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'''Ping''' is a [[computer network]] tool used to test whether a particular [[node (networking)|host]] is reachable across an [[Internet protocol suite|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 [[Internet Control Message Protocol|ICMP]] “echo request” [[packet (information technology)|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==
[[Image:ping deny.png|thumb|right|350px|A server denying a ping request because of the request's size.]]
[[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]], "'''P'''acket '''I'''nter'''N'''et '''G'''roper" (sometimes also defined as "'''P'''acket '''I'''nter-'''N'''etwork '''G'''roper"). <!-- "Groper" is correct, *not* "gopher."-->

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

This was partly due to the increasing use of ping for target reconnaissance, for example by [[Computer worm|Internet worms]] such as [[Welchia]] that flood the Internet with ping requests in order to locate new [[Computer|host]]s 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 [[router]]s across the Internet.

Although [http://rfc.net/rfc1122.html#p42 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.

== ICMP packet ==
{| class="wikitable" style="margin: 0 auto; text-align: center;"
|+ ICMP packet
|-----
! &nbsp;
! Bit 0 - 7
! Bit 8 - 15
! Bit 16 - 23
! Bit 24 - 31
|----- bgcolor="skyblue"
! rowspan="5" | IP Header<br>(160 bits OR 20 Bytes)
| Version/IHL
| Type of service
| colspan="2" | Length
|----- bgcolor="skyblue"
| colspan="2" | Identification
| colspan="2" |''flags'' et ''offset''
|----- bgcolor="skyblue"
| Time To Live(TTL)
| Protocol
| colspan="2" | Checksum
|----- bgcolor="skyblue"
| colspan="4" | Source IP address
|----- bgcolor="skyblue"
| colspan="4" | Destination IP address
|----- bgcolor="ffaaaa"
! rowspan="3" | ICMP Payload<br>(64+ bits OR 8+ Bytes)
| Type of message
| Code
| colspan="2" | Checksum
|----- bgcolor="ffaaaa"
| colspan="4" | Quench
|----- bgcolor="ffaaaa"
| colspan="4" | Data (''optional'')
|}

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 [citation needed; what about the [[ping of death]] ?]).

==Sample pinging==
=== Sample with Linux ===
The following is a sample output of pinging <tt>en.wikipedia.org</tt> under [[Linux]] with the iputils version of ping:
admin@localhost# ping en.wikipedia.org
PING rr.pmtpa.wikimedia.org (66.230.200.100) 56(84) bytes of data.
64 bytes from rr.pmtpa.wikimedia.org (66.230.200.100): icmp_seq=1 ttl=52 time=87.7 ms
64 bytes from rr.pmtpa.wikimedia.org (66.230.200.100): icmp_seq=2 ttl=52 time=95.6 ms
64 bytes from rr.pmtpa.wikimedia.org (66.230.200.100): icmp_seq=3 ttl=52 time=85.4 ms
64 bytes from rr.pmtpa.wikimedia.org (66.230.200.100): icmp_seq=4 ttl=52 time=95.8 ms
64 bytes from rr.pmtpa.wikimedia.org (66.230.200.100): icmp_seq=5 ttl=52 time=87.0 ms
64 bytes from rr.pmtpa.wikimedia.org (66.230.200.100): icmp_seq=6 ttl=52 time=97.6 ms
--- rr.pmtpa.wikimedia.org ping statistics ---
10 packets transmitted, 10 received, 0% packet loss, time 8998ms
rtt min/avg/max/mdev = 78.162/89.213/97.695/6.836 ms

This output shows that <tt>en.wikipedia.org</tt> is a [[Domain Name System|DNS]] CNAME record for <tt>rr.pmtpa.wikimedia.org</tt> which then resolves to <tt>66.230.200.100</tt>.

The output then shows the results of making 10 pings to 66.230.200.100 with the results summarized at the end. (To stop the program in Linux or Windows, press Ctrl+C.)
* shortest [[Round-trip delay time|round trip time]] was 78.162 milliseconds
* average round trip time was 89.213 milliseconds
* maximum round trip time was 97.695 milliseconds
* [[Standard deviation]] of the round-trip time was 6.836 milliseconds

=== Sample with Windows ===
The following is a sample output of pinging <code>en.wikipedia.org</code> under [[Microsoft Windows|Windows]] ([[Windows Vista|Vista]] used in the following example) from within the [[Command Prompt (Windows)|Command Prompt]]:

[localhost] ping en.wikipedia.org
Pinging rr.pmtpa.wikimedia.org [66.230.200.100] with 32 bytes of data:
Reply from 66.230.200.100: bytes=32 time=57ms TTL=44
Reply from 66.230.200.100: bytes=32 time=59ms TTL=44
Reply from 66.230.200.100: bytes=32 time=59ms TTL=44
Reply from 66.230.200.100: bytes=32 time=54ms TTL=44
Ping statistics for 66.230.200.100:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 54ms, Maximum = 59ms, Average = 57ms

=== Sample with Mac OS X ===
The following is a sample output of pinging <tt>en.wikipedia.org</tt> under [[Mac OS X Leopard]] using the [[Terminal (application)|Terminal]]:

