ef9e6dc7ee
Turn this behavior off using '-Q'. This makes '-v' useless other than as an ICMP-sniffer, which tcpdump is better at anyway. Print out another couple of ICMP messages, and fix the printing of the original packet (mostly byte order problems).
346 lines
10 KiB
Groff
346 lines
10 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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.\"
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.Dd December 11, 1993
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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 dfnqrvRQ
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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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.Sh DESCRIPTION
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.Nm Ping
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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 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 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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This option is incompatible with the
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.Fl f
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option.
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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 ping
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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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.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 ``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 Q
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Somewhat quiet output.
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Don't 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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Many hosts ignore or discard this 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 (e.g., after the interface was dropped by
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.Xr routed 8 ) .
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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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.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 ping
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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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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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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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.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 ping
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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 ping
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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, 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 ping
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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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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 the
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.Fl p
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option of
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.Nm ping .
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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 (4.3
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.Tn BSD
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uses 30, 4.2 used
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15).
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.Pp
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The maximum possible value of this field is 255, and most Unix 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 ``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 Unix 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 Unix 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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.Xr from
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the remote system
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.Em to
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the
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.Nm ping 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 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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.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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.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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.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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