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16 .\" $Header: traceroute.8,v 1.7 96/09/27 20:02:41 leres Exp $
19 .TH TRACEROUTE 8 "27 September 1996"
22 traceroute \- print the route packets take to network host
24 .. while ((op = getopt(argc, argv, "dnrvg:M:m:P:p:q:s:t:w:")) != EOF)
72 The Internet is a large and complex aggregation of
73 network hardware, connected together by gateways.
74 Tracking the route one's packets follow (or finding the miscreant
75 gateway that's discarding your packets) can be difficult.
77 utilizes the IP protocol `time to live' field and attempts to elicit an
78 ICMP TIME_EXCEEDED response from each gateway along the path to some
81 The only mandatory parameter is the destination host name or IP number.
82 The default probe datagram length is 40 bytes, but this may be increased
83 by specifying a packet length (in bytes) after the destination host
89 Print a summary of how many probes were not answered for each hop.
92 Specify a loose source route gateway (8 maximum).
95 Set the initial time-to-live value used in outgoing probe packets.
96 The default is 1, i.e., start with the first hop.
99 Set the max time-to-live (max number of hops) used in outgoing probe
100 packets. The default is
102 hops (the same default used for TCP
106 Print hop addresses numerically rather than symbolically and numerically
107 (saves a nameserver address-to-name lookup for each gateway found on the
111 Send packets of specified IP protocol. The currently supported protocols
112 are: UDP, TCP and GRE. Other protocols may also be specified (either by
113 name or by number), though
115 does not implement any special knowledge of their packet formats. This
116 option is useful for determining which router along a path may be
117 blocking packets based on IP protocol number. But see BUGS below.
120 Protocol specific. For UDP and TCP, sets
121 the base port number used in probes (default is 33434).
122 Traceroute hopes that nothing is listening on UDP ports
126 at the destination host (so an ICMP PORT_UNREACHABLE message will
127 be returned to terminate the route tracing). If something is
128 listening on a port in the default range, this option can be used
129 to pick an unused port range.
132 Set the number of probes per hop (default is 3).
135 Bypass the normal routing tables and send directly to a host on an attached
137 If the host is not on a directly-attached network,
138 an error is returned.
139 This option can be used to ping a local host through an interface
140 that has no route through it (e.g., after the interface was dropped by
144 Use the following IP address (which must be given as an IP number, not
145 a hostname) as the source address in outgoing probe packets. On
146 hosts with more than one IP address, this option can be used to
147 force the source address to be something other than the IP address
148 of the interface the probe packet is sent on. If the IP address
149 is not one of this machine's interface addresses, an error is
150 returned and nothing is sent.
155 in probe packets to the following value (default zero). The value must be
156 a decimal integer in the range 0 to 255. This option can be used to
157 see if different types-of-service result in different paths. (If you
158 are not running 4.4bsd, this may be academic since the normal network
159 services like telnet and ftp don't let you control the TOS).
160 Not all values of TOS are legal or
161 meaningful \- see the IP spec for definitions. Useful values are
162 probably `-t 16' (low delay) and `-t 8' (high throughput).
165 Verbose output. Received ICMP packets other than TIME_EXCEEDED and
166 UNREACHABLEs are listed.
169 Set the time (in seconds) to wait for a response to a probe (default 5
172 This program attempts to trace the route an IP packet would follow to some
173 internet host by launching UDP probe
174 packets with a small ttl (time to live) then listening for an
175 ICMP "time exceeded" reply from a gateway. We start our probes
176 with a ttl of one and increase by one until we get an ICMP "port
177 unreachable" (which means we got to "host") or hit a max (which
180 hops & can be changed with the \-m flag). Three
181 probes (change with \-q flag) are sent at each ttl setting and a
182 line is printed showing the ttl, address of the gateway and
183 round trip time of each probe. If the probe answers come from
184 different gateways, the address of each responding system will
185 be printed. If there is no response within a 5 sec. timeout
186 interval (changed with the \-w flag), a "*" is printed for that
189 We don't want the destination
190 host to process the UDP probe packets so the destination port is set to an
191 unlikely value (if some clod on the destination is using that
192 value, it can be changed with the \-p flag).
194 A sample use and output might be:
198 [yak 71]% traceroute nis.nsf.net.
199 traceroute to nis.nsf.net (35.1.1.48), 64 hops max, 38 byte packet
200 1 helios.ee.lbl.gov (128.3.112.1) 19 ms 19 ms 0 ms
201 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
202 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
203 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 39 ms
204 5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 39 ms 39 ms 39 ms
205 6 128.32.197.4 (128.32.197.4) 40 ms 59 ms 59 ms
206 7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 59 ms
207 8 129.140.70.13 (129.140.70.13) 99 ms 99 ms 80 ms
208 9 129.140.71.6 (129.140.71.6) 139 ms 239 ms 319 ms
209 10 129.140.81.7 (129.140.81.7) 220 ms 199 ms 199 ms
210 11 nic.merit.edu (35.1.1.48) 239 ms 239 ms 239 ms
214 Note that lines 2 & 3 are the same. This is due to a buggy
215 kernel on the 2nd hop system \- lbl-csam.arpa \- that forwards
216 packets with a zero ttl (a bug in the distributed version
217 of 4.3BSD). Note that you have to guess what path
218 the packets are taking cross-country since the NSFNet (129.140)
219 doesn't supply address-to-name translations for its NSSes.
