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16 .\" $Id: traceroute.8,v 1.19 2000/09/21 08:44:19 leres Exp $
24 .Nd "print the route packets take to network host"
40 .Op Fl z Ar pausemsecs
45 The Internet is a large and complex aggregation of
46 network hardware, connected together by gateways.
47 Tracking the route one's packets follow (or finding the miscreant
48 gateway that's discarding your packets) can be difficult.
50 utilizes the IP protocol `time to live' field and attempts to elicit an
51 ICMP TIME_EXCEEDED response from each gateway along the path to some
54 The only mandatory parameter is the destination host name or IP number.
55 The default probe datagram length is 40 bytes, but this may be increased
56 by specifying a packet length (in bytes) after the destination host
62 Turn on AS# lookups for each hop encountered.
64 Turn on AS# lookups and use the given server instead of the
67 Firewall evasion mode.
68 Use fixed destination ports for UDP, UDP-Lite, TCP and SCTP probes.
69 The destination port does NOT increment with each packet sent.
71 Set the initial time-to-live used in the first outgoing probe packet.
73 Set the "don't fragment" bit.
75 Enable socket level debugging.
77 When an ICMP response to our probe datagram is received,
78 print the differences between the transmitted packet and
79 the packet quoted by the ICMP response.
80 A key showing the location of fields within the transmitted packet is printed,
81 followed by the original packet in hex,
82 followed by the quoted packet in hex.
83 Bytes that are unchanged in the quoted packet are shown as underscores.
85 the IP checksum and the TTL of the quoted packet are not expected to match.
86 By default, only one probe per hop is sent with this option.
88 Specify a loose source route gateway (8 maximum).
90 Specify a network interface to obtain the source IP address for
91 outgoing probe packets. This is normally only useful on a multi-homed
94 flag for another way to do this.)
96 Use ICMP ECHO instead of UDP datagrams. (A synonym for "-P icmp").
98 Set the initial time-to-live value used in outgoing probe packets.
99 The default is 1, i.e., start with the first hop.
101 Set the max time-to-live (max number of hops) used in outgoing probe
102 packets. The default is the value of the
105 (the same default used for TCP
108 Print hop addresses numerically rather than symbolically and numerically
109 (saves a nameserver address-to-name lookup for each gateway found on the
112 Send packets of specified IP protocol. The currently supported protocols
113 are: UDP, UDP-Lite, TCP, SCTP, GRE and ICMP. Other protocols may also be
114 specified (either by name or by number), though
116 does not implement any special knowledge of their packet formats. This
117 option is useful for determining which router along a path may be
118 blocking packets based on IP protocol number. But see BUGS below.
120 Protocol specific. For UDP, UDP-Lite, TCP and SCTP, sets
123 number used in probes (default is 33434).
124 Traceroute hopes that nothing is listening on UDP ports (or UDP-Lite ports
127 and supported by the peer)
130 .Em port + (max_ttl - first_ttl + 1) * nprobes
131 at the destination host (so an ICMP PORT_UNREACHABLE message will
132 be returned to terminate the route tracing). If something is
133 listening on a port in the default range, this option can be used
134 to pick an unused port range.
136 Set the number of probes per hop (default is 3,
142 Bypass the normal routing tables and send directly to a host on an attached
144 If the host is not on a directly-attached network,
145 an error is returned.
146 This option can be used to ping a local host through an interface
147 that has no route through it (e.g., after the interface was dropped by
150 Use the following IP address (which usually is given as an IP number, not
151 a hostname) as the source address in outgoing probe packets. On
152 multi-homed hosts (those with more than one IP
153 address), this option can be used to
154 force the source address to be something other than the IP address
155 of the interface the probe packet is sent on. If the IP address
156 is not one of this machine's interface addresses, an error is
157 returned and nothing is sent. (See the
159 flag for another way to do this.)
