398 lines
14 KiB
Groff
398 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 November 25, 2020
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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 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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