343 lines
12 KiB
Groff
343 lines
12 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Van Jacobson.
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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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.\" @(#)traceroute.8 8.1 (Berkeley) 6/6/93
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.\"
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.Dd March 7, 1996
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.Dt TRACEROUTE 8
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.Os BSD 4.3
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.Sh NAME
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.Nm traceroute
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.Nd print the route packets take to network host
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.Sh SYNOPSIS
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.Nm traceroute
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.Op Fl g Ar gateway
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.Op Fl m Ar max_ttl
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.Op Fl n
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.Op Fl p Ar port
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.Op Fl q Ar nqueries
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.Op Fl r
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.Bk -words
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.Op Fl s Ar src_addr
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.Ek
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.Op Fl t Ar tos
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.Op Fl v
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.Op Fl w Ar waittime
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.Ar host
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.Op Ar packetsize
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.Sh DESCRIPTION
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The Internet is a large and complex aggregation of
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network hardware, connected together by gateways.
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Tracking the route one's packets follow (or finding the miscreant
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gateway that's discarding your packets) can be difficult.
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.Nm Traceroute
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utilizes the IP protocol `time to live' field and attempts to elicit an
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.Tn ICMP
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.Dv TIME_EXCEEDED
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response from each gateway along the path to some
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host.
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.Pp
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The only mandatory parameter is the destination host name or IP number.
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The default probe datagram length is 38 bytes, but this may be increased
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by specifying a packet size (in bytes) after the destination host
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name.
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.Pp
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Other options are:
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.Bl -tag -width Ds
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.It Fl g Ar gateway
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Add a loose-source-route IP option onto the ICMP packet to direct traffic
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to traverse the specified gateway.
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Multiple gateway options may be specified on the command line.
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.It Fl m Ar max_ttl
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Set the max time-to-live (max number of hops) used in outgoing probe
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packets. The default is 30 hops (the same default used for
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.Tn TCP
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connections).
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.It Fl n
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Print hop addresses numerically rather than symbolically and numerically
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(saves a nameserver address-to-name lookup for each gateway found on the
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path).
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.It Fl p Ar port
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Set the base
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.Tn UDP
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.Ar port
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number used in probes (default is 33434).
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.Nm Traceroute
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hopes that nothing is listening on
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.Tn UDP
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ports
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.Em base
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to
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.Em base+nhops-1
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at the destination host (so an
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.Tn ICMP
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.Dv PORT_UNREACHABLE
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message will
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be returned to terminate the route tracing). If something is
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listening on a port in the default range, this option can be used
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to pick an unused port range.
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.It Fl q Ar nqueries
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Set the number of probes per ``ttl'' to
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.Ar nqueries
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(default is three probes).
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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,
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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 src_addr
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Use the following IP address
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(which must be given as an IP number, not
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a hostname) as the source address in outgoing probe packets. On
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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 tos
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Set the
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.Em type-of-service
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in probe packets to the following value (default zero). The value must be
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a decimal integer in the range 0 to 255. This option can be used to
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see if different types-of-service result in different paths. (If you
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are not running a
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.Bx 4.3 tahoe
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or later system, this may be academic since the normal network
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services like telnet and ftp don't let you control the
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.Dv TOS ) .
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Not all values of
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.Dv TOS
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are legal or
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meaningful \- see the IP spec for definitions. Useful values are
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probably
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.Ql \-t 16
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(low delay) and
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.Ql \-t 8
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(high throughput).
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.It Fl v
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Verbose output. Received
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.Tn ICMP
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packets other than
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.Dv TIME_EXCEEDED
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and
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.Dv UNREACHABLE Ns s
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are listed.
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.It Fl w
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Set the time (in seconds) to wait for a response to a probe (default 3
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sec.).
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.El
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.Pp
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This program attempts to trace the route an IP packet would follow to some
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internet host by launching
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.Tn UDP
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probe
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packets with a small ttl (time to live) then listening for an
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.Tn ICMP
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"time exceeded" reply from a gateway. We start our probes
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with a ttl of one and increase by one until we get an
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.Tn ICMP
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"port unreachable"
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(which means we got to "host") or hit a max (which
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defaults to 30 hops & can be changed with the
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.Fl m
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flag). Three
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probes (changed with
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.Fl q
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flag) are sent at each ttl setting and a
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line is printed showing the ttl, address of the gateway and
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round trip time of each probe. If the probe answers come from
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different gateways, the address of each responding system will
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be printed. If there is no response within a 3 sec. timeout
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interval (changed with the
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.Fl w
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flag), a "*" is printed for that
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probe.
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.Pp
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We don't want the destination
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host to process the
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.Tn UDP
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probe packets so the destination port is set to an
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unlikely value (if some clod on the destination is using that
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value, it can be changed with the
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.Fl p
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flag).
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.Pp
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A sample use and output might be:
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.Bd -literal
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[yak 71]% traceroute nis.nsf.net.
