431 lines
13 KiB
Groff
431 lines
13 KiB
Groff
.\" $NetBSD: ping.8,v 1.23 1998/09/14 17:08:55 tv Exp $
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.\"
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.\" Copyright (c) 1985, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)ping.8 8.2 (Berkeley) 12/11/93
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.\"
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.Dd March 11, 1997
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.Dt PING 8
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.Os BSD 4.3
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.Sh NAME
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.Nm ping
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.Nd send
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.Tn ICMP ECHO_REQUEST
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packets to network hosts
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.Sh SYNOPSIS
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.Nm
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.Op Fl dfnoqrvDPQRL
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.Op Fl c Ar count
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.Op Fl g Ar gateway
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.Op Fl i Ar interval
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.Op Fl I Ar ifaddr
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.Op Fl l Ar preload
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.Op Fl p Ar pattern
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.Op Fl s Ar packetsize
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.Op Fl t Ar tos
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.Op Fl T Ar ttl
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.Op Fl w Ar maxwait
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.Ar host
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.Sh DESCRIPTION
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.Nm
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uses the
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.Tn ICMP
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protocol's mandatory
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.Tn ECHO_REQUEST
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datagram to elicit an
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.Tn ICMP ECHO_RESPONSE
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from a host or gateway.
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.Tn ECHO_REQUEST
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datagrams (``pings'') have an IP and
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.Tn ICMP
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header,
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followed by a
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.Dq struct timeval
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and then an arbitrary number of ``pad'' bytes used to fill out the
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packet.
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl c Ar count
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Stop after sending (and receiving)
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.Ar count
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.Tn ECHO_RESPONSE
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packets.
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.It Fl d
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Set the
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.Dv SO_DEBUG
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option on the socket being used.
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.It Fl D
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Set the
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.Dv Don't Fragment
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bit in the IP header.
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This can be used to determine the path MTU.
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.It Fl f
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Flood ping.
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Outputs packets as fast as they come back or one hundred times per second,
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whichever is more.
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For every
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.Tn ECHO_REQUEST
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sent a period ``.'' is printed, while for every
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.Tn ECHO_REPLY
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received a backspace is printed.
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This provides a rapid display of how many packets are being dropped.
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Only the super-user may use this option.
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.Bf -emphasis
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This can be very hard on a network and should be used with caution.
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.Ef
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.It Fl g Ar gateway
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Use Lose Source Routing to send the ECHO_REQUEST packets via
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.Ar gateway .
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.It Fl i Ar interval
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Wait
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.Ar interval
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seconds
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.Em between sending each packet .
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The default is to wait for one second between each packet,
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except when the -f option is used the wait interval is 0.01 seconds.
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.It Fl I Ar ifaddr
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Send multicast datagrams on the network interface specified by the
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interface's hostname or IP address.
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.It Fl h Ar host
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is an alternate way of specifying the target host instead of as the
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last argument.
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.It Fl l Ar preload
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If
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.Ar preload
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is specified,
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.Nm
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sends that many packets as fast as possible before falling into its normal
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mode of behavior.
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Only the super-user may use this option.
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.It Fl L
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Disable loopback when sending to multicast destinations,
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so the transmitting host doesn't see the ICMP requests.
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.It Fl n
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Numeric output only.
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No attempt will be made to look up symbolic names for host addresses.
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.It Fl o
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Exit successfully after receiving one reply packet.
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.It Fl p Ar pattern
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You may specify up to 16 ``pad'' bytes to fill out the packet you send.
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This is useful for diagnosing data-dependent problems in a network.
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For example,
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.Dq Li \-p ff
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will cause the sent packet to be filled with all
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ones.
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.It Fl P
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Use a psuedo-random sequence for the data instead of the default,
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fixed sequence of incrementing 8-bit integers.
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This is useful to foil compression on PPP and other links.
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.It Fl q
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Quiet output.
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Nothing is displayed except the summary lines at startup time and
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when finished.
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.It Fl Q
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Do not display responses such as Network Unreachable ICMP messages
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concerning the ECHO_REQUESTs sent.
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.It Fl r
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Bypass the normal routing tables and send directly to a host on an attached
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network.