221 A more interesting example is:
225 [yak 72]% traceroute allspice.lcs.mit.edu.
226 traceroute to allspice.lcs.mit.edu (18.26.0.115), 64 hops max
227 1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
228 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 19 ms 19 ms
229 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 19 ms
230 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 19 ms 39 ms 39 ms
231 5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 20 ms 39 ms 39 ms
232 6 128.32.197.4 (128.32.197.4) 59 ms 119 ms 39 ms
233 7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 39 ms
234 8 129.140.70.13 (129.140.70.13) 80 ms 79 ms 99 ms
235 9 129.140.71.6 (129.140.71.6) 139 ms 139 ms 159 ms
236 10 129.140.81.7 (129.140.81.7) 199 ms 180 ms 300 ms
237 11 129.140.72.17 (129.140.72.17) 300 ms 239 ms 239 ms
239 13 128.121.54.72 (128.121.54.72) 259 ms 499 ms 279 ms
244 18 ALLSPICE.LCS.MIT.EDU (18.26.0.115) 339 ms 279 ms 279 ms
248 Note that the gateways 12, 14, 15, 16 & 17 hops away
249 either don't send ICMP "time exceeded" messages or send them
250 with a ttl too small to reach us. 14 \- 17 are running the
251 MIT C Gateway code that doesn't send "time exceeded"s. God
252 only knows what's going on with 12.
254 The silent gateway 12 in the above may be the result of a bug in
255 the 4.[23]BSD network code (and its derivatives): 4.x (x <= 3)
256 sends an unreachable message using whatever ttl remains in the
257 original datagram. Since, for gateways, the remaining ttl is
258 zero, the ICMP "time exceeded" is guaranteed to not make it back
259 to us. The behavior of this bug is slightly more interesting
260 when it appears on the destination system:
264 1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
265 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 39 ms
266 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 39 ms 19 ms
267 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 19 ms
268 5 ccn-nerif35.Berkeley.EDU (128.32.168.35) 39 ms 39 ms 39 ms
269 6 csgw.Berkeley.EDU (128.32.133.254) 39 ms 59 ms 39 ms
276 13 rip.Berkeley.EDU (128.32.131.22) 59 ms ! 39 ms ! 39 ms !
280 Notice that there are 12 "gateways" (13 is the final
281 destination) and exactly the last half of them are "missing".
282 What's really happening is that rip (a Sun-3 running Sun OS3.5)
283 is using the ttl from our arriving datagram as the ttl in its
284 ICMP reply. So, the reply will time out on the return path
285 (with no notice sent to anyone since ICMP's aren't sent for
286 ICMP's) until we probe with a ttl that's at least twice the path
287 length. I.e., rip is really only 7 hops away. A reply that
288 returns with a ttl of 1 is a clue this problem exists.
289 Traceroute prints a "!" after the time if the ttl is <= 1.
290 Since vendors ship a lot of obsolete (DEC's Ultrix, Sun 3.x) or
291 non-standard (HPUX) software, expect to see this problem
292 frequently and/or take care picking the target host of your
295 Other possible annotations after the time are
300 (got a host, network or protocol unreachable, respectively),
304 (source route failed or fragmentation needed \- neither of these should
305 ever occur and the associated gateway is busted if you see one),
307 (communication administratively prohibited), or
309 (ICMP unreachable code N).
310 If almost all the probes result in some kind of unreachable, traceroute
311 will give up and exit.
313 This program is intended for use in network testing, measurement
315 It should be used primarily for manual fault isolation.
316 Because of the load it could impose on the network, it is unwise to use
318 during normal operations or from automated scripts.
322 Implemented by Van Jacobson from a suggestion by Steve Deering. Debugged
323 by a cast of thousands with particularly cogent suggestions or fixes from
324 C. Philip Wood, Tim Seaver and Ken Adelman.
326 The current version is available via anonymous ftp:
329 .I ftp://ftp.ee.lbl.gov/traceroute.tar.Z
332 When using protocols other than UDP, functionality is reduced.
333 In particular, the last packet will often appear to be lost, because
334 even though it reaches the destination host, there's no way to know
335 that because no ICMP message is sent back.
338 should listen for a RST from the destination host (or an intermediate
339 router that's filtering packets), but this is not implemented yet.
341 Please send bug reports to traceroute@ee.lbl.gov.