ping
From Wikipedia, the free encyclopedia
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. 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, and 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.
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[edit] 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 (a network packet) at the target, which then bounces from the target and is received by the operator. Later David L. Mills provided a backronym, "Packet InterNet Grouper (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 filtered 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 SP1 will not respond to an echo request on the public Internet in the default configuration.
Proponents of not honoring echo requests say that this practice increases network security. However, attackers can still send network packets to a machine, regardless of whether it responds to a ping. Those who insist that the standard be followed say that not honoring ping interferes with network diagnostics.
[edit] ICMP packet
| Bit 0 - 7 | Bit 8 - 15 | Bit 16 - 23 | Bit 24 - 31 | |
|---|---|---|---|---|
| IP Header (160 bits OR 20 Bytes) |
Version/IHL | Type of service | Length | |
| Identification | flags et offset | |||
| Time To Live(TTL) | Protocol | Checksum | ||
| Source IP address | ||||
| Destination IP address | ||||
| ICMP Payload (64+ bits OR 8+ Bytes) |
Type of message | Code | Checksum | |
| Quench | ||||
| Data (optional) | ||||
Composition of an ICMP Echo Reply 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)
- 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).
[edit] Sample pinging
[edit] Sample with Linux
The following is a sample output of pinging en.wikipedia.org under Linux with the iputils version of ping:
herlitzcorp@admin# 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.babunlaut 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 en.wikipedia.org is a DNS CNAME record for rr.pmtpa.wikimedia.org which then resolves to 66.230.200.100.
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 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
[edit] Sample with Windows
The following is a sample output of pinging en.wikipedia.org under Windows (Vista used in the following example) from within the 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
[edit] Sample with Mac OS X
The following is a sample output of pinging en.wikipedia.org under Mac OS X Leopard using the Terminal:
Macintosh:~ simonh$ 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
[edit] Message format
[edit] Echo request
The echo request is an 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.
| 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 ::: | |||||||||||||||||||||||||||||||
- 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.
[edit] 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.
[edit] 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
[edit] In gaming
In network multiplayer games like Unreal Tournament, Quake, Battlefield 2142, etc. as well as free online games and MMOs such as those hosted on sites like ijji, 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.
[edit] See also
- Traceroute, mtr (My traceroute)
- fping
- List of DOS commands
- Pingotron
- Ping (video games)
- Ping of death
- List of Unix programs
[edit] References
[edit] External links
- The Story of the PING Program by its author, Mike Muuss
- : send ICMP ECHO_REQUEST to network hosts – Linux man page
- Online PING script for educational purposes
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