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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. The upper six
168 bits are the Differentiated Services Codepoint (RFC4594). The lower two
169 bits are the Explicit Congestion Notification field (RFC3168).
171 Verbose output. Received ICMP packets other than
177 Set the time (in seconds) to wait for a response to a probe (default 5
180 Toggle ip checksums. Normally, this prevents traceroute from calculating
181 ip checksums. In some cases, the operating system can overwrite parts of
182 the outgoing packet but not recalculate the checksum (so in some cases
183 the default is to not calculate checksums and using
185 causes them to be calculated). Note that checksums are usually required
186 for the last hop when using ICMP ECHO probes
188 So they are always calculated when using ICMP.
189 .It Fl z Ar pausemsecs
190 Set the time (in milliseconds) to pause between probes (default 0).
191 Some systems such as Solaris and routers such as Ciscos rate limit
192 icmp messages. A good value to use with this this is 500 (e.g. 1/2 second).
195 This program attempts to trace the route an IP packet would follow to some
196 internet host by launching UDP probe
197 packets with a small ttl (time to live) then listening for an
198 ICMP "time exceeded" reply from a gateway. We start our probes
199 with a ttl of one and increase by one until we get an ICMP "port
200 unreachable" (which means we got to "host") or hit a max (which
201 defaults to the amount of hops specified by the
204 and can be changed with the
209 flag) are sent at each ttl setting and a
210 line is printed showing the ttl, address of the gateway and
211 round trip time of each probe. If the probe answers come from
212 different gateways, the address of each responding system will
213 be printed. If there is no response within a 5 sec. timeout
214 interval (changed with the
216 flag), a "*" is printed for that
219 We don't want the destination
220 host to process the UDP probe packets so the destination port is set to an
221 unlikely value (if some clod on the destination is using that
222 value, it can be changed with the
226 A sample use and output might be:
227 .Bd -literal -offset 4n
228 % traceroute nis.nsf.net.
229 traceroute to nis.nsf.net (35.1.1.48), 64 hops max, 38 byte packet
230 1 helios.ee.lbl.gov (128.3.112.1) 19 ms 19 ms 0 ms
231 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
232 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
233 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 39 ms
234 5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 39 ms 39 ms 39 ms
235 6 128.32.197.4 (128.32.197.4) 40 ms 59 ms 59 ms
236 7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 59 ms
237 8 129.140.70.13 (129.140.70.13) 99 ms 99 ms 80 ms
238 9 129.140.71.6 (129.140.71.6) 139 ms 239 ms 319 ms
239 10 129.140.81.7 (129.140.81.7) 220 ms 199 ms 199 ms
240 11 nic.merit.edu (35.1.1.48) 239 ms 239 ms 239 ms
243 Note that lines 2 & 3 are the same. This is due to a buggy
244 kernel on the 2nd hop system \- lilac-dmc.Berkeley.EDU \- that forwards
245 packets with a zero ttl (a bug in the distributed version
246 of 4.3BSD). Note that you have to guess what path
247 the packets are taking cross-country since the NSFNet (129.140)
248 doesn't supply address-to-name translations for its NSSes.
250 A more interesting example is:
251 .Bd -literal -offset 4n
252 % traceroute allspice.lcs.mit.edu.
253 traceroute to allspice.lcs.mit.edu (18.26.0.115), 64 hops max
254 1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
255 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 19 ms 19 ms
256 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 19 ms
257 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 19 ms 39 ms 39 ms
258 5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 20 ms 39 ms 39 ms
259 6 128.32.197.4 (128.32.197.4) 59 ms 119 ms 39 ms
260 7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 39 ms
261 8 129.140.70.13 (129.140.70.13) 80 ms 79 ms 99 ms
262 9 129.140.71.6 (129.140.71.6) 139 ms 139 ms 159 ms
263 10 129.140.81.7 (129.140.81.7) 199 ms 180 ms 300 ms
264 11 129.140.72.17 (129.140.72.17) 300 ms 239 ms 239 ms
266 13 128.121.54.72 (128.121.54.72) 259 ms 499 ms 279 ms
271 18 ALLSPICE.LCS.MIT.EDU (18.26.0.115) 339 ms 279 ms 279 ms
274 Note that the gateways 12, 14, 15, 16 & 17 hops away
275 either don't send ICMP "time exceeded" messages or send them
276 with a ttl too small to reach us. 14 \- 17 are running the
277 MIT C Gateway code that doesn't send "time exceeded"s. God
278 only knows what's going on with 12.