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If the host is not on a directly-attached network, an error is returned.
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This option can be used to ping a local host through an interface
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that has no route through it (e.g., after the interface was dropped by
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.Xr routed 8 ) .
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.It Fl R
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Record Route.
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Includes the
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.Tn RECORD_ROUTE
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option in the
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.Tn ECHO_REQUEST
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packet and displays the route buffer on returned packets.
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Note that the IP header is only large enough for eight such routes,
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and only six when using the
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.Fl g
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option.
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This is why it was necessary to invent
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.Xr traceroute 8 .
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Many hosts ignore or discard this option.
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.It Fl s Ar packetsize
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Specifies the number of data bytes to be sent.
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The default is 56, which translates into 64
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.Tn ICMP
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data bytes when combined
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with the 8 bytes of
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.Tn ICMP
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header data.
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The maximum allowed value is 65468 bytes.
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.It Fl T Ar ttl
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Use the specified time-to-live.
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.It Fl t Ar tos
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Use the specified hexadecimal type of service.
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.It Fl v
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Verbose output.
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.Tn ICMP
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packets other than
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.Tn ECHO_RESPONSE
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that are received are listed.
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.It Fl w Ar maxwait
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Specifies the number of seconds to wait for a response to a packet
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before transmitting the next one.
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The default is 10.
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.El
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.Pp
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When using
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.Nm
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for fault isolation, it should first be run on the local host, to verify
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that the local network interface is up and running.
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Then, hosts and gateways further and further away should be ``pinged''.
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.Pp
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Round-trip times and packet loss statistics are computed.
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If duplicate packets are received, they are not included in the packet
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loss calculation, although the round trip time of these packets is used
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in calculating the minimum/average/maximum round-trip time numbers.
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.Pp
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When the specified number of packets have been sent (and received) or
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if the program is terminated with a
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.Dv SIGINT ,
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a brief summary is displayed.
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The summary information can be displayed while
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.Nm
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is running by sending it a
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.Dv SIGINFO
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signal (see the
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.Dq status
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argument for
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.Xr stty 1
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for more information).
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.Pp
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.Nm
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continually sends one datagram per second, and prints one line of
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output for every ECHO_RESPONSE returned.
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On a trusted system with IP Security Options enabled, if the network
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idiom is not MONO,
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.Nm
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also prints a second line containing the hexadecimal representation
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of the IP security option in the ECHO_RESPONSE.
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.Pp
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If the
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.Fl c
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count option is given, only that number of requests is sent.
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No output is produced if there is no response.
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Round-trip times and packet loss statistics are computed.
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If duplicate packets are received, they are not included in the
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packet loss calculation, although the round trip time of these
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packets is used in calculating the minimum/average/maximum round-trip
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time numbers.
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When the specified number of packets have been sent (and received)
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or if the program is terminated with an interrupt (SIGINT), a brief
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summary is displayed.
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.Pp
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When not using the
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.Fl f
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(flood) option, the first interrupt, usually generated by control-C or DEL,
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causes
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.Nm
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to wait for its outstanding requests to return.
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It will wait no longer than the longest round trip time encountered
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by previous, successful pings.
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The second interrupt stops ping immediately.
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.Pp
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This program is intended for use in network testing, measurement and
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management.
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Because of the load it can impose on the network, it is unwise to use
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.Nm
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during normal operations or from automated scripts.
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.Sh ICMP PACKET DETAILS
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An IP header without options is 20 bytes.
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An
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.Tn ICMP
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.Tn ECHO_REQUEST
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packet contains an additional 8 bytes worth
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of
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.Tn ICMP
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header followed by an arbitrary amount of data.
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When a
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.Ar packetsize
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is given, this indicated the size of this extra piece of data (the
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default is 56).
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Thus the amount of data received inside of an IP packet of type
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.Tn ICMP
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.Tn ECHO_REPLY
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will always be 8 bytes more than the requested data space
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(the
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.Tn ICMP
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header).
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.Pp
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If the data space is at least eight bytes large,
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.Nm
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uses the first eight bytes of this space to include a timestamp to compute
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round trip times.
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If less than eight bytes of pad are specified, no round trip times are
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given.