161 Print a summary of how many probes were not answered for each hop.
165 in probe packets to the following value (default zero). The value must be
166 a decimal integer in the range 0 to 255. This option can be used to
167 see if different types-of-service result in different paths. (If you
168 are not running 4.4bsd, this may be academic since the normal network
169 services like telnet and ftp don't let you control the TOS).
170 Not all values of TOS are legal or
171 meaningful \- see the IP spec for definitions. Useful values are
178 Verbose output. Received ICMP packets other than
184 Set the time (in seconds) to wait for a response to a probe (default 5
187 Toggle ip checksums. Normally, this prevents traceroute from calculating
188 ip checksums. In some cases, the operating system can overwrite parts of
189 the outgoing packet but not recalculate the checksum (so in some cases
190 the default is to not calculate checksums and using
192 causes them to be calculated). Note that checksums are usually required
193 for the last hop when using ICMP ECHO probes
195 So they are always calculated when using ICMP.
196 .It Fl z Ar pausemsecs
197 Set the time (in milliseconds) to pause between probes (default 0).
198 Some systems such as Solaris and routers such as Ciscos rate limit
199 icmp messages. A good value to use with this this is 500 (e.g. 1/2 second).
202 This program attempts to trace the route an IP packet would follow to some
203 internet host by launching UDP probe
204 packets with a small ttl (time to live) then listening for an
205 ICMP "time exceeded" reply from a gateway. We start our probes
206 with a ttl of one and increase by one until we get an ICMP "port
207 unreachable" (which means we got to "host") or hit a max (which
208 defaults to the amount of hops specified by the
211 and can be changed with the
216 flag) are sent at each ttl setting and a
217 line is printed showing the ttl, address of the gateway and
218 round trip time of each probe. If the probe answers come from
219 different gateways, the address of each responding system will
220 be printed. If there is no response within a 5 sec. timeout
221 interval (changed with the
223 flag), a "*" is printed for that
226 We don't want the destination
227 host to process the UDP probe packets so the destination port is set to an
228 unlikely value (if some clod on the destination is using that
229 value, it can be changed with the
233 A sample use and output might be:
234 .Bd -literal -offset 4n
235 % traceroute nis.nsf.net.
236 traceroute to nis.nsf.net (35.1.1.48), 64 hops max, 38 byte packet
237 1 helios.ee.lbl.gov (128.3.112.1) 19 ms 19 ms 0 ms
238 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
239 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
240 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 39 ms
241 5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 39 ms 39 ms 39 ms
242 6 128.32.197.4 (128.32.197.4) 40 ms 59 ms 59 ms
243 7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 59 ms
244 8 129.140.70.13 (129.140.70.13) 99 ms 99 ms 80 ms
245 9 129.140.71.6 (129.140.71.6) 139 ms 239 ms 319 ms
246 10 129.140.81.7 (129.140.81.7) 220 ms 199 ms 199 ms
247 11 nic.merit.edu (35.1.1.48) 239 ms 239 ms 239 ms
250 Note that lines 2 & 3 are the same. This is due to a buggy
251 kernel on the 2nd hop system \- lilac-dmc.Berkeley.EDU \- that forwards
252 packets with a zero ttl (a bug in the distributed version
253 of 4.3BSD). Note that you have to guess what path
254 the packets are taking cross-country since the NSFNet (129.140)
255 doesn't supply address-to-name translations for its NSSes.
257 A more interesting example is:
258 .Bd -literal -offset 4n
259 % traceroute allspice.lcs.mit.edu.
