1.\" Copyright (c) 1989, 1995, 1996, 1997, 1999, 2000 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, 7.\" advertising materials, and other materials related to such 8.\" distribution and use acknowledge that the software was developed 9.\" by the University of California, Berkeley. The name of the 10.\" University may not be used to endorse or promote products derived 11.\" from this software without specific prior written permission. 12.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR 13.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED 14.\" WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. 15.\" 16.\" $Id: traceroute.8,v 1.19 2000/09/21 08:44:19 leres Exp $
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111.B \-e 112Firewall evasion mode. 113Use fixed destination ports for UDP and TCP probes. 114The destination port does NOT increment with each packet sent. 115.TP 116.B \-f 117Set the initial time-to-live used in the first outgoing probe packet. 118.TP 119.B \-F 120Set the "don't fragment" bit. 121.TP 122.B \-d 123Enable socket level debugging. 124.TP 125.B \-D 126When an ICMP response to our probe datagram is received, 127print the differences between the transmitted packet and 128the packet quoted by the ICMP response. 129A key showing the location of fields within the transmitted packet is printed, 130followed by the original packet in hex, 131followed by the quoted packet in hex. 132Bytes that are unchanged in the quoted packet are shown as underscores. 133Note, 134the IP checksum and the TTL of the quoted packet are not expected to match. 135By default, only one probe per hop is sent with this option. 136.TP 137.B \-g 138Specify a loose source route gateway (8 maximum). 139.TP 140.B \-i 141Specify a network interface to obtain the source IP address for 142outgoing probe packets. This is normally only useful on a multi-homed 143host. (See the 144.B \-s 145flag for another way to do this.) 146.TP 147.B \-I 148Use ICMP ECHO instead of UDP datagrams. (A synonym for "-P icmp"). 149.TP 150.B \-M 151Set the initial time-to-live value used in outgoing probe packets. 152The default is 1, i.e., start with the first hop. 153.TP 154.B \-m 155Set the max time-to-live (max number of hops) used in outgoing probe 156packets. The default is 157.I net.inet.ip.ttl 158hops (the same default used for TCP 159connections). 160.TP 161.B \-n 162Print hop addresses numerically rather than symbolically and numerically 163(saves a nameserver address-to-name lookup for each gateway found on the 164path). 165.TP 166.B \-P 167Send packets of specified IP protocol. The currently supported protocols 168are: UDP, TCP, GRE and ICMP. Other protocols may also be specified (either by 169name or by number), though 170.I traceroute 171does not implement any special knowledge of their packet formats. This 172option is useful for determining which router along a path may be 173blocking packets based on IP protocol number. But see BUGS below. 174.TP 175.B \-p 176Protocol specific. For UDP and TCP, sets 177the base port number used in probes (default is 33434). 178Traceroute hopes that nothing is listening on UDP ports 179.I base 180to 181.I base + nhops * nprobes - 1 182at the destination host (so an ICMP PORT_UNREACHABLE message will 183be returned to terminate the route tracing). If something is 184listening on a port in the default range, this option can be used 185to pick an unused port range. 186.TP 187.B \-q 188Set the number of probes per hop (default is 3, 189unless 190.B -D 191is specified, 192when it is 1). 193.TP 194.B \-r 195Bypass the normal routing tables and send directly to a host on an attached 196network. 197If the host is not on a directly-attached network, 198an error is returned. 199This option can be used to ping a local host through an interface 200that has no route through it (e.g., after the interface was dropped by 201.IR routed (8C)). 202.TP 203.B \-s 204Use the following IP address (which usually is given as an IP number, not 205a hostname) as the source address in outgoing probe packets. On 206multi-homed hosts (those with more than one IP 207address), this option can be used to 208force the source address to be something other than the IP address 209of the interface the probe packet is sent on. If the IP address 210is not one of this machine's interface addresses, an error is 211returned and nothing is sent. (See the 212.B \-i 213flag for another way to do this.) 214.TP 215.B \-S 216Print a summary of how many probes were not answered for each hop. 217.TP 218.B \-t 219Set the 220.I type-of-service 221in probe packets to the following value (default zero). The value must be 222a decimal integer in the range 0 to 255. This option can be used to 223see if different types-of-service result in different paths. (If you 224are not running 4.4bsd, this may be academic since the normal network 225services like telnet and ftp don't let you control the TOS). 