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.Sh DUPLICATE AND DAMAGED PACKETS
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.Nm
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will report duplicate and damaged packets.
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Duplicate packets should never occur, and seem to be caused by
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inappropriate link-level retransmissions.
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Duplicates may occur in many situations and are rarely (if ever) a
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good sign, although the presence of low levels of duplicates may not
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always be cause for alarm.
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.Pp
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Damaged packets are obviously serious cause for alarm and often
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indicate broken hardware somewhere in the
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.Nm
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packet's path (in the network or in the hosts).
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.Sh TRYING DIFFERENT DATA PATTERNS
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The (inter)network layer should never treat packets differently depending
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on the data contained in the data portion.
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Unfortunately, data-dependent problems have been known to sneak into
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networks and remain undetected for long periods of time.
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.Pp
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In many cases the particular pattern that will have problems is something
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that doesn't have sufficient ``transitions'', such as all ones or all
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zeros, or a pattern right at the edge, such as almost all zeros.
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It isn't necessarily enough to specify a data pattern of all zeros (for
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example) on the command line because the pattern that is of interest is
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at the data link level, and the relationship between what you type and
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what the controllers transmit can be complicated.
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.Pp
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This means that if you have a data-dependent problem you will probably
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have to do a lot of testing to find it.
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If you are lucky, you may manage to find a file that either can't be sent
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across your network or that takes much longer to transfer than other
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similar length files.
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You can then examine this file for repeated patterns that you can test
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using
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.Nm
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.Fl p .
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.Sh TTL DETAILS
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The
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.Tn TTL
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value of an IP packet represents the maximum number of IP routers
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that the packet can go through before being thrown away.
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In current practice you can expect each router in the Internet to decrement
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the
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.Tn TTL
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field by exactly one.
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.Pp
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The
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.Tn TCP/IP
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specification states that the
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.Tn TTL
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field for
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.Tn TCP
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packets should
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be set to 60, but many systems use smaller values
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.Po
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.Bx 4.3
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uses 30,
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.Bx 4.2
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used 15
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.Pc .
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.Pp
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The maximum possible value of this field is 255, and most
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.Ux
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systems set the
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.Tn TTL
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field of
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.Tn ICMP ECHO_REQUEST
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packets to 255.
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This is why you will find you can ``ping'' some hosts, but not reach them
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with
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.Xr telnet 1
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or
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.Xr ftp 1 .
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.Pp
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In normal operation ping prints the ttl value from the packet it receives.
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When a remote system receives a ping packet, it can do one of three things
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with the
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.Tn TTL
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field in its response:
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.Bl -bullet
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.It
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Not change it; this is what Berkeley
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.Ux
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systems did before the
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.Bx 4.3 tahoe
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release.
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In this case the
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.Tn TTL
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value in the received packet will be 255 minus the
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number of routers in the round-trip path.
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.It
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Set it to 255; this is what current Berkeley
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.Ux
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systems do.
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In this case the
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.Tn TTL
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value in the received packet will be 255 minus the
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number of routers in the path
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.Em from
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the remote system
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.Em to
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the
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.Nm "" Ns Em ing
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host.
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.It
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Set it to some other value.
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Some machines use the same value for
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.Tn ICMP
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packets that they use for
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.Tn TCP
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packets, for example either 30 or 60.
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Others may use completely wild values.
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.El
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.Sh EXIT STATUS
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.Nm
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returns 0 on success (the host is alive),
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and non-zero if the arguments are incorrect or the host is not responding.
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.Sh BUGS
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Many Hosts and Gateways ignore the
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.Tn RECORD_ROUTE
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option.
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.Pp
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The maximum IP header length is too small for options like
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.Tn RECORD_ROUTE
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to
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be completely useful.
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There's not much that that can be done about this, however.
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.Pp
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Flood pinging is not recommended in general, and flood pinging the
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broadcast address should only be done under very controlled conditions.
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.Sh SEE ALSO
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.Xr netstat 1 ,
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.Xr ifconfig 8 ,
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.Xr routed 8 ,
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.Xr traceroute 8 ,
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.Xr spray 8
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.Sh HISTORY
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The
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.Nm
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command appeared in
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.Bx 4.3 .
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