8d4401b9b0
inconsistent. This patch fixes that and improves the precision of the description. Thanks to Tom Marcoen for reporting the issue and providing an initial patch, on which this change is based. PR: 237723 Reviewed by: bcr@ MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D20708
399 lines
14 KiB
Groff
399 lines
14 KiB
Groff
.\" Copyright (c) 1989, 1995, 1996, 1997, 1999, 2000
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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 are permitted
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.\" provided that the above copyright notice and this paragraph are
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.\" duplicated in all such forms and that any documentation,
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.\" advertising materials, and other materials related to such
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.\" distribution and use acknowledge that the software was developed
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.\" by the University of California, Berkeley. The name of the
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.\" University may not be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
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.\" WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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.\"
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.\" $Id: traceroute.8,v 1.19 2000/09/21 08:44:19 leres Exp $
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.\" $FreeBSD$
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.\"
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.Dd June 20, 2019
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.Dt TRACEROUTE 8
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.Os
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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
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.Bk -words
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.Op Fl adDeFISnrvx
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.Op Fl f Ar first_ttl
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.Op Fl g Ar gateway
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.Op Fl M Ar first_ttl
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.Op Fl m Ar max_ttl
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.Op Fl P Ar proto
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.Op Fl p Ar port
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.Op Fl q Ar nprobes
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.Op Fl s Ar src_addr
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.Op Fl t Ar tos
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.Op Fl w Ar waittime
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.Op Fl A Ar as_server
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.Op Fl z Ar pausemsecs
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.Ar host
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.Op Ar packetlen
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.Ek
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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
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utilizes the IP protocol `time to live' field and attempts to elicit an
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ICMP TIME_EXCEEDED 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 40 bytes, but this may be increased
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by specifying a packet length (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 a
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Turn on AS# lookups for each hop encountered.
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.It Fl A Ar as_server
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Turn on AS# lookups and use the given server instead of the
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default.
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.It Fl e
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Firewall evasion mode.
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Use fixed destination ports for UDP, UDP-Lite, TCP and SCTP probes.
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The destination port does NOT increment with each packet sent.
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.It Fl f Ar first_ttl
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Set the initial time-to-live used in the first outgoing probe packet.
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.It Fl F
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Set the "don't fragment" bit.
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.It Fl d
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Enable socket level debugging.
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.It Fl D
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When an ICMP response to our probe datagram is received,
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print the differences between the transmitted packet and
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the packet quoted by the ICMP response.
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A key showing the location of fields within the transmitted packet is printed,
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followed by the original packet in hex,
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followed by the quoted packet in hex.
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Bytes that are unchanged in the quoted packet are shown as underscores.
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Note,
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the IP checksum and the TTL of the quoted packet are not expected to match.
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By default, only one probe per hop is sent with this option.
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.It Fl g Ar gateway
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Specify a loose source route gateway (8 maximum).
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.It Fl i Ar iface
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Specify a network interface to obtain the source IP address for
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outgoing probe packets. This is normally only useful on a multi-homed
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host. (See the
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.Fl s
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flag for another way to do this.)
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.It Fl I
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Use ICMP ECHO instead of UDP datagrams. (A synonym for "-P icmp").
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.It Fl M Ar first_ttl
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Set the initial time-to-live value used in outgoing probe packets.
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The default is 1, i.e., start with the first hop.
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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 the value of the
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.Va net.inet.ip.ttl
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.Xr sysctl 8
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(the same default used for 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 proto
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Send packets of specified IP protocol. The currently supported protocols
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are: UDP, UDP-Lite, TCP, SCTP, GRE and ICMP. Other protocols may also be
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specified (either by name or by number), though
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.Nm
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does not implement any special knowledge of their packet formats. This
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option is useful for determining which router along a path may be
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blocking packets based on IP protocol number. But see BUGS below.
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.It Fl p Ar port
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Protocol specific. For UDP, UDP-Lite, TCP and SCTP, sets
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the base
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.Ar port
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number used in probes (default is 33434).
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Traceroute hopes that nothing is listening on UDP ports (or UDP-Lite ports
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if used by
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.Nm
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and supported by the peer)
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.Em port + 1
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to
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.Em port + (max_ttl - first_ttl + 1) * nprobes
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at the destination host (so an ICMP PORT_UNREACHABLE 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 nprobes
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Set the number of probes per hop (default is 3,
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unless
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.Fl D
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is specified,
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when it is 1).
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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 (which usually is 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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multi-homed hosts (those with more than one IP
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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. (See the
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.Fl i
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flag for another way to do this.)
