ping(8)ping(8)NAMEping - Sends ICMP ECHO_REQUEST packets to network hosts
SYNOPSIS
/usr/sbin/ping [-dfnqruvLR] [-b num] [-c count] [-i wait] [-l preload]
[-p pattern] [-s packetsize] [-tnumber] [-I interface] [-G[!]
@addr1@addr2...] [-V version] host
OPTIONS
Specifies the size of the receive buffer. You can use this when speci‐
fying very large packet sizes with the -s option. By default, the size
of the receive buffer is set to 48K or to the size specified by the -s
option, whichever is greater. The -b option overrides the default.
Stops after sending (and receiving) count ECHO_RESPONSE packets. Set
the SO_DEBUG option on the socket being used. Floods ping. Outputs
packets as fast as they come back or 100 times per second, whichever is
more. For every ECHO_REQUEST sent, a (dot) is printed, while for every
ECHO_REPLY received a backspace is used. This provides a rapid display
of how many packets are being dropped. Only the superuser may use this
option. This can be very hard on a network and should be used with
caution (see Cautions). Specifies the source route for packets to
travel to the destination host. The route consists of one or more node
names or addresses. Use the ampersand character (@) to separate multi‐
ple addresses. You can specify up to 10 addresses.
The exclamation mark (!) indicates that this is a strict source
route; ping uses only the specified hosts for intermediate hops.
If any of the specified addresses is a hostname, a lookup is
performed and the protocol common to all addresses is used. If
there is no common protocol (for example, one host has only IPv4
address and one host has only IPv6 address), an error is
printed. If all hosts have both IPv4 and IPv6 addresses, IPv6
is used. You can override this option with the -V option.
Waits wait seconds between sending each packet. The default is
to wait for 1 second between each packet. This option is incom‐
patible with the -f option. [IPv6 only] Sends packets through
interface instead of using the interface specified in the rout‐
ing tables for the host. Displays every 100th reply only and
displays a message indicating lost packets.
A packet loss rate of just 1% is enough to seriously impact UDP-
based protocols like NFS. This option enables you to measure
loss rates and to determine how bursty they are. All lost mes‐
sages are reported with the following message:
Lost sequence number(s) number
The number value is a single number or a range or numbers. If
preload is specified, ping sends that many packets as fast as
possible before falling into its normal mode of behavior. Only
the superuser may use this option. This can be very hard on a
network and should be used with caution (see Cautions). Numeric
output only. No attempt will be made to look up symbolic names
for host addresses. This occurs only when displaying ICMP pack‐
ets other than ECHO_RESPONSE. You may specify up to 16 pad
bytes to fill out the packet you send. This is useful for diag‐
nosing data-dependent problems in a network. For example, -p ff
will cause the sent packet to be filled with all 1s (ones).
Quiets output. Nothing is displayed except the summary lines at
start-up time and when finished. [ICMP over IPv4 only]
Records route. Includes the RECORD_ROUTE option in the
ECHO_REQUEST packet and displays the route buffer on returned
packets. Note that the IP header is only large enough for nine
such routes. Many hosts ignore or discard this option. Bypasses
the normal routing tables and directly sends to a host on an
attached network. If the host is not on a directly attached
network, an error is returned. This option can be used to send
ping to a local host through an interface that has no route
through it (for example, after the interface was dropped by
routed). Specifies the number of data bytes to be sent. The
default is 56, which translates into 64 ICMP data bytes when
combined with the 8 bytes of ICMP header data. Sets the timeout
period (in seconds) for ping to wait before terminating. The
default timeout period is 10 seconds. This option is only use‐
ful with -c 1 option. Displays the time in microseconds (three
decimal places). In order to ensure this microsecond precision,
the NTP_TIME and MICRO_TIME kernel options must be on. By
default NTP_TIME and MICRO_TIME kernel options are off. If
these kernel options are off and this option is used, the time
is displayed to three decimal places, but in milliseconds.
Specifies verbose output. ICMP packets other than ECHO_RESPONSE
that are received are listed. Specifies the Internet Protocol
(IP) version number to enable the resolver to return the correct
address. If you are issuing a ping command to a host name (not
IP address) that has both IPv4 and IPv6 addresses, by default
the command is issued using the IPv6 address. Use the -V4
option if you want to use the IPv4 address.
DESCRIPTION
The ping command uses the ICMP (Internet Control Message Protocol) pro‐
tocol's mandatory ECHO_REQUEST datagram to elicit an ICMP ECHO_RESPONSE
from the specified host or gateway host, where host is a network name
or IP address. ECHO_REQUEST datagrams (pings) have an IP (Internet
Protocol) and ICMP header, followed by a struct timeval and then an
arbitrary number of pad bytes used to fill out the packet. The operat‐
ing system supports both ICMPv4 and ICMPv6.
