand remark in July 1983 by Dr. Dave Mills ... I named it after the sound that a sonar makes, inspired by the whole principle of echo-location ... From my point of view PING is not an acronym standing for Packet InterNet Grouper, it's a sonar analogy. However, I've heard second-hand that Dave Mills offered this expansion of the name, so perhaps we're both right. /wiki/Mike_Muuss ↩

4. Salus, Peter (1994). A Quarter Century of UNIX. Addison-Wesley. ISBN 978-0-201-54777-1. 978-0-201-54777-1 ↩

5. Mike Muuss. "The Story of the PING Program". U.S. Army Research Laboratory. Archived from the original on 25 October 2019. Retrieved 8 September 2010. My original impetus for writing PING for 4.2a BSD UNIX came from an offhand remark in July 1983 by Dr. Dave Mills ... I named it after the sound that a sonar makes, inspired by the whole principle of echo-location ... From my point of view PING is not an acronym standing for Packet InterNet Grouper, it's a sonar analogy. However, I've heard second-hand that Dave Mills offered this expansion of the name, so perhaps we're both right. /wiki/Mike_Muuss ↩

6. Mills, D.L. (December 1983). Internet Delay Experiments. IETF. doi:10.17487/RFC0889. RFC 889. Retrieved 26 November 2019. /wiki/David_L._Mills ↩

7. "man page ping section 8". www.manpagez.com. http://www.manpagez.com/man/8/ping/ ↩

8. "ibiblio.org FreeDOS Package -- ping (Networking)". www.ibiblio.org. http://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/distributions/1.2/repos/pkg-html/ping.html ↩

9. "GitHub - reactos/reactos: A free Windows-compatible Operating System". 8 August 2019 – via GitHub. https://github.com/reactos/reactos ↩

10. R. Braden, ed. (October 1989). Requirements for Internet Hosts -- Communication Layers. Network Working Group. doi:10.17487/RFC1122. STD 3. RFC 1122. Internet Standard 3. Updated by RFC 1349, 4379, 5884, 6093, 6298, 6633, 6864, 8029 and 9293. Every host MUST implement an ICMP Echo server function that receives Echo Requests and sends corresponding Echo Replies. /wiki/Bob_Braden ↩

11. "ICMP: Internet Control Message Protocol". repo.hackerzvoice.net. 13 January 2000. Archived from the original on 4 August 2016. Retrieved 4 December 2014. https://web.archive.org/web/20160804032607/http://repo.hackerzvoice.net/depot_madchat/ebooks/TCP-IP_Illustrated/icmp_int.htm ↩

12. J. Postel (September 1981). INTERNET CONTROL MESSAGE PROTOCOL - DARPA INTERNET PROGRAM PROTOCOL SPECIFICATION. Network Working Group. doi:10.17487/RFC0792. STD 5. RFC 792. Internet Standard 5. Updates RFC 760, 777, IENs 109, 128. Updated by RFC 950, 4884, 6633 and 6918. /wiki/Jon_Postel ↩

13. "RFC Sourcebook's page on ICMP". Archived from the original on 6 July 2018. Retrieved 20 December 2010. https://web.archive.org/web/20180706090020/http://networksorcery.com/enp/protocol/icmp.htm#ICMP%20Header%20Checksum ↩

14. J. Postel (September 1981). INTERNET CONTROL MESSAGE PROTOCOL - DARPA INTERNET PROGRAM PROTOCOL SPECIFICATION. Network Working Group. doi:10.17487/RFC0792. STD 5. RFC 792. Internet Standard 5. Updates RFC 760, 777, IENs 109, 128. Updated by RFC 950, 4884, 6633 and 6918. /wiki/Jon_Postel ↩

15. A. Conta; S. Deering (March 2006). M. Gupta (ed.). Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification. Network Working Group. doi:10.17487/RFC4443. STD 89. RFC 4443. Internet Standard 89. Obsoletes RFC 2463. Updates RFC 2780. Updated by RFC 4884. /wiki/Steve_Deering ↩

16. "What is a Ping Flood | ICMP Flood | DDoS Attack Glossary | Imperva". Learning Center. Retrieved 26 July 2021. https://www.imperva.com/learn/ddos/ping-icmp-flood/ ↩