sbin/ping/ping.8

.\"	$OpenBSD: ping.8,v 1.65 2021/02/21 17:18:01 jmc Exp $
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\"     @(#)ping.8	8.2 (Berkeley) 12/11/93
.\"
.Dd $Mdocdate: February 21 2021 $
.Dt PING 8
.Os
.Sh NAME
.Nm ping ,
.Nm ping6
.Nd send ICMP ECHO_REQUEST packets to network hosts
.Sh SYNOPSIS
.Nm ping
.Op Fl DdEefgHLnqRv
.Op Fl c Ar count
.Op Fl I Ar sourceaddr
.Op Fl i Ar interval
.Op Fl l Ar preload
.Op Fl p Ar pattern
.Op Fl s Ar packetsize
.Op Fl T Ar toskeyword
.Op Fl t Ar ttl
.Op Fl V Ar rtable
.Op Fl w Ar maxwait
.Ar host
.Nm ping6
.Op Fl DdEefgHLmnqv
.Op Fl c Ar count
.Op Fl h Ar hoplimit
.Op Fl I Ar sourceaddr
.Op Fl i Ar interval
.Op Fl l Ar preload
.Op Fl p Ar pattern
.Op Fl s Ar packetsize
.Op Fl T Ar toskeyword
.Op Fl V Ar rtable
.Op Fl w Ar maxwait
.Ar host
.Sh DESCRIPTION
.Nm
uses the ICMP protocol's mandatory
.Dv ECHO_REQUEST
datagram to elicit an ICMP
.Dv ECHO_REPLY
from a host or gateway.
These datagrams
.Pq pings
have an IP and ICMP header,
followed by a
.Qq struct timeval
and then an arbitrary number of pad bytes used to fill out the packet.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl c Ar count
Stop sending after
.Ar count
.Dv ECHO_REQUEST
packets have been sent.
If
.Ar count
is 0, send an unlimited number of packets.
.It Fl D
Don't fragment IP packets.
.It Fl d
Set the
.Dv SO_DEBUG
option on the socket being used.
This option has no effect on
.Ox .
.It Fl E
Emit an audible beep (by sending an ASCII BEL character to the
standard error output) when no packet is received before the next
packet is transmitted.
To cater for round-trip times that are longer than the interval between
transmissions, further missing packets cause a bell only if the maximum
number of unreceived packets has increased.
This option is disabled for flood pings.
.It Fl e
Emit an audible beep (by sending an ASCII BEL character to the
standard error output) after each non-duplicate response is received.
This option is disabled for flood pings.
.It Fl f
Flood ping.
Outputs packets as fast as they come back or one hundred times per second,
whichever is more.
For every
.Dv ECHO_REQUEST
sent, a period
.Sq \&.
is printed, while for every
.Dv ECHO_REPLY
received a backspace is printed.
This provides a rapid display of how many packets are being dropped.
Only the superuser may use this option.
.Bf -emphasis
This can be very hard on a network and should be used with caution.
.Ef
.It Fl g
Provides a visual display of packets received and lost.
For every
.Dv ECHO_REPLY
received, an exclamation mark
.Sq \&!
is printed, while for every missed packet a period
.Sq \&.
is printed.
Duplicate and truncated replies are indicated with
.Sq D
and
.Sq T
respectively.
.It Fl H
Try reverse lookups for addresses.
.It Fl h Ar hoplimit
.Pq IPv6 only
Set the hoplimit.
.It Fl I Ar sourceaddr
Set the source address to transmit from, which is useful on machines
with multiple interfaces.
For unicast and multicast pings.
.It Fl i Ar interval
Send one packet every
.Ar interval
seconds.
The default is one second.
The
.Ar interval
may contain a fractional portion.
Only the superuser may specify a value less than one second.
This option is incompatible with the
.Fl f
option.
.It Fl L
Disable the loopback, so the transmitting host doesn't see the ICMP
requests.
For multicast pings.
.It Fl l Ar preload
Send
.Ar preload
packets as fast as possible before reverting to normal behavior.
Only root may set a preload value.
.It Fl m
.Pq IPv6 only
Do not fragment unicast packets to fit the minimum IPv6 MTU.
If specified twice,
do this for multicast packets as well.
.It Fl n
Numeric output only.
No attempt will be made to look up symbolic names from addresses in the reply.
.It Fl p Ar pattern
Specify up to 16 pad bytes to fill out the packet sent.
This is useful for diagnosing data-dependent problems in a network.
For example,
.Qq -p ff
causes the sent packet to be filled with all ones.
.It Fl q
Quiet output.
Nothing is displayed except the summary lines at startup time and
when finished.
.It Fl R
.Pq IPv4 only
Record route.
Includes the
.Dv RECORD_ROUTE
option in the
.Dv ECHO_REQUEST
packet and displays
the route buffer on returned packets.
Note that the IP header is only large enough for nine such routes.