260 traceroute to allspice.lcs.mit.edu (18.26.0.115), 64 hops max
261 1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
262 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 19 ms 19 ms
263 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 19 ms
264 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 19 ms 39 ms 39 ms
265 5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 20 ms 39 ms 39 ms
266 6 128.32.197.4 (128.32.197.4) 59 ms 119 ms 39 ms
267 7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 39 ms
268 8 129.140.70.13 (129.140.70.13) 80 ms 79 ms 99 ms
269 9 129.140.71.6 (129.140.71.6) 139 ms 139 ms 159 ms
270 10 129.140.81.7 (129.140.81.7) 199 ms 180 ms 300 ms
271 11 129.140.72.17 (129.140.72.17) 300 ms 239 ms 239 ms
273 13 128.121.54.72 (128.121.54.72) 259 ms 499 ms 279 ms
278 18 ALLSPICE.LCS.MIT.EDU (18.26.0.115) 339 ms 279 ms 279 ms
281 Note that the gateways 12, 14, 15, 16 & 17 hops away
282 either don't send ICMP "time exceeded" messages or send them
283 with a ttl too small to reach us. 14 \- 17 are running the
284 MIT C Gateway code that doesn't send "time exceeded"s. God
285 only knows what's going on with 12.
287 The silent gateway 12 in the above may be the result of a bug in
288 the 4.[23]BSD network code (and its derivatives): 4.x (x <= 3)
289 sends an unreachable message using whatever ttl remains in the
290 original datagram. Since, for gateways, the remaining ttl is
291 zero, the ICMP "time exceeded" is guaranteed to not make it back
292 to us. The behavior of this bug is slightly more interesting
293 when it appears on the destination system:
294 .Bd -literal -offset 4n
295 1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
296 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 39 ms
297 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 39 ms 19 ms
298 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 19 ms
299 5 ccn-nerif35.Berkeley.EDU (128.32.168.35) 39 ms 39 ms 39 ms
300 6 csgw.Berkeley.EDU (128.32.133.254) 39 ms 59 ms 39 ms
307 13 rip.Berkeley.EDU (128.32.131.22) 59 ms ! 39 ms ! 39 ms !
310 Notice that there are 12 "gateways" (13 is the final
311 destination) and exactly the last half of them are "missing".
312 What's really happening is that rip (a Sun-3 running Sun OS3.5)
313 is using the ttl from our arriving datagram as the ttl in its
314 ICMP reply. So, the reply will time out on the return path
315 (with no notice sent to anyone since ICMP's aren't sent for
316 ICMP's) until we probe with a ttl that's at least twice the path
317 length. I.e., rip is really only 7 hops away. A reply that
318 returns with a ttl of 1 is a clue this problem exists.
319 Traceroute prints a "!" after the time if the ttl is <= 1.
320 Since vendors ship a lot of obsolete
325 software, expect to see this problem
326 frequently and/or take care picking the target host of your
329 Other possible annotations after the time are:
330 .Bl -hang -offset indent -width 12n
336 Protocol unreachable.
340 Fragmentation needed.
341 The RFC1191 Path MTU Discovery value is displayed.
343 Destination network unknown.
345 Destination host unknown.
347 Source host is isolated.
349 Communication with destination network administratively prohibited.
351 Communication with destination host administratively prohibited.
353 For this ToS the destination network is unreachable.
355 For this ToS the destination host is unreachable.
357 Communication administratively prohibited.
359 Host precedence violation.
361 Precedence cutoff in effect.
363 ICMP unreachable code <num>.
366 These are defined by RFC1812 (which supersedes RFC1716).
367 If almost all the probes result in some kind of unreachable,
369 will give up and exit.
371 This program is intended for use in network testing, measurement
373 It should be used primarily for manual fault isolation.
374 Because of the load it could impose on the network, it is unwise to use
376 during normal operations or from automated scripts.
382 Implemented by Van Jacobson from a suggestion by Steve Deering. Debugged
383 by a cast of thousands with particularly cogent suggestions or fixes from
384 C. Philip Wood, Tim Seaver and Ken Adelman.
386 When using protocols other than UDP, functionality is reduced.
387 In particular, the last packet will often appear to be lost, because
388 even though it reaches the destination host, there's no way to know
389 that because no ICMP message is sent back.
392 should listen for a RST from the destination host (or an intermediate
393 router that's filtering packets), but this is not implemented yet.
395 The AS number capability reports information that may sometimes be
396 inaccurate due to discrepancies between the contents of the
397 routing database server and the current state of the Internet.