226Not all values of TOS are legal or 227meaningful \- see the IP spec for definitions. Useful values are 228probably 229.RB ` -t 230.IR 16 ' 231(low delay) and 232.RB ` -t 233.IR 8 ' 234(high throughput). 235.TP 236.B \-v 237Verbose output. Received ICMP packets other than TIME_EXCEEDED and 238UNREACHABLEs are listed. 239.TP 240.B \-w 241Set the time (in seconds) to wait for a response to a probe (default 5 242sec.). 243.TP 244.B \-x 245Toggle ip checksums. Normally, this prevents traceroute from calculating 246ip checksums. In some cases, the operating system can overwrite parts of 247the outgoing packet but not recalculate the checksum (so in some cases 248the default is to not calculate checksums and using 249.B \-x 250causes them to be calculated). Note that checksums are usually required 251for the last hop when using ICMP ECHO probes 252.RB ( \-I ). 253So they are always calculated when using ICMP. 254.TP 255.B \-z 256Set the time (in milliseconds) to pause between probes (default 0). 257Some systems such as Solaris and routers such as Ciscos rate limit 258icmp messages. A good value to use with this this is 500 (e.g. 1/2 second). 259.PP 260This program attempts to trace the route an IP packet would follow to some 261internet host by launching UDP probe 262packets with a small ttl (time to live) then listening for an 263ICMP "time exceeded" reply from a gateway. We start our probes 264with a ttl of one and increase by one until we get an ICMP "port 265unreachable" (which means we got to "host") or hit a max (which 266defaults to 267.I net.inet.ip.ttl 268hops & can be changed with the 269.B \-m 270flag). Three 271probes (change with 272.B \-q 273flag) are sent at each ttl setting and a 274line is printed showing the ttl, address of the gateway and 275round trip time of each probe. If the probe answers come from 276different gateways, the address of each responding system will 277be printed. If there is no response within a 5 sec. timeout 278interval (changed with the 279.B \-w 280flag), a "*" is printed for that 281probe. 282.PP 283We don't want the destination 284host to process the UDP probe packets so the destination port is set to an 285unlikely value (if some clod on the destination is using that 286value, it can be changed with the 287.B \-p 288flag). 289.PP 290A sample use and output might be: 291 292.RS 293.nf 294[yak 71]% traceroute nis.nsf.net. 295traceroute to nis.nsf.net (35.1.1.48), 64 hops max, 38 byte packet 296 1 helios.ee.lbl.gov (128.3.112.1) 19 ms 19 ms 0 ms 297 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms 298 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms 299 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 39 ms 300 5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 39 ms 39 ms 39 ms 301 6 128.32.197.4 (128.32.197.4) 40 ms 59 ms 59 ms 302 7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 59 ms 303 8 129.140.70.13 (129.140.70.13) 99 ms 99 ms 80 ms 304 9 129.140.71.6 (129.140.71.6) 139 ms 239 ms 319 ms 30510 129.140.81.7 (129.140.81.7) 220 ms 199 ms 199 ms 30611 nic.merit.edu (35.1.1.48) 239 ms 239 ms 239 ms 307.fi 308.RE 309 310Note that lines 2 & 3 are the same. This is due to a buggy 311kernel on the 2nd hop system \- lilac-dmc.Berkeley.EDU \- that forwards 312packets with a zero ttl (a bug in the distributed version 313of 4.3BSD). Note that you have to guess what path 314the packets are taking cross-country since the NSFNet (129.140) 315doesn't supply address-to-name translations for its NSSes. 316.PP 317A more interesting example is: 318 319.RS 320.nf 321[yak 72]% traceroute allspice.lcs.mit.edu. 322traceroute to allspice.lcs.mit.edu (18.26.0.115), 64 hops max 323 1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms 324 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 19 ms 19 ms 325 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 19 ms 326 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 19 ms 39 ms 39 ms 327 5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 20 ms 39 ms 39 ms 328 6 128.32.197.4 (128.32.197.4) 59 ms 119 ms 39 ms 329 7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 39 ms 330 8 129.140.70.13 (129.140.70.13) 80 ms 79 ms 99 ms 331 9 129.140.71.6 (129.140.71.6) 139 ms 139 ms 159 ms 33210 129.140.81.7 (129.140.81.7) 199 ms 180 ms 300 ms 33311 129.140.72.17 (129.140.72.17) 300 ms 239 ms 239 ms 33412 * * * 33513 128.121.54.72 (128.121.54.72) 259 ms 499 ms 279 ms 33614 * * * 33715 * * * 33816 * * * 33917 * * * 34018 ALLSPICE.LCS.MIT.EDU (18.26.0.115) 339 ms 279 ms 279 ms 341.fi 342.RE 343 344Note that the gateways 12, 14, 15, 16 & 17 hops away 345either don't send ICMP "time exceeded" messages or send them 346with a ttl too small to reach us. 14 \- 17 are running the 347MIT C Gateway code that doesn't send "time exceeded"s. God 348only knows what's going on with 12. 