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1.\" Copyright (c) 1989, 1995, 1996
2.\" The Regents of the University of California. All rights reserved.
3.\"
4.\" Redistribution and use in source and binary forms are permitted
5.\" provided that the above copyright notice and this paragraph are
6.\" duplicated in all such forms and that any documentation,
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9.\" by the University of California, Berkeley. The name of the
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12.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
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15.\"
16.\" $Header: traceroute.8,v 1.7 96/09/27 20:02:41 leres Exp $
17.\" $FreeBSD: src/contrib/traceroute/traceroute.8,v 1.6.2.2 2002/11/27 17:05:29 fenner Exp $
1de703da 18.\" $DragonFly: src/contrib/traceroute/Attic/traceroute.8,v 1.2 2003/06/17 04:24:07 dillon Exp $
984263bc
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19.\"
20.TH TRACEROUTE 8 "27 September 1996"
21.UC 6
22.SH NAME
23traceroute \- print the route packets take to network host
24.SH SYNOPSIS
25.. while ((op = getopt(argc, argv, "dnrvg:M:m:P:p:q:s:t:w:")) != EOF)
26.na
27.B traceroute
28[
29.B \-Sdnrv
30] [
31.B \-g
32.I gw_host
33] [
34.B \-M
35.I min_ttl
36]
37.br
38.ti +8
39[
40.B \-m
41.I max_ttl
42] [
43.B \-P
44.I proto
45] [
46.B \-p
47.I port
48]
49.br
50.ti +8
51[
52.B \-q
53.I nqueries
54] [
55.B \-s
56.I src_addr
57] [
58.B \-t
59.I tos
60]
61.br
62.ti +8
63[
64.B \-w
65.I waittime
66]
67.I host
68[
69.I packetlen
70]
71.ad
72.SH DESCRIPTION
73The Internet is a large and complex aggregation of
74network hardware, connected together by gateways.
75Tracking the route one's packets follow (or finding the miscreant
76gateway that's discarding your packets) can be difficult.
77.I Traceroute
78utilizes the IP protocol `time to live' field and attempts to elicit an
79ICMP TIME_EXCEEDED response from each gateway along the path to some
80host.
81.PP
82The only mandatory parameter is the destination host name or IP number.
83The default probe datagram length is 40 bytes, but this may be increased
84by specifying a packet length (in bytes) after the destination host
85name.
86.PP
87Other options are:
88.TP
89.B \-S
90Print a summary of how many probes were not answered for each hop.
91.TP
92.B \-g
93Specify a loose source route gateway (8 maximum).
94.TP
95.B \-M
96Set the initial time-to-live value used in outgoing probe packets.
97The default is 1, i.e., start with the first hop.
98.TP
99.B \-m
100Set the max time-to-live (max number of hops) used in outgoing probe
101packets. The default is
102.I net.inet.ip.ttl
103hops (the same default used for TCP
104connections).
105.TP
106.B \-n
107Print hop addresses numerically rather than symbolically and numerically
108(saves a nameserver address-to-name lookup for each gateway found on the
109path).
110.TP
111.B \-P
112Send packets of specified IP protocol. The currently supported protocols
113are: UDP, TCP, GRE and ICMP. Other protocols may also be specified (either by
114name or by number), though
115.I traceroute
116does not implement any special knowledge of their packet formats. This
117option is useful for determining which router along a path may be
118blocking packets based on IP protocol number. But see BUGS below.
119.TP
120.B \-p
121Protocol specific. For UDP and TCP, sets
122the base port number used in probes (default is 33434).
123Traceroute hopes that nothing is listening on UDP ports
124.I base
125to
126.I base + nhops - 1
127at the destination host (so an ICMP PORT_UNREACHABLE message will
128be returned to terminate the route tracing). If something is
129listening on a port in the default range, this option can be used
130to pick an unused port range.
131.TP
132.B \-q
133Set the number of probes per hop (default is 3).
134.TP
135.B \-r
136Bypass the normal routing tables and send directly to a host on an attached
137network.
138If the host is not on a directly-attached network,
139an error is returned.
140This option can be used to ping a local host through an interface
141that has no route through it (e.g., after the interface was dropped by
142.IR routed (8C)).