280 The silent gateway 12 in the above may be the result of a bug in
281 the 4.[23]BSD network code (and its derivatives): 4.x (x <= 3)
282 sends an unreachable message using whatever ttl remains in the
283 original datagram. Since, for gateways, the remaining ttl is
284 zero, the ICMP "time exceeded" is guaranteed to not make it back
285 to us. The behavior of this bug is slightly more interesting
286 when it appears on the destination system:
287 .Bd -literal -offset 4n
288 1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
289 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 39 ms
290 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 39 ms 19 ms
291 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 19 ms
292 5 ccn-nerif35.Berkeley.EDU (128.32.168.35) 39 ms 39 ms 39 ms
293 6 csgw.Berkeley.EDU (128.32.133.254) 39 ms 59 ms 39 ms
300 13 rip.Berkeley.EDU (128.32.131.22) 59 ms ! 39 ms ! 39 ms !
303 Notice that there are 12 "gateways" (13 is the final
304 destination) and exactly the last half of them are "missing".
305 What's really happening is that rip (a Sun-3 running Sun OS3.5)
306 is using the ttl from our arriving datagram as the ttl in its
307 ICMP reply. So, the reply will time out on the return path
308 (with no notice sent to anyone since ICMP's aren't sent for
309 ICMP's) until we probe with a ttl that's at least twice the path
310 length. I.e., rip is really only 7 hops away. A reply that
311 returns with a ttl of 1 is a clue this problem exists.
312 Traceroute prints a "!" after the time if the ttl is <= 1.
313 Since vendors ship a lot of obsolete
318 software, expect to see this problem
319 frequently and/or take care picking the target host of your
322 Other possible annotations after the time are:
323 .Bl -hang -offset indent -width 12n
329 Protocol unreachable.
333 Fragmentation needed.
334 The RFC1191 Path MTU Discovery value is displayed.
336 Destination network unknown.
338 Destination host unknown.
340 Source host is isolated.
342 Communication with destination network administratively prohibited.
344 Communication with destination host administratively prohibited.
346 For this ToS the destination network is unreachable.
348 For this ToS the destination host is unreachable.
350 Communication administratively prohibited.
352 Host precedence violation.
354 Precedence cutoff in effect.
356 ICMP unreachable code <num>.
359 These are defined by RFC1812 (which supersedes RFC1716).
360 If almost all the probes result in some kind of unreachable,
362 will give up and exit.
364 This program is intended for use in network testing, measurement
366 It should be used primarily for manual fault isolation.
367 Because of the load it could impose on the network, it is unwise to use
369 during normal operations or from automated scripts.
375 Implemented by Van Jacobson from a suggestion by Steve Deering. Debugged
376 by a cast of thousands with particularly cogent suggestions or fixes from
377 C. Philip Wood, Tim Seaver and Ken Adelman.
379 When using protocols other than UDP, functionality is reduced.
380 In particular, the last packet will often appear to be lost, because
381 even though it reaches the destination host, there's no way to know
382 that because no ICMP message is sent back.
385 should listen for a RST from the destination host (or an intermediate
386 router that's filtering packets), but this is not implemented yet.
388 The AS number capability reports information that may sometimes be
389 inaccurate due to discrepancies between the contents of the
390 routing database server and the current state of the Internet.