349.PP 350The silent gateway 12 in the above may be the result of a bug in 351the 4.[23]BSD network code (and its derivatives): 4.x (x <= 3) 352sends an unreachable message using whatever ttl remains in the 353original datagram. Since, for gateways, the remaining ttl is 354zero, the ICMP "time exceeded" is guaranteed to not make it back 355to us. The behavior of this bug is slightly more interesting 356when it appears on the destination system: 357 358.RS 359.nf 360 1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms 361 2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 39 ms 362 3 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 39 ms 19 ms 363 4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 19 ms 364 5 ccn-nerif35.Berkeley.EDU (128.32.168.35) 39 ms 39 ms 39 ms 365 6 csgw.Berkeley.EDU (128.32.133.254) 39 ms 59 ms 39 ms 366 7 * * * 367 8 * * * 368 9 * * * 36910 * * * 37011 * * * 37112 * * * 37213 rip.Berkeley.EDU (128.32.131.22) 59 ms ! 39 ms ! 39 ms ! 373.fi 374.RE 375 376Notice that there are 12 "gateways" (13 is the final 377destination) and exactly the last half of them are "missing". 378What's really happening is that rip (a Sun-3 running Sun OS3.5) 379is using the ttl from our arriving datagram as the ttl in its 380ICMP reply. So, the reply will time out on the return path 381(with no notice sent to anyone since ICMP's aren't sent for 382ICMP's) until we probe with a ttl that's at least twice the path 383length. I.e., rip is really only 7 hops away. A reply that 384returns with a ttl of 1 is a clue this problem exists. 385Traceroute prints a "!" after the time if the ttl is <= 1. 386Since vendors ship a lot of obsolete (DEC's Ultrix, Sun 3.x) or 387non-standard (HPUX) software, expect to see this problem 388frequently and/or take care picking the target host of your 389probes. 390 391Other possible annotations after the time are 392.BR !H , 393.BR !N , 394or 395.B !P 396(host, network or protocol unreachable), 397.B !S 398(source route failed), 399.B !F\-<pmtu> 400(fragmentation needed \- the RFC1191 Path MTU Discovery value is displayed), 401.B !U 402or 403.B !W 404(destination network/host unknown), 405.B !I 406(source host is isolated), 407.B !A 408(communication with destination network administratively prohibited), 409.B !Z 410(communication with destination host administratively prohibited), 411.B !Q 412(for this ToS the destination network is unreachable), 413.B !T 414(for this ToS the destination host is unreachable), 415.B !X 416(communication administratively prohibited), 417.B !V 418(host precedence violation), 419.B !C 420(precedence cutoff in effect), or 421.B !<num> 422(ICMP unreachable code <num>). 423These are defined by RFC1812 (which supersedes RFC1716). 424If almost all the probes result in some kind of unreachable, traceroute 425will give up and exit. 426.PP 427This program is intended for use in network testing, measurement 428and management. 429It should be used primarily for manual fault isolation. 430Because of the load it could impose on the network, it is unwise to use 431.I traceroute 432during normal operations or from automated scripts. 433.SH SEE ALSO 434pathchar(8), netstat(1), ping(8) 435.SH AUTHOR 436Implemented by Van Jacobson from a suggestion by Steve Deering. Debugged 437by a cast of thousands with particularly cogent suggestions or fixes from 438C. Philip Wood, Tim Seaver and Ken Adelman. 439.LP 440The current version is available via anonymous ftp: 441.LP 442.RS 443.I ftp://ftp.ee.lbl.gov/traceroute.tar.gz 444.RE 445.SH BUGS 446When using protocols other than UDP, functionality is reduced. 447In particular, the last packet will often appear to be lost, because 448even though it reaches the destination host, there's no way to know 449that because no ICMP message is sent back. 450In the TCP case, 451.I traceroute 452should listen for a RST from the destination host (or an intermediate 453router that's filtering packets), but this is not implemented yet. 454.PP 455Please send bug reports to traceroute@ee.lbl.gov.
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