This article is about the IP network utility. For other uses, see Ping (disambiguation). Ping is a computer network administration utility used to test the reachability of a host on an Internet Protocol (IP) network and to measure the round-trip time for messages sent from the originating host to a destination computer. The name comes from active sonar terminology.
Ping operates by sending Internet Control Message Protocol (ICMP) echo request packets to the target host and waiting for an ICMP response. In the process it measures the time from transmission to reception (round-trip time)[1] and records any packet loss. The results of the test are printed in form of a statistical summary of the response packets received, including the minimum, maximum, and the mean round-trip times, and sometimes the standard deviation of the mean.
Ping may be run using various options (command line switches) depending on the implementation that enable special operational modes, such as to specify the packet size used as the probe, automatic repeated operation for sending a specified count of probes, time stamping options, or to perform a ping flood. Flood pinging may be abused as a simple form of denial-of-service attack, in which the attacker overwhelms the victim with ICMP echo request packets.
The usefulness of ping in assisting the diagnosis of Internet connectivity issues was impaired starting in 2003, when a number of Internet service providers began filtering out ICMP Type 8 (ICMP Echo Request) messages at their network boundaries.[citation needed] 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 computers 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.[citation needed]
However host discovery or ping scanning or ping sweep is still a part of network scanning tools like nmap, as it may give basic evidence about the existence of a remote machine.
Although RFC 1122 prescribes that any host must accept an echo-request and issue an echo-reply in return, this has been characterized as a security risk.[3]
Generic composition of an ICMP packet[4]
Ping operates by sending Internet Control Message Protocol (ICMP) echo request packets to the target host and waiting for an ICMP response. In the process it measures the time from transmission to reception (round-trip time)[1] and records any packet loss. The results of the test are printed in form of a statistical summary of the response packets received, including the minimum, maximum, and the mean round-trip times, and sometimes the standard deviation of the mean.
Ping may be run using various options (command line switches) depending on the implementation that enable special operational modes, such as to specify the packet size used as the probe, automatic repeated operation for sending a specified count of probes, time stamping options, or to perform a ping flood. Flood pinging may be abused as a simple form of denial-of-service attack, in which the attacker overwhelms the victim with ICMP echo request packets.
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History
The ping utility was authored by Mike Muuss in December 1983 as a tool to troubleshoot problems in an IP network. He named it after the sound pulses of active sonar, which also involves sending a signal and measuring the time until any echo is received.[1][2]The usefulness of ping in assisting the diagnosis of Internet connectivity issues was impaired starting in 2003, when a number of Internet service providers began filtering out ICMP Type 8 (ICMP Echo Request) messages at their network boundaries.[citation needed] 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 computers 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.[citation needed]
However host discovery or ping scanning or ping sweep is still a part of network scanning tools like nmap, as it may give basic evidence about the existence of a remote machine.
Although RFC 1122 prescribes that any host must accept an echo-request and issue an echo-reply in return, this has been characterized as a security risk.[3]
ICMP packet
| Bit 0 - 7 | Bit 8 - 15 | Bit 16 - 31 | ||
|---|---|---|---|---|
| IP Header (20 bytes) | Version/IHL | Type of service | Length | |
| Identification | flags and offset | |||
| Time To Live (TTL) | Protocol | Checksum | ||
| Source IP address | ||||
| Destination IP address | ||||
| ICMP Payload (8+ bytes) | Type of message | Code | Checksum | |
| Quench | ||||
| Data (optional) | ||||
- Header (in blue):
- Protocol set to 1 and Type of Service set to 0.
- Payload (in red):
- 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). It is the 16-bit one's complement of the one's complement sum of the ICMP message starting with the Type field[5]
- 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]).
- Data Transportation
Sample ping test
The following is a sample output of pinging en.wikipedia.org 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 msThe output shows the results of 10 pings to 66.230.200.100 with the results summarized at the end. The program is stopped by pressing Ctrl-C.
- shortest 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
Message format
Echo request
The echo request is an ICMP message whose data is expected to be received back in an echo reply ("ping"). The host must respond to all echo requests with an echo reply containing the exact data received in the request message.| 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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Type = 8 | Code = 0 | Header Checksum | |||||||||||||||||||||||||||||
| Identifier | Sequence Number | ||||||||||||||||||||||||||||||
| Data ::: | |||||||||||||||||||||||||||||||
- 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.| 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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Type = 0 | Code = 0 | Header Checksum | |||||||||||||||||||||||||||||
| Identifier | Sequence Number | ||||||||||||||||||||||||||||||
| 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.
Other replies
In case of error, destination host or intermediate router will send back an ICMP error message, i.e. host unreachable or TTL exceeded in transit. In addition these messages include the first 8 bytes of original message (in this case header of ICMP echo request, including quench value), so ping utility can match it to originating query.[citation needed]Payload
The payload of the packet is generally filled with ASCII characters, as the output of the tcpdump utility 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
The payload includes a timestamp of when the message was sent, as well a sequence number. This allows ping to compute the round trip time in a stateless manner without needing to record when packets were sent. In cases of no answer and no error message, most implementations of ping display nothing, or periodically print notifications about timing out.[citation needed]Other types of pinging
The term ping is commonly used to describe the transmission of an effectively content-less message that is used for a variety of purposes. For example, a ping may be sent using the User Datagram Protocol (UDP) to a device located behind a network address translator (NAT) to keep the port binding on the NAT translator from timing out and removing the forward mapping. Other examples are short or empty instant messages, emails, voice mails, or missed-call notification to indicate availability.[citation needed]In gaming
Main article: ping (video gaming)
In various network multi-player games, 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 latency, with lower ping times being desirable. Note that this style of ping typically does not use ICMP packets.See also
References
- ^ a b Mike Muuss. "The Story of the PING Program". Adelphi, MD, USA: U.S. Army Research Laboratory. Archived from the original on 08 September 2010. Retrieved 08 September 2010. "I named it after the sound that a sonar makes, inspired by the whole principle of echo-location."
- ^ Salus, Peter (1994). A Quarter Century of UNIX. Addison-Wesley. ISBN 0201547775.
- ^ "Shields Up, Firewall Test. You get a warning about the dangers of ping if your computer answers ping request". Retrieved 4 June 2010.
- ^ RFC 792
- ^ "RFC Sourcebook's page on ICMP". Retrieved 20 December 2010.
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