443 lines
12 KiB
Groff
443 lines
12 KiB
Groff
.\" 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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.\" $FreeBSD$
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.\"
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.Dd March 1, 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 ping
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.Op Fl QRadfnqrv
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.Op Fl c Ar count
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.Op Fl i Ar wait
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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 S Ar src_addr
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.Bo
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.Ar host |
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.Op Fl L
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.Op Fl I Ar interface
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.Op Fl T Ar ttl
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.Ar mcast-group
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.Bc
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.Sh DESCRIPTION
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.Nm Ping
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uses the
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.Tn ICMP
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.No protocol Ap 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
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.Pq Dq pings
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have an IP and
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.Tn ICMP
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header, followed by a
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.Dq struct timeval
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and then an arbitrary number of
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.Dq pad
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bytes used to fill out the packet. The options are as follows:
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.Bl -tag -width indent
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.It Fl a
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Audible. Include a bell
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.Pq ASCII 0x07
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character in the output when any packet is received. This option is ignored
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if other format options are present.
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.It Fl c Ar count
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Stop after sending
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.Pq and receiving
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.Ar count
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.Tn ECHO_RESPONSE
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packets.
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If this option is not specified,
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.Nm
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will operate until interrupted.
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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 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
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.Dq \&.
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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 i Ar wait
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Wait
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.Ar wait
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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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The wait time may be fractional, but only the super-user may specify
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values less then 1 second.
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This option is incompatible with the
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.Fl f
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option.
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.It Fl I Ar interface
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Source multicast packets with the given interface address.
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This flag only applies if the ping destination is a multicast address.
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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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Suppress loopback of multicast packets.
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This flag only applies if the ping destination is a multicast address.
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.It Fl n
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Numeric output only.
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No attempt will be made to lookup symbolic names for host addresses.
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.It Fl p Ar pattern
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You may specify up to 16
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.Dq pad
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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 Q
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Somewhat quiet output.
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.No Don Ap t
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display ICMP error messages that are in response to our query messages.
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Originally, the
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.Fl v
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flag was required to display such errors, but
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.Fl v
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displays all ICMP error messages. On a busy machine, this output can
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be overbearing. Without the
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.Fl Q
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flag,
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.Nm
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prints out any ICMP error messages caused by its own ECHO_REQUEST
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messages.
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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 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
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the route buffer on returned packets.
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Note that the IP header is only large enough for nine such routes;
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the
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.Xr traceroute 8
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command is usually better at determining the route packets take to a
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particular destination.
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If more routes come back than should, such as due to an illegal spoofed
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packet, ping will print the route list and then truncate it at the correct
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spot.
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Many hosts ignore or discard the
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.Tn RECORD_ROUTE
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option.
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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
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.Po
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e.g., after the interface was dropped by
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.Xr routed 8
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.Pc .
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.It Fl s Ar packetsize
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Specify 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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Only the super-user may use this option.
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.It Fl S Ar src_addr
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Use the following IP address as the source address in outgoing packets.
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On hosts with more than one IP address, this option can be used to
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force the source address to be something other than the IP address
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of the interface the probe packet is sent on. If the IP address
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is not one of this machine's interface addresses, an error is
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returned and nothing is sent.
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.It Fl T Ar ttl
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Set the IP Time To Live for multicasted packets.
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This flag only applies if the ping destination is a multicast address.
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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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.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
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.Dq pinged .
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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 round-trip time statistics.
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When the specified number of packets have been sent
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.Pq and received
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or if the program is terminated with a
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.Dv SIGINT ,
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a brief summary is displayed, showing the number of packets sent and
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received, and the minimum, maximum, mean, and standard deviation of
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the round-trip times.
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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 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
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.Pq the 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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.Pq the Tn ICMP 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 which
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it uses in the computation of 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 Ping
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will report duplicate and damaged packets.
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Duplicate packets should never occur when pinging a unicast address,
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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
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.Pq if ever
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a 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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Duplicates are expected when pinging a broadcast or multicast address,
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since they are not really duplicates but replies from different hosts
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to the same request.
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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
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(inter)network
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layer should never treat packets differently depending on the data
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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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In many cases the particular pattern that will have problems is something
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that does not have sufficient
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.Dq transitions ,
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such as all ones or all zeros, or a pattern right at the edge, such as
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almost all zeros.
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It is not
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necessarily enough to specify a data pattern of all zeros (for example)
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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
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cannot
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be sent across your network or that takes much longer to transfer than
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other 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 the
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.Fl p
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option of
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.Nm Ns .
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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 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
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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
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.Dq ping
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some hosts, but not reach them 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
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.Nm
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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
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.Bx
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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
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.Bx
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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 RETURN VALUES
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The
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.Nm
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command returns an exit status of zero if at least one response was
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heard from the specified
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.Ar host ;
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a status of two if the transmission was successful but no responses
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were received; or another value
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.Pq from Aq Pa sysexits.h
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if an error occurred.
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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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.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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.Sh AUTHORS
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The original
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.Nm
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command was written by
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.An Mike Muuss
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while at the US Army Ballistics
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Research Laboratory.
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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 be completely useful.
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.No There Ap s
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not much 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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.Pp
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The
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.Fl v
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option is not worth much on busy hosts.
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