143.TP
144.B \-s
145Use the following IP address (which must be given as an IP number, not
146a hostname) as the source address in outgoing probe packets. On
147hosts with more than one IP address, this option can be used to
148force the source address to be something other than the IP address
149of the interface the probe packet is sent on. If the IP address
150is not one of this machine's interface addresses, an error is
151returned and nothing is sent.
152.TP
153.B \-t
154Set the
155.I type-of-service
156in probe packets to the following value (default zero). The value must be
157a decimal integer in the range 0 to 255. This option can be used to
158see if different types-of-service result in different paths. (If you
159are not running 4.4bsd, this may be academic since the normal network
160services like telnet and ftp don't let you control the TOS).
161Not all values of TOS are legal or
162meaningful \- see the IP spec for definitions. Useful values are
163probably `-t 16' (low delay) and `-t 8' (high throughput).
164.TP
165.B \-v
166Verbose output. Received ICMP packets other than TIME_EXCEEDED and
167UNREACHABLEs are listed.
168.TP
169.B \-w
170Set the time (in seconds) to wait for a response to a probe (default 5
171sec.).
172.PP
173This program attempts to trace the route an IP packet would follow to some
174internet host by launching UDP probe
175packets with a small ttl (time to live) then listening for an
176ICMP "time exceeded" reply from a gateway. We start our probes
177with a ttl of one and increase by one until we get an ICMP "port
178unreachable" (which means we got to "host") or hit a max (which
179defaults to
180.I net.inet.ip.ttl
181hops & can be changed with the \-m flag). Three
182probes (change with \-q flag) are sent at each ttl setting and a
183line is printed showing the ttl, address of the gateway and
184round trip time of each probe. If the probe answers come from
185different gateways, the address of each responding system will
186be printed. If there is no response within a 5 sec. timeout
187interval (changed with the \-w flag), a "*" is printed for that
188probe.
189.PP
190We don't want the destination
191host to process the UDP probe packets so the destination port is set to an
192unlikely value (if some clod on the destination is using that
193value, it can be changed with the \-p flag).
194.PP
195A sample use and output might be:
196
197.RS
198.nf
199[yak 71]% traceroute nis.nsf.net.
200traceroute to nis.nsf.net (35.1.1.48), 64 hops max, 38 byte packet
201 1 helios.ee.lbl.gov (128.3.112.1) 19 ms 19 ms 0 ms
202 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
203 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
204 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 39 ms
205 5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 39 ms 39 ms 39 ms
206 6 128.32.197.4 (128.32.197.4) 40 ms 59 ms 59 ms
207 7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 59 ms
208 8 129.140.70.13 (129.140.70.13) 99 ms 99 ms 80 ms
209 9 129.140.71.6 (129.140.71.6) 139 ms 239 ms 319 ms
21010 129.140.81.7 (129.140.81.7) 220 ms 199 ms 199 ms
21111 nic.merit.edu (35.1.1.48) 239 ms 239 ms 239 ms
212.fi
213.RE
214
215Note that lines 2 & 3 are the same. This is due to a buggy
216kernel on the 2nd hop system \- lbl-csam.arpa \- that forwards
217packets with a zero ttl (a bug in the distributed version
218of 4.3BSD). Note that you have to guess what path
219the packets are taking cross-country since the NSFNet (129.140)
220doesn't supply address-to-name translations for its NSSes.
221.PP
222A more interesting example is:
223
224.RS
225.nf
226[yak 72]% traceroute allspice.lcs.mit.edu.
