ping - Sends ICMP ECHO_REQUEST packets to network hosts
/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
Specifies the size of the receive buffer. You can use
this when specifying 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 multiple 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 incompatible with the -f option. [IPv6 only]
Sends packets through interface instead of using
the interface specified in the routing 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 messages
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
packets other than ECHO_RESPONSE. You may specify
up to 16 pad bytes to fill out the packet you send.
This is useful for diagnosing 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 useful
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.
The ping command uses the ICMP (Internet Control Message
Protocol) protocol'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 operating system supports both ICMPv4 and
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 running. Then, hosts and gateways
further and further away should be sent the ping command.
Round-trip times and packet loss statistics are computed.
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
summary 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 [Toc] [Back]
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 indicates 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 computation of round-trip times. If less
than 8 bytes of pad are specified, no round-trip times are
Duplicate and Damaged Packets [Toc] [Back]
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 indicate broken hardware somewhere in the ping
packet's path (in the network or in the hosts).
Trying Different Data Patterns [Toc] [Back]
The (inter)network layer should never treat packets differently
depending 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 pattern
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 necessarily 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 manage 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 [Toc] [Back]
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 decrement 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 compatible 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 example, either 30 or 60. Others may use completely
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.
Specifies the command path
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.
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