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.It Fl S
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Print a summary of how many probes were not answered for each hop.
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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 4.4bsd, this may be academic since the normal network
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services like telnet and ftp don't let you control the TOS).
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Not all values of TOS 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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.Fl t Ar 16
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(low delay) and
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.Fl t Ar 8
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(high throughput).
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.It Fl v
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Verbose output. Received ICMP 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 Ar waittime
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Set the time (in seconds) to wait for a response to a probe (default 5
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sec.).
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.It Fl x
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Toggle ip checksums. Normally, this prevents traceroute from calculating
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ip checksums. In some cases, the operating system can overwrite parts of
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the outgoing packet but not recalculate the checksum (so in some cases
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the default is to not calculate checksums and using
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.Fl x
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causes them to be calculated). Note that checksums are usually required
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for the last hop when using ICMP ECHO probes
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.Pq Fl I .
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So they are always calculated when using ICMP.
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.It Fl z Ar pausemsecs
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Set the time (in milliseconds) to pause between probes (default 0).
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Some systems such as Solaris and routers such as Ciscos rate limit
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icmp messages. A good value to use with this this is 500 (e.g. 1/2 second).
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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 UDP probe
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packets with a small ttl (time to live) then listening for an
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ICMP "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 ICMP "port
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unreachable" (which means we got to "host") or hit a max (which
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defaults to the amount of hops specified by the
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.Va net.inet.ip.ttl
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.Xr sysctl 8
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and can be changed with the
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.Fl m
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flag). Three
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probes (change 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 5 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 UDP 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 -offset 4n
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% traceroute nis.nsf.net.
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traceroute to nis.nsf.net (35.1.1.48), 64 hops max, 38 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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.Pp
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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 \- lilac-dmc.Berkeley.EDU \- that forwards
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packets with a zero ttl (a bug in the distributed version
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of 4.3BSD). Note that you have to guess what path
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the packets are taking cross-country since the NSFNet (129.140)
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doesn't supply address-to-name translations for its NSSes.
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.Pp
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A more interesting example is:
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.Bd -literal -offset 4n
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% traceroute allspice.lcs.mit.edu.
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traceroute to allspice.lcs.mit.edu (18.26.0.115), 64 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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.Pp
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Note that the gateways 12, 14, 15, 16 & 17 hops away
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either don't send ICMP "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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MIT 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]BSD 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 ICMP "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 -offset 4n
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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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.Pp
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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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ICMP reply. So, the reply will time out on the return path
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(with no notice sent to anyone since ICMP's aren't sent for
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ICMP's) 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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Traceroute 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 HP-UX
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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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.Pp
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Other possible annotations after the time are:
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.Bl -hang -offset indent -width 12n
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.It Sy !H
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Host unreachable.
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.It Sy !N
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Network unreachable.
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.It Sy !P
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Protocol unreachable.
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.It Sy !S
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Source route failed.
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.It Sy !F\-<pmtu>
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Fragmentation needed.
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The RFC1191 Path MTU Discovery value is displayed.
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.It Sy !U
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Destination network unknown.
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.It Sy !W
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Destination host unknown.
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.It Sy !I
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Source host is isolated.
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.It Sy !A
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Communication with destination network administratively prohibited.
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.It Sy !Z
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Communication with destination host administratively prohibited.
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.It Sy !Q
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For this ToS the destination network is unreachable.
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.It Sy !T
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For this ToS the destination host is unreachable.
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.It Sy !X
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Communication administratively prohibited.
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.It Sy !V
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Host precedence violation.
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.It Sy !C
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Precedence cutoff in effect.
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.It Sy !<num>
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ICMP unreachable code <num>.
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.El
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.Pp
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These are defined by RFC1812 (which supersedes RFC1716).
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If almost all the probes result in some kind of unreachable,
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.Nm
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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
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during normal operations or from automated scripts.
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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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.Xr ping6 8 ,
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.Xr traceroute6 8 .
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.Sh AUTHORS
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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 BUGS
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When using protocols other than UDP, functionality is reduced.
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In particular, the last packet will often appear to be lost, because
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even though it reaches the destination host, there's no way to know
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that because no ICMP message is sent back.
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In the TCP case,
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.Nm
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should listen for a RST from the destination host (or an intermediate
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router that's filtering packets), but this is not implemented yet.
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.Pp
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The AS number capability reports information that may sometimes be
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inaccurate due to discrepancies between the contents of the
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routing database server and the current state of the Internet.
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