227traceroute to allspice.lcs.mit.edu (18.26.0.115), 64 hops max
228 1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
229 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 19 ms 19 ms
230 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 19 ms
231 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 19 ms 39 ms 39 ms
232 5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 20 ms 39 ms 39 ms
233 6 128.32.197.4 (128.32.197.4) 59 ms 119 ms 39 ms
234 7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 39 ms
235 8 129.140.70.13 (129.140.70.13) 80 ms 79 ms 99 ms
236 9 129.140.71.6 (129.140.71.6) 139 ms 139 ms 159 ms
23710 129.140.81.7 (129.140.81.7) 199 ms 180 ms 300 ms
23811 129.140.72.17 (129.140.72.17) 300 ms 239 ms 239 ms
23912 * * *
24013 128.121.54.72 (128.121.54.72) 259 ms 499 ms 279 ms
24114 * * *
24215 * * *
24316 * * *
24417 * * *
24518 ALLSPICE.LCS.MIT.EDU (18.26.0.115) 339 ms 279 ms 279 ms
246.fi
247.RE
248
249Note that the gateways 12, 14, 15, 16 & 17 hops away
250either don't send ICMP "time exceeded" messages or send them
251with a ttl too small to reach us. 14 \- 17 are running the
252MIT C Gateway code that doesn't send "time exceeded"s. God
253only knows what's going on with 12.
254.PP
255The silent gateway 12 in the above may be the result of a bug in
256the 4.[23]BSD network code (and its derivatives): 4.x (x <= 3)
257sends an unreachable message using whatever ttl remains in the
258original datagram. Since, for gateways, the remaining ttl is
259zero, the ICMP "time exceeded" is guaranteed to not make it back
260to us. The behavior of this bug is slightly more interesting
261when it appears on the destination system:
262
263.RS
264.nf
265 1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
266 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 39 ms
267 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 39 ms 19 ms
268 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 19 ms
269 5 ccn-nerif35.Berkeley.EDU (128.32.168.35) 39 ms 39 ms 39 ms
270 6 csgw.Berkeley.EDU (128.32.133.254) 39 ms 59 ms 39 ms
271 7 * * *
272 8 * * *
273 9 * * *
27410 * * *
27511 * * *
27612 * * *
27713 rip.Berkeley.EDU (128.32.131.22) 59 ms ! 39 ms ! 39 ms !
278.fi
279.RE
280
281Notice that there are 12 "gateways" (13 is the final
282destination) and exactly the last half of them are "missing".
283What's really happening is that rip (a Sun-3 running Sun OS3.5)
284is using the ttl from our arriving datagram as the ttl in its
285ICMP reply. So, the reply will time out on the return path
286(with no notice sent to anyone since ICMP's aren't sent for
287ICMP's) until we probe with a ttl that's at least twice the path
288length. I.e., rip is really only 7 hops away. A reply that
289returns with a ttl of 1 is a clue this problem exists.
290Traceroute prints a "!" after the time if the ttl is <= 1.
291Since vendors ship a lot of obsolete (DEC's Ultrix, Sun 3.x) or
292non-standard (HPUX) software, expect to see this problem
293frequently and/or take care picking the target host of your
294probes.
295
296Other possible annotations after the time are
297.BR !H ,
298.BR !N ,
299or
300.B !P
301(got a host, network or protocol unreachable, respectively),
302.B !S
303or
304.B !F
305(source route failed or fragmentation needed \- neither of these should
306ever occur and the associated gateway is busted if you see one),
307.B !X
308(communication administratively prohibited), or
309.B !<N>
310(ICMP unreachable code N).
311If almost all the probes result in some kind of unreachable, traceroute
312will give up and exit.
313.PP
314This program is intended for use in network testing, measurement
315and management.
316It should be used primarily for manual fault isolation.
317Because of the load it could impose on the network, it is unwise to use
318.I traceroute
319during normal operations or from automated scripts.
320.SH SEE ALSO
321netstat(1), ping(8)
322.SH AUTHOR
323Implemented by Van Jacobson from a suggestion by Steve Deering. Debugged
324by a cast of thousands with particularly cogent suggestions or fixes from
325C. Philip Wood, Tim Seaver and Ken Adelman.
326.LP
327The current version is available via anonymous ftp:
328.LP
329.RS
330.I ftp://ftp.ee.lbl.gov/traceroute.tar.Z
331.RE
332.SH BUGS
333When using protocols other than UDP, functionality is reduced.
334In particular, the last packet will often appear to be lost, because
335even though it reaches the destination host, there's no way to know
336that because no ICMP message is sent back.
337In the TCP case,
338.I traceroute
339should listen for a RST from the destination host (or an intermediate
340router that's filtering packets), but this is not implemented yet.
341.PP
342Please send bug reports to traceroute@ee.lbl.gov.