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traceroute to nis.nsf.net (35.1.1.48), 30 hops max, 56 byte packet
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1 helios.ee.lbl.gov (128.3.112.1) 19 ms 19 ms 0 ms
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2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
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3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
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4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 39 ms
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5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 39 ms 39 ms 39 ms
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6 128.32.197.4 (128.32.197.4) 40 ms 59 ms 59 ms
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7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 59 ms
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8 129.140.70.13 (129.140.70.13) 99 ms 99 ms 80 ms
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9 129.140.71.6 (129.140.71.6) 139 ms 239 ms 319 ms
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10 129.140.81.7 (129.140.81.7) 220 ms 199 ms 199 ms
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11 nic.merit.edu (35.1.1.48) 239 ms 239 ms 239 ms
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.Ed
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Note that lines 2 & 3 are the same. This is due to a buggy
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kernel on the 2nd hop system \- lbl-csam.arpa \- that forwards
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packets with a zero ttl (a bug in the distributed version
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of 4.3
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.Tn BSD ) .
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Note that you have to guess what path
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the packets are taking cross-country since the
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.Tn NSFNet
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(129.140)
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doesn't supply address-to-name translations for its
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.Tn NSS Ns es .
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.Pp
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A more interesting example is:
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.Bd -literal
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[yak 72]% traceroute allspice.lcs.mit.edu.
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traceroute to allspice.lcs.mit.edu (18.26.0.115), 30 hops max
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1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
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2 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 19 ms 19 ms
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3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 19 ms
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4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 19 ms 39 ms 39 ms
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5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 20 ms 39 ms 39 ms
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6 128.32.197.4 (128.32.197.4) 59 ms 119 ms 39 ms
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7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 39 ms
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8 129.140.70.13 (129.140.70.13) 80 ms 79 ms 99 ms
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9 129.140.71.6 (129.140.71.6) 139 ms 139 ms 159 ms
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10 129.140.81.7 (129.140.81.7) 199 ms 180 ms 300 ms
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11 129.140.72.17 (129.140.72.17) 300 ms 239 ms 239 ms
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12 * * *
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13 128.121.54.72 (128.121.54.72) 259 ms 499 ms 279 ms
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14 * * *
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15 * * *
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16 * * *
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17 * * *
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18 ALLSPICE.LCS.MIT.EDU (18.26.0.115) 339 ms 279 ms 279 ms
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.Ed
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Note that the gateways 12, 14, 15, 16 & 17 hops away
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either don't send
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.Tn ICMP
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"time exceeded" messages or send them
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with a ttl too small to reach us. 14 \- 17 are running the
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.Tn MIT
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C Gateway code that doesn't send "time exceeded"s. God
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only knows what's going on with 12.
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.Pp
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The silent gateway 12 in the above may be the result of a bug in
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the 4.[23]
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.Tn BSD
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network code (and its derivatives): 4.x (x <= 3)
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sends an unreachable message using whatever ttl remains in the
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original datagram. Since, for gateways, the remaining ttl is
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zero, the
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.Tn ICMP
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"time exceeded" is guaranteed to not make it back
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to us. The behavior of this bug is slightly more interesting
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when it appears on the destination system:
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.Bd -literal
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1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
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2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 39 ms
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3 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 39 ms 19 ms
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4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 19 ms
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5 ccn-nerif35.Berkeley.EDU (128.32.168.35) 39 ms 39 ms 39 ms
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6 csgw.Berkeley.EDU (128.32.133.254) 39 ms 59 ms 39 ms
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7 * * *
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8 * * *
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9 * * *
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10 * * *
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11 * * *
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12 * * *
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13 rip.Berkeley.EDU (128.32.131.22) 59 ms ! 39 ms ! 39 ms !
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.Ed
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Notice that there are 12 "gateways" (13 is the final
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destination) and exactly the last half of them are "missing".
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What's really happening is that rip (a Sun-3 running Sun OS3.5)
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is using the ttl from our arriving datagram as the ttl in its
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.Tn ICMP
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reply. So, the reply will time out on the return path
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(with no notice sent to anyone since
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.Tn ICMP's
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aren't sent for
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.Tn ICMP's )
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until we probe with a ttl that's at least twice the path
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length. I.e., rip is really only 7 hops away. A reply that
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returns with a ttl of 1 is a clue this problem exists.
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.Nm Traceroute
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prints a "!" after the time if the ttl is <= 1.
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Since vendors ship a lot of obsolete
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.Pf ( Tn DEC Ns \'s
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Ultrix, Sun 3.x) or
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non-standard
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.Pq Tn HPUX
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software, expect to see this problem
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frequently and/or take care picking the target host of your
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probes.
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Other possible annotations after the time are
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.Sy !H ,
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.Sy !N ,
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.Sy !P
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(got a host, network or protocol unreachable, respectively),
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.Sy !S
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or
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.Sy !F
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(source route failed or fragmentation needed \- neither of these should
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ever occur and the associated gateway is busted if you see one). If
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almost all the probes result in some kind of unreachable,
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.Nm traceroute
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will give up and exit.
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.Pp
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This program is intended for use in network testing, measurement
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and management.
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It should be used primarily for manual fault isolation.
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Because of the load it could impose on the network, it is unwise to use
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.Nm traceroute
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during normal operations or from automated scripts.
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.Sh AUTHOR
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Implemented by Van Jacobson from a suggestion by Steve Deering. Debugged
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by a cast of thousands with particularly cogent suggestions or fixes from
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C. Philip Wood, Tim Seaver and Ken Adelman.
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.Sh SEE ALSO
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.Xr netstat 1 ,
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.Xr ping 8
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.Sh HISTORY
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The
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.Nm traceroute
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command first appeard in 4.4
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.Tn BSD
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