<pre>Macintosh:~ user$ ping -c 10 en.wikipedia.org
PING rr.knams.wikimedia.org (91.198.174.2): 56 data bytes
64 bytes from 91.198.174.2: icmp_seq=0 ttl=53 time=40.019 ms
64 bytes from 91.198.174.2: icmp_seq=1 ttl=53 time=47.502 ms
64 bytes from 91.198.174.2: icmp_seq=2 ttl=53 time=43.208 ms
64 bytes from 91.198.174.2: icmp_seq=3 ttl=53 time=50.851 ms
64 bytes from 91.198.174.2: icmp_seq=4 ttl=53 time=46.556 ms
64 bytes from 91.198.174.2: icmp_seq=5 ttl=53 time=42.180 ms
64 bytes from 91.198.174.2: icmp_seq=6 ttl=53 time=49.853 ms
64 bytes from 91.198.174.2: icmp_seq=7 ttl=53 time=45.556 ms
64 bytes from 91.198.174.2: icmp_seq=8 ttl=53 time=41.186 ms
64 bytes from 91.198.174.2: icmp_seq=9 ttl=53 time=48.836 ms

--- rr.knams.wikimedia.org ping statistics ---
10 packets transmitted, 10 packets received, 0% packet loss
round-trip min/avg/max/stddev = 40.019/45.575/50.851/3.588 ms</pre>

== Message format ==
=== Echo request ===
The ''echo request'' is an [[Internet Control Message Protocol|ICMP]] message whose data is expected to be received back in an ''echo reply'' ("pong"). The host must respond to all echo requests with an echo reply containing the exact data received in the request message.

{| class="wikitable"
! 00 || 01 || 02 || 03 || 04 || 05 || 06 || 07
! 08 || 09 || 10 || 11 || 12 || 13 || 14 || 15
! 16 || 17 || 18 || 19 || 20 || 21 || 22 || 23
! 24 || 25 || 26 || 27 || 28 || 29 || 30 || 31
|-
|colspan="8" align="center"| Type = 8
|colspan="8" align="center"| Code = 0
|colspan="16" align="center"| Header Checksum
|-
|colspan="16" align="center"| Identifier
|colspan="16" align="center"| Sequence Number
|-
|colspan="32" align="center"| Data :::
|}

*Type must be set to 8.
*Code must be set to 0.
*The Identifier and Sequence Number can be used by the client to match the reply with the request that caused the reply. In practice, 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 data received by the Echo Request must be entirely included in the Echo Reply.

=== Echo reply===
The ''echo reply'' is an ICMP message generated in response to an echo request, and is mandatory for all hosts and routers.

{| class="wikitable"
! 00 || 01 || 02 || 03 || 04 || 05 || 06 || 07
! 08 || 09 || 10 || 11 || 12 || 13 || 14 || 15
! 16 || 17 || 18 || 19 || 20 || 21 || 22 || 23
! 24 || 25 || 26 || 27 || 28 || 29 || 30 || 31
|-
|colspan="8" align="center"| Type = 0
|colspan="8" align="center"| Code = 0
|colspan="16" align="center"| Header Checksum
|-
|colspan="16" align="center"| Identifier
|colspan="16" align="center"| Sequence Number
|-
|colspan="32" align="center"| Data :::
|}

*''Type'' and ''code'' must be set to 0.
*The ''identifier'' and ''sequence number'' can be used by the client to determine which echo requests are associated with the echo replies.
*The data received in the echo request must be entirely included in the echo reply.

== Payload ==

The payload of the packet is generally filled with letters of the alphabet as this ASCII tcpdump shows

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

== In gaming ==
{{main|ping (video games)}}

In network multiplayer games like [[Unreal Tournament]], [[Quake]], [[Battlefield 2142]], etc., the server notes the time it requires for a game packet to reach a client and a response to be received. This round-trip time is usually reported as the player's 'ping'. It is used as an effective measurement of the player's [[lag]], with lower ping times being desirable. Note that this style of ping typically does not use ICMP packets.

== See also ==
* [[Traceroute]], [[mtr (My traceroute)]]
* [[fping]], command for sending ICMP packets to multiple hosts in parallel
* [[dping]], [[AIX]] command included in IBM Cluster Systems Management for sending ICMP packets to multiple hosts in parallel
* [[List of DOS commands]]
* [[Pingotron]]
* [[Ping (video games)]]
* [[Ping of death]]
* [[List of Unix programs]]

[http://www.osischool.com/tools/ping/Ping-basics/ Ping Animation]

==References==
* RFC 792

==External links==
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| LINKS. If you think that your link might be useful, do not add it here, |
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| See [[Wikipedia:External links]] and [[Wikipedia:Spam]] for details |
===========================({{NoMoreLinks}})===============================-->
* [http://ftp.arl.mil/~mike/ping.html The Story of the PING Program] by its author, Mike Muuss
* {{man|1|ping||send ICMP ECHO_REQUEST to network hosts}}

{{Unix commands}}
{{Windows commands}}

[[Category:Network analyzers]]
[[Category:Open source network management software]]
[[Category:Network-related software]]
[[Category:Unix software]]
[[Category:Windows communication and services]]
[[Category:Windows administration]]

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[[ko:핑]]
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[[ml:പിങ്]]
[[nl:Ping (netwerk)]]
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Revision as of 17:13, 1 November 2008

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