When using ping for fault isolation, it should first be run on the
local host to verify that the local network interface is up and run‐
ning. Then, hosts and gateways further and further away should be sent
the ping command. Round-trip times and packet loss statistics are com‐
puted. If duplicate packets are received, they are not included in the
packet loss calculations, although the round-trip time of these packets
is used in calculating the minimum, average, and maximum round-trip
time numbers. When the specified number of packets have been sent (and
received) or if the program is terminated with a SIGINT, a brief sum‐
mary is displayed.
This program is intended for use in network testing, measurement, and
management. Because of the load it can impose on the network, it is
unwise to use ping during normal operations or from automated scripts.
ICMPv4 Packet Details
An IPv4 header without options is 20 bytes. An ICMPv4 ECHO_REQUEST
packet contains an additional 8 bytes worth of ICMPv4 header followed
by an arbitrary amount of data. When a packetsize is given, this indi‐
cates the size of this extra piece of data (the default is 56). Thus,
the amount of data received inside of an IPv4 packet of type ICMP
ECHO_REPLY will always be 8 bytes more than the requested data space
(the ICMPv4 header).
If the data space is at least 8 bytes large, ping uses the first 8
bytes of this space to include a timestamp, which it uses in the compu‐
tation of round-trip times. If less than 8 bytes of pad are specified,
no round-trip times are given.
Duplicate and Damaged Packets
The ping command will report duplicate and damaged packets. Duplicate
packets should never occur, and seem to be caused by inappropriate
link-level retransmissions. Duplicates may occur in many situations and
are rarely (if ever) a good sign, although the presence of low levels
of duplicates may not always be cause for alarm.
Damaged packets are obviously serious cause for alarm and often indi‐
cate broken hardware somewhere in the ping packet's path (in the net‐
work or in the hosts).
Trying Different Data Patterns
The (inter)network layer should never treat packets differently depend‐
ing on the data contained in the data portion. Unfortunately, data-
dependent problems have been known to sneak into networks and remain
undetected for long periods of time. In many cases the particular pat‐
tern that will have problems is something that does not have sufficient
transitions, such as all 1s (ones) or all 0s (zeros), or a pattern
right at the edge, such as almost all 0s (zeros). It is not necessar‐
ily enough to specify a data pattern of all 0s (zeros) (for example) on
the command line because the pattern that is of interest is at the
data-link level, and the relationship between what you enter and what
the controllers transmit can be complicated.
This means that if you have a data-dependent problem you will probably
have to do a lot of testing to find it. If you are lucky, you may man‐
age to find a file that either cannot be sent across your network or
that takes much longer to transfer than other similar length files. You
can then examine this file for repeated patterns that you can test
using the -p option of ping.
IPv4 TTL Details
The TTL value of an IPv4 packet represents the maximum number of IPv4
routers that the packet can go through before being thrown away. In
current practice you can expect each router in the Internet to decre‐
ment the TTL field by exactly 1 (one).
The TCP/IP specification states that the TTL field for TCP packets
should be set to 60, but many systems use smaller values (4.3BSD uses
30, 4.2BSD used 15).
The maximum possible value of this field is 255, and most UNIX compati‐
ble systems set the TTL field of ICMP ECHO_REQUEST packets to 255. This
is why you will find you can use the ping command on some hosts, but
not reach them with telnet or ftp.
In normal operation, ping prints the TTL value from the packet it
receives. When a remote system receives a ping packet, it can do one
of three things with the TTL field in its response: Not change it; this
is what Berkeley UNIX compatible systems did before the 4.3BSD release.
In this case, the TTL value in the received packet will be 255 minus
the number of routers in the round-trip path. Set it to 255; this is
what current Berkeley UNIX compatible systems do. In this case, the
TTL value in the received packet will be 255 minus the number of
routers in the path from the remote system to the host that received
the ping command. Set it to some other value. Some machines use the
same value for ICMPv4 packets that they use for TCP packets; for exam‐
ple, either 30 or 60. Others may use completely wild values.
CAUTIONS
Many hosts and gateways ignore the RECORD_ROUTE option.
Flooding and preloading the ping command is not recommended in general,
and flooding ping on the broadcast address should only be done under
very controlled conditions.
FILES
Specifies the command path
SEE ALSO
Commands: netstat(1), ifconfig(8)
Daemons: gated(8), routed(8)
RFC 792, Internet Control Message Protocol, Postel, J.
RFC 2463, Internet Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification, Conta, A., and Deering, S.
ping(8)