If more routes come back than should, such as due to an illegal spoofed
packet,
.Nm
will print the route list and then truncate it at the correct spot.
Many hosts ignore or discard this option.
.It Fl s Ar packetsize
Specify 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.
The maximum packet size is 65467 for IPv4 and 65527 for IPv6.
.It Fl T Ar toskeyword
Change the IPv4 TOS or IPv6 Traffic Class value.
.Ar toskeyword
may be one of
.Cm critical ,
.Cm inetcontrol ,
.Cm lowdelay ,
.Cm netcontrol ,
.Cm throughput ,
.Cm reliability ,
or one of the DiffServ Code Points:
.Cm ef ,
.Cm af11 ... af43 ,
.Cm cs0 ... cs7 ;
or a number in either hex or decimal.
.It Fl t Ar ttl
.Pq IPv4 only
Use the specified time-to-live.
.It Fl V Ar rtable
Set the routing table to be used for outgoing packets.
.It Fl v
Verbose output.
ICMP packets other than
.Dv ECHO_REPLY
that are received are listed.
.It Fl w Ar maxwait
Specify the maximum number of seconds to wait for responses
after the last request has been sent.
The default is 10.
.El
.Pp
When using
.Nm
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
.Dq pinged .
.Pp
Round trip times and packet loss statistics are computed.
If duplicate packets are received, they are not included in the packet
loss calculation, although the round trip time of these packets is used
in calculating the minimum/average/maximum round trip time numbers and
the standard deviation.
.Pp
When the specified number of packets have been
sent (and received), or if the program is terminated with a
.Dv SIGINT ,
a brief summary is displayed.
The summary information can also be displayed while
.Nm
is running by sending it a
.Dv SIGINFO
signal (see the
.Cm status
argument of
.Xr stty 1
for more information).
.Pp
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
.Nm
during normal operations or from automated scripts.
.Sh ICMP PACKET DETAILS
An IP header without options is 20 bytes.
An ICMP
.Dv ECHO_REQUEST
packet contains an additional 8 bytes worth of
ICMP header followed by an arbitrary amount of data.
When a
.Ar 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 IP packet of type ICMP
.Dv ECHO_REPLY
will always be 8 bytes more than the requested data space
(the ICMP header).
.Pp
If the data space is at least 24 bytes,
.Nm
uses the first sixteen bytes of this space to include a timestamp which
it uses in the computation of round trip times.
The following 8 bytes store a message authentication code.
If less than 24 bytes of pad are specified, no round trip times are
given.
.Sh DUPLICATE AND DAMAGED PACKETS
.Nm
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.
.Pp
Damaged packets are obviously serious cause for alarm and often
indicate broken hardware somewhere in the
.Nm
packet's path (in the network or in the hosts).
.Sh TRYING DIFFERENT DATA PATTERNS
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 doesn't have sufficient
.Dq transitions ,
such as all ones or all
zeros, or a pattern right at the edge, such as almost all zeros.
It isn't necessarily enough to specify a data pattern of all 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 type and
what the controllers transmit can be complicated.
.Pp
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 can't 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
.Fl p
option of
.Nm ping .
.Sh TTL DETAILS
The TTL value of an IP packet represents the maximum number of IP 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 one.
.Pp
The TCP/IP specification states that the TTL field
for TCP packets should be set to 60,
but many systems use smaller values
.Po
.Bx 4.3
uses 30,
.Bx 4.2
used 15
.Pc .
.Pp
The maximum possible value of this field is 255, and most
.Ux
systems set the TTL field of ICMP
.Dv ECHO_REQUEST
packets to 255.
This is why you will find you can
.Dq ping
some hosts, but not reach them
with
.Xr telnet 1
or
.Xr ftp 1 .
.Pp
In normal operation,
.Nm
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:
.Bl -bullet
.It
Not change it; this is what Berkeley
.Ux
systems did before the
.Bx 4.3 Tahoe
release.
In this case the TTL value in the received packet will be
255 minus the number of routers in the round trip path.
.It
Set it to 255; this is what current Berkeley
.Ux
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 pinging host.
.It
Set it to some other value.
Some machines use the same value for ICMP packets
that they use for TCP packets, for example either 30 or 60.
Others may use completely wild values.
.El
.Sh EXIT STATUS
.Nm
exits 0 if at least one reply is received,
and >0 if no reply is received or an error occurred.
.Sh SEE ALSO
.Xr netstat 1 ,
.Xr ifconfig 8
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.3 .
The
.Nm ping6
command was originally a separate program
and first appeared in the WIDE Hydrangea IPv6 protocol stack kit.
.Sh BUGS
Many hosts and gateways ignore the
.Dv RECORD_ROUTE
option.
.Pp
The maximum IP header length is too small for options like
.Dv RECORD_ROUTE
to
be completely useful.
There's not much that can be done about this, however.
.Pp
Flood pinging is not recommended in general, and flood pinging the
broadcast address should only be done under very controlled conditions.